Reaction behaviour of highly concentrated whey protein isolate under defined heat treatments

For better development of extrusion processes, more information about the reaction behaviour of highly concentrated whey protein isolate (WPI) at elevated temperatures is necessary. Therefore, temperature and time sweep analyses were performed under defined extrusion-like conditions using a closed-cavity rheometer. WPI samples taken after various temperature-time treatments were analysed by size-exclusion chromatography and fluorescence spectroscopy. Together with the inline rheological data, G′ and G″, information about the reaction behaviour such as onset temperature of aggregation and degradation were obtained. Aggregation was observed during the isothermal time sweep measurements for all temperatures applied (80-160 °C). High temperature treatments (T ≥ 120 °C) resulted in non-disulphide covalent cross-links and degradation reactions. The results showed that non-disulphide covalent cross-links include isopeptides and Maillard reaction products, and that their formation is accelerated with increasing temperature.