做青工艺对乌龙茶香气组成化学模式的影响

在室内控温控湿环境(22±1)℃、RH(71±4)%]条件下,借助茶叶香气成分GC-MS指纹图谱检测和代谢组学数据分析平台,以清香型乌龙茶、闽南乌龙茶和闽北乌龙茶工艺制法在制品和毛茶为对照样,探讨了做青工艺萎凋程度（鲜叶减重率）×做青强度（摇青次数）]对做青叶在制品香气组成特征的影响。通过“云图”绘制和主成分分析结果表明,“晾青失水”可明显改变做青叶在制品香气组成的化学模式,伴随萎凋程度（鲜叶减重率）的加重,α-法呢烯、苯乙醛、香叶醇、3-己烯-1-醇和(Z)-己酸-3-己烯酯含量逐渐增多,而叶绿醇、吲哚、2,6-二叔丁基对甲酚和乙基苯等成分含量则呈减少趋势,但仅结合不同强度的“单次摇青”将无法促成乌龙茶特有香型品质。做青是形成乌龙茶特殊香型品质的关键工序,带有类似花果香型的吲哚、反式-橙花叔醇和苯乙醛等香气成分可作为乌龙茶做青工艺品质控制的主要化学评测指标。

Effects of Green-making Technique on Aroma Pattern of Oolong Tea

Under controlled indoor air conditions set at (22±1)℃ with relative humidity of (71±4)%, a two-factor experiment, including degree of withering and intensity of rocking, was designed to investigate the effects of green-making technique on aroma characteristics of WIP (work in process) as compared with tea samples prepared during the respective process of Fresh-scent Oolong tea, South Fujian Oolong tea, and North Fujian Oolong tea. Aroma fingerprints of all tea samples were determined by gas chromatography coupled with mass spectrometry and processed with metabolomics analysis platform. The results from cloud plot and principal component analysis indicated that aroma pattern of WIPs would be obviously altered according to weight loss percentage of green leaves, accompanied with the increase on the contents of α-farnesene, benzeneacetaldehyde, geraniol, 3-hexen-1-ol and cis-3-hexenyl hexanoate, and the contents of phytol, indole, butylated hydroxytoluene and ethylbenzene were be decreased accordingly. However, the aromas pertinent to Oolong tea would not be fully formed only combinating on single shaking action with different intensity. Green-making was the essential procedure to bring about special aroma quality of Oolong tea, and the contents of floral scent compositions in tea samples, such as indole, trans-nerolidol, phenylacetaldehyde, etc., could be considered as the most important chemical indicators for quality control, in the green-making process of Oolong tea.