All tea comes from the Camellia sinensis plant, but processing determines the specific type. Not only does processing affect the color of the tea, but it can also change the balance of beneficial components in the final product. Aside from the tea leaves themselves, the water used to steep the tea, the brewing method and time allowed to steep can all affect the nutritional composition of a cup of tea.
Black Tea
To make black tea, the leaves of the tea plant are broken or rolled and then allowed to oxidize completely before being dried. This oxidation destroys some compounds in the leaves, but allows others to become activated. Two beneficial compounds created during the oxidation process in black tea, theaflavins and thearubigins, may have antioxidant and antimicrobial properties. Black tea contains flouride in amounts ranging from 0.2 mg to 0.5 mg per 8 oz. cup, an amount sufficient to provide protection against dental cavies but not enough to cause fluoride toxicity. Black tea also contains the flavonols kaempferol, quercetin and myricitin, which may act as antioxidants in the body and also operate on the cell-signaling pathways that prevent cells from becoming cancerous. Consuming 3 cups of black tea a day has been linked to a reduced risk of myocardial infraction in small epidimiological studies, but more research is needed, according to the Linus Pauling Institute at Oregon State University.
Green Tea
Green tea is steamed or fired shortly after picking and then dried without being allowed to oxidize first. Green tea contains the catechins epicatechin, or EC, epigallocatechin, or EGC, epicatechin gallate, or ECG, and epigallocatechin gallate, or EGCG. The catechin EGCG is particularly abundant in green tea compared with other varieties and may play a role in blood vessel dilation. Kaempferol, quercetin and myricitin are also present in green tea. Green tea has 0.3 to 0.4 mg of fluoride per 8 oz. A 2006 study in the "Journal of the American Medical Association" found an association between green tea consumption and a reduced risk of death from cardiovascular disease as well as a reduced risk of death from all causes.
Oolong Tea
Oolong tea, also called Wulong tea, has a health profile somewhere between green and black teas. Oolong tea contains a moderate amount of catechins, theaflavins and thearubigins. Oolong tea also has polphenol oxidase, an enzyme that is released when these tea leaves are bruised and oxidized slightly before being heated and dried. Oolong tea also contains kaempferol, quercetin and myricitin. The fluoride content is between 0.1 and 0.2 mg per 8 oz.
White Tea
White tea is processed in a similar manner to green tea, but is made from the tender buds and young leaves instead of more mature leaves. Because of this difference in origin, white tea has a different catechin profile than green tea, such as having less EGCG, but catechins are present in similar overall amounts. The flavonols kaempferol, quercetin and myricitin also occur in white tea. White tea is often grouped with green tea with regard to fluoride content and has not been separately measured.
References
- Linus Pauling Institute at Oregon State University: Tea
- Journal of the American Medical Association: Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study.
- University of Maryland Medical Center: Green Tea
- Journal of Food Protection: Antimicrobial activities of tea catechins and theaflavins and tea extracts against Bacillus cereus.
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