Characterization of the Key Aroma Compounds in Dong Ding Oolong Tea by Application of the Sensomics Approach

The Dong Ding oolong tea (DDT), grown and produced in Taiwan, is widely appreciated for its unique flavor. Despite its popularity, research on the aroma components of DDT remains incomplete. To address this gap, this study employed a sensomics approach to comprehensively characterize the key aroma compounds in DDT. Firstly, sensory evaluation showed that DDT had a prominent caramel aroma. Subsequent analysis using gas chromatography-olfactory mass spectrometry (GC-O-MS) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS) identified a total of 23 aroma-active compounds in DDT. Notably, three pyrazine compounds with roasted notes, namely 2-ethyl-5-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, and 2,3-diethyl-5-methylpyrazine, along with seven floral- and fruit-smelling compounds, namely 6-methyl-5-hepten-2-one, 3,5-octadien-2-one, linalool, (E)-linalool oxide, geraniol, (Z)-jasmone, and (E)-nerolidol, were identified as the key aroma compounds of DDT. Omission experiments further validated the significant contribution of the three pyrazines to the caramel aroma of DDT. Moreover, the content of 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, (Z)-jasmone, 6-methyl-5-hepten-2-one and 2-ethyl-5-methylpyrazine was found to be higher in the high-grade samples, while (E)-nerolidol, linalool, geraniol and 3,5-octadien-2-one were found to be more abundant in the medium-grade samples. These findings provide valuable information for a better understanding of the flavor attributes of DDT.