Effect of soaking and heat processing on the levels of antinutrients and digestible proteins in seeds of Vigna aconitifolia and Vigna sinensis

The effect of soaking, cooking and autoclaving on the levels of total free phenolics, tannins, phytic acid and in vitro protein digestibility (IVPD) were studied in Vigna aconitifolia and Vigna sinensis. Though soaking significantly reduced the content of tannins alone in V. aconitifolia, both total free phenolics and tannins were markedly reduced in V. sinensis. Greater loss of total free phenolics as well as tannins occurred under autoclaving compared to soaking and cooking in both the legumes investigated. In V. aconitifolia, soaking in distilled water for 6 h and cooking for 30 min reduced the phytic acid content by up to 43%. Maximum reduction in the level of phytic acid (36%) was observed under distilled water soaking compared to cooking and autoclaving in V. sinensis. Limited loss in content of phytic acid was noticed under autoclaving compared to soaking and cooking in both the pulses studied. In vitro protein digestibility (IVPD) of V. aconitifolia and V. sinensis was enhanced to 12.5 and 14.8%, respectively, under autoclaving. Of all the processing methods, autoclaving seemed to be the most efficient for reduction in content of the antinutrients, except phytic acid, and improving IVPD in both the pulses. (C) 1998 Elsevier Science Ltd. All rights reserved.