Studies On The Characteristic Aroma Components Of Qimen Black Tea

Qimen ( also known as Keemun) black tea is one of traditional Chinese congou black tea, mainly produced in Qimen county of Anhui province, and its adjacent counties as Dongzhi, Guichi, Shitai,Yixian and Fuliang county of Jiangxi province. Qimen black tea enjoys high reputation for its fresh and lasting fragrance, flowery and fruity honey-like aroma, which is highly honored as "Keemun aroma". Qimen black tea, as well as Darjeeling black tea ( India) and Uva black tea (Sri Lanka) are recognized as the top three of high aroma black tea in the world.In this paper, the aroma components of the samples, which include different grades of Qimen black tea, Qimen black tea from different producing areas and several congou black tea from Guangdong, Guangxi and Guizhou, as well as the samples from each process of the manufacturing of orthodox Qimen black tea, were extracted with simultaneous distillation extraction (SDE) method and analyzed by gas chromatography-mass spectroscopy (GC/MS). The collected data were applied to the statistical analysis with principal components to assess and rank the aroma quality of Qimen black tea. The major results of this paper were as following.1. The changes of aroma constituents of Qimen black tea during processing. The samples from each process of the manufacturing of Qimen black tea were collected and were applied to the analysis of aromatic constituents with SDE and GC/MS. The results showed that seven groups of aroma components were identified, which included alcohols, aldehydes, ketones, esters, acids, saturated hydrocarbons and unsaturated hydrocarbons. Among them, the main constituents were alcohols, aldehydes and acids. The alcohols and aldehydes increased distinctively in the rolling process, while the ketones and hydrocarbons had no significant changes during the whole processing.2. The characteristic aroma components of the different grades of Qimen black tea. The aroma components in 7 samples of Qimen black tea with different grades were extracted by SDE, separated and identified by GC/MS, respectively. Based on the method of principal component analysis (PCA), the main components in Qimen black tea for assessing and ranking the aroma quality were trans-geraniol , linalool and its oxides, cis-3-hexene-1-ol, phenylethyl alcohol,benzyl alcohol,E-2-hexen-1-ol, benzeneacetaldehyde,nonanal,cis-jasmone,phytol,n-hexanol,heptanal,E-citral,(E,E)-farnesylacetone, 6,10,14-trimethyl-2-pentadecanone, methyl linoleate, methyl linolenate, benzyl salicylate etc. 3. The characteristic aroma components of Qimen black teas from different producing areas. The total fragrant oils in samples produced at Dongzhi, Guichi and Shitai which are geographically adjacent to Qimen, were extracted by SDE, and 70 kinds of aroma components were separated and identified by GC/MS. Based on PCA method, the main aroma components of Qimen black tea in above three counties were identified, which included trans-geraniol, linalool and its oxides, cis-3-hexene-1-ol, phenylethyl alcohol, benzyl alcohol, E-2-hexen-1-ol, benzeneacetaldehyde, nonanal, cis-jasmone, isophytol,geranyl linalool isomer B,β-cyclocitral,α-ionone, cis-3-hexenyl benzoate, neophytadiene, pentadecane , 2,6,10,14-tetramethyl.4. The characteristic aroma components of congou black tea from Guangdong, Guangxi and Guizhou provinces. The total fragrant oils in samples produced at Guangdong, Guangxi and Guizhou provinces were extracted by SDE, and 64 kinds of aroma components were separated and identified by GC/MS. Based on PCA method, the main aroma components of black tea in above three provinces were identified, which were composed of trans-geraniol ,linalool and its oxides, cis-3-hexene-1-ol,nonanal,isophytol,pentadecanal,heptanal,beta.-Sinensal,6,10,14-trimethyl-2-pentadecanone,trans-.beta.-ionone,methyl salicylate,decane, neophytadiene, pentadecane, pentadecane ,2,6,10,14-tetramethyl.5. Modeling of aroma quality evaluation on Qimen black tea with principal component analysis. The total fragant oil in 10 different kinds of Qimen black tea were extracted by SDE and further identified and quantified by GC/MS method. Based on PCA method, a model was established for assessing and ranking the aroma quality of Qimen black tea, which was further validated with traditional sensory evaluation. With treatment the variance contribution rate of different eigenvalueβi (i = 1,2, ... ..., k) as the weighted coefficient, integrated evaluation function F =β₁F₁ +β₂F₂ + ... ... +β_kF_k had been established which was used to calculate the sample score. Further, the aroma quality of tea samples were sorted and evaluated. The results indicate that the model is acceptable and available.