| Tea aroma is an important quality index of tea.With the development of science and technology,the category,content and distribution of tea aroma components have been widely reported.The study of tea aroma chemistry used to focus on the analysis of volatile components in different kinds of tea,however,there was still a lack of further scientific research on the distribution of key odorants in tea volatiles and how the key odorants work together to influence tea aroma.In this study,the aroma components of baked green tea were analyzed by classical molecular organomics,and the key odorants were identified and quantified.Then,the key odorants were identified by s-curve method and OAV method,the interaction types(synergistic,additive,masking or non-effect)were investigated from three latitudes,namely,aroma recognition threshold,aroma intensity and aroma contribution.On this basis,the aroma interaction was verified by recombination experiments.Finally,we also built interaction network of key odorants in baked green.This study aims to deepen the theory of tea aroma quality and provide scientific guidance for tea aroma quality promotion and directional regulation,which has important theoretical significance and practical application value.The main results of this study are as follows:1.The aromatic profiles in fresh tea leaves and corresponding baked green tea with five levels of tenderness of two cultivars were analysed by stir bar sorptive extraction-gas chromatography-mass spectrometry.The results showed that the aromatic profiles of different tea cultiviars were different,while the number and chemical structure distribution of aromatic compounds of different tenderness tea samples processed by same cultiviar were similar.113 and 111 aromatic components were identified from fresh leaves and the corresponding baked green tea samples of ‘Zhongcha 302’ while 114 and 101 aromatic components were identified from ‘Zhongcha 108’.And then,the least squares analysis was performed after Pareto scaling to evaluate the distribution differences among the same series of tea samples with different tenderness to find out the key odorants,the results showed that the aromatic components of fresh tea leaves with different tenderness and the corresponding baked green tea were different: 14 and 19 aromatic compounds were found in fresh tea leaves and baked green tea of ‘Zhongcha 302’,which were related to the tenderness of fresh tea leaves,among them,pyridine,geraniol and linalool were positively correlated with the tenderness of fresh tea leaves while 2,4-di-tert-butylphenol,pyridine and cisjasmonone were positively correlated with tenderness of baked green tea.15 and 20 aromatic compounds were found in fresh tea leaves and baked green tea of ‘Zhongcha 108’,which were related to the tenderness level of fresh tea leaves,the contents of γ-terpene,styrene and indole in fresh tea leaves were positively correlated with the tenderness of fresh tea leaves,and the contents of phytoalcohol,coumarin and phenylethanol in baked green tea were positively correlated with the tenderness,besides,cis-linalool oxide(furanoid)and methyl salicylate exhibited significantly increasing trends as samples of all series matured while there was no common odorant related to all series tenderness.2.The contens,ER values and the dynamic changes of 15 target chiral odorants in fresh tea leaves,semi-fininshed samples and corresponding baked green tea processed by ‘Zhongcha 302’ were also analysed by enantioselective-GC-MS.The result showed that the concentrations of most enantiomers in fresh tea leaves and finished baked green tea were significantly higher in tea samples with higher maturity,and the concentrations of all target enantiomers changed obviously during the processing.The results showed that: 1)the content distribution of chiral odorants in fresh tea leaves with different tenderness was significantly different.The content of R-nonlactone was the highest in one bud fresh tea leaf sample,the contents of R-limonene,(2S,5S)-linalool oxide A,(2S,5R)-linalool oxide B,S-(E)-nerolide,Rdihydroactinidiolide and S-dihydroactinidiolide were the highest in the one bud with three leaves,while the contents of R-limonene,(2S,5S)-linalool oxide A,(2S,5R)-linalool oxide B,S-(E)-nerolide,R-α-ionone,R-dihydroactinidiolide and S-dihydroactinidiolide were the highest in the samples with a bud with four leaves.2)Except for R-γ-nonlactone,S-(E)-nerolidol and R-limonene,the contents of chiral odorant enantiomer in samples with a bud with three/four leaves leaves were significantly higher than other tea samples.The contents of R-γ-nonlactone and S-(E)-nerolidol in sample with a bud with three leaves were significantly lower than that in a bud with four leaves,while the contents of R-limonene in sample with a bud with three leaves were higher than that in a bud with four leaves.3)Except for limonene,dihydroactinidiolide and α-terpineol,the ER values of most chiral odorants were less affected by tenderness and tea processing techniques,after drying,the ER value of R-limonene decreased sharply to87.18%,and the S-α-terpineol decreased continuously after spreading while increased slightly after rolling and drying;the main configuration of dihydroactinidiolide changed from R-dihydroactinidiolide to Sdihydroactinidiolide after rolling,which indicating that spreading,blanching and drying are the key processes steps which affecting the distribution of these chiral odorant components.3.Qualitative,absolute quantitative and aroma intensity(AI)analysis of odorants in baked green tea processed by ‘Zhongcha 302’,‘Zhongcha 108’ and ‘Fuding Dabai’ cultivar were conducted,and then the FD values in all tea samples were identified by AEDA experiment,and then the aroma recombination experiment of ‘Zhongcha 302’ baked green tea was performed based on the quantitative results of the odorants.Finally,the contents of odorants,FD values and AI values in different tea samples was analysed.The results showed that: 1)the amounts of odorant in three baked green tea were similar,57 species(Zhongcha 302),50 species(Zhongcha 108)and 59 species(Fudingdabai).2)the odorants of three cultivars were divided into six categories according to their odor categories: green,herb,flower,sweet,roasted and other,and the sum of their aroma intensity is: 149.44(fuding Dabai)> 147.82(Zhongcha302)>121.06(Zhongcha 108).3)The flavor dilution factors of odorants were also different among three tea cultivars.In "Zhongcha 302" baked green tea,geraniol(512)and β-citral(256)were the highest while trans-β-ionone(256),coumarin(256),Geraniol(128)and cis-citral(128)were the highest in ‘Zhongcha108’ baked green tea;trans-β-ionone(512),coumarin(512),geraniol(256),cis-citral(256)and β-pinene(256)were the highest in ‘Fuding Dabai’ baked green tea.4)There were also 11 key odorants in three tea cultivars have the same distribution trend in three dimensions: content level,FD value and AI value.4.The actual odor threshold of the odorants in ‘Zhongcha 302’ baked green tea was measured by 3-AFC method,and then identified seven key odorants through omission and addition experiments.Finally,threshold method and OAV method were used to study the interaction effects of binary mixtures of seven key odorants.The result revealed that there were four types of interaction effect: thirteen groups show cooperation,six show inhibition,one shows promotion and one shows ineffectiveness.The results obtained by threshold method and OAV method are completely consistent,which shows that the two methods have high accuracy in studing the binary interaction effect of key odorants in baked green tea.5.Based on the binary interaction effects,the interaction mechanism in tea samples was further explored.The result showed there were only two groups of binary mixtures have the same interaction rules between solvent background and blank tea matrixs,while the other groups have different interaction rules. |
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