| Oolong tea is one of the six major tea in China,and Fenghuang Dancong is a special category of oolong tea.It is produced in Chaozhou,Guangdong province,and it is screen separation from the quality varieties of Fenghuang narcissus series tea.It is a high-flavored tea variety resource with the highest natural floral fragrance,the most floral type,and unique flavor in Chinese tea varieties.In this study,the volatile substances in drying Fenghuang Dancong was extracted by solvent assisted flavor extraction method,combined with GC-MS detection technology to analyze volatile substance changes,again quantitative analysis of the changes of the glycosidically aroma precursors by derivatization combined with GC-MS derivative method,to explore the relationship between glycosidically aroma precursors and volatile substance changes and discuss their role in aroma formation.The main conclusions are as follows:1.A total of 79 volatile aroma substance were detected from Fenghuang Dancong in this product,including 29 alcohols,11 esters,25 olefins,3 benzenes,3 aldehydes,5ketones,and other three kinds of compounds,with the highest content of alcohols.In the dried sample,the highest 5 volatile substances were alpha-farnesene(24.05%),nerolidol(22.63%),linalool(11.58%),indole(4.28%),dehydrolinalool(2.95%).The kinds of aroma compounds and the main aroma components whose relative contents were more than 1% reached their peaks at the second and the third rocking respectively,indicating that Fenghuang Dancong tea during rocking process had the best aroma in the processing samples.There were 23 kinds of aroma substances detected in the fresh leaves to the drying leaves samples.They were nerolidol,alpha-farnesene,linalool,dehydrolinalool,Linalool Oxides I.Linalool Oxides II,Linalool Oxides III,Linalool Oxides IV,Indole,o-xylene,p-xylene,?-caprolactone,methyl salicylate,nerol,geraniol,alpha-citral,copaene,cis-3-hexenyl hexanoate,cis-jasmone,caryophyllene,mollerene,d-juniol,and cedarol.These aroma components were the main aroma of the samples.A total of 22 kinds of aroma substances were newly produced during the processing,among which 12 were produced during withering process and 10 were produced during rocking process.2.A total of 14 glycosidically aroma precursors were detected in this product,including 6 glucosides,namely cis-3-hexenyl-glucoside,benzyl glucoside,2-phenylethyl glucoside,and Linalool Oxide I glucoside,Linalool Oxide II glucoside and methyl salicylate glucoside,8 primeverosides,including cis-3-hexenyl-primeveroside,benzyl primeveroside,2-phenylethyl primeveroside,linalool primeveroside,Linalool Oxide I primeveroside,Linalool Oxide IIprimeveroside,methyl salicylate primeveroside,and geranyl primeveroside.The content of glucoside and primeveroside increased during the processing,and the total amount of glycosidically aroma precursors increased from 550.73 ?g/g to 843.06 ?g/g,increased by 52.99%.In each process sample,the content of primeveroside was higher than that of glucoside,but the content of primeveroside was increased slowly,and the content of glucoside increased obviously.From the point of view of glycosides,the fastest increase was 2-phenylethanyl glucoside.The three highest content glycosides were2-phenylethyl primeveroside,benzyl glucoside and benzyl primeveroside.On the basis of the ligand,the content of benzyl glycoside is the highest.From the processing point of view,the contents of benzyl primeveroside,2-phenylethanyl primeveroside,Linalool Oxides I primeveroside and methyl salicylate primeveroside were correspondingly reduced during rocking process;in the fixation process,benzyl glucoside,Linalool Oxide II glucoside,linalool primeveroside,Linalool Oxide II primeveroside and geranyl primeveroside also decreased correspondingly,and other components increased in other process.Among them,the content of Linalool Oxide I glucoside,Linalool Oxide II glucoside,linalool primeveroside,Linalool Oxide I primeveroside,Linalool Oxide II primeveroside during processing increase was not significant or basically unchanged.3.Combined with the changes in the content of glycosidically aroma precursors and their corresponding free scent compounds ligands in the sample during processing,it was known that the glycosidically aroma precursors were hydrolyzed to corresponding aroma compounds during rocking process.Obviously,rocking process was one of the important reasons for the superior quality of Fenghuang Dancong cluster aroma.During processing corresponding precursors of glycosides react with the synthesis of glycosides.This reaction continued until the processing of tea leaves is completed.This was also the reason of increase in the processing of glycoside aroma precursors in tea samples.Because the synthesis and hydrolysis of glycosidically aroma precursors is a process of dynamic balance,and different kinds of glycoside species differences with each other,the speed of the reaction directly influenced the change of the content of glycosidically aroma precursors.In addition to processing except rocking process,the synthesis rate of glycosides was faster,and the content of each glycoside was increased.From the whole processing process,the content of glycoside aroma precursors increased significantly compared with fresh leaves,but the relative content of free aroma compounds corresponding to the corresponding ligands did not increase.It can be seen that the hydrolysis of glycoside aroma precursors into volatile aroma substances only takes place during the shaking phase,while the formation of other aromas may not come from the hydrolysis of glycosidic aroma precursors. |
PDF Full Text Request