What is lemon verbena

Lemon verbena (Aloysia citrodora) also called lemon beebrush, Verbena grass Louise or Arabic tea ¹⁾, is an edible perennial flowering plant in the verbena family Verbenaceae, growing in late spring or early summer to 2–3 m high ²⁾. The 8-cm-long, glossy, pointed leaves are slightly rough to the touch and emit a powerful scent reminiscent of lemon when bruised (hence the Latin specific epithet citrodora—lemon-scented) ³⁾. Lemon verbena (Aloysia citrodora) is native to western South America and was brought to Europe by the Spanish and the Portuguese in the 17th century and cultivated for its oil ⁴⁾. Lemon verbena extracts have strong anti-oxidant capacity due to polyphenols contained in it ⁵⁾.

Sprays of tiny purple or white flowers appear . Lemon verbena is sensitive to cold, losing leaves at temperatures below 0 °C (32 °F), although the wood is hardy to −10 °C (14 °F). Due to its many culinary uses, lemon verbena is widely listed and marketed as a plant for the herb garden.

Lemon verbena leaves are used to add a lemon flavor to fish and poultry dishes, vegetable marinades, salad dressings, jams, puddings, Greek yogurt and beverages.

Figure 1. Lemon verbena

Lemon verbena uses

In Morocco, Lemon verbena is cultivated for more than a century and has been used in folk medicine as herbal tea preparations, for its antispasmodic, digestive, stomachic, sedative, and antipyretic properties ⁶⁾. The essential oil extracted from the dried Lemon verbena leaves is indicated for anxiety, stress, insomnia, some depressions, nervous fatigue, multiple sclerosis, psoriasis, tachycardia, rheumatism, enterocolitis, Crohn’s disease, anorexia, dyspepsia, intestinal parasites (amebiasis and amebic cysts), and prevention of asthma attacks ⁷⁾. The broad range of biological activities of lemon verbena essential oils could be generally correlated to the chemical composition. It is well established that sesquiterpenoids and their derivatives are credited with many biological activities such as anti-inflammatory, antibacterial, antiasthmatic, and antifungal properties ⁸⁾. Lemon verbena essential oil chemical composition: l,8-Cineole, geranial, 6-methyl-5-hepten-2-one, neral, limonene, β-caryophyllene, ar-curcumene, spathulenol ⁹⁾.

Lemon verbena leaves, commonly used to make herbal teas and refreshing beverage, demonstrated antioxidant and anti-inflammatory properties ¹⁰⁾. Lemon verbena leaves are also added to standard tea in place of actual lemon (as is common with Moroccan tea). Lemon verbena can also be used to make a sorbet.

The results of dextran sulfate sodium-induced colitis (experimental colitis in animals) in rats showed that, although the histological lesions and myeloperoxidase activity were not significantly improved, the herbal Lemon verbena (Aloysia citrodora) infusion increased colonic superoxide dismutase activity and decreased the levels of malondialdehyde ¹¹⁾. This rat study showed consumption of lemon verbena infusion offered some antioxidative protection during experimental colitis by stimulating superoxide dismutase activity and decreasing lipid peroxidation ¹²⁾.

Several test tube and animal studies have shown lemon verbena leaves water-based extracts antioxidative and anti-inflammatory effects ¹³⁾, ¹⁴⁾, ¹⁵⁾. Out of six human studies ¹⁶⁾, ¹⁷⁾, ¹⁸⁾, ¹⁹⁾, ²⁰⁾, ²¹⁾, only one human pilot study was published investigating lemon verbena extract on the muscular damage biomarker, creatine kinase and liver biomarker related to oxidative stress ²²⁾. This study showed some effects on cytokines and oxidative stress markers in neutrophils, but no functional parameters like muscle strength or muscle soreness were assessed ²³⁾. This study ²⁴⁾ preliminary findings suggest that lemon verbena extract supplementation may reduce exercise-induced muscle damage compared to placebo. In addition, several studies ²⁵⁾, ²⁶⁾, ²⁷⁾ have revealed that moderate doses of dietary polyphenols diminish this exercise-induced oxidative stress and decrease inflammatory markers.

Lemon verbena has a long history of folk uses in treating colds, fever, insomnia, and anxiety ²⁸⁾. Also, Lemon verbena leaf is used in Persian folk medicine for memory improvement, antidizziness, as analgesic for neuralgic pain, sedative, antihysteria and for treating unilateral headache pain ²⁹⁾.

Table 1. Lemon verbena aromatic water constituents results from gas chromatography–mass spectrometry analysis

Component	Lemon verbena
1,8-Cineole	3.82
Borneol	4
Carveol (trans)	0.77
Caryophyllene (trans)	9.5
Caryophyllene oxide	0.72
Geranial	13.72
Limonene	20.55
Methyl hexadecanoate	7.95
Neral	6.42
Nerol	3.42
Nerolidol (trans)	0.68
α-Pinene	2.78
α-Terpineol	6.3
Terpinene-4-ol	5.1
Thymol	4.87

[Source ³⁰⁾]

Table 2. Lemon verbena from Morocco essential oil chemical composition results from gas chromatography–mass spectrometry analysis

Peak number	Componenta	RIb	% Essential oil of Agadir	% Essential oil of Beni Mellal	% Essential oil of Berkane	% Essential oil of Demnate	% Essential oil of Marrakech
1	α-Pinene	909	0.23	0.39	0.17	0.21	0.2
2	α-Thujene	927	0.09	0.14	0.08	0.09	0.08
3	β-Pinene	964	0.14	0.14	0.09	0.12	0.09
4	Sabinene	972	0.04	0.05	0.03	0.04	0.04
5	6-Methyl-5-hepten-2-one	987	0.03	0.02	0.02	0.02	0.02
6	β-Myrcene	988	0.03	0.02	0.02	0.02	0.04
7	α-Terpinene	1017	0.12	0.1	0.08	0.08	0.09
8	Paracymene	1024	0.02	—	—	—	—
9	Limonene	1027	0.71	0.63	0.36	0.5	0.39
10	1,8-Cineole	1031	1.97	1.44	1.66	1.41	1.97
11	cis-β-Ocimene	1037	0.02	0.02	—	0.02	0.01
12	trans-β-Ocimene	1045	0.04	0.03	0.05	0.03	0.05
13	γ-Terpinene	1054	0.33	0.13	0.15	0.18	0.14
14	trans-Sabinene hydrate	1096	0.29	0.14	0.17	0.17	0.13
15	6-Camphenol	1110	0.08	0.04	0.05	0.06	0.05
16	cis-Limonene oxide	1117	0.16	0.1	0.14	0.13	0.22
17	Campholene aldehyde	1125	0.58	0.26	0.4	0.4	0.4
18	trans-p-Mentha-2,8-dienol	1127	0.18	0.17	0.16	0.1	0.12
19	cis-p-Mentha-2,8-dien-1-ol	1131	0.33	0.18	0.2	0.21	0.15
20	trans-Verbenol	1144	0.64	0.34	0.47	0.38	0.45
21	cis-Verbenol	1153	7.78	4.87	5.22	5.82	4.41
22	1,3,4-Trimethyl-3-cyclohexene-1-carboxaldehyde	1171	0.7	0.63	0.59	0.53	0.62
23	cis-p-Mentha-1(7),8-dien-2-ol	1185	0.13	0.09	0.14	0.07	0.07
24	Verbenyl ethyl ether	1186	0.31	0.3	0.24	0.35	0.31
25	2-Carene	1189	1.71	0,86	1.11	1.03	0.84
26	Myrtenol	1193	0.58	0.33	0.36	0.37	0.32
27	trans-2-Caren-4-ol	1222	0.53	0.29	0.43	0.33	0.42
28	D-Carvone	1223	0.27	0.22	0.26	0.19	0.34
29	cis-Carveol	1226	0.06	0.03	0.04	0.05	0.03
30	Nerol	1228	1.85	2.16	1.56	2.05	1.6
31	Neral	1242	10.02	7.23	8.57	8.18	6.37
32	Piperitone	1250	0.15	0.11	0.14	0.12	0.07
33	2,6,6-Trimethyl-1-cyclohexene-1-acetaldehyde	1254	0.27	0.12	0.19	0.18	0.15
34	Perillic aldehyde	1257	0.03	0.03	0.02	0.03	0.04
35	para-Cymen-7-ol	1289	0.05	0.09	0.13	0.05	0.1
36	8,11,14-Eicosatrienoic acid. (Z.Z.Z)-	1294	0.04	0.05	0.03	0.03	0.03
37	1-(1,3-Dimethyl-buta-1.3-dienyl)-3,7,7-trimethyl-2-oxa- bicyclo[3.2.0]hept-3-ene	—	0.03	0.03	0.03	0.03	0.06
38	trans-Carvyl acetate	1342	0.07	0.07	0.07	0.08	0.04
39	Eugenol	1356	0.19	0.22	0.2	0.21	0.31
40	Geranyl acetate	1365	0.66	1.22	0.91	1.29	1.06
41	α-Copaene	1375	1.25	1.73	1.27	1.45	2.16
42	Isoledene	1377	3.48	4.46	3.89	4.19	4.04
43	7-Tetracyclo [6.2.1.0 (3.8)0(3.9)] Undecanol, 4,4,11,11-tetramethyl-	—	0.1	0.17	0.12	0.14	0.13
44	Di-epi-α-cedrene	1412	0.67	0.96	0.67	0.82	0.68
45	β-Caryophyllene	1420	3.11	3.26	2.77	4.18	1.85
46	ç-Elemene	1433	2.3	3.04	2.77	2.99	2.93
47	trans-α-Bergamotene	1434	0.09	0.09	0.08	0.09	0.04
48	Aromadendrene	1440	0.06	0.05	0.06	0.1	0.05
49	α-Humulen	1453	0.6	0.49	0.59	0.61	0.2
50	Alloaromadendrene	1460	1.66	1.36	1.02	1.3	1
51	Germacrene-D	1480	0.28	0.39	0.29	0.36	0.31
52	Ar-curcumene	1483	11.47	13.38	11.28	14.15	11.3
53	β-Guaiene	1490	0.01	0.01	0.02	0.02	0.01
54	Tricyclo[5.2.2.0(1.6)]undecan-3-ol, 2-methylene-6,8,8-trimethyl-	1498	0.49	0.68	0.56	0.56	0.65
55	α-Muurolene	1499	—	0.04	—	0.04	—
56	ç-Himachalene	1505	0.34	0.6	0.47	0.46	0.64
57	Calamenene	1514	0.09	0.16	0.11	0.12	0.13
58	9-Isopropyl-1-methyl-2-methylene-5-oxatricyclo[5.4.0.0(3,8)]undecane	1522	0.05	0.09	0.07	0.08	0.09
59	γ-Cadinene	1523	0.17	0.26	0.19	0.23	0.22
60	ç-Cadinene	1524	3.89	5.04	4.57	4.99	4.86
61	β-Spathulenol	1576	13.27	10.19	15.61	9.42	13.42
62	trans-Caryophyllene oxide	1580	13.52	13.25	14.14	13.28	14.22
63	Ledene oxide-(I)	1631	1.75	2.96	2.41	2.25	3.01
64	8-Cedren-13-ol	1657	—	0.02	0.03	0.01	0.05
65	Alloaromadendrene oxide-(1)	1672	3.06	4.26	4.37	3.79	4.35
66	Alloaromadendrene oxide-(2)	1678	0.28	0.5	0.4	0.4	0.79
67	Eudesma-4,11-dien-2-ol	1690	0.31	0.46	0.46	0.45	0.62
68	trans-Nuciferol	1727	2.31	3.1	2.6	3.1	3.86
69	cis-Nuciferol	1734	2.17	3.3	2.32	2.8	3.17
70	Murolan-3,9(11)-diene-10-peroxy	—	0.36	0.53	0.5	0.48	0.73
71	Ledene oxide-(II)	2062	0.35	0.45	0.47	0.45	0.57
72	Tricyclo[5.2.2.0(1.6)]undecan-3-ol, 2-methylene-6,8,8-trimethyl-	—	0.97	1.25	1.31	1.33	1.35

Notes: ^aCompounds are listed in order of their elution from a DB-5 column. ^bLinear retention index taken from NIST 08, National Institute of Standards and Technology, Mass Spectral Library (NIST/EPA/NIH). ^cEssential oil of Agadir. ^dEssential oil of Beni Mellal. ^eEssential oil of Berkane. ^fEssential oil of Demnate. ^gEssential oil of Marrakech.

[Source ³¹⁾]

Molecules belonging to five biochemical families, namely, sesquiterpenes (Ar-curcumene 12.32%), terpene oxides (caryophyllene oxide 13.68%), sesquiterpenols (spathulenol 12.38%), monoterpene aldehydes (neral 8.07%), and monoterpenols (cis-verbenol 6.28%), constitute 53% of the essential oil’s major compounds (see Table 3).

Table 3. Major compounds of essential oil of lemon verbena analyzed by gas chromatography–mass spectrometry analysis

Molecules	% Essential oil of Agadir	% Essential oil of Beni Mellal	% Essential oil of Berkane	% Essential oil of Demnate	% Essential oil of Marrakech
trans-Caryophyllene oxide	13.52	13.25	14.14	13.28	14.22
β-Spathulenol	13.27	10.19	15.61	9.42	13.42
Ar-curcumene	11.47	13.38	11.28	14.15	11.30
Neral	10.02	7.23	8.57	8.18	6.37
cis-Verbenol	7.78	—	5.22	5.82	—

[Source ³²⁾]

Packaging methods and storage duration affect essential oil content and composition of lemon verbena ³³⁾. In packaging this study ³⁴⁾ showed that the packaging of lemon verbena leaves with nitrogen preserved the highest essential oil content at the end of 8 months of storage. Although vacuum packed lemon verbena leaves preserved the highest amount of citral during storage, the highest amount of limonene and desired contents of citral and 1,8‐cineole were found in leaves packed with nitrogen ³⁵⁾.

What is lemon oil

Lemon (Citrus limon L. Burm) is a flowing plant belonging to the Rutaceae family native to Asia. Lemon essential oil has shown antifungal ¹⁾ and antioxidative activities ²⁾, as well as improved hippocampus function ³⁾. Citrus essential oil has been identified in different parts of fruits as well as in leaves (particularly present in fruit), showing that limonene, b-myrcene, a-pinene, p-cymene, b-pinene, terpinolene, and other elements are the major aromatic compounds of many citrus species ⁴⁾. Citrus lemon essential oil is used for many applications such as food, medicines, cosmetics and perfumes, detergents, aromatherapy, pathogen inhibition, and insect control ⁵⁾.

The bioactive compounds in lemon essential oil are limonene, β-pinene, and γ-terpinene ⁶⁾. In addition, minor components such as α-pinene, myrcene, and geraniol are present ⁷⁾. Limonene, a major compound in lemon essential oil, showed lipid-lowering effects via upregulation of peroxisome proliferator-activated receptor alpha and liver X receptor beta in mice with high-fat diet-induced obesity ⁸⁾. γ-Terpinene also had a lipid-lowering effect ⁹⁾.

Lemon essential oil is able to accelerate the production of white blood cells, strengthen the immune system, and help in the digestion processes ¹⁰⁾. The main constituents of lemon essential oil have demonstrated antiseptic, astringent, and detoxifying properties for blemishes associated with oily skin ¹¹⁾.

Figure 1. Lemon essential oil

Lemon oil production processes

Several processes are used to produce lemon oil. Expressed lemon oil are produced by pressing the outer rind of the ripe lemon fruits by sponge-press (i.e., by hand) or machines ¹²⁾. Lemon oil may be produced more economically using an integrated juice-oil procedure such as the Brown Oil Extractor ¹³⁾, where citrus fruit is partially submerged in water and abraded by metal discs. The oil is separated from the juice as a water-emulsion, and further separated using centrifugation to obtain the oil. The yield of expressed lemon oil is approximately 4% for lemons based on the weight of whole fruit ¹⁴⁾. Lemon oil is also produced by distillation of expressed oil or direct distillation of fruit ¹⁵⁾. Lemon oil is distilled (rectified) for removal of terpenes in order to improve solubility and permit use for flavoring carbonated beverages ¹⁶⁾. Lemon oil can also be steam distilled to remove nonvolatile furocoumarins and are subsequently marketed as “psoralen free” (LOLI Global Industries). The type of lemon oil added to cosmetics are not regulated by law, nor limited by recommendations of appropriate trade organizations.

Lemon essential oil phototoxicity

Lemon oil are added as fragrances to a number of perfumed cosmetic products ¹⁷⁾. Many of these products are intended for use on sun-exposed skin. Clinical and experimental studies have found that lime oil are phototoxic. A phototoxic reaction may occur when certain chemicals are applied to the skin and subsequently exposed to the sun. Phototoxic reactions result from direct damage to tissue caused by light activation of the photosensitising agent. This is called photocontact dermatitis. Photodermatitis is a self-limited problem that resolves spontaneously once the offending agent is removed or avoided. If avoiding the offending agent is not practical, then affected individuals should follow sun protection strategies, including wearing sun protective clothing and using sunscreen. The U.S. Food and Drug Administration (FDA) has reported the oil from the Persian lime (Citrus aurantifolia, var. Swingle) is presented as a cause of photodermatitis, and 11 cases are reported in which this reaction was observed ¹⁸⁾. Because of their phototoxicity, the International Fragrance Association has recommended safe use levels for “leave on products” applied to sun-exposed skin. These safe use levels are intended to avoid short-term phototoxicity. However, long-term effects have not been addressed.oxypeucedanin and

The phototoxicity elicited by lemon oil has been associated with naturally occurring furocoumarins. Two of these furocoumarins, 5-methoxypsoralen (bergapten) and oxypeucedanin, have been identified as the probable phototoxins in both lemon oil and lime oil ¹⁹⁾. The levels of these furocoumarins have been found to vary significantly with growing conditions. The phototoxic potency of oxypeucedanin was only one-quarter of that of 5-methoxypsoralen (bergapten). However, the amounts of these two phototoxic compounds present in lemon oils produced in different regions of the world varied by a factor of more than 20 (5-methoxypsoralen, 4-87 ppm; oxypeucedanin, 26-728 ppm), and their ratio was not constant. The two compounds accounted for essentially all of the phototoxic activity of all lemon-oil samples. Among various other citrus-essential oils investigated, lime oil and bitter-orange oil also contained large amounts of oxypeucedanin. Oxypeucedanin was found to elicit photopigmentation on colored-guinea-pig skin without preceding visible erythema.

While the photogenotoxicity of 5-methoxypsoralen is well established, the photogenotoxicity of oxypeucedanin is unknown ²⁰⁾. Bacterial mutagenesis studies indicated that oxypeucedanin is not mutagenic, however photogenotoxicity studies of oxypeucedanin are not available. Additionally, the mutagenicity and photomutagenicity of mixtures of coumarins and furocoumarins in lemon oil and lime oil have not been assessed ²¹⁾. The photogenotoxicity of oxypeucedanin alone or in mixtures of compounds representative of lemon oil and lime oil has not been assessed. These photogenotoxicity studies are needed. Additional studies on photocarcinogenicity should be conducted if coumarins or furocoumarins are significantly photogenotoxic as individual compounds or in complex mixtures (e.g. lemon or lime oil).

Lemon oil and lime oil were selected by the Center for Food Safety and Applied Nutrition for photogenotoxicity and photocarcinogenesis studies since these phototoxic oils contain furocoumarins. Furocoumarins such as 5-methoxypsoralen have been shown to be photocarcinogenic and are present in lemon and lime oils ²²⁾.

The phototoxicity of lemon oil and lime oil has been demonstrated in both experimental models and humans. Naganuma et al. ²³⁾, studied the phototoxicity of lemon oil obtained from different geographic locations. Lemon oil was diluted in ethanol (100% lemon oil, 50% lemon oil, and 20% lemon oil) and applied to backs of shaved, albino guinea pigs. Animals were then exposed to UVA radiation (320-400 nm, 13 J/cm²). Erythema was evaluated at 24, 48 and 72 hr after irradiation. Undiluted lemon oil and 50% lemon oil elicited phototoxicity for most of the samples tested. Lemon oil from Australia and Brazil elicited a weaker phototoxic than lemon oil from the Ivory Coast, Sicily, California, or Argentina. In an effort to identify the phototoxic components in lemon oil, these investigators fractionated samples by solvent extraction and subsequent phototoxicity testing of isolated components. Two phototoxic components were identified: oxypeucedanin and 5-methoxypsoralen (see Figure 2).

Figure 2. Major Coumarins and Furocoumarins in Lemon oil

Forbes et al. ²⁴⁾, have investigated the phototoxicity of a large number of fragrance raw materials including lemon oil and lime oil. Fragrance raw materials were tested using humans, pigs and albino, hairless mice. Several irradiation sources were used including sunlight, a solar simulator and a UVA radiation source (black light). Expressed lime oil was phototoxic in all three species under all three radiation sources. Distilled lime oil usually elicited no phototoxic response in any species. Two samples of distilled lime oil (derived from expressed lime oil), however, were found to be phototoxic. Lemon oil from Greece, Italy and from Florida (Persian limes) was reported to be phototoxic.

Coumarins and Furocoumarins Occurring in Lemon Oil and Lime Oil

Investigators have examined the level of coumarins and furocoumarins in lemon oil and lime oil (Table 1). A large body of evidence indicates that these secondary metabolites are photoactivated phytoalexins, produced to protect plants from bacterial, fungal, parasitic, and insectile infestations ²⁵⁾. Consistent with their protective function, levels of coumarins and furocoumarins vary widely. Naganuma et al. ²⁶⁾, found that levels of oxypeudedanin doubled in lemon oil derived from the same growing area in Australia between 1979 and 1980. The levels of oxypeudedanin in lemon oil from the Ivory Coast, Sicily and California diminished nearly three-fold in the same time period.

The photogenotoxicity and photocarcinogenicity of several linear furocoumarins (psoralens) have been well documented ²⁷⁾. 5-Methoxypsoralen (bergapten), a component of lemon and lime oil, is photogenototic in both prokaryotic and eukaryotic test systems. In addition, 5-methoxypsoralen (bergapten) has been found to be photocarcinogenic in an experimental model ²⁸⁾. Little is known about the photogenotoxicity and photocarcinogenicity of other furocoumarins found in lemon oil and lime oil. The mutagenicity of oxypeucedanin has been assessed in 6 tester strains of Salmonella typhimurium by Uwaifo ²⁹⁾. Oxypeucedanin was not mutagenic, however, photomutagenicity was not assessed.

