Tea polyphenols are one of the most important components of tea, making up from 18-46% of dry matter in processed tea leaves.
Under this family includes the following main types:
Group Tea Leaves Content Examples
Catechins 12-24% Gallocatechin, Gallocatchingallate, Epigallocatechin 3-gallate (ECGC) etc.
Flavones 3-4% Flavones & flavonols
Anthocyanin 2-3% Leucoanthocyanidin & anthocyans
Phenolic acids & depsides 5%
(Source: 中国茶经 2011 edited by陈宗懋)
Here are just 2 examples of the effects of tea polyphenols:
Lowering of Cholesterol Levels
In 1998, a study was conducted [1] by Chinese scientists to study the effects of tea polyphenols on cholesterol levels on lab rats.
The results showed that rats that were injected with tea polyphenols extracts saw their total cholesterol levels drop by 21.6% on the average. At the same time, the HDL-Cholesterol levels (colloquial speak for good cholesterol) saw no significant change.
The polyphenol extracts had the effect of lowering total cholesterol while maintaining the ‘good cholesterol’ which simply means the LDL or bad cholesterol levels were the ones that was lowered in lab rats.
Reducing the Effect of Radiation
The chemotherapy treatment ranged from 1 to 3 months and those tested were divided into 2 groups- 1 that was given green tea extracts and the other that was not.
Thereafter it was discovered that while the white blood cell count of those who consumed the green tea extract shown no significant changes, those who didn’t consume the extracts saw their white blood cell count fall to an average of 70.2% of their initial white blood cell levels.
In other words, the consumption of green tea extracts- 3 times a day and 6 tablets of 0.24g each- over that period effectively mitigated the damage caused by the radiation on the white blood cell count.
Others
Polyphenols is also associated with among other things:
i) Reducing effect of free radicals
ii) Reducing cancer cells
iii) Anti-inflammation
How does it Taste Like?
Polyphenols and Catechins are associated with astringency and part of the bitterness (anthocyans). On its own, it would seem that this healthful component implies that there is a trade-off between health and taste concerns.
However that could not be further from the truth. L-theanine is a compound that is generally higher in tea leaves that have higher polyphenols content and it gives a sweet and brisk quality that offsets the bitterness and astringency, giving it a more rounded fuller taste.
Sweetness and briskness without a controlled element of bitterness and astringency results in a one dimensional drink that is lacking in depth.
*The relationship between polyphenols and L-theanine is also vital to understanding how we approach brewing tea and will be a topic for a future post.*
Which Tea has the most Polyphenols?
There is no one line answer to this but there are a number of factors:
Picking Position
Comparison of Composition (Mg per G)
Tea Product Bud 1st Leaf 2nd Leaf 3rd Leaf
L-Theanine 47.3±4.3 42.3±2.5 26.4±2.0 18.9±1.4
Catechin 3.0±0.2 5.1±0.3 6.5±0.5 5.5±0.3
EGC 2.3±0.05 4.1±0.3 4.0±3.8 2.7±0.3
EGCG 29.4±1.8 27.1±2.2 21.0±1.3 11.6±0.8
EC 0.06±0.01 1.3±0.1 1.6±0.2 0.5±0.05
ECG 5.2±0.4 5.7±0.3 4.9±0.4 2.9±0.2
Above table extracted from Capillary Electrophoretic Determination of Theanine, Caffeine and Catechins in Fresh Tea Leaves and Oolong Tea and Their Effects on Rat Neurosphere Adhesion and Migration published by Chia-Nan Chen et al (National Taiwan University)
The above table based on a study by Chen et al of National Taiwan University investigated the relationship between picking position and chemical content.
It was found that Catechins and other tea polyphenols were most heavily concentrated in the bud and 1st leaf.
To put it into context, in general these are the picking position of the different categories of tea:
Green tea- generally 1 bud to 1 or 2 leaves
White tea- 1 bud 1 leaf extracted for silver needles, 1 bud 2 leaf for white peony, anything goes for Shou Mei
Yellow tea- buds to 1 bud 2 leaves depending
Oolong tea- 3-4 leaves
Black tea- 1 bud to 2 leaves
Dark tea- matured leaves, 4-5 leaves
Method of Production
Professor Yang Wei Li of Hunan Agricultural University led a fascinating study (fascinating to us tea nerds) in 2001.
He and his team used leaves grown in the same location, same cultivar and same pickings requirement and processed them in the manner of the 6 major categories of tea.
The research he and his team conducted produced the following results (abridged version):
Type
Amino acid (%)
Tea Polyphenols (%)
Dissolvable Carbohydrates (%)
Water Extract Compounds (%)
Raw leaves
1.592
23.59
11.78
45.6
White Tea
3.155
13.78
12.50
31.9
Green Tea
1.475
22.49
9.97
44.4
Oolong Tea
1.425
12.78
9.06
27.9
Black Tea
0.970
7.93
8.06
23.9
Dark Tea
1.375
15.51
9.45
24.7
Yellow Tea
1.361
16.71
16.71
27.6
(Table extracted and translated from 白茶-科学，技术与市场 editor叶乃兴 published by中国农业出版社)
Hence a very simplified answer is that all else being equal, green tea in general has the highest tea polyphenols content. When you factor in picking requirements, you would expect white and yellow tea to be next.
Cultivar
This is a massive topic on its own and the cultivar used- i.e. the ‘sub-variety’ of the Camellia Sinensis plant- affects the chemical content.
For further reading, you can read this.
See here for other frequently asked tea related questions
See here for more articles related to tea and health
[1] 沈薪南，陆瑞芳-茶多酚对老龄大鼠血脂及体内抗氧化能力的影响。中华预防医学杂志 (1998)