Decaffination Of Tea Catechins And Effect Of Catechins On ACE Inactivity

Ethyl acetate, n-butanol and n-hexane were used as solvents to separate catechins from green tea extract solution and the catechins were decaffeinated using citric acid solution. Ethyl acetate was confirmed to be an appropriate solvent for isolating catechins from tea extract, based on the yield of catechins and the concentration of caffeine. The optimum extraction conditions were that 100 g tea was extracted in 3 L water at 80℃for 40 min and the catechins in the extracted solution were isolated using 1.5 L ethyl acetate for three times. The extracted catechins complex in the ethyl acetate phase was then decaffeinated by washing the organic phase with 1.5 L of 10 g·L-1 citric acid solution for three times. The obtained dried product contained 694.47 mg·g-1 catehchins and 37.89 mg·g-1 caffeine, with 78.8% caffeine being removed. The method is considered to be an alternative to replace traditional chloroform decaffeination method.N-vinylpyrrolidone-grafted fir sawdust lignocellulose (GFSL) was evaluated as an adsorbent to remove caffeine from tea extract solution. The adsorption capacity of total catechins for the GFSL was further increased by 49.47% compared to that of un-grafted FSL. The time at which sorbent capacity reached 99% was for un-grafted FSL, but 50 min for the GFSL. The adsorption process of GFSL to catechins was fitted well to the pseudo-second order rate equation.The effects of five kinds of teas (34 tea samples)on angiotensin converting enzyme (ACE) activity were studied using green tea (GT). oolong tea (OT), white tea (WT), black tea (BT) and dark tea (DT). In vitro ACE inhibitory activity of various teas was in the following sequence:green tea> oolong tea> white tea> black tea> dark tea. Tea extracts were separated into two fractions, i.e. fraction with molecular weight (MW)<3 kDa and fraction with MW> 3 kDa. Substrate-dependence reaction kinetics was studied using GT, BT and polyphenolics using the two fractions. It revealed that enzyme active velocity curves was fitted allosteric model instead of Michaelis-Menten relationships. The inhibition activity was weakly dependent on substrate concentration for GT fraction with MW> 3 kDa, but independent on substrate concentration for all other GT and BT size fractions, and green tea polyphenolic isolate (GTPI). Furthermore, GTPI had inactivation activity directly on ACE. It suggests that tea polyphenolics exerted a mixed mode of in vitro inhibition on ACE.