Effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel

To elucidate the effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel, Ca2+ induced gelation of soybean protein were investigated by rheological approaches, electrophoresis analysis, confocal scanning laser microscopy (CSLM) and surface hydrophobicity (S0). The results showed that, both CaCl2 concentration (20-40 mM) and preheating temperature (80-120 °C) took significant influence on the dynamic viscoelasticity of the gel samples. The bands distribution of samples preheated at 120 °C were different from the bands distribution of samples preheated below 100 °C in denature and native electrophoresis. The CSLM analysis showed that the gel became coarser as the Ca2+ increased. On the other hand, two different kinds of gel were shown under the same Ca2+ concentration: a bead-like structure (below 100 °C) and a filamentous structure (above 100 °C). According to fractal theory, weak-linked gel (α was >0.8) was formed when preheating below 100 °C, while a transition gel (α = 0.52-0.62) was obtained when preheating over 100 °C. All these results suggested that the preheating temperature influence the type of cold-set gel.