Effect of Soaking and Germination on Nutrient and Antinutrient Contents of Fenugreek (trigonella Foenum Graecum L.)

Fenugreek seeds (raw, soaked and germinated) were analyzed for their chemical composition. Raw fenugreek seeds contained higher amount of dietary jiber 46.50% followed by 42.12% in soaked seeds and 32.50% in germinated seeds. Soaking reduced the level of total soluble sugars, reducing sugars, nonreducing sugars, dietary fiber and improved the protein and starch digestibility and availability of minerals. Germinated fenugreek seeds had significantly higher contents of total protein (29%) and total lysine (6.48 g/ 100 g protein) compared to unprocessed seeds. Germination decreased dietary fiber and starch thereby raising the level of sugars. In vitro starch and protein digestibility and availability of Ca, Fe and Zn were also increased appreciably due to reduction in antinutrient contents (phytic acid and polyphenols) afer 48 h germination. INTRODUCTION Fenugreek (Trigonella foenum-graecum L.) is undoubtedly one of the oldest cultivated medicinal plants. It is an erect annual herb native to Southern Europe and Asia, belonging to the family Leguminosae. Over 80% of the total world's production of this seed is contributed by India, one of the major producers and exporters of fenugreek legume in the world. The seeds are known to have hypoglycemic (Neeraja and Rajyalakshmi 1996; Shashi Kaia 1997) and hypocholesterolemic (Khosla et al. 1995) properties. Fenugreek seeds can be a good supplement to cereals because of its ' Corresponding Author: Department of Foods and Nunition, CCS Haryana Agricultural University, Hisar-125 004, India. FAX: 0091 1662 34952, EMAIL: [email protected] Journal of Food Biochemistry 27 (2003) 165-176. All Rights Reserved. Vbpyright 2003 by Food & Nutrition Press, Inc., Trumbull, Connecticut. 165 166 S . HOODA and S . JOOD high protein (25%), lysine (5.7 g116 g N), soluble (20%) and insoluble (28%) dietary fiber besides being rich in calcium, iron and beta-carotene (NIN 1987). Various traditional recipes of North India namely Laddo, Methi, Suhali, etc. prepared from wheat-fenugreek blends, mainly consumed by the diabetic and hypercholesterolemic people (Sharma 1986; Shashi Kala 1997). However, the seeds are bitter in taste due to presence of bitter saponins, which limit their acceptability in foods (Sharma 1986; Udayasekhera and Sharma 1987). It has been possible to debitter fenugreek seeds by employing various processing methods such as soaking, germination, roasting, etc. (Sharma 1986; Shashi Kala 1997). As fenugreek seeds are rich in mucilaginous fiber and other dietary essentials, their use can be exploited as functional and nutritional foods as well as therapeutic agent. By keeping these facts in view various value-added baked and extruded products from wheat-fenugreek flour blends have been developed. Organoleptic (taste, flavor, color, texture, etc.) and nutritional characteristics have also been studied (Hooda 2002). This paper reports the effect of processing methods include soaking and germination on nutrients, in vitro digestibility, in vitro availability and antinutrient contents of fenugreek seeds. MATERIALS AND METHODS Materials The fenugreek seeds of Pusa early bunching variety were obtained from the Department of Plant Breeding, CCS Haryana Agricultural University, Hisar, India. Processing Soaking. Fenugreek seeds were first cleaned and freed from broken seeds, dust and other foreign materials and then soaked in tap water for 12 h at 37C. A seed to water ratio of 1:5 (w/v) was used. The unimbibed water was discarded. The soaked seeds were rinsed twice in distilled water and then dried at 55-6OC. Germination. The soaked seeds were germinated in sterile petri dishes lined with wet filter paper for 48 h at 37C with frequent watering. The sprouts were rinsed in distilled water and dried at 55-60C. The dried samples of raw, soaked and germinated seeds were ground to fine powder in an electric grinder and then stored in plastic containers for further use. EFFECT OF SOAKING AND GERMINATION ON FENUGREEK 167 Chemical Analysis Proximate Composition and Total Lysine. The treated and untreated samples were analyzed for moisture, protein, fat, ash and crude fiber by adopting standard methods (AOAC 1995). Total carbohydrate was calculated by subtraction from 100. Total lysine was estimated as per the method described by Miyahara and Jikoo (1967). Sugars, Dietary Fiber and Starch Digestibility. Total soluble sugars were extracted by refluxing in 80% ethanol (Cerning and Guilbot 1973). Quantitative determination of total soluble sugars was carried out according to the colorimetric method (Yemm and Willis 1954). Reducing sugars were estimated by Somogyi’s modified method (Somogyi 1945). Nonreducing sugars were determined by calculating the difference between total soluble sugars and reducing sugars. Total, soluble and insoluble dietary fiber constituents were determined by the enzymatic method given by Furda (1981). In v i m starch digestibility was assessed by employing pancreatic amylase and incubating at 37C for 2 h. Liberated maltose was measured colorimetrically by using dinitrosalicylic acid reagent (Singh et al. 1982). Total and Available Minerals. Calcium, iron and zinc in acid digested samples were determined by Atomic Absorption Spectrophotometer 2380, Perkin Elmer (Shelton, Conn.) according to the method of Lindsey and Norwell (1969). Available calcium and zinc were extracted by the method of Kim and Zemel (1986). Ionizable iron in the samples was extracted according to the procedure of Rao and Prabhavathi (1978). Ionizable iron was determined as described by AOAC (1995). Protein Digestibility. Protein digestibility (in vitro) was assessed by employing pepsin and pancreatin (Akeson and Stahmann 1964). The nitrogen contents of the sample and the undigested residue were determined by the microkjeldahl method (AOAC 1995). The digested protein of the sample was calculated by subtracting residual protein from total protein of the sample. Digested protein Total protein Protein digestibility (%) = Antinutritional Factors. Phytic acid was determined by the method of Haug and Lantzsch (1983). Total polyphenols were extracted by the method of Singh and Jambunathan (1981), and estimated as tannic acid equivalent according to Folin-Denis procedure (Swain and Hills 1959). 168 S. HOODA and S. JOOD RESULTS AND DISCUSSION Moisture content of unprocessed (raw) fenugreek flour increased from 13.70 to 14.20%, respectively on dry weight basis (Table 1). There was significant (P<0.05) increase in protein (25.90 to 29.00%) in germinated fenugreek flour. This might be due to reduction of seed nitrates into plant protein or ammonium compounds during germination (Youngs and Varner 1959), crude fiber (6.88 to 9.42%) and ash (2.88 to 3.15%) contents, respectively in raw, soaked and germinated fenugreek flour. However, crude fat decreased by about 22% of the original amount on germination. These changes agree with those mentioned by El-Mahdy and EL-Sebaiy (1983) for germinated fenugreek seeds. Carbohydrate contents of fenugreek flour ranged from 43.74 to 38.83%, respectively in raw, soaked and germinated fenugreek seed flour. Fenugreek seeds are very rich source of lysine, which are comparable with the egg protein (FA