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The Relation of Copper and Ascorbic Acid to Oxidized Flavor in Market Milk¹

Department of Dairy Husbandry, Purdue University Agricultural Experiment Station, Lafayette, Indiana

ABSTRACT

The copper and ascorbic acid content of milk and their relation to the development of oxidized flavor in the milk were studied.

The increased temperature during the processing of the milk caused the greatest copper contamination.

The development of oxidized flavor in market milk was found to vary greatly even though the same equipment was used for the processing.

The amounts of copper and ascorbic acid in the milk from individual cows varied inversely throughout the lactation period. The copper content was the highest at the beginning of the lactation period while the ascorbic acid was at a maximum at the end. The gradual decrease of the ascorbic acid in the milk did not affect the loss resulting from the 24-hour storage period.

The pasteurization of milk in the presence of different metals resulted in various degrees of copper contamination, oxidation of ascorbic acid and the development of oxidized flavor. The milk pasteurized in the copper tube had the highest copper content, lowest ascorbic acid and developed an oxidized flavor shortly after pasteurization. The milk pasteurized in the stainless steel tube with alloy fitting had the next highest copper content and almost as much reduction of ascorbic acid. The milk pasteurized in the tinned copper container had less copper contamination with no development of oxidized flavor and the ascorbic acid oxidized at a slower rate than either the milk pasteurized in the copper or stainless steel with the alloy fitting.

The loss of ascorbic acid due to pasteurizing the milk in stainless steel and glass was only slightly more than the same milk held for 24 hours without pasteurization.

These studies indicate that stainless steel or glass equipment used for the processing of milk will result in low copper and a relatively high ascorbic acid content of the milk.

¹ Published with the approval of the Director of the Purdue University Agricultural Experiment Station, Journal Paper No. 49.