Efficiency of the extraction of catechins from green tea

The effects of various experimental conditions that may affect the extraction efficiency of green tea catechins were studied using aqueous buffers. Some catechins were absorbed by certain types of filtration membranes which caused errors in their analysis. At higher pH conditions, the amounts of the major catechins (EC, EGG, ECg and EGCg) extracted from tea were decreased and the amounts of minds catechins (C, GC, Cg and GCg) were increased. This observed shift in the levels extracted is considered a consequence of epimerization of the major catechins to the minor catechins. In general, the major differences in the extraction efficiency of major catechins by difference of pH were observed with a lower tea concentration. Also, at the same pH value, extraction efficiencies varied, depending on the catechins and the tea-water ratio. (C) 1999 Elsevier Science Ltd. All rights reserved.