flender gmbh bamberg H3-DH-7-D Helical gear boxes H3

Flender/Flender Gear Units/Helical gear boxes H3

e present only in very small quantities in black tea. Oxidized products of epigallocatechin coupled with gallicacid form series of colorless substances known as bisavanols (Fig. , which occur in very small quantities in black tea (. Fig. 3 Theaavin formation. 7 Nagalakshmi Fig. 4 Theaavic acids formation. 2.1.1 Thearubigins During the formation of black tea, about 1% of tea catechins remain unchanged and 1% are accounted for by theaavin, theaavic acid, and bisavanol formation. About 7%of the catechins are converted to complex, poorly dened, and incompletely separatedgroup of substances, known as thearubigins because of their red-brown color. Molecular weight determinations indicate range of 7,0. Reductive hydrolysis of thearubi- gins yields small quantities of all of the catechins found in tea. Evidence exists for the pres-ence of polymeric proanthocyanidine, which accounts for only small fraction. Thearubigins constitute the largest group of compounds in black tea (up to 2% of dry weight) and contribute signicantly to color, strength, and mouth feel of the beverage.The oxidized polyphenol complex of black tea is generally referred to as tannin but has no relationship to tannic acid (pentadigalloyl ester of glucose), which does not occur in tea. Thearubigins impart specic bright and vivid red color to the liquor. The ratio of Fig. 5 Bisavanols formation. Tea 7 Fig. 6 Theaavin and thearubigin. theaavin to thearubigins is taken as an index of strength of the liquor. The control of these two factors depends upon fermentation time and temperature (6, . The structure of thearubigin is illustrated in Fig. 6. 2.1.1 Aroma Formation The oxidized catechin reacts with the precursor molecules present in green tea and pro- duces the volatile compounds in black tea, which are mainly dependent on genetic, cul-tural, and manufacturing variables. Oxidation of amino acids, carotenes, and unsaturated lipids leads to the formation of aroma compounds during the fermentation p