Thermal behavior of soy protein fractions depending on their preparation methods, individual interactions, and storage conditions.

Different soy protein isolates (SPI) and whey soy protein (WSP) samples were obtained from fresh and stored soybean flour. Some samples were subjected to a long, cold storage. DSC thermograms of SPI showed the two characteristic endotherms, corresponding to denaturation of β-conglycinin and glycinin. Low value of denaturation enthalpy and high glycinin denaturation temperature were related to a reduction of protein solubility of SPI. DSC thermograms of WSP also showed two characteristic endotherms, corresponding to Kunitz trypsin inhibitor and lectin. The methods and conditions of preparation and storage of WSP samples were factors that modified their thermal behavior. Some SPI-WSP mixtures (1:1) exhibited more complex thermograms and higher denaturation temperatures. Thermograms of SPI-denatured WSP mixtures showed that the thermal stabilization of soybean storage proteins was attributed to protein-protein interactions. The differences in the thermal behavior of single or mixed SPI and WSP could not be explained on the basis of mineral content.