Changing oxidation in whey fat concentrate upon addition of green tea extract

Whey products with a high fat content are recognised to be more prone to oxidation compared to other dairy products, since whey fat is high in unsaturated phospholipids. Thus, strategies for inhibition of oxidation during processing and storage of high-fat whey products need to be developed. The purpose of the present study was to find an antioxidant which effectively inhibits oxidation in whey fat concentrate (WFC) during accelerated storage (60 degrees C) and to investigate the effect of the antioxidant on primary and secondary oxidation. The development of secondary lipid oxidation products was measured using a number of different antioxidants: Trolox (TRX), propyl gallate (PG), Grindox 1021 (GRX), green tea extract (GTE) and rosemary extract (RE). The development of the secondary lipid oxidation product hexanal was inhibited by all the tested antioxidants, and GTE was found to be the most efficient of the tested antioxidants. The effect of GTE concentrations (0, 50 and 500 mu g/g whey solid) on oxidation was investigated further by measuring hydroperoxide and hexanal accumulation during accelerated storage (60 degrees C). Hydroperoxides were accumulated after a lag phase which was prolonged in the samples supplemented with 500 mu g GTE/g whey solid. The accumulation of hexanal was highly reduced in the presence of GTE, and hexanal was accumulated without a lag phase. Thus, the results show that GTE effectively inhibits oxidation in WFC and suggest that GTE acts both as a chain-breaking antioxidant and as a transition metal ion chelator.