Table 1. Levels of Major Coumarins and Furocoumarins in Lemon Oil and Lime Oil

[Source ³⁰⁾]

Lemon essential oil uses

Lemon (Citrus limon L. Burm) is grown in many parts of the world for juice production and like the other citrus fruits, the peels are considered as waste. Lemon peels are in use in Chinese medicine and African folklore in the management of degenerative conditions, though there is dearth of information on
the scientific basis for the use of lemon peels. Much of the bioactivity of citrus peels have been linked to the phenolic content ³¹⁾, which are more concentrated in the lemon peels that in the juices and seeds. However, there are a lot of other bioactive constituents, such as essential oils, which also contribute to their observed medicinal uses. Essential oils can be obtained in significant quantities from the peels of citrus fruits and they contain numerous compounds rich in polypohenols and terpene hydrocarbons ³²⁾. While, the juice have been shown to possess anticholiensterase and antioxidative properties, there is scarce of information on the medicinal potentials of the lemon peels, especially the essential oils, which are a major component of the peels and can be extracted in significant amount.

Recent trends in the management of neurodegenerative conditions, especially Alzheimer’s disease is to increase brain acetylcholine levels with the use of cholinesterase inhibitors. This is because in Alzheimer’s disease conditions there is elevated cholinesterase activities ³³⁾ which serve to break down the neurotransmitters acetylcholine and butyrylcholine thereby giving rise to the symptoms observed in Alzheimer’s disease. However, due to the side effects associated with the use of synthetic cholinesterase inhibitors, attention is been given to natural sources of cholinesterase inhibitors. Some sea weeds ³⁴⁾, citrus juices ³⁵⁾, vegetables and herbs ³⁶⁾ have been shown to be sources of cholinesterase inhibitors. In addition, the use of foods rich in antioxidants have been proposed to be beneficial in the prevention and management of neurodegenerative conditions because the high oxygen consumption of the brain cells and neurons especially, attack by reactive oxygen species ³⁷⁾. This test tube study ³⁸⁾ showed the inhibition of cholinesterases and Fe2+ and quinolinic acid-induced Malondialdehyde production as well as radicals (DPPH*, ABTS*, hydroxyl radicals and nitric oxide) scavenging abilities are possible mechanisms by which lemon peel essential oil could be used in the management and/or prevent neurodegenerative conditions. However, further in vivo experiments and clinical trials are recommended.

The bioactive compounds in lemon essential oil, as analyzed by gas chromatography, are shown in Table 2. The amount of limonene, β-pinene, and γ-terpinene in lemon essential oil was 66.57%, 10.00%, and 9.95%, respectively, indicating that limonene is the major bioactive compound. Besides these, sabinene, α-pinene, myrcene, and geraniol were present in a range of 1~2%. Seven other bioactive compounds were also detected in small quantities.

Plasma lipid levels, particularly cholesterol and LDL “bad” cholesterol levels are positively associated with atherosclerosis development due to hypercholesterolemia. In this animal study ³⁹⁾ , lemon essential oil decreased plasma total cholesterol levels in hypercholesterolemia-induced rabbits, which was significantly higher than the effects from limonene. In addition, the HDL “good” cholesterol level was significantly increased in the limonene group. Moreover, LDL “bad” cholesterol levels in the lemon essential oil and limonene groups were reduced although no significances were found. Limonene had cholesterol-lowering effects in hypercholesterolemia-induced animals ⁴⁰⁾ via downregulation of PPARα and LXRβ ⁴¹⁾. Moreover, γ-terpinene in lemon essential oil, has exhibited cholesterol-lowering effects in animals ⁴²⁾. These effects were greater than those of limonene, a major bioactive compound in lemon essential oil, suggesting that the synergistic effects of bioactive compounds in lemon essential oil were stronger than the effects of limonene alone. Besides limonene, 13 other bioactive compounds (including sabinene, β-pinene, γ-terpinene, α-pinene, myrcene, and geraniol) were detected. In particular, the antioxidative effect of γ-terpinene has been reported to be 3-fold higher than that of limonene ⁴³⁾. Future research studies are needed to elucidate the mechanisms through which lemon essential oil prevents atherosclerosis as well as to determine its effect on inflammation and immune responses.

Table 2. Chemcial composition of lemon essential oil

Compound	Relative area (%)
Limonene	66.57
β-Pinene	10.00
γ-Terpinene	9.95
Sabinene	1.60
α-Pinene	1.95
Myrcene	1.59
geraniol	1.17
Neral	0.87
β-Bisabolene	0.59
Neryl acetate	0.53
trans-α-Bergamotene	0.43
Geranyl acetate	0.35
Terpinolene	0.29
α-Terpineol	0.12

[Source ⁴⁴⁾]

Lemon, have been shown to be effective against Candida strains ⁴⁵⁾. However, the reports on the antifungal potential of lemon essential oil against Candida yeasts are ambiguous ⁴⁶⁾. Some literature data recommend it as highly effective, while other reports that the effects of its use are quite ordinary ⁴⁷⁾, ⁴⁸⁾. Devkatte et al. ⁴⁹⁾ obtained the Minimum Inhibitory Concentration (MIC) value of 0.5 % and the average zone of inhibition of approximately 17.5 mm for the lemon essential oil tested by them, while the zones of inhibition for the selected Candida strains determined by Warnke et al. ⁵⁰⁾ measured 16–43 mm. Higher mean values related to the zones of inhibition for Candida albicans, ranging from 23 to 45 mm, may be due to the differences in diffusion of particular essential oil ingredients in agar ⁵¹⁾ and the concentration of biologically active substances, mainly citral, geraniol and verbenol. Thus, when evaluating the essential oils produced from a particular plant, it is good to know their chemical composition. According to many authors, the essential oil volatile phase composition depends on the conditions in which the plant has grown, its development stage and the way it is stored ⁵²⁾. In the case of citrus fruits, climatic conditions and the region of origin of the fruit are important ⁵³⁾. Differences in potential fungicidal properties of lemon essential oils may be due to variable qualitative and quantitative composition of individual essential oils and are related to the development stage of the fruit prior to extraction, fruit condition and quality as well as plant growing conditions ⁵⁴⁾.

According to Fisher and Phillips ⁵⁵⁾, the content of volatile substances in lemon essential oils may range from 85 to 99 %. The qualitative composition—proportions between the content of particular monoterpenes, sesquiterpenes and their oxygenated derivatives—changes as well ⁵⁶⁾. The highest concentration of volatile substances in lemon essential oils is observed in oils produced from medium-ripe fruit ⁵⁷⁾. Citrus essential oils are among the oils generally regarded as safe (GRAS) by the US Food and Drug Administration ⁵⁸⁾.

Lemon essential oils had different chemical compositions, but, except the Aromatic Art essential oil, they contained almost exclusively terpenes and oxygenated terpenes ⁵⁹⁾. The content of monoterpenes in the tested essential oils is shown in Table 3, monoterpenoids in Table 4 and sesquiterpenes, oxygenated sesquiterpenes and other compounds of the six tested essential oils in Table 5.

Table 3. Monoterpenes in lemon essential oils

	ETJA	Vera-Nord	Avicenna-Oil	Dufti by Gies	Croce Azzurra	Aromatic Art
	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)
Aliphatic monoterpenes
ß-myrcene	4.11	1.46	0	6.94	5.42	0.37
trans-ocimene	0.13	0.49	0	0	0	0
Monocyclic monoterpenes
ß-felandrene	0	0	0	0.4	15.03	0
limonene	48.27	23.39	42.03	63.2	38.5	22.42
α-terpinene	0.4	0.12	0	0	0.14	0
γ-terpinene	4.85	5.87	0	4.78	0.16	0
terpinolene	1.19	0.3	0	0.34	0.04	0
Bi- and tricyclic monoterpenes
bornylene	0	0	0.49	0	0	0
camphene	0.35	0	0.17	0	0	0
3-carene	0	0	0	0.16	0	0
α-pinene	11.06	1.44	3.42	3.61	5.56	0.16
ß-pinene	15.14	8.93	15.15	14.31	19.98	2.21
3-thujene	0	0.3	0.22	0.33	1.25	0
sabinene	0	0.65	0	0	0	0.1
tricyclene	0.21	0	0	0	0	0
Monoterpenes	85.7	42.96	61.49	94.07	86.07	25.27

[Source ⁶⁰⁾]

Table 4. Oxygenated monoterpenes in lemon essential oils

	ETJA	Vera-Nord	Avicenna-Oil	Dufti by Gies	Croce Azzurra	Aromatic Art
	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)
Oxygenated aliphatic monoterpenes
citral (mix of isomers)	0	0.23	0.7	1.06	2.63	0
trans-citral	7.14	15.52	0	0	0.16	0.36
cis-citral	4.3	19.41	0	0.3	1.54	0
citronellal	0.2	0	0	0.7	0.29	0
geranyl acetate	0.91	0.59	0	0	0	0
cis-geraniol	0	4.96	0	0	0	0
trans-geraniol	0	3.39	1.58	0	0	0
Linalool	0.29	0	0.63	1.73	1.51	0
linalyl propanoate	0	0.25	0	0.24	0	0
bergamol	0	0	0	0	0	9.53
neryl acetate	0.49	0.42	0	0.16	1.14	0.21
Oxygenated monocyclic monoterpenes
trans-carveol	0	0	3.36	0	0	0
carvone	0	0	7.28	0.1	0	0
trans-p-2,8-mentadien-1-ol	0	0	1.84	0	0	0
menthol	0,12	0	0	0	0	0
menthone	0,06	0	0	0	0	0
1-terpinen-4-ol	0	0	5.57	0	0.42	0
Oxygenated bi- and tricyclic monoterpenes
pinene oxide	0.17	0	0	0.65	0	0
pinocarveol	0	0	5.44	0	0	0
verbenol	0.08	0	4.9	0	0	0
trans-verbenol	0	0	1.5	0	0	0
Oxygenated monoterpenes	13.76	44.76	32.8	4.93	7.67	10.09

[Source ⁶¹⁾]

Table 5. Sesquiterpenes, oxygenated sesquiterpenes and others compounds in lemon essential oils

	ETJA	Vera-Nord	Avicenna-Oil	Dufti by Gies	Croce Azzurra	Aromatic Art
	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)	Area (%)
Sesquiterpenes
α-bergamotene	0	0.95	2.31	0	0.89	0
ß-bergamotene	0	0	0	0	1.54	0
ß-bisabolene	0	0.48	0	0	1.82	0
α-cadinene	0	0	0	0.13	0	0
ß-cadinene	0	0	0	0.09	0	0
calarene	0	0	0	0.15	0	0
caryophyllene	0	0.24	0	0.29	1.11	0.12
α-caryophyllene	0	6.09	0	0	0.06	0
ß-farnesene	0	0	0	0	0.06	0
germacene B	0	0	0	0	0.38	0
valencene	0	0	0	0.32	0	0
Sesquiterpenes	0	7.76	2.31	0.98	5.84	0.12
Oxygenated sesquiterpenes
caryophyllene oxide	0	0	3.2	0	0	0
farnesol	0	4.48	0	0	0	6.12
Oxygenated sesquiterpenes	0	4.48	3.2	0	0	6.12
Others
hexanoic acid	0	0	0	0	0	0.47
hydrocinnamic acid	0	0	0	0	0	6.54
ß-ionene	0	0	0	0	0	7.81
isopropyl myristate	0	0	0	0	0	42.78
1,1-dimethoxy-2-phenylopropane	0	0	0	0	0	0.36
Others	0	0	0	0	0	57.6

[Source ⁶²⁾]

Despite the fact that all tested lemon essential oils contained limonene, their impact on the growth of the tested Candida yeasts was different. The Dufti essential oil, although contained the largest amounts of limonene, did not inhibit the growth of any of the tested yeast strains. The Croce Azzurra essential oil also proved to be ineffective as far as the inhibition of the growth of the tested strains is concerned. Therefore, the inhibitory effect of essential oils does not depend on the concentration of limonene but on the presence of other biologically active substances and the sensitivity of yeasts. Candida glabrata and Candida tropicalis strains are much less sensitive than the Candida albicans strain. Thus, only some essential oils at higher concentrations exhibit the antifungal potential against these yeast strains. Candida glabrata 33 and Candida glabrata 35 strains were the most resistant to the tested lemon essential oils (none of the tested products inhibited their growth). Lemon essential oils with high content of monoterpenoids may be an ingredient of products against candidiasis caused by Candida.

Limonene—a monocyclic terpene—was the main ingredient of the tested lemon essential oils. However, the antimicrobial activity depended on the content of oxygenated monoterpenes—the higher the content, the better fungicidal effects were observed. This is confirmed by the literature data ⁶³⁾. Vera-Nord and Avicenna-Oil essential oils contain 44.8 and 32.8 % of oxygenated monoterpenes, respectively, and exhibit antifungal potential against Candida albicans across the full range of the concentrations used and may be used as antifungal preparations against this yeast strain. The Aromatic Art essential oil, which is less effective as far as the inhibition of the growth of Candida albicans is concerned, contains hydrocinnamic acid and bergamol—compounds known for their antimicrobial properties ⁶⁴⁾.

Candida glabrata and Candida tropicalis strains were less sensitive to the tested essential oils than the Candida albicans strain—their growth was inhibited by essential oils used at higher concentrations. The Vera-Nord essential oil contains significant amounts of cis- and trans-citral isomers or geraniol and γ-terpinene known for their fungicidal properties ⁶⁵⁾.

The growth of Candida glabarata was inhibited by two lemon essential oils: Avicenna-Oil and ETJA, which both contains citral and verbenol. Essential oils exhibit antifungal properties when they contain, at the same time, large amounts of one of these oxygenated monoterpenes and small amounts of the second one, may be the reason for the growth inhibition of the tested Candida glabarata yeasts.

The tested essential oils contained also other valuable ingredients, such as carvone, 1-terpinen-4-ol and γ-terpinene—all of these compounds also exhibit antifungal potential, which has already been described in the literature ⁶⁶⁾.

The use of lemon essential oils in all kinds of candidiasis seems to be an interesting solution because of their documented safety. It should also be noted that some of the authors at the same time emphasize that it is necessary to conduct tests on the toxicity and possible allergenic effects of selected essential oils ⁶⁷⁾. Therefore, understanding the relationship between the chemical composition of essential oils and their antimicrobial activity is of great importance due to the potential use of lemon essential oil-based products as natural remedies against candidiasis caused by Candida albicans.

Lemon oil for skin

Lemon oil reported uses for skin conditions but are unproven and lacking studies in human for treating abscesses, acne, antiseptic, athlete’s foot, blisters, boils, cellulite, corns, cuts, grazes, greasy and oily conditions, insect bites, mouth ulcers, rosacea, sores,ulcers, viral infections (cold sores, herpes, verrucae,and warts), and wounds ⁶⁸⁾, ⁶⁹⁾, ⁷⁰⁾, ⁷¹⁾, ⁷²⁾, ⁷³⁾, ⁷⁴⁾, ⁷⁵⁾.

Summary

Regardless of the frequency of the therapeutic claims made for lemon essential oil and the laboratory test tube activity, most evidence of the therapeutic efficacy of lemon essential oil has been published in books about aromatherapy and not in peer-reviewed journals. A few clinical trials have emerged, but their results are rarely confirmed completely to substantiate lemon essential oil effectiveness. More rigorous clinical trials would establish confidence from the medical professionals for the benefits of patients and consumers ⁷⁶⁾.

What is cassia

Cassia (Cinnamomum cassia Presl) commonly known as Chinese cassia or Chinese cinnamon, is one of several species of Cinnamomum from Lauraceae family used primarily for their aromatic bark. The dried stem bark of Cinnamomum cassia, i.e., cassia bark, is an important spice ingredient in food and cosmetic industry, in the United States, United Kingdom, and India, Chinese cassia is the most common type of cinnamon used. Cinnamomum cassia buds are also used as a spice, especially in India, and were once used by the ancient Romans. Cassia bark is also considered to have medicinal properties, such as antimicrobial ¹⁾, anti-cancer ²⁾, ³⁾, ⁴⁾, anti-inflammatory ⁵⁾ and anti-diabetic properties ⁶⁾, ⁷⁾. Cinnamomum cassia extract has anti-invasion and anti-migration effects of highly metastatic human lung carcinoma cells, while cinnamomum cassia extract exerts no cytotoxicity of normal human lung cell lines as a combination medication with adjuvant chemotherapy on human lung cancer patients ⁸⁾. In addition, the methanol extract of Cinnamomum cassia twigs was found to possess tyrosinase inhibitory activity ⁹⁾. Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasma, age spots and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation ¹⁰⁾. The twigs of cassia is popularly used in China to treat inflammatory processes, pain, menstrual disorders, hypertension, fever etc ¹¹⁾.

Hyperuricemia is a metabolic disease characterized by elevated blood uric acid levels ¹²⁾. Hyperuricemia results from increased production or impaired excretion of uric acid ¹³⁾ and elevated uric acid levels cause accumulation of urate crystals in joints and the kidneys, leading to gout and gouty arthritis ¹⁴⁾. It was also recently shown that hyperuricemia is associated with hyperlipidemia, hypertension, cardiovascular diseases, and diabetes ¹⁵⁾. Therefore, uric acid level regulation may play an important role in the prevention and treatment of various diseases, including hyperuricemia. Uric acid is a final product of purine catabolism and is produced via the catalytic activities of xanthine oxidase, a rate-limiting enzyme responsible for converting hypoxanthine to xanthine, which is subsequently converted to uric acid ¹⁶⁾.

It has been reported that Cinnamomum indicum flower and Cinnamomum cassia bark have served as the main ingredients in several prescriptions designed to treat hyperuricemia and gout in traditional Chinese medicine ¹⁷⁾. According to a recent report, in a test tube study of traditional Chinese medicinal plants, methanol extracts of Cinnamomum indicum flower and Cinnamomum cassia bark inhibited xanthine oxidase activity ¹⁸⁾, ¹⁹⁾. Oil extracts from Cinnamomum indicum flower, Cinnamomum cassia bark, and Cinnamomum osmophloeum leaves reduced serum uric acid levels in potassium oxonate-induced hyperuricemic animals ²⁰⁾. These findings indicate that Cinnamomum indicum flower and Cinnamomum cassia bark have antihyperuricemic effects.

Cassia is an evergreen tree originating in southern China, and widely cultivated there and elsewhere in southern and eastern Asia (India, Indonesia, Laos, Malaysia, Taiwan, Thailand, and Vietnam) ²¹⁾. The cassia tree grows to 10–15 m tall, with greyish bark and hard, elongated leaves that are 10–15 cm long and have a decidedly reddish color when young.

Chinese cassia is a close relative to Ceylon cinnamon (Cinnamomum verum), Saigon cinnamon (Cinnamomum loureiroi), also known as “Vietnamese cinnamon”, Indonesian cinnamon (Cinnamomum burmannii), also called “korintje”, and Malabar cinnamon (Cinnamomum citriodorum) from Sri Lanka. In “all five species”, the dried cassia bark is used as a spice. Chinese cassia’s flavor is less delicate than that of Ceylon cinnamon. Its bark is thicker, more difficult to crush, and has a rougher texture than that of Ceylon cinnamon.

Figure 1. Cassia bark (Cinnamomum cassia Presl)

Figure 2. Cinnamomum cassia tree

It is known that plant essential oil has various functional properties, such as a pleasant aroma, insect and animal repellant, as well as inhibitory effects against microorganisms. The essential oil from the relative cinnamon species, Cinnamomum zeylanicum Blume, has been reported to show anti-tyrosinase activity, and cinnamaldehyde was found to be mainly responsible for this inhibition effect ²²⁾. The Cinnamomum cassia essential oil) has hypouricemic ²³⁾ and antifungal activities ²⁴⁾. A number of tyrosinase inhibitors from both natural and synthetic sources that inhibited monophenolase, diphenolase or both of these activities have been identified to date ²⁵⁾. These tyrosinase inhibitors include plant polyphenols and aldehydes, fungal metabolites, derivatives of natural compounds, and synthetics origins. The tyrosinase inhibitory constituents of the essential oil extracted from Cinnamomum cassia ²⁶⁾ and relative cinnamon species, Cinnamomum zeylanicum ²⁷⁾ have been well documented. Cinnamaldehyde was found to be the major constitute of the essential oil. However, the inhibitory pattern of cinnamaldehyde isolated from Cinnamomum cassia ²⁸⁾, Cinnamomum zeylanicum ²⁹⁾, olive oil (Kubo and Kinst-Hori 1999) and the root of Pulsatilla cernua was rather controvesial. Cinnamaldehyde from Cinnamomum cassia was a competitive tyrosinase inhibitor whereas those from Cinnamomum zeylanicum, olive oil and and the root of Pulsatilla cernua was a noncompetitive tyrosinase inhibitor.

Cassia vs Cinnamon

Cinnamon is a spice obtained from the inner bark of several tree species from the genus Cinnamomum. Cinnamomum verum or Sri Lanka or Ceylon cinnamon is sometimes considered to be “true cinnamon”, but most cinnamon in international commerce is derived from related species, also referred to as “cassia” ³⁰⁾. In 2016, Indonesia and China produced 75% of the world’s supply of cinnamon.

Cinnamomum verum (formerly Cinnamomum zeylanicum), “true cinnamon” or Sri Lanka or Ceylon cinnamon, is a small evergreen tropical tree in the Lauraceae (laurel family) that originated in Sri Lanka and is one of several Cinnamomum species that produce the commercially important spice known as cinnamon. Although Cinnamomum cassia (Cinnamomum aromaticum), which is less expensive and has a stronger flavor, is often marketed as “cinnamon,” Cinnamomum verum is generally considered to have a more delicate flavor that is more suitable for desserts.

The names “cinnamon” and “cassia” cause considerable confusion, as they are often used interchangeably. In the U.S., the spice produced from the dried, ground bark of any of Cinnamomum species is referred to as “cinnamon,” without distinguishing among species. In addition, “cinnamon” may also refer to the spice obtained from the aromatic bark of an unrelated species, Canella winterana (in the Canellaceae). When the spice is sold in bark form, rather than ground, Cinnamomum verum (Sri Lanka or Ceylon cinnamon) can be distinguished from Cinnamomum cassia (Cinnamomum aromaticum) because it comes in tight rolls (quills) rather than in looser flakes with curled edges. It can be distinguished from the related Indonesian cinnamon (Cinnamomum burmanii) by the quills having many soft layers, which can easily be ground in a coffee grinder, as opposed neat quills composed of a single extremely hard layer.

