Emulsifying properties of whey protein–dextran conjugates at low pH and different salt concentrations

The emulsifying behaviour of glyco-protein complexes of the non-ionic polysaccharide dextran (500 kDa) with whey protein isolate (WPI) have been investigated in systems containing (20 vol.% oil phase) medium-chain triglyceride oil, silicone oil, orange oil, and n-tetradecane under acidic and high electrolyte concentrations. Covalent coupling of protein to polysaccharide is achieved by dry heat treatment of protein+polysaccharide mixtures. Emulsions were made with WPI and whey protein isolate-dextran (WPI-DX) conjugate, and stability was followed by determining changes in average droplet size and extent of serum separation with time, with gum arabic (GA) chosen as reference emulsifier. The results show that the WPI-DX conjugate gives much better stability than the whey protein alone or GA under similar conditions. The improved emulsifying properties of WPI on complexing with dextran is probably due to the enhanced steric stabilization provided by the bulky hydrophilic polysaccharide moiety.