Evidence continues to accumulate as to the health benefits of drinking decoctions of the Camellia sinensis plant (tea). Human clinical trials and epidemiological studies show that tea provides a panacea of health effects, likely due to its antioxidant nutrients. Animal studies and cell culture studies support this view and also suggest that some of the components of tea may regulate gene expression, perhaps through modulation of oxidative stress. Tea is available in a number of forms, with the most common classification taking into account the manufacturing method. Black tea is ‘fermented’, although this is a misnomer because the tea is oxidised. ‘Fermentation’ occurs by spreading out the leaves and allowing the enzyme polyphenol oxidase to react with the natural catechin antioxidants in the leaves. This causes the catechins to be converted to theaflavins, which give black tea its characteristic taste. Theaflavins then react with more catechins to produce thearubigins, which produce the dark colour.
The oxidation of catechins in the manufacture of black tea lowers the catechin content considerably, In contrast, the thearubigin and theaflavin content increases as these are the products of the oxidation process. Consuming black tea therefore allows ingestion of high amounts of theaflavins and thearubigins, whereas green tea, that has not been oxidised, allows ingestion of high amounts of catechins. Darjeeling tea is partially oxidised and therefore part way between black and green tea in composition. Darjeeling tea can therefore be an effective way of obtaining the benefits of both black and green tea. Oolong tea is also partly oxidised.
Further reactions occur between the thearubigins and other nutrients such as sugars and amino acids, and this produces more taste changes. The degree of oxidation and the amount of polyphenols in the original leaf, therefore have a considerable influence on the final taste of the tea. The final concentration and type of theaflavins contribute to the final taste, while the thearubigins and their derivatives contribute to the colour. Controlling the growth of the plant, and its subsequent exposure to oxidation can therefore allow the production of a range of teas with different chemistry. This chemistry in turn, may play a particular role in conferring differing health effects depending on the type of tea that is drunk. Studies have shown that black tea may possess many of the same health effects as green tea, which has traditionally been considered superior in terms of its health giving properties. However, black teas may produce similar effects. Consuming both types of tea may ensure optimal exposure to a variety of tea components.
Eat Well, Stay Healthy, Protect Yourself
RdB