The Cinnamomum verum tree grows to around 10 m (30 ft), and has leathery leaves, usually opposite, that are lanceolate to ovate, 11 to 16 cm (4.5 to 6.25 in) long, with pointed tips. The inconspicuous yellow flowers, which are tubular with 6 lobes, grow in panicles (clusters) that are as long as the leaves. The fruit is a small, fleshy berry, 1 to 1.5 cm (0.25 to 0.5 in) long, that ripens to black, partly surrounded by a cup-like perianth (developed from the outer parts of the flower).

The spice form of cinnamon is obtained by removing the outer bark of the tree, and scraping from it the inner bark, which is dried and ground into power. Cultivated trees may also be coppiced (cut back to encourage shoot development), so that the coppiced shoots can be harvested. Cinnamon oil is steam distilled from the leaves and twigs.

Cinnamon from various species has been used as a spice since ancient times. It is widely used to flavor baked goods, puddings and other desserts, and candies, as well as soups and stews, curries, meat and poultry dishes, and pickles. Cinnamon is also used to flavor beverages, including teas and mulled wine.

FAO estimates that total commercial production of all forms of cinnamon (derived from several species of Cinnamomum, including Cinnamomum cassia (Cinnamomum aromaticum), as well as canella (Canella winterana) was 155,000 metric tons, harvested from 186,000 hectares. China, Indonesia, Sri Lanka, and Vietnam together produced around 98% of the world’s total.

Cassia essential oil

The essential oil extracted by steam distillation from the stem bark of Cinnamomum cassia Presl was quantitatively analyzed using gas chromatography coupled with mass spectrometry ³¹⁾. The 16 constituent compounds identified, along with the retention times and Kovats indices, are listed in Table 1. The results showed that the two major constituents of Cinnamomum cassia essential oil were cis-2-methoxycinnamic acid (43.06%) and cinnamaldehyde (42.37%) and that the minor compounds were o-methoxycinnamaldehyde (5.11%), 1,2-dimethoxy-4-(3-methoxy-1-propenyl) benzene (2.05%), cinnamyl acetate (1.83%) and other compounds (1.25~0.16%) in that study ³²⁾. For comparison, a previous study reported that cinnamaldehyde (92.2%) was the most plentiful constituent in the Cinnamomum cassia essential oil ³³⁾. Different extraction processes and assay methods could have contributed to differences in cinnamaldehyde levels of Cinnamomum cassia essential oils ³⁴⁾. Cinnamaldehyde (77.1%) was also found to be the major constituent of volatile oil of the bark of Cinnamomum zeylanicum ³⁵⁾. Several studies have demonstrated that cinnamaldehyde has antimicrobial ³⁶⁾, antimutagenic (Shaughnessy et al. 2001), antitumorigenic (Ka et al. 2003) and immunomodulatory activities (Koh et al. 1998); furthermore, cinnamaldehyde is considered to possess tyrosinase-inhibitory effects with IC50 values from 0.52~0.97 mM (Lee 2002; Lee et al. 2000; Ngoc et al. 2009). Lee (2002) reported that 2-methoxycinnamic acid that had been isolated from Pulsatilla cernua root was a potent noncompetitive inhibitor of mushroom tyrosinase with an IC50 value of 0.34 mM. In addition, benzaldehyde, one of the flavor compounds characterized in anise oil, showed potent tyrosinase inhibitory activity with an IC50 of 0.82 mM (Kubo and Kinst-Hori 1998). Because the Cinnamomum cassia essential oil contained major in cinnamaldehyde and cis-2-methoxycinnamic acid, and trace readings of benzaldehyde. Furthermore, cinnamic aldehyde, the major constituent of leaf essential oil from Cinnamomum cassia, has been demonstrated to exhibit antibacteria activities, anti-lipopolysaccharide-induced NF-κB transcriptional activities ³⁷⁾. Cinnamic aldehyde which has α, β unsaturated carbonyl moiety exerted suppressive effect on toll-like-receptor-4- (TLR4-) mediated signaling ³⁸⁾. Cinnamomum cassia essential oil could inhibit cell proliferation and induce apoptosis in human oral squamous cell carcinoma HSC-3 cells ³⁹⁾.

Coumarins posses strong anticoagulant properties and can have potentially toxic effects on the liver ⁴⁰⁾. The coumarin content in Ceylon cinnamon (“true cinnamon”) is negligible and is not known to cause detrimental health effects, whereas the coumarin level in Cinnamomum cassia is much higher and can cause health risks if consumed in larger quantities on a regular basis ⁴¹⁾. Several countries have restricted the regular usage of Cinnamomum cassia as a result of this potential health hazard associated with high levels of coumarins ⁴²⁾.

Table 1. Analysis of the Cinnamomum cassia Presl essential oil

Note: ^aRetention time (min); ^bKovats index.

[Source ⁴³⁾]

Figure 3. Cinnamomum cassia chemical compounds (cinnamic aldehyde, cinnamic alcohol, cinnamic acid, and coumarin)

[Source ⁴⁴⁾]

Cassia Oil Toxicity

Studies have shown that the median lethal dose value (LD50 – is the amount of the substance required (usually per body weight) to kill 50% of the test population) of orally administered cinnamon oil in mouse 2670mg/kg body weight ⁴⁵⁾, cinnamon oil in rats 2800mg/kg body weight ⁴⁶⁾, cinnamon oil on rabbit skin 320mg/kg body weight ⁴⁷⁾, cinnamon oil mouse intra-peritoneum 500mg/kg body weight ⁴⁸⁾, cinnamaldehyde in animals is 1850 ± 37 mg/kg body weight ⁴⁹⁾. TOXICITY RATINGS: 3 = MODERATELY TOXIC: PROBABLE ORAL LETHAL DOSE (HUMAN) 0.5-5 g/kg body weight; between 1 oz and 1 pt (or 1 lb) for 70 kg person (150 LB) ⁵⁰⁾. Previous studies on Cinnamomum cassia have not documented any probable adverse effects related to the regular use of cinnamon in humans, in spite of Cinnamomum cassia containing potentially hepatotoxic coumarin levels ⁵¹⁾, ⁵²⁾.

In a 12-week rat feeding study on a mixture of cinnamyl compounds there was slight retardation of growth of males and lowering of food utilization in both sexes at 90 mg/kg body-weight/day. In another study lasting for 16 weeks groups of 10 male and 10 female rats were fed diets containing 0, 0.1, 0.25 and 1.0 per cent. of aldehyde. At the highest level there was slight swelling of hepatic cells and some hyperkeratosis of the epithelium of the forestomach ⁵³⁾.

A 7 1/2 yr old boy ingested 2 oz.(about 60 mL) of cinnamon oil and immediately felt a burning sensation in his mouth, chest, and stomach lasting for about 15 minutes ⁵⁴⁾. He then developed double vision, dizziness, vomiting, and collapse. Following ipecac and activated charcoal he developed diarrhea, more vomiting, dizziness, abdominal cramps, and burning in the rectal area. The white blood count was 29,800/cu mm. Gastrointestinal symptoms and sleepiness persisted for 5 hours ⁵⁵⁾.

Three cases of acute contact sensitivity to a new toothpaster (Close-Up). In all cases there was positive reaction to 0.5% cinnamon oil in petrolatum ⁵⁶⁾.

The European Food Safety Authority (EFSA) Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concludes that: cinnamaldehyde is safe at the maximum use level of 125 mg/kg complete feed for salmonids, veal calves and dogs, and at 25 mg/kg for the remaining target species ⁵⁷⁾.

What is camphor

Camphor occurs naturally in the fragrant camphor tree (Cinnamomum camphora) that has been traditionally obtained through the distillation of the wood of the camphor tree and can also be man-made using mainly turpentine as a starting material ¹⁾. Camphor is a major essential oil component of many aromatic plant species, as it is biosynthetically synthesized. Camphor, in its pure form, has a penetrating odor and exists as colorless or white crystals. Camphor is volatile, reactive and flammable. Camphor dissolves in water.

The fragrant camphor tree and its products, such as camphor oil, have been used since ancient times. The camphor tree was used as a fragrant wood in Babylon and Egypt. Camphor was used as a fumigant during the Black Death in Europe and considered as a valuable ingredient in both perfume and embalming fluid. Camphor is used as a plasticizer or cellulose nitrate, moth repellant, in varnish, chemical intermediate, mildew proofings, lacquers, insecticides, other explosives ²⁾, preservative, cosmetic ingredient, pyrotechnics and anti-infection agent ³⁾. Camphor is common in many liniments. Camphor is used in perfuming industrial products. Camphor has also been widely used as a fragrance in cosmetics, as a food flavorant, as a common ingredient in household cleaners, as well as in topically applied analgesics and rubefacients for the treatment of minor muscle aches and pains.

Camphor exhibits a number of biological properties such as insecticidal, antimicrobial ⁴⁾, ⁵⁾, antiviral, anticoccidial, anti-nociceptive, anticancer and antitussive activities, in addition to its use as a skin penetration enhancer. However, camphor is a very toxic substance and numerous cases of camphor poisoning have been documented ⁶⁾. Poisoning in adults and children can occur from swallowing, breathing, or dermal contact with preparations containing camphor. Camphor poisoning can result in nervous system and kidney effects. Other symptoms include colic, nausea, vomiting, diarrhea, anxiety, delirium, convulsions, seizures, coma, or rarely, death. In response to a series of poisoning cases of unintentional ingestion of camphor medicinal products, the U.S. Food and Drug Administration in 1982 restricted camphor content in these products to less than 11%. The American Conference of Governmental Industrial Hygienists ⁷⁾ determined that camphor was “Not Classifiable as a Human Carcinogen”. This is based on an absence of human data and reports of no tumor responses in animal studies following application to or under, the skin.

Camphor acts as a counter-irritant, rubefacient and mild analgesic and is included in liniments for relief of fibrositis, neuralgia and similar conditions. A rubefacient is a substance for skin application that produces redness of the skin e.g. by causing dilation of the capillaries and an increase in blood circulation. By ingestion camphor has irritant and carminative properties (relieving flatulence or prevent formation of gas in the gastrointestinal tract) and has been used as a mild expectorant and to relieve griping. Camphor has been used as a circulatory and respiratory stimulant (as a solution in oil given subcutaneously or intramuscularly), this use is considered hazardous. It has been used in combination with menthol and chenodeoxycholic acid to aid dispersal of bile duct stones, although this is no longer recommended ⁸⁾.

In response to several toxicity reports, the United States Food and Drug Administration evaluated the efficacy and toxicity of camphor-containing products. A limit of 11% in consumer products was set in 1983 and products labeled as camphorated oil, camphor oil, camphor liniment and camphorated liniment were banned completely ⁹⁾. However in most countries, especially in developing countries, medicaments containing camphor as high as 20% are easily available. According to 2001 data from the American Association of Poison Control Centers Toxic Exposure Surveillance System (TESS), 8,505 exposures to camphor products were reported, many of which resulted in mild symptoms with 89 moderate to severe outcomes but no fatalities ¹⁰⁾.

Dietary exposure to camphor arises from the consumption of foods flavored by using either herbs (e.g. basil, coriander, marjoram, rosemary, sage), their essential oils or the chemically defined flavoring substance d-camphor ¹¹⁾. Camphor is easily absorbed in the gastrointestinal tract. The major metabolic pathway is the oxidation to 5- and 3-hydroxycamphor, followed by conjugation and excretion. Camphor did not show mutagenic activity in Salmonella typhimurium strains and did not induce chromosome aberrations in vitro with and without metabolic activation. There was no evidence of reproductive and developmental toxicity after oral administration to rats and rabbits. The available data on toxicity of camphor are limited and thus a tolerable daily intake (TDI) cannot be derived. However, based on the available toxicity data and the European Food Safety Authority (EFSA) Panel´s conservative estimate of chronic exposure (15 mg/day equivalent to 250 μg/kg body weight (bw)/day) calculated using the maximum limits suggested by the Council of Europe, the European Food Safety Authority (EFSA) Panel considered that there would be no safety concern regarding chronic toxicity.

The reported acute toxicity data on adults and children arise mostly from accidental ingestion of camphor-containing medications. The probable lethal oral bolus dose has been reported to be in the range of 50 to 500 mg/kg body weight. No acute toxicity was reported after doses lower than 2 mg/kg body weight and clinically insignificant signs of toxicity may be seen in sensitive individuals at doses of 5 mg/kg body weight and higher, whereas clinically manifest toxicity in sensitive persons would require doses higher than 30 mg/kg body weight. Potential acute exposure related to the consumption of large amounts of certain foods on a single day was estimated by the European Food Safety Authority (EFSA) Panel for several age groups. It was lowest in adults (from 0.14 to 0.34 mg/kg body weight according to the food commodity) and highest in children under 6 (from 0.41 to 0.83 mg/kg body weight according to the food commodity). The commodity leading to the highest potential acute exposure was fresh cheese in all age groups.

The acute exposure estimates for children and adults are about 60-120 times and 150-360 times, respectively, lower than the probable lowest lethal oral bolus dose of 50 mg/kg body weight. The acute exposure estimates for children and adults are about 2-5 times and 6-14 times, respectively, lower than the dose of 2 mg/kg body weight below which no acute effects have been reported in human case studies. Although these margins might appear to be low, the large number of cases describing the dose-response relationship suggests that the data sufficiently cover inter-individual variability in sensitivity. Therefore, the European Food Safety Authority (EFSA) Panel concluded that it is unlikely that acute effects may occur in relation to consumption of foods providing less than 2mg/kg body weight in one large portion.

However, maximum permitted levels for d-camphor are not currently set in the European Union legislation and there is uncertainty on its actual upper use levels in foods and beverages currently on the market and on the high consumption of food flavored with d-camphor all over Europe. The European Food Safety Authority (EFSA) Panel therefore suggests that maximum limits should be set to ensure that exposure to camphor does not exceed 2 mg/kg body weight on a single day in any age group ¹²⁾.

Camphor is rapidly oxidized to campherols (2-hydroxycamphor and 3-hydroxycamphor), and then conjugated in the liver to the glucuronide form ¹³⁾. Camphor-related metabolites are relatively fat-soluble and may accumulate in fatty tissue. Campherol conjugated to glucuronic acid is eliminated mainly in the urine as an inactive compound ¹⁴⁾. Trace amounts are eliminated by the lungs.

The majority of drugs administered to humans and animals are eliminated by a combination of hepatic metabolism and renal excretion ¹⁵⁾. In the human body, camphor is oxygenated to alcohol campherol and then conjugated with glucuronic acid in the liver to become soluble in water before being excreted in the urine. Following oral ingestion, high concentrations of camphor have been detected in the fetal brain, liver, kidney, blood, as well as in amniotic fluid ¹⁶⁾. The exact mechanism of camphor-induced toxicity has not been completely elucidated, but a study by Park et al. ¹⁷⁾ indicated camphor specifically inhibits the nicotinic acethylcholine receptors (nAChRs), thereby causing inhibition of catecholamine secretion. This inhibition may be one cause of the toxicity as nicotinic acethylcholine receptors are known to play a major role at neuromuscular junctions ¹⁸⁾. Camphor ingestion may lead to abortion as it crosses the placenta and fetuses lack the enzymes to hydroxylate and conjugate with glucuronic acid ¹⁹⁾. No teratogenicity was noted during the foetal period of organogenesis after oral (+)-camphor administration to pregnant rats and rabbits at doses up to 1,000 mg/kg bodyweight/day and 681 mg/kg bodyweight/day respectively. However, the high dose of 1,000 mg/kg body weight/day caused toxic symptoms including clonic convulsions, pilo-erection and reduced motility in rats, but no retardations or malformations were observed. In the rabbit model a high dose of 681 mg/kg body weight/day resulted in reduced body weight gain and food consumption, but no retardations or malformations were observed ²⁰⁾.

As mentioned previously, camphor is a major component of many aromatic plant species. Millet et al. ²¹⁾ investigated the toxicity of some commercial essential oils including sage (Salvia officinalis), hyssop (Hyssopus officinalis), thuja (Thuja occidentalis) and cedar (Juniperus and Cupressus spp.). For sage (Salvia officinalis) oil, 3.2 g/kg of sage oil caused tonic-clonic convulsions in unanesthetized rats resulting in death. It was determined that the toxicity of sage (Salvia officinalis) oil appeared to be related to the presence of camphor ²²⁾.

Physical Properties and Sources of Camphor

Camphor is a waxy, white or transparent solid with a strong aromatic odor ²³⁾ which sublimates at room temperature and melts at 180 °C ²⁴⁾. Camphor is practically insoluble in water, but soluble in alcohol, ether, chloroform and other organic solvents. It is a terpenoid (1,7,7-trimethylbicyclo[2.2.1]-2-heptanone) with a chemical formula of C10H16O and exists in two enantiomeric forms: (1S)-(−)-and (1R)-(+)-camphor (Figure 1). These two enantiomers have a similar camphoraceous odor, but how the stereochemistry impacts on the biological activity is still unknown ²⁵⁾. Synthetic camphor is synthesized mainly from α-pinene obtained from turpentine oil, whilst natural camphor, i.e., (+)-camphor, is obtained through distillation of the wood from the camphor laurel tree (Cinnamomum camphora) found especially in Borneo and Taiwan; the Borneo camphor tree (Dryobalanops aromatica) and the East African camphorwood tree (Ocotea usambarensis) (see Figure 2A). In Asia, a major source of camphor is camphor basil (Ocimum kilimandscharicum). Camphor is also present as a major essential oil component of many aromatic plant species ²⁶⁾.

Figure 1. Camphor

Note: The chemical structure of the (1R)-(+) and (1S)-(−) enantiomers of camphor.

[Sources ²⁷⁾ and ²⁸⁾]

The fragrant camphor tree, Cinnamomum camphora (L.) J. Presl (Lauraceae), occurs naturally in Asian countries including Japan, Taiwan and China, but has been naturalised in other parts of the World. The tree is large with pale brown bark, dark green to yellowish leaves (Figure 2A) and small white flowers followed by small purple berries. All the plant parts have the distinctive, easy-to-recognise camphoraceous odor. The essential oil is distilled from the wood (Figure 2B) which yields the active ingredient (1R)-(+)-camphor, i.e., natural camphor ²⁹⁾.

Figure 2. Cinnamomum camphora tree, wood and seeds

[Source ³⁰⁾]

Biosynthesis and Chemical Synthesis of Camphor

The biosynthesis of camphor was extensively investigated and elucidated by Croteau et al. ³¹⁾ in their work on Salvia officinalis ³²⁾. After several elegant experiments they determined the basic biosynthesis of camphor (Scheme 1) and the enzymes involved to be as follows: Camphor is biosynthetically produced in plants by way of the biotransformation of the starting material geranyl diphosphate which is the preferred substrate. Cyclisation of geranyl diphosphate, by the enzyme (+)-bornyl diphosphate synthase yields (+)-bornyl diphosphate. (+)-Bornyl diphosphate is then hydrolysed to (+)-borneol through the action of bornyl-diphosphate diphosphatase. The last step is catalysed by (+)-borneol dehydrogenase as it oxidises (+)-borneol to (+)-camphor ³³⁾.

The synthetic production of camphor involves using turpentine oil as a starting material. Turpentine is used as the source of α-pinene through a distillation process; α-pinene is converted into camphene through the catalysis of a strong acid with acetic acid as the solvent; the camphene then undergoes Wagner-Meerwein rearrangement into the isobornyl cation, which is captured by acetate; the isobornyl acetate subsequently formed is hydrolysed to isoborneol, which is finally converted to camphor through dehydrogenation. The synthetic route from α-pinene produces a racemic mixture, i.e., a 1:1 ratio of (−) and (+)-camphor.

Figure 3. Biosynthesis of camphor

[Source ³⁴⁾]

Camphor uses

Camphor has a long-valued history for its extensive and diverse uses in the East: the Chinese used camphor as a circulatory stimulant and analeptic (tending to restore a person’s health or strength; restorative), whilst the Japanese used it in torch-light material and added small quantities to fireworks to make them brighter ³⁵⁾. Camphor was used as a fumigant during the Black Death, a plague that spread through Europe in the 14th century, as well as during outbreaks of smallpox and cholera. Rosewater together with camphor as a perfume ingredient was sprinkled over corpses before shrouding ³⁶⁾. In India, camphor is commonly burnt in temples during religious rituals because unlike any other aromatic smoke, camphoric fumes are non-irritant to eyes ³⁷⁾. Camphor has been widely used as a fragrance in cosmetics, as a flavoring food additive and as a preservative in confectionary goods; in homes it is commonly used as an insect repellent, a plasticiser and as an intermediate in the synthesis of aroma chemicals ³⁸⁾, ³⁹⁾. Camphor is one of the most well-known and widespread commercially important aroma chemicals, with an annual market value of US$ 80–100 million ⁴⁰⁾.

Camphor exhibits several biological properties such as antimicrobial ⁴¹⁾, ⁴²⁾, antiviral and antitussive effects ⁴³⁾, ⁴⁴⁾, ⁴⁵⁾. Camphor is a common ingredient in modern medicine in topically applied analgesics and rubefacients for treatment of minor muscle aches and pains and it is reported that camphor has been used to relieve pain caused by breast engorgement by intramuscular injections ⁴⁶⁾. It has been applied as a topical anti-infective and anti-pruritic and internally as a stimulant and carminative ⁴⁷⁾. However, camphor is poisonous when ingested and can cause seizures, confusion, irritability and neuromuscular hyperactivity. The lethal dose in humans is reported to be 50–500 mg per kg bodyweight ⁴⁸⁾.

What is camphor used for

Camphor is a solid, translucent, white crystal with penetrating aromatic odor used as a rubefacient/counter-irritant medication. Camphor is used exclusively because of its local effects. When rubbed on the skin, it acts as a rubefacient and causes localized vasodilatation (mediated by way of an axon reflex), which gives feelings of comfort and warmth. As an anti-pruritic gent, when applied gently on the skin, it may create a feeling of coolness, and a mild, local anesthetic effect, which may be followed by numbness. In dermatology, when it is applied as lotion (0.1 to 3%), camphor is an anti-pruritic and surface anesthetic (when applied gently, it creates a feeling of coolness). Camphor is also used in liniments as a counter-irritant for fibromyalgia, neuralgia, and similar conditions.

Camphor is used:

• as a rubefacient. As with all rubefacients, it should not be applied to abraded, irritated skin.
• as a plasticizer for cellulose esters and ethers
• in the manufacture of plastics (especially celluloid)
• in lacquers and varnishes
• in explosives and pyrotechnics
• as a moth repellent
• in the manufacture of cymene
• as a preservative in pharmaceuticals and cosmetics.

When camphor is applied on the skin, it is analgesic. It is also used in liniments as a counter-irritant in fibrositis, neuralgia, and similar conditions.

