Effect of Copper on Ascorbic Acid Content, Redox Potential and Development of Oxidized Flavor in Milk of Cows and Buffaloes

Abstract

The effect of copper on ascorbic acid content, redox potential (Eh) of milk, and development of oxidized flavor is discussed. Oxidized flavor appeared in cow milk only after a marked rise in Eh due to the oxidation of ascorbic acid, whereas in buffalo milk oxidized flavor developed without any appreciable change in Eh. In buffalo milk, copper at low concentrations failed to cause sufficient oxidation of ascorbic acid to effect an increase in Eh. The Eh of cow milk began to rise appreciably when more than half of the ascorbic acid normally present in milk was oxidized. The pro-oxidant action of ascorbic acid in cow milk at concentrations normal to milk is not merely due to conversion of copper to cuprous form; it is suggested that the activation energy involved in this conversion is an important factor in the lipid oxidation which follows. Ascorbic acid did not promote copper-catalyzed oxidation of buffalo milk as it is not involved in the reversible oxidation.