What is fennel

Fennel (Foeniculum vulgare belonging to the Umbelliferae [Apiaceae] family) is an ancient seasonal herb that is widely cultivated and also grows wild, for its edible, strongly flavored leaves and fruits ¹⁾. The fennel plant originated in the southern Mediterranean region and through naturalization and cultivation it grows wild throughout the Northern, Eastern, and Western hemispheres, specifically in Asia, North America, and Europe ²⁾. The fennel herb was well-known to the ancient Egyptians, Romans, Indians, and Chinese. The Romans grew it for its aromatic seeds and the edible fleshy shoots are still a very common vegetable in southern Italy ³⁾. Emperor Charlemagne was known to have encouraged its cultivation in Central Europe. It is an indispensable ingredient in modern French and Italian cooking. All parts of the fennel plant are aromatic and can be used in many ways. As a typical, seasonal fresh fruit, fennels are an important constituent of the regional diet of Europe and other regions. Different varieties of fennel parts are widely used in many of the cooking dishes all over world (Table 1). Fennel shoots, tender leaves, and stems are chewed and sucked due to their exquisite aniseed flavor. All these parts are also commonly used as vegetables. They are added raw to salads, stewed with beans and chickpeas, used to stuff fish for grilling, and placed in soups and bread bouillons. Besides seasoning, fennel is used to preserve food. Flowering stems, sugar, and honey macerating in brandy produce a highly valorized spirit. Herbal teas prepared with fresh tender or dried flowering stems are consumed chilled or hot, depending on the season. F. vulgare is famous for its essential oil. The characteristic anise odour of F. vulgare, which is due to its essential oil, makes it an excellent flavoring agent in baked goods, meat and fish dishes, ice-cream, and alcoholic beverages. The culinary uses of fennel are so diverse/widespread that it has been exported from country to country for centuries ⁴⁾.

Table 1. Uses of fennel as a food ingredient as reported in the literature

Number	Region/Nation	Local name	Part used and edible application.	References
1	Campania, Italy	Finucchio, finucchiello, finochietto	Stem is used as an aromatizer for pickled olives.	5)
2	Campania, Italy	Finocchiella, fenùcciu	Seed is employed in preparation of salted meats.	6)
3	Spain	Hinojo, Fenoll	Tender leaves and stems, raw as a snack, are used in salads or stewed.	7)
4	Spain	Fiallo, millau	Aerial part or seeds used for seasoning olives, as preservative for dry figs, and for preparing herbal tea or liqueur.	8)
5	Trás-os-Montes (Northeast Portuguese)	Fialho, fionho, erva-doce	Shoots, tender leaves, and stems used in snacks, salads, soups, stews, and spices. Flowering stems used in beverages, spirits, and spices. Stems used as brochettes and herbal teas. Seeds used as spices, flavour for cakes, biscuits, and sweets, and chestnuts.	9)
6	Arrábida and Açor (Center Portuguese)	Funcho, erva-doce	Seeds used as flavour for cakes and pastries and for cooking chestnuts.	10)
7	Alentejo and Algarve (South Portuguese)	Funcho, fialho, funcho-doce, funcho-amargo	Shoots, tender leaves, and stems are fried with eggs, used in omelettes, used in fish stuff, stewed with different kinds of beans and chickpeas, and used in fish and bread bouillons, soups, and sauces. Tender leafy stems are used in grilled fish and fish dishes in general. Seeds are used as spices, flavour for cakes, bread, and biscuits, and chestnuts. Whole plant used in olives brines, figs preserves, and for aromatizing brandy.	11)
8	Jammu and Kashmir, India	Saunf	The fruits with other ingredients are given to the animal if it stops taking food during diarrhea.	12)
9	Liguria, Italy	Fenucéttu-sarvègu	Aerial parts of plant mixed with shoots of Clematis and Rubus used as food integrator for sheep.	13)

Fennel is an upright, branching perennial herb (Figure 2 A) with soft, feathery, almost hair-like foliage growing up to 6.6 ft. (2 m) tall. Fennel plant looks similar to dill. It is typically grown in vegetable and herb gardens (Figure 2 F) for its anise-flavored foliage and seeds, both of which are commonly harvested for use in cooking. Fennel plant is erect and cylindrical, bright green, and smooth as to seem polished, with multiple branched leaves (Figure 2 C) cut into the finest of segments. The leaves grow up to 40 cm long; they are finely dissected, with the ultimate segments filiform (threadlike), about 0.5 mm wide. The bright golden flowers, produced in large, flat terminal umbels, with thirteen to twenty rays, bloom in July and August (Figure 2 D). Fennel flowers are small, yellow, and found in large flat-topped umbels (Figure 2 D). Fruits are oblong to ovoid with 0.12–0.2 inches (3–5 mm) long and 1.5–2.0 mm broad (Figure 2 E). The stylopodium persists on the fruit. The fennel fruits are elongated and have strong ribs. The most esteemed fennel seeds vary from three to five lines in length and are elliptical, slightly curved, and somewhat obtuse at the ends (Figure 3). They are greenish-yellow, the color of hay, from which the term fennel is derived. Wild fennel fruits are short, dark colored and blunt at their ends, and have a less agreeable flavor and odor than those of sweet fennel. Fennel seeds ripen from September to October. Fennel plant can reproduce from crown or root fragments but freely reproduces from fennel seed.

Fennel is a traditional and popular herb with a long history of use as a medicine. Fennel has been used in traditional medicine for a wide range of ailments related to digestive, endocrine, reproductive, and respiratory systems. Additionally, it is also used as a galactagogue agent for lactating mothers. Fennel maybe consumed daily, in the raw form as salads and snacks, stewed, boiled, grilled, or baked in several dishes and even used in the preparation of herbal teas or spirits. A diet with desired quantity of fennel could bring potential health benefits due to its valuable nutritional composition with respect to presence of essential fatty acids ¹⁴⁾. In recent years, increased interests in improvement of agricultural yield of fennel due to its medicinal properties and essential oil content has encouraged cultivation of the plant on large scale.

Figure 1. Fennel bulb

Figure 2. Fennel plant

Figure 3. Fennel seeds

Fennel nutritional value

Fennel is widely grown for its edible fruit or seeds. These are sweet and dry; a fully ripe specimen is an exquisite fruit. The fruit is often dried for later use and this dried fruit called fennel is a major item of commerce. Table 2 lists the nutrient composition of fennel bulb. Fennels are one of the highest plant sources of potassium, sodium, phosphorus, and calcium. According to United States Department of Agriculture Agricultural Research Service (USDA) data for the Mission variety, fennels are richest in dietary fiber and vitamins, relative to human needs. They have smaller amounts of many other nutrients.

Table 4 summarizes the chemical composition and the nutritional value ¹⁵⁾ of different parts of fennel, namely, shoots, leaves, stems, and inflorescence. Leaves and stems show the highest moisture content (76.36 and 77.46 g/100 g, respectively), while the complete flower head of a plant (inflorescence) exhibits the lowest content (71.31 g/100 g). Carbohydrates are the most abundant macronutrients in all the parts and range from 18.44 to 22.82 g/100 g. Proteins, reducing sugars, and fats are the less abundant macronutrients; proteins varied between 1.08 g/100 g in stems and 1.37 g/100 g in inflorescences. The inflorescences and stems revealed the highest fat content (1.28 g/100 g) and reducing sugar content (1.49 g/100 g), respectively, amongst all the parts of fennel. On the basis of the proximate analysis, it can be calculated that a fresh portion of 100 g of these parts yields, on average, 94 Kcal of energy. The highest values were obtained for inflorescences, while leaves and stems gave the lowest energy contribution.