In dermatology, when it is applied as lotion (0.1 to 3%), it is an anti-pruritic and surface anaesthetic (when applied gently, it creates a feeling of coolness).

In dentistry, it is prepared with parachlorophenol 35% (and 65% camphor) and used as an antibacterial for infected root canals.

Taken internally, it is an irritant and carminative. It has been used as a mild expectorant and to relieve griping (abdominal discomfort) (this use is now discouraged because of toxicity).

Camphor was formerly administered as a solution in oil by subcutaneous or intramuscular injection to act as a circulatory and respiratory stimulant, but there is no evidence of its value for this purpose ⁴⁹⁾.

According to the Dutch Information Medicamentorum (1986), camphor is used:

• For pruritus: lotion with 1 to 70 mg/g
• For muscular pains: oil with 40 to 250 mg/g or alcohol solution with 100 mg/ml
• For colds: chest liniment, with 20 to 100 mg/g; nose ointment, with 20 to 50 mg/g: nose drops/spray, with 0.15 mg/ml.

When ingested in small amounts, it creates feelings of warmth and comfort in the stomach, but given in large doses it acts as an irritant.

Camphor is no longer used as a pesticide in the US. Other uses of camphor include insect repellant use (particularly to control clothes moths); cosmetic ingredient.

• It is dangerous to place camphor into infants’ nostrils, since it can cause instant collapse ⁵⁰⁾.

Antibacterial and Antifungal Activities

Plants have been a valuable source of natural products for maintaining human health and the use of plant compounds for their antimicrobial activity has gradually increased worldwide. Numerous investigations have shown various essential oils of several species containing camphor as the major components, exhibited antimicrobial activity. The composition of essential oil from the aerial parts of sweet wormwood (Artemisia annua) includes camphor (44%), germacrene D (16%), trans-pinocarveol (11%), β-selinene (9%), β-caryophyllene (9%) and artemisia ketone (3%). Significant activity of the essential oil was noted against the Gram-positive bacteria, Enterococcus hirae, as well as against the fungi Candida albicans and Saccharomyces cerevisiae using the liquid diffusion method ⁵¹⁾.

Some studies found camphor as a single compound only exhibited weak antimicrobial activity ⁵²⁾. Greek sage (Salvia fruticosa) essential oil, containing camphor as the main component, exhibited poor activity against all of the bacteria tested (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus, Rhizobium leguminosarum and Bacillus subtilis) ⁵³⁾. Santoyo et al. ⁵⁴⁾ investigated the antimicrobial activity of rosemary essential oil obtained via supercritical fluid extraction and molecules including camphor against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger by the disc diffusion and broth dilution methods. The test samples were active against all the test organisms with the most susceptible organism being Staphylococcus aureus and the least susceptible Aspergillus niger. The standards exhibit activity against all the micro-organisms tested in the order of effectiveness: borneol > camphor > verbenone. In another study, a yarrow variety (Achillea sintenisii) was found to contain camphor (14.8%) as its major component. The essential oil was further fractionated and the antibacterial and antifungal activities determined against a variety of micro-organisms. Data analysis revealed camphor to be the more active compound together with 1,8-cineole, as notable activity against Candida albicans and Candida krusei was reported. The fractions showed the same or higher activity than the neat essential oil in the majority of cases ⁵⁵⁾. Mevy et al. ⁵⁶⁾ confirmed that elemol, 1,8-cineole, camphor and p-cymene can be considered as the principal antimicrobial components of tea bush (Lippia chevalieri) oil. The antimicrobial activity of rosemary (Rosmarinus officinalis) and several other oils against organisms implicated in meat spoilage was investigated by Ouattara et al. ⁵⁷⁾. In a 1/100 dilution, rosemary (Rosmarinus officinalis) oil, containing mainly camphor, was one of the most efficient antibacterial oils having antibacterial activity against two Gram-negative (Pseudomonas fluorescens and Serratia liquefaciens) and four Gram-positive (Brochothrix thermosphacta, Carnobacterium piscicola, Lactobacillus curvatus, and Lactobacillus sake) bacteria ⁵⁸⁾. The essential oils of Salvia macrochlamys and decorative sage (Salvia recognita), rich in camphor (11% and 42%, respectively), exhibited no antimicrobial activity against methicillin-resistant Staphylococcus aureus, Mycobacterium intracellulare, Cryptococcus neoformans and Aspergillus fumigatus, but moderate antifungal activity against Colletotrichum acutatum, Colletotrichum fragariae, and Colletotrichum gloeosporoides was noted at a concentration of 200 µg/mL. However, in the same study, (−)-camphor and (+)-camphor tested singularly exhibited no activity against the test bacteria and fungi ⁵⁹⁾. Viljoen et al. ⁶⁰⁾ determined, using time-kill studies, that a synergistic antimicrobial effect occurs between 1,8-cineole and (−)-camphor. These two compounds are the two major essential oil components of the mountain daisy (Osmitopsis asteriscoides). The study showed that both (+)-camphor and (−)-camphor have negligible antifungal activity on C. albicans, whereas in the case of (−)-camphor combined with 1,8-cineole, a total reduction of colony forming units (CFUs) was observed at 15 min. It was deduced therefore that camphor may act in a synergistic manner with other essential oil components possessing antimicrobial activity ⁶¹⁾.

Antiviral Activity

Viral diseases are an increasing health concern worldwide and there has been an intensive search for more effective but less toxic antivirals than those currently used. Aromatic plants, especially their essential oils, are known to exhibit antiviral properties. Sivropoulou et al. ⁶²⁾ investigated the antimicrobial, cytotoxic and antiviral activities of Greek sage (Salvia fruticosa) essential oil. The results demonstrated the essential oil of Greek sage (Salvia fruticosa) and its four main components (1,8-cineole, α- and β-thujone, and camphor) exhibited high levels of virucidal activity against herpes simplex virus type-1 (HSV-1), however, this positive effect was accompanied by cytotoxic activity against African Green Monkey kidney (Vero) cells. Lavender cotton (Santolina insularis) essential oil, which is rich in camphor, deactivated herpes simplex type-1 (HSV-1) and type-2 (HSV-2) in vitro using plaque reduction assays with an IC50 value of 0.88 µg/mL for HSV-1 and 0.7 µg/mL for HSV-2. Reduction of plaque formation assays showed inhibition of cell-to-cell transmission of both HSV-1 and HSV-2 ⁶³⁾.

Antitussive Activity

Coughing is a very common clinical symptom with largely ineffective current therapies. Aromatic vapors have been widely used in the symptomatic treatment of upper respiratory tract infections due to their known antitussive effects. Burrow and co-workers ⁶⁴⁾ investigated the effects of camphor vapor on nasal resistance to airflow and nasal sensation of airflow. Inhalation of camphor had no effect on nasal resistance to airflow, but a cold sensation in the nose with the sensation of improved airflow was described. The results indicated that camphor stimulated cold receptors in the nose ⁶⁵⁾. Laude et al. ⁶⁶⁾ reported the action of camphor on the cough reflex in conscious guinea-pigs. Three concentrations (50, 133 and 500 mg/L) of camphor vapor were administered and 500 mg/L camphor significantly reduced (33%) cough frequency. An increase in cough latency coincided with the reduction in cough frequency. Further studies revealed camphor activated cold receptors now identified as TRPM8, the minty-cool ion channel, but the mechanism whereby TRPM8 activation inhibits cough is still not understood ⁶⁷⁾. In another study, camphor was used to synthesize camphor lactam (α-camphidone) by treatment with hydroxylamine-O-sulfonic acid and glacial acetic acid with a Beckmann-like rearrangement in structure. Both camphor and camphor lactam were tested for their antitussive activity in guinea-pigs with citric-acid induced cough. It was noted that this minor modification in chemical structure significantly increased cough latency whilst reducing cough frequency. In addition, prior exposure to the camphor lactam at concentrations of 125, 250, and 500 μg/L had a higher inhibitory cough response compared to camphor ⁶⁸⁾.

Anti-Nociceptive Activity

Camphor has an extensive history in its use as a topical analgesic in balms and liniments. In 1990, Green ⁶⁹⁾ found camphor to be a relatively weak sensory irritant having a modest excitatory effect on thermosensitive (and perhaps nociceptive) cutaneous fibers. Xu et al. ⁷⁰⁾ further investigated the mechanism of camphor anti-nociceptive (analgesic) activity and reported that camphor activated and de-sensitized the capsaicin receptor (TRPV1) whilst inhibiting the garlic receptor (TRPA1). Both are part of the recently elucidated transient receptor potential (TRP) superfamily, a group of structurally similar ion channels, heavily expressed in nociceptive sensory neurons. Therefore, it is possible that the analgesic effects of camphor may be due to de-sensitisation of TRPV1 and blocking of TRPA1 ⁷¹⁾. The pain-relieving effects of California sagebrush (Artemisia californica), containing the two major compounds 1,8-cineole (24%) and camphor (18%), were reviewed. Anecdotal use reported successful pain relief in all cases for patients suffering from lower back pain, arthritis, bruises, muscle and ligaments strains, broken bones and even cancer. An alcoholic liniment provided rapid pain relief lasting 2–3 hours with an onset of action of 20 min. The analgesic activity of terpenoids is as a result of binding to TRPV1, TRPV3 and TRPM8 receptors. Camphor is a known agonist of TRPV2, TRPA1 as well as TRPV1 quickly deactivating TRP channels resulting in long-term pain relief ⁷²⁾.

Antimutagenic and Anticancer Activity

Few animal studies demonstrating the potential of camphor in the treatment of cancer have been conducted, but those undertaken included improvement of immune function ⁷³⁾, enhancement of enzymatic breakdown of carcinogens ⁷⁴⁾ and the increased susceptibility of cancer cells to radiation ⁷⁵⁾. Goel et al. ⁷⁶⁾ demonstrated that camphor had a radiomodifying effect. An increase in the frequency of sister-chromatid exchanges in mice bone marrow cells occurs after exposure to gamma radiation, but after a single dose of camphor, administered at 0.5 µM/g bodyweight, this frequency was significantly low. Kanematsu and Shibata ⁷⁷⁾ reported on possible DNA damage as shown by a positive result of the rec-assay using two strains of Bacillus subtilis. Camphor, often used in endodontic formulations, presented a positive result in the “rec-assay”, showing that camphor may cause genetic toxicity in cells, however, drugs showing positive results do not necessarily cause tumour formation. This shows that more studies on the genotoxicity of camphor are required and that camphor should be used with care. Cultivated sage (Salvia officinalis) rich in camphor reduced UV-induced mutagenesis when screened with the repair-proficient strain, and had no effect on spontaneous mutation frequency in mismatch repair-deficient strains. It also enhanced the formation of Lac+ recombinants, but not as a consequence of SOS induction. This result suggested a protective effect through enhanced re-combinational repair ⁷⁸⁾. In a subsequent study, Vuković-Gacić et al. ⁷⁹⁾ investigated the inhibitory potential of cultivated sage essential oil and its monoterpenes on UV-induced mutations tested with SY252 and D7. Camphor showed antimutagenic effects at very low concentrations compared with other monoterpenes screened (about 40% reduction of UV-induced revertant at 0.5 and 1 μg/plate), although higher concentrations failed to increase antimutagenic effects. Nikolić et al. ⁸⁰⁾ demonstrated that camphor can reduce UV/4NQO mutagenesis in the NER+, but not the NER− strain of Escherichia coli and increased spontaneous and UV-induced recombination in recA730 and recA+ cells. Low doses of camphor are antigenotoxic against 4NQO in mammalian cells and stimulate DNA repair, acting as a bioantimutagen. De-Oliveira et al. ⁸¹⁾ hypothesised based on previous findings how the genotoxicity of mutagens may be modulated through cytochrome P4502B subfamily enzyme inhibition. In a study including various monoterpenes using pentoxyresorufin-O-depenthylase (PROD) as a model substrate for cytochrome P4502B1-enzymes, camphor was found to have an inhibitory effect on the PROD enzyme with an IC50 value of 7.89 μM. Through this mechanism of action it is possible for camphor to be considered antimutagenic ⁸²⁾, but more studies are required.

Insecticidal Activity

Certain currently used synthetic pesticides threaten the integrity of the earth’s ozone layer and other environmental buffers, therefore alternatives to these commercial chemicals are urgently needed ⁸³⁾. Essential oils are considered good candidates because of their low toxicity to mammals, high volatility, ready availability in tropical countries and economical viability ⁸⁴⁾. Monoterpenoids believed to aid plants in chemical defence against phytophagous insects are capable of toxic interference with the biochemical and physiological functions of herbivorous insects ⁸⁵⁾. Numerous studies have indicated that camphor has insect repellent activity against stored-product pests. Using contact toxicity, grain treatment and repellency assays, the essential oil of camphor basil (Ocimum kilimandscharicum) and its major component, camphor, were investigated against four beetles. The doses of 100 mg/filter paper and 100 µg/insect induced over 93% and 100% mortalities in Sitophilus granarius, Sitophilus zeamais and Prostephanus truncatus, but only 70% and 100% mortality in Tribolium castaneum after 24 hour exposure. Development of eggs and immature stages within grain kernels, as well as progeny emergence, was completely inhibited in camphor-treated grain ⁸⁶⁾. Bekele and Hassanali ⁸⁷⁾ revealed the insecticidal activity of camphor basil (O. kilimandscharicum) against Rhyzopertha dominica and S. zeamais was due to camphor and the combined effects of different components, but camphor had no effect on the rice weevil (Sitophilus oryzae) with an LC50 of greater than100 μL/L. Another report indicated that camphor, as a pure compound, showed contact and fumigant activity against Sitophilus oryzae and Rhyzopertha dominica, but had no effect on Tribolium castaneum after 24 hours exposure at a dose of 0.1 μL/720 mL volume ⁸⁸⁾. Liska et al. ⁸⁹⁾ found camphor exhibited the highest mortality (78.5%) just after 24 h at the highest tested dose (10.0 μL/adult) for contact toxicity; for fumigant toxicity, camphor at its highest dose (120 μL/350 mL vol.) caused 93.5% mortality. These results were in agreement with an earlier report by Qiantai and Yongcheng ⁹⁰⁾, who observed that camphor, as the major isolate from essential oils of Chinese cinnamon (Cinnamomum cassia), Chinese star anise (Illicium verum) and camphor laurel (Cinnamomum camphora), showed contact efficacy against the lesser grain borer (Rhyzopertha dominica) and the maize weevil (Sitophlus zeamais). Insect repellent activity, rather than insecticidal activity, against the confused flour beetle (Tribolium castaneum) was noted. Exposure of the newly-laid eggs of the pulse beetle (Callosobruchus chinensis) to concentrations of 0, 12, 24, 48, and 96 ppm of camphor crystals in air-tight containers for one and four weeks resulted in 65.0% to zero (0%) hatching. Postembryonic development was affected when the newly-hatched larvae penetrated into the cowpea seeds; very few adults emerged from the infested seeds exposed to camphor ⁹¹⁾.

Camphor was the most effective of the tested monoterpenoids to prevent the multi-colored Asian lady beetle, Harmonia axyridis (Pallas), from overwintering in buildings as determined by the olfactometer bioassay ⁹²⁾. It also exhibited fumigation toxicity against false powder post beetle (Dinoderus bifloveatus) after 48 hours exposure ⁹³⁾. Several monoterpenes (e.g., 1,8-cineole, citronellol, α and β-pinene, linalool, isopinocamphone, camphor) tested against cattle-tick (Boophilus microplus) larvae and camphor, in a 60 min-period, was lethal to 100% of the larvae ⁹⁴⁾. Blattella germanica (German cockroach) is one of the most important pests of the indoor environment, a major source of allergens and a potential carrier of faecal pathogens ⁹⁵⁾. Using the filter-paper contact toxicity bioassay, both (1R)-(+)-camphor and (1S)-(−)-camphor were toxic against female B. germanica with LD50 values of 0.10 mg/cm2 and 0.13 mg/cm2, respectively. There was no significant difference in toxicity between (1R)-(+)-camphor and (1S)-(−)-camphor ⁹⁶⁾.

Mosquitoes are known disease vectors of malaria, hemorrhagic dengue and yellow fever, in addition to being considered a nuisance ⁹⁷⁾. Most commercial mosquito repellents contain DEET (N,N-diethyl-m-methylbenzamide), but this compound exerts toxic reactions and may damage plastic, synthetic fabrics and painted surfaces ⁹⁸⁾. Bioassays conducted on a number of essential oils showed repellency against mosquitoes attributed to the presence of its main compounds. However, it was noted that synergy between the essential oil components may lead to an increased repellant response; therefore, the neat oil may be more effective compared to the individual components ⁹⁹⁾. A review published in 2011 noted 144 patent inventions containing plant essential oils for mosquito repellency. These patents, mostly from Asian countries, listed various essential oil components including amongst many others citronella (Cymbopogon spp.) and eucalyptus (Eucalyptus spp.), whilst camphor (Cinnamomum camphora) was mentioned in >10% of these patents ¹⁰⁰⁾. As a major component of the essential oil of aromatic plants, camphor has shown repellency against Anopheles culicifacies, Culex quinquefasciatus ¹⁰¹⁾, Anopheles gambiae and Anopheles funestus ¹⁰²⁾. It is evident that camphor has great potential for development as an alternative green commercial insect repellent to replace the harmful synthetic agents currently in use.

Cardiovascular Effects

For centuries, camphor has been used for the stimulation of heart and peripheral circulation. Osborne ¹⁰³⁾ reported that in cardiac failure and collapsed conditions characterized by cold skin, a feeble pulse and failing heart, the subcutaneous injection of camphor in sterile oil caused the surface of the skin to become flushed, dilated the peripheral blood vessels and improved the whole circulation. The results of controlled clinical studies on the cardiovascular effects of (+)-camphor have been published ¹⁰⁴⁾. Belz and Loew ¹⁰⁵⁾ investigated the effects of (+)-camphor (extracted from fresh Crataegus berries) in orthostatic hypotension using independent, double-blind, randomised, placebo-controlled studies. It was determined that (+)-camphor, as well as the extract from fresh hawthorn (Crataegus) berries, contributed to the pressoric effects with (+)-camphor inducing the initial rapid effect and the extract is responsible for the long-lasting effect ¹⁰⁶⁾.

Camphor as a Potential Skin Penetration Enhancer

It has been suggested that terpenes, present in plant essential oils, are clinically acceptable skin penetration enhancers ¹⁰⁷⁾. Previous studies also indicated menthol in combination with camphor enhanced the skin penetration of methyl salicylate and inhibited both the in vivo and in vitro hydrolysis of methyl salicylate to salicylic acid ¹⁰⁸⁾. The efficacy of some terpenes on skin permeation of tea catechins and theophylline were systemically evaluated using a series of in vitro and in vivo methods ¹⁰⁹⁾. It was found that all the evaluated terpenes had significant effects on the (+)-catechin delivery relative to the control. The rank order of enhancement was α-terpineol ≥ menthone >linalool > 1,8-cineole > farnesol ≥ fenchone > cymene ≥ nerolidol > (+)-limonene > camphor. Camphor and fenchone showed the least enhancement amongst the oxygen-containing monoterpenes, which may be related to their bicyclic structure.

Ramesh et al. ¹¹⁰⁾ reported the flux of carvedilol obtained from solutions containing camphor, transcutol, d-limonene, carvone, labrasol and menthol were 7.81, 7.26, 6.52, 5.91, 4.21 and 2.28 times higher respectively, than that observed with the control, using excised rat abdominal skin mounted in Franz diffusion cells. Camphor showed maximum permeation and basil oil (Ocimum basilicum) containing methyl chavicol, eugenol, linalool, camphor and methyl cinnamate showed potential in vitro penetration enhancement of labetolol hydrochloride ¹¹¹⁾. In a recent study, camphor was found to markedly prevent the permeation of benzocaine across the skin while promoting skin accumulation after 12 hours ¹¹²⁾.

Other Applications

Interestingly, according to Iranian folk medicine, camphor was used both as an aphrodisiac and antiaphrodisiac agent. The effect of camphor on the sexual activity of male rats was investigated by Jamshidzadeh et al. ¹¹³⁾, by measuring the parameters mount latency and frequency as well as intromission latency and frequency. The results indicated enhanced sexual desire and performance when camphor was administered at 50 mg/kg. It was speculated that the effects of camphor may be due to modulation of the sympathetic nervous system, or its effect on serum testosterone levels ¹¹⁴⁾. Camphor could also have an effect on the reproductive function of the testes in mice, as it was revealed that administration of camphor to young male mice may result in vascularisation and proliferation of sexual cells which can affect maturation of seminiferous tubules ¹¹⁵⁾.

Sweet wormwood (Artemisia annua) leaves and chemical constituents, including camphor, were investigated for its activity against coccidian parasites. A 5% dried leaf supplement addition to chick feed for 3 weeks resulted in infection protection against Eimeria tenella but not Eimeria acervulina or Eimeria maxima. Camphor fed at 119 ppm protected weight gains and protected against E. tenella and E. acervulina ¹¹⁶⁾.

The essential oil of absinthe wormwood (Artemisia absinthium), containing 27.40% camphor, showed activity against promastigote (MIC 0.0097 μL/mL) and axenic amastigote forms (EC50 0.24 nL/mL) of both Leishmania aethiopica and Leishmania donovani. It also showed a weak haemolytic effect with a slightly decreased selectivity index (SI = 0.8) against the THP-1 cell line. This study demonstrated the potential use of Artemisia absinthium oil as source of an innovative agent for the treatment of leishmaniasis ¹¹⁷⁾.

