SENSORY CHANGES AND FREE SH-GROUPS IN UHT MILK

Whole milk that was standardized to 3 % fat and pasteurized was indirectly UHT-treated and aseptically packaged in two different experiments. Oxygen content was varied during UHT treatment, as well as during storage. Storage was carried out at different temperatures. The milk was analyzed for free SH-groups, and a sensory evaluation was performed; the experiments also included analyses of oxygen. The results showed that both the flavor development and the free SH-groups were dependent on both the oxygen concentration and the storage temperature. The number of free SH-groups correlated with the degree of cooked/UHT flavor. After addition of oxygen to a maximally degassed milk, an initial oxygen concentration of 3.3-3.5 ppm was adequate to greatly accelerate the disappearance of cooked/UHT flavor when the milk was packaged in a carton with a low oxygen barrier, but not when packaged with a higher oxygen barrier. In the carton with the higher oxygen barrier, the initial oxygen concentration should be higher than 3.3 ppm to ensure a more rapid oxidation of free SH-groups and a more acceptable flavor.