Ho

Violaxanthin

Violaxanthin

Figure 4. Tea carotenoids.

(18). Other hydrophobic compounds such as plant waxes and sterols may be sufficiently extracted to affect beverage appearance (19). Chlorophyll is of significance as a possible precursor of some dark-colored pigments in manufactured tea.

Enzymes

Tea leaf polyphenol oxidase that catalyzes the aerobic oxidation of the catechins during manufacture of black tea is of prime importance. It contains copper (0.32%) and exists as a mixture of several isoenzymes. Its main component has a molecular weight of 142,000 (20). Peroxidase also takes part in the polyphenol oxidation processes (21).

The complex enzyme systems involved in the synthesis of the flavanols and related tea leaf components have been described in two reviews (22,23). Alcohol dehydrogenase (24) and leucine a-ketoglutarate transaminase (25) contribute to the development of aroma components during manufacture. Glycosidases catalyze the breakdown of several glucosides to yield other important aroma components (26).

Minerals

In addition to the common plant minerals, the tea plant is rich in potassium and fluoride and also accumulates aluminum if soil conditions so favor (27).

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