fennel bulb

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

NumberRegion/NationLocal namePart used and edible application.References
1Campania, ItalyFinucchio, finucchiello, finochiettoStem is used as an aromatizer for pickled olives.5)

2Campania, ItalyFinocchiella, fenùcciuSeed is employed in preparation of salted meats.6)

3SpainHinojo, FenollTender leaves and stems, raw as a snack, are used in salads or stewed.7)

4SpainFiallo, millauAerial part or seeds used for seasoning olives, as preservative for dry figs, and for preparing herbal tea or liqueur.8)

5Trás-os-Montes (Northeast Portuguese)Fialho, fionho, erva-doceShoots, 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)

6Arrábida and Açor (Center Portuguese)Funcho, erva-doceSeeds used as flavour for cakes and pastries and for cooking chestnuts.10)

7Alentejo and Algarve (South Portuguese)Funcho, fialho, funcho-doce, funcho-amargoShoots, 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)

8Jammu and Kashmir, IndiaSaunfThe fruits with other ingredients are given to the animal if it stops taking food during diarrhea.12)

9Liguria, ItalyFenucéttu-sarvèguAerial 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

fennel bulb

Figure 2. Fennel plant

fennel plant
Fennel plant

Figure 3. Fennel seeds

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

NutrientUnitValue per 100 gbulb 234 g
Approximates
Waterg90.21211.09
Energykcal3173
EnergykJ129302
Proteing1.242.9
Total lipid (fat)g0.20.47
Ashg1.052.46
Carbohydrate, by differenceg7.317.08
Fiber, total dietaryg3.17.3
Sugars, totalg3.939.2
Minerals
Calcium, Camg49115
Iron, Femg0.731.71
Magnesium, Mgmg1740
Phosphorus, Pmg50117
Potassium, Kmg414969
Sodium, Namg52122
Zinc, Znmg0.20.47
Copper, Cumg0.0660.154
Manganese, Mnmg0.1910.447
Selenium, Seµg0.71.6
Vitamins
Vitamin C, total ascorbic acidmg1228.1
Thiaminmg0.010.023
Riboflavinmg0.0320.075
Niacinmg0.641.498
Pantothenic acidmg0.2320.543
Vitamin B-6mg0.0470.11
Folate, totalµg2763
Folic acidµg00
Folate, foodµg2763
Folate, DFEµg2763
Choline, totalmg13.230.9
Vitamin B-12µg00
Vitamin B-12, addedµg00
Vitamin A, RAEµg48112
Retinolµg00
Carotene, betaµg5781353
Carotene, alphaµg00
Cryptoxanthin, betaµg00
Vitamin A, IUIU9632253
Lycopeneµg00
Lutein + zeaxanthinµg6071420
Vitamin E (alpha-tocopherol)mg0.581.36
Vitamin E, addedmg00
Vitamin D (D2 + D3)µg00
Vitamin DIU00
Vitamin K (phylloquinone)µg62.8147
Lipids
Fatty acids, total saturatedg0.090.211
04:00:00g00
06:00:00g00
08:00:00g00
10:00:00g00
12:00:00g00
14:00:00g0.0020.005
16:00:00g0.0790.185
18:00:00g0.0090.021
Fatty acids, total monounsaturatedg0.0680.159
16:1 undifferentiatedg0.0020.005
18:1 undifferentiatedg0.0650.152
20:01:00g00
22:1 undifferentiatedg00
Fatty acids, total polyunsaturatedg0.1690.395
18:2 undifferentiatedg0.1690.395
18:3 undifferentiatedg00
18:04:00g00
20:4 undifferentiatedg00
20:5 n-3 (EPA)g00
22:5 n-3 (DPA)g00
22:6 n-3 (DHA)g00
Fatty acids, total transg00
Cholesterolmg00
Other
Alcohol, ethylg00
Caffeinemg00
Theobrominemg00
Flavanones
Eriodictyolmg1.12.5
Flavonols
Quercetinmg0.20.5
Isoflavones
Daidzeinmg00
Genisteinmg00
Total isoflavonesmg00
[Source: United States Department of Agriculture Agricultural Research Service 20)]

