GREEN TEA COMPOSITION
The chemical composition of green tea is complex: proteins (15-20% dry weight), whose enzymes constitute an important fraction; amino acids (1-4% dry weight) such as theanine or 5-N-ethylglutamine, glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, and lysine; carbo hydrates (5-7% dry weight) such as cellulose, pectins, glucose, fructose, and sucrose; minerals and trace elements (5% dry weight) such as calcium, magnesium, chromium, manganese, iron, copper, zinc, molybdenum, selenium, sodium, phosphorus, cobalt, strontium, nickel, potassium, fluorine, and aluminum; and trace amounts of lipids (linoleic and a-linolenic acids), sterols (stigmasterol), vitamins (B, C, E), xanthic bases (caffeine, theophylline), pigments (chlorophyll, carotenoids), and volatile comp ounds (aldehydes, alcohols, esters, lactones. hydrocarbons). Due to the great importance of the mineral presence in tea, many studies have determined their levels in tea leaves and their infusions (Table 1). Fresh leaves contain, on average, 3-4% of alkaloids known as methylxanthines, such as caffeine, theobromine, and theophylline. In addition, there are phenolic acids such as gallic acids and characteristic amino acid such as theanine present.
Green tea contains polyphenols, which include flavanols, flavandiols, flavonoids, and phenolic acids; these compounds may account for up to 30% of the dry weight. Most of the green tea polyphenols (GTPs) are flavonols, commonly known as catechins. Products derived from green tea are mainly extracts of green tea in liquid or powder form that vary in the proportion of polyphenols (45-90%) and caffeine content (0.4-10%). The major flavonoids of green tea are various catechins, which are found in greater amounts in green tea than in black or Oolong tea. There are four kinds of catechins mainly find in green tea: epicatechin, epigallocatechin, epicatechin-3-gallate, and EGCG. The prepara tion methods influence the catechins both quantitatively and qualitatively; the amount of catechins also varies in the original tea leaves due to differences in variety, origin, and growing conditions. The preparation of fresh green tea cannot totally extract catechins from the leaves; therefore, the concentration found differs from the absolute values determined through the complete extraction of leaves. Moreover, catechins are relatively unstable and could be quantitatively and qualitatively modified during the time frame of an experiment. Thus, comparison of ingested doses in animal studies is not possible because the catechin quantification before administration is often not known.
HEALTH BENEFITS OF GREEN TEA IN HUMAN AND ANIMALS
Studies using animal models show that green tea catechins provide some protection against degenerative diseases. Some studies indicated that green tea has an antiproliferative activity on hepatoma cells and a hypolipidemic activity in hepatoma-treated rats, well as as the prevention of hepatoxicity and as a preventive agent against mammary cancer post-initiation. Green tea catechins could also act as antitumorigenic agents and as immune modulators in immunodysfunction caused by transplanted tumors or by carcinogen treatment.. Moreover, green tea, its extract, and its isolated constituents were also found to be effective in preventing oxidative stress and neurological problems.
Green tea consumption has also been linked to the prevention of many types of cancer, including lung, colon, esophagus, mouth, stomach, small intestine, kidney, pancreas, and mammary glands. Several epidemiological studies and clinical trials showed that green tea
(and black and Oolong teas to a lesser extent) may reduce the risk of many chronic diseases. This beneficial effect has been attributed to the presence of high amounts of polyphenols, which are potent antioxidants. In particular, green tea may lower blood pressure and thus reduce the risk of stroke and coronary heart disease. Some animal’s studies suggested that green tea might protect against the development of coronary heart disease by reducing blood glucose levels and body weight. However, all these data are based on middle-aged animals’ populations. not the elderly populations, which nutritional status tends to be more adversely influenced by age related biological and socioeconomic factors.
Tea components possess antioxidant, antimutagenic, and anticarcinogenic effects and could protect humans against the risk of cancer by environmental agents. Sano et al. reported the inhibitory effects of green tea leaves against tert butyl hydroperoxide-induced lipid peroxidation, and a similar antioxidant effect on the kidney was observed after oral administration of the major tea polyphenol EGCG. The antioxidative potency of crude catechin powder and individual catechins was tested in experiments using the active oxygen method. Crude catechins reduced the formation of peroxides far more effectively than dl -a-tocopherol. Shim et al. studied the chemopreventive effect of green tea among cigarette smokers and found that it can block the cigarette-induced increase in sister chromatid exchange frequency.
The effectiveness of green tea in treating any type of diarrhea and typhoid has been known in Asia since ancient times. Green tea catechins have an inhibitory effect on Helicobacter pylori infection. Effects of green tea against the influenza virus, especially in its earliest stage, as well as against the Herpes simplex virus have also been demonstrated. Furthermore, Weber et al. observed that adenovirus infection is inhibited in vitro by green tea catechins
