| "Fresh scent" is the typical flavor type of green tea,and is also a key sensory evaluation characteristic of the premium green tea aroma quality.In this study,green tea samples with the distinctive "fresh scent" flavor were used as the research objects.The volatile compounds were detected by stir bar sorptive extraction(SBSE)combined with gas chromatography-mass spectrometry(GC-MS).Key aroma compounds that determine the "fresh scent" quality of green tea were identified by using gas chromatography-olfactometry(GC-O)combined odor activity value(OAV)calculation method as well as the aroma recombination.Finally,a widely-targeted metabolomics technique was used to make a preliminary comparative analysis of the differences in chemical compound bases of "fresh scent" and "chestnut flavor" green teas.The research results are as follows:1.Single factor and orthogonal experiments were performed on parameters such as stir bar type,extraction temperature,extraction time,tea to water ratio,agitation rate,and NaCl content.The optimal conditions for extracting the volatile compounds in "fresh scent" green tea by SBSE method were determined as: PDMS twister,60:1(mg/ml)tea-water ratio,5% NaCl solvent,80 ? extraction temperature,90 minutes extraction,1250 r/min agitation rate.Based on this,an optimized SBSE-GC-MS analytical method for volatile compounds of "fresh scent" green tea was established.The analysis showed that the repeatability and recoveries(between 80% ~ 120%)of this method were satisfactory.2.Data obtained from the present study revealed that 151 volatile compounds from 16 different chemical classes were identified by SBSE-GC-MS analysis,including enols,alkenes,alkanes,aldehydes,olefin aldehydes,alcohols,esters,lactones,allyl esters,ketenes,ketones,organic acids,sulfur compounds,nitrogen heterocyclic compounds,oxygen heterocyclic compounds,and aromatic hydrocarbons.Alkanes(31)and esters(22)formed the largest groups,followed by ketones(16),aldehydes(15),and aromatic hydrocarbons(13).Enols(8096 ?g/kg),alkanes(6744 ?g/kg),aldehydes(6442 ?g/kg),and esters(6161 ?g/kg)were the four major chemical classes which own high relative contents in "fresh scent" green tea.3.Twenty-one volatile compounds with high aroma intensity were identified by GC-O analysis,while 44 volatile compounds with OAVs > 1 were obtained by OAV calculation.Fourteen aroma compounds including 2-methyl butanal,dimethyl sulfoxide,heptanal,benzaldehyde,1-octen-3-ol,(E,E)-2,4-heptadienal,benzeneacetaldehyde,linalool oxide ?,(E,E)-3,5-octadien-2-one,linalool,nonanal,methyl salicylate,geraniol,and ?-ionone,were identified as key aroma compounds according to the GC-O analysis and OAV calculation.These 14 volatile compounds were subjected to aroma recombination with deodorized tea powder as a blank matrix,and the results showed that the aroma quality of "fresh scent" green tea can be successfully simulated by the recombinated tea infusion.4.A preliminary comparative analysis of the chemical compositions between "fresh scent" and "chestnut flavor" green tea samples were conducted by widely-targeted metabolomics technique,and 173 different metabolites were screened.Among them,seven chemical substances,including ?-linolenic acid,palmitoleic acid,vanillin,?-aminobutyric acid,kaempferol-3-O-rutinoside,cryptochlorogenic acid,and L-methionine were regarded as the important ones which may be involved in tea aroma formation.Moreover,the contents of cryptochlorogenic acid and L-methionine were found to be prominent in "fresh scent" green tea samples,whilst the contents of ?-linolenic acid,palmitoleic acid,vanillin,?-aminobutyric acid and kaempferol-3-O-rutinoside were dominated in "chestnut flavor" green tea samples. |
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