An analytical approach to the evaluation of heat damage in commercial milks

Various samples of pasteurized, UHT, and in-bottle sterilized milk have been analyzed, and two indices of heat damage determined: 1) soluble serum protein as percentage of total proteins and 2) protein surface hydrophobicity determined by a fluorescence test. which enables the number and affinity of bonds between protein hydrophobic sites and fluorophor 8-aniline naphthalene I-sulfonate to be evaluated. Results show that the soluble serum protein index permits a definite distinction to be made between pasteurized and sterilized milk but not between UlIT and in-bottle sterilized milk. However, the protein surface hydrophobicity index enables a distinction to be made between UHT-treated and in-bottle sterilized mille. In a plot of PSH versus SSP indices, separate areas are identified for raw, pasteurized, UHT, and in-bottle sterilized milk. The combination of the two indices makes it possible to obtain a reliable a posteriori indication of the type and severity of heat treatment the milk has undergone. The possibility of identifying improperly treated milles is also discussed.