STUDIES ON PRESERVATION OF CONSTITUENTS I N CANNED DRINKS .5. A NEW EXTRACTION PROCEDURE FOR DETERMINATION OF CAFFEINE AND CATECHINS IN GREEN TEA

In our previous study, it was shown that tea catechins isomerized to i ts corresponding epimer by heating in infusion, suggesting that the an alytical value of catechins in tea leaves closely depended upon the ex traction temperature, time and media. For a simultaneous determination of caffeine and catechins by HPLC, a comparative study of extraction procedure to prevent isomerization of catechins was performed with con ventional hot water and aqueous acetonitrile at an ambient temperature . Green tea was extracted with 100 (w/v) times of cold water (20 degre es C), hot water (80 degrees C), acetonitrile (20 degrees C), and aque ous acetonitrile (20 degrees C) of different concentrations [75, 60, 5 0, 40 and 25% (v/v)]. It was found that catechins were slightly solubl e in acetonitrile, but stable and maximum analytical value of catechin s were obtained by the extraction of aqueous acetonitrile with the pre vention of isomerization, and epimerization of catechins was proceeded during extraction with hot water which resulted in unstable analytica l value. The proposed procedure was to extract green tea with aqueous acetonitrile (50%) at 20 degrees C for 40 min with stirring. By this p rocedure, maximum and stable analytical value of caffeine and catechin s were obtained for the original concentrations in green tea. It was a lso found that at pH of extraction media above 6.0 green tea catechins isomerized to its corresponding epimer during extraction at 60 degree s C for 3 min, and browning of the infusion was accelerated.