Effect of heat-treatment on the antioxidant and pro-oxidant activity of milk

The changes in antioxidant and pro-oxidant activity of milk were studied using different heat treatments. At each heating temperature, samples showed an initial increase and a subsequent decrease in pro-oxidant activity. The latter was associated with an increase in the antioxidant properties. The changes in the reducing properties of milk upon heating were attributed not only to the thermal degradation of natural occurring antioxidants, but also to the formation of novel oxidative species in the early stages of the Maillard reaction. The results indicate that short heat treatments can be potentially responsible for a depletion in the overall antioxidant properties of milk. By contrast, only the application of severe heat treatments, associated with the formation of brown melanoidins, allows a recovery, and even a possible increase in milk antioxidant properties. (C) 2003 Elsevier Ltd. All rights reserved.