Thermal aggregation behaviour of soy protein: characteristics of different polypeptides and sub-units.

ABSTRACT

BACKGROUND: Due to the differences in structure and composition of glycinin and ß-conglycinin, they exhibit different characteristics during heat treatment. In present study, the thermal aggregation behaviour of glycinin, ß-conglycinin and their isolated sub-units was investigated at pH 7.0. RESULTS: Acidic polypeptides, basic polypeptides, αα' and ß sub-units of soy protein were denatured during the isolation process. The degree of aggregation of protein fractions after heat treatment was in the order denatured basic polypeptides > native glycinin > denatured ß sub-unit > native ß-conglycinin > denatured acidic polypeptides > denatured αα' sub-units. Glycinin, ß-conglycinin, acidic polypeptides and αα'/ß sub-units exhibited different changing trends of surface hydrophobicity with increasing temperature. The αα' sub-units showed higher ability to suppress thermal aggregation of basic polypeptides than ß sub-units during heat treatment. The ß sub-units were shown to form soluble aggregates with glycinin after heating. CONCLUSION: The interaction mechanism of αα' and ß sub-units heated with basic polypeptides was proposed. For the ß sub-units-basic polypeptides mixed system, more hydrophobic chains were binding together and buried inside during heat treatment, which resulted in lower surface hydrophobicity. The αα' sub-units-basic polypeptides mixed system was considered to be a stable system with higher surface hydrophobicity after being heated.