Study on the Glycosidic Flavor Constituents in Green Tea Based on Modification-specific Metabolomics Approach

Author:Li Peng Liang

Supervisor:lin zhi ni de jiang

Database:Doctor

Degree Year:2018

Download:344

Pages:98

Size:5337K

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Glycoside compounds are essential to the taste,aroma and bioactivities of tea and can be classified into glycosidically bound non-volatiles(GBNVs)and glycosidically bound volatiles(GBVs)according to the volatility of the linked aglycones.However,limited by the current analytical methods,only a small number of high-abundant glycosides are discovered and identified.A large number of middle-and low-abundant glycosides are rarely concerned about.To detect the glycoside compounds in tea massively and specifically,and investigate their effect on green tea quality,the research and the results are as follows:1 A nontargeted modification-specific metabolomics method has been developed for specifically detecting the glycosides in tea in a high-throughput manner using ultra-high performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry(UHPLC-Q-TOF/MS)by applying in-source collision-induced dissociation(ISCID)voltages.We analyzed the glycosides in the fresh leaves of 10 tea cultivars using this method.A total of 118 glycoside compounds containing 92 GBNVs and 26 GBVs were discovered.Among them,27 glycosides(16 GBNVs and 11 GBVs)were confirmed by authentic standards.2 Variations of glycosides during green tea manufacturing were also detected by the nontargeted modification-specific metabolomics method with the raw materials of Longjing 43 cultivar.Cluster analysis and principle component analysis(PCA)showed the contents of glycosides changed greatly during the stage of pan firing and drying of green tea.Notably,the contents of GBVs significantly increased by 1.12-4.46-fold during pan firing.In contrast,the contents of the corresponding volatiles decreased by 2%-20%during pan firing.The glucose was also significantly decreased during pan firing.Correlation analysis showed that the content of GBVs was negatively related to the contents of volatiles and glucose(correlation coefficients<-0.8,P<0.05).Model experiment confirmed that the enzymatic synthesis contributed to the increase in the content of GBVs with the substrate of volatiles and sugars during the pan firing of green tea,and the result also demeonstrated that the GBVs did not appear to be the contributors to the aroma of green tea.3 A kind of Amadori compound named N-(1-Deoxy-1-fructosyl)theanine was discovered and identified.LC-MS analysis showed this compound was formed at the drying stage of green tea.At low level of concentration,this compound revealed umami taste,and at high level of concentration,this compound showed sour taste.However,the N-(1-Deoxy-1-fructosyl)theanine had no apparent contribution to green tea taste because of its high taste threshold of 22.32 mmol L-1.The pyrolysis compounds of N-(1-Deoxy-1-fructosyl)theanine were also detected by HS-SPME-GC-MS after heated at 60,70,80,90,and 100°C,respectively.A total of 66 volatiles mainly containing pyrazines,furans and pyrroles were discovered,which have potential effect on green tea aroma(nutty,roasty and caramel-like).