Changes in Soybean Protein Components during its Gel Formation Process

Abstract

Influences of heat treatmentof water extract of defatted soybean on protein components during gel formation process were studied in relation to physical properteies ofgels. Though only about 30% of protein in unheated extract was salted out by 33% saturation of ammonium sulphate, about 70% of protein was salted out in case of extract which was heated at 90°C for 5min. Amount of cold insoluble fraction (CIF) also varied with heating temperature of water extract. Whereas about 20% of the extracted protein was insolubilized when heating temperature was below 50°C, only 3-4% CIF was precipitated from the extract when heated above 80°C. Water extracted protein consisted fo conponents corresponding the bands A to E in no urea system of polyacrylamide gel electrophoresis pattern. When the extract was heated at 90°C, bands A, C, D and E almost disappeared, and band B and new band B' appeared prominent. It was observed that heating at 70°C served as a borderline of these changes. CIF gave prominent band B and slight band B'by heat treatment. Influences of heating and urea on the viscosity of CIF were more prominent than those on the viscosity of residual fractions. It was also recognized that the gel from CIF Was remarkably tough and elastic than that from the residual fractions.
From these results, the behavior of protin components in gel formation was discussed.