Table 3. Fennel seeds nutrition facts

NutrientUnitValue per 100 gtsp, whole 2 g
Approximates
Waterg8.810.18
Energykcal3457
EnergykJ144329
Proteing15.80.32
Total lipid (fat)g14.870.3
Ashg8.220.16
Carbohydrate, by differenceg52.291.05
Fiber, total dietaryg39.80.8
Minerals
Calcium, Camg119624
Iron, Femg18.540.37
Magnesium, Mgmg3858
Phosphorus, Pmg48710
Potassium, Kmg169434
Sodium, Namg882
Zinc, Znmg3.70.07
Copper, Cumg1.0670.021
Manganese, Mnmg6.5330.131
Vitamins
Vitamin C, total ascorbic acidmg210.4
Thiaminmg0.4080.008
Riboflavinmg0.3530.007
Niacinmg6.050.121
Vitamin B-6 1mg0.470.009
Vitamin B-12µg00
Vitamin A, RAEµg70
Retinolµg00
Vitamin A, IUIU1353
Vitamin D (D2 + D3)µg00
Vitamin DIU00
Lipids
Fatty acids, total saturatedg0.480.01
16:00:00g0.480.01
Fatty acids, total monounsaturatedg9.910.198
18:1 undifferentiatedg9.910.198
Fatty acids, total polyunsaturatedg1.690.034
18:2 undifferentiatedg1.690.034
Cholesterolmg00
Phytosterolsmg661
Amino Acids
Tryptophang0.2530.005
Threonineg0.6020.012
Isoleucineg0.6950.014
Leucineg0.9960.02
Lysineg0.7580.015
Methionineg0.3010.006
Cystineg0.2220.004
Phenylalanineg0.6470.013
Tyrosineg0.410.008
Valineg0.9150.018
Arginineg0.680.014
Histidineg0.3310.007
Alanineg0.7890.016
Aspartic acidg1.8330.037
Glutamic acidg2.9560.059
Glycineg1.1070.022
Prolineg0.90.018
Serineg0.90.018
[Source: United States Department of Agriculture Agricultural Research Service 21)]

