Time for coffee and tea
Tea Production and make up
Black and green teas are produced in different ways this results in a cup of green tea having a different chemical composition than that of black tea. Black tea is fermented and oxidised leading to its antioxidants being polyphenolic and acting differently in the body to those of the monophenolic antioxidants that are found in green tea.
In addition to the differences in preparation the variety of tea used in the production of green tea is often different to that of black tea. Many black teas are made from the Assam variety; these can not be used for green teas as they have a very bitter taste if they do not undergo a fermentation process. Green tea is made from the leaves of Camellia sinensis var. sinensis. One of the first steps in the processing of Camellia sinensis leaves in the production of tea is a heating process. This destroys the enzyme polyphenol oxidase. The removal of this enzyme from tea is the reason that green tea does not have the same color as black tea. It is this oxidase that oxidises tea flavonols and produces dark polyphenolic compounds.
The composition of black and green tea has a lot of similarities when looking at the dry content of the leaves. Fiber represents about 26% of dry leaf content, followed by proteins (20%), minerals (5%), Lipids (7%), other carbohydrates (7%), amino acids (4%) and 2% pigments. The area where green and black tea leaves differ is the phenolic compounds.
1. Black tea has 30% phenolic compounds, 25% of which are oxidised. The main types of phenolic compounds in black tea are theaflavins and thearubigins.
2. Green tea also has 30% phenolic compounds, however these are not oxidised and are mainly in the form of flavonoids.
It can be seen that although coming from essentially the same plant the composition of tea is dependent upon the production process that they are subjected to. The above data is based upon dry weight of teas. The infusion process itself will totally change the composition of a cup of tea. For example fiber and proteins, which make up 40% of tea leaf dry weight are barely detectable in a brewed cup of black tea.
References Cabrera et al (2006). Beneficial effects of green tea - a review.
J. Am. Coll. Nutr. 25: 79 to 99 Willson (1999) Coffee, Cocoa and Tea. New York: CABI Publishing