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Phenolic Content in Tea

Natural phenols and polyphenols are compounds found naturally in plants. A group of natural phenols called the flavonoids are of most popular interest because researchers have found them to have the potential to contribute to better health.[1][2][3][4][5]

Tea has one of the highest contents of flavonoids among common food and beverage products.[6] A group of flavonoids called catechins is responsible for the majority of flavonoids in the growing tea leaves.[7] Most of them are retained in processed green tea.[7] The green tea catechin epigallocatechin-3-gallate (EGCG) is studied in great detail in relation to its health contributing potential.[4]

Other flavonoids in tea, in much lower concentrations, include kaempferol, myricetin, quercetin, and minute quantities of apigenin and luteolin.[6][7]

According to a report released by USDA, in a 200-ml cup of tea, the mean total content of flavonoids is 266.68 mg for green tea, and 233.12 mg for black tea.[6] The tea is to be prepared with 1 gram of tea leaves to 100 ml of hot water. The mean averages are much lower for instant tea mixes, decaffeinated, flavored, or ready-to-drink tea products.[6]

Contents

Catechins: the main phenolics in green tea

Tea catechin is a most researched subject concerning the health potential of tea.[1][4] The catechins in green tea are epicatechin (EC), epicatechin-3-gallate (ECg), epigallocatechin (EGC), epigallocatechin-3-gallate (EGCG), catechin, and gallocatechin (GC).

Of all the catechins, EGCG receives large scientific attention, being singled out in a number of them as a key contributive element to the possible health effects of tea.[1][2][3][4][5]

Catechins constitute about 25% of the dry weight of fresh tea leaf,[8] although total catechin content varies widely depending on clonal variation, growing location, season, light variation, and altitude. They are present in nearly all teas made from Camellia sinensis, including white tea, green tea, black tea and oolong tea. Nevertheless, the so-called Pu-Erh teas, which are fermented with microbes, contain very little catechins due to their unique microbial breakdown process, whilst black tea contains very little catechins due to the full oxidization process which converts catechins to Theaflavins. [9]

Theaflavins: the polyphenol in black tea associated with health effects

Darjeeling black tea infusion: Finer black tea has a more orange tone than red as a result of higher theaflavins content.

The catechin monomer structures breakdown and become dimers theaflavins and oligomers thearubigins with increasing degrees of oxidation of the tea leaves.[7]. Theaflavins directly contribute to the bitterness and astringency of steeped black tea.

Three main types of theaflavins are found in black tea, namely theaflavin (TF-1), theaflavin-3-gallate (TF-2), and theaflavin-3,3-digallate (TF-3). A number of studies on their possible health effects have shown positive results.[10][11]

The mean amount of theaflavins in a cup of black tea (200 ml) is 12.18 mg.[6]

Thearubigins are of unknown structure,[7] and no specific studies have been focused on them for health effects.[citation needed]

About tannins in tea

Tea (Camellia sinensis) is a source of dietary polyphenols, notably tannin, which is an astringent, bitter polyphenolic compound, also found in many other plants. Those in green tea are mainly flavan-3ols (catechins). Although tea contains various types of polyphenols and tannin, it does not contain tannic acid.[12] Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.[13]

Metabolism

4-Hydroxybenzoic acid, 3,4-dihydroxybenzoic acid (protocatechuic acid), 3-methoxy-4-hydroxy-hippuric acid and 3-methoxy-4-hydroxybenzoic acid (vanillic acid) are the main catechins metabolites found in humans after consumption of green tea infusions.[14]

See also

References

  1. ^ a b c Chung S. Yang et al, Antioxidative and anti-carcinogenic activities of tea polyphenols, Archives of Toxicology 83(1): 11-25, 2009
  2. ^ a b Kevin C. Maki et al, Green Tea Catechin Consumption Enhances Exercise-Induced Abdominal Fat Loss in Overweight and Obese Adults, Journal of Nutrition 139: 264–270, 2009
  3. ^ a b Jun-ichi Suzuki et al, Tea Polyphenols Regulate Key Mediators on Inflammatory Cardiovascular Diseases, Mediators of Inflammation Volume 2009, Article ID 494928
  4. ^ a b c d Carmen Cabrera et al, Beneficial Effects of Green Tea—A Review, Journal of the American College of Nutrition, 25(2): 79–99, 2006
  5. ^ a b Joshua D. Lambert et al, Mechanisms of Cancer Prevention by Tea Constituents, Journal of Nutrition 133: 3262S-3267S, 2003
  6. ^ a b c d e U.S. Department of Agriculture, USDA Database for the Flavonoid Content of Selected Foods, Release 2.1, January 2007
  7. ^ a b c d e Julia Peterson et al, Major flavonoids in dry tea, Journal of Food Composition and Analysis 18: 487–501, 2005
  8. ^ Balentine DA, Harbowy ME, Graham HN (1998). “Tea: the Plant and its Manufacture; Chemistry and Consumption of the Beverage”. In Spiller GA. Caffeine. Boca Raton: CRC Press. ISBN 0-8493-2647-8.
  9. ^ [1]
  10. ^ Amy R. Cameron et al, Black tea polyphenols mimic insulin/insulin-like growth factor-1 signaling to the longevity factor FOXO1a, Aging Cell 7: 69–77, 2008
  11. ^ Chih-Li Lin et al, Theaflavins attenuate hepatic lipid accumulation through activating AMPK in human HepG2 cells, Journal of Lipid Research 48: 2334~2340, 2007
  12. ^ Steven Wheeler: Science Magazine.
  13. ^ Tannin Chemistry pg 11
  14. ^ Catechin metabolites after intake of green tea infusions. P. G. Pietta, P. Simonetti, C. Gardana, A. Brusamolino, P. Morazzoni and E. Bombardelli, BioFactors, 1998, Volume 8, Issue 1-2, pp. 111–118,doi:10.1002/biof.5520080119

This article uses material from the Wikipedia article phenolic content in tea, which is released under the Creative Commons Attribution-Share-Alike License 3.0.

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