Enzymatic Synthesis Of Lipid-Soluble Tea Polyphenols And Study On Its Antioxidant Activity

The natural lipid-soluble antioxidants can not meet the needs of the markets. The chemical synthesis antioxidants can not be widely recognized because of its security. Tea polyphenols have good antioxidant activity. But it is soluble in water, insoluble in oil, which limited its application in oil. Therefore, this study is aimed to synthesis the modified tea polyphenols. In this study, the mild and selective enzymatic method was selected. Tea polyphenols were added to the non-polar molecules of fatty acid chains, then the polarity of the modified polyphenols became smaller.It is due to the fact that esterified catechin of tea polyphenols can not participate in the lipase-catalyzed transesterification. So tea polyphenols were hydrolyzed by tannase and the products were characterized and quantified by HPLC. The results show that Epigallocatechin-3-O-gallate (EGCG) and epicatechin-3-O-gallate (ECG) were completely converted to epicatechin (EC), epigallocatechin (EGC) and gallic acid (GA) by tannase degallation.The effect of reaction solvent, lipase, substrate molar ratio, reaction time and reaction temperature on the esterification rate of tea polyphenols were studied.The optimal solvent was15mL of acetoneand isooctane (2:3). In the optimal reaction solvent system, the catalytic effect of10%Novozyme435and20%Lipozyme TL IM is the best. Response surface methodology (RSM) were empolyed to estimate the effects of reaction parameters. The optimal reaction conditions were showed as follows:29.25h,53.50℃, enzyme amount of30.70%, and substrate molar ratios (soybean oil:tea polyphenols) of3.15:1and the maximum conversion of tea polyphenols was52.20%.The solubility of modified tea polyphenols is much better than tea polypheols in soybean oil. At25℃and60℃, the solubility of modified tea polyphenols are300-400mg/100g soybean oil, and tea polyphenols are only50-100mg/100g soybean oil. And in soybean oil, the antioxidant effect of modified tea polyphenols are also significantly better than tea polyphenols, VE, BHT, BTA, but slightly lower than TBHQ.The reaction of EGC and triolein was studied preliminarily as a model. The results showed that m/z=837was oleic acid acylated catechin by HPLC-ESI-MS detection.In this study, the lipid-soluble tea polyphenols using enzymatic esterification is a mixed ester, which has good antioxidant activity. The lipid-soluble tea polyphenols can be used as a fat-soluble antioxidant.