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Effect of Temperature on Rate of Autoxidation of Milk Fat

Department of Dairy and Food Industry, Iowa State University, Ames¹

ABSTRACT

Milk fat was autoxidized at 50, 35, 21, 4, —10, and —27 C, and the reaction monitored by peroxide and thiobarbituric acid (TBA) values and organoleptic examination. The season of production and addition of 0.1 ppm of copper as copper palmitate had little effect on the flavor response, and the same character and sequence of flavors were observed at all temperatures. Equations were fitted statistically to the pooled organoleptic data to predict the effect of time and temperature on the flavor responses. Peroxide and TBA values showed significant correlation with the flavors at higher temperatures, but at lower temperatures no increases in peroxide and TBA values could be observed. Autoxidation flavors were observed at all temperatures and were actually more intense at —27 than at —10 C. Apparent heats of activations were calculated for the peroxide, TBA, and flavor reactions. The heat of activation of the TBA reaction was significantly higher than the others. The TBA and peroxide values were significantly stimulated by addition of copper, but copper did not affect the apparent heats of activation of the reactions.

¹ Journal Paper no. J-5699 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project 1517. Supported in part by a grant from the American Dairy Association.