Phenolic content in tea

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

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 be of health contributing potential.^{[1][2][3][4][5]}

Tea has one of the highest contents of flavonoids among common food and beverage products.^[6][7] A group of flavonoids called catechins is responsible for the majority of flavonoids in the growing tea leaves.^[8] Most of them are retained in processed green tea.^[8] Epigallocatechin 3-gallate (EGCg), aka EGCG, is the single most studied catechin in relation to health contributing potential.^[4] It constitutes 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 lower concentrations, include kaempferol, myricetin, quercetin, and minute quantities 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 phenolics 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 studies have been done on their possible health effects with positive results.^[14][15]

The mean 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. Nevertheless, the so-called Pu-Erh teas, which are post-fermented, contain very little -if at all- catechin as a result of long time fermentation. ^[19]

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.^[20]

Non exhaustive list of phenolic compounds found in tea

• Catechin
• Epigallocatechin gallate (EGCG)
• Gallocatechol
• Theaflavin

See also

• List of health effects of tea

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". http://teaguardian.com/health/healthbenefits.html. 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". http://teaguardian.com/health/tea_flavonoids_nature.html. Retrieved 18 February 2011. 
10. ^ ^{a b} The Tea Guardian. "Tea Polyphenols: Are You Getting Enough?". http://teaguardian.com/health/tea_catechins_quantity_differences.html. Retrieved 18 February 2011. 
11. ^ The Tea Guardian. "Burn That Fat! (in the section about tea quality)". http://teaguardian.com/health/fight_obesity.html. Retrieved 18 February 2011. 
12. ^ The Tea Guardian. "Baked Green Teas: Huangshan Maofeng". http://teaguardian.com/Tea_Varieties/green_baked_huangshanmaofeng.html. Retrieved 18 February 2011. 
13. ^ The Tea Guardian. "Steamed Green Tea Uji Gyokuro: Tasting Notes". http://teaguardian.com/Tea_Varieties/green_steamed_gyokuro_tasting.html. 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. Caffeine. Boca Raton: CRC Press. ISBN 0-8493-2647-8. 
19. ^ [1]
20. ^ 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