Kinetics of NaCl induced gelation of soy protein aggregates: Effects of temperature, aggregate size, and protein concentration
Résumé
Soy protein aggregates with different sizes were prepared by heating soy protein isolate (SPI) in solution and characterized with light scattering. NaCl induced gelation of aqueous solutions of these aggregates was investigated as a function of protein concentration (10–75 g L−1), NaCl concentration (0–0.5 M) and temperature (20–80 °C). The structure and the mechanical properties of the gels were investigated with confocal laser scanning microscopy and oscillatory shear measurements. The gel stiffness did not depend on the size of the preformed aggregates nor on the salt concentration, but increased with increasing protein concentration. Gelation of preformed aggregates was compared with that of native SPI, which showed that gelation of aggregates was faster and occurred at lower protein concentrations and temperatures. The stiffness of gels formed by native SPI and preformed aggregates was not significantly different, but the structure of gels formed by aggregates was more homogeneous. For all systems, the gel time had an Arrhenius temperature dependence characterized by an activation energy of 72 kJ mol−1. A more limited investigation of gelation induced by adding CaCl2 was done to study the effect of the valence of the cation.