Most of the polyphenols in green tea are flavan-3-ols (catechins).

The phenolic content in tea refers to the phenols and polyphenols, natural plant compounds which are found in tea. These chemical compounds affect the flavor and mouthfeel of tea. Polyphenols in tea include catechins, theaflavins, tannins, and flavonoids.

Polyphenols found in green tea include, but are not limited to, epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin; flavanols such as kaempferol, quercetin, and myricitin are also found in green tea.[1]

Catechins

Green tea UV 280 nm chromatogram. Highest peak is caffeine, second highest is EGCG

Catechins include epigallocatechin-3-gallate (EGCG), epicatechin (EC), epicatechin-3-gallate (ECg), epigallocatechin (EGC), catechin, and gallocatechin (GC). The content of EGCG is higher in green tea.[2]

Catechins constitute about 25% of the dry mass of a fresh tea leaf,[3] although total catechin content varies widely depending on species, 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.

A 2011 analysis by the European Food Safety Authority found that a cause and effect relationship could not be shown for a link between tea catechins and the maintenance of normal blood LDL-cholesterol concentration.[4]

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.[5]

Theaflavins

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

Catechin monomer structures are metabolized into dimers theaflavins and oligomers thearubigins with increasing degrees of oxidation of tea leaves.[6] Theaflavins contribute to the bitterness and astringency of black tea. The mean amount of theaflavins in a cup of black tea (200 ml) is 12.18 mg.[7]

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).[8]

Tannins

Tannins are astringent, bitter polyphenolic compounds that bind to and precipitate organic compounds. Gallic acid conjugates all of the catechins, such as EGCG (Epigallocatechin gallate), which are tannins with astringent qualities.[9]

Flavonoids

See also: Polyphenol § Research

Phenols called flavonoids are under preliminary research, as of 2020, but there is no evidence that flavonoids have antioxidant activity in vivo, or affect physical health or diseases.[10][11] Tea has one of the highest contents of flavonoids among common food and beverage products.[7] Catechins are the largest type of flavonoids in growing tea leaves.[6] 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.[7]

Research

A 2020 review found low- to moderate-quality evidence that daily tea consumption might lower the risk for cardiovascular disease and death.[12]

See also

References

  1. ^ Khan N, Mukhtar H (2013). "Tea and health: studies in humans". Current Pharmaceutical Design (Literature Review). 19 (34): 6141–7. doi:10.2174/1381612811319340008. PMC 4055352. PMID 23448443.
  2. ^ Thermo Scientific (Dionex) Application Note 275. Sensitive Determination of Catechins in Tea by HPLC . Retrieved 3 August 2013.
  3. ^ Balentine DA, Harbowy ME, Graham HN (1998). "Tea: the Plant and its Manufacture; Chemistry and Consumption of the Beverage". In Spiller GA (ed.). Caffeine. Boca Raton: CRC Press. p. 35. ISBN 978-0-8493-2647-9.
  4. ^ EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies) (2011). "Scientific Opinion on the substantiation of health claims related to Camellia sinensis (L.) Kuntze (tea), including catechins in green tea, and improvement of endothelium-dependent vasodilation (ID 1106, 1310), maintenance of normal blood pressure". EFSA Journal. 9 (4): 2055. doi:10.2903/j.efsa.2011.2055.
  5. ^ Pietta, P. G.; Simonetti, P.; Gardana, C.; Brusamolino, A.; Morazzoni, P.; Bombardelli, E. (1998). "Catechin metabolites after intake of green tea infusions". BioFactors. 8 (1–2): 111–8. doi:10.1002/biof.5520080119. PMID 9699018. S2CID 37684286.
  6. ^ a b Peterson, J.; Dwyer, J.; Bhagwat, S.; Haytowitz, D.; Holden, J.; Eldridge, A.L.; Beecher, G.; Aladesanmi, J. (2005). "Major flavonoids in dry tea". Journal of Food Composition and Analysis. 18 (6): 487–501. doi:10.1016/j.jfca.2004.05.006. hdl:10113/7266.
  7. ^ a b c U.S. Department of Agriculture, USDA Database for the Flavonoid Content of Selected Foods, Release 2.1, January 2007[non-primary source needed]
  8. ^ Del Rio, Daniele; Stewart, Amanda J.; Mullen, William; Burns, Jennifer; Lean, Michael E. J.; Brighenti, Furio; Crozier, Alan (2004). "HPLC-MSnAnalysis of Phenolic Compounds and Purine Alkaloids in Green and Black Tea". Journal of Agricultural and Food Chemistry. 52 (10): 2807–15. doi:10.1021/jf0354848. PMID 15137818.
  9. ^ Crozier, Alan; Jaganath, Indu B.; Clifford, Michael N. (2009). "Dietary phenolics: Chemistry, bioavailability and effects on health". Natural Product Reports. 26 (8): 1001–43. CiteSeerX 10.1.1.608.4407. doi:10.1039/b802662a. PMID 19636448.
  10. ^ "Flavonoids". Linus Pauling Institute, Oregon State University, Corvallis. 2016. Retrieved 2020-04-15.
  11. ^ EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)2, 3 European Food Safety Authority (EFSA), Parma, Italy (2010). "Scientific Opinion on the substantiation of health claims related to various food(s)/food constituent(s) and protection of cells from premature aging, antioxidant activity, antioxidant content and antioxidant properties, and protection of DNA, proteins and lipids from oxidative damage pursuant to Article 13(1) of Regulation (EC) No 1924/20061". EFSA Journal. 8 (2): 1489. doi:10.2903/j.efsa.2010.1489.((cite journal)): CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  12. ^ Chung, Mei; Zhao, Naisi; Wang, Deena; Shams-White, Marissa; Karlsen, Micaela; Cassidy, Aedín; Ferruzzi, Mario; Jacques, Paul F.; Johnson, Elizabeth J.; Wallace, Taylor C. (19 February 2020). "Dose–Response Relation between Tea Consumption and Risk of Cardiovascular Disease and All-Cause Mortality: A Systematic Review and Meta-Analysis of Population-Based Studies". Advances in Nutrition. 11 (4): 790–814. doi:10.1093/advances/nmaa010. PMC 7360449. PMID 32073596.
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