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

BACKGROUND Due to the differences in structure and composition of glycinin and β ‐conglycinin, they exhibit different characteristics during heat treatment. In present study, the thermal aggregation behaviour of glycinin, β ‐conglycinin and their isolated sub‐units was investigated at pH 7.0. RESULTS Acidic polypeptides, basic polypeptides, αα ′ and β 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 β sub‐unit > native β ‐conglycinin > denatured acidic polypeptides > denatured αα ′ sub‐units. Glycinin, β ‐conglycinin, acidic polypeptides and αα ′/ β 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 β sub‐units during heat treatment. The β sub‐units were shown to form soluble aggregates with glycinin after heating. CONCLUSION The interaction mechanism of αα ′ and β sub‐units heated with basic polypeptides was proposed. For the β 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. © 2015 Society of Chemical Industry