Green tea extract

Green tea extracts are herbal derivatives from green tea leaves (camellia sinensis). Containing antioxidant ingredients – mainly green tea catechins (GTC) – green tea and its derivatives are sought-after amongst people who pursue health.

The green tea extracts categories

1, Strong infusions During the strong infusion green tea leaves are processed by soaking in the aqueous solution of alcohol (theaspect content is about 2% w/w) [1:143].

2, Soft extracts To obtain soft extracts, the solution m ade by strong infusion beforehand is further concentrated to 20–25% (the catechin content is about 20% w/w) [1:143].

3, Dry extracts After the strong infusions have been concentrated to 40–50% solids (the catechin content is above 25% w/w)，they are sprayed and then become dehydrated extract and powder [1:143]. The leftovers - water content, which is less than 5% w/w, and the extract - are usually processed as a powder containing inert processing aids to become suitable for a variety of uses (tablets, capsules, dry mixes, etc.) [1:143].

4, Partly purified extracts Further purification processes, for example, solvent extraction or column chromatography techniques, as well as new techniques such as membrane extraction and separation, are utilized in order to acquire a higher content of tea catechins [1:143]. .

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) [2].

Other components include three kinds of flavonoids, known as kaempferol, quercetin, and myricetin [3]. 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 [1:140].

Caffeine may be excluded in green tea extracts in order to avoid side-effects; caffeine-free green tea extract supplements are available nowadays [4].

Chemical Aspects

Green tea extract is 20 times more antioxidant-active than Vitamin C. The main attribution is supposed to be EGCG [5].

In alkaline solutions (pH > 8) GTC (green tea catechins) is rather unstable; in acidic solutions (pH < 4), however, GTC shows excellent stability. The stability in alkaline solutions varies between four components of GTC in green tea extracts. Recent study demonstrates that EGCG and EGC is more unstable than EC and ECG in a basic solution, giving an explanation to the fact that EGCG and EGC do not circulate in the basic sodium phosphate buffer fluid of human body [2].

In a high temperature environment, GTC is not stable: an epimerization change is likely to occur, because heating results in the conversion from EGCG to GCG [2]. Thus it is considered inappropriate to infuse green tea or its extracts with overheated water.

Biochemical Aspects

The biochemical properties of green tea extracts can be generally divided into four aspects – antioxidant, anti-cancer, anti-inflammation, and anti-radiation [1] [7].

Green tea extracts exhibit stronger antioxidant protection for human body than vitamin C and vitamin E [6]. Scavenging effect of lipid free-radicals (one antioxidant property) of polyphenols in green tea extracts can be clearly observed in experiments [7:125]. 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 [7:125]. 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 [2]. It should be mentioned that from the antioxidant perspective, green tea extracts are, generally speaking, more effective than black tea extracts due to the better preservation of catechins [7:121].

Moreover, the anti-cancer property make the green tea extracts a hotspot in recent scientific researches. In many experiments, green tea extracts show inhibitory effects on cancer cells. In vitro assays, Catechin and caffeine, which are main components in green tea extracts, block the cell cycle of cancer cells (cytotoxicity) and induce programmed cell death [1:135]; in vivo, green tea extracts also inhibits prostatic carcinoma transplanted in nude mice [7:220].

In addition, green tea extracts also contain a wide-ranged anti-inflammation characteristic, so it may be helpful in treating chronic inflammatory states [1:136]. The bactericidal activity against S.mutans is conspicuous in Japanese green tea extracts [7:179], and the maltose level in mouth is consistently lower after drinking tea [1:136]. Therefore, green tea extracts may be effective in oral hygiene maintenance.

Green tea extracts show anti-radiation property on white rats in radioactive isotope experiments [7:126].

Other Related applications

Because of the high antioxidant activity of green tea extracts, they are hopefully to be used as a kind of innovative food additive to preserve pork, chicken meat, vegetable oil, fish oil and fish flesh, food emulsions and animal fat [1:144]. This alternative antioxidant is suggested to be a healthier choice; a fairly successful instance may well be the application in Moon cake – the extracts both increase the shelf life and improve the flavor [1:144].

In addition, green tea extracts are a promising solution to prevent apple juice and other foods from microbial contamination [1:144]. Japanese scientists even have discovered that tea extracts can be developed as dyes that are not susceptible to microbial contamination and possess strong deodorant ability against smells [1:145].

Dosage & Side-effects

Green tea extract supplements are accessible over the counter in various forms [6].Standardized green tea extract is 90 percent total polyphenols, and 1 capsule equals 5 cups of tea [8] [9]. For a green tea extract standardized for 80 percent polyphenols and 55 percent EGCG, a daily dose of 300 to 400 mg green tea extracts is recommended [6]. Some green tea extracts may have as little as 15 percent polyphenols, usually these are far less expensive. Keep in mind that undivided green tea extracts have synergistic and therefore are better than any individual tea component [1:139]. Scientists also conclude that tea extracts are better to be taken between meals rather than during the meal in order to avoid the decrease of iron absorption.

Though green tea extracts show the potential anticancer capacity - under some conditions by working together with other drugs and suppressing the multidrug resistance in cancer cells - it is not suggested to be used alone as a chemotherapy agent for cancer treatment [7:225].

Excessive intake of green tea / extracts containing Caffeine has side effects [10]; a too high concentration may act as a pro-oxidant to damage DNA [1:141].

References

[1] I.T. Johnson & G. Williamson, Phytochemical functional foods, Cambridge, UK: Woodhead Publishing, 2003, pp. 135-145.

[2] Q.Y. Zhu, Antioxidative activities of green tea catechins, Hong Kong: The Chinese University of Hong Kong (Hong Kong), 1999, p. III.

[3]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.

[4] E. Mindell, Earl Mindell's Vitamin Bible for the 21st Century, [S.l.] E-Rights/E-Reads, Ltd., 1999, p. 135.

[5] A. Magaziner, The complete idiot's guide to living longer & healthier, New York: N.Y. Alpha Books, 2000, p. 61.

[6] F. Murray, 100 super supplements for a longer life, Los Angeles: CA McGraw-Hill Professional, 2000, pp. 181–182.

[7] 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.

[8] A.H. Pressman & S. Buff, The complete idiot's guide to vitamins and minerals, New York: New York Alpha Books, 1997, p. 283.

[9] A. Bascom, Incorporating herbal medicine into clinical practice, Philadelphia: F.A. Davis Company, 2002, p. 153.

[10] B. Capon, Botany for gardeners: An introduction guide, Portland: Or. Timber Press, Inc.， 1990, p. 94.