Guangdong Provincial Key Laboratory of Tea Plant Resources Innovation & Utilization, Tea Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China.
Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China.
Food Res Int. 2018 Jun;108:413-422. doi: 10.1016/j.foodres.2018.03.052. Epub 2018 Mar 19.
Oolong tea is a typical semi-fermented tea and is famous for its unique aroma. The aim of this study was to compare the volatile compounds during manufacturing process to reveal the formation of aroma. In this paper, a method was developed based on head-space solid phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) combined with chemometrics to assess volatile profiles during manufacturing process (fresh leaves, sun-withered leaves, rocked leaves and leaves after de-enzyming). A total of 24 aroma compounds showing significant differences during manufacturing process were identified. Subsequently, according to these aroma compounds, principal component analysis and hierarchical cluster analysis showed that the four samples were clearly distinguished from each other, which suggested that the 24 identified volatile compounds can represent the changes of volatile compounds during the four steps. Additionally, sun-withering, rocking and de-enzyming can influence the variations of volatile compounds in different degree, and we found the changes of volatile compounds in withering step were less than other two manufacturing process, indicating that the characteristic volatile compounds of oolong tea might be mainly formed in rocking stage by biological reactions and de-enzyming stage through thermal chemical transformations rather than withering stage. This study suggested that HS-SPME/GC-MS combined with chemometrics methods is accurate, sensitive, fast and ideal for rapid routine analysis of the aroma compounds changes in oolong teas during manufacturing processing.
乌龙茶是一种典型的半发酵茶，以其独特的香气而闻名。本研究旨在比较加工过程中的挥发性化合物，以揭示香气的形成。本文采用顶空固相微萃取/气相色谱-质谱联用（HS-SPME/GC-MS）结合化学计量学的方法，评估了加工过程中（鲜叶、萎凋叶、摇青叶和酶解叶）的挥发性成分。共鉴定出 24 种在加工过程中表现出显著差异的香气化合物。随后，根据这些香气化合物，主成分分析和层次聚类分析表明，这四个样本彼此之间明显区分开来，这表明这 24 种鉴定出的挥发性化合物可以代表四个步骤中挥发性化合物的变化。此外，萎凋、摇青和酶解都会不同程度地影响挥发性化合物的变化，我们发现萎凋过程中挥发性化合物的变化小于其他两个加工过程，这表明乌龙茶的特征挥发性化合物可能主要是在摇青阶段通过生物反应形成的，在酶解阶段通过热化学反应形成的，而不是在萎凋阶段形成的。本研究表明，HS-SPME/GC-MS 结合化学计量学方法是准确、灵敏、快速的，是乌龙茶加工过程中快速常规分析香气化合物变化的理想方法。
