EFFECT OF DOMESTIC PROCESSING AND COOKING METHODS ON SOME ANTINUTRITIONAL FACTORS OF MOTH BEAN

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1 J. Dairying, Foods & H.S., 27 (2) : , 2008 EFFECT OF DOMESTIC PROCESSING AND COOKING METHODS ON SOME ANTINUTRITIONAL FACTORS OF MOTH BEAN Anju Negi, P. Boora and N. Khetarpaul Department of Foods and Nutrition, CCS Haryana Agricultural University, Hisar , India ABSTRACT Effect of soaking ( 12 h), soaking-dehulling, germination (60 h), pressure cooking and microwave cooking on antinutritional factors on four varieties of moth bean i.e. one local variety commonly used by the farmers and three newly released high yielding varieties namely Jwala, RMO 225 and RMO 257, were studied. All the four varieties differed significantly in phytic acid, polyphenol content and trypsin inhibitor activity. The newly evolved varieties had lower levels of antinutritional factors than local. The domestic processing and cooking methods like soaking, dehulling and germination, pressure-cooking and microwave cooking reduced the level of antinutritional factors to varying extent. Germination had marked lowering effect on the level of phytic acid and polyphenol content and pressure-cooking and microwave cooking on trypsin inhibitor activity. INTRODUCTION Moth bean [Vigna aconitifolia (Jacq) Marechal] is one of the major pulse crop of the semi-arid regions of India. Because of its drought tolerance and hardiness, it is major pulse crop for the semi-arid tropics. The grains of moth bean are used as human food whereas plants make quality forage. Moth bean is rich source of protein, digestible carbohydrates, minerals and exhibits fairly high levels of crude lipids. But like other plant foods, their utilization for human nutrition is limited due to the presence of antinutritional factors. Phytic acid lowers the bioavailability of minerals (Ali and Harnald, 1991) and inhibits proteases and amylases (Deshpande and Cheryen, 1984). Polyphenols decrease the digestibility of carbohydrates and proteins and the availability of vitamins and minerals (Rao and Deosthale, 1982) and interact with protein to make them insoluble (Singh, 1984). Trypsin inhibitor disrupts digestive process and may lead to other undesirable physiological reactions. In India, grain legumes are processed and consumed in a variety of forms. The various domestic processing and cooking methods including soaking, dehulling, sprouting, ordinary cooking, pressure cooking and fermentation may bring about changes in antinutritional factors. The present investigation was carried out to determine the extent to which domestic processing and cooking methods affect the antinutritional factors of moth bean. MATERIAL AND METHODS Material : The seeds of four varieties of moth bean, Local, Jawla, RMO 225 and RMO 257, were procured from the Department of Plant Breeding, Haryana Agricultural University, Hisar, India. Processing and cooking methods : 1. Soaking : Seeds were soaked in D.W. for 12 h at room temperature (30 0 C), using seed to water ratio of 1:4. 2. Dehulling : Soaked seed (12 h) were dehulled manually. 3. Germination : Soaked seeds (12 h) were kept in trays lined with wet filter paper for 60 hrs at room temperature 30 0 C. The seeds were kept moist by sprinkling distilled water frequently. 4. Pressure cooking : The unsoaked, soaked and dehulled seeds were pressure cooked using the seed to-water ratio for unsoaked seeds 1:3 (w/v) for 15 min, for soaked 1:2 (w/v) 10 min and for soakeddehulled 1:1 (w/v) 5 min.

