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[10] [11] Tea has one of the highest contents of flavonoids among common food and beverage products. [7] Catechins are the largest type of flavonoids in growing tea leaves. [6] According to a report released by USDA, in a 200-ml cup of tea, the mean total content of flavonoids is 266.68 mg for green tea, and 233.12 mg for black tea. [7]
It is found in high content in the dried leaves of green tea (7380 mg per 100 g), white tea (4245 mg per 100 g), and in smaller quantities, black tea (936 mg per 100 g). [2] During black tea production, the catechins are mostly converted to theaflavins and thearubigins via polyphenol oxidases .
Mainly found in the fruit skins and seeds, high levels of polyphenols may reflect only the measured extractable polyphenol (EPP) content of a fruit which may also contain non-extractable polyphenols. Black tea contains high amounts of polyphenol and makes up for 20% of its weight. [20] Concentration can be made by ultrafiltration. [21]
Theaflavin (TF) and its derivatives, known collectively as theaflavins, are antioxidant polyphenols that are formed from the condensation of flavan-3-ols in tea leaves during the enzymatic oxidation (sometimes erroneously referred to as fermentation) of black tea.
Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of Camellia sinensis, an evergreen shrub native to East Asia which probably originated in the borderlands of south-western China and northern Myanmar.
Foods with a high flavonoid content include parsley, onions, blueberries and strawberries, black tea, bananas, and citrus fruits. [11] One study found high flavonoid content in buckwheat. [12] Citrus flavonoids include hesperidin (a glycoside of the flavanone hesperetin), quercitrin, rutin (two glycosides of quercetin, and the flavone tangeritin.
The phenolic unit can be found dimerized or further polymerized, creating a new class of polyphenol. For example, ellagic acid is a dimer of gallic acid and forms the class of ellagitannins, or a catechin and a gallocatechin can combine to form the red compound theaflavin, a process that also results in the large class of brown thearubigins in tea.
A Flowering tea, green tea with jasmine flowers.. Teas blended with other additives were developed in ancient China. As far back as the Jin dynasty (266–420), ground up tea leaves were boiled with scallions, ginger, and orange peels as reported in the Guangya dictionary (c. 3rd century CE). [2]