Table 4. Nutrient content of different parts of fennel plant

CompositionContents
LeavesInflorescencesStemsShoots
Moisturea76.36 ± 0.3371.31 ± 4.0177.46 ± 1.0373.88 ± 0.83
Asha3.43 ± 0.043.23 ± 0.021.62 ± 0.122.39 ± 0.02
Fata0.61 ± 0.161.28 ± 0.280.45 ± 0.070.49 ± 0.05
Proteina1.16 ± 0.031.37 ± 0.051.08 ± 0.001.33 ± 0.04
Carbohydratesa18.44 ± 0.0622.82 ± 3.0619.39 ± 0.6521.91 ± 0.55
Fructosea0.49 ± 0.051.10 ± 0.041.49 ± 0.041.51 ± 0.06
Glucosea0.76 ± 0.122.94 ± 0.113.43 ± 0.204.71 ± 0.15
Sucrosea0.04 ± 0.000.03 ± 0.00nd0.35 ± 0.06
Reducing sugarsa0.72 ± 0.041.20 ± 0.191.49 ± 0.291.14 ± 0.10
ω3 fatty acidb43.72 ± 0.3617.69 ± 0.0123.04 ± 1.3036.96 ± 0.51
ω6 fatty acidb23.25 ± 0.0738.94 ± 0.2338.22 ± 0.6839.99 ± 0.68
ω6/ω30.53 ± 0.002.20 ± 0.011.66 ± 1.121.08 ± 0.03
C6:0b0.02 ± 0.000.41 ± 0.020.19 ± 0.010.06 ± 0.00
C8:0b0.08 ± 0.000.37 ± 0.010.48 ± 0.030.33 ± 0.00
C10:0b0.04 ± 0.000.09 ± 0.000.13 ± 0.010.06 ± 0.00
C11:0b0.25 ± 0.020.29 ± 0.010.04 ± 0.000.07 ± 0.00
C12:0b0.31 ± 0.020.43 ± 0.060.11 ± 0.010.21 ± 0.02
C14:0b1.43 ± 0.011.68 ± 0.100.49 ± 0.060.75 ± 0.03
C14:1b0.61 ± 0.040.28 ± 0.020.37 ± 0.040.17 ± 0.03
C15:0b0.17 ± 0.000.35 ± 0.030.41 ± 0.040.18 ± 0.00
C16:0b20.15 ± 0.0923.89 ± 0.0725.43 ± 0.0012.78 ± 0.09
C17:0b0.74 ± 0.000.58 ± 0.020.61 ± 0.040.24 ± 0.02
C18:0b1.61 ± 0.082.62 ± 0.041.99 ± 0.061.53 ± 0.08
C18:1n9cb4.35 ± 0.375.05 ± 0.004.35 ± 0.522.55 ± 0.33
C18:2n6cb23.25 ± 0.0738.94 ± 0.2338.22 ± 0.6839.99 ± 0.68
C18:3n3b43.55 ± 0.4017.55 ± 0.022.86 ± 1.3136.84 ± 0.52
C20:0b0.56 ± 0.001.78 ± 0.060.84 ± 0.031.06 ± 0.09
C20:1cbnd0.26 ± 0.030.06 ± 0.00nd
C20:2cb0.08 ± 0.010.31 ± 0.010.14 ± 0.000.38 ± 0.07
C20:3n3 + C21:0b0.16 ± 0.020.15 ± 0.010.19 ± 0.000.12 ± 0.01
C22:0b0.77 ± 0.041.52 ± 0.041.20 ± 0.031.12 ± 0.02
C23:0b0.82 ± 0.131.89 ± 0.110.68 ± 0.010.36 ± 0.15
C24:0b1.03 ± 0.041.58 ± 0.021.21 ± 0.021.20 ± 0.08
Total SFAb27.99 ± 0.0237.47 ± 0.2533.81 ± 0.0619.95 ± 0.12
Total MUFAb4.96 ± 0.405.59 ± 0.134.78 ± 0.572.72 ± 0.36
Total PUFAb67.05 ± 0.4256.94 ± 0.1261.41 ± 0.6277.33 ± 0.24
Energyc83.90 ± 1.34108.23 ± 10.3785.91 ± 3.0297.37 ± 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

NumberAilment/usePart/preparation usedLocalityReferences
1Mouth ulcerTender leaves, chewed and stuck on ulcerBasilicata, Italy31)

2AperitifTender parts-raw or boiledRome, Italy32)

3Gum disorderFruit and seed, used as a mouth wash for gum disorderCentral Serbia33)

4InsomniaInfusion of tea leafBrazil34)

5ConstipationSeeds, decoctionSouth Europe35)
Seeds mixed with sugarJammu and Kashmir, India36)

6CancerLeaf and flower, aqueous infusion, drinkLoja, Ecuador37)

7ConjunctivitisLeaf and flower, aqueous infusion, drinkLoja, Ecuador38)

8GastritisLeaf, flower, aqueous infusion, drinkLoja, Ecuador39)

9DiuresisRoot and seed, decoctionMiami, Florida, USA40)

10Abdominal painsEach plant part, decoctionRome, Italy41)
Leaf and seeds, infusionNorthern Badia, Jordan,42)
Leaves, pasteManisa, Turkey43)

11ColdFruits and floral tops, decoctionRome, Italy44)

12RefreshingRoots/whole plant, decoctionRome, Italy45)

13Swollen stomachLeaves, decoction with a little honeyRome, Italy46)

14Hair growSeed oilMiddle Navarra47)

15AntiemeticFruit, simple powderNortheastern Majorcan area48)

16Antihypertensive and Anti-cholesterolemicLeaf directly chewednorth-eastern Majorcan area49)

