Study On The Bitterness And Astringency Compounds Of Green Tea(Camellia Sinensis)

Bitter and astringent taste is the important sensory characteristic to evaluate the taste and quality of green tea.The taste flavour of tea results from the interactions of many compounds.For a long time,the contributions of many polyphenols other than catechins and caffeine to the bitterness and astringency of tea have often been neglected.In this paper,the key compounds contributed to the bitter and astringent taste of green tea were analyzed and revealed through widely targeted metabolomic technology,which provides the technical and theoretical basis for the quality control of tea,and provides a new insight to solve the bitter taste of tea in summer and autumn.The main results are as follows:First,in this paper,a widely targeted metabolomics quantification method for compounds related to tea quality was established.Based on the mass spectra information of accurate precursor ions and their product ions,a total of 106 compounds in tea were identified qualitatively through the high-resolution UPLC-MS technique.Optimizing the parameters of MRM,such as fragmentation voltage and ion pair collision energy,a widely targeted metabolomics quantification method for compounds was established through UPLC-MRM-MS-based targeted technique.The relative and absolute content of compounds in nearly 100 green tea samples from the main tea-producing provinces of China were confirmed,respectively,and the detection limits of different compounds in tea were also determined.According to the structure characteristics of the polyphenols,phenolic compounds of tea are resulted from four typical derivatization reactions in tea plants including galloylation,polymerization of flavan-3-ols,glycosylation of flavonoids,and hydroxylation reactions in the B-ring of flavonoids.The correlation matrix analysis between polyphenol constituents showed that interactions took place among different compounds.For example,the constituents of the B-ring monohydroxyl flavonols and the acyl derivatives of polyphenols(except galloylated catechins)had no or negative correlations with other phenolic substances.The absolute quantitative analysis results showed that the average content of ester catechins is much higher than that of non-ester catechins,and the content of catechins with trihydroxy at B-ring and with galloyl group vary greatly.Secondly,the key compounds related to the astringent taste of green tea were screened by the widely targeted metabolomics quantification method.The astringency taste and intensity scores of nearly 50 green teas from tea producing areas in southwestern and southeastern China were analyzed through the traditional Chinese sensory evaluation protocol of green tea coupled with quantitative sensory evaluation technology based on astringency scores of the EGCG solution.The polyphenols related to tea quality in the 47 tea samples were relatively quantified by using the widely-targeted detection method.The correlation analysis of the astringency and compounds related to tea quality was performed by using the methods of PLS and PCA.The results showed that the metabolic difference of compounds related to tea quality can not fully explain the difference of astringency intensity of green tea samples,but it can distinguish the green tea samples with different astringency characteristics,such as grassy astringency,coarse astringency.There are significant metabolic differences in hydroxylation in the B-ring of flavonoids,glycosylation,acylation and condensation reaction of polyphenols in tea samples with different astringency characteristics.Among them,the content level of proanthocyanidins in tea samples with coarse astringency characteristics is higher while tea samples with grassy astringency characteristics have higher level of hydrolyzable tannins.Thirdly,the key compounds related to the bitterness of green tea were screened by widely targeted metabolomics quantification method.The bitterness intensity scores of 50 green teas from tea producing areas in southwestern and southeastern China were analyzed through the traditional Chinese sensory evaluation protocol of green tea coupled with quantitative sensory evaluation technology based on bitterness scores of the quinine dihydrochloride solution.The compounds related to tea quality in the 50 tea samples were relatively quantified by using the widely-targeted detection method.Orthogonal partial least squares regression analysis suggested that the metabolic differences of green tea from tea producing areas in southwestern and southeastern China could used to distinguish green tea samples with different bitterness intensity scores.The loading plot and the compounds determined to be of variable importance(VIP >1)showed proanthocyanidins(especially the proanthocyanidins with galloyl group),caffeine,theobromine and flavonols are related to the bitterness intensity of green tea.Pearson correlation analysis showed that the proanthocyanidins(especially the proanthocyanidins with galloyl group),caffeine and theobromine have positive correlation with bitterness of green teas at extremely significant level.However,the flavonols have negative correlation with bitterness of green teas.Metabolic flow analysis showed that the content of alkaloids,derivatives of phenolic acid and catechins,several flavone glycosides are higher in the green teas with higher bitterness intensity,suggesting they may can increase the bitter taste of green tea.Fourthly,through widely targeted metabolomics quantification method,factors influencing the accumulation level of the compounds related to tea quality were analyzed,including tea variety with different leaf colors,different tissues and organs,development period of tea leaf and harvesting season.The results showed that,compared with the green leaves and yellow leaves,“ZJ” tea with purple leaves accumulated not only higher content of anthocyanins,but also higher content of dimer proanthocyanidins,methoyl derivatives and derivatives of phenolic acids and catechins.However,HSBY 1 tea plant with yellow leaves contained higher content of flavone and flavonol glycosides,and lower content of catechins.Hydrolysable tannins,galloyllated catechins,alkaloids mainly accumulate in bud and tender leaves.With the development of leaves,the content of hydrolysable tannins decreased,while the content of flavone and flavonols glycosides increased.Higher content of PAs accumulated in stem,while glycosides in mature leaves.Hydrolysable tannins were mainly accumulated in fresh leaves collected in spring,while higher accumulation level of proanthocyanidins is found in leaves collected in late summer and autumn.