Green tea cateachins (GTC). namely (-) epicatechin (EC), (-) epicatechin gallate (ECG), (-) epigallocatechin (EGC), and (-) epigallocatechin gallate (EGCG), have been studied extensively for their wide-ranging biological activities. The goal of the present study was to examine the stability of GTC as a mixture under various processing conditions. The stability study demonstrated that GTC was stable in water at room temperature. When it was brewed at 98 degrees C for 7 h, longjing GTC degraded by 20%. When longjing GTC and pure EGCG were autoclaved at 120 degrees C for 20 min, the epimerization of EGCG to (-) gallocatechin gallate (GCG) was observed. The relatively high amount of GCG found in some tea drinks was most likely the epimerization product of EGCG during autoclaving. If other ingredients were absent, the GTC in aqueous solutions was pH-sensitive: the lower the pH, the more stable the GTC during storage. When it was added into commercially available soft drinks or sucrose solutions containing citric acid and ascorbic acid, longjing GTC exhibited varying stability irrespective of low pH value. This suggested that other ingredients used in production of tea drinks might interact with GTC and affect its stability. When canned and bottled tea drinks are produced, stored, and transported, the degradation of GTC must be taken into consideration.

Dimeric procyanidins can be detected in human plasma as early as 30 min after the consumption of a flavanol-rich food such as cocoa.

Green tea catechins (GTCs), which include (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG), possess a variety of biological activities. We have previously studied the effect of dietary GTCs as a mixture on membrane oxidation of red blood cells and found that GTCs were partially absorbed and detected in the blood of rats given an oral ingestion of 100 mg of GTCs. To explain the partial absorption of GTCs and their varying free-radical scavenging capacity at different pH, the present paper was to study further the pH stability of these GTC isomers because there is a sharp increase in pH from the acidic stomach to the slightly alkaline intestine. Longjing GTCs as a mixture in alkaline solutions (pH > 8) were extremely 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, the stability of GTCs was pH-dependent, i.e., the lower the pH, the greater the stability. Four epicatechin isomers examined demonstrated varying stability in alkaline solutions with EGCG and EGC being equally instable, and EC and ECG being relatively stable. The present results suggest that part of the mechanism by which GTCs were partially absorbed may be attributed to instability of EGCG and EGC in the intestine where the pH is neutral or alkaline.

While the antioxidative properties of green and black tea have been extensively studied, less attention has been given to these properties in oolong tea. The reducing powers, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities, the amount of total phenolic compounds, the inhibitory effect on FeCl(2)/H(2)O(2) (Fenton reaction system)-induced DNA damage, and the inhibitory effect on erythrocyte hemolysis of an oolong tea water extract (OTE) were evaluated in the present study. The OTE was found to have strong antioxidative activities in all of the model systems tested. When the OTE was separated into different fractions according to molecular weight, it was found that the fractions with higher amounts of phenolic compounds (lower molecular weight) have stronger antioxidative activities. The present results support the concept that oolong tea contains several low molecular weight antioxidants that may have health promotion activities.

Cocoa flavanols and procyanidins possess wide-ranging biological activities. The present study investigated the stability of the cocoa monomers, (-)-epicatechin and (+)-catechin, and the dimers, epicatechin-(4beta-8)-epicatechin (Dimer B2) and epicatechin-(4beta- 6)-epicatechin (Dimer B5), in simulated gastric and intestinal juice and at different pH values. The dimers were less stable than the monomers at both acidic and alkaline pH. Incubation of Dimer B2 and Dimer B5 in simulated gastric juice (pH 1.8) or acidic pH resulted in degradation to epicatechin and isomerization to Dimer B5 and Dimer B2, respectively. When incubated in simulated intestinal juice or at alkaline pH, all four compounds degraded almost completely within several hours. These results suggest that the amount, and type, of flavanols and procyanidins in the gastrointestinal tract following the consumption of cocoa can be influenced by the stability of these compounds in both acidic and alkaline environments.