Polyphenols in green and black teas

Flavonoids are secondary metabolites that help a plant to grow strong and attain its various biological characters, such as its smell, colour or self-defense.

Main Flavonoids of a Living Tea Leaf

Flavonoids are secondary metabolites (a group of naturally occurring biochemicals) that help a plant to grow strong and attain its various biological characters, such as its smell, colour or self-defense. Their amount and varieties differ in different plants and in different parts and growing stages of a plant. The most predominant flavonoids in a growing young tea leaf are:

Catechins:
Catechin, Epigallocatechin (EGC)
Epigallocatechin 3-gallate (EGCg, or EGCG, or EGC3G)
Epicatechin (EC)
Epicatechin 3-gallate (ECg, or ECG, or EC3G)

Flavonols:
Kaempherol, Myricetin, Quercetin

Flavones:
Apigenin, Luteolin

Catechins: Definitive Factor of Tea Character

Those readers who are familiar with health food supplements may be aware that these are also product names of extracts. That’s right, these potent anti-oxidants/anti-mutagens/anti-inflammatory/anti-pathogens can be delivered wholesomely in a cup of delicious tea.

Of all the catechins, EGCG, a unique catechin in tea, has repeatedly demonstrated itself as the most potent health contributive factor in tea (12). It accounts for 50~75% of the catechins in green teas.

Once a tea leaf is plucked, its flavonoids very slowly undergo a process of enzyme triggered oxidation that cause them, in particular the catechins, to transform into various substances, some are other forms of flavonoids, some yet other substances that may influence the taste and aroma of the final product. The production of various categories of tea is largely based on the control of this oxidation phenomenon. This oxidation of catechins is called “fermentation” in the tea production process.

Flavonoids in green tea

In the case of a fine green tea, the plucked leaf is withered very briefly for slight dehydration and then put through heat to halt the enzyme-triggered oxidation. The most original and quantity of flavonoids are thus kept. They can take up an average of 30% of the dry weight of the tea (13), dependent on the tea variety, pluck quality and harvest season. That means you have on average 300 mg of catechins and other flavonoids in each gram of tealeaves (14).

Very often we read from tea sites that the least processing is done to white teas so these are the teas with the maximum catechins. This is not true. Genuine white teas undergo a much more tedious withering process than green tea and the health contributing nature of white teas are because of a very complex combination of substances the synergy effects of which the science community has yet to conduct more studies.

On the note of white teas, we have also read ridiculous comments that they are more potent with flavonoids because they contain more leaf shoots than green teas, and some others say they grow in very different environments. These are all misunderstandings caused by popular lack of common sense of what green and white teas are. Readers are encouraged to read related articles in this site to find out more. We shall discuss more about the health effects of white teas in future articles.

Infusion of finer black teas are always more orange than red, with a golden yellow rim on the perimeter of the surface. Theaflavins, a group of flavonoids in black tea, and a quality indicator, is yellowish orange in colour.

Flavonoids in black tea

When the fresh leaves are taken to produce black tea, a large proportion of these flavonoids and catechins is oxidized to become other substances, mostly flavonoids of larger molecular structures, such as:

Theaflavins (TF)
Thearubigins (TR)
and Theabrownins (TB)

While most of medical researches on tea’s health potential focus around green tea catechins, in particular EGCG, there are a number done on theaflavins, finding that they may also be contributive to reduction of cardiovascular diseases and prevention of diabetes. Theaflavins contribute to the yellowish orange colour of the black tea infusion, a highlight of which can be visible in that made from a fine selection, at the perimeter of the surface of the liquid. They make up on average 6% of the black tea flavonoids.

Much fewer studies have been done on theabrownins, which are a lot more abundant in post-fermented teas, but with promising result on cholesterol control.

Thearubigins, which is the red colour of black tea, have not been isolated in health studies, and although they are 58% of the total black tea flavonoids.

EGCG in black tea averages for 11% of the total flavonoids. All other flavonoids, such as myricetin and quercetin have dramatically reduced in quantity and are of decimal portions.

footnotes

12. C.S. Yang et al, Antioxidative and anti-carcinogenic activities of tea polyphenols, Archives of Toxicology 2009 January ; 83(1): 11

13. C. Cabrera et al, Beneficial Effects of Green Tea—A Review, Journal of the American College of Nutrition, Vol. 25, No. 2, 79–99 (2006)

14. Normally a significant percentage of these is dissolved in the cup of tea, but the proportion is dependent of the form style of the tea, the infusion method and length of infusion. Remember this is an average — the difference between the maximum and the minimum can be a few hundred times! (Refer to the USDA Flavonoid report)