The Study Of Flavor Characteristic Of Premium Keemun Black Tea

On the basis of the previous study of Keemun black tea,at first,the characteristic flavor of Keemun black tea,which contained Teming Keemun Gongfu black tea(the top grade),Teji Keemun Xiangluo(the top grade)and Teji Keemun Maofeng(the top grade)was studied by Human's sensory evaluation,electronic sensory evaluation and chemical analysis.Then,Keemun Gongfu black tea was chosen as the study subject,as its flavor showed the largest impact on the overall sensory quality.The characteristic flavor was compared between Teming Keemun Gongfu black tea and Erji Keemun Gongfu black tea(the fourth grade)by sensory analysis and chemical analysis.In addition,the predominant aroma-active compounds in Teming Keemun Gongfu black tea were qualified and quantified by liquid liquid continuous extraction(LLCE),solvent assisted flavor extraction(SAFE),solid phase micro extraction(SPME),aroma extraction dilution analysis(AEDA),stable isotope dilution analysis(SIDA),Gas Chromatography-Olfactometry(GC-O)with flavor dilution value(FD value)and odor activity value(OAV).The main results and conclusions are as follows:(1)The results of Human's sensory evaluation showed,there was no significant difference in infusion color,aroma,taste,leaves and total score between Teming Keemun Gongfu black tea,Teji Keemun Xiangluo and Teji Keemun Maofeng(p?0.05).Among the five factors,taste and aroma showed the highest correlation with the total score.Among the three samples,Teming Keemun Gongfu black tea showed the most significant correlation between taste and aroma and total score and had higher scores in taste and aroma attributes than the other two samples.The results of electronic sensory evaluation showed,electronic nose and electronic tongue can distinguish the three type samples of premium Keemun black tea.(2)There were significant differences in tea polyphenols,caffeine and free amino acids among Teming Keemun Gongfu black tea,Teji Keemun Xiangluo and Teji Keemun Maofeng(p<0.05).The three compounds had different correlation with taste attributes.By SPME and Gas Chromatography-Mass Spectrum(GC-MS),there were 29 common volatile compounds identified.Among the compounds,the concentration of methyl salicylate was the highest with the average concentration 369 ug/L.On the basis of volatile compounds,principal component analysis(PCA)distinguished the three samples and the loading plot reflected the relationship between volatiles and samples.(3)The results of Human's sensory evaluation showed the sensory quality of Teming Keemun Gongfu black tea was higher than that of Erji Keemun Gongfu black tea.The three samples of Teming Keemun Gongfu black tea showed no significant difference in total score,appearance,infusion color,aroma and taste(p?0.05).Their sensory quality showed the consistency.Their flavor also showed the significant positive correlation with total score.However,there was significant difference in total score,appearance,infusion color,aroma and taste(p<0.05).Their sensory quality did not show the consistency.The results of electronic sensory analysis showed,electronic nose and electronic tongue can distinguish Teming Keemun Gongfu black tea and Erji Keemun Gongfu black tea(4)There were more tea polyphenols,caffeine and free amino acids in Teming Keemun Gongfu black tea than Erji Keemun Gongfu black tea.In Teming Keemun Gongfu black tea,free amino acids showed significant positive correlation with the taste attribute "fresh and brisk".In Erji Keemun Gongfu black tea,tea polyphenols showed significant positive correlation with the taste attribute "astringent".Among Teming Keemun Gongfu black tea,there were 24 common volatile compounds.Among Erji Keemun Gongfu black tea,there were 25 common volatile compounds.There were 17 common volatile compounds among Teming and Erji Keemun Gongfu black tea.(5)63 aroma-active compounds were identified by RI,standard,MS and odor.Among the 63 compounds,32 aroma-active compounds were positively identified and 26 compounds were tentatively identified.There were 37 common aroma-active compounds among the three samples of Teming Keemun Gongfu black tea.They were the representative aroma-active compounds of premium Keemun Gongfu black tea.By AEDA,the FD factors of aroma-active compounds were determined and 29 aroma-active compounds were determined as predominant odrants in LLCE extraction.(6)The exact concentrations of predominant odorants were determined by SIDA and the isotope labeled internal standard combined with the Scan mode and SIM mode of MS analysis.The concentrations of all the predominant odorants were from 0.25 ng/mL to 4643 ng/mL.On the basis of exact quantification,the OAVs were calculated and the predominant odorants were determined.The compounds,which contributed to the characteristic aroma of Keemun Gongfu black tea,were ?-ionone,phenylacetaldehyde,geraniol,linalool,coumarin,(E)-?-damascenone and vanillin.In addition,?-ionone contributed floral arma,fruity aroma and sweet aroma.Geraniol contributed floral aroma and fruity aroma.