The Relationship of SH and S-S Exchange Reaction to the Expansion of Tofu-gels for Aburaage-making

Studies on Aburaage-making Part II

Abstract

The mechanism of less expansion of Tofu-gels by excess-heating was investigated. The main results are as follows; (1) The expansion of Tofu-gels was inhibited by blocking or oxidizing reagents for SH groups in soybean proteins, whereas it was accelerated by reducing reagents for S-S bonds. The facts suggest that SH groups take an important role in the expansion of Tofu-gels. (2) The Tofu-gels could not expand considerably when prepared from soybean protein solutions where either SH groups were oxidized into S-S bonds or S-S bonds were reduced into SH groups. On the other hand, Tofu-gels prepared by mixing two soybean protein solutions expanded well. It suggests that SH and S-S exchange reaction is certainly involved in the mechanism of expansion of Tofu-gels. (3) Theexpansion rate of Tofu-gels markedly decreased by heating soybean protein solution under the conditions, where the proteins easily associated or aggregated. On the contrary the expansion rate rapidly increased by mercaptoethanol or high urea concentration due to the protein dissociation. It suggests that the association or aggregation of proteins by excess-heating may prevent Tofu-gel from the expansion.