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Fenugreek (Trigonella foenum-graecum L.) Oils
Chapter 47
Fenugreek (Trigonella foenum-graecum L.) Oils Shyamapada Mandal1, Manisha DebMandal2 1University 2MGM
of Gour Banga, Laboratory of Microbiology and Experimental Medicine, Department of Zoology, Malda, West Bengal, India; Medical College and LSK Hospital, Department of Physiology, Kishanganj, Bihar, India
List of Abbreviations FGHF Fenugreek hexane extract FGMF Fenugreek methanol extract GRAS Generally recognized as safe MDR Multidrug resistant MIC Minimum inhibitory concentration ZDI Zone diameter of inhibition SNP Silver nanoparticles synthesized with the help of T. foenum-graecum seed extract TFSE T. foenum-graecum seed extract
INTRODUCTION Fenugreek (Greek hay), also called methi in Bengali (Trigonella foenum-graecum; diploid with 2n = 16)—an aromatic leguminous plant—is an important spice and has been commonly used as a traditional food and medicine; the dried seeds of the plant have extensive application in foods and beverages as a flavoring additive. The plant is native to many Asian, Middle Eastern, and European countries, and India being the leading producer of fenugreek is recognized as the major consumer for its culinary usage and medicinal application. In Ayurveda, both fenugreek seeds and leaves are used to prepare extracts or powders for medicinal use. The physicochemical characteristics of fenugreek seed oil such as acid value (4.75; mg KOH/g of oil), saponification value (195; mg KOH/g of oil), ester value of 190.25, free fatty acids content (2.38; Oleic acid/100 g oil), and the refractive index of 1.464 indicate fenugreek seed oil as an edible oil, if its characteristic pungent odor is minimized (Sulieman et al., 2008). The fenugreek protein fraction is found to be lysine-rich and comparable in quality to that of soybean protein, and hence seeds are used as food and offer a superlative nutritional profile.
BOTANICAL ASPECTS Fenugreek, also called Greek hay, belongs to the subfamily Papilionaceae of the family Leguminosae (bean family, Fabaceae). Fenugreek is cultivated all over the world as a semiarid crop. The yields can be significantly augmented in quantity and quality through suitable management of cultivation, irrigation, harvesting, and pest management. Fenugreek is a self-pollinating annual leguminous bean, and seeds sown in well-prepared soil sprout in 3 days; the plants mature in about 4 months and attain a height of 30–60 cm. In this plant, flowering starts after 30–40 days of sawing. The plant has compound pinnate, trifoliate leaves, white to yellow axillary flowers, and 10–15-cm-long thin pointed hoop-like beaked pods (Meghwal and Goswami, 2012) each carrying 10–20 seeds (Figure 1). Trigonella foenum-graecum seeds are small (5 mm long), hard, yellowish brown and angular, and are flattened with a characteristic oblong rhomboidal outline (Moradi kor and Moradi, 2013; Mullaicharam et al., 2013). The seed holds a central hard yellow embryo bounded by a large corneous white and semi-transparent endosperm (Betty, 2008).
Essential Oils in Food Preservation, Flavor and Safety. http://dx.doi.org/10.1016/B978-0-12-416641-7.00047-X Copyright © 2016 Elsevier Inc. All rights reserved.
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422 PART | II Named Essential Oils
FIGURE 1 Water-soaked methi, Trigonella foenum-graecum, seeds (processed by the second author and photographed by the first author).
USAGE AND APPLICATIONS Trigonella foenum-graecum seeds and green leaves, which are used in food as well as in medicinal application, is an old practice of human history. The fresh green leaves of T. foenum-graecum consumed as vegetables, dried seeds are used as spice in food preparation, and both leaves and seeds are used in flavoring foods in many countries including India; the seed constitutes an essential part of Bengali five-spice mixture panch foron that makes the food tasty and provide attractive flavor during preparation. The T. foenum-graecum seed can be cooked or sprouted and can even be eaten raw; the whole seeds are taken as an antacid and against dysentery and stomach disturbances. The T. foenum-graecum cold water extract, known as fenugreek tea, has been traditionally used against respiratory infections (bronchitis and pneumonia), and since it nourishes the body during illness, the herb has also been used to reduce fever, when taken with lemon and honey. Trigonella foenum-graecum has been shown to possess hypoglycemic, antihypertensive, and hypolipidemic activities (Micallef and Garg, 2009). Fenugreek also has a long history of use in the treatment of reproductive disorders, in inducing labor, treating hormonal disorders, increasing milk supply, and reducing menstrual pain. The plant has been known to have health potential with the ability to maintain blood glucose and cholesterol levels, and hence in the prevention and treatment of diabetes and heart disorders. Trigonella foenum-graecum has also been reported to exhibit pharmacological properties including antiviral, antimicrobial, hypotensive, antioxidant, antiinflammatory, and antitumor activity (Mullaicharam et al., 2013). Al-Oqail et al. (2013) demonstrated a decrease in the cell viability of cancerous cells exposed to seed oil of fenugreek.
