Heat-induced aggregation and sulphydryl/disulphide reaction products of soy protein with different sulphydryl contents

•Soy protein was reduced to obtain increasing sulphydryl groups content.•Larger aggregates and more viscous dispersion were obtained when heated.•Disulphide bond content and production of disulphide lined polymer were decreased.•Sulphydryl/disulphide reaction was not the driving force for aggregation. In this study, soy proteins were reduced with 0.1–10mM dithiothreitol (DTT) to obtain an increasing number of sulphydryl groups (SH) with a similar particle size. Aggregation was promoted by increasing the degree of reduction when heated (100°C, 30min), resulting in larger sized aggregates (from 40 to 70nm) and a higher viscosity of the aggregate dispersion. The disulphide bond (SS) content decreased and the less SS linked polymer, which was composed of acidic (A) polypeptide of glycinin, basic (B) polypeptides of glycinin, and a small amount of α′ and α subunits of β-conglycinin, was formed with increasing reduction degree, suggesting that SH/SS polymerisation was not the driving force for aggregation. The larger aggregates with increasing degrees of reduction were composed of more B of glycinin and β of β-conglycinin, suggesting that the A and the small amount of α′ and α in the SS linked polymer have an inhibiting effect on protein aggregates formation.