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Phenolic content in tea

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Most of the polyphenols in Green tea are catechins

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

Tea has one of the highest content of flavonoids in daily food and beverage products.[6][7] A group of flavonoids called catechins is responsible for the majority of flavonoids in the growing tealeaves.[8] Most of them are retained in the processed green tea.[8] Epigallocatechin 3-gallate (EGCg), aka EGCG, is the single most studied catechin in relation to health contributing potential.[4] It constitute 50 to 75% of the total flavonoid content in green tea.[9]

Most of these catechins are oxidized during black tea production to become the thearubigins that take up an average of 58% of the resultant flavonoids, and the theaflavins that amount to 6%.[9]

Other flavonoids in tea, in much lesser content, include kaempferol, myricetin, quercetin, and minute quantity of apigenin and luteolin.[6][8]

According to a report released by USDA, in a cup of tea of 200 ml, 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 tealeaves to 100 ml of hot water. The mean averages are much lower for instant tea mixes, decaf, flavored, or ready-to-drink tea products.[6]

Catechins: the main polyphenols in green tea

Tea catechins 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 has the most 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] It is found that the content of EGCg is the highest in the first young leaf immediately below the leaf bud.[10] Its content is 3 times that of the 4th young leaf.[10] This finding reinforced the tradition of prizing green tea made entirely of very young leaves.[11] In premium green tea production, only the bud and the first leaf, some with also the second leaf is plucked.[12]

In terms of taste, catechins are bitter. EGCg is one of the more bitter catechins. It is bitter with astringency. EC and EGC are bitter with sweet after taste.[9] Bitterness is an important element for a fine taste profile of a tea.[9] Seasoned tea drinkers control the amount of bitterness released into the tea liquid by adjusting infusion temperature, duration and tea leaves to water ratio.[9][13]

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.

When the tea leaves are processed into black tea, most of their catechins are oxidized.[9] The catechins are turned from the monomer structure to become the dimers that are the theaflavins and the oligomers that are thearubigins.[8] Depending on the quality and style of the black tea, a mean amount of 11% of the original EGCg may remain.[9]

There are chiefly three types of theaflavins in black tea, namely theaflavin (TF-1), theaflavin-3-gallate (TF-2), and theaflavin-3,3-digallate (TF-3). A number of researches have been done on their possible health effects with positive results.[14][15]

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

Thearubigins are of unknown structure[8] and no specific studies have been focused on them for health effects. They are the reason for the red color of black tea, while theaflavins contribute a yellowish orange color.[9] Typically a finer black tea has more theaflavins content and thus a more orange tone.[9]

About tannins in tea

Tea (Camellia sinensis) is a source of dietary polyphenols. Those in green tea are mainly flavan-3ols (catechins). Although tea contains various types of polyphenols and tannin, tea does not contain tannic acid.[16] Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.[17] Catechins constitute about 25% of the dry weight of fresh tea leaf,[18] although total catechin content varies widely depending on clonal variation, growing location, seasonal/ 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.

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. ^ The Tea Guardian. "Health Benefits of Tea". Retrieved 18 February 2011.
  8. ^ a b c d e Julia Peterson et al, Major flavonoids in dry tea, Journal of Food Composition and Analysis 18: 487–501, 2005
  9. ^ a b c d e f g h i The Tea Guardian. "Polyphenols in Green and Black Teas". Retrieved 18 February 2011.
  10. ^ a b The Tea Guardian. "Tea Polyphenols: Are You Getting Enough?". Retrieved 18 February 2011.
  11. ^ The Tea Guardian. "Burn That Fat! (in the section about tea quality)". Retrieved 18 February 2011.
  12. ^ The Tea Guardian. "Baked Green Teas: Huangshan Maofeng". Retrieved 18 February 2011.
  13. ^ The Tea Guardian. "Steamed Green Tea Uji Gyokuro: Tasting Notes". Retrieved 18 February 2011.
  14. ^ 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
  15. ^ 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
  16. ^ Steven Wheeler: Science Magazine.
  17. ^ Tannin Chemistry pg 11
  18. ^ 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. ISBN 0-8493-2647-8.{{cite book}}: CS1 maint: multiple names: authors list (link)
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