About twenty-one fatty acids were identified and quantified from the above mentioned parts of fennel (Tables 1 to 3). These are caproic acid, caprylic acid, capric acid, undecanoic acid, lauric acid, myristic acid, myristoleic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, linoleic acid, α-linolenic acid, arachidic acid, eicosanoic acid, cis-11,14-eicosadienoic acid, cis-11,14,17-eicosatrienoic acid + heneicosanoic acid, behenic acid, tricosanoic acid, and lignoceric acid. Thus, Barros and his coworker ¹⁶⁾ conclude polyunsaturated fatty acids (PUFA) to be the main group of fatty acids present in all the fennel parts. On the other hand Vardavas and his coworker ¹⁷⁾ reported monounsaturated fatty acids (MUFA) as the main group of fatty acids in fennel. Nevertheless, unsaturated fatty acids range from 66% to 80% and predominate over saturated fatty acids ¹⁸⁾. The highest concentration of omega-3 fatty acids was found in fennel leaves, while the lowest concentration was found in inflorescences. The ratio of ω6 (omega 6 fatty acid) to ω3 omega-3 fatty acids has an important role in the human diet. The highest levels of omega-3 fatty acids found in leaves contributed to its lowest ratio of ω6 to ω3 fatty acids. The lowest levels of omega-3 fatty acids found in inflorescences contributed to its highest ratio of ω6 to ω3 fatty acids.

Fennels have smaller amounts of many other nutrients. On a weight basis, fennels contain more calcium (49 mg/100 g) as compared with apples (7.14 mg/100 g), bananas (3.88 mg/100 g), dates (25.0 mg/100 g), grapes (10.86 mg/100 g), orange (40.25 mg/100 g), prunes (18.0 mg/100 g), raisins (40.0 mg/100 g), and strawberries (14.01 mg/100 g). Phenolics are an important constituent of fruit quality because of their contribution to the taste, color, and nutritional properties of fruit. Amongst the phenolics analyzed in the fennel fruit of fennel plant are neochlorogenic acid (1.40%), chlorogenic acid (2.98%), gallic acid (0.169%), chlorogenic acid (6.873%), caffeic acid (2.960%), p-coumaric acid (4.325%), ferulic acid-7-o-glucoside (5.223%), quercetin-7-o-glucoside (3.219%), ferulic acid (3.555%), 1,5 dicaffeoylquinic acid (4.095%), hesperidin (0.203%), cinnamic acid (0.131%), rosmarinic acid (14.998%), quercetin (17.097%), and apigenin (12.558%) ¹⁹⁾.

Table 2. Fennel bulb (raw) nutrition facts

Nutrient	Unit	Value per 100 g	bulb 234 g
Approximates
Water	g	90.21	211.09
Energy	kcal	31	73
Energy	kJ	129	302
Protein	g	1.24	2.9
Total lipid (fat)	g	0.2	0.47
Ash	g	1.05	2.46
Carbohydrate, by difference	g	7.3	17.08
Fiber, total dietary	g	3.1	7.3
Sugars, total	g	3.93	9.2
Minerals
Calcium, Ca	mg	49	115
Iron, Fe	mg	0.73	1.71
Magnesium, Mg	mg	17	40
Phosphorus, P	mg	50	117
Potassium, K	mg	414	969
Sodium, Na	mg	52	122
Zinc, Zn	mg	0.2	0.47
Copper, Cu	mg	0.066	0.154
Manganese, Mn	mg	0.191	0.447
Selenium, Se	µg	0.7	1.6
Vitamins
Vitamin C, total ascorbic acid	mg	12	28.1
Thiamin	mg	0.01	0.023
Riboflavin	mg	0.032	0.075
Niacin	mg	0.64	1.498
Pantothenic acid	mg	0.232	0.543
Vitamin B-6	mg	0.047	0.11
Folate, total	µg	27	63
Folic acid	µg	0	0
Folate, food	µg	27	63
Folate, DFE	µg	27	63
Choline, total	mg	13.2	30.9
Vitamin B-12	µg	0	0
Vitamin B-12, added	µg	0	0
Vitamin A, RAE	µg	48	112
Retinol	µg	0	0
Carotene, beta	µg	578	1353
Carotene, alpha	µg	0	0
Cryptoxanthin, beta	µg	0	0
Vitamin A, IU	IU	963	2253
Lycopene	µg	0	0
Lutein + zeaxanthin	µg	607	1420
Vitamin E (alpha-tocopherol)	mg	0.58	1.36
Vitamin E, added	mg	0	0
Vitamin D (D2 + D3)	µg	0	0
Vitamin D	IU	0	0
Vitamin K (phylloquinone)	µg	62.8	147
Lipids
Fatty acids, total saturated	g	0.09	0.211
04:00:00	g	0	0
06:00:00	g	0	0
08:00:00	g	0	0
10:00:00	g	0	0
12:00:00	g	0	0
14:00:00	g	0.002	0.005
16:00:00	g	0.079	0.185
18:00:00	g	0.009	0.021
Fatty acids, total monounsaturated	g	0.068	0.159
16:1 undifferentiated	g	0.002	0.005
18:1 undifferentiated	g	0.065	0.152
20:01:00	g	0	0
22:1 undifferentiated	g	0	0
Fatty acids, total polyunsaturated	g	0.169	0.395
18:2 undifferentiated	g	0.169	0.395
18:3 undifferentiated	g	0	0
18:04:00	g	0	0
20:4 undifferentiated	g	0	0
20:5 n-3 (EPA)	g	0	0
22:5 n-3 (DPA)	g	0	0
22:6 n-3 (DHA)	g	0	0
Fatty acids, total trans	g	0	0
Cholesterol	mg	0	0
Other
Alcohol, ethyl	g	0	0
Caffeine	mg	0	0
Theobromine	mg	0	0
Flavanones
Eriodictyol	mg	1.1	2.5
Flavonols
Quercetin	mg	0.2	0.5
Isoflavones
Daidzein	mg	0	0
Genistein	mg	0	0
Total isoflavones	mg	0	0

[Source: United States Department of Agriculture Agricultural Research Service ²⁰⁾]

