THERMAL AGGREGATION OF SOY PROTEIN ISOLATES

Thermal behavior of soy protein isolates under different conditions of temperature, time, pH, protein concentration, and presence of reducin g agents was studied. Thermal treatments above 85 degrees C showed a d ecrease in concentration of the AB-11S subunit and of the two protein species of 20 and 29 kDa, and a gradual increase in the concentration of the A and B polypeptides of glycinin. None of the thermal treatment s tested led to modifications of the relative proportions either of th e high molecular weight aggregates (100-200 kDa) observed in the elect rophoretic profiles or of the alpha' and alpha subunits of beta-congly cinin. Increasing the pH to 9 or 10 and increasing the protein isolate concentration enhanced AB-11S aggregation during the thermal treatmen t. Either the presence of Na2SO3 or the pH 9-10 favored the beta-beta- conglycinin/B-glycinin aggregation. This interaction requires an incre ase of SH groups. Initially the beta-beta-conglycinin/B-glycinin aggre gates were stabilized by hydrophobic interactions and later by SS bond s.