17DepurativeLeaf and stem, comestibleIberian Peninsula, Spain50)

18HypnoticSeed, leaf, and stem, infusion and edibleNorth Iran51)

19DiarrhoeaSeeds, roots, and fresh leavesNorthern Portugal52)
Seeds grounded with Root tubers of Hemidesmus indicus and the paste taken with jaggery twice a day for three daysBhandara, Maharashtra, India53)

20Kidney ailmentsAerial part, infusionAlto, Bolivia54)
Seed, decoctionGujranwala, Pakistan55)

21Colic in childrenLeaf and fruit, infusionBrazil56)

22Irritable colonLeaf and seeds, infusionNorthern Badia, Jordan,57)

23GastralgiaLeaf, decoctionsouthern Spain58)

24PurgativeSeed, infusion and edibleGujranwala, Pakistan59)

25LaxativeSeed, infusion and edibleGujranwala, Pakistan60)

26Liver painSeedPernambuco, Northeast Brazil61)

27MosquitocidalRoot boiled and drunk as teaSomali Region, Ethiopia62)

28ArthritisLeaf, an infusion made from the leaves is drunkSouth Africa63)

29FeverLeaf, an infusion made from the leaves is drunkSouth Africa64)

30Fat deductionGreen fruit is chewed to reduce fatSouth Africa65)

31LeucorrhoeaA 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 morningRajasthan, India66)

32Problem of repeated abortionsMixture of its 50 g seed powder, 50 g fruit powder of Trapa natans, and 50 g sugar is given daily to pregnant ladiesRajasthan, India67)

33Digestive systemFruits, decoctionBasilicata, Italy68)
Seed, decoction (drink one tea cup after food)Balikesir, Turkey69)
Whole plantWestern cape of South Africa70)
Fruit, powder for digestive ailmentsMiddle, West, and South Bosnia71)
Seeds, decoctionSouth Europe72)
Seeds, roots, and fresh leavesNorthern Portugal.73)
Seed, decoctionSouthern Spain74)

34CarminativeTender parts, raw or boiledRome, Italy75)
Whole plantWestern cape of South Africa76)
Seeds, decoctionSouth Europe77)
Seed, leaf, and stem, infusion and edibleNorth Iran78)
Leaves and/or fruitsSouth Africa79)

35DiureticTender parts, raw or boiledRome, Italy80)
Whole plantWestern cape of South Africa81)
Seeds, decoctionSouth-Europe82)
Seeds, roots, and fresh leavesNorthern Portugal.83)
Leaf, an infusion made from the leaves is drunkSouth Africa84)

36EmmenagogueAerial part, raw with carrotRome, Italy85)
Fruit, simple powderNorth-eastern Majorcan area86)
SeedHaryana, India87)

37Milk stimulant in pregnant women (Galactagogue)Leaf, an infusion made from the leaves is drunkSouth Africa88)
Fruits, as condiment or chewedRome, Italy89)
Fruit, simple powdernorth-eastern Majorcan area90)
Aerial part-infusionAlto, Bolivia91)

38Gingival woundFruit-pasteUttarakhand, India92)
Whole plant, decoctionAndalusia, Spain93)

39Eye blurry and itchingAerial parts, inhaled into eyesBalikesir, Turkey94)
Seeds, roots, and leavesNorthern Portugal95)
Seed, infusion, edibleGujranwala, Pakistan96)
Leaves and/or fruitsSouth Africa97)

40CoughWhole plant, oral infusionGuerrero, Mexico98)
Whole plant, decoctionSouthern Spain99)
Whole plantWestern cape of South Africa100)

41StomachacheWhole plant, oral infusionGuerrero, Mexico101)
FruitMiddle Navarra102)
Seed decoction is used against stomach acheLiguria, Italy103)
Seed, leaf, and stem-infusion, edibleNorth Iran104)

42Stress removalApical shoots is used as sedative for childrenLiguria, Italy105)
Southern Punjab, Pakistan106)