Allelopathic Activity

Allelopathy is the interaction of one plant with another through the release of biochemical compounds into the environment and can be indirect, direct, harmful or beneficial. Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. Allelopathy can occur through several mechanisms including decay with or without micro-organisms, excretion, exudation, volatilisation and leaching. Allellochemicals can be present in any plant part as well as in the surrounding soil and are mostly secondary metabolites and include alkaloids, phenyl propanes, naphthaquinones, steroids and terpenoids amongst others. Allelopathic activity can lead to suppression of growth of one plant by another ¹¹⁸⁾. In a significant study by Schenk ¹¹⁹⁾ the allelopathic influence of the camphor laurel tree (Cinnamomum camphora) was investigated on the seedling growth of fifty-two plant species and twenty-seven soil algal populations. The leaves had a direct allelopathic effect by significantly delaying germination and causing a reduction of radicle and shoot length, leaf area and leaf number, specifically in species associated with camphor laurel (Cinnamomum camphora) communities. In addition, many of the soil algal species disappeared from the soil or exhibited reduced vigour, therefore the allelopathic effect may also be indirect as soil algae are necessary for soil wettability, moisture retention and seed germination enhancement. The persistence and dominance of camphor laurel trees (Cinnamomum camphora) may also be enhanced as the allelopathic activity reduced the competitiveness of surrounding vegetations ¹²⁰⁾. In another study, the chemical release from leaf powder of the camphor laurel tree (C. camphora) was studied by monitoring soil and air concentrations of (+)-camphor. The growth of the receiver plant—rice seedlings—was inhibited when planted in soil which contained the leaf powder. (+)-Camphor was detected in this soil as well as the soil water and it was therefore determined to be the main phytotoxic allelochemical responsible for the growth suppression ¹²¹⁾. The allelopathic activity of camphor and other monoterpenes were studied by determining the antigerminative ability in radish (Raphanus sativus) and garden cress (Lepidium sativum) seeds 120 hours after sowing. The radish (Raphanus sativus) seeds were found to be more sensitive than the garden cress (Lepidium sativum) seeds and at 10−3 M, camphor significantly inhibited the germination of radish (Raphanus sativus) seedlings by 44% and affected the radicle growth of garden cress (Lepidium sativum) seeds. From this study, the authors concluded that monoterpenes such as camphor, which exhibits phytotoxic activity, are therefore potential bio-herbicides which could be developed into natural pesticides ¹²²⁾.

Camphor toxicity

The toxicity of camphor has been well-documented. The ingestion of 3.5 g of camphor can cause death, whilst 2.0 g causes toxic effects in adults leading to congestion of the gastrointestinal tract, kidney and brain; the immediate collapse of an infant has been reported after the application of a small dose to the nostrils ¹²³⁾. Toxic effects appear after the ingestion of approximately 2 g (lethal dose adults: 4 g, children: 0.5-1 g, infants: 70 mg/kg of pure camphor). The main target organs of camphor exposure are the CNS (central nervous system – brain and spinal cord) and kidneys. Convulsions, depression, apnea, asystole, gastric irritation, colic, nausea, vomiting, diarrhea, anxiety, excitement, delirium, and severe post-convulsive coma may occur after oral intake of camphor. The symptoms may appear 5 to 90 minutes after ingestion depending on the product ingested (solid or liquid). Poisoning by camphor is associated with an initial excitatory phase, with vomiting, diarrhea and excitement, followed by CNS depression and death. In humans, the characteristic symptoms of camphor poisoning after ingestion are nausea, vomiting, headache, dizziness, muscular excitability causing tremor and twitching, convulsions and delirium depending on the dosage. In a severe overdose, status epilepticus persisting for several hours occurs, ultimately causing coma and death by asphyxia or exhaustion ¹²⁴⁾. Camphor inhalation may cause irritation of the mucous membranes above 2 ppm and respiratory depression and apnoea may occur. Camphor can also cause skin and eye irritation on contact. Inhalation and skin exposure may result in acute poisoning depending on the dose with symptoms described above. After ingestion, rapid onset of vomiting improves the prognosis but simultaneous intake of alcohol, or oily solutions, enhance the absorption of camphor and therefore the toxic effect. Camphor poisoning is treated symptomatically as no antidote is known ¹²⁵⁾.

Acute camphor toxicity begins with nausea and vomiting and quickly progresses to CNS (central nervous system – brain and spinal cord) depression, seizures, respiratory failure, and death from respiratory arrest or status epilepticus ¹²⁶⁾. Symptoms of camphor toxicity usually begin 5 to 90 minutes after ingestion and are often abrupt in onset. Spontaneous emesis, with the odor of camphor readily apparent, typically occurs first. CNS stimulation ensues with restlessness, confusion, delirium, and increased muscular activity. Severe toxicity may include seizures, apnea, and coma. Death results from respiratory depression or status epilepticus ¹²⁷⁾.

Camphor administered in doses of 60 mg-4 g was reported to cause flickering, darkening or veiling of vision along with noises in the ears. Corneal erosions have been reported in association with the use of inhalant capsules containing camphor ¹²⁸⁾.

Chronic ingestion of camphor can cause a variety of symptoms clinically similar to Reye’s syndrome. In chronic ingestion, CNS findings may or may not be present, depending on the dosage. Gastrointestinal symptoms may include nausea, vomiting, epigastric pain, and hepatic enzymes elevation. Pathologic hepatic changes often include such findings as granulomatous hepatitis and fatty metamorphosis ¹²⁹⁾.

Heavy exposures (concentrations not specified) to camphor are reported to cause nausea, anxiety, dizziness, confusion, headache, twitching of facial muscles, spasticity, and with severe poisoning convulsions and coma. Camphor may be expected to be irritating to the eye, but no serious injuries have been noted ¹³⁰⁾.

There have been reports of instant collapse in infants after camphor has been applied to their nostrils ¹³¹⁾. Camphor is irritating to the eyes, skin and mucous membranes. When camphor is applied on the skin, it is analgesic. Taken internally, it is an irritant and relieves flatulence or prevent formation of gas in the gastrointestinal tract (SRP: an agent used to reduce gas in the gastrointestinal tract). Camphor has been used as a mild expectorant (a medicine which aid in the clearance of mucus from the airways, lungs, bronchi, and trachea – used to treat coughs). Camphor is a CNS (central nervous system – brain and spinal cord) stimulant whose effects range from mild excitation to grand-mal convulsions or status epilepticus. These effects result from excitation of the cerebrum and lower structures of the CNS. Gastric irritation, together with cortical and medullary stimulation, frequently causes vomiting and diarrhea. It is not clear whether camphor toxicity is due to the parent compound, a metabolite (secondary alcohols, including borneol and isomers of hydroxy-camphor), or both.

Inhalation of concentrations above 2 ppm irritates the nose and throat (mucous membranes). Respiratory depression and apnea may occur. Very large exposures will cause the same clinical features as ingestion ¹³²⁾.

With chronic dermal exposure, systemic effects and contact dermatitis can occur as well as significant allergic responses. Ocular exposure results primarily in irritation only, although oral intake has been associated with visual problems ¹³³⁾.

Central serous chorioretinopathy of the right eye was reported in a 50-year old female of Chinese origin who had used Chinese herbal medicinal patches containing camphor as the main ingredient for more than 20 years ¹³⁴⁾.

Camphor is not a human carcinogen, and the topical use of camphorated oil in pregnancy was not associated with teratogenic effects. However, camphor ingestion may lead to abortion and/or a death of the fetus because camphor crosses the placenta and fetuses lack the enzymes needed to hydroxylate and conjugate with glucuronic acid. Camphor crosses the placenta and has been implicated in fetal and neonatal death. It has been used to induce abortions. Camphor poisoning during pregnancy was reported in four cases and, in each case, camphorated oil was mistaken for castor oil. The topical use of camphorated oil in pregnancy was not associated with teratogenic effects ¹³⁵⁾.

Animal studies

A study investigating the toxicological effects of camphor on the rabbit (Oryctolagus cuniculus) kidney involved the oral administration of different concentrations of camphor solution for a period of ten days, which resulted in mild edema, glomerulonephritis, glomerular lobulations, tubular necrosis and congestion of the blood cells. Histologically, camphor administration distorted and disrupted the cytoarchitecture of the kidney ¹³⁶⁾.

Carcinogenicity tests in animals have been negative. Neuronal necrosis produced experimentally in mice by administration of multiple doses. In developmental studies, D-camphor elicited no evidence of teratogenicity when administered orally during the fetal period of organogenesis to pregnant rats at doses up to 1000 mg/kg body weight/day, and to pregnant rabbits at doses up to 681 mg/kg body weight/day. Camphor is not mutagenic with the Ames test but sister chromatid exchange has been reported in mice given 80 mg/kg doses of camphor intraperitoneal, demonstrating possible genotoxicity.

Summary

Camphor is a multipurpose molecule with a most diverse range of applications, ranging from being used to treat medical conditions in humans to being used as a natural poison to kill insects, which seems divergent. In fact, the toxicity of camphor in humans remains a cause for concern as many cases of accidental poisoning, with serious symptoms, have occurred. However not only pure camphor should be considered, it is important to remember many products, plants and essential oils contain camphor. The overwhelmingly distinct aroma of camphor has led to its wide use in ointments and inhalants, particularly as an adjunct to treat the common cold. Scientifically, numerous biological activities have been attributed to camphor including antibacterial, antifungal, antimutagenic, antitussive and insecticidal properties, but it is important to note that bioactivity was determined in many cases using an essential oil rich in camphor and not pure camphor. Due to the high percentage of camphor, these activities may be incorrectly attributed to camphor, whilst synergism seems much more likely as was shown in the example of 1,8-cineole and (−)-camphor. Other studies showed pure camphor did not possess the same activity as the neat essential oil. Clearly, if these properties are to be confirmed, further research on camphor alone needs to follow up on these essential oil studies. In addition to its many medicinal uses, camphor is a useful molecule in chemical reactions where it is used extensively as a catalyst and has served as a chiral starting material and auxiliary. It is evident from this review that camphor is a most versatile molecule with a multitude of applications.

What is arrowroot

Arrowroot (Maranta arundinaceae) is a tropical plant that produces an edible starchy tubers (rhizomes) widely used by indigenous peoples for medicine and cooking. The arrowroot plant is native to South America, and to the West Indies where the native Arawaks used the plant as a dietary staple and also used the arrowroot powder to draw out toxins from people wounded by poison arrows. Native Americans in both North and South America apply arrowroot as a poultice for snakebite, insect stings or bites, and skin sores. There is evidence this plant has been cultivated for at least 7,000 years. The arrowroot plant is an herbaceous perennial that dies to the ground each winter when the tubers can be dug. The plants grow about 4 foot tall in full sun to light shade, and bear small white flowers in the summer. The cylindrical underground arrowroots grow 6-8 inches long, on average, and are sharply pointed at the end (hence the name arrowroot).

At the end of the growing season there will be a cluster of these arrowroot tubers under each plant. Each individual tuber will grow a new plant for the following year so they can multiply rapidly if you dig and replant the parts that you don’t consume. In areas where the ground doesn’t freeze, just leave a few tubers in the ground after harvest. In colder climates, store the tubers in a cool dry location and replant them in the spring.

Arrowroot makes clear, shimmering fruit gels and prevents ice crystals from forming in homemade ice cream. It can also be used as a thickener for acidic foods, such as Asian sweet and sour sauce. It is used in cooking to produce a clear, thickened sauce, such as a fruit sauce. It will not make the sauce go cloudy, like cornstarch, flour, or other starchy thickening agents would.

Arrowroot thickens at a lower temperature than flour or cornstarch, is not weakened by acidic ingredients, has a more neutral taste, and is not affected by freezing. Arrowroot does not mix well with dairy, forming a slimy mixture. It is recommended that arrowroot be mixed with a cool liquid before adding to a hot fluid. The mixture should be heated only until the mixture thickens and removed immediately to prevent the mixture from thinning. Overheating tends to break down arrowroot’s thickening property. Two teaspoons of arrowroot can be substituted for one tablespoon of cornstarch, or one teaspoon of arrowroot for one tablespoon of wheat flour.

Allergic reactions to arrowroot has been reported like this case of generalized urticaria caused by arrowroot ingestion ¹⁾.

Figure 1. Arrowroot

Arrowroot benefits

The arrowroot tubers can be eaten boiled, roasted, baked, or fried. According to Marsono ²⁾, boiled arrowroot has a low glycemic index (GI) as little as 14. In the Victorian era arrowroot was used, boiled with a little flavoring added, as an easily digestible food for children and people with dietary restrictions. With today’s greater understanding of its limited nutritional properties, arrowroot is no longer used in this way. In some cultures they are ground and made into pastries. In Burma, arrowroot tubers, which are called artarlut, are boiled or steamed and eaten with salt and oil. Kudzu arrowroot (Pueraria lobata) is used in noodles in Korean and Vietnamese cuisine.

Test tube and animal study indicated that the diet containing arrowroot extracts increased the serum IgG, IgA and IgM levels in mice ³⁾. These results revealed that the arrowroot tuber extracts have immunostimulatory effects in vivo as well as in vitro. However further work is needed to better define the mechanisms for immunomodulation and the active substances in arrowroot extracts. Preliminary data suggests that there are two kinds of active substances in arrowroot extracts, one is kind of starch and the other one is protein, which could form some kind of prebiotic fibers that can modulate parameters in gut-associated lymphoid tissue, as well as the systemic immune system ⁴⁾.

In traditional medicine, the easily digested arrowroot starch was often used to soothe bowel irritations by dissolving in hot water or hot milk where it forms a gelatinous solution that cools to a jelly-like mass ⁵⁾. A tablespoon of arrowroot starch to a pint of liquid forms a sufficient consistency. It should first be formed into a smooth paste with a little cold water and then the hot liquid should be added while stirring briskly. A little lemon juice, or herbs and spices may be added for flavor. Arrowroot is bland, making it suitable for neutral diets, especially for people who are feeling nauseous ⁶⁾. In a small pilot study ⁷⁾ involving 11 patients, all of whom had irritable bowel syndrome (IBS) with diarrhea as a feature. The patients took 10 mL arrowroot powder three times a day for one month and discontinued the treatment for the subsequent month. Questionnaires were completed after one month on treatment and at the end of the trial after one month off treatment. The result of that small pilot study showed arrowroot reduced diarrhea and had a long-term effect on constipation. It also eased abdominal pain ⁸⁾. However, larger randomized controlled trials are needed to substantiate these preliminary results.

Arrowroot flour

Arrowroot flour can be used for gluten-free baking and is mainly used in cookies and baked goods. The lack of gluten in arrowroot flour makes it useful as a replacement for wheat flour for those with a gluten intolerance. It is, however, relatively high in carbohydrates (approximately 88.15%) and low in protein (approximately 0.3%) and does not provide a complete substitute for wheat flour in bread-making. Arrowroot can be consumed in the form of biscuits, puddings, jellies, cakes, hot sauces, and also with beef tea, milk or veal broth. Substitution with 30% arrowroot flour in the cookie bars resulted in the lighter color and the more easily crumbled texture and showed higher total dietary fibers and resistant starch content ⁹⁾. One recent study suggested that the arrowroot flour is a potential source of prebiotics and has an immunomodulatory effect ¹⁰⁾.

Arrowroot tubers contain about 23% starch. The extraction of the arrowroot starch is a somewhat laborious process: The tubers are first washed and then cleaned of the paper-like scale. The scales must be carefully removed before extracting the starch because they impart a disagreeable flavor. After removing the scale, the arrowroots are washed again, drained and finally pounded to a pulp by beating them in mortars or subjecting them to the action of a wheel rasp, rinsed in clean water, fibrous parts are removed, and the starchy water is allowed to settle. The milky liquid thus obtained is passed through a coarse cloth or hair sieve and the pure starch, which is insoluble, is allowed to settle at the bottom. The wet starch is dried in the sun. The starch yield is about 1/5 of the original weight of the tubers. The result is arrowroot starch, the “arrowroot” of commerce, that is quickly packed for market in air-tight cans, packages or cases.

Figure 2. Arrowroot flour / Arrowroot starch

Arrowroot starch

Arrowroot starch has in the past been quite extensively adulterated with potato starch and other similar substances. Pure arrowroot starch, like other pure starches, is a light, white powder (the mass feeling firm to the finger and crackling like newly fallen snow when rubbed or pressed), odorless when dry, but emitting a faint, peculiar odor when mixed with boiling water, and swelling on cooking into a perfect jelly, which can be used to make a food that is very smooth in consistency—unlike adulterated articles, mixed with potato flour and other starches of lower value, which contain larger particles.

The arrowroot starch can be used as a thickener  in many foods such as sauces, gravies, puddings, jellies, cookies, and other baked goods or pie fillings, or as a clear glaze for fruit pies. As a thickener, it is two to three times as effective as cornstarch. In Suriname, the Amerindians use the starch as a baby powder.

Arrowroot powder nutrition

The starch from arrowroot flour has a nutrition composition of 11.37% water, 0.08% ash, 21.9-29.4% amylose, 7.7% protein, 0.1% fat, 8.7% insoluble dietary fiber, 5.0% soluble dietary fiber and 15.9-33.2% resistant starch ¹¹⁾.

Table 1. Arrowroot (raw) nutrition facts

Nutrient	Unit	Value per 100 g
Approximates
Water	g	80.75
Energy	kcal	65
Energy	kJ	271
Protein	g	4.24
Total lipid (fat)	g	0.2
Ash	g	1.42
Carbohydrate, by difference	g	13.39
Fiber, total dietary	g	1.3
Minerals
Calcium, Ca	mg	6
Iron, Fe	mg	2.22
Magnesium, Mg	mg	25
Phosphorus, P	mg	98
Potassium, K	mg	454
Sodium, Na	mg	26
Zinc, Zn	mg	0.63
Copper, Cu	mg	0.121
Manganese, Mn	mg	0.174
Selenium, Se	µg	0.7
Vitamins
Vitamin C, total ascorbic acid	mg	1.9
Thiamin	mg	0.143
Riboflavin	mg	0.059
Niacin	mg	1.693
Pantothenic acid	mg	0.292
Vitamin B-6	mg	0.266
Folate, total	µg	338
Folic acid	µg	0
Folate, food	µg	338
Folate, DFE	µg	338
Vitamin B-12	µg	0
Vitamin A, RAE	µg	1
Retinol	µg	0
Carotene, beta	µg	11
Carotene, alpha	µg	0
Cryptoxanthin, beta	µg	0
Vitamin A, IU	IU	19
Vitamin D (D2 + D3)	µg	0
Vitamin D	IU	0
Lipids
Fatty acids, total saturated	g	0.039
14:00:00	g	0.002
16:00:00	g	0.035
18:00:00	g	0.002
Fatty acids, total monounsaturated	g	0.004
16:1 undifferentiated	g	0
18:1 undifferentiated	g	0.004
Fatty acids, total polyunsaturated	g	0.092
18:2 undifferentiated	g	0.074
18:3 undifferentiated	g	0.018
Fatty acids, total trans	g	0
Cholesterol	mg	0
Isoflavones
Daidzein	mg	0
Genistein	mg	0
Total isoflavones	mg	0.01

[Source: United States Department of Agriculture Agricultural Research Service ¹²⁾]

Table 2. Arrowroot flour nutrition facts

Nutrient	Unit	Value per 100 g
Approximates
Water	g	11.37
Energy	kcal	357
Energy	kJ	1494
Protein	g	0.3
Total lipid (fat)	g	0.1
Ash	g	0.08
Carbohydrate, by difference	g	88.15
Fiber, total dietary	g	3.4
Minerals
Calcium, Ca	mg	40
Iron, Fe	mg	0.33
Magnesium, Mg	mg	3
Phosphorus, P	mg	5
Potassium, K	mg	11
Sodium, Na	mg	2
Zinc, Zn	mg	0.07
Copper, Cu	mg	0.04
Manganese, Mn	mg	0.47
Vitamins
Vitamin C, total ascorbic acid	mg	0
Thiamin	mg	0.001
Riboflavin	mg	0
Niacin	mg	0
Pantothenic acid	mg	0.13
Vitamin B-6	mg	0.005
Folate, total	µg	7
Folic acid	µg	0
Folate, food	µg	7
Folate, DFE	µg	7
Vitamin B-12	µg	0
Vitamin A, RAE	µg	0
Retinol	µg	0
Vitamin A, IU	IU	0
Vitamin D (D2 + D3)	µg	0
Vitamin D	IU	0
Lipids
Fatty acids, total saturated	g	0.019
14:00:00	g	0.001
16:00:00	g	0.017
18:00:00	g	0.001
Fatty acids, total monounsaturated	g	0.002
16:1 undifferentiated	g	0
18:1 undifferentiated	g	0.002
Fatty acids, total polyunsaturated	g	0.045
18:2 undifferentiated	g	0.036
18:3 undifferentiated	g	0.009
Cholesterol	mg	0
Amino Acids
Tryptophan	g	0.004
Threonine	g	0.012
Isoleucine	g	0.01
Leucine	g	0.019
Lysine	g	0.013
Methionine	g	0.006
Cystine	g	0.006
Phenylalanine	g	0.012
Tyrosine	g	0.009
Valine	g	0.014
Arginine	g	0.012
Histidine	g	0.004
Alanine	g	0.014
Aspartic acid	g	0.047
Glutamic acid	g	0.05
Glycine	g	0.014
Proline	g	0.009
Serine	g	0.013

[Source: United States Department of Agriculture Agricultural Research Service ¹³⁾]

Table 3. Arrowroot starch nutrition facts

Nutrient	Unit	Value per 100 g
Approximates
Energy	kcal	344
Protein	g	0
Total lipid (fat)	g	0
Carbohydrate, by difference	g	87.5
Fiber, total dietary	g	3.1
Sugars, total	g	0
Minerals
Calcium, Ca	mg	0
Iron, Fe	mg	0
Sodium, Na	mg	0
Vitamins
Vitamin C, total ascorbic acid	mg	0
Vitamin A, IU	IU	0
Lipids
Fatty acids, total saturated	g	0
Fatty acids, total trans	g	0

[Source: United States Department of Agriculture Agricultural Research Service ¹⁴⁾]

What is angelica

Angelica is a genus of about 90 species of tall biennial and perennial herbs in the family Apiaceae (Umbelliferae), that are widely distributed in Asia, Europe, and North America. They grow to 1–3 m (3 ft 3 in–9 ft 10 in) tall, with large bipinnate leaves and large compound umbels of white or greenish-white flowers (see Figure 1). In these, a total of 45 Angelica species (32 endemic species) are distributed in China ¹⁾. Various species of Angelica have been used in the traditional systems of medicine for several centuries  to treat many ailments. Angelica essential oils have been used for the treatment of various health problems, including malaria, gynecological diseases, fever, anemia, and arthritis ²⁾. Angelica essential oils are complex mixtures of low molecular weight compounds, especially terpenoids and their oxygenated compounds. These components deliver specific fragrance and biological properties to essential oils. Previously, several scientists reported the volatile composition of different Angelica species using various extraction techniques such as steam distillation, hydrodistillation, solvent-free solid injector, and supercritical fluid extraction.

Figure 1. Angelica plant

Figure 2. Angelica root

Angelica root essential oil

Angelica essential oils exhibit several pharmacological activities, such as antioxidant, antibacterial, antifungal, antimicrobial, and insecticidal activities ³⁾.

