Variation Of Main Chemical Components As Well As Influencing Factors In Fresh Leaves Of Famous And Excellent Green-tea During Spreading

This thesis, with fresh tea leaves of famous green tea as materials, applying liquid nitrogen ultra-hypothermia freezing / freeze-dried fixing and room-temperature extraction, systematically studied the effects of spread process and spread environment on the change of main biochemistry components in fresh tea leaves, and illustrated the variation rule of substance related to the quality of tea. The results obtained finally were as the follows:1. There is obvious difference of biochemistry components between the traditionary hot-air fixing method and the freezing fixing one. Contents of total amino acids and free amino acids, total catechins and catechins, and total soluble sugar, in the tea of hot-air fixing, were higher than that treated by the freezing fixing method, but content of reserve of protein, tea polyphenols and total chlorophyll lower. There existed gallocatechin (GC) in the tea by the hot-air fixing treatment, but not in the tea by the freezing fixing treatment.2. The moisture content in fresh tea leaves droped increasedly during spreading. There were obvious effects of environment on moisture loss of fresh tea leaves during spreading. Rate of moisture in fresh tea leaves droped with the increase of the spread time, and the trend quickened. The loss speed of moisture was higher three times when below 70% of water content than when above 70%. There appeared obvious effects of environment humidity, temperature and tea materials on change of moisture in fresh tea leaves. There were different spread time and rate of moisture loss between different tea materials. High temperature and low humidity profited moisture loss of fresh tea leaves.3. Multiplicate factors lead to complicated change of main chemic components in fresh tea leaves during spreading.①Contents of tea polyphenols and total catechins decreased at first and then increased during spreading; there were obvious change of contents of catechin components and proportion: content of total Esters-catechins decreased gradually, but content of simple catechins increased.②Content of total amino acids in fresh tea leaves increased during spreading, with different rule for different components.③Content of caffeine in fresh tea leaves increased during spreading, maybe because of decline of dry fresh tea leaves weight or still synthesising during spreading.④Water-extracts increased because of hydrolysis of protein, amylase and pectin, which improved the thickness and taste of broth, but it declined at the late period of spreading.⑤Content of total soluble sugar increased at a certain extent during spreading.⑥Content of total chlorophyll declined at a certain extent, because of hydrolyzing by chlorophyllase.4. There was noted difference of conventional components in fresh tea leaves between spread environment (temperature and humidity). Tea polyphenols had complicated change when spreading under different environments. High temperature (25℃) and low humidity (60%) could obviously decrease contents of tea polyphenols, and low temperature (20℃) and medial humidity (75%) or low temperature (20℃) and high humidity (90%) benefited to maintain content of tea polyphenols. There was a little difference of effects of chemic components under different environments, only under relative low temperature (20℃) and high humidity (90%), contents of caffeine, amino acids and total soluble sugar increased significantly.Except the treatment of high temperature(25℃) and low humidity(60%), spreading could increase content of total amino acids in fresh tea leaves, most of free amino acids increased at a certain extent. Contents of total catechins and total Esters-catechins in fresh tea leaves both with 60% and 75% environment humidity decreased at a certain extent or were similar, but content of total catechins and total Esters-catechins in fresh tea leaves with 90% environment humidity increased at a certain extent. There was no gallocatechin (GC) checked out in all of fresh tea leaves under different spread environments.5. Variation of biochemistry components in fresh tea leaves could influence the taste, aroma and soup color of tea. Comprehensive consideration to variation rule of chemical components, flavor quality and requirement of latter process on physical characteristic of fresh tea leaves, 70% of water content is the best of moisture of fresh tea leaves after spreading. Comprehensive consideration to taste and scent, single bud under low temperature(20℃) and high humidity (90%) , and one leaf and one bud under low temperature and medial humidity (20℃, 75%) could get the tea best quality.