USAGE AND APPLICATIONS IN FOOD SCIENCE Trigonella foenum-graecum oil possesses a pungent odor with bitter taste and is used as an insect repellent agent in order to protect food grains. The seeds, as spice, are essential ingredients in food preparation, and because of the presence of characteristic pungent aromatic compounds the seeds add flavor and color to the foods, especially curries and pickles, making them attractive and tasty. Fenugreek oil is used in flavoring canned food and syrups, such as artificial maple syrup, which is flavored with fenugreek seed extract since T. foenum-graecum odor imitates the maple syrup smell. Due to the presence of galactomannan gum in fenugreek seed, its extracts are used as a thickening agent in foods and as a food emulsifier. The fenugreek essential oils and extracts, as natural agents, are found to be very important in preserving foods due to their excellent antioxidant, antibacterial, and antifungal activities, and also in preparing foods as spices discussed below, including their chemistry and nutritional requirements.
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TABLE 1 Percentage of Carbohydrate, Protein, and Fat in Fenugreek Leaves and Seeds Plant Parts
Carbohydrate
Protein
Fat
References
Seed
62.48
28.55
4
Sulieman et al. (2008)
Seed
45−60
20–30
5−10
Mehrafarin et al. (2010)
Seed
42.3
9.5
7.5
Hemavathy and Prabhakar (1989)
Seed
42.3
25.4
7.9
Meghwal and Goswami (2012)
Leaf
6.6
4.4
0.9–1
Meghwal and Goswami (2012), Snehlata and Payal (2012)
Seed
−
20–30
6.53
Sheikhlar (2013)
Seed
44
24.7
7.6
Abdel Aal et al. (1985), Shankaracharya and Nalarjan (1973)
Seed
58
23−26
6−7
Lu et al. (2008)
Nutritional Value The edible part of T. foenum-graecum leaves contains moisture (86.1%), carbohydrate (6%), protein (4.4%), minerals (1.5%), fiber (1.1%), and fat (0.9%), while the contents of carbohydrate, protein, fat, fiber, and moisture in T. foenum-graecum seeds are 44.1, 26.2, 5.8, 7.2, and 13.7%, respectively (fenugreek oil: www.kazimaperfumers.com). Trigonella foenum-graecum seed is good source of protein, fat, and sugar; requirements of food types that can be obtained from T. foenum-graecum are represented in Table 1. Fenugreek is a natural source of minerals (Ca, P, Fe, Zn, and Mn) and vitamins such as A, B1, C, and nicotinic acid (Moradi kor and Moradi, 2013). It has been reported that fresh 100 g fenugreek leaves contain ascorbic acid of 220.97 mg and β-carotene of 19 mg (Meghwal and Goswami, 2012), while Srinivasan (2006) reported vitamin C, β-carotene, thiamine, riboflavin, nicotinic acid, and folic acid contents as 52 mg, 2.3 mg, 40 μg, 310 μg, 800 μg, 0 (zero) μm in leaves, and 43 mg, 96 μg, 340 μg, 290 μg, 1.1 mg, 84 μg in seeds, respectively. According to the report of Shakuntala et al. (2011), germinated endosperm, ungerminated endosperm, germinated sprouts, germinated seed coat, and ungerminated seed coat contain 39.25, 48.20, 36.12, 10.51, and 7.35% of protein, respectively, and 11.44, 12.26, 6.65, 1.75, and 1.22% of fat, respectively.
Antispoilage Activity Food-borne illness is an important public health problem, and outbreak of food-borne diseases is not uncommon (Sasidharan et al., 2011). Microorganisms, including different fungi and bacteria, cause spoilage of foods altering their color, texture, and odor, making them unfit for human consumption, such as souring of milk, fungal growth on bread, jam, and jelly, and rotting of fruits and vegetables. This type of spoilage is known as microbial spoilage of food. Food spoilage is also caused due to oxidation causing the destruction of vital biochemical compounds or the plant and animal cells or both. When oils and spices, including T. foenum-graecum, are added with salt and sugar to foods, they prevent growth of microorganisms in foods. Trigonella foenum-graecum has antibacterial, antifungal, and antioxidant properties and thus can effectively prevent the growth of microbial pathogens and help in food preservation. Thus, foodstuffs wrapped in the fenugreek-coated paper have their freshness preserved for long time because no pathogens such as bacteria and fungi can grow on their surface, and hence shelf life of the foods is protected. Hegazy (2011) reported that fenugreek seed flour when mixed into beef burger patties, instead of soybean flour, had effective antimicrobial properties and high antioxidant activity that help in preserving the food.
Antibacterial Activity Trigonella foenum-graecum oil possesses broad-spectrum antibacterial property against bacteria involved in food spoilage as well as food poisoning, and bacteria related to food-borne diseases of humans. The antibacterial activity of T. foenum-graecum seed oil (100%) has been determined in terms of zone diameter of inhibition (ZDI), and has been recorded as 10, 20, 15 mm for Staphylococcus aureus, Escherichia coli, and Salmonella typhimurium, respectively (Sulieman et al., 2008). It has been reported that the essential oil of T. foenum-graecum showed strong inhibition against S. aureus and Pseudomonas aeruginosa, and the inhibition was found to be concentration
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FIGURE 2 MIC of methanolic Trigonella foenum-graecum seed extract against clinical bacterial isolates (Dubey et al., 2010: text data converted). MIC: minimum inhibitory concentration.
