Molecular Sensory Studies On Tea Aroma

Aroma is the key factor of the quality of tea,which brings the sensory experience for consumer and impacts the commercial value of the tea products.Tea has hundreds of volatiles,but only a small portion of them is odor active Previous studies related to tea aroma focused mainly on the volatile composition,but laked sensory characterization of the moleculescontributing to tea aroma.Molecular sensory science studies the origin of food sensory character and to elucidate the generation of key sensory-impact mlecules during food processing.Armed with sophisticated technology of analytical and sensory sciences,food flavors can be unraveled qualitatively and quantitatively down to the molecular level.By means of molecular sensory science,the key odor active compounds of tea can be identified and the sensory character of tea can be explained.The knowledge provides solid basis for further systematic studies on plant cultivation,process innovation,quality assessment,consumer preference,etc.In this study,molecular sensory science was applied to the fundamental research of tea aroma formation during processing,characterization of white tea aroma,and discovery of orchide-like aroma in premium tea leaves Advanced techniques of aroma preparation,chemical analysis,and sensory study used in this reseach include solvent-assisted flavor evaporation(SAFE),solid phase extraction(SPE),solvent extraction,headspace adsorption sampling,solid phase microextraction(SPME),quantitative description analysis(QDA),aroma extraction dilution analysis(AEDA),gas chromatography olfactometry(GCO),odor activity value(OAV),addition and omission test,aroma reconstitution,etc.The main research contents and achievements are summarized as follows:1)Comprehensive analysis of the aroma of six types of tea produced by the model processes revealed that the aroma molecules of tea mainly came from four precursor groups: glycosides,fatty acids,carotenoids,amino acids and carbohydrates.In the processing of green tea and yellow tea,the Maillard reaction played an important role.In black tea and oolong tea,the oxidation of fatty acids was the key to form their aroma,while in the processing of white tea and black tea,the hydrolysis of glycosides and the degradation of fatty acids resulted in the formation of their characteristic aroma.2)Using the concept of molecular sensory science,the corresponding key aromatic compounds were identified in four styles of Fujian white tea(Baihaoyinzhen,Baimudan,Gongmei and Shoumei).The most active compounds were determined by aroma extraction dilution analysis.Standard addition method was used to quantify the selected key odorants.Odor activity values(OAV)were obtained to assess the aroma contribution of the molecules.Aroma reconstitution was carried out using addition and omission tests.Finally,the key odorandts in the four styles of Fujian white tea were determined.3)In the light of comparative molecular sensory studies on the orchids-like aroma of selected premium tea leaves,of the origin of "orchid-like" aroma was determined to be the(Z)-methyl epijasmonate(epi-Me JA).Epi-Me JA is found in many oolong teas,while in other tea types,such as green and black teas,the reported levels of this compound are often too low to contribute significantly to the aroma of tea infusions.Methyl jasmonate is mainly produced in the process of tea withering.The biochemical processes and tea-making conditions of plants are conducive to the formation of their epi structure,while the thermodynamic equilibrium of stereoisomers is conducive to the formation of more stable non-epi structure.Therefore,high temperature and long-term storage in the tea making process are not conducive to the production of epi-MeJA.