Modifications can make antioxidant assays more informative but not necessarily more correct: An illustration in heat-treated milk

Abstract

In vitro antioxidant assays, using extreme conditions, have received intense criticism in food science for inability to predict behaviour when antioxidants are used under normal conditions. Here it is demonstrated that an antioxidant assay gave substantially different results depending on conditions that were used, illustrating a weakness of such assays. Heat-treated milk and antioxidant standards, EDTA, ascorbic acid, Trolox, and cysteine, all behaved differently in the assay. EDTA and ascorbic acid behaved like heated milk, where antioxidant activity appeared to decrease as copper concentration increased; this was not apparent for Trolox and cysteine. Therefore, the antioxidant activity of heat-treated milk ambiguously depended on both the antioxidant standard used for comparisons, and assay conditions. This made quantification of antioxidant activity equivalents of heat-treated milk inappropriate. However, comparisons of the qualitative behaviour of antioxidant standards and heat-treated milk, under different assay conditions, appears informative.