Analysis of the isoflavone content, antioxidant activity, and SDS-PAGE of cheese analogs produced with different proteolysis and soymilk residue contents

Abstract

We investigated the heat coagulation, SDS-PAGE, isoflavone content, and hydrogen-donating activity of cheese analogs produced with different hydrolysis time (0.3 % Flavourzyme® for 0, 20, 25, and 30 min) and soymilk residue contents (0, 7, 14, and 21 %) to improve the protein functionality and to use the by-product of soymilk. SDS gel electrophoresis of samples treated with Flavourzyme confirmed that the Flavourzyme treatments not only decreased the molecular weight of the proteins but also removed lipoxygenase, which results in the beany flavor of soy cheese, and Kunitz inhibitor (KTI), the antinutritional factor. The results of SDS-PAGE in the soy flour group and the roasted soy flour group treated with Flavourzyme® for 25 min and the determined soy milk residue contents indicated the recovery of some fractions (50, 32, and 18 kDa) of 7S and 11S globulin. The heat coagulation ratio increased as the amount of added soymilk residue was increased up to 14 % (p < 0.001). The glycoside (daidzin and genistin) and total isoflavone content increased in both the soy flour group and the roasted soy flour group as the amount of added soymilk residue was increased, but the contents of non-glycosidic compounds and the anti-oxidative activity were the highest in soy flour samples to which 7 % soymilk residue was added(p < 0.001). The variation in the anti-oxidative activity was similar to the variation in the contents of non-glycosidic compounds.