Green tea extract
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A green tea extract is a herbal derivative from green tea leaves (Camellia sinensis). Containing antioxidant ingredients – mainly green tea catechins (GTC) – green tea and its derivatives are sometimes used as dietary supplements and in alternative medicine.
History of tea extracts
Green tea extracts have been used in traditional Chinese and Indian medicine for a variety of uses.[1]
Forms
Green tea leaves are initially processed by soaking in an alcohol solution, which may be further concentrated to various levels; byproducts of the process are also packaged and used. Extracts may be sold in liquid, powder, capsule, or tablet form.[2] Decaffeinated versions are also available.[3]
Green tea extract supplements are accessible over the counter in various forms. Standardized green tea extract is 90 percent total polyphenols, and 1 capsule equals 5 cups of tea.[4][5]
Chemistry and biochemistry
Constituents
The cardinal antioxidative ingredient in the green tea extract is green tea catechins (GTC), which comprise four major epicatechin derivatives; namely, epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG). Of which, EGCG accounts for more than 40% of the total content.
Other components include three kinds of flavonoids, known as kaempferol, quercetin, and myricetin.[6] A remarkably higher content of myricetin is detected in tea and its extracts than in many other plants, and this high concentration of myricetin may have some implications with the bioactivity of tea and its extracts.[2]
Chemical properties
Green tea extract is approximately two times more antioxidant-active than Vitamin C. The main attribution is supposed to be EGCG.[7] One study by the Drug and Food department of Iran in 2008 compared antioxidant properties of various green tea compounds with those of vitamin C and vitamin E: the study concluded that green tea extracts -for a total of approximately 68 mg of combined phenols, flavonoids and anthocyanidin present from 1g of a sample of "Chinas green tea" leaves, the grade yielding the highest content of bioactive chemicals- had the equivalent antioxidant power found in 50 mg-275 mg of vitamin C and 156 mg-813 mg of vitamin E [8]
Biochemical properties
The biochemical properties of green tea extracts can be generally divided into four aspects – antioxidant, anticarcinogen, anti-inflammatory, and anti-radiation.[2][9]
Scavenging effect of lipid free-radicals (one antioxidant property) of polyphenols in green tea extracts can be observed in experiments.[9] The ability of GTP in green tea extracts to eliminate lipid-derived free radicals is noticeably stronger (almost 50 times) than that of ginkgo biloba extracts.[9] Further investigations indicate that the boosting level of superoxide dismutase (SOD) and glutathione dismutase (GSHPx) may account for the inhibitory effect of GTC against lipid oxidation (rancidification).[10] Generally speaking, green tea extracts are more effective as antioxidants than black tea extracts are due to the better preservation of catechins contained in green tea extracts.[9]
Moreover, the anticarcinogenic properties of green tea extracts have been a focus of recent scientific research. In many experiments, green tea extracts show inhibitory effects on cancer cells. Invitro assays have shown that catechin and caffeine, which are main components in green tea extracts, block the cell cycle of cancer cells (cytotoxicity) and induce programmed cell death;[2] in vivo, green tea extracts also inhibit prostatic carcinoma transplanted in nude mice.[9]
References
- ^ "Green tea". Complementary and Alternative Medicine Guide. University of Maryland Medical Center. Retrieved 3 May 2015.
- ^ a b c d I.T. Johnson & G. Williamson, Phytochemical functional foods, Cambridge, UK: Woodhead Publishing, 2003, pp. 135-145
- ^ "Update on the USP Green Tea Extract Monograph". USP. April 10, 2009.
- ^ A.H. Pressman & S. Buff, The complete idiot's guide to vitamins and minerals, New York: New York Alpha Books, 1997, p. 283.
- ^ A. Bascom, Incorporating herbal medicine into clinical practice, Philadelphia: F.A. Davis Company, 2002, p. 153.
- ^ Committee on Diet, Nutrition, and Cancer, Assembly of Life Sciences, National Research Council, Diet, nutrition, and cancer, Washington: D.C National Academies Press, 1982, p. 286.
- ^ Comparison between vitamin C, green tea extracts and olive leaf extracts : Dr Stevenson, L,. et al. Oxygen Radical Absorbance Capacity (ORAC) Report on Olive Leaf Australia's Olive Leaf Extracts, Southern Cross University, 2005.
- ^ "Determination Of Total Antioxidant Capacity Of Green Teas By The Ferric Reducing-Antioxidant Power Assay" by M. Hajimahmoodi,M. Hanifeh,M. R. Oveisi,N. Sadeghi,B. Jannat, (Drug and Food Control Department, Faculty of Pharmacy &Medical Sciences,University of Tehran, and Ministry of Health and Medical Education, Tehran Iran), published in "Iran. J. Environ. Health. Sci. Eng., 2008, Vol. 5, No. 3, pp. 167-172" , website: http://journals.tums.ac.ir/upload_files/pdf/_/8255.pdf "
- ^ a b c d e Y.S. Zhen, Z.M. Chen, S.J. Cheng & M.L. Chen, Tea: bioactivity and therapeutic potential, London, UK: New York Taylor & Francis, 2002, pp. 121–225.
- ^ Cite error: The named reference
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