Effect of pH, ionic strength, and composition on emulsion stabilising properties of chitosan in a model system containing whey protein isolate

In a model emulsion system containing chitosan (CN) as stabiliser, whey protein isolate (WPI) as emulsifier, and canola oil (10%), we have compared the effect of combinations of various factors (pH, concentrations of CN and WPI) and ionic strength, on the stabilising properties of CN with various characteristics. Phase separation evolution measurements in tubes revealed two types of phase separation phenomena: a rapid syneresis at pH≤5.0 due to the depletion flocculation between droplets, and a lot more stable small gradient creaming with fine lipid dispersion at pH≥5.5. Syneresis was favoured by increasing the WPI/CN ratio or by adjusting the pH≈pI of WPI. Gradient creaming tended to destabilise towards syneresis at high WPI/CN ratio (10:1), or when μ=0.3 M, where a low deacetylated CN mainly showed a better stability. The optimal stability was obtained at pH 6.0 condition, where the inability of WPI or CN alone for stabilisation clearly showed a synergistic effect of mixed components on emulsion stability. The gradient creaming phenomenon was explained by interfacial stabilisation caused by the coadsorption of CN with proteins, as suggested by results of protein concentration in creamed layer. The strong influence of pH, ionic strength, and WPI/CN ratio on emulsion stability is indicative of the predominance of electrostatic interactions, which promote interfacial coadsorption between WPI and CN, where electrostatic interfacial stabilisation is important.