TEXTURE-STRUCTURE RELATIONSHIPS IN HEAT-INDUCED SOY PROTEIN GELS

Structural factors responsible for textural properties of heat-induced soy protein gels were investigated using microscopic and mechanical testing techniques. The gels were prepared by heating 20% soy protein pastes for 30 min at temperatures ranging from 25 to 130°C . Gel hardness increased linearly with the heating temperature up to 80°C , and decreased when the gels were heated at over 90°C , especially over 120°C . The equilibrium modulus estimated by tensile stress relaxation experiments was of the order of 10⁴ - 10⁵ dyne/cm², suggesting the presence of crosslinks, and there was a good correlation between the equilibrium modulus and the hardness of the gels. Solubility in phosphate buffer containing 2 -mercaptoethanol and/or urea suggested that the gel network was formed through crosslinking of the disulfide-, hydrogen- and hydrophobic-bonding types, and that the textural properties were governed by the degree of the network formation controlled by the heating temperature. SEM images of the 80°C -induced hard gels revealed a porous structure having membranous walls of thin compact film. With the 40°C -induced soft gels, the formation of the porous structure was not yet adequate, while a partial collapse of this structure was observed in the 120°C -induced fragile gels.