| Abstract
| - Green tea catechins (GTCs), which include (−)-epicatechin (EC),(−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG),possess a variety of biologicalactivities. We have previously studied the effect of dietary GTCsas a mixture on membrane oxidationof red blood cells and found that GTCs were partially absorbed anddetected in the blood of ratsgiven an oral ingestion of 100 mg of GTCs. To explain the partialabsorption of GTCs and theirvarying free-radical scavenging capacity at different pH, the presentpaper was to study furtherthe pH stability of these GTC isomers because there is a sharp increasein pH from the acidic stomachto the slightly alkaline intestine. Longjing GTCs as a mixture inalkaline solutions (pH > 8) wereextremely unstable and degraded almost completely in a few minutes,whereas in acidic solutions(pH < 4) they were very stable. For the pH between 4 and 8, thestability of GTCs was pH-dependent,i.e., the lower the pH, the greater the stability. Fourepicatechin isomers examined demonstratedvarying stability in alkaline solutions with EGCG and EGC being equallyinstable, and EC andECG being relatively stable. The present results suggest that partof the mechanism by whichGTCs were partially absorbed may be attributed to instability of EGCGand EGC in the intestinewhere the pH is neutral or alkaline. Keywords: Epicatechin; epicatechin gallate; epigallocatechin gallate;epigallocatechin; longjingtea
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