Influence of protein concentration, pH, and calcium sequestering salts on rehydration and physicochemical properties of casein-based powders recovered from expired pasteurized milk

Acid casein, sodium caseinate, co-precipitate, and rennet casein were prepared from expired pasteurized milk. The effects of two calcium sequestering salts, trisodium citrate (TSC) and disodium phosphate (DSP) and two pH values (unchanged and 9) were evaluated upon solubilization of casein-based powders. The powders were first dispersed in 30 mmol L−1 TSC and heated at 60 °C for 45 min. Due to their poor solubility, rennet casein and co-precipitate were further examined in 112 mmol L−1 DSP. Dispersions were characterized for particle size distribution and microstructure. Selected combinations of explored conditions caused an improved solubility but were not enough effective in dissociating the para-casein network of rennet casein. Capillary zone electrophoresis of the insoluble material indicated the preferential solubilization of modified, presumably glycated, caseins. This study provides new findings on the behaviour of casein powders recovered from expired pasteurized milk, thus contributing to implementation of strategies for food waste valorisation.