43FlatulenceLeaf and fruit, infusionBrazil107)
Leaf and seeds, infusionNorthern Badia, Jordan,108)
Fresh fruit, decoctionNorth Bengal, India109)
[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

Fennel phytochemicals

Table 6. Fennel essential oil volatile compounds

NumberCompounds
1α-Thujene
21,8-Cineol
3β-Ocimene
4Linalool
5Germacrene D
6Anisketone
7Apiol
8n-Hexadecanoic acid
9Cubebene
10Benzene-1-methyl-4-(1-methylethyl)-p-cymene
111,3,6-Octatriene, 3,7-dimethyl-, (E)-3-carene
122-Heptene
133-Methyl-butanal
14β-Pinene
15Camphene
16Hexanal
17α-Pinene
18β-Phellandrene
19α-Phellanrrene
20β-Myrcene
214-Carene
222-Heptanohe
23Limonene
244-Methyl-bicyclo[3.1.0]hex-2-ene
25Eucalyptol
26α-Pinene
27γ-Terpinene
287-Dimethyl-1,3,7-octriene
292,4-Dimethyl-benzenamine
303-Carene
31Cathine
322-Heptanol
332-Propyn-1-ol
342,6-Dimethyl-2,4,6-octatriene
35Fenchone
361-Methyl-4-(1-methylethyl)-benzene
37cis-Limonene oxide
38trans-Limonene oxide
396-Methylene-bicyclo[3.1.0]hexane
40Sabinene hydrate
41Fenchyl acetate
42Camphor
43Benzaldehyde
441,3-Butanediol
45Dicyclopropyl carbinol
46Fenchol
471-Octanol
485-Methyl-2-heptanol
49Tetradecyl-oxirane
50Estragole
51Transp-2,8-menthadien-1-ol
52β-Terpinol
53cisp-2,8-Menthadien
544-Methyl-1-(methylethyl)-3-cyclohexen
552-Methyl-5-(1-methylethyl)-2-cyclohexen-1-one
56Phenylmethyl-formic ester
572,3-Cyclohexen-1-methanol
58 Epi-bicyclosesquiphellardrene
59cisp-Menth-2,8-dienol
601,4-Dimethoxy-benzene
611-Methoxy-4-(1-propenyl)-benzene
621,2,4a,5,8,8a-Hexadehyde-naphthalene
634-Methyl-bicyclo[3.1.1]hept-3-en-2-ol
64trans-Anethole 73.20 73.27 66.71
65Allantoic acid
662-Methyl-5-(1-methylethyl)-phenol
67Mannoheptulose
682-Methyl-5-(1-methylethyl)-2-cyclohexen-1-ol
691-Undecanol
70Benzothiazole
71E-Pinane
722-Cyclohexen-1-ol
732-Methyl-bezenemethanol
744-Methoxy-benzaldehyde
751,6-Hexanediol
762-Methoxycyclohexanone
77β-Elemenone
78Mephenesin
794′-Methoxy-acetophenone
802-Methyl-3-methylethyl-butanoic acid
81Folic acid
821-(Methoxyphenyl)-2-propanone
831-Methyl-3-(1-methylethyl)-benzene
844-Fluorohistamine
851,2-Dimethoxy-4-(1-propenyl)-benzene
86(E)-2-Hydroxy-4-cyano-stilbene
871-(3-Methoxyphenyl)-1-propanone
[Source 116)]

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

NumberBiological activitiesPart usedaPhytochemicalsReference
1OestrogenicSDEODianethole,
photoanethole
117)

2HepatoprotectiveSDEOβ-Myrcene,
Limonene
118)

3AntithromboticSDEOtrans-Anethole119)

4Human liver cytochrome P450-3A4 inhibitorySD5-Methoxypsoralen120)