dependent; the highest activity was noted at 100% (ZDI 24 and 22 mm for S. aureus and P. aeruginosa, respectively), and lowest activity was noted at 12.5% (ZDI 12 and 10 mm for S. aureus and P. aeruginosa, respectively) (Wagh et al., 2007). The five bacterial isolates Proteus, E. coli, S. aureus, P. aeruginosa, and Klebsiella pneumoniae were sensitive to essential oil of T. foenum-graecum (at 75% dilution), based upon the ZDI 9.3, 13, 11.67, 12.33, and 10.5 mm, respectively, for the isolates (Mehani and Segni, 2012). Dubey et al. (2010) determined ZDI of methanolic T. foenum-graecum seed extract for E. coli (16 mm), P. aeruginosa (16 mm), Enterobacter faecalis (12 mm), K. pneumonia (19 mm), Streptococcus facecalis (11 mm), S. aureus (14 mm), and Proteus mirabilis (10 mm); the minimum inhibitory concentrations (MICs) for the isolates ranged between 8 and 46 μg/mL (Figure 2). The MIC values of methanol T. foenum-graecum extract have been recorded as 64 μg/mL against Shigella dysenteriae, Salmonella typhi, and E. coli, and 32 μg/mL against Pseudomonas spp., while the MICs of acetone extract were 64 and 32 μg/mL against Pseudomonas spp. and S. dysenteriae, and 16 μg/mL against E. coli (Dash et al., 2011). The MIC of ethanolic T. foenum-graecum seed extract has been reported as 400 mg/mL for E. coli, S. typhi, Vibrio cholerae, S. aureus, and Bacillus subtilis (Khanra et al., 2010). Pooloth (2013) demonstrated the antimicrobial activity of silver nanoparticles synthesized with the help of T. foenum-graecum seed extract and the T. foenum-graecum seed aqueous extract against multidrug resistant gram positive (S. aureus, Str. pneumonia) and gram negative (P. aeruginosa, Pr. vulgaris) and found the nanoparticles thus synthesized as highly toxic to the test bacterial strains (Figure 3). Combinations like aqueous extract of cumin and fenugreek showed synergistic activity against Pr. vulgaris and additive effects against S. aureus, Bacillus cereus, and Aspergillus niger (Das et al., 2012). The bacterial isolates mentioned herein are associated with foodborne diseases, food poisoning in humans, and spoilage of food.
Antifungal Activity The importance of fenugreek seed and its oil as an antimicrobial agent to be used as a food preservative or in medical industries is known. The fenugreek seed oil completely inhibited the growth of A. niger, which can potentially cause black mold on fruits (Sulieman et al., 2008). Das et al. (2012) showed additive effect of aqueous extract of fenugreek in combination with cumin extract against A. niger. The T. foenum-graecum seed essential oil was found active against two potential human pathogens—A. niger and A. fumigatus—having ZDI 22 mm and 24 mm, respectively (at 100% concentration), while the activity was reduced at 12.5% showing ZDI 8 mm and 10 mm, respectively (Wagh et al., 2007). The post-harvest green mold from Penicillium digitatum infection is a universal disease that leads to the spoilage of almost all kinds of mature citrus fruits. Kanan and Al-Najar (2008) reported that the ZDI of ethanolic T. foenum-graecum seed extract (97 μg/mL) against P. digitatum isolates from spoiled citrus orange (Citrus sinensis L.), and lemon (Citrus limon L.) fruits ranged 38–41 mm, and the percent inhibition ranged 8.5–58.23 at concentrations 50−520 μg/mL, with IC50 value of 142 μg/mL (Figure 4). Kanan and Al-Najar (2009) reported that the extract of T. foenum-graecum seed (520 μg/mL) gave inhibition values 25.79–31.38% against four isolates of Penicillium italicum causing a universal post-harvest disease of citrus fruits (Prusky et al., 2004).
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FIGURE 3 ZDI for bacterial isolates due to the action of fenugreek extract (FGE) and silver nanoparticles (SNP) (Data table converted from Pooloth, 2013). ZDI: zone diameter of inhibition; FGE: fenugreek extract; SNP: silver nanoparticles synthesized with the help of T. foenum-graecum seed extract.
FIGURE 4 Antifungal activity of fenugreek seed extract (Kanan and Al-Najar, 2008; text data converted). FGHF: fenugreek hexane extract; FGMF: fenugreek methanol extract.
Antioxidant Activity Fenugreek can act as potent source of antioxidant, and such activity is due to the presence of polyphenols and flavonoids. The phenolic and flavonoid levels in the leaf extracts of T. foenum-graecum have been reported as 414 μmol/mL and 0.7 μg/mL, respectively (Joglekar et al., 2012). Premanath et al. (2011) determined the level of polyphenols (4.9 mg/g) in the ethanol extract of leaves with flavonoid content of 0.47 mg/g and a total antioxidant activity of 47 μM Fe (II)/g. Trigonella foenum-graecum that is used as food and in food preparation removes ions like copper, iron, and nickel and helps preserve foods because in their free state those ions increase oxidation of foods. The total phenolic content was determined as 1.35–6.85 mg/g of the fenugreek extract, which was highest in ethanol extract (6.85 mg/g) and lowest in hexane extract (1.35 mg/g); the flavonoid content of ethanol fenugreek seed extract was 653 and 208 μg/g in hexane extract (Bukhari et al., 2008).
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FIGURE 5 Polyphenolic contents in fenugreek seeds. (Shakuntala et al., 2011; text data converted).
The polyphenol content in fenugreek seeds, as has been reported by Shakuntala et al. (2011), is depicted in Figure 5, and the antioxidant activity (at 200 ppm extract concentrations) of seed coat, sprouts, and endosperm of germinated seed was determined as 79.87, 49.05, and 13.42%, respectively; the ungerminated seed coat and endosperm had 90.94 and 10.13% antioxidant activity.
