Further Studies on Oxidation of Vitamin a and Carotene in Milk Fat

Our previous study (2) of the effect of storage temperature upon the rates of destruction of vitamin A and carotene in milk fat protected from the light but exposed to the air has indicated that following an induction, period, simultaneous progressive destruction of vitamin A and carotene occurs in samples held at 40 °, 50 °, and 60 ° C. Since that time additional data have been obtained concerning the changes in vitamin A and carotene contents of the milk fat held at lower temperatures than its melting point; namely, the region within which under favorable conditions the fractional crystallization of glycerides takes place. We also reported that the reconstitution test is very useful in recognizing the flavor defects of the milk fat and thus the extent of oxidative deterioration. This was evident from the fact that the milk made of pasteurized skimmilk and post-induction period fat developed off flavors, which continued to increase rapidly in their intensities instantaneously after processing, while the one containing fresh fat showed fairly good keeping quality. Subsequently it was observed that the latter milk at the end of 24 hours' storage at 5 ° C. developed off flavor, although of much lower intensity than the other but nevertheless identified by judges as slightly oily or tallowy and which lowered its score from 23 to 21 points, as compared with the score of zero for the first milk at the end of the same period. Since the conditions for oxidation appear to be favorable, when fat is redispersed in skimmilk, we can assume that the above technique can be of value in readily detecting changes in the resistance of milk fat to oxidation, whether these changes are brought about during storage, by exposure to light, or any other factor. For these studies the vitamin A and carotene contents of the fat were determined by the Koehn and Sherman method (3), while in the preparation of milk fat we followed the same procedure as described in the former paper (2). EXPERIMENTAL