Heat denaturation and aggregation of β-lactoglobulin enriched WPI in the presence of arginine HCl, NaCl and guanidinium HCl at pH 4.0 and 7.0

The heat denaturation and aggregation behaviour of β-lactoglobulin (β-LG) enriched WPI was investigated at pH 4.0 and 7.0 in the presence of arginine HCl, NaCl and GdnHCl using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). Beside the classical endothermic signal attributed to protein heat denaturation, DSC thermograms displayed appearance of an additional exothermic peak in the presence of cosolute. Using in situ DLS, it was shown that the appearance of the exothermic peaks is linked to protein aggregation, in particular to a strong increase in aggregate size. Upon increased cosolute concentration at pH 4.0 the exothermic peak occurred at temperatures lower than the actual denaturation peak (∼85 °C). At this pH, negatively charged chloride anions interact with β-LG leading to charge screening and physical aggregation. At pH 7.0, exothermic peaks appeared at higher temperatures than the denaturation peak (∼75 °C). Upon increased cosolute concentration the exothermic peak was shifted to lower temperatures, indicating protein destabilisation in the presence of cosolutes. Charge screening of β-LG by the positively charged cations (arginine, Na and guanidinium) reduced repulsion forces and promoted aggregation.