Fenugreek Chemistry The biological and pharmacological actions of fenugreek are attributed to the variety of its constituents including steroids, polyphenolic substances, volatile constituents, amino acids, etc. (Mehrafarin et al., 2010). The T. foenum-graecum water extracts contain flavonoids, saponins, volatile oils, and phenolics; while methanol extracts contain flavonoids, saponins, alkaloids, phenolics, and volatile oils (Sheikhlar et al., 2013). Moradikor and Moradi (2013) documented that fenugreek seed contains alkaloids (trigonelline: 0.2–0.38%, choline: 0.5%), gentianine and carpaine, flavonoids (apigenin, luteolin, orientin, quercetin, vitexin, and isovitexin), free amino acids, (4-hydroxyisoleucine: 0.09%, arginine: histidine and lysine), saponins (0.6–1.7%), glycosides steroidal sapogenins (diosgenin, yamogenin, tigogenin, neotigogenin). Pande et al. (2011) reported that T. foenum-graecum had antifungal (against A. niger) and antibacterial (against S. aureus) activity that might be due to the constituents presented in Figure 6. Hamden et al. (2011) demonstrated identification of 13 compounds representing 97.2% of the total fenugreek essential oil (Figure 7). The galactomannans (fenugreek gum derived from the seed endosperm) are water-soluble polysaccharides, which are used as thickening, water holding, and emulsifying agents in food products (Brummer et al., 2003). Volatile constituents contribute to the aroma and flavor of fenugreek: anethol, an aromatic compound, occurs in fenugreek and produces a licorice-like aroma, and sotolone (3-hydroxy-4,5-dimethyl-2(5H)-furanone) has been recognized as the main constituent contributing to the flavor of fenugreek in foods.
SAFETY AND TOXICITY Fenugreek has gained “generally recognized as safe” status by the US Food and Drug Administration. Although it has conventionally been considered safe and well tolerated, toxic effects associated with its use are not uncommon, and some such cases include transient diarrhea, flatulence, mild hepatitis, and dizziness. It has also been considered as allergenic (Faeste et al., 2009), thus caution is warranted in persons allergic to fenugreek. Fenugreek showed antifertility activity
Fenugreek (Trigonella foenum-graecum L.) Oils Chapter | 47 427
FIGURE 6 Fenugreek volatile seed contents showing antimicrobial activity (Pande et al., 2011).
FIGURE 7 Chemical composition of fenugreek essential oil. (Hamden et al., 2011: data table partially converted to figure; http://www.lipidworld.com/ content/10/1/226).
in experimental rabbits (Kassem et al., 2006). Since T. foenum-graecum possesses glucose-lowering activity, its use by hypoglycemic individuals may lead to serious health problems if consumed without proper monitoring of blood glucose levels. Turner (2011, 2012) reported an outbreak of E. coli infection, which was spread by contaminated T. foenum-graecum sprouts, that swept across northern Germany infecting thousands and killing 53; E. coli strain O104 produces proteins that help it stick to food and to the human gut.
SUMMARY POINTS Methi (T. foenum-graecum) is a popular kitchen herb due to its unique aroma and benefits to human health. Methi seeds, which are bitter and aromatic, are important in having restorative and nutritive properties; its germinated endosperm is rich in protein and seed coat is rich in dietary fiber and unsaturated fatty acids. l Its seeds are used as a spice and the leaves are consumed as a green vegetable. l Methi endosperm contains high amounts of saponin and protein, while the husk contains high amounts of polyphenols and total dietary fiber. l l
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The essential oils and plant extracts are considered as potential alternatives to synthetic antimicrobials, and as a lead compound for nonantibiotic drugs. l Its extracts and oils provide a promising alternative to chemical preservatives, used in food products, because of the antimicrobial and antioxidative activities. l Sotolone (3-Hydrocy-4,5-dimethyl-2(5H)-furanone) present in fenugreek essential oil is the main reason for the characteristic strong odor of the plant that provides the sweet smell of curry/foods. l When plant oils and extracts are to be used in order to preserve foods, addressing the issues of safety and toxicity is required. l
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Pooloth, J., 2013. Biosynthesis of silver nanoparticles using Trigonella foenum-graecum and the determination of their antimicrobial activity. Intern. J. Sci. Res. 2, 287–290. Premanath, R., Sudisha, J., Aradhya, S.M., 2011. Antibacterial and antioxidant activities of fenugreek (Trigonella foenum-graecum L.) leaves. Res. J. Med. Plant 2. http://dx.doi.org/10.3923/rjmp.2011. Prusky, D., McEvoy, J.L., Saftner, R., Conway, W.S., Jones, R., 2004. Relationship between host acidification and virulence of Penicillium spp. on apple and citrus fruit. Biochem. Cell. Biol. 94, 44–51. Sasidharan, S., Prema, B., Yoga, L.L., 2011. Antimicrobial drug resistance of Staphylococcus aureus in dairy products. Asian Pac. J. Trop. Biomed. 1, 130–132. Shakuntala, S., Naik, J.P., Jeyarani, T., Naidu, M.M., Srinivas, P., 2011. Characterisation of germinated fenugreek (Trigonella foenum-graecum L.) seed fractions. Intern. J. Food Sci. Technol. 46, 2337–2343. Shankaracharya, N.B., Nalarjan, C.P., 1973. Chemical composition of raw and roasted fenugreek seeds. J. Food Sci. Technol. 10, 179–181. Sheikhlar, A., Alimon, A.R., Daud, H.M., Saad, C.R., Shanagi, H., 2013. Screening of Morus alba, Citrus limon and Trigonella foenum-graecum extracts for antimicrobial properties and phytochemical compounds. J. Biol. Sci. 13, 386–392. Sheikhlar, A., 2013. Trigonella foenum-graecum L. (Fenugreek) as a medicinal herb in animals growth and health. Sci. Int. 1, 194–198. Snehlata, H.S., Payal, D.R., 2012. Fenugreek (Trigonella foenum-graecum L.): an overview. Int. J. Curr. Pharm. Rev. Res. 2, 169–187. Srinivasan, K., 2006. Fenugreek (Trigonella foenum-graecum): a review of health beneficial physiological effects. Food Rev. Int. 22, 203–224. Sulieman, A.M.E., Ahmed, H.E., Abdelrahim, A.M., 2008. The chemical composition of fenugreek (Trigonella foenum-graceum L.) and the antimicrobial properties of its seed oil. Gezira J. Eng. Appl. Sci. 3, 52–71. Turner, M., 2011. Microbe outbreak panics Europe. Nature 474, 137. Turner, M., 2012. Reform falters after Europe’s E. coli scare. Nature 485, 559. Wagh, P., Rai, M., Deshmukh, S.K., Durate, M.C.T., 2007. Bio-activity of oils of Trigonella foenum-graecum and Pongamia pinnata. Afr. J. Biotechnol. 6, 1592–1596.
