Effects of sucrose and sorbitol on the gel formation of a whey protein isolate

Thermal analysis by differential scanning calorimetry and dynamic rheology were used to evaluate possible effects of sucrose and sorbitol at various concentrations on the thermogelation of a 150 g kg(-1) whey protein isolate solution at pH 6.0 and 8.5. At both pH values, addition of these solutes caused an increase in the thermal transition temperature of the protein denaturation/aggregation process T-tr, with a linear relationship between solute concentration (on a w/w basis) and T-tr. Dynamic oscillation tests showed that the gelation temperature T-gel was raised accordingly. The transition enthalpy DeltaH(tr) was only affected slightly and non-specific (changes within 1 J g(-1) protein). Calculation of the apparent activation energy of the gelsetting E-a(app) based on the temperature dependence of the gelation time t(gel), as well as the G* value, obtained after slow heating of the solutions, revealed effects of both sucrose and sorbitol at pH 6.0 but not at pH 8.5, especially at high concentrations of these solutes. This lead to the conclusion that the interactions between the polyhydric solutes and the whey proteins (mainly beta-lactoglobulin) were of a very weak nature. Furthermore, based on differences in the gelation mechanism of whey proteins at pH 6.0 and 8.5, it was suggested that sucrose and sorbitol affect protein-protein interactions in gels through enhancement of hydrophobic interactions. (C) 2002 Elsevier Science Ltd. All rights reserved.