| Zhangping shuixian tea is the only one kind of compressed tea among Oolong teas,which compressed into quadrate tea cake by wood model,and it combined with Minbei shuixian and Minnan Tieguanyin,s processing.The quality characteristics of Zhangping shuixian tea mainly due to its special ZuoQing technology,this process is important for illustrating its quality formation mechanism in processing.Furthermore,figure it out would improve the processing technology of Zhangping shuixian tea,it will provide a theoretical basis not only for the use of potential aroma source,but also for the improvement of aroma quality in the future.This essay was studied on the dynamic variation of glycosidic aroma substance during the process of making Zhangping shuixian tea and the impact in aroma formation in the zuoqing section.Based on sensory evaluation,the aromatic components of Zhangping shuixian teas from four regions,including Wuxi village,Nanyang village,Beiliao village and Zhongcun village,were detected by gas chromatography mass spectrometry,proton transfer reaction time of flight mass spectrometer and electronic nose.The data were analyzed by chemometrics and the results were as follows:(1)The mainly six kinds of glycosidic aromatic precursors in Zhangping shuixian tea were identified,they were leaf alcohol,linalool,methyl salicylate,geraniol,benzyl alcohol and phenylethyl alcohol.Glycosidic aromatic precursors of Zhangping shuixian tea were extracted by using a series of methods,boiling ethanol firstly,and then aromatic substanees were released through bipolar enzymatic hydrolysis and finally were identified according to the standard mass spectrometry library retrieval and mass spectrum and retention time compared with standard sample.Glycosidic aroma precursors of tea samples which were collected from 12 processes among the whole process of making Zhangping shuixina tea were deternined and the results showed that,though there were same kinds of glyscosidie aroma precursors between Spring tea and Autumn tea in each process of making tea,the content of each component were different from each other and the total content of glyscosidic aroma precursors in Autumn tea was higher than the Spring one obviously.The amount of glycosidic aroma precursors in withering leaves had increased significantly after the fresh leaves withered,among them,the content of leaf alcohol,geraniol and benzyl alcohol in withering process increased obviously,however the increase extent of linalool,methyl salicylate and phenylethyl alcohol were smaller.Glycosidic aroma precursors were significantly increased in cooling leaves compared with the fresh leaves,the content of glycosidic aroma precursors changed because of rotating process.In the whole process of rotating,the amount of glycosidic aroma precursors decreased compared with withering leaves,and that change were ups and downs in different rotating,the amount of glycosidic aroma precursors decreased in the first and second rotating,though it increased in the third rotating,it decreased again in the fourth rotating.Those results indicated that dynamic balance of glycoside synthesis and the enzymatic hydrolysis existed in the process of rotating leaves.(2)61,56,67 and 54 kinds of aromatic components were contained in different Zhangping shuixian teas samples which were made in the Wuxi village,Nanyang village,Beiliao village and Zhong village respectively were all detected by using SPME-GC-MS method,those aromatic components mainly could be classified alcohols,aldehydes,esters,ketones,alkene,hydrocarbon compounds.All samples of Zhangping shuixian teas could be roughly divided into four classes according to cluster analysis.Most samples in each class were from the same place and only a small number of samples from other places.The results showed that the four places'Zhangping shuixian teas achieved the better clustering and different aroma characteristics significantly in different region were further illustrated and a certain similarity among different regions' teas existed at the same time.(3)Zhangping Shuixian tea samples' aroma were detected and analyzed by electronic nose technology.S7,S8 sensor showed relatively strong response to Zhangping Shuixian tea aroma volatiles among the sensor S1-S10,while the other sensor is relatively weak.Discriminant function of four places' Zhangping Shuixian tea,which was established by combining characteristic values of the 10 electronic nose sensors and marching type,could be used to judge four places' Zhangping Shuixian tea effectively because of the total initial total judgment rate and cross validation of the overall positive judgment rate were 88.9%and 83.3%respectively.Electronic nose sensor's characteristic value data which were response to tea samples of different tea regions were analyzed through dimension reduction since those sensors were too many.Then 91.25%of the original variable information could be explained by the three common factors which were extracted from factor analysis.The results of the sensory evaluation and the electronic nose sensory testing were basically the same by comparing the score of sensory evaluation and integration of electronic nose's response characteristic value.On the other hand,it is hard to evaluate the two similar quality tea aroma due to the constraints of traditional sensory evaluation itself,while the delicate difference could be detected according to the total score by electronic nose.(4)Zhangping Shuixian tea aroma were detected by PTR-MS and their places were analyzed by discriminant analysis and the results were showed as follows:The positive judgment rate were all 100.0%in Wuxi Village,Nanyang village and Zhong village's Zhangping Shuixian tea during initial determination;Beiliao village Zhangping Shuixian tea's positive judgment rate was 88.9%,only one sample was judge incorrectly,one was judged mistakenly as Nanyang village and its initial total determination rate was 97.2%.Cross validation results showed that the positive judgment rate of Zhangping Shuixian tea in Wuxi Village and Zhong Village were both 100.0%,while in Nanyang village was 88.9%,in Beiliao Village was 66.7%.The total cross validation positive judgment was 88.9%.In conclusion,Zhangping Shuixian tea samples in what regions could be judged accurate relatively by using PTR-MS technology. |
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