乌龙茶品种鲜叶加工白茶过程中香气成分动态变化规律

乌龙茶品种茶树鲜叶加工白茶具有明显的花香特征。为探明该原料在白茶加工过程中香气成分的形成与变化规律,在室内控温控湿（温度18~22℃,湿度45%~60%）环境条件下,选用福鼎大毫茶、福安大白茶和福云6号制成的传统白茶为对照,采用顶空固相微萃取法-气质联用法对茗科1号等10个适制乌龙茶品种鲜叶的萎凋在制品及其成品茶（简称花香白茶）进行了香气成分检测和化学计量分析。结果表明,花香白茶与传统白茶存在迥然不同的香气组成化学模式。各乌龙茶品种鲜叶加工的花香白茶及其在制品的香气组成化学模式具有较高相似度;随着鲜叶萎凋减重率的增加,其香气组成在主成分分析二维得分视图中的模式分布渐趋离散,并发生群体定向逐步偏移。聚类分析结果显示,花香白茶在加工过程中香气组成的动态变化与采制原料的品种特性密切相关。鲜叶萎凋减重率30%~60%为影响花香白茶香气品质形成的关键发展阶段,并以萎凋后期（减重率≥45%）对其在制品香气组成的影响最为突出。从乌龙茶品种试样中可检出的136种香气成分显著富集于3种变化趋势模型,其中芳樟醇及其氧化物、香叶醇、橙花醛、水杨酸甲酯、β-紫罗酮、二氢猕猴桃内酯等香气成分可视为花香白茶香气品质工艺耦合调控的主要化学评测指标。

Aroma Profiling of Fresh Leaves of Oolong Tea Cultivars during White Tea Processing

White teas processed from fresh leaves of oolong tea cultivars can be always detected with flower flavor characteristics. In order to investigate the formation and changes of aroma components during the manufacture of such fragrant white tea, fresh leaves harvested from 10 oolong tea cultivars including Mingke1 were respectively processed into white teas under controlled indoor air conditions set at 18-22℃ and humidity of 45%-60%. Compared with traditional white teas produced from Fudingdahao-cha, Fuandabai-cha and Fuyun 6, the aroma components of white teas and the WIP (work in process) samples prepared according to the weight loss rate of fresh leaves from oolong tea cultivars were isolated by head space solids-phase micro-extraction (HS-SPME) and determined by gas chromatography-mass spectrometry (GC-MS) in combination with stoichiometric analysis. The results show that there were very different chemical patterns of aroma components between fragrant white teas and traditional white teas. The aroma patterns of white teas and in-process products obtained from oolong tea cultivars were of high similarity. With the increase of the weight loss rate of fresh leaves, the distribution of these tea samples in the two-dimensional score plot obtained from principal component analysis tended to disperse gradually, resulting in oriented migration as a group. It could be seen that the dynamic changes of aroma components during the processing of fragrant white tea were also closely related to the properties of the raw materials from each tea cultivars by cluster analysis. From 30% to 60% of the weight loss rate was the key development stage affecting the formation of aroma quality of fragrant white tea, especially for the weight loss rate≥45%. The 136 aroma components detected in tea samples from oolong tea cultivars were significantly enriched in three changing trend models, including linalool and its oxide, geraniol, geranial, methyl salicylate, β-ionone and dihydroactinidiolide and some other volatile components with pleasant flavor, which can be regarded as the most important chemical indicators for the coupling process to regulate aroma quality of fragrant white tea.