Studied On The Thermal Stability Of Epigallocatechin Gallate

Epigallocatechin gallate （EGCG） is the most important catechin in green tea whichhas many health benefits. But EGCG is very unstable and can be easy influenced byvarious factors like temperature, pH and metal ions in the process of machining andstoring of tea beverage.The occurred degradation and epimerization will change theformer biological activity of EGCG and also exert negative influence on the quality of teabeverage. The effect of temperature on EGCG was studied and the chemical kinetics ofvarious EGCG reactions were analyzed.The effects of L-cys and L-Vc on the thermalreaction of EGCG were also discussed. The red compounds produced form the thermalreaction of EGCG adding L-cys were purified and analyzed. Following conclusions wereobtained:1This degradation, epimerization, de-gallateand acid and oxidation reaction of EGCGunder different heat treatment were studied, and the related kinetic predicting modelswere established by using Arrhenius equation.The results showed that Ea （activationenergy） and A （frequency factor） of the degradation, epimerization, de-gallate acid andoxidation reaction of EGCG in predicting model were53.90kJ/mol and5.698×10⁴,98.60kJ/mol and7.315×10¹²,85.34kJ/mol and5.112×10¹⁰,89.24kJ/mol and1.720×10¹⁰,respectively. It showed that the degradation of EGCG could be vulnerable occured andthe epimerization of EGCG was difficult, the de-gallate acid and oxidation reaction ofEGCG were close. The relative error between the model predicted value and actual valuewas less than13%. Therefore, the heating variation of EGCG could be predicted byArrhenius equation.2By adding L-cys and L-Vc to control the oxidation of EGCG, the experience foundthat L-cys and L-Vc was not consistent. L-cys, promoted the epimerization whileinhibiting oxidation, however, L-Vc also inhibited the epimerization while inhibitingoxidation. After adding L-cys and L-Vc with equal molar concentration （0.23mmol/L） toEGCG and treating at100℃for60min,found that L-cys retained96.56%of EGCG andGCG, while70.71%of EGCG epimerized to GCG; L-Vc retained96.21%of EGCG andGCG, while7.73%of EGCG epimerized to GCG.3The mechanism that L-cys promoted EGCG epimerization and inhibited EGCGoxidation was analyzed by means of chemical kinetics. The results showed that addingL-cys into EGCG solution during heat treatment, activation energy of degradationincreased from53.90kJ/mol to72.67kJ/mol, which could inhibit the degradation of EGCG; while the activation energy epimerization decreased from98.60kJ/mol to88.49kJ/mol, which which could promote the epimerization of EGCG. It showed thatL-cys inhibited the EGCG degradation while inhibited the EGCG epimerization.4The red water-soluble compounds were produced in EGCG solution added L-cysafter heat treatment. The compounds had the characteristic absorption peak at500nm andwere purified by HPD-400macroporous resin. The purified products showed4newsubstance peaks at500nm by HPLC detection.