Fenugreek (Trigonella foenum-graecum L.) Oils Shyamapada Mandal1, Manisha DebMandal2 1University 2MGM
of Gour Banga, Laboratory of Microbiology and Experimental Medicine, Department of Zoology, Malda, West Bengal, India; Medical College and LSK Hospital, Department of Physiology, Kishanganj, Bihar, India
List of Abbreviations FGHF Fenugreek hexane extract FGMF Fenugreek methanol extract GRAS Generally recognized as safe MDR Multidrug resistant MIC Minimum inhibitory concentration ZDI Zone diameter of inhibition SNP Silver nanoparticles synthesized with the help of T. foenum-graecum seed extract TFSE T. foenum-graecum seed extract
INTRODUCTION Fenugreek (Greek hay), also called methi in Bengali (Trigonella foenum-graecum; diploid with 2n = 16)—an aromatic leguminous plant—is an important spice and has been commonly used as a traditional food and medicine; the dried seeds of the plant have extensive application in foods and beverages as a flavoring additive. The plant is native to many Asian, Middle Eastern, and European countries, and India being the leading producer of fenugreek is recognized as the major consumer for its culinary usage and medicinal application. In Ayurveda, both fenugreek seeds and leaves are used to prepare extracts or powders for medicinal use. The physicochemical characteristics of fenugreek seed oil such as acid value (4.75; mg KOH/g of oil), saponification value (195; mg KOH/g of oil), ester value of 190.25, free fatty acids content (2.38; Oleic acid/100 g oil), and the refractive index of 1.464 indicate fenugreek seed oil as an edible oil, if its characteristic pungent odor is minimized (Sulieman et al., 2008). The fenugreek protein fraction is found to be lysine-rich and comparable in quality to that of soybean protein, and hence seeds are used as food and offer a superlative nutritional profile.
BOTANICAL ASPECTS Fenugreek, also called Greek hay, belongs to the subfamily Papilionaceae of the family Leguminosae (bean family, Fabaceae). Fenugreek is cultivated all over the world as a semiarid crop. The yields can be significantly augmented in quantity and quality through suitable management of cultivation, irrigation, harvesting, and pest management. Fenugreek is a self-pollinating annual leguminous bean, and seeds sown in well-prepared soil sprout in 3 days; the plants mature in about 4 months and attain a height of 30–60 cm. In this plant, flowering starts after 30–40 days of sawing. The plant has compound pinnate, trifoliate leaves, white to yellow axillary flowers, and 10–15-cm-long thin pointed hoop-like beaked pods (Meghwal and Goswami, 2012) each carrying 10–20 seeds (Figure 1). Trigonella foenum-graecum seeds are small (5 mm long), hard, yellowish brown and angular, and are flattened with a characteristic oblong rhomboidal outline (Moradi kor and Moradi, 2013; Mullaicharam et al., 2013). The seed holds a central hard yellow embryo bounded by a large corneous white and semi-transparent endosperm (Betty, 2008).
Essential Oils in Food Preservation, Flavor and Safety. http://dx.doi.org/10.1016/B978-0-12-416641-7.00047-X Copyright © 2016 Elsevier Inc. All rights reserved.
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FIGURE 1 Water-soaked methi, Trigonella foenum-graecum, seeds (processed by the second author and photographed by the first author).
