Autoxidation of Milk Lipids. II. The Relationship of Sensory to Chemical Methods for Measuring the Oxidized Flavor of Milk Fats

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Abstract
Sixteen milk fat samples were collected from mixed herd milk over a 6-month period. Each sample was oxidized to a different stage yielding peroxide values ranging from 0 to 64 for the 16 samples. The TBA (2-thiobarbituricacid) number, peroxide value, total saturated and unsaturated carbonyls, volatile saturated and un-saturated carbonyls, individual volatile monocarbonyls; and the absolute flavor threshold of each sample were determined. Statistical analyses of the data revealed that all chemical tests were highly correlated with each other. From 97 to 99% of the carbonyl-reactive material in oxidizing milk fats was nonvolatile. Relatively large amounts of nonvolatile carbonyls also were observed in fresh milk fat. The mean percentage of saturated carbonyls in the volatile monocarbonyls of 16 oxidized fats was 88.72. The correlation coefficients between all of the chemical tests for oxidized flavor intensity and the reciprocal of the absolute flavor treshold (1/FTV) were significant at the 1% level, the volatile unsaturated carbonyls giving the highest, 0.996. Of the individual carbonyls, the correlation between non-2-enal and 1/FTV was the highest, 0.942.