Table 1. Angelica essential oils and their major components

S. No.	Species	Parts	Extraction Method; Extraction Time; Yield	Place of Collection	Major Components	References
1	Angelica archangelica L.	Seeds (fruits) from three habitats	Hydrodistillation; 2 h; 0.8–1.4%	Svencionys, Prienai and Vilnius districts in Lithunia	β-phellandrene (33.6–63.4%) and α-pinene (4.2–12.8%)	4)
		Fruit of two chemotypes	Steam distillation; 5 h; 0.17–0.51%	Reykjavik, Iceland	α-pinene (41.4%, 28.9%, 14.4%), bicyclogermacrene (10.1%), and β-phellandrene (37.8% and 55.2%)	5)
		Root (1–2, 3–4 and >5 mm)	Hydrodistillation; 30 min	Rome, Italy	α-pinene (23.89–32.69%) and δ-3-carene (3.41–17.07%)	6)
		Root (3 habitats)	Hydrodistillation; 2 h; 0.2–0.5%	Svencionys, Prienai and Vilnius districts in Lithuania	α-pinene (15.7–20.8%), δ-3-carene (15.4–16.9%), limonene (8.0–9.2%), β-phellandrene (13.5–15.4%), α-phellandrene (8.0–9.1%), and p-cymene (6.8–10.6%)	7)
		Root (3 different altitudes)	Hydrodistillation; 3 h; 0.28–0.35%	Uttarakashi, Rudraprayag and Pothiwasa in Uttarakhand, India	dillapiole (35.93–91.55%) and nothoapiole (0.14–62.81%)	8)
		Root	Hydrodistillation; 2 h; 0.9%	Urbino, Italy	α-pinene (21.3%), δ-3-carene (16.5%), limonene (16.4%), and α-phellandrene (8.7%)	9)
2	Angelica acutiloba (Siebold & Zucc.) Kitag.	Leaves, petiole and root	Hydrodistillation; 3 h; 0.44%	Rutgers University, New Brunswick, NJ, USA	Leaves: ligustilide (11.61%) and butylidene phthalide (7.29%) Petiole: butylidene phthalide (10.76%) Root: nonane (24.85%) and α-pinene (31.59%)	10)
		Root	Solvent free solid injector; injection time—5 min and pre-heating time—7 min)	Yeosu Province, Republic of Korea	butylidene phthalide (17.82%), furfural (13.67%), 2-furanmethanol (11.97%), 5-methyl furfural (8.50%), maltol (7.28%), and butylidene dihydro-phthalide (5.78%)	11)
		Root, stem and leaves	Steam distillation; 5 h; 0.05 (root), 0.06 (stem), and 0.12 (leaves)	Nantou, Taiwan	3n-butyl phthalide (30.8–37.9%), γ-terpinene (21.1–27.2%), p-cymene (3.6–11.6%), and cis-β-ocimene (7.0–7.4%)	12)
			Headspace-solid phase microextraction; 20 min	Nantou, Taiwan	γ-terpinene (41.2–52.1%), p-cymene (10.6–17.0%), β-myrcene (6.7–8.6%), cis-β-ocimene (4.9–7.4%), and alloocimene (4.2–5.3%)	13)
3	Angelica glauca Edgew	Whole plant	Hydrodistillation; 3 h, 0.17%	Jammu and Kashmir, Pakistan	α-phellandrene (18.0%), β-pinene (14.0%), trans-carveol (16.4%), β-caryophyllene (8.6%), and β-caryophyllene oxide (8.0%).	14)
		Aerial parts	Hydrodistillation; 3 h; 0.12%	Khillanmarg areas of Kashmir, India	α-phellandrene (13.5%), trans-carveol (12.0%), β-pinene (11.7%), thujene (7.5%), β-caryophyllene oxide (7.2%), β-caryophyllene (7.0%), γ-terpinene (6.7%), nerolidol (6.5%), and β-bisabolene (5.2%)	15)
		Root	Hydrodistillation; 5 h; 0.3% and 1.8%	Himalayan locations of Uttarakhand, India	(Z)-ligustilide (40.6–53.0%), (Z)-butylidene phthalide (20.7–32.8%), and (E)-butylidene phthalide (2.5–5.9%)	16)
4	Angelica gigas Nakai	Leaves, petiole and root	Hydrodistillation; 3 h; 0.18%	Rutgers University, New Brunswick, NJ, USA	Leaves: nonane (10.75%), α-pinene (33.07%), and germacrene (10.05%) Petiole: nonane (8.85%), α-pinene (40.59%), β-phellandrene (7.52%), and myrcene (6.38%) Root: γ-terpinene (14.08%) and ligustilide (46.63%)	17)
		Root	Hydrodistillation; 4 h	Yeosu Province, Republic of Korea	nonane (19.99%), α-pinene (44.31%), camphene (6.66%), and δ-limonene (6.26%)	18)
			Solvent-free solid injector; injection time—5 min and pre-heating time—7 min)	Yeosu Province, Republic of Korea	decursin (29.34%), decursinol angelate (16.83%), lomatin (10.25%), and marmesin (9.33%)	19)
			Simultaneous steam distillation (n-pentane/diethyl ether); 2 h; 0.31%	Gwangju, Republic of Korea	α-pinene (30.89%), 2,4,6-trimethyl heptane (13.39%), α-limonene (4.29%), and camphene (4.10%)	20)
			Steam distillation; 1 h 30 min; 0.31%	Pyeongchang, Republic of Korea	α-pinene (28.64%), β-eudesmol (14.80%), nonane (8.49%), and γ-eudesmol (5.97%)	21)
			Supercritical CO2 extraction; 1 h; 1.67%	Pyeongchang, Republic of Korea	decursin (40.13%), decursinol angelate (28.44%), and β-eudesmol (7.84%)	22)
5	Angelica sinensis (Oliv.) Diels	Root	Hydrodistillation; 8 h; 0.3%	Gansu Province, China	(Z)-ligustilide 78.61% and (Z)-butylidenephthalide 7.99%	23)
			Solvent free solid injector; injection time—5 min and pre-heating time—7 min)	Yeosu Province, Republic of Korea	butylidene dihydro-phthalide, (15.23%), butylidene phthalide (14.27%), furfural (16%), camphene (10.66%), and 4-pyridinol (7.17%)	24)
			Steam distillation; 3 h; 0.02%	Chiang Mai province, Thailand	3-N-butylphthalide, butylidenephthalide, ligustilide and di-iso-octyl phthalate	25)
6	Angelica koreana Maxim.	Root	Steam distillation; 0.28%	Jinbu, Gangwon-do, Republic of Korea	sabinene (31.85%), m-cresol (4.46%), α-pinene (4.00%), and α-bisabolol (3.63%)	26)
7	Angelica dahurica (Fisch. Ex Hoffm.) Benth. & Hook.	Root	Supercritical CO2 extraction; 2 h; 1.8%	Jilin, China	dodecyl alcohol (13.71%), elemene (7.54%), hexadecanoic acid, ethyl ester (7.32%), 1-pentadecanol (6.08%), and α-pinene (6.25%),	27)
			Hydrodistillation; 3 h; 0.45%	Beijing, China	α-pinene (46.3%), sabinene (9.3%), myrcene (5.5%), 1-dodecanol (5.2%), and terpinen-4-ol (4.9%).	28)
8	Angelica pancicii Vandas ex Velen.	Root	Hydrodistillation; 2 h	Balkan mountains, Serbia	Liquid and headspace injection modes: β-phellandrene (54.9% and 60.1%), α-pinene (14.5% and 20.1%), and α-phellandrene (4.5% and 4.3%).	29)
9	Angelica pubescentis Maxim.	Root	Hydrodistillation; 3 h; 0.65%	Beijing, China	α-pinene (37.6%), p-cymene (11.6%), limonene (8.7%), and cryptone (6.7%)	30)
10	Angelica urumiensis (Mozaffarian)	Stem	Hydrodistillation; 3 h; 0.2%	Uremia, Province West Azerbaijan, Iran	Stem: α-cadinol (9.24%), (epi)-α-cadinol (5.76%), and δ-cadenine (6.11%)	31)
11	Angelica urumiensis (Mozaffarian)	Leaves	Hydrodistillation; 3 h; 0.18%	Uremia, Province West Azerbaijan, Iran	Leaves: α-cadinol (20.2%), hexahydrofarnesyl acetone (10.03%), 1-dodecanol (7.55%), linoleic acid (6.37%) and oleic acid (5.34%)	32)
12	Angelica viridiflora (Turcz.) Benth. ex Maxim.	Aerial parts	Steam distillation; 2 h; 0.2%	Shkotovskii District, Primorsky Krai, Russia	caryophyllene oxide (61.7%) and 3,4-dimethyl-3-cyclohexan-1-carboxaldehdye (5.8%)	33)
13	Angelica cincta Boissieu	Aerial parts	Steam distillation; 2 h; 0.2%	Shkotovskii District, Primorsky Krai, Russia	α-pinene (67.2%), sabinene (5.8%) and β-pinene (4.9%)	34)

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Table 2. Angelica essential oils biological activities

S. No.	Species	Parts	Biological activity	Model	References
1	Angelica archangelica L.	Seeds	Antioxidant	Aldehyde/Carboxylic Acid Assay, DPPH radical scavenging assay, and Malonaldehyde/Gas Chromatography Assay	36)
		Fruit of two chemotypes	Cytotoxic effect	Human pancreas cancer cell line PANC-1 and the mouse breast cancer cell line Crl	37)
		Root	Anti-seizure	Maximal electroshock and pentylenetetrazol-induced seizures in mice	38)
			Anti-aflatoxigenic and antioxidant activities	Aspergillus flavus DPPH radical scavenging assay	39)
			Antimicrobial	Fusarium genus, Botrytis cinerea, and Alternaria solani, Clostridium difficile, Clostridium perfringens, Enterococcus faecalis, Eubacterium limosum, Peptostreptococcus anaerobius, and Candida albicans	40)
2	Angelica gigas Nakai	Root	Nicotine Sensitization	Repeated nicotine-induced locomotor activity and extracellular dopamine levels in the nucleus accumbens of rats	41)
			Human EEG	Increased absolute low beta (left temporal and left parietal) activity	42)
		Leaves	Immunotoxicity	Larvae of Aedes aegypti	43)
3	Angelica glauca Edgew	Whole plant	Antioxidant, antimicrobial, and phytotoxic	Bacteria: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pasteurella multocida Fungi: Candida albicans, Microsporum canis, Aspergillus flavus and Fusarium solani. DPPH radical scavenging assay Phytotoxic activity against Lemna minor	44)
			Broncho-relaxant	Airway was induced using histamine aerosol in guinea pigs and ovalbumin aerosol in albino mice.	45)
4	Angelica sinensis (Oliv.) Diels	Root	Anti-inflammatory	Carrageenan-induced rats	46)
			Antioxidant	DPPH, ABTS scavenging, and β-carotene bleaching assays.	47)
			Anti-inflammatory	Carrageenan-induced rats and mechanism by plasma metabolomics approach	48)
			Antibacterial	Staphylococcus aureus, Staphylococcus chromogenes, and Streptococcus uberis	49)
			Anti-inflammatory	Carrageenan-induced acute inflammation model rats	50)
			Anti-inflammatory	Lipopolysaccharide-induced inflammation rat model	51)
			Anxiolytic	Elevated plus-maze, light/dark and stress-induced hyperthermia tests	52)
				Social interaction test of anxiety and the hole-board test	53)
			Repellent	Against Aedes aegypti	54)
5	Angelica koreana Maxim.	Root	Antifungal and antioxidant	Aspergillus (A. flavus, A. fumigaus, A. niger, A. terreus and A. versicolor) and Trichophyton (T. mentagrophytes, T. rubrum and T. tonsurans) species DPPH scavenging, nitrite inhibition, and reducing power	55)
6	Angelica dahurica (Fisch. Ex Hoffm.) Benth. & Hook.	Root	Anti-inflammatory and immunomodulating properties	Xylene-induced acute ear swelling and carrageenan-induced acute paw edema in mice; anti-inflammatory and immunomodulating properties in Freund’s complete adjuvant (FCA)-induced arthritis in rats.	56)
			Enhance sensitivity of MCF-7/ADR breast cancer cells to doxorubicin	MDR human breast cancer MCF-7/ADR cells	57)
			Insecticidal	Yellow fever mosquito, Aedes aegypti, and azalea lace bugs, Stephanitis pyrioides	58)
			Antibacterial	Staphylococcus aureus, Staphylococcus chromogenes, and Streptococcus uberis	59)
			Immunotoxicity	Larvae of Aedes aegypti	60)
7	Angelica pubescentis Maxim.	Root	Antifungal and Insecticidal	Colletotrichum acutatum, Colletotrichum fragariae, and Colletotrichum gloeosporioides, Yellow fever mosquito, Aedes aegypti, and azalea lace bugs, Stephanitis pyrioides	61)
8	Angelica anomala Avé-Lall., Angelica cartilagino-marginata var. distans, Angelica czernevia, Angelica decursiva (Miq.) Franch. & Sav., Angelica fallax H. Boissieu , Angelica japonica A. Gray	Leaves	Immunotoxicity	Larvae of Aedes aegypti	62)
9	Angelica species	Root	Penetration Enhancers for Transdermal Administration of Ibuprofen	Therapeutic efficacy of ibuprofen with essential oil was evaluated using dysmenorrheal model mice	63)
			Skin permeation of drugs	Skin permeation of ibuprofen across rat abdominal skin	64)

Note: DPPH: 1,1-diphenyl-1-picrylhydrazyl; ABTS: 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid); EEG: electroencephalographic activity; MDR: multidrug resistance.

[Source ⁶⁵⁾]

Angelica essential oils chemical composition

The main aim of this review is to offer an overview on the chemical composition of essential oils from different species of Angelica growing in various countries. Table 1 above shows the plant name, plant parts, extraction methods, yield, and the major components of essential oils in relation to different species of Angelica. The published reports revealed that the essential oils of the genus Angelica isolated by steam distillation or the hydrodistillation method mainly consist of monoterpene hydrocarbons. Figure 3 below depicts the chemical structure of some of the major components of essential oils from Angelica species.

In Angelica archangelica seed essential oils, β-phellandrene (33.6–63.4%) and α-pinene (4.2–12.8%) were detected as the most abundant components ⁶⁶⁾. On the other hand, α-pinene (21.3%), δ-3-carene (16.5%), limonene (16.4%), and α-phellandrene (8.7%) were the most abundant components in the essential oil of Angelica archangelica roots growing in Italy ⁶⁷⁾. Nivinskiene et al. ⁶⁸⁾ studied the essential oil composition of Angelica archangelica roots collected from three habitats (Svencionys, Prienai, and Vilnius districts in Lithuania) between 1995–2002. α-Pinene (15.7–20.8%) was the major essential oil component in two localities, whereas β-phellandrene (13.8–18.5%) and α-pinene (11.4–15.0%) were registered as the major essential oil components in the third locality. The Angelica essential oils contained 67.3–79.9% of monoterpenes, 9.6–19.4% of sesquiterpenes, and 3.9–6.3% of macrocyclic lactones. Chauhan et al. ⁶⁹⁾ found that the essential oils of Angelica archangelica rhizomes obtained from three different altitudes of western Himalaya mainly contained dillapiole (35.93–91.55%) and nothoapiole (0.1–62.8%). Further, the authors reported that the composition of essential oils varied greatly with the altitude of collection. Pasqua et al. ⁷⁰⁾ investigated the accumulation of essential oils in the roots of Angelica archangelica subsp. archangelica at different developmental stages. A high concentration of α- and β-phellandrene was found only in taproots exceeding 5 mm in diameter.

The essential oil of the Angelica glauca whole plant collected from Jammu and Kashmir mainly contains α-phellandrene (18.0%), trans-carveol (16.4%), β-pinene (14.0%), β-caryophyllene (8.6%), and β-caryophyllene oxide (8.0%) ⁷¹⁾. Agnihotri et al. ⁷²⁾ investigated the composition of essential oil from fresh aerial parts of Angelica glauca growing in Kashmir valley in higher Himalaya (India), and found that α-phellandrene (13.5%), trans-carveol (12.0%), and β-pinene (11.7%) were the major components. The essential oils from the roots of Angelica glauca collected from two alpine Himalayan locations in Uttarakhand (India) highly contain (Z)-ligustilide (40.6–53.0%) and (Z)-butylidene phthalide (20.7–32.8%) ⁷³⁾.

Kim et al. ⁷⁴⁾ determined the essential oil composition from the rhizomes of Angelica gigas, Angelica sinensis, and Angelica acutiloba by solvent-free solid injector method. Coumarin derivatives such as decursinol angelate (16.83%) and decursin (29.34%) were found to be the most abundant components, followed by lomatin (10.25%), and marmesin (9.33%) in Angelica gigas. Butylidene dihydro-phthalide, (15.23%), butylidene phthalide (14.27%), furfural (16%), and camphene (10.66%) were the main components in Angelica sinensis. Similarly, butylidene phthalide (17.82%) and furfural (13.67%) were registered as the major components in Angelica acutiloba.

Sowndhararajan et al. ⁷⁵⁾ compared the essential oil composition of Angelica gigas root by steam distillation and supercritical carbon dioxide extract. The essential oil mainly composed of monoterpene hydrocarbons (52.83%), followed by oxygenated sesquiterpenes (25.53%). In these, α-pinene (28.64%), β-eudesmol (14.80%), nonane (8.49%), and γ-eudesmol (5.97%) were the major components in the essential oil of Angelica gigas root. However, decursin (40.13%) and decursinol angelate (28.44%) were detected as the most abundant components in supercritical carbon dioxide extract. α-Pinene (30.89%) was also the major component in the essential oil of Angelica gigas extracted by simultaneous steam distillation and extraction method ⁷⁶⁾. In another study, the roots of Angelica gigas and Angelica acutiloba were collected from the field of Snyder Research and Extension Farm Rutgers University, New Jersey, and analyzed for their essential oil composition. The main constituents of the Angelica gigas root essential oil were ligustilide (47%) and γ-terpinene (14%). In the case of Angelica acutiloba root essential oil, α-pinene (32%) and nonane (25%) were the major components ⁷⁷⁾.

Chen et al. ⁷⁸⁾ compared the volatile compositions of Angelica acutiloba roots, stems, and leaves using steam distillation and headspace solid-phase microextraction. In all three parts, a total of 61 and 33 compounds were detected by steam distillation and headspace solid-phase microextraction, respectively. In the steam distillation, 3n-butyl phthalide, γ-terpinene, p-cymene, and cis-β-ocimene were the main compounds. On the other hand, γ-terpinene and p-cymene were the main compounds in headspace solid-phase microextraction. Further, the authors reported that monoterpene components were found to be higher in the headspace solid-phase microextraction sampling method when compared with steam distillation.

In the essential oil of Angelica major, α-pinene (21.8%) and cis-β-ocimene (30.4%) were found to be the most abundant components ⁷⁹⁾. The main components in Angelica dahurica essential oil were α-pinene (46.3%), sabinene (9.3%), myrcene (5.5%), 1-dodecanol (5.2%), and terpinen-4-ol (4.9%). In regards to Angelica pubescentis root essential oil, α-pinene (37.6%), p-cymene (11.6%), limonene (8.7%), and cryptone (6.7%) were found to be the major components ⁸⁰⁾. Champakaew et al. ⁸¹⁾ found that 3-N-butylphthalide, butylidene phthalide, ligustilide, and di-iso-octyl phthalate were the main components in Angelica sinensis essential oil. The composition of essential oils of the stem and leaves of Angelica urumiensis were studied by Mohammadi et al. ⁸²⁾. In the essential oil from the leaves, α-cadinol (20.2%), hexahydrofarnesyl acetone (10.03%), and 1-dodecanol (7.55%) were the major components. On the other hand, α-cadinol (9.24%) and δ-cadenine (6.11%) were the major components in the essential oil from the stem. The essential oil compositions of Angelica pancicii were compared by gas chromatography–mass spectrometry liquid injection and headspace-gas chromatography–mass spectrometry modes. In total, 40 compounds were identified in the essential oil by gas chromatography–mass spectrometry liquid injection, and 44 by headspace-gas chromatography–mass spectrometry. In both cases, the main components were β-phellandrene, α-pinene, and α-phellandrene ⁸³⁾. Caryophyllene oxide (61.7%) and α-pinene (67.2%) were detected as the most abundant components in essential oils of Angelica viridiflora and Angelica cincta aerial parts, respectively ⁸⁴⁾.

Figure 3. Angelica essential oils chemical components

[Source ⁸⁵⁾]

Angelica essential oils potential health benefits and uses

Antioxidant

1,1-Diphenyl-2-picrylhydrazil (DPPH) and 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS) radical scavenging activities are extensively used measures to evaluate the antioxidant potential of plant extracts or compounds. DPPH, nitrite inhibition, and reducing power were determined to assess the antioxidant activity of Angelica koreana essential oil and its major components. m-Cresol (56.12%) showed stronger DPPH scavenging activity than essential oil (19.31%) and sabinene (4.45%) at the concentration of 16 mg/mL ⁸⁶⁾. Additionally, sabinene exhibited the strongest reducing power and nitric oxide scavenging activities than the essential oil fraction or m-cresol. Irshad et al. ⁸⁷⁾ reported that Angelica glauca essential oil exhibited good DPPH radical scavenging and peroxidation inhibition activities. Angelica seed oil showed 39% of DPPH radical scavenging activity at the concentration of 200 μg/mL ⁸⁸⁾. The antioxidant activity of Angelica sinensis was investigated by DPPH, ABTS, and beta-carotene bleaching assays. Angelica sinensis essential oil and coniferyl ferulate rich fractions 1 and 2 showed strong DPPH (IC50 of 194.7, 42.4 and 15.2 μg/mL, respectively) and ABTS (IC50 of 98.8, 15.9 and 7.8 μg/mL, respectively) radical scavenging activities. Further, coniferyl ferulate rich fractions 1 and 2 exhibited good β-carotene bleaching activity with IC50 values of 11.0 and 2.0 μg/mL, respectively ⁸⁹⁾. In another study, the DPPH radical scavenging activity of Angelica archangelica essential oil, α-terpineol, phenyl ethyl alcohol, and their combination were determined. The IC50 values of Angelica archangelica essential oil, α-terpineol, and their essential oil-based combination were 1.04, 66.6, and 3.89 μL/mL, respectively ⁹⁰⁾.