5Antiradical scavengingFW3-Caffeoylquinic acid, quercetin-3-O-galactoside,
kaempferol-3-O-glucoside,
kaempferol-3-O-rutinoside,
rosmarinic acid
121)
AP3,4-Dihydroxyphenethyl-alchohol-6-O-caffeoyl-β-D-glucopyranoside,
3′,8′-binaringenin
122)

6AntioxidantFTcis-Miyabenol C123)

7AnticancerSDEOAnethole124)

8AntibacterialSTDillapiol,
psoralen,
bergapten,
scopoletin,
imperatorin,
dillapional,
125)

9AntimycobacterialST, LF2,4-Undecadienal,
linoleic acid,
oleic acid,
1,3-benzenediol,
undecanal
126)

10RepellentFT(z)-9-Octadecanoic acid,
fenchone
127)

11AcaricidalSDEOpara-Anisaldehyde128)

12InsecticidalSDEO1,8-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

ActivityPlant part usedDosage form/type of extractConcentration/dosagesTested living system/organ/cell/type of studyResultsReferences
AntiinflammatoryFruitMethanolic
Extract
200 mg/kg: oral administrationInvivo, male ICR mice, BALB/c mice, and Sprague-Dawley ratsInhibitory effects against acute and subacute inflammatory diseases and type IV allergic reactions138)

HepatoprotectiveSeedEssential oil0.4 mL/kgInvivo, carbon tetrachloride induced liver injury model in male Sprague-Dawley ratsDecreases the level of serum enzymes, namely, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and bilirubin139)

HypoglycaemicSeedEssential oil30 mg/kgInvivo, streptozotocin induced diabetic ratsIngestion 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 pancreas140)

AntihirsutismSeedFennel extractCreams containing 1%, 2% of fennel extract and placebo45 female patients aged 16–53 years with mild to moderate forms of idiopathic hirsutismCream containing 2% fennel is better than the cream containing 1% fennel and these two were more potent than placebo141)

CytoprotectiveFruitMethanolic
extract
200 μg/mLNormal human blood lymphocyteProvides more cytoprotection for normal human lymphocytes as compared with standard sample, that is, doxorubicin142)

AntitumorFruitMethanolic
extract
25 to 200 μg/mLB16F10 melanoma cell line70% methanolic extract shows good antitumour activity at the concentration of 200 μg/mL.143)

AntioxidantSeedEthanol and water extract100 μg of ethanol and water extractInvitro, not stated77.5% and 99.1% inhibition of peroxidation in linoleic acid system, respectively.144)

OestrogenicSeedAcetone extractNot statedInvivo, female ratsWeight of mammary glands increases also increases the weight of oviduct, endometrium, myometrium, cervix, and vagina145)

Vascular effectsLeafAqueous extracts0.1 to 0.4 mL injectionInvivo, pentobarbital-anaesthetised Sprague-Dawley ratsSignificant dose-related reduction in arterial blood pressure, without affecting the heart rate or respiratory rate146)

AntistressFruitAqueous extracts50, 100 and 200 mg/kgInvivo, scopolamine-induced amnesic ratsSignificant inhibition of the stress induced biochemical changes in vanillyl mandelic acid and ascorbic acid.147)

Memory-enhancingFruitAqueous extracts50, 100, and 200 mg/kgInvivo, scopolamine-induced amnesic ratsThe significant reduction is achieved in amnesia in extract-treated groups as compared with the control group of animals148)

ChemopreventiveSeedTest diet of fennel4% and 6% test diets of FennelIn-vivo, DMBA-induced skin and B(a)P-induced forestomach papillomagenesis in Swiss albino miceSignificant reduction in the skin and the forestomach tumor incidence and tumor multiplicity as compared to the control group of animal149)

OculohypotensiveSeedAqueous extract0.3%, 0.6%, and 1.2% (w/v)Invivo, rabbitsIt 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 extract150)

AnticarcinogenicSeedMethanolic extract100 mg/kgInvivo, Swiss albino miceSignificant increase in malondialdehyde levels and the significant decrease in catalase activity and glutathione content in liver and tumor tissue in mice bearing Ehrlich ascites carcinoma151)

