Chapter 46 - Green Tea Extract

Abstract

Worldwide, green tea (Camellia sinensis) infusions are a popular beverage. Green tea extract is consumed as a nutraceutical for a variety of health benefits. Green tea differs from black and oolong teas because the tea leaves are heated immediately after harvest. Flame-heating and pan-frying of the leaves denatures proteins and blocks the polyphenol oxidase-linked oxidative polymerization and the formation of bisflavanols, theaflavins, thearubigins, and other oligomer complexes. Green tea extracts are prepared using a variety of solvents. Many extraction procedures enhance the extractions of the catechins many times greater than the concentrations achieved with hot water and water-alcohol solvents. The predominant purine alkaloids in green tea infusions and extracts are caffeine and theophylline. Four catechins are considered to have beneficial effects. These are (−)-catechin-3-gallate, (−)-epicatechin-3-gallate, (−)-epigallocatechin-3-gallate, and (−)-gallocatechin-3-gallate. Of these (−)-epigallocatechin-3-gallate is considered to be the most important. There is evidence that other phytochemicals in green tea extract are important for its phytopharmaceutic pharmacodynamics. Many of the catechins in green tea have limited absorption. The majority of catechins that are absorbed from the gut are rapidly metabolized. Studies suggest that an inverted “U” shape response curve does exist for the antioxidant activity of green tea extracts and infusions. At low doses, green tea extract induces oxidation, and this may be protective due to upregulation of endogenous antioxidants. Purified green tea catechins have antiviral activity and have regulatory approval as a treatment for genital warts. Green tea extracts are used as antiobesity, antimetabolic syndrome, and antidiabetic treatments and as a treatment for reduced insulin sensitivity. Green tea extracts are immune system modulators, reduce chronic cardiovascular inflammation, and are being studied as antineoplastic agents. Green tea infusions and extracts have an effect on gut microbial populations, and there is some evidence that microbial metabolites of phytochemicals in green tea have beneficial effects. Hepatotoxicity and toxic effects in the gastrointestinal tract limit the dose of green tea extracts. Green tea infusions using water as the solvent are considered safe.