A lot of research has been done in recent years on the active ingredients in tea. Many studies are based on information derived from extractions of the contents of tea leaves using solvents. This information will show what is effectively in the transformed plant, but will not give an accurate picture of what exactly may be consumed when drinking tea, since this is dependent on water solubility and also is affected by the synergy of different compounds in the tea leaf – the sum of which appears to be more powerful than the isolated parts.
The catechins in tea are much talked about. Essentially of four types; epicatechin (EC), epicatechin 3-gallate (ECg), epigallocatechin (EGC), epigallocatechin 3-gallate (EGCg), catechin, and gallocatechin (GC), they form part of a sub-class of polyphenols, known as flavonoids.
So what are all these names and what is their importance? Let’s start here:
Raw Tea Leaves
Fresh unprocessed tea leaves are made up of about 75% water and 25% solids. The solids comprise of organic and inorganic compounds.
Fresh tea leaves contain about 36% polyphenolic compounds, 25% glucids, 15% proteins (and a type of enzyme called Polyphenol Oxydase which plays an important role in the transformation of polyphenols), 6.5% lignins, 4% amino acids, 2% lipids, 1.5% organic acids, 0.5% chlorophyls/叶绿素 and carotenoids, 0.1% volatile compounds and 3% minerals. 45% of these compounds are in the glucids and protids in the cell walls of the plant.
The plant uses polyphenols for interactions with the environment, typically; pollenisation, defense against mutagenicity due to U.V. (flavonoids), to repel pests (catechins), protection against micro-oranisms (both flavonoids and catechins).
So clearly the polyphenols, and notably the four mentioned at the beginning of this passage form the largest part of the solid compounds in tea. In the process of tea manufacture, water is removed through wilting, frying or roasting and then drying. In sun dried mao cha that is the raw material for Puer tea, the water content is about 12%. So this means that the polyphenol content in dried mao cha may reach about 35% of the dry weight. Catechins may make up to 80% of the total polyphenols.
What may be a little less well known is that raw sinensis assamica tea leaves also have ample fungal and bacterial communities present on the fresh leaves, which clearly play a role in the subsequent processing.
Free Radicals and Antioxidants
Because unstable molecules called free radicals (oxidants) are caused by UV light, our environment (pollution) and more still are produced by the body itself, it is of value to take foods which counter their effects. i.e. have an anti-oxidant effect.
Free radicals are molecules that are chemically unstable. In order to try to stabilise, they bond with other molecules, typically proteins, lipids, and DNA. When this happens, an electronic charge (electron) is either lost or gained by the free radical thus producing a stable molecule, but in the process creating yet another free radical, and thus a cascade effect of free radicals. Antioxidants are found in many foods; they have a positive effect because they bind to free radicals and effectively remove them from the body.
Polyphenols
The polyphenols/茶多酚are a large group of compounds found in plants. They are of interest to us because of their antioxidant properties. They largely comprise of two sub-classes; tannins and flavonoids and are water soluble. Many plants and foodstuffs have tannin in them and tea is notably rich in flavonoids. i.e; theaflavin-3-gallate and tannic acid.
Flavonoids
A type of antioxidant, flavonoids/黄酮类化合物 are a sub-class of polyphenols that are abundant in tea. They have anti-inflammatory and antibiotic properties. Flavonoids are important plant pigments; giving flowers and fruits their colours. Plants that are red, yellow, orange all get their pigmentation from flavonoids. i.e. they have good anti-oxidant properties. Tea is rich in Quercetin/槲皮素, a common plant flavanoid/黄烷类 and anti-oxidant.
Catechins
Catechins/儿茶素 are a class of Flavanol; a sub-class of plant Flavonoids. (as distinct from flavonols which are a separate class of Flavanoids). We get catechins mostly from tea, wine and fruits.
The main catechins found in tea are epicatechin (EC)/儿茶素, epigallocatechin (EGC)/表没食子儿茶素, epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)/表儿茶素没食子酸酯. All are powerful antioxidants. The last is found in high concentrations in green tea and is the most potent -and most studied – of the four.