Antimicrobial

Angelica koreana essential oil and its main components, sabinene and m-cresol, showed antifungal activity against different species of Aspergillus and Trichophyton with minimal inhibitory concentrations (MICs) of 125–1000 μg/mL. In addition, essential oil exhibited synergistic activity when combined with itraconazole ⁹¹⁾. The essential oil of Angelica glauca showed appreciable antimicrobial activity against selected strains of bacteria (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pasteurella multocida) and fungi (Candida albicans, Microsporum canis, Aspergillus flavus, and Fusarium solani). Among the bacterial strains tested, Escherichia coli and Staphylococcus aureus were the most sensitive bacteria with minimum inhibitory concentration (MIC) values of 141.3 and 159.3 µg/mL, respectively. In regards to fungal strains, Microsporum canis was the most sensitive organism with a MIC value of 178.1 µg/mL ⁹²⁾.

The essential oil of Angelica archangelica root showed considerable antimicrobial activity against Clostridium difficile, Clostridium perfringens, Enterococcus faecalis, Eubacterium limosum, Peptostreptococcus anaerobius, and Candida albicans. Further, Angelica archangelica essential oil showed a weaker antimicrobial activity against the intestinal microflora such as bifidobacteria and lactobacilli. In another study, the essential oil showed antifungal activity against some species of the Fusarium genus, Botrytis cinerea, and Alternaria solani ⁹³⁾. A combination of Angelica archangelica essential oil: Phenyl ethyl alcohol (PEA): α-terpineol (1:1:1) inhibited the growth of Aspergillus flavus NKDW-7 (aflatoxigenic strain) and aflatoxin B1 production at 2.25 and 2.0 μL/mL, respectively. At the concentration of 2.0 μL/mL, the combination showed a >90% decrease in ergosterol content in the plasma membrane of Aspergillus flavus ⁹⁴⁾.

Cavaleiro et al. ⁹⁵⁾ evaluated the antifungal activity of the essential oil of Angelica major and its major components, α-pinene and cis-β-ocimene, against clinically important yeasts and molds. Angelica major essential oil exhibited a broad spectrum of antifungal activity, including all tested fungi (animal and human pathogenic species or spoilage fungi): Candida spp., Candida neoformans, Aspergillus spp., and dermatophytes. α-Pinene was more active against all of the tested fungi than cis-β-ocimene. Angelica sinensis and Angelica dahurica essential oils exhibited significant antibacterial activity against three mastitis-causing pathogens: Staphylococcus aureus, Staphylococcus chromogenes, and Streptococcus uberis ⁹⁶⁾. Tabanca et al. ⁹⁷⁾ reported that Angelica pubescentis root essential oil exhibited weak antifungal activity against Colletotrichum acutatum, Colletotrichum fragariae, and Colletotrichum gloeosporioides. In the case of Angelica dahurica root essential oil, there was no antifungal activity observed against tested fungal strains.

Insecticidal

Essential oils from the root of Angelica dahurica and Angelica pubescentis were studied as pest management prospectives. When compared with Angelica pubescentis essential oil, Angelica dahurica essential oil showed better biting deterrent and insecticidal activity against Aedes aegypti and Stephanitis pyrioides. In mosquito bioassays, components of Angelica dahurica essential oil, 1-dodecanol and 1-tridecanol, showed antibiting deterrent activity against Aedes aegypti ⁹⁸⁾. Chung et al. ⁹⁹⁾ investigated the immunotoxicity effect of essential oils from the leaves of Angelica anomala, Angelica cartilagino-marginata var. distans, Angelica czernevia, Angelica dahurica, Angelica decursiva, Angelica fallax, Angelica gigas, and Angelica japonica. Among them, the essential oil of Angelica dahurica showed a significant toxic effect against early fourth-stage larvae of Aedes aegypti, with a LC50 value of 43.12 ppm. In another study, out of 33 plant species tested, Angelica sinensis essential oil showed the best repellent activity against Aedes aegypti, with a median complete protection time of 7.0 hours ¹⁰⁰⁾.

Behavioral

Repeated administration of nicotine can produce behavioral sensitization, and this is a good model for studying drug addiction. Zhao et al. ¹⁰¹⁾ reported that the inhalation of Angelica gigas essential oil significantly ameliorated nicotine-induced behavioral sensitization by decreasing dopamine release in the nucleus accumbens and locomotor activity in repeated nicotine-induced rats. Pathak et al. ¹⁰²⁾ found that the essential oil of the Angelica archangelica root exhibited antiseizure activity against electrically and chemically-induced seizures in mice. Chen et al. ¹⁰³⁾ investigated the anxiolytic activity of Angelica essential oil in a mice model. The results revealed that the essential oil of Angelica exhibited considerable anxiolytic-like effects at the concentration of 30.0 mg/kg (orally), as measured in the elevated plus-maze, the light/dark, and the stress-induced hyperthermia tests. In addition, Angelica essential oil significantly improved the behavioral performances in the social interaction test of anxiety and the hole-board test of exploration and locomotor activity in rats ¹⁰⁴⁾. Sharma et al. ¹⁰⁵⁾ reported that the essential oil of Angelica glauca exhibited broncho-relaxant activity against histamine and ovalbumin-induced bronchoconstriction in guinea pigs by decreasing absolute blood eosinophil count, serum levels of immunoglobulin E, and the number of eosinophils and neutrophils in bronchoalveolar lavage fluid. Sowndhararajan et al. ¹⁰⁶⁾ investigated the effect of inhalation of essential oil of Angelica gigas root on electroencephalographic activity in humans. The results revealed that absolute low beta significantly increased at left temporal and left parietal region during the inhalation of the essential oil of Angelica gigas root, and these changes may contribute to the enhancement of language learning abilities in humans.

Anti-Inflammatory

Zhang et al. ¹⁰⁷⁾ used the metabonomics based on gas chromatography–mass spectrometry to study the possible anti-inflammatory mechanisms of essential oil of Angelica sinensis in rats with acute inflammation. In the carrageenan-injected rats, treatment with the essential oil of Angelica sinensis significantly restored the levels of prostaglandin E2, histamine, and 5-hydroxytryptamine in the inflammatory fluid, similar to the normal group. Gas chromatography–mass spectrometry analysis identified 14 metabolite biomarkers detected in the inflammatory fluid. Zhong et al. ¹⁰⁸⁾ evaluated the anti-inflammatory effect of essential oils obtained from processed products of Angelica sinensis. For this purpose, essential oils from stir-fried Angelica sinensis, fried Angelica sinensis with alcohol, cooked Angelica sinensis with soil, and fried Angelica sinensis with sesame oil were applied to intervene the carrageenan-induced acute inflammation of the model rats. The results showed that the essential oils of Angelica sinensis significantly inhibited the release of prostaglandin E2, histamine, 5-hydroxytryptamine, and tumor necrosis factor-α. Furthermore, Angelica sinensis exhibited an anti-inflammatory effect against the lipopolysaccharide (LPS)-induced inflammation rat model by regulating the Krebs cycle, enhancing the glucose content, and restoring the fatty acid metabolism ¹⁰⁹⁾.

Li et al. ¹¹⁰⁾ investigated the effects of Angelica sinensis essential oil on the lipopolysaccharide-induced acute inflammation rat model. Angelica sinensis essential oil exhibited anti-inflammatory and liver protection effects by inhibiting the secretion of the pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), the inflammatory mediators (histamine, 5-hydroxytryptamine, prostaglandin E2, and nitric oxide), the inflammation-related enzymes (inducible nitric oxide synthase and cyclooxygenase 2), as well as promoting the production of the anti-inflammatory cytokines interleukin-10. Wang et al. ¹¹¹⁾ reported that the essential oil of Angelica dahurica (at 100 mg/kg) showed anti-inflammatory activity against xylene-induced ear swelling and carrageenan-induced paw edema in a mice model. In addition, the essential oil significantly alleviated Freund’s complete adjuvant-induced arthritis in rats by improving hind paw swelling and reducing the serum levels of nitric oxide, tumor necrosis factor-α, prostaglandin E2, and serum nitric oxide synthase activity.

Skin permeation enhancer of drugs

It is well known that essential oils can reversibly overcome the stratum corneum barrier to improve the skin permeation of drugs. Chen et al. ¹¹²⁾ studied the penetration enhancement effect of five essential oils (clove, Angelica, Chuanxiong, Cyperus, and cinnamon) on the transdermal drug delivery of ibuprofen using dysmenorrheal model mice. Among five essential oils tested, Chuanxiong and Angelica oils effectively enhanced the transdermal drug delivery of ibuprofen. In another study, turpentine, Angelica, Chuanxiong, Cyperus, cinnamon, and clove oils (at 3% w/v) were evaluated for the potential to enhance the skin penetration of ibuprofen in rats. When compared with azone, the tested essential oils had significantly higher penetration enhancement effect and lower skin irritation potential. The results revealed that essential oils can enhance the skin permeation of ibuprofen mainly by disturbing the stratum corneum lipids ¹¹³⁾.

Angelica root benefits

Traditionally, Angelica sinensis, Angelica gigas, and Angelica acutiloba are the most important Angelica species, which are mainly found in Korea, China, and Japan, respectively ¹¹⁴⁾. In China, Angelica sinensis has been used for the treatment of various ailments such as gynecological diseases, apoplexia, constipation, malaria, chills, fever, and hemorrhoids. The plant has also been used as a hematinic for nourishing blood, regulating menstruation, and relaxing bowels ¹¹⁵⁾. In the Korean traditional medicine, Angelica root part of Angelica gigas has been to treat anemia, gynecological diseases, circulatory diseases, and arthritis. It has also been used as sedative, analgesic, and tonic agents ¹¹⁶⁾. Angelica acutiloba is traditionally used to treat gynecological diseases and anemia ¹¹⁷⁾. Angelica archangelica is commonly used in traditional medicine to cure nervousness, insomnia, stomach and intestinal disturbances, skin diseases, respiratory problems, and arthritis ¹¹⁸⁾. Angelica glauca has been used to treat bilious complaints, infantile atrophy, and constipation ¹¹⁹⁾. Angelica dahurica has been mainly used to treat headaches, rhinitis, toothaches, rheumatism, and sore throat ¹²⁰⁾. Angelica pubescentis has been used to cure rheumatoid arthritis, headache, paralysis, and insomnia ¹²¹⁾.

Summary

From the research thus far, it seems the active compounds of Angelica root are the essential oils.  Essential oils have been isolated from different plant parts of Angelica species. The most abundant components in the essential oils were α-pinene, β-pinene, α-phellandrene, β-phellandrene, δ-3-carene, sabinene, γ-terpinene, limonene, p-cymene, ligustilide, butylidene phthalide, α-cadinol, and β-eudesmol. Based on the previous reports, the essential oils from different Angelica species exhibit appreciable antioxidant, antimicrobial, insecticidal and anti-inflammatory activities. In addition, essential oils significantly enhance behavioral performances and promote the skin permeation of drugs. Among the different Angelica species, Angelica archangelica, Angelica sinensis, and Angelica dahurica were the most studied plant species in relation to the biological activities of essential oils. Now further studies including clinical trials are needed to validate and confirm Angelica essential oil biological activities in the treatment of diseases and health conditions.

What is marjoram

Marjoram (Origanum majorana L.) commonly known as sweet marjoram from the family Lamiaceae, is a perennial herb that is native to Mediterranean region and cultivated in many countries of Asia, North Africa, and Europe, for example, Spain, Hungary, Portugal, Germany, Egypt, Poland, and France ¹⁾. Marjoram (Origanum majorana L.) grows up to 30 to 60 cm. Marjoram is a perennial bushy plant. It has oblique rhizome, hairy shrub like stalks, opposite dark green oval leaves and white or red flowers in clustered bracts. The leaves are whole, larger ones being fragmented, oblate to broadly elliptical ²⁾. In some Middle Eastern countries, marjoram is synonymous with oregano, and there the names sweet marjoram and knotted marjoram are used to distinguish it from other plants of the genus Origanum. Marjoram plant is widely used as a garnish and is used for different medicinal purposes in traditional and folklore medicine of different countries. Sweet marjoram has been used for variety of diseases in traditional and folklore medicines, including ocular disorder, nasopharyngeal disorders, asthma, cold, coughs, cramps, depression, dizziness, gastrointestinal disorders, hay fever, headache, toothache, and sinus congestion and as a diuretic and to promote menstruation ³⁾ and for cardiac, rheumatologic, and neurological disorders ⁴⁾.

Various compounds have been identified in sweet marjoram. Also, different pharmacological activities have been attributed to this plant. Essential oil containing monoterpene hydrocarbons and oxygenated monoterpenes as well as phenolic compounds are chemical constituents isolated and detected in marjoram. Wide range of pharmacological activities including antioxidant, hepatoprotective, cardioprotective, anti-platelet, gastroprotective, antibacterial and antifungal, antiprotozoal, antiatherosclerosis, anti-inflammatory, antimetastatic, antitumor, antiulcer, and anticholinesterase inhibitory activities have been reported from this plant in modern medicine ⁵⁾.

Figure 1. Marjoram (sweet marjoram)

Figure 2. Dried marjoram (marjoram herb)

Marjoram uses

Traditional medicine uses

Ethnomedicinal uses of sweet marjoram in different countries are shown in Table 1. The parts of sweet marjoram that are used in folklore medicine are dried leaves, leaves extract, and essential oil. Marjoram leaves have been claimed to have antimicrobial and emmenagogue (a substance that stimulates or increases menstrual blood flow) properties and be useful for treatment of respiratory and gastrointestinal problems ⁶⁾. Marjoram has been used in Morocco as an antihypertensive plant ⁷⁾. The marjoram essential oil has been used for pains, gastrointestinal problems, and respiratory tract disorders ⁸⁾.

Table 1. Traditional medicine uses of marjoram

Region	Plant Part Used	Traditional Uses
Iran 9)	Leaves	Antimicrobial, antiseptic, antidote, carminative, antitussive and used for gastrointestinal disorder, head cool, sniffle, vision performance, otitis, melancholia accompanied by flatulence, unilateral facial paralysis, headache, epilepsy, cataract, weakness of sight, ear pain, dyspnea, cardiac pain, dysrhythmia, cramp, obstruction of large intestine, emmenagogue, strangury, dropsy, spondilolysthesis, groin pain, back pain, fatigue, freckle, migraine
Azerbaijan 10)	Essential oil	Flatulence, nervousness, diuretic, sedative
England 11)	Leaves	Cold, bronchial coughs, asthmatic whooping
Egypt 12)	Leaves	Cold, chill
India 13)	Essential oil	Toothache, soothe joints, muscular pain
Austria 14)	Leaves	Gastrointestinal tract diseases, infections
Turkey 15)	Essential oil	Asthma, indigestion, headache, rheumatism
Morocco 16)	Leaves	Hypertension

[Source ¹⁷⁾]

Phytochemical constituents of marjoram

Table 2. Structure and phytochemical category of compounds isolated from different parts of sweet marjoram.

Compound	Chemical Category	Part/Extract
α-Pinene	Monoterpene hydrocarbon	Essential oil18)
β-Pinene	Monoterpene hydrocarbon	Essential oil19)
ρ-Cymene	Monoterpene hydrocarbon	Essential oil20)
Camphene	Monoterpene hydrocarbon	Essential oil21)
α-Phellandrene	Monoterpene hydrocarbon	Essential oil 22)
β-Phellandrene	Monoterpene hydrocarbon	Essential oil 23)
γ-Terpinene	Monoterpene hydrocarbon	Essential oil24)
d-Limonene	Monoterpene hydrocarbon	Essential oil 25)
α-Terpinene	Monoterpene hydrocarbon	Essential oil 26)
Terpinolene	Monoterpene hydrocarbon	Essential oil 27)
β-Myrcene	Monoterpene hydrocarbon	Essential oil 28)
2-Carene	Monoterpene hydrocarbon	Essential oil 29)
β-Ocimene	Monoterpene hydrocarbon	Essential oil 30)
Sabinene	Monoterpene hydrocarbon	Essential oil 31)
α-Thujene	Monoterpene hydrocarbon	Essential oil 32)
Carvone	Monoterpene hydrocarbon	Essential oil 33)
Citronellol	Monoterpene hydrocarbon	Essential oil 34)
Terpinen-4-ol	Oxygenated monoterpene	Essential oil 35) / Leaf 36)
cis-Sabinene hydrate	Oxygenated monoterpene	Essential oil 37)
trans-Sabinene hydrate	Oxygenated monoterpene	Essential oil 38)
Linalool	Oxygenated monoterpene	Leaf 39) / Essential oil 40)
Thymol	Oxygenated monoterpene	Essential oil 41)
α-Terpineol	Oxygenated monoterpene	Essential oil 42)
Linalyl acetate	Oxygenated monoterpene	Essential oil 43)
Carvacrol	Oxygenated monoterpene	Essential oil 44)
1,8-Cineol	Oxygenated monoterpene	Essential oil 45)
Fenchyl alcohol	Oxygenated monoterpene	Essential oil 46)
Piperitol	Oxygenated monoterpene	Essential oil 47)
trans-Carveol	Oxygenated monoterpene	Essential oil 48)
cis-Carveol	Oxygenated monoterpene	Essential oil 49)
Anethole	Oxygenated monoterpene	Essential oil 50)
Geraniol	Oxygenated monoterpene	Essential oil 51)
α-Terpinyl acetate	Oxygenated monoterpene	Essential oil 52)
Geranyl acetate	Oxygenated monoterpene	Essential oil 53)
α-Cubebene	Sesquiterpene hydrocarbon	Essential oil 54)
Longicyclene	Sesquiterpene hydrocarbon	Essential oil 55)
Copaene	Sesquiterpene hydrocarbon	Essential oil 56)
β-Longipinene	Sesquiterpene hydrocarbon	Essential oil 57)
β-Caryophyllene	Sesquiterpene hydrocarbon	Essential oil 58)
Aromadendrene	Sesquiterpene hydrocarbon	Essential oil 59)
α-Humulene	Sesquiterpene hydrocarbon	Essential oil 60)
β-Farnesene	Sesquiterpene hydrocarbon	Essential oil 61)
Alloaromadendrene	Sesquiterpene hydrocarbon	Essential oil 62)
α-Selinene	Sesquiterpene hydrocarbon	Essential oil 63)
ar-Curcumene	Sesquiterpene hydrocarbon	Essential oil 64)
Germacrene D	Sesquiterpene hydrocarbon	Essential oil 65)
Valencene	Sesquiterpene hydrocarbon	Essential oil 66)
α-Muurolene	Sesquiterpene hydrocarbon	Essential oil 67)
α-Farnesene	Sesquiterpene hydrocarbon	Essential oil 68)
Spathulenol	Sesquiterpene alcohol	Essential oil 69)
Caryophyllene oxide	Oxygenated sesquiterpene	Essential oil70)
Carnosic acid	Diterpenoid	Water extract 71)
Carnosol	Diterpenoid	Water extract 72)
Ursolic acid	Triterpenoid	Water extract 73)
Sinapic acid	Phenolic acid	Essential oil 74)
Vanillic acid	Phenolic acid	Hydroalcoholic extract 75) / Essential oil 76)
Ferulic acid	Phenolic acid	Hydroalcoholic extract 77) / Essential oil 78)
Caffeic acid	Phenolic acid	Hydroalcoholic extract 79) / Essential oil 80)
Syringic acid	Phenolic acid	Hydroalcoholic extract 81) / Essential oil 82)
ρ-Hydroxybenzoic acid	Phenolic acid	Hydroalcoholic extract 83) / Essential oil 84)
m-Hydroxybenzoic acid	Phenolic acid	Hydroalcoholic extract 85)
Coumarinic acid	Phenolic acid	Essential oil 86)
Gallic acid	Phenolic acid	Hydroalcoholic extract 87)
Neochlorogenic acid	Phenolic acid	Hydroalcoholic extract 88)
Protocatechuic acid	Phenolic acid	Hydroalcoholic extract 89)
Caftaric acid	Phenolic acid	Hydroalcoholic extract 90)
Rosmarinic acid	Phenolic acid	Ethyl acetate extract 91) / Essential oil 92)
Chlorogenic acid	Phenolic acid	Hydroalcoholic extract 93)
Cryptochlorogenic acid	Phenolic acid	Hydroalcoholic extract 94)
Coumaric acid	Phenolic acid	Hydroalcoholic extract 95)
Lithospermic acid	Phenolic acid	Water extract 96)
Methyl rosmarinate	Phenolic compound	Hydrophilic extract 97)
Hydroquinone	Phenolic compound	Ethyl acetate extract 98) / Essential oil 99)
Arbutin	Phenolic glycosides	Ethyl acetate extract 100) / Essential oil 101)
Methyl arbutin	Phenolic glycoside	Essential oil 102)
Vitexin	Phenolic glycoside	Essential oil 103)
Orientinthymonin	Phenolic glycoside	Essential oil 104)
Hesperetin	Flavonoid	Ethyl acetate extract 105)
Catechin	Flavonoid	Hydroalcoholic extract 106)
Quercetin	Flavonoid	Hydroalcoholic extract 107)
Kaempferol	Flavonoid	Hydroalcoholic extract 108)
Naringenine	Flavonoid	Hydroalcoholic extract 109)
Eriodictyol	Flavonoid	Hydroalcoholic extract 110)
Diosmetin	Flavonoid	Essential oil 111)
Luteolin	Flavonoid	Essential oil 112)
Apigenin	Flavonoid	Essential oil 113)
5,6,3′-Trihydroxy-7,8,4′-trimethoxyflavone	Flavonoid	Ethyl acetate extract 114)
Kaempferol-3-O-glucoside	Flavonoid glycoside	Hydroalcoholic extract 115)
Quercetin-3-O-glucoside	Flavonoid glycoside	Hydroalcoholic extract 116)
Narigenin-O-hexoside	Flavonoid glycoside	Hydroalcoholic extract 117)
Apigenin-glucuronide	Flavonoid glycoside	Water extract 118)
Rutin	Flavonoid glycoside	Hydroalcoholic extract 119)
Luteolin-7-O-β-glucuronide	Flavonoid glycoside	Hydrophilic extract 120)
Eugenol	Phenyl propene	Essential oil 121)
Ethyl cinnamate	Ester	Essential oil 122)
Sitosterol	Phytosterol	Essential oil 123)
Oleanolic acid	Fatty acid	Essential oil 124)
Vitamin A	Vitamin	Essential oil 125)
Vitamin C	Vitamin	Essential oil 126)

[Source ¹²⁷⁾]

Figure 3. Marjoram active compounds

[Source ¹²⁸⁾]

Marjoram phenolic compounds

Vanillic acid, gallic acid, ferulic acid, caffeic acid, syringic acid, p- and m-Hydroxybenzoic acid, coumaric acid, neochlorogenic acid, protocatechuic acid, chlorogenic acid, cryptochlorogenic acid, caftaric acid are phenolic acids that have been detected in hydroalcoholic extract of leaves of sweet marjoram ¹²⁹⁾. Rosmarinic acid, sinapic acid, vanillic acid, ferulic acid, caffeic acid, syringic acid, p- and m-hydroxybenzoic acid, and coumarinic acid have been identified in essential oil of sweet marjoram ¹³⁰⁾. Arbutin, methyl arbutin, vitexin, and orientinthymonin have been reported to be the most predominant phenolic glycosides in essential oil of sweet marjoram.10 Hesperetin, catechin, quercetin, kaempferol, naringenine, eriodictyol, diosmetin, luteolin, and apigenin are the most abundant flavonoids detected in sweet marjoram10,21 and kaempferol-3-O-glucoside, quercetin-3-O-glucoside, narigenin-O-hexoside, and rutin are flavonoid glycosides identified in sweet marjoram ¹³¹⁾.

