Jasmine green tea is an excellent source of natural polyphenol antioxidants including mainly (-) epicatechin (EC), (-) epicatechin gallate (ECG), (-) epigallocatechin (EGC) and (-) epigallocatechin gallate (EGCG). The present study was to test our hypothesis that ingestion of jasmine tea would protect red blood cell (RBC) membrane from free radical-induced oxidation if jasmine tea epicatechin isomers could be absorbed and circulated in blood. When incubated with RBC suspension, all four epicatechin isomers purified from jasmine tea exhibited a strong protection for RBC membrane to hemolysis induced by 2,2'-azo-bis(2-amidinopropane) dihydrochloride (AAPH), an azo free radical initiator. The inhibitory effect was dose-dependent at the concentrations of 2.5 microM to 40 microM. The fatty acid analysis revealed that all four epicatechin isomers significantly prevented loss of arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) in RBC incubated under the same conditions. Although the in vitro antioxidative activity of EGCG and ECG was more effective than EGC and EC, the latter two isomers were more important in vivo in scavenging free radicals. This was because only EGC and EC instead of EGCG and ECG were circulating in blood stream after a gavage-dose of 100 mg jasmine tea GTP mixture. In fact, ingestion of jasmine tea GTP extracts was associated with a significant decrease in susceptibility of RBC to hemolysis in rats.