Gallo catechins are more active than catechins and easily transform into the latter, and into thearubigins and theaflavins, in the oxidation process of black tea manufacture. The gallo catechins are, because of this, considered better anti-oxidants.
The results of research on the effects of catechins on human health appear divided; there are claims and counter-claims about the results of catechin-related studies on humans, but they are doubtless strong free radical scavengers and there is much research to suggest that they are beneficial. Epicatechins have been sited as particularly helpful in reducing risk of certain cardiovascular diseases, cancer and diabetes.
Gallic Acid
Gallic acid is another phytochemical. i.e. a plant generated chemical which is found in many plant tissues; both as a free compound and as a component of larger polyphenolic compounds. When Gallic acid bonds with other molecules to form yet larger molecules it is known as a gallate. e.g. the catechins epigallocatechin-3-gallate (EGCG) and Epicatechin gallate. These are forms of tannin/单宁
Gallic acid is also an antioxidant and appears from research to have anti-microbial and anti-cancer effects in animals. It is thought to be useful because of it’s functions in weight loss and cholesterol reduction. In wodui or pile fermented Puer tea, the catechins are more or less all converted into polymers; predominantly Gallic Acid, but also some thearubigin, etc.
Theaflavin & Thearubigin
Theaflavin/茶黄素 and thearubigin/茶红素 are polymers of catechins. When polyphenols are oxidised by polyphenol oxidase (enzymatic oxidation – known in the industry as fermentation), they form compounds called theaflavins which in turn produce thearubigins. These too have anti-oxidant properties and have been studied in the treatment of cancer and other conditions, such as high cholesterol.
Theaflavins and thearubigins form the largest amount of anti-oxidants found in black teas. They produce a red colour; their presence in fully oxidised black tea is what gives the reddish liquor.
Theaflavins and thearubigins are slightly soluble in water and fully soluble when in the presence of catechins, so when there are poor levels of catechins, these compounds may have low availability.
The Puer Tea Making Process
Puer tea is often talked about for it’s health properties, which of course, along with other teas it has. In light of the above information on the active ingredients in tea, we will look at some ideas about research on Puer tea.
Many research authors do not distinguish between the two forms of Puer tea; ‘Raw’ and ‘Cooked’. The former being a tea made by an age-old process in which maocha or loose unprocessed tea is pressed into cakes. Many believe this tea can be drunk immediately, though the quality is a determining factor in this decision – personal preference being the other. But this type of tea has traditionally been stored in order that it ages; a process of both fermentation and oxidation.
The second form of tea is an artificially fermented tea that is said to simulate an aged Puer of perhaps 7-10 years. This kind of Puer is made by a process which likely involves the actions of aspergillus, penicillium, yeasts and other micro-flora. There are some important distinctions to be made between the two. Not simply in the manufacture process, but also in the active compounds produced by either method.
Production and Storage
If one subscribes to the idea that Puer tea can only be given that moniker once it has reached an (arbitrary) degree of maturity, then it may be fair to describe storage as part of the production process. This view is contentious and has no practical or regulatory support at present. Others hold that the raw tea, once pressed into cakes, can be called Puer tea as the process of ageing, whilst still in it’s infancy, has begun.
If one believes that young raw tea has already begun the ageing process and can therefor be called Puer (following current Government guidelines), then storage is something that is separate and distinct from production – like making and storing wine.
Raw Puer tea has ample catechins and gallo catechins. As the tea ages naturally, these gallo catechins and catechins are converted into other substances; gallo catechins into catechins, Gallic acid, thearubigins, theaflavins etc. In naturally aged teas that are several years old there is still a balance of catechins alongside increasing amounts of Gallic Acid, thearubigins, etc.
In the process of pile fermentation (wodui/渥堆 or ‘wet pile’ ) all the catechins are converted entirely: mostly converted to Gallic acid and some to thearubigin which, given the lack of catechins may have limited bio-availability.
There are some contradictory research results available on comparisons between shou cha and aged sheng. Some maintain that the constituents in an aged sheng and shou cha are very similar. Other research suggests this is not so. In any case, like comparing apples and oranges, from a biochemical point of view they may be very similar, but they still look and taste very different.
Please see here for more detailed information on the process of making Puer tea.