Heat denaturation and aggregation of β-lacto globulin 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 beta-lactoglobulin (P-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 (similar to 85 degrees C). At this pH, negatively charged chloride anions interact with beta-LG leading to charge screening and physical aggregation. At pH 7.0, exothermic peaks appeared at higher temperatures than the denaturation peak (similar to 75 degrees C). Upon increased cosolute concentration the exothermic peak was shifted to lower temperatures, indicating protein destabilisation in the presence of cosolutes. Charge screening of beta-LG by the positively charged cations (arginine, Na and guanidinium) reduced repulsion forces and promoted aggregation. (c) 2005 Elsevier Ltd. All rights reserved.