Effect of xanthan gum on physicochemical properties of whey protein isolate stabilized oil-in-water emulsions

The effect of xanthan gum (XG) addition on physicochemical properties of 2 wt% whey protein isolate (WPI) stabilized oil-in-water (O/W) emulsions containing 20% v/v menhaden oil was investigated by measuring droplet size, viscosity, microstructure, creaming profile and oxidative stability. In fresh emulsions, addition of XG at different concentrations did not show any significant effect on the surface-area-average droplet size (d32). However, emulsion microstructure and creaming profile indicated that the degree of flocculation is a function of XG concentration: when XG=0%, there was no flocculation; when XG=0.02–0.15 wt%, there was limited flocculation; when XG=0.2 wt%, there was extensive flocculation leading to the formation of an emulsion gel; and when XG=0.5 wt%, there was little or no flocculation. Lipid oxidation of the emulsions was inhibited by the addition of 0.15 or 0.2 wt% XG. In the presence of 0.5 wt% XG, the emulsion exhibited a high yield stress, which appreciably inhibited creaming. Nevertheless, addition of 0.5 wt% XG was believed to have interacted with unadsorbed WPI in the aqueous phase, which inhibited the antioxidant property of WPI. Thus, addition of 0.5 wt% XG had a net prooxidant effect in the 2 wt% WPI stabilized emulsions containing 20% v/v menhaden oil.