Table 3. Fennel seeds nutrition facts

Nutrient	Unit	Value per 100 g	tsp, whole 2 g
Approximates
Water	g	8.81	0.18
Energy	kcal	345	7
Energy	kJ	1443	29
Protein	g	15.8	0.32
Total lipid (fat)	g	14.87	0.3
Ash	g	8.22	0.16
Carbohydrate, by difference	g	52.29	1.05
Fiber, total dietary	g	39.8	0.8
Minerals
Calcium, Ca	mg	1196	24
Iron, Fe	mg	18.54	0.37
Magnesium, Mg	mg	385	8
Phosphorus, P	mg	487	10
Potassium, K	mg	1694	34
Sodium, Na	mg	88	2
Zinc, Zn	mg	3.7	0.07
Copper, Cu	mg	1.067	0.021
Manganese, Mn	mg	6.533	0.131
Vitamins
Vitamin C, total ascorbic acid	mg	21	0.4
Thiamin	mg	0.408	0.008
Riboflavin	mg	0.353	0.007
Niacin	mg	6.05	0.121
Vitamin B-6 1	mg	0.47	0.009
Vitamin B-12	µg	0	0
Vitamin A, RAE	µg	7	0
Retinol	µg	0	0
Vitamin A, IU	IU	135	3
Vitamin D (D2 + D3)	µg	0	0
Vitamin D	IU	0	0
Lipids
Fatty acids, total saturated	g	0.48	0.01
16:00:00	g	0.48	0.01
Fatty acids, total monounsaturated	g	9.91	0.198
18:1 undifferentiated	g	9.91	0.198
Fatty acids, total polyunsaturated	g	1.69	0.034
18:2 undifferentiated	g	1.69	0.034
Cholesterol	mg	0	0
Phytosterols	mg	66	1
Amino Acids
Tryptophan	g	0.253	0.005
Threonine	g	0.602	0.012
Isoleucine	g	0.695	0.014
Leucine	g	0.996	0.02
Lysine	g	0.758	0.015
Methionine	g	0.301	0.006
Cystine	g	0.222	0.004
Phenylalanine	g	0.647	0.013
Tyrosine	g	0.41	0.008
Valine	g	0.915	0.018
Arginine	g	0.68	0.014
Histidine	g	0.331	0.007
Alanine	g	0.789	0.016
Aspartic acid	g	1.833	0.037
Glutamic acid	g	2.956	0.059
Glycine	g	1.107	0.022
Proline	g	0.9	0.018
Serine	g	0.9	0.018

[Source: United States Department of Agriculture Agricultural Research Service ²¹⁾]

Table 4. Nutrient content of different parts of fennel plant

Composition	Contents
	Leaves	Inflorescences	Stems	Shoots
Moisturea	76.36 ± 0.33	71.31 ± 4.01	77.46 ± 1.03	73.88 ± 0.83
Asha	3.43 ± 0.04	3.23 ± 0.02	1.62 ± 0.12	2.39 ± 0.02
Fata	0.61 ± 0.16	1.28 ± 0.28	0.45 ± 0.07	0.49 ± 0.05
Proteina	1.16 ± 0.03	1.37 ± 0.05	1.08 ± 0.00	1.33 ± 0.04
Carbohydratesa	18.44 ± 0.06	22.82 ± 3.06	19.39 ± 0.65	21.91 ± 0.55
Fructosea	0.49 ± 0.05	1.10 ± 0.04	1.49 ± 0.04	1.51 ± 0.06
Glucosea	0.76 ± 0.12	2.94 ± 0.11	3.43 ± 0.20	4.71 ± 0.15
Sucrosea	0.04 ± 0.00	0.03 ± 0.00	nd	0.35 ± 0.06
Reducing sugarsa	0.72 ± 0.04	1.20 ± 0.19	1.49 ± 0.29	1.14 ± 0.10
ω3 fatty acidb	43.72 ± 0.36	17.69 ± 0.01	23.04 ± 1.30	36.96 ± 0.51
ω6 fatty acidb	23.25 ± 0.07	38.94 ± 0.23	38.22 ± 0.68	39.99 ± 0.68
ω6/ω3	0.53 ± 0.00	2.20 ± 0.01	1.66 ± 1.12	1.08 ± 0.03
C6:0b	0.02 ± 0.00	0.41 ± 0.02	0.19 ± 0.01	0.06 ± 0.00
C8:0b	0.08 ± 0.00	0.37 ± 0.01	0.48 ± 0.03	0.33 ± 0.00
C10:0b	0.04 ± 0.00	0.09 ± 0.00	0.13 ± 0.01	0.06 ± 0.00
C11:0b	0.25 ± 0.02	0.29 ± 0.01	0.04 ± 0.00	0.07 ± 0.00
C12:0b	0.31 ± 0.02	0.43 ± 0.06	0.11 ± 0.01	0.21 ± 0.02
C14:0b	1.43 ± 0.01	1.68 ± 0.10	0.49 ± 0.06	0.75 ± 0.03
C14:1b	0.61 ± 0.04	0.28 ± 0.02	0.37 ± 0.04	0.17 ± 0.03
C15:0b	0.17 ± 0.00	0.35 ± 0.03	0.41 ± 0.04	0.18 ± 0.00
C16:0b	20.15 ± 0.09	23.89 ± 0.07	25.43 ± 0.00	12.78 ± 0.09
C17:0b	0.74 ± 0.00	0.58 ± 0.02	0.61 ± 0.04	0.24 ± 0.02
C18:0b	1.61 ± 0.08	2.62 ± 0.04	1.99 ± 0.06	1.53 ± 0.08
C18:1n9cb	4.35 ± 0.37	5.05 ± 0.00	4.35 ± 0.52	2.55 ± 0.33
C18:2n6cb	23.25 ± 0.07	38.94 ± 0.23	38.22 ± 0.68	39.99 ± 0.68
C18:3n3b	43.55 ± 0.40	17.55 ± 0.0	22.86 ± 1.31	36.84 ± 0.52
C20:0b	0.56 ± 0.00	1.78 ± 0.06	0.84 ± 0.03	1.06 ± 0.09
C20:1cb	nd	0.26 ± 0.03	0.06 ± 0.00	nd
C20:2cb	0.08 ± 0.01	0.31 ± 0.01	0.14 ± 0.00	0.38 ± 0.07
C20:3n3 + C21:0b	0.16 ± 0.02	0.15 ± 0.01	0.19 ± 0.00	0.12 ± 0.01
C22:0b	0.77 ± 0.04	1.52 ± 0.04	1.20 ± 0.03	1.12 ± 0.02
C23:0b	0.82 ± 0.13	1.89 ± 0.11	0.68 ± 0.01	0.36 ± 0.15
C24:0b	1.03 ± 0.04	1.58 ± 0.02	1.21 ± 0.02	1.20 ± 0.08
Total SFAb	27.99 ± 0.02	37.47 ± 0.25	33.81 ± 0.06	19.95 ± 0.12
Total MUFAb	4.96 ± 0.40	5.59 ± 0.13	4.78 ± 0.57	2.72 ± 0.36
Total PUFAb	67.05 ± 0.42	56.94 ± 0.12	61.41 ± 0.62	77.33 ± 0.24
Energyc	83.90 ± 1.34	108.23 ± 10.37	85.91 ± 3.02	97.37 ± 2.44

Note: ^a Nutrients composition (g/100 g), ^b ω3 (omega 3 fatty acid) and ω6 (omega 6 fatty acid) and fatty acid content (percent), and ^c energetic value (Kcal/100 g) of the different parts of fennel. nd: not detected. Values are expressed as mean ± SD, n = 3 experiments in each group

[Source ²²⁾]

Fennel uses

Fennel has been extensively used in traditional medicine for a wide range of ailments. Fennel is used in various traditional systems of medicine like in the Ayurveda, Unani, Siddha, in the Indian, and Iranian traditional systems of alternative and balancing medicine ²³⁾. Fennel stem, fruit, leaves, seeds, and whole plant itself are medicinally used in different forms in the treatment of a variety of diseased conditions. The preparation methods, uses, and application of fennel are well documented in the common ethnobotanical literature ²⁴⁾. Table 5 lists the ethnomedicinal uses of fennel for 43 different types of ailments in Bolivia, Brazil, Ecuador, Ethiopia, India, Iran, Italy, Jordan, Mexico, Pakistan, Portugal, Serbia, South Africa, Spain, Turkey, and USA ²⁵⁾. It is used to treat simple ailments (e.g., cough/cold, cuts) to very complicated ailments (e.g., kidney ailments, cancer). It also has a wide range of veterinary uses ²⁶⁾. Fennel is used in many parts of the world for the treatment of a number of diseases, for example, abdominal pains, antiemetic, aperitif, arthritis, cancer, colic in children, conjunctivitis, constipation, depurative, diarrhea, dieresis, emmenagogue, fever, flatulence, gastralgia, gastritis, insomnia, irritable colon, kidney ailments, laxative, leucorrhoea, liver pain, mouth ulcer, and stomachache (Table 5).

