Quality Analysis And Control Of Congou Black Tea Based On Sensomics

Tea flavor,which is an important part of tea quality,is very difficult to accurately measure but has been rated as the strongest determinant of comsumer acceptability.Actually,consumers tend to prefer some particular flavor of beverage and expect the character is consistent.However,it is very difficult to maintain the sensory quality of tea stable and consistent,due to natural conditions such as climate and soil,as well as tea varieties,harvesting season,processing methods and so on.Therefore,this doctoral thesis focused on the sensory quality and flavor chemical components of Congou black tea,trying to systematically represent the flavor characteristics and its chemical basis,and identify the key compounds that cause differences in sensory quality by means of multivariate statistical analysis and data mining.Moreover,this strategy was applied to control the sensory quality of Chuanhong Congou black tea.The main findings were as follows:1.The aroma of Chinese Congou black tea were clustered into 5 groups by sensory analysis.The first group,without a potent aroma attribute nor “oil and spicy” aroma,had moderate “sweet”,“floral”,“fruity”,and “roasted” odors.The second group,with a typicality of “sweet and fruity” notes,also was rich in “floral and green” aromas.The third group was strong in “floral”,“fruity”,and “green” aromas,while weak in “sweet and roasted” aromas.The fourth group had strong “off-odor and spicy” aromas,despite other moderate attributes.The fifth had a strong “roasted” aroma,whereas the other attributes were weak.The sweet and fruity aromas were extremely significantly positively correlated with the overall quality of the aroma,while the floral aroma was significantly positively correlated.Green,oil and off-odor were extremely significantly negatively correlated with the overall quality of the aroma,and spicy also had a negative impact.Sweet was positively correlated with floral and fruity,but significantly negatively correlated with spicy.Floral was positively correlated with green,but negatively correlated with roasted,spicy,oil and off-odor.There was an extremely significant negative correlation between with roasted and green,and a significant positive correlation between oily and off-odor.The interaction between the taste attributes was significantly stronger than the aroma attributes,and the penalist were not sensitive to the changes of taste attributes.2.The taste of Chinese Congou black tea were also clustered into 5 groups by sensory analysis,namely sweet-mellow type,sweet-umami type,sweet-slightly acidic type,heavy-strong type,gone-off and tainted type.There was a significant positive correlation between sweetness and the overall quality of the taste,and bitterness was significantly negatively correlated.Sourness,astringent and abnormal taste were negatively correlated with taste quality,while umami,thick,and sweet after taste were positively correlated with it,but the correlation coefficient did not reach the significant level.There were significant positive correlations among the attributes of bitterness,astringent and sourness,and significant negative correlation between sweetness and bitterness,astringency and sourness.Umami was significantly negatively correlated with sourness,but significantly positively correlated with sweetness and sweet after taste.Abnormal taste was extremely significantly negatively correlated with sweetness,and significantly negatively correlated with umami.3.136 volatile compounds were identified by headspace solid-phase micro extraction/gas chromatography–mass spectrometry(SPME/GC-MS),among which 12 compounds were presented in all samples: benzaldehyde,benzyl alcohol,phenylacetaldehyde,linalool,(Z)-pyran linalool oxide,phenylethyl alcohol,methyl salicylate,nerolidol,hotrienol,geraniol,(E)-5,6-epoxy-?-ionone,and methyl hexadecanoate.By application of GC-O,linalool,(E)-furan linalool oxide,(Z)-pyran linalool oxide,phenylethyl alcohol,?-myrcene,and methyl salicylate were present in five representative samples,implying their essential role in the formation of basic Congou black tea aroma.The results of multivariate statistical analysis showed that 55 compounds were determined as the key factors for the six sensory attributes.4-Hydroxy-2,5-dimethyl-3(2H)-furanone had a significant influence on the “sweet” aroma,followed by(E)-2-hexenal,dodecanal,?