Heat Turns Antioxidant Into Pro-oxidant

The effect of heat-induced decomposition of caffeic acid, a phenol antioxidant commonly found in coffee (as well as apples, bell peppers, pears, various herbs and other foods), was studied to determine if the resulting compounds had pro-oxidant activity. Researchers in Spain and Italy subjected a hydroalcoholic solution containing caffeic acid and heated at 90 °C to simulate the heat maintenance of coffee brews in a thermos for antioxidant and pro-oxidant activity. They also assessed the decomposition products by HPLC. Initially, the heat caused a decrease in antioxidant capacity, which researchers linked to a significant increase in pro-oxidant activity from the development of pro-oxidant compounds. Further heating created an increase in antioxidant activity, due to a decrease in the pro-oxidants previously formed and the formation of polymers with higher antioxidant activity. The scientists proposed a mechanistic route of caffeic acid decomposition under thermal conditions according to the HPLC analysis, and concluded that study clearly showed that caffeic acid, may also act as pro-oxidant due to thermal decomposition.