In addition to its medicinal uses, aerial parts, namely, leaf, stem, and fruit/seed of fennel, are extensively used as galactagogues not only for increasing the quantity and quality of milk but also for improving the milk flow of breastfeeding mothers ²⁷⁾. From ancient times, fennel seeds have been used as an ingredient for removing any foul smell of the mouth ²⁸⁾. The natural light green dye obtained from leaves is used in cosmetics, for coloring of textiles/wooden materials and as food colorant. Yellow and brown color dyes are obtained by combining the flowers and leaves of fennel ²⁹⁾. In Portugal, Italy, Spain, and India, the stem, fruit, leaves, seeds, and whole plant are used as a vegetable. Sugar coated and uncoated fennel seeds are used in mukhwas (Mouth freshener) ³⁰⁾. In many parts of India and Pakistan, roasted fennel seeds are consumed as mukhwas (Mouth freshener). Mukhwas is a colorful after-meal mouth freshener or digestive aid. It can be made of various seeds and nuts but often found with fennel seeds, anise seeds, coconut, and sesame seeds. They are sweet in flavor and highly aromatic due to the presence of sugar and the addition of various essential oils. Fennel seeds can be savory, coated in sugar, and brightly colored.

Table 5. Traditional and contemporary uses of fennel

Number	Ailment/use	Part/preparation used	Locality	References
1	Mouth ulcer	Tender leaves, chewed and stuck on ulcer	Basilicata, Italy	31)
2	Aperitif	Tender parts-raw or boiled	Rome, Italy	32)
3	Gum disorder	Fruit and seed, used as a mouth wash for gum disorder	Central Serbia	33)
4	Insomnia	Infusion of tea leaf	Brazil	34)
5	Constipation	Seeds, decoction	South Europe	35)
		Seeds mixed with sugar	Jammu and Kashmir, India	36)
6	Cancer	Leaf and flower, aqueous infusion, drink	Loja, Ecuador	37)
7	Conjunctivitis	Leaf and flower, aqueous infusion, drink	Loja, Ecuador	38)
8	Gastritis	Leaf, flower, aqueous infusion, drink	Loja, Ecuador	39)
9	Diuresis	Root and seed, decoction	Miami, Florida, USA	40)
10	Abdominal pains	Each plant part, decoction	Rome, Italy	41)
		Leaf and seeds, infusion	Northern Badia, Jordan,	42)
		Leaves, paste	Manisa, Turkey	43)
11	Cold	Fruits and floral tops, decoction	Rome, Italy	44)
12	Refreshing	Roots/whole plant, decoction	Rome, Italy	45)
13	Swollen stomach	Leaves, decoction with a little honey	Rome, Italy	46)
14	Hair grow	Seed oil	Middle Navarra	47)
15	Antiemetic	Fruit, simple powder	Northeastern Majorcan area	48)
16	Antihypertensive and Anti-cholesterolemic	Leaf directly chewed	north-eastern Majorcan area	49)
17	Depurative	Leaf and stem, comestible	Iberian Peninsula, Spain	50)
18	Hypnotic	Seed, leaf, and stem, infusion and edible	North Iran	51)
19	Diarrhoea	Seeds, roots, and fresh leaves	Northern Portugal	52)
		Seeds grounded with Root tubers of Hemidesmus indicus and the paste taken with jaggery twice a day for three days	Bhandara, Maharashtra, India	53)
20	Kidney ailments	Aerial part, infusion	Alto, Bolivia	54)
		Seed, decoction	Gujranwala, Pakistan	55)
21	Colic in children	Leaf and fruit, infusion	Brazil	56)
22	Irritable colon	Leaf and seeds, infusion	Northern Badia, Jordan,	57)
23	Gastralgia	Leaf, decoction	southern Spain	58)
24	Purgative	Seed, infusion and edible	Gujranwala, Pakistan	59)
25	Laxative	Seed, infusion and edible	Gujranwala, Pakistan	60)
26	Liver pain	Seed	Pernambuco, Northeast Brazil	61)
27	Mosquitocidal	Root boiled and drunk as tea	Somali Region, Ethiopia	62)
28	Arthritis	Leaf, an infusion made from the leaves is drunk	South Africa	63)
29	Fever	Leaf, an infusion made from the leaves is drunk	South Africa	64)
30	Fat deduction	Green fruit is chewed to reduce fat	South Africa	65)
31	Leucorrhoea	A mixture of its 100 g seed powder, 200 g seed powder of Papaver somniferum, 100 g fruit powder of Coriander sativum, and 200 g of sugar is prepared and 50 g of this mixture is taken by the tribal ladies early in the morning	Rajasthan, India	66)
32	Problem of repeated abortions	Mixture of its 50 g seed powder, 50 g fruit powder of Trapa natans, and 50 g sugar is given daily to pregnant ladies	Rajasthan, India	67)
33	Digestive system	Fruits, decoction	Basilicata, Italy	68)
		Seed, decoction (drink one tea cup after food)	Balikesir, Turkey	69)
		Whole plant	Western cape of South Africa	70)
		Fruit, powder for digestive ailments	Middle, West, and South Bosnia	71)
		Seeds, decoction	South Europe	72)
		Seeds, roots, and fresh leaves	Northern Portugal.	73)
		Seed, decoction	Southern Spain	74)
34	Carminative	Tender parts, raw or boiled	Rome, Italy	75)
		Whole plant	Western cape of South Africa	76)
		Seeds, decoction	South Europe	77)
		Seed, leaf, and stem, infusion and edible	North Iran	78)
		Leaves and/or fruits	South Africa	79)
35	Diuretic	Tender parts, raw or boiled	Rome, Italy	80)
		Whole plant	Western cape of South Africa	81)
		Seeds, decoction	South-Europe	82)
		Seeds, roots, and fresh leaves	Northern Portugal.	83)
		Leaf, an infusion made from the leaves is drunk	South Africa	84)
36	Emmenagogue	Aerial part, raw with carrot	Rome, Italy	85)
		Fruit, simple powder	North-eastern Majorcan area	86)
		Seed	Haryana, India	87)
37	Milk stimulant in pregnant women (Galactagogue)	Leaf, an infusion made from the leaves is drunk	South Africa	88)
		Fruits, as condiment or chewed	Rome, Italy	89)
		Fruit, simple powder	north-eastern Majorcan area	90)
		Aerial part-infusion	Alto, Bolivia	91)
38	Gingival wound	Fruit-paste	Uttarakhand, India	92)
		Whole plant, decoction	Andalusia, Spain	93)
39	Eye blurry and itching	Aerial parts, inhaled into eyes	Balikesir, Turkey	94)
		Seeds, roots, and leaves	Northern Portugal	95)
		Seed, infusion, edible	Gujranwala, Pakistan	96)
		Leaves and/or fruits	South Africa	97)
40	Cough	Whole plant, oral infusion	Guerrero, Mexico	98)
		Whole plant, decoction	Southern Spain	99)
		Whole plant	Western cape of South Africa	100)
41	Stomachache	Whole plant, oral infusion	Guerrero, Mexico	101)
		Fruit	Middle Navarra	102)
		Seed decoction is used against stomach ache	Liguria, Italy	103)
		Seed, leaf, and stem-infusion, edible	North Iran	104)
42	Stress removal	Apical shoots is used as sedative for children	Liguria, Italy	105)
			Southern Punjab, Pakistan	106)
43	Flatulence	Leaf and fruit, infusion	Brazil	107)
		Leaf and seeds, infusion	Northern Badia, Jordan,	108)
		Fresh fruit, decoction	North Bengal, India	109)

