DYNAMIC VISCOELASTIC PROPERTIES OF GLYCININ AND BETA-CONGLYCININ GELSFROM SOYBEANS

The effects of heating temperature on gel properties and conformationa l changes were investigated in glycinin and beta-conglycinin gels usin g theological and Fourier transform it (FTIR) methods. Solutions of 15 wt % glycinin or beta-conglycinin in 35 mM phosphate buffer at pH 7.6 were heated at various temperatures for 30 min and theological proper ties were measured at 20 degrees C. The storage modulus G' as a functi on of frequency changed from a monotonical decrease with decreasing fr equency to a plateau in the range from 0.0018 to 40 Hz by heating at t emperatures higher than 80 degrees C for glycinin and 65 degrees C for beta-conglycinin. A band at 1618 cm(-1) (associated with the beta-she et structure) on it spectra increased with the formation of heat-induc ed gels. The value of the storage modulus G' correlated well with the increase in absorbance at 1618 cm(-1). These results suggest that the formation of a beta-sheet structure may be closely related to the valu e of the storage modulus G' for heat-induced gels in soybean proteins and that heat-induced gels of glycinin and beta-conglycinin are formed by cross-links with intermolecular beta-sheet structures. (C) 1994 Jo hn Wiley and Sons, Inc.