USAGE AND APPLICATIONS Trigonella foenum-graecum seeds and green leaves, which are used in food as well as in medicinal application, is an old practice of human history. The fresh green leaves of T. foenum-graecum consumed as vegetables, dried seeds are used as spice in food preparation, and both leaves and seeds are used in flavoring foods in many countries including India; the seed constitutes an essential part of Bengali five-spice mixture panch foron that makes the food tasty and provide attractive flavor during preparation. The T. foenum-graecum seed can be cooked or sprouted and can even be eaten raw; the whole seeds are taken as an antacid and against dysentery and stomach disturbances. The T. foenum-graecum cold water extract, known as fenugreek tea, has been traditionally used against respiratory infections (bronchitis and pneumonia), and since it nourishes the body during illness, the herb has also been used to reduce fever, when taken with lemon and honey. Trigonella foenum-graecum has been shown to possess hypoglycemic, antihypertensive, and hypolipidemic activities (Micallef and Garg, 2009). Fenugreek also has a long history of use in the treatment of reproductive disorders, in inducing labor, treating hormonal disorders, increasing milk supply, and reducing menstrual pain. The plant has been known to have health potential with the ability to maintain blood glucose and cholesterol levels, and hence in the prevention and treatment of diabetes and heart disorders. Trigonella foenum-graecum has also been reported to exhibit pharmacological properties including antiviral, antimicrobial, hypotensive, antioxidant, antiinflammatory, and antitumor activity (Mullaicharam et al., 2013). Al-Oqail et al. (2013) demonstrated a decrease in the cell viability of cancerous cells exposed to seed oil of fenugreek.
USAGE AND APPLICATIONS IN FOOD SCIENCE Trigonella foenum-graecum oil possesses a pungent odor with bitter taste and is used as an insect repellent agent in order to protect food grains. The seeds, as spice, are essential ingredients in food preparation, and because of the presence of characteristic pungent aromatic compounds the seeds add flavor and color to the foods, especially curries and pickles, making them attractive and tasty. Fenugreek oil is used in flavoring canned food and syrups, such as artificial maple syrup, which is flavored with fenugreek seed extract since T. foenum-graecum odor imitates the maple syrup smell. Due to the presence of galactomannan gum in fenugreek seed, its extracts are used as a thickening agent in foods and as a food emulsifier. The fenugreek essential oils and extracts, as natural agents, are found to be very important in preserving foods due to their excellent antioxidant, antibacterial, and antifungal activities, and also in preparing foods as spices discussed below, including their chemistry and nutritional requirements.
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TABLE 1 Percentage of Carbohydrate, Protein, and Fat in Fenugreek Leaves and Seeds Plant Parts
Carbohydrate
Protein
Fat
References
Seed
62.48
28.55
4
Sulieman et al. (2008)
Seed
45−60
20–30
5−10
Mehrafarin et al. (2010)
Seed
42.3
9.5
7.5
Hemavathy and Prabhakar (1989)
Seed
42.3
25.4
7.9
Meghwal and Goswami (2012)
Leaf
6.6
4.4
0.9–1
Meghwal and Goswami (2012), Snehlata and Payal (2012)
Seed
−
20–30
6.53
Sheikhlar (2013)
Seed
44
24.7
7.6
Abdel Aal et al. (1985), Shankaracharya and Nalarjan (1973)
Seed
58
23−26
6−7
Lu et al. (2008)
Nutritional Value The edible part of T. foenum-graecum leaves contains moisture (86.1%), carbohydrate (6%), protein (4.4%), minerals (1.5%), fiber (1.1%), and fat (0.9%), while the contents of carbohydrate, protein, fat, fiber, and moisture in T. foenum-graecum seeds are 44.1, 26.2, 5.8, 7.2, and 13.7%, respectively (fenugreek oil: www.kazimaperfumers.com). Trigonella foenum-graecum seed is good source of protein, fat, and sugar; requirements of food types that can be obtained from T. foenum-graecum are represented in Table 1. Fenugreek is a natural source of minerals (Ca, P, Fe, Zn, and Mn) and vitamins such as A, B1, C, and nicotinic acid (Moradi kor and Moradi, 2013). It has been reported that fresh 100 g fenugreek leaves contain ascorbic acid of 220.97 mg and β-carotene of 19 mg (Meghwal and Goswami, 2012), while Srinivasan (2006) reported vitamin C, β-carotene, thiamine, riboflavin, nicotinic acid, and folic acid contents as 52 mg, 2.3 mg, 40 μg, 310 μg, 800 μg, 0 (zero) μm in leaves, and 43 mg, 96 μg, 340 μg, 290 μg, 1.1 mg, 84 μg in seeds, respectively. According to the report of Shakuntala et al. (2011), germinated endosperm, ungerminated endosperm, germinated sprouts, germinated seed coat, and ungerminated seed coat contain 39.25, 48.20, 36.12, 10.51, and 7.35% of protein, respectively, and 11.44, 12.26, 6.65, 1.75, and 1.22% of fat, respectively.
Antispoilage Activity Food-borne illness is an important public health problem, and outbreak of food-borne diseases is not uncommon (Sasidharan et al., 2011). Microorganisms, including different fungi and bacteria, cause spoilage of foods altering their color, texture, and odor, making them unfit for human consumption, such as souring of milk, fungal growth on bread, jam, and jelly, and rotting of fruits and vegetables. This type of spoilage is known as microbial spoilage of food. Food spoilage is also caused due to oxidation causing the destruction of vital biochemical compounds or the plant and animal cells or both. When oils and spices, including T. foenum-graecum, are added with salt and sugar to foods, they prevent growth of microorganisms in foods. Trigonella foenum-graecum has antibacterial, antifungal, and antioxidant properties and thus can effectively prevent the growth of microbial pathogens and help in food preservation. Thus, foodstuffs wrapped in the fenugreek-coated paper have their freshness preserved for long time because no pathogens such as bacteria and fungi can grow on their surface, and hence shelf life of the foods is protected. Hegazy (2011) reported that fenugreek seed flour when mixed into beef burger patties, instead of soybean flour, had effective antimicrobial properties and high antioxidant activity that help in preserving the food.