AntiagingSeedFennel extractFormulation containing 4% extractMale volunteers with mean age of 48 yearsFormulation showed significant effects on skin moisture and transepidermal water loss152)

ApoptoticFruitEthanol extract100 to 300 μg/mLNine human cell lines: ML-1, J-45.01, HL-60, 1301, U-266B1, WICL, C-8166, EOL, and H-9—human T cellHighest mortality in Trypan blue test for J45 cell line, 4% of viable cells and for C8166 cell line, 100% of mortality153)

AntiulcerogenicAerial partsAqueous extract75, 150, 300 mg/kgInvivo, ethanol induced gastric lesions in Sprague-Dawley ratsPretreatment with extracts significantly reduced ethanol induced gastric damage.154)

CytotoxicRoot (ground part)Dichloromethane and methanol (1 : 1) extract700 μg/mLMurine fibrosarcoma L929sA cells and on the human breast cancer cells MDA-MB231 and MCF7Cytotoxic activity may act via inhibition of the NFkB pathway.155)

AntimycobacterialAerial partsChloroform, hexane, methanol, and aqueous extracts100 to 200 μg/mLInvitro, M. tuberculosis H37Rv (27294)Hexane extract is active against pan sensitive strain of M. tuberculosis H37RV156)

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

Sr. numberPart usedaType of extractActive strainsbMethodReference standardEffective concentrationReference
1SDEssential oilS.a., Enterococcus sp., P.a., E.c., and Salmonella sp.Filter paper disc diffusion method0.5 Mac Farland’s Standard (1.5 × 108 CFU/mL)10 μL/disk157)

2FTEssential oilE.c., B.m.,and 27
phytopathogenic bacterial species
Agar diffusion methodRifampicin1.6 mg/mL158)

3APAqueous, ethanol and ethyl-acetate extractsA.r.t., Er.c., P.f.,and P.g. Filter paper disc diffusion methodChloramphenicol, streptomycin, and tetracycline15 mg per disc.159)

4SDEssential oilE.a., S.t., S.a., St.e., E.c., P.a.,and C.a. Filter paper disc diffusion methodAmoxicillin and cefazolin15 μL/disk160)

5FL, FTEssential oilA.a., F.o., and R.s. Filter paper disc diffusion methodNS10 and 40 ppm161)

6FL, LF, TWEssential oilBacilli sp., P.a., Acinetobacter sp., and A.f. Agar diffusion methodFleroxacin30, 25, 20, 15 and 10 μL per well162)

7SD, ST, LF, RTEssential oilS.a., B.s., E.c., P.a., C.a., C.t., M.s., M.c., and M.x. Agar dilution methodNSNM163)

8SDEssential oilE.c., B.s., A.n., F.s.,and Rh.s. Filter paper disc diffusion methodAmoxycillin and flumequine300 μg/disc164)

9FTEssential oil and ethanolic and methanolic extractsB.c., B.m., B.p., B.s., E.c., K.p., M.l., P.p., P.s., and C.a. Filter paper disc diffusion methodCefoperazone, sulbactam, ofloxacin, and netilmicin30 mg/mL165)

10SDAqueous/organic extractsE.f., S.a., E.c., K.p., P.a., Sa.t., S.t., and S.f. Agar well and disc diffusion methodChloramphenicol, gentamicin, and ampicillinNM166)

11SDEssential oilE.c., P.a., S.a., B.s., A.n., and C.a. Filter paper disc diffusion techniqueAmpicillin and miconazole nitrate10 μL/disk167)

12SDEthanol, methanol, and aqueous extractsE.c., K.p., P.v., E.a., Sa.t., B.c.,and S.a. Agar well and disc diffusion methodStreptomycinNM168)

13SDEssential oilE.c., P.a., S.a., C.a.,and A.n. Cylinder-plate diffusion methodNS0.25 to 2.0%169)

14FTEssential oilsS.a., B.c., P.a., E.c.,and C.a. Disc paper and broth microdilution methodsNSNM170)

