Interactions of hydrolyzed whey protein fractions / ι-carrageenan. Their impact in the formation of sub-micrometer o/w emulsions

Commercial hydrolysed whey proteins (WPH) were used and residual whey protein aggregates were separated by acidification and centrifugation. Two fractions were then obtained: the supernatant (WPHSU) and the sediment (WPHSE) differing in their denatured protein amount. Turbimetric titrations of proteins and their mixtures with ι-carrageenan were carried out at different pH. Fine o/w emulsions were prepared by using a high pressure homogenizer containing different WPH fractions, ι-carrageenan and canola oil. The droplet size and the viscosity were measured. In titration experiments, turbidity change was related to protein aggregates formation at specific pH, which was more pronounced in WPSE solutions. A complex coacervation phase was noticed in WPH fractions/ ι-carrageenan fractions at specific pH. Weaker and more gradual associations of WPHSU/ι-carrageenan were noticed than in respective mixtures with WPH or WPHSE. Double layer, stable emulsions of high uniformity were prepared by adding different WPH fractions. The finest emulsions (effective diameter 225 nm) were produced by using the WPHSU fraction. These samples had an almost Newtonian behaviour. Protein aggregation and shear-thickening effects were noticed in emulsions containing WPH or WPHSE. Compared to emulsions that contained WPISU (supernatant of whey protein isolate without any hydrolysis with negligible denatured fraction), their viscosity was much lower. In the latter a shear-thinning behavior was noticed. The denatured fraction of the proteins can influence both the complex formation between protein and ιcarrageenan and the droplet size reduction during homogenization process.