Effects of heating on protein quality of soybean flour devoid of Kunitz inhibitor and lectin

The effects of autoclaving on protein quality of soybean flours prepared from a conventional soybean (CSB) and an isoline lacking Kunitz inhibitor and lectin (KFLF) were studied. The heating was efficient in the urease, trypsin inhibitors and lectin inactivation, being 15 min sufficient to reduce more than 90% of these compounds and provide protein solubility over 80%. The results of PER, NPR and weight gain showed that heating equally improved the nutritional quality of both soybean flours, although higher autoclaving time was required for KFLF. No significant improvement was observed on NPU and in vivo digestibility of the diets containing KFLF at any heating time. As these later results were similar to those obtained with diets containing CSB, they show the importance of the heating to improve the nutritional value and show that other components rather than trypsin inhibitors and lectins impair the nutritive value of raw soybean.