Green tea is an infusion of processed leaves of tea plant, Camellia sinensis, a member of the Theaceae family.
It is the most consumed beverages in Asia, particularly in China and Japan.
Western populations consume black tea more frequently than green tea. However, in recent years, thanks to its health benefits, it has been gaining their attention.
Currently, it accounts for 20% of the tea consumed worldwide.
As all other types of tea, it is produced from fresh leaves of Camellia sinensis.
The peculiar properties of the beverage depend on the type of processing that the leaves undergo. In fact, they are processed in such a way as to minimize both enzymatic and chemical oxidation processes of the substances contained in them, in particular catechins.
Therefore, among the different types of tea, it undergoes the lowest degree of oxidation during processing.
At the end of the processing, tea leaves retain their green color, thanks to the little chemical modifications/oxidations they have undergone. The infusion shows off a yellow-gold color.
Finally, the processing of tea leaves ensures that green tea flavor is more delicate and lighter than black tea.
- Processing of tea leaves
- Benefits of green tea
Processing of tea leaves
Heat treatment, short and gentle, is the crucial step for the quality and properties of the beverage.
It occurs with steam (the traditional Japanese method) or by dry cooking in hot pans (a large wok, the traditional Chinese method). Heat treatment has the purpose of:
- inactivate the enzymes present in the tissues of the leaves, thus stopping enzymatic oxidation processes, particularly of polyphenols;
- eliminate the grassy smell in order to stand out tea flavor;
- evaporate part of the water present in the fresh leaf (water constitutes about 75% of the weight of the leaf), making it softer, so as to make the next step easier.
The rolling step follows the heat treatment of the leaves; this step has the purpose of:
- facilitate the next stage of drying;
- destroy the tissues of the leaves in order to favor, later, the release of aromas, thus improving the quality of the product.
Benefits of green tea
All types of tea are rich in polyphenols, compounds that are also present in fruits, vegetables, extra virgin olive oil, and red wine.
Fresh tea leaves are rich in water-soluble polyphenols, especially catechins (or flavanols) and glycosylated catechins (both belonging to the class of flavonoids), molecules which are believed to be the responsibles of the benefits of green tea.
The major catechins in green tea are epigallocatechin-3-gallate (EGCG, see figure), epigallocatechin, epicatechin-3-gallate, epicatechin, epicatechin, but also catechin, gallocatechin, catechin gallate, and gallocatechin gallate are present, even if in lower amount.
Catechin absorption and lemon juice
In vitro studies have shown the high antioxidant power of catechins, greater than that of vitamin C and vitamin E. In vitro, EGCG is generally considered the most biologically active catechin.
In vivo studies and several epidemiologic studies have shown the possible preventive effects of green tea catechins, especially EGCG, in preventing the development of:
- cardiovascular disease, such as hypertension and stroke;
- some cancers, such as lung cancer (but not among smokers) and oral and digestive tract cancers.
For these reasons, it is essential to maximize the intestinal absorption of catechins.
Catechins are stable in acidic environment, but not in non-acidic environment, as in the small intestine; also for this reason, after digestion, less than 20% of the total remains.
Studies with models of the digestive tract of rat and man, that simulate digestion in stomach and small intestine, have shown that the addition of citrus juice or vitamin C to green tea significantly increases the absorption of catechins.
Among tested citrus juices, lemon juice is the best, followed by orange, lime and grapefruit juices. Citrus juices seem to have a stabilizing effect on catechins that goes beyond what would be predicted solely based on their ascorbic acid content.
Clifford M.N., van der Hooft J.J.J., and Crozier A. Human studies on the absorption, distribution, metabolism, and excretion of tea polyphenols. Am J Clin Nutr 2013;98:1619S-1630S. doi:10.3945/ajcn.113.058958
Dwyer J.T. and Peterson J. Tea and flavonoids: where we are, where to go next. Am J Clin Nutr 2013;98:1611S-1618S. doi:10.3945/ajcn.113.059584
Green R.J., Murphy A.S., Schulz B., Watkins B.A. and Ferruzzi M.G. Common tea formulations modulate in vitro digestive recovery of green tea catechins. Mol Nutr Food Res 2007;51(9):1152-1162. doi:10.1002/mnfr.200700086
Huang W-Y., Lin Y-R., Ho R-F., Liu H-Y., and Lin Y-S. Effects of water solutions on extracting green tea leaves. ScientificWorldJournal 2013;Article ID 368350. doi:10.1155/2013/368350
Sharma V.K., Bhattacharya A., Kumar A. and Sharma H.K. Health benefits of tea consumption. Trop J Pharm Res 2007;6(3):785-792.