| Tea flavor substances are mainly composed of aroma substances and taste substances.Based on the seven stages of airing,water-removing,twisting,primary drying,re-drying and finished tea products involved in the production and processing of Hanzhong Chaoqing green tea,this study focused on the formation and the analysis of changesof tea aroma compounds and main flavor substances,the main research contents and experimental results are as follows.Based on the single-factor experiment,the Box-Benhnken test design was used,and the aroma compounds of Hanzhong Chaoqing green tea were taken as the research object.The total peak area was used as the judgment standard to optimize the extraction and separation process of Solid-Phase Microextraction method(SPME).The best process condition parameters obtained were the DVB / CAR / PDMS extraction fibers,the sample weight was 8.00 g,and headspace adsorption in a 50? water bath for 56 minutes;under this condition,the total integral area of volatile substances obtained from Hanzhong Chaoqing green tea was the largest,131 kinds of aroma compounds were detected.The results showed that the optimized SPME/GC-MS process conditions have practical application value,which can be used for the extraction and separation of volatile compounds of Hanzhong Chaoqing green tea,which laid a reliable preparation process for the follow-up analysis of Hanzhong green tea aroma compounds.Through the optimized SPME process conditions,the aroma compounds of Hanzhong Chaoqing green tea at different processing stages were extracted separately,and the volatile components extracted were combined with GC-MS mass spectrometry library for qualitative and quantitative analysis.A total of 131 aroma compounds were identified.The volatile compounds were composed of alcohols,aldehydes,esters,ketones,phenols,heterocycles,acids,terpenes and hydrocarbons.In the whole processing process of Hanzhong Chaoqing greens tea,the contents of alcohols was the highest,reaching to 33.81%-56.80%;the contents of ester compounds was second only to alcohols,accounting for 12.45%-32.99%;and there were no obvious changes in the contents of phenols and acidification compounds,being 0.18%-2.39% and 0.81%-1.33%respectively.However,in the fresh leaves,water-removing,twisting,and re-drying stages,the contents of aroma compounds of enterpenes and heterocycles were similar,being 1.66%-11.29% and 1.77%-5.19%,respectively.In addition,the contents of aldehyde compounds was 2.70% to 5.64%,and after twisting,it increased from 3.35% to 5.64% in the drying stage;while the ketone compounds reached the peak at the primary drying stage,and the contentswas 1.71% to 7.08%.The research results showed that the processing technology significantly affects the conversion and contents of aroma compounds: water-removing is a key link in the processing of green tea and an important stage of the conversion of aroma compounds;twisting is an important link in roasting and shaping.After twisting,the fragrance appeared first in Hanzhong green tea,the representative compounds were terpene alcohol,cis-3-hexenol,etc.;the process of primary drying,re-drying,and tea products removed excess water from the tea leaves,consolidates the shape of the tea,develops the aroma to the greatest extent,which made them the important stages of aroma formation.The results of GC and GC-MS analysis showed that there were certain differences in the composition of aroma compounds in the seven stages of production of Hanzhong green tea.The detected aroma compounds were: 100 in the fresh leaf stage,103 in the airing stage,104 in the water removing stage,108 in the twisting stage,105 in the primary drying stage,106 in the re-drying stage,and 103 in the finished production stage;among them,74 compounds were common to each stage.These 74 aroma components included 25 alcohol compounds,23 ester compounds,16 aldehyde compounds,13 terpene compounds,11 heterocyclic compounds,7 ketone compounds,7 phenol compounds and 6 compounds acid compounds.In addition,some compounds were unique to a certain stage,such as hexyl acetate,methyl benzoate,terpinolene only existed in fresh leaves;while citronellate acetate,3-methyl-2-butenal,Butyl isovalerate,etc.were detected in the airing stage.Corresponding to this,some compounds were not detected at a certain stage,such as phenylacetaldehyde,(E)-2-decenal,and thymol,which existed at other stages,were not detected at the water removing staget;and dodecanal was not detected in the finished tea products stage.Analysis showed that among the aroma components of Hanzhong Chaoqing green tea,there were 7 compounds that had an important contribution to the formation of floral aroma,including linalool,linalool oxide I,linalool oxide II,linalool oxide III,Linalool oxide IV,geraniol,and ?-ionone;two compounds that contribute significantly to the formation of green fragrance,namely(Z)-3-hexenol and E-hexanoate;there were three kinds of important contribution compounds to the formation of nut aroma,namely 2-ethyl-5-methylpyrazine,benzothiazole and 2-acetylpyrrole;and there were three kinds of compounds that had important contribution to the formation of fruit aroma,namely isopentyl Hexyl acid,heptanal,methyl heptenone.The research results show that the different stages of production and processing have different effects on the aroma components of Hanzhong Chaoqing green tea,so as to form a certain flavor of green tea and specific green tea quality.Through HPLC or UV analysis,the effects of different links in the processing process on the changes in the content of the main flavoring substances tea polyphenols,catechins,caffeine and gallic acid in Hanzhong green tea were discussed.During the whole processing of Hanzhong Chaoqing green tea,the content of tea polyphenols gradually decreased in the water removing stage,from 13.10 mg /100 mL to 12.96 mg /100 mL,while in the twisting and drying stage,it gradually increased from 9.09 mg /100 mL to 74.28 mg /100mL;The content of catechins in the whole process showed a downward trend,from 66.10 mg / 100 mL to 16.77 mg /100mL;and the content of caffeine gradually decreased from fresh leaves to the stage of re-drying,and its content change was 15.06 mg /100mL-5.73 mg /100 mL,while in the finished production stage it rose to 32.14 mg /100mL;in addition,the gallic acid content in the entire process of the downward trend is basically stable,its content changed appear to be 1.28-0.31 mg /100 mL.The analysis results showed that Hanzhong Chaoqing green tea flavoring substances catechin and gallic acid were completed in sequence with the processing process,and their mass fractions were showing a gradual downward trend as a whole,but there were also slight differences;while the content of tea polyphenols declined in theairing and water removing stage,and gradually increased in the twisting and drying stages;the caffeine content only rose in the finished stage.The change in the mass fraction of these taste substances is mainly due to the isomerization of chemical molecules with the temperature change during processing.On the other hand,the cells lose more water due to high temperature and enzymatic action at the water removing stage.Oxidation and degradation cause the content of taste substances to decrease.The results of this study can provide a scientific reference for the process improvement of tea quality based on the change of aroma compounds and taste substances during the processing of Hanzhong Chaoqing green tea,as well as the shaping of specific quality tea products in the region. |
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