| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 87 === The contents of catechins, flavonols, phenolic acids, theaflavins and alkaloids during the processing of pouchong tea (Taiwan Tea No. 12) were determined by HPLC. It was found that each stage of pouchong tea processing would affect the amounts of polyphenols and alkaloids.
Tea catechins are composed of (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and (-)-gallocatechin gallate (GCG). They were present at 1.91-7.30mg/g (dried leaves), 16.01-53.51mg/g, 12.32-31.32mg/g, 46.56-106.10mg/g and 10.20-74.28mg/g, respectively. The trends of catechins of changes during pouchong tea processing were similar for the tea leaves picked at different seasons. However, the extents of the changes were different, especially GCG in winter tea. On the average, catechins increased 7% after solar withering and decreased 7% after indoor withering. Catechins increased about 30% after fixing except spring tea.
Flavonols in teas are myricetin and quercetin, existed as their glycosides. Quantitative analysis of tea flavonols was performed by analyzing their aglycones after acid hydrolysis. Myricetin and quercetin were found to be 2.32-3.88mg/g and 1.45-2.22mg/g respectively. Two flavonols did not show significant changes during processing of pouchong tea.
Phenolic acids are mainly consisted of gallic acid and theogallin. After fixing, the amount of gallic acid reduced 81% on an average. But the change in theogallin was insignificant during tea processing.
Theaflavins (TFs) are the well-defined group of flavonoid oxidative products. They existed in trace amount in tea leaves, usually less than 0.5mg/g. Theaflavins were found in fresh tea leaves before solar withering, then gradually increased during indoor withering. They were gradually reduced after the 2nd rotating and increased again after the 3rd rotating. After fixing, TFs reduced significantly (except TF4), and the loss exceeded 50%.
Caffeine and theobromine are the alkaloids in tea. Variations in alkaloids contents in tea leaves during pouchong tea processing were insignificant. The amounts of caffeine and theobramine in tea leaves were found to be 17.59-27.95mg/g and 0.16-0.93mg/g
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