2 Vol. 27, No. 2, Microwave cooking: Unsoaked, soaked and soaked-dehulled seeds were cooked in microwave oven with seed to water ratio of 1:3, 1:2 and 1:1, respectively. All the processed and unprocessed samples were dried in hot air oven at 60 0 C to a constant weight. Dried samples were ground to a fine powder to pass through 0.5 mm mesh size and stored in air tight plastic container for further analysis. Chemical Analysis : Phytic acid content was determined by the method of Davies and Reid (1979). The polyphenolic compounds were extracted by the method of Singh and Jambunathan (1981) and were estimated as tannic acid equivalent according to Folin-Denis procedure (Swain and Hills, 1959). Trypsin inhibitor activity was determined by the modified method for Roy and Rao (1971). Statistical Analysis : The data obtained were subjected to statistical analysis using completely randomized design (C.R.D.) (Panse and Sukhatme, 1961). RESULTS AND DISCUSSION Phytic Acid : The phytic acid content differed significantly from to mg/100g among all the four varieties of moth bean, with Jwala having lowest and Local having highest phytic acid content (Table 1). A wide variation for phytic acid content of different varieties was observed by different workers (Khokhar and Chauhan 1986, Vijayakumari et al. 1998). Soaking (12 h) as well as dehulling of soaked seeds significantly lowered down the phytic acid content of all the four varieties of moth bean. Phytic acid decreased by % when seeds of mothbean were soaked for 12 h. (Table 1). When the soaked seeds were dehulled, the losses were higher and ranged from 16 to 18 per cent. The loss in phytic acid after soaking may be due to leaching of phytate ions into the soaking water under the influence of concentration gradient. Similar results for reduction in phytic acid content of soaked legumes were also reported (Kaur and Kapoor, 1990, Velverde et al. 1994). Soaking for 12 h followed by germination for 60 h; lowered phytic acid content by 66 to 68 per cent (Table 1). Loss of phytic acid during germination may be attributed to hydrolytic activity of phytase. Earlier workers have also reported diminished amounts of phytic acid in germinated legumes (Khokar and Chauhan, 1986, Sharma and Sehgal, 1992b, Bishnoi et al. 1994). Pressure cooking of unsoaked, soaked as well as soaked-dehulled moth beans brought about a significant reduction in the phytic acid content of all the four varieties of moth bean when compared to unprocessed seed (Table 1). Pressure cooking of unsoaked seeds reduced the phytic acid content by 20 to 22 per cent, soaking of seeds prior to pressure cooking further reduced the phytic acid content by 28 to 30 per cent. Pressure cooking of soaked-dehulled seeds resulted in about 40 to 42 per cent reduction in phytic acid content. Microwave cooking caused more pronounced effect than pressure cooking in reducing phytic acid content. Microwave cooking of unsoaked, soaked, and soaked-dehulled seeds brought about 22 to 26, 32 to 35 and 43 to 45 per cent losses in phytic acid content, respectively. The apparent decrease observed in phytic acid content due to cooking may be attributed to the formation of insoluble complexes between phytic acid and other components (Kumar et al. 1978). Similar decline in phytic acid content in heat treated samples of legumes have been reported earlier (Khalil and Mansour, 1995; Chau and Cheung, 1997). Polyphenols : The polyphenolic content of raw unprocessed sample was found to differ significantly from to mg/100g (Table 2). Jwala had the highest polyphenolic content followed by Local, RMO 225 and RMO 257.

