Effect of Heat-Induced Association of Whey Proteins and Casein Micelles on Yogurt Texture

We investigated the role of the nature of the casein micelle surface, as affected by adsorption of heat-denatured whey proteins, on yogurt texture.Depending on the heating process and heat intensity, a proportion of 13-lactoglobulin and t~-lactalbumin bound to the casein.As shown by electron microscopy, filaments of denatured ~l-lactoglobulin developed on the micellar surface and offered a barrier to micelle fusion when milk was fermented, resulting in inferior yogurt texture.At higher heat intensities, o~-lactalbumin also commenced to precipitate onto the micelle, which apparently filled up the gaps formed by the I~-lactoglobulin filaments and caused a smoother micellar surface.During fermentation, coalescence of the micelles improved texture.The heat-induced association of t~-lactalbumin with the casein particles appeared to be important for fusion and hydration of the mi-ceUes during subsequent fermentation, which determined the rheological properties of yogurt.