Abstract:
Tea (Camellia sinensis) is widely consumed all over the world. Generally, tea can be classified into six categories, including green, white, yellow, oolong, black, and dark teas, based on their fermentation degrees. Tea contains diverse bioactive ingredients, such as polyphenols (e.g., catechins and tannins), polysaccharides, proteins, pigments (e.g., theaflavin and theabrownin), free amino acids (e.g., L-theanine), alkaloids (e.g., caffeine), saponins, and some volatile components. Catechins, Especially Epigallocatechin Gallate (EGCG), are the most predominant bioactive ingredients in tea, while their bioavailability is relatively low. Recent studies suggest that gut microbiota take part in the biotransformation and metabolism of tea catechins, and consequently enhance their bioavailability and bioactivities. So far, tea has been demonstrated with various health benefits, such as antioxidant, anti-cancer, cardiovascular protective, anti-diabetic, anti-obesity, neuro-protective, anti-hyperuricemia, and anti-depressant effects. Moreover, it is considered that drinking tea is generally safe for humans, while the supplementation of high-dose tea catechin nutraceuticals may have potential health risks, like hepatotoxicity. In recent years, many tea-related food products, such as tea beverages, solid beverages, milk tea, and instant tea, have been developed, and many of them are quite popular as healthy foods. Moreover, tea extracts and bioactive ingredients are also developed into functional foods or nutraceuticals that can be beneficial in preventing and managing certain chronic disorders. In conclusion, tea can be considered a typical example of “Food as Medicine”.