3 116 J. DAIRYING, FOODS & H.S. Table 1. Effect of processing and cooking on phytic acid content (mg/100g) of moth bean (on dry matter basis) Treatment Variety Local Jwala RMO 225 RMO 257 Unprocessed ± ± ± ±0.28 Processing Soaked (12h) ±0.19(-11) ±0.06(-10) ±0.02(-11) ±0.28(-10) Soaked & dehulled ±0.04(-16) ±0.05(-17) ±0.08(-16) ±0.02(-18) Germination (60h) ±0.19(-68) ±0.19(-67) ±0.20(-66) ±0.24(-68) Pressure cooking Unsoaked ±0.23(-20) ±0.10(-20) (0.08(-21) ±0.34(-22) Soaked ±0.21(-30) ±0.27(-28) ±0.25(-31) ±0.17(-29) Soaked & dehulled ±0.15(-42) ±0.08(-42) ±0.07(-40) ±0.08(-41) Microwave cooking Unsoaked ±0.25(-25) ±0.05(-22) ±0.12(-26) ±0.28(-23) Soaked ±0.07(-32) ±0.11(-33) ±0.02(-35) ±0.16(-32) Soaked & dehulled ±0.08(-43) ±0.24(-45) ±0.07(-45) ±0.12(-43) Values are mean ± SD of three independent determinations Significant at 5% level of significant CD for variety 0.46 Treatment 0.74 Interaction 1.47 Figures in parentheses indicate percent decrease (-) over control values Soaking of moth bean (12 h) resulted in marked reduction in polyphenol content i.e. from 21 to 29 per cent (Table 2). Dehulling of soaked seeds had the prounduced effect on the reduction of polyphenols. After dehulling of soaked seeds, 70 to 78 per cent reductions in polyphenol content were observed. Since polyphenolic compounds are present in the periphery of the grain, their passing out into the soaking medium through seed coat is possible. Similar results have been obtained by previous workers in different legumes (Kaur and Kapoor, 1990; Bishnoi et al. 1994). Germination also had a lowering effect in polyphenol content of all the four varieties of moth bean (Table 2). After 60 h germination, reduction of 70 per cent in polyphenol content of all the four varieties of moth bean was observed. The loss of polyphenols during sprouting may be attributed to the presence of polyphenol oxidases and enzymatic hydrolyses. Some of the losses may also be expected from leaching of these polyphenols into water (Rao and Deosthale, 1982). Previous workers (Giami, 1993; Paramjyothi and Mulimani, 1996) also reported similar reduction in polyphenol content of different germinated legumes. Pressure-cooking of soaked as well as unsoaked seeds resulted in significantly reduction in polyphenol content of all the four varieties of moth bean (Table 2). The losses were from per cent and per cent for unsoaked and soaked pressure-cooked seeds, respectively. The polyphenol content decreased to a larger extent (88 to 90%) in dehulled pressure cooked seeds as compared to unsoaked and soaked pressure cooked seeds. Microwave cooking was more effective in reducing polyphenol content of moth bean seeds. Microwave cooking reduced the polyphenol content of unsoaked, soaked and dehulled seeds by 37 to 39, 52 to 53 and 90 to 93 per cent, respectively. The observed decrease during cooking may be due to binding of polyphenols with other organic substances and proteins, or from alterations in the chemical structure of polyphenols, that cannot be determined by

4 available chemical methods (Reddy et al. 1985). Decrease in polyphenol content due to cooking has been noticed earlier by different workers in different legumes (Shinde et al. 1991; Adewusi and Falade, 1996). Trypsin Inhibitor Activity (TIA): Trypsin inhibitors are the characteristic constituent of legume grains. It is known that trypsin inhibitor affect the digestibility and hence, the protein quality of legumes. The TIA of moth bean differs significantly from to mg/100g sample (Table 3). Local had highest TIA followed by Jwala, RMO 225 and RMO 257. Khokhar and Chauhan (1986) also reported similar range of TIA in moth bean. Soaking of moth bean seeds for 12 h significantly reduced the TIA by 26 to 30 per cent (Table 3). The highest loss being in RMO 257 and lowest in RMO 225. Dehulling of soaked seeds (12 h) further reduced the TIA by 32 to 35 per cent. Since trypsin inhibitors are low molecular weight proteins and hence they are likely to pass out easily from the seed to the soaking medium against concentration gradient. Vol. 27, No. 2, Table 2. Effect of processing and cooking on polyphenol content (mg/100g) of moth bean (on dry matter basis) Treatment Variety Local Jwala RMO 225 RMO 257 Unprocessed ± ± ± ±0.02 Processing Soaked (12h) ±0.13(-21) ±0.25(-29) ±0.05(-25) ±0.08(-24) Soaked & dehulled ±0.10(-78) ±0.13(-77) ±0.34(-70) ±0.03(-76) Germination (60h) ±0.04(-70) ±0.19(-70) ±0.08(-70) ±0.18(-70) Pressure cooking Unsoaked ±0.10(-30) ±0.05(-32) ±0.12(-32) ±0.10(-31) Soaked ±0.09(-52) ±0.12(-51) ±0.17(-50) ±0.17(-50) Soaked & dehulled ±0.20(-90) ±0.02(-89) ±0.04(-88) 91.03±0.01(-90) Microwave cooking Unsoaked ±0.18(-39) ±0.16(-39) ±0.22(-37) ±0.07(-38) Soaked ±0.08(-52) ±0.07(-52) ±0.03(-53) ±0.13(-53) Soaked & dehulled 86.75±0.10(-92) 77.21±0.13(-93) 97.64±0.07(-90) 90.03±0.03(-90) Values are mean ± SD of three independent determinations Significant at 5% level of significant CD for variety 1.39 Treatment 2.20 Interaction 4.38 Figures in parentheses indicate percent decrease (-) over control values Germination of soaked moth bean for 60 h decreased the TIA by per cent (Table 3). The reduction in TIA during germination may probably be attributed to the mobilization and breakdown of chemical constituent including TI. Similar reduction in moth bean after soaking and germination has been reported by earlier workers (Kadam et al. 1986; Khokhar and Chauhan, 1986). Pressure cooking of moth bean seeds reduced the TIA drastically (Table 3). Pressure cooking of unsoaked, soaked and soakeddehulled seeds reduced TIA by 82 to 85 %, 90 to 92 % and 95 to 97 %, respectively, in all the four varieties of moth bean. Microwave cooking of unsoaked, soaked and soaked-dehulled seeds reduced TIA by 85 to 86 %, 91 to 93 % and 97 to 98 %, respectively. The heat labile nature of trypsin inhibitors may explain the destroying effect of cooking on TIA. The rate of inactivation is greatly increased with increasing moisture content of the food material (Buera et al. 1984). This may explain greater losses of TIA in soaked pressure-cooked

5 118 J. DAIRYING, FOODS & H.S. Table 3. Effect of processing and cooking on trypsin inhibitor activity (mg/100g) of moth bean (on dry matter basis) Treatment Variety Local Jwala RMO 225 RMO 257 Unprocessed 20.24± ± ± ±0.61 Processing Soaked (12h) 14.70±0.12(-27) 13.96±0.10(-28) 13.05±0.03(-26) 12.07±0.19(-30) Soaked & dehulled 13.12±0.08(-35) 12.94±0.29(-33) 12.17±0.08(-32) 11.64±0.04(-32) Germination (60h) 5.86±0.03(-71) 5.91±0.37(-70) 5.04±0.01(-72) 4.86±0.02(-72) Pressure cooking Unsoaked 3.01±0.17(-85) 3.17±0.40(-84) 2.64±0.12(-85) 3.11±0.06(-82) Soaked 1.59±0.43(-92) 1.88±0.09(-90) 1.39±0.18(-92) 1.52±0.12(-91) Soaked & dehulled 1.01±0.09(-95) 0.59±0.42(-97) 0.94±0.22(-95) 0.60±0.15(-96) Microwave cooking Unsoaked 2.81±0.32(-86) 2.88±0.29(-85) 2.47±0.06(-86) 2.58±0.19(-85) Soaked 1.33±0.09(-93) 1.74±0.25(-91) 1.68±0.09(-91) 1.37±0.11(-92) Soaked & dehulled 0.40±0.40(-98) 0.58±0.14(-97) 0.41±0.13(-98) 0.51±0.07(-97) Values are mean ± SD of three independent determinations Significant at 5% level of significant CD for variety 0.02 Treatment 0.04 Interaction 0.07 Figures in parentheses indicate percent decrease (-) over control values and microwave cooked seeds. Diminishing effect of heat treatment of TIA of legumes has been reported earlier (Bansal et al. 1988, Hajela et al, 1998). From these studies, it is evident that germination (60 h) is the best method followed by microwave cooking, pressure cooking, dehulling and soaking for lowering the levels of phytic acid and polyphenols in moth bean. In case of TIA, microwave cooking and pressurecooking reduces the TIA to greater extent followed by germination, dehulling and soaking. These are simple and inexpensive processing and cooking methods, which can be followed to increase the nutritional quality of moth bean. REFERENCES Adewusi, S.R.A. and Falade, O.S Food Sci. Technol. Alimentos. 2 (4): Ali, H.I. and Harnald, B.F Cereal Chem. 68 (3): Bansal, K.K. et al. (1988) J. Food Sci. Technol. 25 (1): Bishnoi, S. et al. (1994) Plant Foods Human Nutr. 45: Buera, M.P. et al. (1984) J. Food Sci. 49: Chau, C.F. and Cheung, P.C.K. (1997) J. Agric. Food Chem. 45: Davies, N.T. and Reid, H. (1979) Br. J. Nutr.41: Deshpande, S.S. and Cheryan, N. (1984) J. Food Sci. 49: Giami, S.Y. (1993) Food Chem. 47: Hajela, N. et al. (1998) J. Food Sci. Technol. 35: Kadam, S.S. et al. (1986) Qualitias. Plantarum. 36 (1): Kaur, D. and Kapoor, A.C. (1990) Food Chem. 37: Khalil, A.H. and Mansour, E.H. (1995) Food Chem. 50: Khokhar, S. and Chauhan, B.M. (1986) J. Food Sci. 51 (3): Kumar, K.G. et al. (1978) J. Food Sci. 43 : Panse, V.G. and Sukhatme, P.V. (1961) Statistical Methods for Agricultural Workers, 2 nd edn. ICAR, New Delhi, pp. 12, 18.

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