Antibacterial Activity Trigonella foenum-graecum oil possesses broad-spectrum antibacterial property against bacteria involved in food spoilage as well as food poisoning, and bacteria related to food-borne diseases of humans. The antibacterial activity of T. foenum-graecum seed oil (100%) has been determined in terms of zone diameter of inhibition (ZDI), and has been recorded as 10, 20, 15 mm for Staphylococcus aureus, Escherichia coli, and Salmonella typhimurium, respectively (Sulieman et al., 2008). It has been reported that the essential oil of T. foenum-graecum showed strong inhibition against S. aureus and Pseudomonas aeruginosa, and the inhibition was found to be concentration
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FIGURE 2 MIC of methanolic Trigonella foenum-graecum seed extract against clinical bacterial isolates (Dubey et al., 2010: text data converted). MIC: minimum inhibitory concentration.
dependent; the highest activity was noted at 100% (ZDI 24 and 22 mm for S. aureus and P. aeruginosa, respectively), and lowest activity was noted at 12.5% (ZDI 12 and 10 mm for S. aureus and P. aeruginosa, respectively) (Wagh et al., 2007). The five bacterial isolates Proteus, E. coli, S. aureus, P. aeruginosa, and Klebsiella pneumoniae were sensitive to essential oil of T. foenum-graecum (at 75% dilution), based upon the ZDI 9.3, 13, 11.67, 12.33, and 10.5 mm, respectively, for the isolates (Mehani and Segni, 2012). Dubey et al. (2010) determined ZDI of methanolic T. foenum-graecum seed extract for E. coli (16 mm), P. aeruginosa (16 mm), Enterobacter faecalis (12 mm), K. pneumonia (19 mm), Streptococcus facecalis (11 mm), S. aureus (14 mm), and Proteus mirabilis (10 mm); the minimum inhibitory concentrations (MICs) for the isolates ranged between 8 and 46 μg/mL (Figure 2). The MIC values of methanol T. foenum-graecum extract have been recorded as 64 μg/mL against Shigella dysenteriae, Salmonella typhi, and E. coli, and 32 μg/mL against Pseudomonas spp., while the MICs of acetone extract were 64 and 32 μg/mL against Pseudomonas spp. and S. dysenteriae, and 16 μg/mL against E. coli (Dash et al., 2011). The MIC of ethanolic T. foenum-graecum seed extract has been reported as 400 mg/mL for E. coli, S. typhi, Vibrio cholerae, S. aureus, and Bacillus subtilis (Khanra et al., 2010). Pooloth (2013) demonstrated the antimicrobial activity of silver nanoparticles synthesized with the help of T. foenum-graecum seed extract and the T. foenum-graecum seed aqueous extract against multidrug resistant gram positive (S. aureus, Str. pneumonia) and gram negative (P. aeruginosa, Pr. vulgaris) and found the nanoparticles thus synthesized as highly toxic to the test bacterial strains (Figure 3). Combinations like aqueous extract of cumin and fenugreek showed synergistic activity against Pr. vulgaris and additive effects against S. aureus, Bacillus cereus, and Aspergillus niger (Das et al., 2012). The bacterial isolates mentioned herein are associated with foodborne diseases, food poisoning in humans, and spoilage of food.
Antifungal Activity The importance of fenugreek seed and its oil as an antimicrobial agent to be used as a food preservative or in medical industries is known. The fenugreek seed oil completely inhibited the growth of A. niger, which can potentially cause black mold on fruits (Sulieman et al., 2008). Das et al. (2012) showed additive effect of aqueous extract of fenugreek in combination with cumin extract against A. niger. The T. foenum-graecum seed essential oil was found active against two potential human pathogens—A. niger and A. fumigatus—having ZDI 22 mm and 24 mm, respectively (at 100% concentration), while the activity was reduced at 12.5% showing ZDI 8 mm and 10 mm, respectively (Wagh et al., 2007). The post-harvest green mold from Penicillium digitatum infection is a universal disease that leads to the spoilage of almost all kinds of mature citrus fruits. Kanan and Al-Najar (2008) reported that the ZDI of ethanolic T. foenum-graecum seed extract (97 μg/mL) against P. digitatum isolates from spoiled citrus orange (Citrus sinensis L.), and lemon (Citrus limon L.) fruits ranged 38–41 mm, and the percent inhibition ranged 8.5–58.23 at concentrations 50−520 μg/mL, with IC50 value of 142 μg/mL (Figure 4). Kanan and Al-Najar (2009) reported that the extract of T. foenum-graecum seed (520 μg/mL) gave inhibition values 25.79–31.38% against four isolates of Penicillium italicum causing a universal post-harvest disease of citrus fruits (Prusky et al., 2004).
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FIGURE 3 ZDI for bacterial isolates due to the action of fenugreek extract (FGE) and silver nanoparticles (SNP) (Data table converted from Pooloth, 2013). ZDI: zone diameter of inhibition; FGE: fenugreek extract; SNP: silver nanoparticles synthesized with the help of T. foenum-graecum seed extract.
FIGURE 4 Antifungal activity of fenugreek seed extract (Kanan and Al-Najar, 2008; text data converted). FGHF: fenugreek hexane extract; FGMF: fenugreek methanol extract.
