Application Of Extrinsic Enzymes To Improve Aroma Quality Of Anxi Tieguanyin

Anxi Tieguanyin is one of the top ten famous tea types of China which is produced inAnxi, Fujian. Spring Tieguanyin has the best overall quality. Autumn Tieguanyin hasstrong aroma but less complex taste. Summer Tieguanyin is considered lower qualitycompared with those produced during autumn and spring. However, the production is morethan a third of the yearly capacity.In order to improve the quality of summer Tieguanyin, different enzymes wereemployed in the processing of Anxi Tieguanyin. The quality of the tea samples werecompared by sensory evaluation and the volatile constituents were investigated by gaschromatograph/mass spectrometer (GC-MS). The suitable parameter of combined-enzymeapplying to summer tea was discussed. The aroma components of Anxi Tieguanyinplucked in different seasons were extracted with SDE method and analyzed by GC-MS.The characteristic aroma components were identified by principal components analysis. Onthis basis, a model was established for assessing and ranking the aroma quality of AnxiTieguanyin.The main results of this paper were as follows:1. Effects of enzymatic treatment after rocking of green leaf on sensory quality andaroma constituents of Anxi Tieguanyin harvested in June to July were investigated.Protease, cellulase, β-glucosidase and laccase were added to the tea samples separatelyafter rocking of green leaf. Sensory evaluation showed that the laccase significantlyenhanced the sensory quality of tea; β-glucosidase improved the aroma, whereas proteaseand cellulase had no obvious improvement on the quality of tea. The aroma constituents oftea were investigated by gas chromatograph/mass spectrometer. The results showed thatβ-glucosidase treatment and laccase significantly enhanced the aromatic constituents,whereas nearly all constituents of the sample treated by cellulase decreased markedly.2. Effects of enzymatic treatment before first firing on sensory quality and aromaconstituents of Anxi Tieguanyin harvested in June to July were investigated. Polyphenoloxidase, cellulase, β-glucosidase, laccase, α-galactosidase and combined-enzyme wereadded to the tea samples separately before first firing. Sensory evaluation showed that thearoma and taste quality of the tea samples treated by polyphenol oxidase and cellulasewere worse than the control sample. β-Glucosidase improved the aroma, but had noobvious improvement on the taste of tea. Both laccase and α-galactosidase improved thearoma and taste quality of summer tea. The tea sample treated by the combined-enzyme with the concentration (0.1g laccase+0.1g α-galactosidase)/L had similar sensory qualityas the early autumn tea, which had flowery smell and tasted mellow and thick.3. Effects of enzymatic treatment before first firing on aroma quality of AnxiTieguanyin harvested in August were investigated. In order to improve the quality of AnxiTieguanyin harvested in August, laccase, α-galactosidase and combined-enzyme wereadded to the tea samples separately before first firing. The quality of the tea samples werecompared by sensory evaluation and the volatile constituents were investigated by GC-MS.The results showed that the relative level of the total aroma oil in the tea samples treatedby enzymes were more than the control sample. α-Galactosidase greatly improved thecontents of aldehydes and alcohols. Laccase greatly improved the contents of esters. Bothof the two enzymes significantly increased the contents of alkenes. Nerolidol, indole andfarnesene were found to be the most important odor-active compounds in Tieguanyin. Therelative contents of the three compounds were all increased in tea samples treated bydifferent enzymes. The sensory evaluation showed that the grassy smell of tea reduced andthe flowery smell appeared by combined-enzyme treatment. The results indicated thatenzymatic treatment improved the aroma quality of Anxi Tieguanyin harvested in August.4. The characteristic aroma components of Anxi Tieguanyin were identified and anaroma quality evaluation model of Anxi Tieguanyin was established based on principalcomponent analysis.74kinds of volatile compounds were extracted and separated from8samples of Anxi Tieguanyin plucked in different plucking seasons. Based on the method ofprincipal component analysis(PCA), the main characteristic aroma components in AnxiTieguanyin were identified as nerolidol, farnesene, indole, phenylethyl alcohol,(E)-2-hexenal, nonanal, benzeneacetaldehyde, methyl linoleate, methyl linolenate, methylpalmitate,(Z)-3-hexenyl hexanoate,3-hexen-1-ol benzoate, octanoic acid,2-phenylethylester, δ-nonalactone, cis-jasmone, farnesyl acetone, palmitic acid, geranyl linalool isomer.An evaluation model was established based on PCA method for assessing and ranking thearoma quality of Anxi Tieguanyin. The aroma quality of tea samples was evaluated by themodel. The evaluation result was tested by sensory evaluation and the two results wereconsistent, which indicated that the model was reasonable and available to evaluate thearoma quality of Anxi Tieguanyin.