Lipid Deterioration in Dairy Products. The Stability of Milk Fat and Fat-Soluble Vitamins as Determined by the Re-Emulsification Test

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Abstract
It has been shown that ascorbic acid plays an important part in the oxi-dative deterioration of milk fat at the end of its storage life (as detd. by the re-emulsification test), resulting in the development of objectionable flavors and losses in vits. A and E, and the carotene content of the fat. The susceptibility of fat to this type of deterioration is detd. primarily by the treatment of milk, the temp. of pasteurization, the type of product, the conditions of storage, and to a lesser extent upon the direct and immediate effect of the exposure to light. The exposure of pure fat to light generated by a mercury vapor lamp (1400 ft- candles) slightly affects its vit. E con-tent. However, it lowers the resistance of vit. E in the stable fat to deterioration as detd. by the re-emulsification test. The re-emulsification test was found useful in determining the end of the storage life of fat when the fat was obtained from products which have not as yet shown any apparent changes in their flavors. This view is supported by the observations showing that the depletion of cream of its total vit. C content, either by oxygenation, or by H2O2, has pre-vented the development of the objectionable flavors for 12 and 24 mos. at -17.7 to -16.1 C, respectively. In the re-emulsification test, however, the fat obtained from oxygenated milk pasteurized up to 76.6 C lost its ability to resist the foregoing type of deterioration at the end of 4-6 mos. of storage, depending on the conditions of processing. Only the fat from butter churned from cream pasteurized at 71.1 and 76.6 C and the pure fat retained their abilities to resist deterioration in the re-emulsification test at the end of 2 yrs.'' storage at -17.7 to -16.1 C.