Rheological studies on preheated β-conglycinin and glycinin

Abstract

This chapter provides an understanding of gel properties of preheated S-conglycinin and glycinin. β-Conglycinin and glycinin are major storage proteins of soybeans and are believed to reflect the functional properties of soybean proteins. It is well known that β-conglycinin and glycinin have different structure and functional properties. Preheated soybean protein isolates (SPIs), which have different compositions of β-conglycinin and glycinin, were prepared by a typical method for manufacturing commercial SPI. Rheological properties were studied by dynamic viscoelastic measurements and penetration testing. The gelation properties of preheated β-conglycinin-rich and glycinin-rich SPIs were investigated using dynamic viscoelastic measurements. In the absence of NaCl, an increase in the storage modulus G' was observed for preheated β-conglycinin-rich SPI, but not for preheated glycinin-rich SPI. In the presence of 2.5% NaCl, an increase in G' was observed for both preheated SPIs in the order β-conglycinin-rich SPI > glycinin-rich SPI. The gel properties of preheated SPIs of β-conglycinin and glycinin fractions were investigated by a penetration test. The initial slope in force-penetration curves increased and the breaking length decreased for preheated β-conglycinin gel by adding NaCl. Preheated glycinin fraction formed only a weak gel in the absence of NaCl; however, gel forming ability was drastically improved by adding NaCl. These results indicate that the gelation and gel properties of preheated β-conglycinin and glycinin are quite different and changed drastically by adding NaCl.