The Enantiomeric Distributions Of Volatile Constituents In Tea

Aroma is one of the important factors in the sensory evaluation of tea,and it has always been the key point in the field of tea chemistry.Tea aroma is a mixture of a variety of volatile constituents in the form of different concentrations.Most of the volatile constituents including enantiomers with different aroma characteristics and odor thresholds have one or more tridimensional centers,and the effect of fragrance caused by their different proportions play an important role in the formation of tea aroma.In this experiment,the extraction,analysis method and quantitative analysis of 15 important volatile constituents in tea were established.Based on three factors of different cultivars,different tea processing methods and different seasons,the distribution of important volatile constituents of 21 tea cultivars in five provinces of China were analyzed.The specific results were as follows:1)Headspace solid-phase microextraction/chiral gas chromatography-mass spectrometry was used to establish the optimal extraction and analysis methods for the 15 enantiomers of volatile compounds in tea.The optimized standard addition method was used to establish each of them.The precise quantitative analysis method of enantiomers obtained the ideal detection limit,linear range,correlation coefficient,spike recovery and relative standard deviation.2)The enantiomeric ratios and content differences of 15 pairs of volatile components in 21 different cultivars of fresh tea leaf samples were analyzed.The results show that most of the enantiomers of volatile components can be detected in different cultivars of fresh tea leaves,but their ER values and content are significantly different among different cultivars.The correlation analysis showed that the distribution of the enantiomers of the volatile components was closely related to the suitability of the tea cultivars and the origin of the cultivars.3)The content of enantiomers of volatile components was significantly different before and after tea processing.Partial least-squares discriminant analysis(PLS-DA)could successfully distinguish green tea,black tea,white tea and oolong tea respectively.The fresh leaves and their corresponding finished tea samples.In addition,different processing techniques have led to a trend in the variation of the enantiomers of the volatile components.The contents of the key enantiomers in green tea have all decreased significantly after processing,and the white tea is reversed.Most of the volatiles in Oolong tea are volatile.The content of the enantiomers of the components decreased significantly after the processing,while the content of S-E-Nerolidol and(1R,2S)-methyl jasmonate increased sharply after the processing of oolong tea;The contents of the key enantiomers are greatly influenced by the tea tree cultivars,and their changing trends are different.4)The effect of production season on the enantiomeric content of volatile components in tea was investigated.The experimental results show that spring and autumn tea samples can be successfully distinguished by a good PLS-DA model.The distribution of the enantiomers of the volatile components was found to change with the seasons.It was found that the white tea and green tea samples showed similar trends among the key differences in the samples of different seasons,and the content of(2S,5S)-linalool oxide A,(2R,5S)-linalool oxide B,2S,5R)-linalool oxide B,R-limonene,(2R,5R)-linalool oxide A,(2S,5S)-Teprane A and R-4-terpineol was higher in autumn,while the content of R-?-pinene,S-?-ionone,S-4-terpineol,and(1S,2R)-methyl jasmonate were higher in spring.