Effects of redox active agents on cyanocobalamin stability in heated milk

Abstract

SummaryReducing agents and oxidising agents have been identified as contributors to vitamin B12 losses associated with food processing and/or storage. We evaluated the effects of redox active agents on cyanocobalamin stability in heat‐treated nonfat milk and neutral pH buffers. The largest average cyanocobalamin losses occurred in the presence of an added thiol (glutathione, cysteine, dithiothreitol, and the thiamine decomposition product 2‐methyl‐3‐furanthiol) or dithionite, whereas cyanocobalamin recoveries generally increased in the presence of an added oxidising agent. Cyanocobalamin instability in the heat‐treated, nonfat milk (~40% loss after 90 min at 100 °C) was attributed to a combination of heat, cystine/cysteine, oxygen, and a low‐level presence of transition metals, a combination also found in many other foods for which B12 instability has been reported. The proposed cyanocobalamin decomposition pathway – complexation with heat‐exposed cysteine thiolate, cobalt reduction, hydrolysis of the complex, conversion to hydroxocobalamin, and irreversible oxidation – follows the sequence described by others.