Heat stability and rheology of high-calorie whey protein emulsion: Effects of calcium ions

In this study, the effect of calcium ions (Ca2+) on the heat stability and rheology of high-calorie (>1.0 kcal/mL) whey protein emulsion (HCWPE) was investigated. The mass fractions of carbohydrate, lipid and protein in the emulsions were 20, 6, and 6 wt%, respectively. It was found that there was little difference in stability and rheology between emulsions (unheated) of different concentrations of Ca2+. However, after high-temperature sterilization (121 °C for 15 min), Ca2+ had a significant effect on the stability of HCWPE. The particle size and flocculation degree increased rapidly when the Ca2+ concentration was above 1.5 mM, and absolute ζ-potential decreased. The change of 3-week particle size and backscattering showed that the emulsion had better storage stability when the Ca2+ concentration was below 1.5 mM. Another interesting result was that after the high temperature sterilization, the rheological behavior of HCWPE changed from shear-thickening to shear-thinning with increase in Ca2+ concentration. It could be explained that free Ca2+ continued to bind with protein during the shearing process. The present study would provide a theoretical reference for calcium fortified functional drinks.