[Source ¹¹⁰⁾]

Fennel phytochemistry

Phytochemical research carried out on fennel has led to the isolation of fatty acids, phenolic components, hydrocarbons, volatile components, and few other classes of secondary metabolites from its different parts (Figure 4). Mostly these phytochemicals are found in essential oil (Table 6). Some of the phytoconstituents of fennel were find application as coloring and antiaging agents ¹¹¹⁾. They also have noteworthy biological and pharmacological activities (Table 7).

Flavonoids are generally considered as an important category of antioxidants in the human diet. Flavonoids are abundant in the plants of Apiaceae family. It has been reported that the presence of flavonol glycosides in fennel species is related to its morphological heterogeneity and variation. Total flavonoid content of hydroalcoholic extracts is about 12.3 ± 0.18 mg/g. Flavonoids like eriodictyol-7-rutinoside, quercetin-3-rutinoside, and rosmarinic acid have been isolated from F. vulgare [65]. Amongst the flavonoids present in fennel, the most prevalent are quercetin-3-glucuronide, isoquercitrin, quercetin-3-arabinoside, kaempferol-3-glucuronide and kaempferol-3-arabinoside, and isorhamnetin glucoside ¹¹²⁾. Quercetin-3-O-galactoside, kaempferol-3-O-rutinoside, and kaempferol-3-O-glucoside have also been reported to occur in the aqueous extract of fennel ¹¹³⁾. The flavonoids like isorhamnetin 3-O-α-rhamnoside, quercetin, and kaempferol were also isolated from the ethyl acetate extract, whereas quercetin 3-O-rutinoside, kaempferol 3-O-rutinoside, and quercetin 3-O-β-glucoside were isolated from the methanol extract. These flavonoids exhibit remarkable antinociceptive and anti-inflammatory activity ¹¹⁴⁾. Further, quercetin, rutin, and isoquercitrin were reported to have the immunomodulatory activities ¹¹⁵⁾.

Figure 4. Fennel phytochemicals

Table 6. Fennel essential oil volatile compounds

Number	Compounds
1	α-Thujene
2	1,8-Cineol
3	β-Ocimene
4	Linalool
5	Germacrene D
6	Anisketone
7	Apiol
8	n-Hexadecanoic acid
9	Cubebene
10	Benzene-1-methyl-4-(1-methylethyl)-p-cymene
11	1,3,6-Octatriene, 3,7-dimethyl-, (E)-3-carene
12	2-Heptene
13	3-Methyl-butanal
14	β-Pinene
15	Camphene
16	Hexanal
17	α-Pinene
18	β-Phellandrene
19	α-Phellanrrene
20	β-Myrcene
21	4-Carene
22	2-Heptanohe
23	Limonene
24	4-Methyl-bicyclo[3.1.0]hex-2-ene
25	Eucalyptol
26	α-Pinene
27	γ-Terpinene
28	7-Dimethyl-1,3,7-octriene
29	2,4-Dimethyl-benzenamine
30	3-Carene
31	Cathine
32	2-Heptanol
33	2-Propyn-1-ol
34	2,6-Dimethyl-2,4,6-octatriene
35	Fenchone
36	1-Methyl-4-(1-methylethyl)-benzene
37	cis-Limonene oxide
38	trans-Limonene oxide
39	6-Methylene-bicyclo[3.1.0]hexane
40	Sabinene hydrate
41	Fenchyl acetate
42	Camphor
43	Benzaldehyde
44	1,3-Butanediol
45	Dicyclopropyl carbinol
46	Fenchol
47	1-Octanol
48	5-Methyl-2-heptanol
49	Tetradecyl-oxirane
50	Estragole
51	Trans–p-2,8-menthadien-1-ol
52	β-Terpinol
53	cis–p-2,8-Menthadien
54	4-Methyl-1-(methylethyl)-3-cyclohexen
55	2-Methyl-5-(1-methylethyl)-2-cyclohexen-1-one
56	Phenylmethyl-formic ester
57	2,3-Cyclohexen-1-methanol
58	Epi-bicyclosesquiphellardrene
59	cis–p-Menth-2,8-dienol
60	1,4-Dimethoxy-benzene
61	1-Methoxy-4-(1-propenyl)-benzene
62	1,2,4a,5,8,8a-Hexadehyde-naphthalene
63	4-Methyl-bicyclo[3.1.1]hept-3-en-2-ol
64	trans-Anethole 73.20 73.27 66.71
65	Allantoic acid
66	2-Methyl-5-(1-methylethyl)-phenol
67	Mannoheptulose
68	2-Methyl-5-(1-methylethyl)-2-cyclohexen-1-ol
69	1-Undecanol
70	Benzothiazole
71	E-Pinane
72	2-Cyclohexen-1-ol
73	2-Methyl-bezenemethanol
74	4-Methoxy-benzaldehyde
75	1,6-Hexanediol
76	2-Methoxycyclohexanone
77	β-Elemenone
78	Mephenesin
79	4′-Methoxy-acetophenone
80	2-Methyl-3-methylethyl-butanoic acid
81	Folic acid
82	1-(Methoxyphenyl)-2-propanone
83	1-Methyl-3-(1-methylethyl)-benzene
84	4-Fluorohistamine
85	1,2-Dimethoxy-4-(1-propenyl)-benzene
86	(E)-2-Hydroxy-4-cyano-stilbene
87	1-(3-Methoxyphenyl)-1-propanone

[Source ¹¹⁶⁾]

Table 7. Biological activities of some phytochemicals reported in different parts of fennel plant

Number	Biological activities	Part useda	Phytochemicals	Reference
1	Oestrogenic	SDEO	Dianethole, photoanethole	117)
2	Hepatoprotective	SDEO	β-Myrcene, Limonene	118)
3	Antithrombotic	SDEO	trans-Anethole	119)
4	Human liver cytochrome P450-3A4 inhibitory	SD	5-Methoxypsoralen	120)
5	Antiradical scavenging	FW	3-Caffeoylquinic acid, quercetin-3-O-galactoside, kaempferol-3-O-glucoside, kaempferol-3-O-rutinoside, rosmarinic acid	121)
		AP	3,4-Dihydroxyphenethyl-alchohol-6-O-caffeoyl-β-D-glucopyranoside, 3′,8′-binaringenin	122)
6	Antioxidant	FT	cis-Miyabenol C	123)
7	Anticancer	SDEO	Anethole	124)
8	Antibacterial	ST	Dillapiol, psoralen, bergapten, scopoletin, imperatorin, dillapional,	125)
9	Antimycobacterial	ST, LF	2,4-Undecadienal, linoleic acid, oleic acid, 1,3-benzenediol, undecanal	126)
10	Repellent	FT	(z)-9-Octadecanoic acid, fenchone	127)
11	Acaricidal	SDEO	para-Anisaldehyde	128)
12	Insecticidal	SDEO	1,8-Cineole, terpineol	129)

Note: ^a AP: aerial part, FT: fruit, LF: leaf, SD: seed, SDEO: seed essential oil, ST: stem, and FW: fennel waste.

