Antioxidant and prooxidant activities of tea polyphenols in oil-in-water emulsions depend on the level used and the location of proteins

We studied the impacts of protein location (interface or aqueous phase) on the antioxidant and prooxidant activities of tea polyphenols (TP) in model oil-in-water emulsions (pH 7) at a low (0.01% w/v) or high (0.04 % w/ v) concentration. TP at 0.01% reduced the levels of both lipid and protein oxidation markers in emulsions, independent of the protein location. However, TP were more potent when proteins were located at the interface. At 0.04%, TP were only weakly antioxidant towards lipids but were prooxidant towards proteins in emulsions with proteins at the interface, whereas they were still somewhat antioxidant for aqueous phase proteins. These results indicate that TP may act as either antioxidants or prooxidants depending on their concentration and also on the location of the proteins in emulsions. The level of TP should be optimized for emulsion-based foods or beverages to achieve optimum antioxidant activity.

Automated summary

This study investigated the effects of protein location on the antioxidant and prooxidant activities of tea polyphenols in oil-in-water emulsions. The results showed that tea polyphenols reduced both lipid and protein oxidation levels in emulsions, regardless of protein location. However, the antioxidant activity was more pronounced when proteins were located at the interface. At higher concentrations, tea polyphenols exhibited weaker antioxidant activity towards lipids and prooxidant activity towards interface proteins, while still retaining some antioxidant activity for aqueous phase proteins.