Chemical Modification On Tea Polyphenols And Study On Lipid-Soluble Tea Polyphenols

Lots of hydroxyls exist in the molecular structure of Tea Polyphenols(TP).These hydroxyls contribute to the water soluble properties of TP. Therefore, TP has the potential use in lipid environment widely and effectively, given that its solubility in oil phase can be enhanced by chemical modification without damaging its premier physiological and biological properties.The traditional way of chemical modification on TP is to use acylation. This procedure"introduces"acyl group onto the phenolic hydroxyls of TP and produces LTP (Lipid-soluble Tea Polyphenols). The optimal reaction temperature is between 30-40℃. The optimal reaction time is 8-9 hours. 89-91% ethanol solution is used to extract the compound. To avoid losing the amount of phenolic hydroxyls during esterification, attempts are made to introduce acyl group onto the phenolic structure of TP. Besides, a new procedure to produce LTP by means of acylation is introduced in this study.These two kinds of LTP made by modifying the TP with esterification and acylation respectively, their antioxidant activity was studied and compared with other antioxidants. The ultra violet characters, lipid solubility, anti-free radical, anti-superoxidation free radical and anti-lipid peroxidation activities of these two kinds of LTP as well as other antioxidants were investigated by ultra violet spectroscopy, TLC, chemilum inescence and redox titration respectively. These two kinds of LTP show differences in Ultra Violet characters and antioxidant activity. LTP made by acylation performed better than LTP made by esterification in lipid solubility. They worked similarly well and better than other anti-oxidants except for TBHQ. Using EGCG as the model for TP, we made Lipid-soluble EGCG by esterification. HSCCC(High Speed Counter-current Chromatography)is used to separate Lipid-soluble EGCG. N-hexane(v)∶ethyl acetate (v)∶methryl(v)∶water(v)=1∶1∶1∶0.5 was used as the solution of chromatography in the study, with the upper phase of which as the mobile phase and the lower phase of which as the stationary phase. The velocity of flow is 1ml/min and the speed is 700 round/min. The five peaks derived from HSCCC was examined for the degree of esterification by GC—MS and HPLC. It was concluded that the major components were separated from each HSCCC peak but not for single component. There showed obvious trends that with the increase in the degree of esterification, the lipid solubility increase; the polarity decreases; retention time decreases in HSCCC procedure; retention time increases in HPLC procedure. The differences in retention time of separation due to the differences in polarity can be explained by the fact that they are combined with different amount of esters. The common structures of compounds with different degree of esterification are identical. They are only different in the amount of esters. Thus it is difficult to obtain the single component separately. This provides the conditions for the optimization of HSCCC procedure, and also contributes to the study of anti-oxidant properties of lipid soluble TP with different degrees of esterification.