-myrcene,?-farnesene,and nerolidol,and 1-octen-3-ol had the highest negative coefficient.Phenethyl butyrate,(Z)-3-hexen-1-yl benzoate,jasmine lactone,phenylacetaldehyde,(E)-citral,and(E)-2-hexenal had significant positive correlation with floral,while ?-Butyrolactone,(E,E)-2,4-hexadienal,and dihydroactinidiolide had negative effect.Dodecanal and nerylacetone were the most positively influential factors of the “fruity” aroma,whereas the negative influential factors were phenethyl butyrate and ?-octalactone.The intensity of the “roasted” aroma was mainly determined by the contents of 2-acetylfuran,2,5-dimethylpyrazine,and 4-hydroxy-2,5-dimethyl-3(2H)-furanone;1-octen-3-ol was the most negative influential factor.?-Terpineol and methyl jasmonate were the most positive influential factors,whereas tetradecanal and geranylacetone could reduce the intensity of the “spicy” aroma.Methyl jasmonate had the most positive effect on the intensity of the “green” aroma,followed by nerylacetone.By contrast,?-butyrolactone,(E,E)-2,4-hexadienal,2-acetylfuran,and ?-damascenone were negatively correlated with it.4.Among the 48 taste components which detected in Congou black tea samples,quercetin-3-O-rutinoside,kaempferol-3-O-rutinoside,kaempferol-3-O-glucoside,theaflavin,theaflavin-3-gallate,theaflavin-3'-gallate,theaflavin-3,3'-digallate,oxalic acid,L-malic acid and aspartic acid were the main taste active ingredients.For astringency,quercetin-3-O-rutinoside had the highest TAV(taste activity value),followed by kaempferol-3-O-rutinoside,theaflavin-3,3'-bisgallate,kaempferol-3-O-glucoside and theaflavin-3'-gallate.Caffeine,gallocatechin gallate(GCG)and epicatechin gallate(ECG)were the major bitter contributors.L-malic acid,oxalic acid and aspartic acid,whose TAV were greater than 1 in all samples,were the main sour ingredients of Congou black tea,followed by gallic acid and succinic acid.Aspartic acid,glutamic acid,asparagine and cysteine were major umami contributors.5.Chuanhong Congou black tea,in which the relative content of geraniol was the highest,followed by phenethyl alcohol,methyl salicylate,linalool and citronellol,had a unique sweet rose aroma.A total of 26 compounds were identified as odor-active components by GC-O procedure,linalool oxides,linalool,phenethyl alcohol,and phenylacetaldehyde had the highest aroma intensity.The calculation of the odor activity value(OAV value)showed that ?-ionone had the highest OAV value,followed by 2-methylbutanal,linalool,phenylacetaldehyde,citronellol and geraniol.Comparing the identification results of GC-O and OAV values,we believed that human perception of aroma was more sensitive than instrumentation,and sensory evaluation was more direct,flexible and more "authentic" in tea quality control.6.In the application of fingerprint technology to aroma quality control,it was found that the result of full spectrum analysis was more similar to sensory evaluation.Key variables in aroma quality control were selected by partial least squares regression-variable importance in projection(PLSR-VIP),they were:(Z)-3-hexenal,heptaldehyde,benzaldehyde,(E)-linalool oxide(furanoid),(Z)-rose oxide,(Z)-5-methyl-2-(1-methylethyl)-cyclohexanone,benzyl acetate,furfural,?-cyclocitral,nerol,citronellol,(Z)-3,7-dimethylocta-2,6-dienal,cis-3-hexen-1-yl valerate,1-hexadecene,(E)-3,7-dimethylocta-2,6-dienal,amyl hexanoate,?-ionone,ethyl nonanoate and citronellyl acetate.The results of canonical correspondence analysis(CCA)analysis showed that the content of(E)-linalol oxide(furanoid)and ?-ionone largely determined the two groups of blending samples.One group were rich in “sweet and floral” aromas,and the other were present floral fragrance.The results of sensory evaluation were far from the key aroma components,it indicated that the ranking results of sensory quality were affected by the content of key aroma components,and also affected by various factors such as evaluation environment and methods.The strategy and standard methods of tea quality control need further study.