[Source ¹³⁰⁾]

Fennel health benefits

A series of studies showed that fennel effectively controls numerous infectious disorders of bacterial ¹³¹⁾, ¹³²⁾, fungal, viral, mycobacterium, and protozoal origin ¹³³⁾, ¹³⁴⁾. Fennel has antioxidant, antitumor, chemopreventive, cytoprotective, hepatoprotective, hypoglycemic, and oestrogenic activities ¹³⁵⁾. Some of the publications stated that fennel has a special kind of memory-enhancing effect and can reduce stress ¹³⁶⁾. Animal experiments and limited clinical trials suggest that chronic use of fennel is not harmful ¹³⁷⁾.

Table 8. Details of pharmacological/biological activities reported on fennel

Activity	Plant part used	Dosage form/type of extract	Concentration/dosages	Tested living system/organ/cell/type of study	Results	References
Antiinflammatory	Fruit	Methanolic Extract	200 mg/kg: oral administration	Invivo, male ICR mice, BALB/c mice, and Sprague-Dawley rats	Inhibitory effects against acute and subacute inflammatory diseases and type IV allergic reactions	138)
Hepatoprotective	Seed	Essential oil	0.4 mL/kg	Invivo, carbon tetrachloride induced liver injury model in male Sprague-Dawley rats	Decreases the level of serum enzymes, namely, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and bilirubin	139)
Hypoglycaemic	Seed	Essential oil	30 mg/kg	Invivo, streptozotocin induced diabetic rats	Ingestion of essential oil to diabetic rats corrected the hyperglycemia and the activity of serum glutathione peroxidase and also improved the pathological changes noticed in their kidney and pancreas	140)
Antihirsutism	Seed	Fennel extract	Creams containing 1%, 2% of fennel extract and placebo	45 female patients aged 16–53 years with mild to moderate forms of idiopathic hirsutism	Cream containing 2% fennel is better than the cream containing 1% fennel and these two were more potent than placebo	141)
Cytoprotective	Fruit	Methanolic extract	200 μg/mL	Normal human blood lymphocyte	Provides more cytoprotection for normal human lymphocytes as compared with standard sample, that is, doxorubicin	142)
Antitumor	Fruit	Methanolic extract	25 to 200 μg/mL	B16F10 melanoma cell line	70% methanolic extract shows good antitumour activity at the concentration of 200 μg/mL.	143)
Antioxidant	Seed	Ethanol and water extract	100 μg of ethanol and water extract	Invitro, not stated	77.5% and 99.1% inhibition of peroxidation in linoleic acid system, respectively.	144)
Oestrogenic	Seed	Acetone extract	Not stated	Invivo, female rats	Weight of mammary glands increases also increases the weight of oviduct, endometrium, myometrium, cervix, and vagina	145)
Vascular effects	Leaf	Aqueous extracts	0.1 to 0.4 mL injection	Invivo, pentobarbital-anaesthetised Sprague-Dawley rats	Significant dose-related reduction in arterial blood pressure, without affecting the heart rate or respiratory rate	146)
Antistress	Fruit	Aqueous extracts	50, 100 and 200 mg/kg	Invivo, scopolamine-induced amnesic rats	Significant inhibition of the stress induced biochemical changes in vanillyl mandelic acid and ascorbic acid.	147)
Memory-enhancing	Fruit	Aqueous extracts	50, 100, and 200 mg/kg	Invivo, scopolamine-induced amnesic rats	The significant reduction is achieved in amnesia in extract-treated groups as compared with the control group of animals	148)
Chemopreventive	Seed	Test diet of fennel	4% and 6% test diets of Fennel	In-vivo, DMBA-induced skin and B(a)P-induced forestomach papillomagenesis in Swiss albino mice	Significant reduction in the skin and the forestomach tumor incidence and tumor multiplicity as compared to the control group of animal	149)
Oculohypotensive	Seed	Aqueous extract	0.3%, 0.6%, and 1.2% (w/v)	Invivo, rabbits	It exhibits 17.49, 21.16, and 22.03% reduction of intraocular pressure (IOP) in normotensive rabbits at 0.3%, 0.6%, and 1.2% (w/v) concentrations of extract	150)
Anticarcinogenic	Seed	Methanolic extract	100 mg/kg	Invivo, Swiss albino mice	Significant increase in malondialdehyde levels and the significant decrease in catalase activity and glutathione content in liver and tumor tissue in mice bearing Ehrlich ascites carcinoma	151)
Antiaging	Seed	Fennel extract	Formulation containing 4% extract	Male volunteers with mean age of 48 years	Formulation showed significant effects on skin moisture and transepidermal water loss	152)
Apoptotic	Fruit	Ethanol extract	100 to 300 μg/mL	Nine human cell lines: ML-1, J-45.01, HL-60, 1301, U-266B1, WICL, C-8166, EOL, and H-9—human T cell	Highest mortality in Trypan blue test for J45 cell line, 4% of viable cells and for C8166 cell line, 100% of mortality	153)
Antiulcerogenic	Aerial parts	Aqueous extract	75, 150, 300 mg/kg	Invivo, ethanol induced gastric lesions in Sprague-Dawley rats	Pretreatment with extracts significantly reduced ethanol induced gastric damage.	154)
Cytotoxic	Root (ground part)	Dichloromethane and methanol (1 : 1) extract	700 μg/mL	Murine fibrosarcoma L929sA cells and on the human breast cancer cells MDA-MB231 and MCF7	Cytotoxic activity may act via inhibition of the NFkB pathway.	155)
Antimycobacterial	Aerial parts	Chloroform, hexane, methanol, and aqueous extracts	100 to 200 μg/mL	Invitro, M. tuberculosis H37Rv (27294)	Hexane extract is active against pan sensitive strain of M. tuberculosis H37RV	156)

Table 9. Antibacterial, antimycobacterial, antifungal, and antiviral studies carried out on fennel

