Tea (Camellia sinensis)
Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.
Tea (Camellia sinensis) is most often used for
Contents of Camellia Sinensis
Plants derived from Camellia Sinensis (Green, Black, White, and Oolong Tea) contain:
- Green Tea catechins
- Bioflavonoids such as Myricetin, Quercetin and Kaempferol as various glycosides
- Polyphenolic compounds beyond Green Tea Catechins (Ellagic Acid, Gallic Acid)
- Pyrroloquinoline quinone
- Caffeine and other xanthines such as theophylline, usually at 10-20mg/g of leaves
- A platelet inhibiting compound called 'L2' with the structure of 2-amino-5-(N-ethylcarboxyamido)-pentanoic acid
- Terpene compounds (Geraniol, Nerol, α-terpinolene, nerolidol, etc.)
Processing of types of Camellia Sinensis
White tea is unique in the fact that it is processed from unopened buds, classified as silver needles (bai hao Yinzhen), or an unopened bud with two leaves covered in white leaf hairs. Afterwards, they are sometimes dried or withered by the air to remove moisture content; this leaves them with a curled silvery appearance.
Oolong tea tends to, like white tea, be partially oxidized.
As they still have active enzymes, some of the catechin content is polymerized into theaflavins and thearubigins.
Green Tea leaves tend to be non-oxidized.
Black tea leaves tend to be fully oxidized.
Pu-erh (Fermented) Tea: Dark Tea
After initial picking, Pu-erh tea leaves are turned into raw Pu-erh by a process called 'kill green' and then fermented by microorganisms for 6-12 months. Some of the more high quality Pu-erh teas are fermented for greater than a decade.
Pu-erh tea has a taste that is described as 'complex, silky smooth, and mellow' but develops a sensory experience similar to green tea after being aged, but perhaps slightly more bitter.
When tea is fermented by bacteria, levels of catechins initially drop. However, new compounds are generated via microorganisms, such as theabrownin and statins, which is produced by the Streptomyces cinereus strain Y11 bacteria.
Overall, green tea is the 'basic' tea that is enzymatically inactive and non-oxidized. White tea and Oolong tea are partially oxidized, but Oolong is still enzymatically active. Black tea is fully oxidized and enzymatically active. Pu-erh tea is fermented and quite unique from the other teas.
Preparation of Tea for Home Consumption
In studies looking at the interactions between milk and tea catechins (ie. adding milk to your tea) the milk can form protein-catechin complexes with the tea catechins which negate the anti-oxidant potential (by sequestering hydroxyl groups). This, however, is not likely to result in a reduced bioavailability. Although the protein-catechin complex is metabolically inactive, it is digested and free catechins are released in the intestines. Bioavailability studies looking at all tea catechins note no differences in overall serum levels of free catechins (green and black tea) when milk is added at a 1:5 ratio of milk:tea, although a partitioning effect has been observed, with less EGCG and ECG being absorbed yet more EC and EGC.
One study noted that milk ingestion with green tea abolished the catechins' beneficial effects on cardiovascular health (vasorelaxation), but has been criticized for its methodology as it took a single measurement 2 hours after ingestion when the benefits associated with green tea could be chronic in nature.
Consumption of tea with milk may alter but does not significantly reduce the bioavailability of green tea catechins; it has been suggested that proteins may abolish the benefits of green tea catechins on heart health, but the lone study supporting this notion has some methodological flaws
Comparison of Tea types
Green Tea Catechin content varies depending on species:
- White tea tends to be in the range of 14.40 to 369.60 mg/g of dry plant material
- Green tea tends to be in the range of 21.38 to 228.20 mg/g of dry plant material
In comparing different sources of Camellia Sinensis:
- White tea appears to have more catechins overall by weight, but when the catechin content is even green tea has a higher anti-oxidant potential
- When fermented, tea tends to lose antioxidative potential; however, some measures of anti-inflammatory status increase (as measured by macrophage NO release via LPS)
- Green tea appears to be the least effective at inhibiting the ACE enzyme in blood pressure regulation, with green < oolong < white < black < dark teas.