Preheated milk proteins improve the stability of grape skin anthocyanins extracts

The effects of casein and whey proteins, preheated at 40-100°C and 45-60°C for 15min, respectively, on color loss and anthocyanins degradation in grape skin anthocyanins extracts (GSAE) at pH 3.2 and 6.3 were evaluated. Preheating milk proteins effectively improved their protective effects against color loss and anthocyanins degradation in GSAE solutions during thermal treatment (at 80°C for 2h), H2O2 oxidation (0.005% H2O2 for 1h) and illumination (at 5000lx for 5 d). Whey proteins and casein, preheated at 50°C and 60°C for 15min, respectively, demonstrated the optimal protective effects. However, preheated whey proteins had a better protective effect on the thermal, oxidation and photo stability of GSAE, decreasing the thermal, oxidative and photo degradation of anthocyanins in GSAE 71.59%, 32.22% and 56.92% at pH 3.2 and 54.91%, 22.89% and 46.68% at pH 6.3, respectively.