Antioxidant Activity Fenugreek can act as potent source of antioxidant, and such activity is due to the presence of polyphenols and flavonoids. The phenolic and flavonoid levels in the leaf extracts of T. foenum-graecum have been reported as 414 μmol/mL and 0.7 μg/mL, respectively (Joglekar et al., 2012). Premanath et al. (2011) determined the level of polyphenols (4.9 mg/g) in the ethanol extract of leaves with flavonoid content of 0.47 mg/g and a total antioxidant activity of 47 μM Fe (II)/g. Trigonella foenum-graecum that is used as food and in food preparation removes ions like copper, iron, and nickel and helps preserve foods because in their free state those ions increase oxidation of foods. The total phenolic content was determined as 1.35–6.85 mg/g of the fenugreek extract, which was highest in ethanol extract (6.85 mg/g) and lowest in hexane extract (1.35 mg/g); the flavonoid content of ethanol fenugreek seed extract was 653 and 208 μg/g in hexane extract (Bukhari et al., 2008).
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FIGURE 5 Polyphenolic contents in fenugreek seeds. (Shakuntala et al., 2011; text data converted).
The polyphenol content in fenugreek seeds, as has been reported by Shakuntala et al. (2011), is depicted in Figure 5, and the antioxidant activity (at 200 ppm extract concentrations) of seed coat, sprouts, and endosperm of germinated seed was determined as 79.87, 49.05, and 13.42%, respectively; the ungerminated seed coat and endosperm had 90.94 and 10.13% antioxidant activity.
Fenugreek Chemistry The biological and pharmacological actions of fenugreek are attributed to the variety of its constituents including steroids, polyphenolic substances, volatile constituents, amino acids, etc. (Mehrafarin et al., 2010). The T. foenum-graecum water extracts contain flavonoids, saponins, volatile oils, and phenolics; while methanol extracts contain flavonoids, saponins, alkaloids, phenolics, and volatile oils (Sheikhlar et al., 2013). Moradikor and Moradi (2013) documented that fenugreek seed contains alkaloids (trigonelline: 0.2–0.38%, choline: 0.5%), gentianine and carpaine, flavonoids (apigenin, luteolin, orientin, quercetin, vitexin, and isovitexin), free amino acids, (4-hydroxyisoleucine: 0.09%, arginine: histidine and lysine), saponins (0.6–1.7%), glycosides steroidal sapogenins (diosgenin, yamogenin, tigogenin, neotigogenin). Pande et al. (2011) reported that T. foenum-graecum had antifungal (against A. niger) and antibacterial (against S. aureus) activity that might be due to the constituents presented in Figure 6. Hamden et al. (2011) demonstrated identification of 13 compounds representing 97.2% of the total fenugreek essential oil (Figure 7). The galactomannans (fenugreek gum derived from the seed endosperm) are water-soluble polysaccharides, which are used as thickening, water holding, and emulsifying agents in food products (Brummer et al., 2003). Volatile constituents contribute to the aroma and flavor of fenugreek: anethol, an aromatic compound, occurs in fenugreek and produces a licorice-like aroma, and sotolone (3-hydroxy-4,5-dimethyl-2(5H)-furanone) has been recognized as the main constituent contributing to the flavor of fenugreek in foods.
SAFETY AND TOXICITY Fenugreek has gained “generally recognized as safe” status by the US Food and Drug Administration. Although it has conventionally been considered safe and well tolerated, toxic effects associated with its use are not uncommon, and some such cases include transient diarrhea, flatulence, mild hepatitis, and dizziness. It has also been considered as allergenic (Faeste et al., 2009), thus caution is warranted in persons allergic to fenugreek. Fenugreek showed antifertility activity
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FIGURE 6 Fenugreek volatile seed contents showing antimicrobial activity (Pande et al., 2011).
FIGURE 7 Chemical composition of fenugreek essential oil. (Hamden et al., 2011: data table partially converted to figure; http://www.lipidworld.com/ content/10/1/226).
in experimental rabbits (Kassem et al., 2006). Since T. foenum-graecum possesses glucose-lowering activity, its use by hypoglycemic individuals may lead to serious health problems if consumed without proper monitoring of blood glucose levels. Turner (2011, 2012) reported an outbreak of E. coli infection, which was spread by contaminated T. foenum-graecum sprouts, that swept across northern Germany infecting thousands and killing 53; E. coli strain O104 produces proteins that help it stick to food and to the human gut.
SUMMARY POINTS Methi (T. foenum-graecum) is a popular kitchen herb due to its unique aroma and benefits to human health. Methi seeds, which are bitter and aromatic, are important in having restorative and nutritive properties; its germinated endosperm is rich in protein and seed coat is rich in dietary fiber and unsaturated fatty acids. l Its seeds are used as a spice and the leaves are consumed as a green vegetable. l Methi endosperm contains high amounts of saponin and protein, while the husk contains high amounts of polyphenols and total dietary fiber. l l
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The essential oils and plant extracts are considered as potential alternatives to synthetic antimicrobials, and as a lead compound for nonantibiotic drugs. l Its extracts and oils provide a promising alternative to chemical preservatives, used in food products, because of the antimicrobial and antioxidative activities. l Sotolone (3-Hydrocy-4,5-dimethyl-2(5H)-furanone) present in fenugreek essential oil is the main reason for the characteristic strong odor of the plant that provides the sweet smell of curry/foods. l When plant oils and extracts are to be used in order to preserve foods, addressing the issues of safety and toxicity is required. l
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