Chapter 3 · 5 / 8
What Is in Tea, Part Two
Catechins, the source of bitterness and astringency. The antioxidant action of EGCG, the anti-allergic action of methylated catechins, and how the balance shifts with the type of tea.
The lessons are narrated in Japanese.
How to turn on English subtitles
- Start the video and click the CC button to switch captions on.
- Open Settings (the gear icon) → Subtitles/CC → Auto-translate.
- Choose English.
These are machine-translated from the Japanese captions, so expect some roughness — particularly around tea terminology. The text on this page is a proper translation, so read the two together.
The lead role in the bitterness and astringency that define tea belongs to catechins.
Catechins are a class of polyphenol. They make up 10 to 20 per cent of the dry weight of the leaf and stand at the centre of both the flavour of tea and its health-related properties.
There are four main types: epicatechin (EC), epigallocatechin (EGC), and the gallate forms of these, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). Of these, EGCG has attracted the most research by some margin.
One reason for the attention on EGCG is its powerful antioxidant action. Reactive oxygen species in excess put oxidative stress on cells and are one cause of ageing and of various diseases; antioxidant action is the work of suppressing this.
Research has reported that EGCG may inhibit the oxidation of LDL (bad) cholesterol, which could be connected to a reduced risk of arteriosclerosis, and that markers of oxidative stress improved with sustained green tea consumption. Establishing the degree of effect in humans, and its mechanism, requires further research.
EGCG tends to be abundant in green tea and white tea, and especially in teas made largely from the tips of the bud — new-season shoots and high-grade sencha.
Methylated catechins are catechins marked by anti-allergic action, on top of strong antioxidant and anti-inflammatory action. Specifically, they have been reported to suppress the release of chemical mediators such as histamine, which cause the symptoms of hay fever and other allergies, and some studies have found this action stronger than that of EGCG.
Methylated catechins occur abundantly in certain tea cultivars in particular. Among Japanese cultivars, Benifūki and Benihomare are the known examples.
Because methylated catechins are reduced during oxidative fermentation, they are most efficiently taken in by drinking the leaf in its unfermented state, as green tea.
Catechins change form under enzymatic oxidation, that is, fermentation. In black tea, oolong and pu-erh, catechins polymerise into other polyphenols such as theaflavins and thearubigins.
The polyphenols of fermented teas are varied — theaflavins (red, astringent) and thearubigins (brown, savoury) in black tea, theabrownins in pu-erh — and they characterise the colour and the taste.
These polymerised polyphenols tend to be poorly absorbed in the small intestine. They therefore reach the large intestine, where it has been reported that they may act on the gut environment in a prebiotic-like way, serving as food for gut bacteria and favouring beneficial species.
More specifically, two possibilities are drawing attention and are under study: that they promote the excretion of bile acids, so that cholesterol in the body is consumed in producing more, with the result of lowering blood cholesterol and body fat; and that they regulate the activity of particular gut bacteria.
Because the change in catechins during fermentation also makes the taste rounder, many people find black tea and pu-erh gentler on the stomach than green tea. Choosing between them according to your condition and the time of day is a piece of practical wisdom.
Knowing catechins well matters for drinking tea intelligently. Observe for yourself which tea’s catechins suit which state you happen to be in.