Sr. number	Part useda	Type of extract	Active strainsb	Method	Reference standard	Effective concentration	Reference
1	SD	Essential oil	S.a., Enterococcus sp., P.a., E.c., and Salmonella sp.	Filter paper disc diffusion method	0.5 Mac Farland’s Standard (1.5 × 108 CFU/mL)	10 μL/disk	157)
2	FT	Essential oil	E.c., B.m.,and 27 phytopathogenic bacterial species	Agar diffusion method	Rifampicin	1.6 mg/mL	158)
3	AP	Aqueous, ethanol and ethyl-acetate extracts	A.r.t., Er.c., P.f.,and P.g.	Filter paper disc diffusion method	Chloramphenicol, streptomycin, and tetracycline	15 mg per disc.	159)
4	SD	Essential oil	E.a., S.t., S.a., St.e., E.c., P.a.,and C.a.	Filter paper disc diffusion method	Amoxicillin and cefazolin	15 μL/disk	160)
5	FL, FT	Essential oil	A.a., F.o., and R.s.	Filter paper disc diffusion method	NS	10 and 40 ppm	161)
6	FL, LF, TW	Essential oil	Bacilli sp., P.a., Acinetobacter sp., and A.f.	Agar diffusion method	Fleroxacin	30, 25, 20, 15 and 10 μL per well	162)
7	SD, ST, LF, RT	Essential oil	S.a., B.s., E.c., P.a., C.a., C.t., M.s., M.c., and M.x.	Agar dilution method	NS	NM	163)
8	SD	Essential oil	E.c., B.s., A.n., F.s.,and Rh.s.	Filter paper disc diffusion method	Amoxycillin and flumequine	300 μg/disc	164)
9	FT	Essential oil and ethanolic and methanolic extracts	B.c., B.m., B.p., B.s., E.c., K.p., M.l., P.p., P.s., and C.a.	Filter paper disc diffusion method	Cefoperazone, sulbactam, ofloxacin, and netilmicin	30 mg/mL	165)
10	SD	Aqueous/organic extracts	E.f., S.a., E.c., K.p., P.a., Sa.t., S.t., and S.f.	Agar well and disc diffusion method	Chloramphenicol, gentamicin, and ampicillin	NM	166)
11	SD	Essential oil	E.c., P.a., S.a., B.s., A.n., and C.a.	Filter paper disc diffusion technique	Ampicillin and miconazole nitrate	10 μL/disk	167)
12	SD	Ethanol, methanol, and aqueous extracts	E.c., K.p., P.v., E.a., Sa.t., B.c.,and S.a.	Agar well and disc diffusion method	Streptomycin	NM	168)
13	SD	Essential oil	E.c., P.a., S.a., C.a.,and A.n.	Cylinder-plate diffusion method	NS	0.25 to 2.0%	169)
14	FT	Essential oils	S.a., B.c., P.a., E.c.,and C.a.	Disc paper and broth microdilution methods	NS	NM	170)
15	SD	Methanol, ethanol, diethyl ether, and hexane extract	E.c., Sa.t., B.c., S.a., C.a.,and As.f.	Filter paper disc diffusion technique	NS	7.5, 10, 12.5, 15, 20 μg/disk	171)
16	LF, FL	Crude, chloroform, and methanol extract	E.c. and S.a.	Filter paper disc diffusion method	NS	NM	172)
17	FT	Essential oil	HSV-1 and PI-3	Using Madin-Darby bovine kidney and Vero cell lines	Acyclovir	0.025 to 0.8 μg/mL	173)
18	LF	Essential oil	S.a., E.c., K.p., P.a., S.e., C.a. and P.m., A.n.,and F.o.	Filter paper disc diffusion method	Gentamicin, amoxicillin, and nystatin	5 μL/disk	174)
19	ST, LF	Hexane extract	M.t.	96-well sterile microtiter plate assay	NS	200 μg/mL	175)
20	SD	Essential oil	S.a., E.c., K.p.,and P.a.	Agar well diffusion method	Imipenem	50 μL/well	176)
21	SD	Essential oil	S.a., E.c., S.c.,and St.f.	Filter paper disc diffusion method	Amoxicillin	10, 50, 100 μL/mL	177)
22	SD	Essential oil	S.a., B.s., B.m., B.c., S.l., S.h., Sa.t., S.d., S.s., Sh.s., S.b., E.c.,and P.a.	Filter paper disc diffusion method	Streptomycin	1 μg/mL	178)
23	FT	Essential oil	C.a.	Agar well and filter paper disc diffusion method	Fluconazole and nystatin	25 μL/well and 15 μL/disc	179)
24	SD	Methanolic extract	E.c., P.a., S.a., and B.p.	Agar diffusion method	Chloramphenicol and ampicillin	NM	180)
25	SD	Aqueous and alcoholic extracts	A.a., M.r.,and A.f.	Agar well diffusion method	NS	NM	181)

Notes:

Summary of fennel health benefits

Fennel plant has been in use for a long period of time without any documented serious adverse effects. Studies carried out in the past and present indicate that fennel possesses diverse health benefits and are an important constituent of food. Studies have shown that various extracts of fennel possess a range of pharmacological actions, such as antiaging, antiallergic, anticolitic, antihirsutism, anti-inflammatory, antimicrobial and antiviral, antimutagenic, antinociceptive, antipyretic, antispasmodic, antistress, antithrombotic, anxiolytic, apoptotic, cardiovascular, chemomodulatory action, cytoprotection and antitumor, cytotoxicity, diuretic, estrogenic properties, expectorant, galactogenic, gastrointestinal effect, hepatoprotective, human liver cytochrome P450 3A4 inhibitory, hypoglycemic, hypolipidemic, memory-enhancing property, nootropic, and oculohypotensive activity supporting its traditional use. However, the most prominent and the well studied effects are the antimicrobial and antioxidant effects of essential oil of fennel in different experimental models. The observed health benefits may be credited to the presence of the various phytochemicals like volatile compounds, flavonoids, phenolic compounds, fatty acids, and amino acids.

Most of the pharmacological studies were conducted using uncharacterized crude extracts of fennel. It is difficult to reproduce the results of these studies and pinpoint the bioactive compounds. Hence, there is a need for chemical standardization and bioactivity-guided identification of bioactive compounds. Among several classes of chemical constituents identified in fennel, volatile components of fennel essential oil and phenolic compounds are assumed to be the main bioactive compounds responsible for the majority of its pharmacological effects. However, the vast traditional use and proven pharmacological activities of fennel indicate that an immense scope still exists for its chemical exploration. Future studies should be focused on validating the mechanism of action responsible for the various beneficial effects and also on understanding which plant based compounds are responsible for the reported effects. The required information when available will enhance our knowledge and appreciation for the use of fennel in our daily diet. Also, the outcome of such chemical studies may further expand its existing therapeutic potential.

Thus, there are many areas of research related to fennel plant that need to be further explored to fully recognize its beneficial effects for society. Factors such as geographical and seasonal variation play an important role in the authentication of the chemical constituents responsible for the activity which also can be an area of interest.

Lastly, fennel also contains mineral and trace elements like aluminum, barium, calcium, cadmium, cobalt, chromium, copper, iron, magnesium, manganese, nickel, lead, strontium, and zinc; fat soluble vitamins such as vitamins A, E, and K; water soluble vitamins like ascorbic acid, thiamine, riboflavin, niacin, and pyridoxine; essential amino acids like leucine, isoleucine, phenylalanine, and tryptophane may contribute to the myriad health beneficial effects at least in part.

