Autoxidation of Milk Lipids. II. The Relationship of Sensory to Chemical Methods for Measuring the Oxidized Flavor of Milk Fats1,2

Abstract

Summary Sixteen milk fat samples were collected from mixed herd milk over a 6-mo. period. Each sample was oxidized to a different stage yielding peroxide values ranging from 0 to 64 for the 16 samples. The TBA number, peroxide value, total saturated and unsaturated carbonyls, volatile saturated and unsaturated 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 threshold (1/FTV) were significant at the 1% level, the volatile unsaturated carbonyls giving the highest, 0.996. Of the individual carbonyls, the correlation coefficient between non-2-enal and 1/FTV was the highest, 0.942. Concentrations of individual volatile monocarbonyls, at the absolute flavor threshold of the fats, were in parts per billion. Based on reported data, the compounds occurred at marginal or subthreshold levels at the FTV of the fat. Multiple correlation coefficients support the view that the oxidized flavor, near the flavor threshold, is due to an additive effect of carbonyl compounds.