Changes in Proteins and Protease Activities during Ripening of Cheese-likeProduct from Soymilk using Penicillium caseicolum

Abstract

A curd coagulated by means of lactic fermentation from heated soymilk was ripened for 3 weeks with inoculation of a white mold starter, Penicillium caseicolum. Changes of proteins during the ripening were investigated by gel filtration and electrophoresis. Activities of proteases (endopeptidase, aminopeptidases and acid carboxypeptidase) in cur were also measured through the ripening. The ratio of water soluble nitrogen to total nitrogen (ripening ratio) reached to approximate 60% at 2 week's ripening and the finished product showed a good flavor and texture. Of water soluble nitrogen, lower molecular weight components such as free amino acids and comparatively higher molecular weight components consisting of partially hydrolyzed soy protein occupied about 30% and 70%, respectively. Electrophoretic analysis of curd proteins showed that subunits of 7S globulin and acidic subunits of 11S globulin decomposed in accordance with progress of ripening and bands of these subunits completely disappeared after 3 week's ripening. Activities of neutral endopeptidase, aminopeptidases (I and II) and acid carboxypeptidase in curd appeared at 1 week's ripening with growth of mold and rapidly increased with the ripening. These activities penetrated into center of portion of curd from surface. Proteases in curd and extracellular proteases of P. caseicolum which extracted from wheat bran medium were identical.