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ABSTRACT

   Different classes of compounds found in tea are discussed: polyphenols, amino acids, caffcinc, nucleoties, carbohydrates, lipids, organic acids, chlorophyil, carotenoids, unsaponifiable compounds, saponins, minerals, and volatile compounds. 
     The apical schools of tea-consisting ideally of the terminal bud and two adjacem leaves, and generally refered to as tea flush- make up the raw material which is processed to black, green, oolong, pouchong, or other forms of tea. Flush has been studied by several workers(1-3), with particular emphasis being paid to the group of polyphenolic compounds because the polyphenols and their transformation products are responsible for the unique character of tea. A generalized picture of the different classes of compounds and their distribution throughout the tea bush (4,5) is presented in Figure V.1.

     POLYPHENOLS

     The total content of polyphenols in tea flush is 25-35% on a dry weight basis. These compounds are mainly flavanols, together with flavonols and flavonol glycosides,  flavones, acids, and depsides, Table V. 1. Some structures of phenolic comopounds listed in Table V. I are shown in Figure V.2.
     During the processing of black tea, about 90-95%of the flavanols [I-VIII] udergo cnzymatic oxidation to products which are directly responsible for the characteristic color of tea brews, their astringency, and unique taste. The chemistry and formation of these oxidation products, named theaflayins and thearubigins, are discussed in the next section of this issue, Process Biochemistry,

      The flavonols and flavonol glycosides undergo hardly any change during the processing of black tea. Early studies (7) developed methods for the quantitative estimation of kaempferol [X] and quercetin [IX] glycosides, and it was demonstrated that the glycoside fraction had a beneficial effect in regulating the permeability of capillary blood vessels. The presence of at least 14 glycosides of myricetin, quercetin, and kaemmpferol, has been established (8,9), and two flavonol triglycerides have been added (10,11). Flavonol glycosides

   

 



 

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