TEA & ANTIOXIDANTS

Black Tea is a Powerful Chemopreventor of Reactive Oxygen and Nitrogen Species: Comparision with its Individual Catechin Constituents and Green Tea
Anasuya Sarkar and Amar Bhaduri, Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Kolkata 700 032, India.

Production of black tea (BT) results in biotransformation of catechins of green tea (GT) to theaflavins and theraubigins. BT was found to be more efficient than GT and its individual catechin constituents in proportionate amounts in abrogating production of NO and O2 in activated murine peritoneal macrophages. In a reconstitution system of BT that is free of all catechins, stepwise addition of catechins showed that though all the constituents contributed to the overall effect of BT, theaflavin was the most powerful in abrogating NO production. RT-PCR analysis also showed theaflavin to be the most important constituent in down-regulating synthesis of ions. Clearly, BT containing theaflavin is an excellent chemopreventor against reactive oxygen and nitrogen species.

Antioxidant Capacity of Tea and Common Vegetables
Guohua Cao, Emin Sofic, Ronald Prior, USDA-ARS, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, Massachusetts 02111, and Nutritional Science Department, University of Connecticut, Storrs, Connecticut 06269

Previously, some fruits were shown to contain high antioxidant activities. In this paper, we report the antioxidant activities of 22 common vegetables, one green tea, and one black tea measured using the automated oxygen radical absorbance capacity assay with three different reactive species; a peroxyl radical generator, a hydroxyl radical generator and Cu2, a transition metal. Based on the fresh weight of the vegetable, garlic had the highest antioxidant activity (mumol of Trolox equiv./g) against peroxyl radicals (19.4) followed by kale (17.7), spinach (12.6), Brussels sprouts, alfalfa sprouts, broccoli flowers, beets, red bell pepper, onion, corn, eggplant (9.8-3.9), cauliflower, potato, sweet potato, cabbage, leaf lettuce, string bean, carrot, yellow squash, iceberg lettuce, celery, and cucumber (3.8-0.5); kale had the highest antioxidant activity against hydroxyl radicals followed by Brussels sprouts, alfalfa sprouts, beets, spinach, broccoli flowers, and the others. The green and black teas had much higher antioxidant activities against peroxyl radicals than all these vegetables. However, the tea also showed a prooxidant activity in the presence of Cu2, which was not found with any of the vegetables studied.

Antioxidant properties of flavonol glycosides from tea
Plumb, G.W., Price, K.R., & Williamson, G., Redox Report, Vol. 4, 1999

We have determined the antioxidant activity of the major flavonols found in tea: a monoglycoside, a diglycoside and two triglycosides of kaempferol and three monoglycosides, a diglycoside and two triglycosides of quercetin. The Trolox equivalent antioxidant capacity (TEAC) and inhibition of iron/ascorbate-induced lipid peroxidation of phosphatidyl choline vesicles were measured. In the aqueous phase TEAC assay, the quercetin monoglycosides and diglycoside were approximately half as effective as quercetin aglycone. The quercetin triglycosides were much less effective than the monoglycosides and the diglycoside. The kaempferol glycosides were 32-39% less effective in the aqueous phase antioxidant assay compared to the kaempferol aglycone. Quercetin monoglycosides and diglycosides were potent inhibitors of lipid peroxidation, in contrast to the triglycoside, which was much less effective. All the kaempferol glycosides were significantly less potent inhibitors of lipid perioxidation compared to the kaempferol aglycone. The compounds described herein demonstrate the antioxidant activity of the major flavonols in tea and indicate the effect of substituting a range of sugar moieties in the phenolic C ring.

Antioxidant Effectiveness of Teas and Their Binding with Lipoproteins
Vinson-J-A, Dabbagh-Y-A, NUTR-RES, 1998, Vol./Issue/Pg. 18/6 (1067-1075), ISSN: 0271-5317, Full

Phenols in tea are responsible for its antioxidant activity. The pure catechins and phenolic acids found in tea are more powerful than the antioxidant vitamins C, E and B-carotene in an in vitro lipoprotein oxidation model. Comparison of the tea fractions indicated that both catechins and theaflavins contribute to the teas' antioxidant characteristics. Black and green teas were not significantly different in phenol content, in antioxidant strength as measured by IC50, or in antioxidant potential as measured by the phenol antioxidant index (PAOXI). The PAOXI of teas was significantly higher than grape juices and wines. Tea catechins and both green and black tea exhibited potent lipoprotein-bound antioxidant activity. Phenol antioxidants from tea were calculated to be a large source of antioxidants in the U.S. diet.