Application of Tea Polyphenols to Edible Oil as Antioxidant by W/O Microemulsion

The lipophilic properties of tea polyphenols have restricted their application as a natural antioxidant in oils. In order to increase the weight percentage of tea polyphenols in edible oil, a water-in-oil (W/O) microemulsion (ME) of Tween 80/Span 80/ethanol/soybean oil/H2O for envelopment of tea polyphenols was prepared. The ternary phase diagram, electrical conductivity, particle size, viscosity, rheological behavior, and oxidation resistance potential of the ME were investigated. The results showed that (1) the W/O ME formed when water content was below 30%; (2) the mean particle size of the ME system was about 8.40 nm and basically remained stable for 45 days; (3) the ME was characterized as pseudoplastic at low shear rate and as Newtonian viscous fluid at high shear rate; moreover, it had acceptable salinity and pH tolerance; and (4) peroxide value determination indicated the antioxidant effect of the ME was enhanced by the addition of tea polyphenols.