Studies on the Changes of the Properties of Soybean Protein by Freezing

Part III. Changes in solubility of soybean protein in several solubilizing reagents by frozen storage

Abstract

It was found in authors' earlier work that soybean protein curd became easy to be squeezed out by freezing and thawing, and on the other hand, soybean protein dissolved in solution became insoluble also by freezing and thawing. In this paper conditions and mechanism under which soybean protein is denatured by freezing are studied by comparing solubilities of acid precipitated soybean protein before and after freezing. The solubility in dilute sodium hydroxide solution is decreased by freezing and more distinctly by frozen storage at -1--3°C. The decrease of the solubility is much more rapid in the case of heat-denatured soybean protein. From the solubility behaviors of the protein in mercaptoethanol, urea and their mixture solutions before and after frozen storage at -1--3°C, disulfide linked polymers of the protein seem to have formed during this process.