Stability of emulsions formed using whey protein hydrolysate: Effects of lecithin addition and retorting

Oil-in-water emulsion (4 wt % soy oil) containing 4 wt % whey protein hydrolysate (WPH) (27% degree of hydrolysis) was prepared in a two-stage homogenizer. Other emulsions containing 4 wt % WPH but including two levels (0.1, 0.25 wt %) of either unmodified commercial soy lecithin or hydroxylated lecithin were similarly prepared. The effect of retorting at 121 degrees C for 16 min on creaming stability, droplet size distribution, microstructure, surface concentration, and surface composition was then studied. The effect of retorting was an immediate destabilization of the lecithin-free emulsions. Addition of unmodified lecithin slightly improved the stability of the retorted emulsions, but did not prevent creaming and coalescence. However, addition of hydroxylated lecithin markedly improved the creaming stability after retorting and retarded coalescence. It appears that the most important factor affecting creaming stability was the particle diameter, in accordance with Stoke's law. Incorporation of unmodified lecithin encouraged coalescence and increased average droplet diameter, but the mechanism by which creaming stability is preserved in systems containing hydroxylated lecithin is unclear.