The antioxidant mechanism of Maillard reaction products in oil-in-water emulsion system

Maillard reaction products (MRPs) were widely used to stabilize oil-in-water (O/W) emulsions to inhibit lipid oxidation due to their great antioxidant capacity, but the detailed antioxidant mechanism was still uncertain. In this study, MRPs produced by dry-heating whey protein isolate with dextran for different reaction time were used to prepare O/W emulsions. The peroxide value (POV value) decreased from 171.44 meq/kg to 30.63 meq/kg verified that the oxidation stability of emulsions was significantly improved by MRPs compared with unmodified protein. The reaction time was found to be positively related to the layer thickness and grafting degree, showing that MRPs with longer reaction time could form thicker interfacial layer. Comparing the antioxidant ability of MRPs with unadsorbed subnatants, it was indicated that MRPs with longer reaction time presented higher antioxidant effect at the interface. POV value of emulsions with subnatants replaced by water was compared with un-replaced emulsions to illustrate the antioxidant roles of MRPs at interfacial layer and in the continuous phase. The results showed that in the initial oxidation stage, thicker interfacial layer would provide critical physical steric hindrance function to inhibit free radicals while MRPs played an unobvious role. In the next stage, MRPs adsorbed at the interface had a pivotal impact on preventing the free radical chain reactions. At the later stage, the un-adsorbed MPRs started to manifest their influence on protecting oil from oxidation.