title: Acid-induced gelation of heat-treated milk studied by diffusing wave spectroscopy.
abstract: Fresh skim milk is a stable colloidal system containing casein micelles and whey proteins. By decreasing the pH, the casein micelles become unstable and a gel is formed. During heat treatment at temperatures higher than 70 degrees C, the major whey proteins, e.g. alpha-lactalbumin and beta-lactoglobulin denature and start to interact with each other and with casein micelles. This changes the colloidal properties of the casein micelles. In this article, the pH-induced gel formation of heat-treated milk and the role of whey proteins was studied. Heat treatment in the range 70-90 degrees C induced a shift in gelation pH of skim milk to more alkaline pH values. This shift was directly related to whey protein denaturation. By using WPF milk it was shown that beta-lactoglobulin is principally responsible for the shift in gelation pH. alpha-lactalbumin caused neither alone nor in combination with beta-lg, an effect on the gelation pH. Heat treatment of milk for 10 min at 90 degrees C resulted in complete denaturation of the beta-lg present in skim milk but it is estimated that the casein micelles are coated only up to 40% by whey proteins when compared with pure whey protein aggregates.
authors.affiliation: NIZO food research, P.O. Box 20, 6710 BA, Ede, The Netherlands
authors.forename: A J.
authors.initials: AJ
authors.lastname: Vasbinder
authors.forename: P J.J.M.
authors.initials: PJ
authors.lastname: van Mil
authors.forename: A
authors.initials: A
authors.lastname: Bot
authors.forename: K G.
authors.initials: KG
authors.lastname: de Kruif