15SDMethanol, ethanol, diethyl ether, and hexane extractE.c., Sa.t., B.c., S.a., C.a.,and As.f. Filter paper disc diffusion techniqueNS7.5, 10, 12.5, 15, 20 μg/disk171)

16LF, FLCrude, chloroform, and methanol extractE.c. and S.a. Filter paper disc diffusion methodNSNM172)

17FTEssential oilHSV-1 and PI-3Using Madin-Darby bovine kidney and Vero cell linesAcyclovir0.025 to 0.8 μg/mL173)

18LFEssential oilS.a., E.c., K.p., P.a., S.e., C.a. and P.m., A.n.,and F.o. Filter paper disc diffusion methodGentamicin, amoxicillin, and nystatin5 μL/disk174)

19ST, LFHexane extractM.t. 96-well sterile microtiter plate assayNS200 μg/mL175)

20SDEssential oilS.a., E.c., K.p.,and P.a. Agar well diffusion methodImipenem50 μL/well176)

21SDEssential oilS.a., E.c., S.c.,and St.f. Filter paper disc diffusion methodAmoxicillin10, 50, 100 μL/mL177)

22SDEssential oilS.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 methodStreptomycin1 μg/mL178)

23FTEssential oilC.a. Agar well and filter paper disc diffusion methodFluconazole and nystatin25 μL/well and 15 μL/disc179)

24SDMethanolic extractE.c., P.a., S.a., and B.p. Agar diffusion methodChloramphenicol and ampicillinNM180)

25SDAqueous and alcoholic
extracts
A.a., M.r.,and A.f. Agar well diffusion methodNSNM181)

Notes:

aAP: aerial part, FL: flower, FT: fruit, LF: leaf, RT: root, SD: seed, ST: stem, and TW: twig.

b A.a.: Alternaria alternate, A.f.: Alcaligenes faecalis, As.f.: Aspergillus flavus, A.n.: Aspergillus niger, A.r.t.: Agrobacterium radiobacter pv. tumefaciens, B.c.: Bacillus cereus, B.m.: Bacillus megaterium, B.p.: Bacillus pumilus, B.s.: Bacillus subtilis, C.a.: Candida albicans, C.t.: Candida tropicalis, E.a.: Enterobacter aerogenes, Er.c.: Erwinia carotovora, E.c.: Escherichia coli, E.f.: Enterococcus faecalis, F.o.: Fusarium oxysporum, F.s.: Fusarium solani, K.p.: Klebsiella pneumonia, M.c.: Mycobacterium chelonae, M.l.: Micrococcus luteus, M.r.: Mucor rouxii, M.s.: Mycobacterium smegmatis, M.t.: Mycobacterium tuberculosis H37Rv ATCC 27294, M.x.: Mycobacterium xenopi, P.a.: Pseudomona aeruginosa, P.f.: Pseudomonas fluorescens, P.g.: Pseudomonas glycinea, P.m.: Phytopathogenic molds, P.p.: Pseudomonas putida, P.s.: Pseudomonas syringae, P.v.: Proteus vulgaris, R.s.: Rhizoctonia solani, Rh.s.: Rhizopus solani, S.a.: Staphylococcus aureus, S.b.: Shigella boydii, S.c.: Staphylococcus coagulase, S.d.: Shigella dysenteriae, S.e.: Salmonella enteritidis, S.e.: Staphylococcus epidermidis, S.f.: Shigella flexneri, St.f.: Streptococcus faecalis, S.h.: Streptococcus haemolyticus, S.l.: Sarcina lutea, S.s.: Shigella shiga, S.t.: Salmonella typhimurium, Sa.t.: Salmonella typhi, and Sh.s.: Shigella sonnei. HSV-1: herpes simplex virus 1 as a representative of DNA viruses and PI-3: parainfluenza-3 virus (PI-3) as representative of RNA viruses.

NS: no reference standard employed and NM: not mentioned.

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.

References   [ + ]