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 10 4 ‐ 10 5 dyne/cm 2 , 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.