ADSORPTION BEHAVIOR OF COMMERCIAL MILK PROTEIN AND MILK POWDER PRODUCTS IN LOW-FAT EMULSIONS

The adsorption behaviour of various terms of milk proteins, as present in commercial low heat skim milk powder (SMP), sodium caseinate and w hey protein isolate (WPI), was investigated in 4% milkfat emulsions at a range of protein concentrations. At all protein concentrations, the SMP-stabilized emulsions had higher protein concentration at the inte rface than the sodium-caseinate- or WPI-stabilized emulsions. For sodi um-caseinate- or WPI- stabilized emulsions, a maximum surface coverage of approximately 2 mg/m(2) was measured compared with 6 mg/m(2) for S MP-stabilized emulsions. In SMP-stabilized emulsions, at low protein c oncentrations, caseins adsorbed at the interface in preference to whey proteins; however, the preference diminished at higher protein concen trations. In sodium-caseinate-stabilized emulsions, alpha(s)-casein sh owed a preference over beta-casein for interfacial adsorption whereas beta-lactoglobulin adsorbed preferentially in WPI-stabilized emulsions . Addition of WPI to either reconstituted skim milk or sodium caseinat e solution, prior to emulsification with fat, caused a decrease in the surface protein concentration in SMP-stabilized emulsions but had no effect in sodium-caseinate-stabilized emulsions. In emulsions containi ng SMP and WPI, increasing concentrations of WPI caused a decrease in the proportion of casein with a corresponding increase in whey protein s at the interface. A similar trend was observed for emulsions contain ing sodium caseinate and WPI.