The Formation Mechanism Of The Quality Difference Of Wuyi Rock Tea Made From Different Tree Ages

Wuyi rock tea is a representative Oolong tea in the northern Fujian area,China.People lived in Mount Wuyi used to divide the tea products according to tree ages which led to remarkable different flavour and taste.However,the mechanism behind still unclear.This thesis selected Fujian-shuixian(Camellia sinensis(L.)O.Kuntze cv.Fujian-shuixian),a national improved cultivar of tea,as a subject,adopt uniform fresh leaf picking standard and processing technology.Tea samples made from tree ages of 10 years(Xincong,XC),35 years(Gaocong,GC),and 55 years old(Laocong,LC).The aroma and taste quality characteristics,chemical compositional profile were analyzed,coupled with the metabolomics and transcriptomics analysis of fresh tea leaves reveal the molecular mechanism that how the age of tree influence the accumulation of main biochemical components.Besides,the difference of pesticide residues in Wuyi rock tea with different tree ages was analyzed.The main results of this thesis were as follows:1.In order to explore the biochemical basis of the differences in the flavor and quality of Wuyi rock tea with different tree ages,sensory evaluation was applied to judge the tea samples made from 3 different age of tree,and the content of 18 compounds were determined and compared.It?s showed that the tea samples with three tree ages differ significantly in flavor quality and have their own characteristics,tea samples of XC group taste fresh and mellow,the tea samples of GC taste full-bodied and tea samples of LC taste strong and full-bodied.The contents of 13 biochemical components,such as tea polyphenols,varied significantly among the ages of the three trees.According to the correlation analysis,the taste quality of Wuyi rock tea with three tree ages was positively correlated with tea polyphenols,amino acids,water extracts,catechins and EGCG contents,The correlation coefficients were 0.582,0.437,0.784,0.451 and 0.623,respectively.2.GC-TOFMS(gas chromatography-time of flight mass spectrography),combined with the evaluation results of aroma quality,the material basis of the difference in aroma quality of Wuyi rock tea with different tree ages was explored.The results showed that the tea samples with three different tree ages had rich aroma components,the difference between tree ages is obvious meanwhile.A total of 35 different aroma components including 2-acrolein and ?--butyrolactone were selected.It is speculated that these may be the material basis of the difference in aroma quality among the tea with three tree age,especially the five volatile terpenoids such as linalool,which is closely related to the quality of oolong tea aroma,their relative contents in XC and LC rock tea significantly higher than that of GC rock tea.At the mean while,the aroma fingerprint of GC-MS was established to distinguish XC,GC and LC rock tea,and 23,13 and 27 volatile compounds related to the aroma characteristics of each tree age were screened out,respectively.3.Based on the non-targeted metabolomics and biochemical component analysis,the differences of tea polyphenols and amino acids in the leaves of tea trees of different ages were determined.The results showed that there were significant differences in the metabolic profiles of the fresh leaves of three trees ages,and the expression levels of 180 metabolites including amino acids,flavonoids,vitamins and organic acids changed significantly.Among them,the expression level of tea polyphenols was the highest in GC leaves,followed by LC,and the lowest in XC.The amino acid consisting mainly of L-theanine had the highest expression in LC leaves,followed by XC,and the lowest in GC,which was consistent with the results of biochemical component analysis of Wuyi rock tea.The accumulation of these metabolites in the leaves of different tea plants is due to the changes in shikimic acid pathway,catechin biosynthesis pathway and theanine biosynthesis pathway.illustrate that the difference of tea taste quality was related to the changes of tea polyphenols and amino acids.4.The molecular mechanism of the quality difference of Wuyi rock tea made from different tree ages was elucidated based on the results of transcriptomics,metabolomics and aroma component analysis.According to the transcriptome data,in leaves of different tree ages,phenylalanine ammonia-lyase gene(PAL)etc.36 functional genes related to metabolism of tea polyphenols,glutamate synthase gene(GOGAT)etc.30 functional genes related to the metabolism of amino acids,linalool synthase gene(LIS)etc.38 functional genes related to metabolism of terpenoids,showed different degrees of differential expression,these results were verified by metabonomics and analysis of aroma components.Indicated that the differential expression of the key functional genes involved in the biosynthesis of tea polyphenols,amino acids,terpenes under different tree ages,which is the basic reason for the quality difference of Wuyi rock tea.5.To investigate the difference of pesticide residues in Wuyi rock tea at different tree ages,a new pesticide detection method was established to determine the residues of 36 commonly used pesticides in Wuyi rock tea.The results showed that the number and detection rate of pesticide residues in the tea samples were low,which generally met the standard of safe drinking of Chinese tea.Further analysis showed that with the increase of tree age,the residues of Carbendazim and other two pesticides in Wuyi rock tea gradually decreased,imidacloprid and thiazinone first decreased and then increased,while Difenoconazole first increased and then decreased,indicating that the change of tree age may have impact on pesticide residues.In conclusion,starting from aroma and taste quality,biochemical and aroma components,this study analyzed the material basis of the quality difference of Wuyi rock tea with different tree ages,and established the aroma fingerprint for distinguishing three groups of Wuyi rock tea.Based on the results of metabonomics,transcriptomics and analysis of aroma components,the formation mechanism of quality difference of Wuyi rock tea of different tree ages was revealed.At the same time,the differences of pesticide residues in Wuyi rock tea of different tree ages were also analyzed.The results provide a scientific explanation for the relationship between the change of tree age and the quality difference of Wuyi rock tea,as well as a test basis for people to drink Wuyi rock tea safely and select low residue pesticides according to tree ages.