RHEOLOGICAL STUDIES ON THE GELATION PROCESS OF SOYBEAN 7S AND 11S PROTEINS IN THE PRESENCE OF GLUCONO-DELTA-LACTONE

Dynamic viscoelastic study and compression testing on gelation of soybean 7S and 11S proteins by glucono-delta-lactone (GDL) were done to elucidate the gelation process of tofu (soybean curd). Gelation curves at constant temperatures observed in dynamic viscoelastic measurement were approximated by first-order reaction kinetics. Both storage and loss moduli at the final stage of the gelation for 7S-GDL gels showed almost the same value as those of 11S gels when concentrations of protein and GDL were the same. However, parameters obtained in the compression testing, i.e., breaking stress and breaking strain of fully gelled 7S, were smaller than those of 11S gels. The rate of gelation for 7S was much slower and the gelation time was longer than for 11S. The gelation rate increased and the gelation time decreased with increasing GDL concentration at a constant 7S concentration as observed for 11S-GDL systems. The gelation time of systems which consist of 7S and GDL at a fixed ratio of 10:1 decreased with increasing 7S concentration. The minimum concentration of 7S protein for the gelation in the presence of GDL was lower than that of 11S-GDL system.