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Oxidative Stability of Milk. I. The Antioxidative Effects of Trypsin Treatment and Aging

Department of Food Science, Cornell University, Ithaca, NY 14850

ABSTRACT

Trypsin treatment, known to retard trace metal-induced lipid peroxidation in milk, was shown also to inhibit oxidative degradation of vitamin A. The aging of milk prior to copper addition provided increased resistance to oxidation with an apparent increase in the antioxidative effectiveness of trypsin. Following both trypsin treatment and aging, total recoverable fat globule membrane material was decreased, but changes in the percent protein were only slight. Electrophoretic studies revealed that tryptic action produced marked hydrolysis of fat globule membrane proteins whereas aging produced only minor changes. Hydrolysis of skim milk proteins also was shown in milks treated with trypsin. Aging produced apparent aggregation of certain skim milk proteins. The antioxidative effect of tryptic action in milk is due primarily to an increase in metal chelating capacity. Spontaneous alteration of the fat globule membrane, coupled with increased chelation capacity in the skim milk, were probably responsible for the increased oxidative stability of aged milk. It was postulated that membrane material released from the fat globule contributed to the increase in chelation capacity and oxidative stability.