Time for coffee and tea
Green tea composition
It is well known that green tea has many associated health benefits. But what are the compounds that make up a tea leaf? As mentioned in other parts of the site the differences in the way black and green teas are processed leads to a difference in their chemical make up. These differences are mainly found in the phenolic compounds.
Phenolic compounds are oxidised in the production of black teas leading to the creation of compounds such as theaflavins and thearubigins. The production of green tea does not have a fermentation stage, therefore the phenolic compounds do not get oxidised and tend to be monomeric in make up, and contain compounds such as flavonols.
The composition of green tea leaf dry weight is given below. Please note that the percentages are variable depending upon growing and production processes.
1. Phenolic compounds 30% (see below)
2. Fiber 26%
3. Proteins: 15%
4. Amino acids 4% Including teanine, glutamic acid, valine, leucine (and others)
5. Carbohydrates 7%. Including cellulose, fructose and pectins (and others)
6. Minerals 5%. Calcium, Magnesium, copper, zinc and many others; these are very variable depending upon growing location.
7. Lipids 7% Linoleic and alpha linolenic acids
8. Pigments 2% chlorophyll, carotenoids
9. Other 4%
10. Vitamins: B, C, E.
More than 4000 types of flavonoids have been identified. As they make up a substantial part of the composition of green tea, then tea should be considered an important dietary source for these compounds. One of the main flavonoids that is found in green teas are catechins. Other polyphenols found in green tea include gallic acid (GA), chlorogenic acids, caffeic acid and the flavonols kaempferol, myricetin and quercetin.
1. epigallocatechin-3-gallate (EGCG) (59%)
2. epigallocatechin (EGC) (19%)
3. epicatechin-3-gallate (ECG) (13.6%)
4. epicatechin (EC) (6.4%)
The proportions of catechins that are found in green teas vary greatly depending upon geographical location of the tea growth and the manufacturing process that the tea has been put through. Processes such as decaffeinating, and the making of instant iced teas can also lead to a lowering of the levels of catechins.
Green tea contains an average of 90mg of catechins in a standard cup, making it an important source of flavonols. Research has shown that green tea contains more catechins than Oolong and black teas. The manufacturing process of black tea means that it has a higher content of gallic acid than that of green tea. In green teas the most abundant catechins that are found is epigallocatechin-3-gallate.
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