Antioxidant properties of marjoram

It has been suggested that phenolic compounds from marjoram, such as flavonoids and phenolic acids, might exert anti-inflammatory properties (Table 3) ¹³²⁾. In this regard, Mueller et al. ¹³³⁾ evaluated the anti-inflammatory activity of marjoram hydrophilic extracts on lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells. Pre-treatment of the cells with with the extracts from marjoram at 500 μg/mL and 200 μg/mL the levels of IL-6 were reduced 20% and 17%, respectively, while the iNOS expression was diminished 66%. Even though Mueller et al. ¹³⁴⁾ did not identify the compounds in the marjoram extracts, they mention that diosmetin, apigenin, luteolin and rosmarinic acid are the compounds to most likely be present in the hydrophilic extracts, so these molecules might be responsible for the activity of marjoram extracts.

Table 3. Summary of the antioxidant capacity of flavonoids and phenolic acids of Marjoram

Extract	Compounds	Plant Part	Antioxidant Assay	Reference
Methanol microwave-assisted	Rosmarinic and caffeic acid, apigenin, rutin	Aerial parts	TPC, DPPH, CUPRAC	135)
Aqueous, methanol	Rosmarinic and caffeic acids	Leaves	TPC, DPPH, β-carotene bleaching	136)
Methanol	Rosmarinic acid, eriodictyol, naringenin, hispidulin, cirsimaritin	Leaves, commercial herbs	TPC, ORAC	137)
Methanol	Rosmarinic acid, epigallocatechin, quercetin, apigenin	Not specified	DPPH, FRAP	138)
Ethanol	Chlorogenic, ferulic, p-coumaric, p-hydroxybenzoic, protocatechuic, rosmarinic and syringic acids, quercetin	Not specified	TPC, DPPH, ABTS	139)

[Source ¹⁴⁰⁾]

Pharmacological Activities of Marjoram

Table 4. Pharmacological properties of marjoram in detail

harmacological Activity	Plant part / Extract	Method	Result	Active Constituent
Antioxidant 141)	Ethanol, n-hexane, supercritical CO2 and water extract of herb	DPPH method and chemiluminometric method	Antioxidant activities of all extracts	Ursolic acid, carnosic acid, carnosol
Antioxidant 142)	Essential oil	DPPH reduction test	Low antioxidant activity with EC50 values >250μg/mL	—
Antioxidant 143)	Essential oil	(1) DPPH assay (2) Percent inhibition in linoleic acid system (3) Bleaching of β-carotene	1)IC50 of 89.2 µg/ml 2) 72.8% inhibition of linoleic acid oxidation 3)showed slow rate of color depletion	—
Antioxidant 144)	Ethyl acetate extract and isolated compounds	DPPH	Significant antioxidant activities from extract and isolated compounds with IC50 of 2.77 and 1.92 µg/mL, respectively	Hydroquinone
Antioxidant 145)	Essential oil / Water extract	ABTS + reducing power were examined for their effect against lipid oxidation in comparison to a tea water extract by measurement of the oil stability index	Remarkable capacity in retarding lipid oxidation with oil stability index 13.9 hours	Bound forms of phenolic compounds such as hydroxycinnamic acid and flavonoids
Antioxidant 146)	Hydroalcoholic extract	ABTS + radical decolorization and DPPH assay	Significant antioxidant capacity with 0.84 and 0.33 mmol TE/g DW, respectively	Polyphenolic compounds
Antioxidant 147)	Essential oil	Glutathione level and lipid peroxidation content as malondialdehyde in the testis, liver and brain in ethanol treatment male albino rat (ethanol induced reproductive disturbances and oxidative damage in different organs and lipid peroxidation due to the formation of free radicals)	Co-administration of the extract resulted in minimizing the hazard effects of ethanol toxicity on male fertility, liver and brain tissues	—
Antioxidant 148)	Essential oil	DPPH, .OH, H2O2, reducing power and lipid peroxidation	IC50 values of 58.67, 67.11, 91.25, 78.67, and 68.75 µg/mL, respectively	—
Antioxidant 149)	Water extract	DPPH	High antioxidant capacity	Phenolic compounds
Antioxidant 150)	Isolated metabolite	Amyloid β–induced oxidative injury in PC12 nerve cells by MTT, LDH, and trypan blue assays	↓ Amyloid β–induced neurotoxic effect	Ursolic acid
Antioxidant 151)	Plant extract	DPPH and ferric ion reducing antioxidant power assays	A direct, positive, and linear relationship between antioxidant activity and total phenolic content of extract	Rosmarinic acid
Antimicrobial 152)	Dried whole plant/oil/leaves aqueous extract	MIC	Better antimicrobial activity of essential oil rather than water extract; inhibition of yeast and lactic acid bacteria by essential oil at a concentration of 5 ppm	—
Antimicrobial 153)	Essential oil	ND	The most susceptible organisms were Beneckea natriegens, Erwinia carotovora, and Moraxella sp. and Aspergillus niger	—
Antimicrobial 154)	n-Hexane extract, aqueous ethanol, ethanolic ammonia extract	Disk-diffusion method for bacteria and serial dilution method for protozoa	n-Hexane extract showed the highest antibacterial activity and the ethanolic ammonia extract reduced the number of viable Pentatrichomonas hominis trophozoites by 50% at 160 µg/ml	—
Antimicrobial 155)	Methanol extract	Filter paper disk diffusion method	Considerable activity against Aspergillus niger, Fusarium solani, and Bacillus subtilis with zone of inhibition 40, 28 and 42 mm, respectively	—
Antimicrobial 156)	Essential oil	(1) Disk diffusion (2) Resazurin microtitre-plate	(1) Large zone of inhibition (16.5-27.0 mm) (2) Small MIC against Staphylococcus aureus, Bacillus cereus, B subtilis, Pseudomonas aeruginosa, Salmonella poona, Escherichia coli (40.9-1250.3 μg/mL)	—
Antimicrobial 157)	Essential oil	Agar diffusion method	Active against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Klebsiella pneumoniae with inhibition zone of 16, 12, 15, and 13 mm, respectively	cis-Sabinene hydrate
Antimicrobial 158)	Essential oil	Microdilution	Inhibitory activity against Staphylococcus aureus and Streptococcus pyogenes with MICs of 125 and 250 μg/mL, respectively	—
Antimicrobial 159)	Essential oil	Diffusion assay	Growth inhibitory activity against dermatophytes	—
Antimicrobial 160)	Methanol extract of leaves	Zone of inhibition	Inhibitory activity against Escherichia coli with 16 mm diameter zone of inhibition	—
Anti-inflammatory 161)	Essential oil	THP-1 human macrophage cells activated by LPS or human ox-LDL, and the cytokine secretion and gene expression, in vitro	Suppression of production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10) and COX-2 and NFκB gene expression	Sabinene hydrate, terpineol
Anticancer 162)	Essential oil	MTT assay	Cytotoxic effect against different cancer cell type, such as MCF-7, LNCaP, NIH-3T3 with IC50 s of 70.0, 85.3, 300.5 µg/ml respectively	—
Anticancer 163)	Ethanol, methanol and water extract	MTT assay, trypan blue dye exclusion, AO/EB staining and fluorescence microscopical analysis and DNA fragmentation analysis	Significant cytotoxic activity of ethanolic extract on fibrosarcoma cancer cell line HT-1080 and least toxicity on normal human lymphocytes	—
Anticancer  164)	Plant extract	Nonradioactive cytotoxicity assay on human lymphoblastic leukemia cell line Jurkat	↓ Viability of cells with increase of concentration of plant extract. Induction of apoptosis through upregulation of p53 protein levels and downregulation of Bcl-2α. Strong radical scavenging activity	—
Anticancer 165)	Ethanol extract	(1) Matrigel invasion assays (2) Gelatin zymography assay (3) Chick embryo tumor growth assay	(1) Significant inhibition of migration and invasion of the MDA-MB-231 cells. Induction of homotypic aggregation of cells associated with an up regulation of E-cadherin protein and decrease the adhesion of cells to HUVECs and inhibition of transendothelial migration of cells through TNF-α-activated HUVECs (2) Suppression of activities of MMP-2 and MMP-9 (3) Inhibition of tumor growth and metastasis	—
Anticancer 166)	Ethyl acetate extract and isolated compounds	BrdU cell proliferation enzyme-linked immunosorbent assay and xCELLigence assay against C6 and HeLa cell lines	Strong antiproliferative activities against C6 and HeLa cells	Hesperetin, Hydroquinone
Antiplatelet 167)	Methanol extract of leaves	Adhesion, aggregation and protein secretion of the activated platelet to laminin-coated plates	40% inhibition of platelet adhesion to laminin-coated wells by ethanol extract at concentration of 200 µg/mL	—
Antiplatelet 168)	Methanol extract	Platelet aggregation induced by collagen; ADP, arachidonic acid and thrombin	Strong inhibition of platelet aggregation induced by ADP, arachidonic acid and thrombin	Arbutin
Antiulcer 169)	Ethanol extract	Hypothermic restraint stress-, indomethacin-, and necrotizing agents–induced ulcers and pylorus ligated Shay rat-model	↓ Incidence of ulcers, basal gastric secretion and acid output. replenishment of the depleted gastric wall mucus and nonprotein sulfhydryls contents and ↓ malondialdehyde	—
Gastric secretory activity 170)	Plant extract	Acid and pepsin secretions in normal Wistar rats	↑ Basal acid and pepsin secretions	—
Cardioprotective activity 171)	Leaves powder and aqueous extract	Isoproterenol-induced myocardial infarction in rats	Alleviation of erythrocytosis, granulocytosis, thrombocytosis, ↓ clotting time, ↑ relative heart weight, ↓ myocardial oxidative stress and the leakage of heart enzymes. inhibition of NO production and lipid peroxidation in heart tissues	—
Hepatoprotective activity 172)	Essential oil	Pralletrin-induced oxidative stress in rats (prallethrin caused a significant decrease in the activity of SOD, CAT, and GST in liver of rats)	Depletion of serum marker enzymes and replenishment of antioxidative status	—
Antiacetylcholinesterase activities 173)	Essential oil	ND	IC50 value was 36.40 µg/mL	—
Anticholinesterase activity 174)	Ethanol extract	In vitro	The Ki value was 6 pM, and IC50 value was 7.5 nM	Ursolic acid
Hormonal activity and regulation of menstrual cycle 175)	Water extract	25 patients were received marjoram tea or a placebo tea twice daily for 1 month. Hormonal and metabolic parameters measured, including FSH, LH, progesterone, oestradiol, total testosterone, DHEA-S, fasting insulin and glucose	↓ DHEA-S and fasting insulin levels	—

Abbreviations: ABTS: 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid); ADP, adenosine diphosphate; CAT, catalase; COX, cyclooxygenase; DHEA-S, dehydroepiandrosterone-sulfate; DPPH, 1,1-diphenyl-2-picryl-hydrazyl; DW, dry weight; EC, effective concentration; FSH, follicle-stimulating hormone; GSH, glutathione S-transferase; IC, inhibitory concentration; IL, interleukin; LDH, lactate dehydrogenase; LH, luteinizing hormone; MIC, minimum inhibitory concentration; MMP, matrix metalloproteinase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; ND, not determined; NO, nitric oxide; PCOS, polycystic ovary syndrome; SOD, superoxide dismutase; TE, trolox equivalent; TNF, tumor necrosis factor.

[Source ¹⁷⁶⁾]

Antimicrobial Activity

Dried whole marjoram plant and its essential oil and water extract of leaves have demonstrated antimicrobial effect and essential oil was more active against lactic acid bacteria and yeasts than water extract ¹⁷⁷⁾. Essential oil showed inhibitory activity against various pathogenic bacteria and fungi, including Beneckea natriegens, Erwinia carotovera, Moraxella, Aspergillus, Staphylococcus aureus, Streptococcus pyogenes, Bacillus cereus, B subtilis, Pseudomonas aeruginosa, Salmonella poona, Escherichia coli, and dermatophytes ¹⁷⁸⁾. Methanol extract of sweet marjoram exhibited antimicrobial activity against E, Aspergillus niger, Fusarium solani, and Bacillus subtilis ¹⁷⁹⁾. The ethanolic ammonia extract reduced the number of viable Pentatrichomonas hominis trophozoites ¹⁸⁰⁾. cis-Sabinene hydrate in essential oil of sweet marjoram have been claimed to be responsible for antibacterial effect ¹⁸¹⁾.

Anti-inflammatory Activity

Sabinene hydrate and terpineol in essential oil of sweet marjoram suppressed the production of Tumor necrosis factor-α (TNFα), interleukin 1β (IL-1β), IL-6, and IL-10 inhibited cyclooxygenase 2 (COX2) and NFκB gene expression ¹⁸²⁾.

Anti-cancer properties of marjoram

Several factors are involved in the onset of cancer such as age, alcohol, cancer-causing substances, diet, hormones, obesity, radiation, tobacco, etc.; and they may play a direct or indirect role in the development and progressions of different types of cancers. The National Cancer Institute ¹⁸³⁾ states that in test tube and in animal studies have shown that the increased presence of antioxidants prevents free radical damage that has been associated with cancer development. Plant foods are the most significance source of natural antioxidants; from which, flavonoids and phenolic acids have attracted the most attention as potential therapeutic agents against cancer. Shukla and Gupta ¹⁸⁴⁾ summarized that the potential anticancer properties of flavonoid and phenolic acid as demonstrated by laboratory studies are due to different mechanisms of action, including antioxidation, induction of detoxification enzymes and inhibition of bioactivation enzymes, estrogenic and anti-estrogenic activity, antiproliferation, cell cycle arrest and apoptosis, promotion of differentiation, regulation of host immune function and inhibition of angiogenesis and metastasis. 5,6,3′-Trihydroxy-7,8,4′-trimethoxyflavone, hesperetin, hydroquinone, arbutin and rosmarinic acid were isolated from the water-soluble ethyl acetate extract of aerial parts of marjoram ¹⁸⁵⁾. Hesperetin isolated from Origanum majorana has shown better antiproliferative activity than 5-fluoroacil against Rattus norvegicus brain glioma (C6) and and cervical epithelial carcinoma (HeLa) cell proliferation ¹⁸⁶⁾. Ethanol extract of plant have shown significant cytotoxicity against fibrosarcoma cancer cell line, promoting cell cycle arrest and apoptosis of the metastatic breast cell and inhibited the migration and invasion of the MDA-MB-231 cells ¹⁸⁷⁾. Hesperetin and hydroquinone isolated from sweet marjoram extract have revealed strong antiproliferative activity ¹⁸⁸⁾. The results showed that the marjoram extract and isolated compounds exhibited significant antioxidant activities. Hence marjoram plant has the potential to be a natural antioxidant in the food industry and an anticancer drug ¹⁸⁹⁾.

Antiplatelet Activity

Methanol extract of sweet marjoram leaves inhibit adhesion of platelet to laminin-coated plate ¹⁹⁰⁾ and strongly inhibited platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid, and thrombin. Arbutin is responsible for this activity ¹⁹¹⁾.

Antiulcerogenetic Effect

Ethanol extract of sweet marjoram significantly decreased the incidence of ulcers, basal gastric secretion, and acid output and replenished the depleted gastric wall mucus ¹⁹²⁾.

Cardioprotective and Hepatoprotective Activity

Leave powder and extract significantly alleviated erythrocytosis, granulocytosis, thrombocytosis, increase heart weight, and myocardial infarction oxidative stress in isoproterenol treated albino rats ¹⁹³⁾. Essential oil of sweet marjoram depleted serum marker enzymes and replenished antioxidant status in hepatic of rat ¹⁹⁴⁾.

Anticholinesterase inhibitory activity

Essential oil and ethanol extract of sweet marjoram have exhibited acetylcholinesterase (AChE) inhibitor activity ¹⁹⁵⁾. Ursolic acid (3 beta-Hydroxyurs-12-en-28-oic acid) is responsible for this effect ¹⁹⁶⁾. Acetylcholinesterase (AChE) inhibitors, which enhance cholinergic transmission by reducing the enzymatic degradation of acetylcholine, are the only source of compound currently approved for the treatment of Alzheimer’s Disease ¹⁹⁷⁾. This study ¹⁹⁸⁾ demonstrated that the ursolic acid of marjoram appeared to be a potent acetylcholinesterase (AChE) inhibitor in Alzheimer’s Disease.

Regulation of menstrual cycle

Sweet marjoram tea significantly reduced dehydroepiandrosterone-sulphate (DHEA-S) and was useful in treatment of polycystic ovary syndrome ¹⁹⁹⁾. Twenty-five patients were assigned to receive marjoram tea or a placebo tea twice daily for 1 month (intervention group: n = 14; placebo group: n = 11) ²⁰⁰⁾. The hormonal and metabolic parameters measured at baseline, as well as after the intervention, were: follicle-stimulating hormone, luteinising hormone, progesterone, oestradiol, total testosterone, dehydroepiandrosterone-sulphate (DHEA-S), fasting insulin and glucose, homeostasis model assessment for insulin resistance and glucose to insulin ratio. Marjoram tea significantly reduced dehydroepiandrosterone-sulphate (DHEA-S) and fasting insulin levels by a mean of 1.4 (0.5) μmol/L and 1.9 (0.8) μU/mL, respectively. In comparison to the placebo group, the change was only significant for DHEA-S but not for insulin. Homeostasis model assessment for insulin resistance was not reduced significantly in the intervention group, although the change was significant compared to the placebo group. The results obtained in the that study show the beneficial effects of marjoram tea on the hormonal profile of polycystic ovary syndrome (PCOS) women because it was found to improve insulin sensitivity and reduce the levels of adrenal androgens. Further research is needed to confirm these results and to investigate the active components and mechanisms contributing to such potential beneficial effects of marjoram herb.

Marjoram essential oil

Monoterpene hydrocarbons, including α and β-pinene, camphene, sabinene, α- and β- phellandrene, ρ-cymene, limonene, β-ocimene, γ-terpinene, terpinolene, α-terpinene, carvone, and citronellol have been detected in marjoram essential oil ²⁰¹⁾. Terpinene 4-ol and cis-sabinene hydrate are 2 main oxygenated monoterpenes isolated from marjoram ²⁰²⁾. Linalool, linalyl acetate, α-terpineol, trans- and cis-carveol, thymol, anethole, geraniol, and carvacrol are other oxygenated compounds identified in essential oil ²⁰³⁾ and leaves of marjorama ²⁰⁴⁾.

The analysis of the chemical composition of marjoram essential oil samples obtained from different geographical locations indicates that the biological activity is directly related to the concentration of the marjoram essential oil components, which may vary according to the region ²⁰⁵⁾, ²⁰⁶⁾. Moreover, season, climate, stage of plant development at harvest, and the technique of extraction of the product may influence the quantity of the plant compounds ²⁰⁷⁾.

Fifteen compounds were identified in the marjoram essential oil (Table 5). The most abundant compounds were γ-terpinene (25.73%), α-terpinene (17.35%), terpinen-4-ol (17.24%), and sabinene (10.8%). This chemical profile is in accordance with what is reported in the literature, with some quantitative variations. Rodrigues et al. ²⁰⁸⁾ and Vági et al. ²⁰⁹⁾ also reported the presence of terpenes as the major components of the marjoram essential oil. Usually, terpinen-4-ol and γ-terpinene are described as the most abundant compounds in marjoram essential oil and sabinene and α-terpinene are also observed ²¹⁰⁾.

Table 5. Chemical composition of Marjoram essential oil

[Source ²¹¹⁾]

Marjoram essential oil uses

Marjoram essential oil have shown significant results in inhibiting the growth of bacteria and fungi and the synthesis of microbial metabolites ²¹²⁾. Because of its antioxidant effects ²¹³⁾, marjoram essential oil or marjoram extract can be used in the prevention of central nervous system disorders ²¹⁴⁾. Marjoram essential oil was also able to partially prevent the ethanol-induced decline in sperm quality, testosterone levels, and the weight of reproductive organs in male rats ²¹⁵⁾. Previous studies have reported the potential use of marjoram ethanolic extract as anticancer agent ²¹⁶⁾, whereas the marjoram tea extract has been shown to have immunostimulant, antigenotoxic and antimutagenic properties ²¹⁷⁾. These activities are attributed to the chemical composition, which is characterized as rich in flavonoids and terpenoids – see Tables 2, 3 and 4 above ²¹⁸⁾.

Marjoram Toxicity

Acute toxicity test has demonstrated a large margin of safety of marjoram extract in mice. Emmenagogue (a substance that stimulates or increases menstrual blood flow) properties of sweet marjoram should be of concerned during pregnancy. Marjoram essential oil must not be used by lactating and pregnant women ²¹⁹⁾.

Summary

Sweet marjoram is a medicinal plant with various proven pharmacological properties, including antioxidant, antibacterial, hepatoprotective, cardioprotective, antiulcer, anticoagulant, anti-inflammatory, antiproliferative, and antifungal activities. The flowering stems are the medicinal parts. Their constituents include 1% to 2% of an essential oil with a containing terpinenes and terpinols, plus tannins, bitter compounds, carotenes, and vitamin C. These substances give sweet marjoram stomachic, carminative, antispasmodic, and weak sedative properties. Monoterpene hydrocarbons (such as α-pinene, β-pinene, camphene, and γ-terpinene), oxygenated monoterpenes particularly terpinene-4-ol, cis-sabinene hydrate and terpineol, phenolic compounds particularly flavonoids (such as apigenin, hesperetin, quercetin, kaempferol), and phenolic glycosides (such as arbutin) are the active components isolated and detected in marjoram. Figure 3 shows the structure of some main active compounds. Various bioactive compounds have been isolated and identified in O majorana, whereas many active compounds for the traditional medicine uses have not been completely evaluated in clinical trials.

Due to marjoram’s emmenagogue properties, marjoram essential oil must not be used by lactating and pregnant women ²²⁰⁾.