Fennel essential oil

The anise odor of fennel is due to its essential oil content. It makes an excellent flavoring agent in various types of food and food related products. Fennel essential oil of fennel has been reported to contain more than 87 volatile compounds ¹⁸²⁾. The accumulation of these volatile compounds inside the plant is variable, appearing practically in any of its parts, namely, roots, stem, shoots, flowers, and fruits ¹⁸³⁾. The molecular structures of major volatile components of fennel seed essential oil have been illustrated in Figure 4 above.

Guillén and Manzanos ¹⁸⁴⁾ investigated the yield and composition of the volatile components found in the pentane extracts of leaves, stems, and seeds of fennel. They identified a total of 37 volatile compounds from pentane extracts of above mentioned parts of fennel by using gas chromatography and gas chromatography-mass spectrometry techniques. In the supercritical CO2 (SC-CO2) seed extracts of fennel, a total of 28 compounds were identified with major compounds being trans-anethole (68.6–75.0%), fenchone (8.40–14.7%), and methylchavicol (5.09–9.10%) whereas only 19 compounds were detected from hydrodistilled oil of fennel ¹⁸⁵⁾. Fang et al. ¹⁸⁶⁾ characterizes 76 volatile components in fennel essential oil. In 2007 Tognolini et al. ¹⁸⁷⁾ investigated the chemical composition of fennel essential oil revealed a total of 18 compounds present in it with anethole being the most abundant. A comparative profile of occurrence of monoterpene hydrocarbons, oxygenated monoterpenes, and phenylpropanoids with respect to various maturity stages (immature, premature, mature, and fully mature) of the fennel fruit was reported by Telci et al. ¹⁸⁸⁾. They concluded that the content of fennel essential oil decreases with increasing maturity. A total of 28 components of fennel essential oil were identified, accounting for 98.0% of the total oil. The principal compound in fennel essential oil was trans-anethole (72.2%) followed by estragole (7.6%), d-limonene (6.8%), and fenchone, that is, 3.9% ¹⁸⁹⁾. Overall, 60 compounds representing 90.1–98.7% of the fennel essential oil were identified in the two cultivars of fennel, namely, Aurelio and Sparta cocultivars. The major constituent of fennel essential oils is trans-anethole (59.8–90.4%). In addition, the fennel essential oils also contains minor amounts of various constituents as limonene (0.1–21.5%), neophytadiene (0–10.6%), (E)-phytol (0.1–6.0%), exo-fenchyl acetate (0.3–3.8%), estragole (0.1–2.5%), and fenchone, that is, 0.1–3.1% ¹⁹⁰⁾. In addition, Zoubiri et al. ¹⁹¹⁾ summarized the comparative profile of volatile compounds found in different varieties of fennel from different countries such as Estonia, Norway, Austria, Moldova, and Turkey. The chemical composition of the Algerian fennel seed oil was different as compared with Turkish ¹⁹²⁾, Serbian ¹⁹³⁾, Indian ¹⁹⁴⁾, and Chinese fennels ¹⁹⁵⁾. The hexane extracts of fennel were analyzed and 78 compounds were identified from these extracts; the major compounds were identified as 1,3-benzenediol, 1-methoxycyclohexene, o-cymene, sorbic acid, 2-hydroxy-3-methyl-2-cyclopenten-1-one, estragole, limonene-10-ol, and 3-methyl-2-cyclopenten-1-one ¹⁹⁶⁾. Diao et al. ¹⁹⁷⁾ identify a total of 28 components from fennel oil, representing 95.8% of the total amount. Trans-Anethole (68.53%), a phenylpropanoid, was found to be the main component, followed by estragole (10.42%) with limonene (6.24%), fenchone (5.45%), and others as minor components.

Fennel toxicity and side effects

In most toxicity experiments carried out on fennel, no sign of toxicity was observed. Shah and his coworker in 1991 ¹⁹⁸⁾ investigated the detailed toxicity account of ethanolic extract of fennel fruit in experimental mice with respect to acute and 90 days longer term toxicity. In experimentation, Shah and his coworker ¹⁹⁹⁾ observed the general symptoms of toxicity and mortality for only 24 h in acute toxicity. Whereas, in another part of toxicity they studied the effect of fennel extract on mice with 90 days long term treatment. Acute toxicity of ethanolic extract of fennel was assessed in 35 mice by using three concentrations, namely, 0.5, 1, and 3 g/kg body weight. In this investigation, fennel exhibited no signs of toxicity and no mortality was observed upto the dose level 3 g/kg body weight. In case of longer term toxicity, ethanolic extract of fennel (100 mg/kg body weight/day) was given in drinking water of animals (30 male and 30 female mice). All external morphological, haematological, and spermatogenic changes, in addition to body and vital organ weights, were recorded. The extract caused no significant chronic mortality as compared to controls during this investigation. The treated male mice gained significant weight during chronic treatment while a loss or no significant change in weight was noticed in the female mice treated with the same extract. The extracts did not show spermatotoxic effects. Thus, Shah and his coworker concluded that fennel extract is safe based on both acute and/or long term toxicity studies ²⁰⁰⁾. Additionally, the plant extract in doses of 0.5, 1, and 3 g/kg (orally) did not cause any deaths. These doses do not show any type of toxicity against several parameters tested, namely, locomotor activity, bizarre reactions, sensitivity to sound, social interaction, tail posture, aggressive behaviour, ataxia, paralysis, convulsions, tremors, prostration, exophthalmos, pupil size, defecation, salivation, urination, pattern of respiration, nasal discharge, cyanosis, and piloerection. Exceptionally, only the 3 g/kg dose showed signs of reduced locomotor activity and piloerection. Otherwise, all other parameters were negative ²⁰¹⁾. In another experiment of acute toxicity, different solvent extracts, namely, n-hexane, methylene chloride, ethyl acetate, and methanol extracts of fennel upto 5.5 g/kg concentration, did not revealed any kind of toxicity in mice, LD50 (lethal dose 50% is the amount of the substance required (usually per body weight) to kill 50% of the test subjects population)being: 6.75, 11.0, 6.92, and 15 g/kg for n-hexane, methylene chloride, ethyl acetate, and methanol extracts, respectively ²⁰²⁾. The fennel plant extract was administered orally at a dose of 100, 200, 400, 600, 800, 1000, and 2000 mg/kg of body weight of mice. Each group of animals was under visual observation for 10 days for the external behavior of neurological toxicity created by plant extract. Even the mice receiving highest dose of fennel extract did not show any mortality or toxicity demonstrating the safety profile of the plant extract ²⁰³⁾.

The acute oral 50% LD50 for anethole in rats was found to be 2090 mg/kg. Repeated doses of one-third the LD50 of anethole (695 mg/kg) given to rat caused mild liver lesions. It would therefore appear that in normal therapeutic dosages anethole would have minimal hepatotoxicity. When anethole was fed to rats daily for one year as 0.25% of the diet, no hepatic damage was seen ²⁰⁴⁾. The acute oral LD50 of essential oil in rats is 1326 mg/kg ²⁰⁵⁾. The use of F. vulgare essential oil as a remedy for control of primary dysmenorrhea increases concern about its potential teratogenicity due to its estrogen like activity. Evaluation of teratogenicity of essential oil using limb bud mesenchymal cells showed that the essential oil may have toxic effect on fetal cells, but there was no evidence of teratogenicity upto concentration of 9.3 mg/mL of culture medium ²⁰⁶⁾. The overall toxicity studies carried out on fennel accounts for its safety at the recommended therapeutic doses.