Comparison of the concentration-dependent emulsifying properties of protein products containing aggregated and non-aggregated milk protein

The emulsifying properties of sodium caseinate (SCN), whey protein concentrate (WPC), milk protein concentrate (MPC-85), and skim milk powder (SMP) have been studied as a function of protein concentration. There is little differentiation between the products containing aggregated casein (MPC-85 and SMP) for all properties studied (emulsifying ability, creaming stability, surface coverage, and composition of the interfacial layer). The non-aggregated caseinate and whey proteins have similar emulsifying abilities, which are greater than the aggregated MPG-85 and SMP. The surface coverages for emulsions made with SCN and WPC are typical of those found in these systems, and are approximately 10 times lower than the aggregated MPC-SS and SMP samples. The casein composition of the interfacial layer in emulsions made with MPC-85 and SMP is independent of protein concentration, and is the same for the adsorbed layer and the whole emulsion. For SCN, alpha(s)-casein replaces beta-casein at the interface as the total protein concentration is increased. The creaming stability of the emulsions shows large differences between the aggregated caseins, the non-aggregated caseins and the whey proteins. The behaviour of SCN, in particular, is anomalous. Differences in creaming stability are discussed in terms of depletion flocculation effects between emulsion droplets and protein aggregates of differing molecular weight and size. (C) 2000 Elsevier Science Ltd. All rights reserved.