Whey protein isolate/gum arabic intramolecular soluble complexes improving the physical and oxidative stabilities of conjugated linoleic acid emulsions

Abstract

Protein/polysaccharide electrostatic complexes have been widely used in food products to confer structure and stability. Intramolecular soluble complexes (ISCs) have superior emulsifying properties in stabilizing oil-in-water (o/w) emulsions. This paper investigates the potential application of ISCs to stabilize polyunsaturated fatty acids that were difficult to disperse and liable to oxidation. The idea was demonstrated using whey protein isolate/gum arabic (WPI/GA) ISCs and conjugated linoleic acid (CLA). Zeta potential measurements indicated a stoichiometry of r = 1.0 for the electrostatic complexation of WPI/GA. Excess of GA (r < 1.0) ensured the formation of stable ISCs in a specific pH range, e.g. pH 4.0–5.4 at r = 0.5. The nano-sized ISCs significantly improved the physical and oxidative stabilities of CLA emulsions in comparison with individual WPI or GA. Optimal stabilization was found at a WPI/GA concentration of 2.0 wt% for emulsions with CLA = 15 wt%. NaCl tended to dissociate ISCs when NaCl > 20 mM and therefore seriously reduced the stability of ISCs-stabilized CLA emulsions. The superiority of ISCs in stabilizing polyunsaturated fatty acids is due to the cooperative adsorption of protein and polysaccharide at the emulsion interface, providing strong steric and electrostatic effects against droplet aggregation and coalescence and thus excellent physical stability. The improved oxidative stability should arise from the free radical scavenging ability of the protein at the emulsion interface, reducing lipid oxidation.