Nutrient retention in microwave cooked germinated legumes

Abstract

The effects of germination on the cooking quality and nutrient retention in pressure and microwave-cooked Bengal gram, green gram and horse gram were studied. Ungerminated (UGL) and germinated legumes (GL) cooked in a microwave oven, and under pressure were analysed for moisture, protein, ash, iron, thiamin, ascorbic acid, in vitro protein digestibility (IVPD) and starch digestibility (IVSD) and bioavailable iron. Results revealed that microwave cooking required more water and time than did pressure cooking. The range of analysed constituents on dry weight basis in UGL and GL legumes, respectively, were as follows: protein, 18.2–23.5 and 19.4–25.7 g, ash, 2.1–2.9 and 2.2–2.9 g, iron, 5.4–7.3 and 7.3–10.3 mg, thiamin, 0.10–0.34 and 0.54–1.83 mg, ascorbic acid, 2.4–3.9 and 3.1–25.6 mg/100 g. The effect of germination and method of cooking on nutrient retention varied, depending on nutrient and severity of heat treatment. Microwave cooking caused 36–57% reduction of ascorbic acid while pressure cooking caused 10–30% loss. The IVSD in raw samples ranged from 18.4% to 22.1% in UGL and 33.6% to 43.6% in GL. Cooking of UGL and GL, by both methods, increased the starch digestibility threefold. The IVPD of raw UGL ranged from 64.6% to 66.2% and that of GL was 72.4–73.9%. In cooked UGL the IVPD ranged from 70.9% to 82.3% and, in GL, from 78.4% to 84.2%, showing a significant difference in cooking methods only in UGL. The iron bioavailability ranged from 11.5% to 18.7% in raw UGL while it was 18.3–20.6% in GL. GL had a higher content of thiamin and ascorbic acid, higher protein and starch digestibility and bioavailable iron, even after cooking.