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In this study, the contents of (Z)-3-hexenal and (E)-2-hexenal during oolong tea processing were measured and four (3Z):(2E)-hexenal isomerase (HI) genes were selected based on transcriptomic data. Meanwhile, the correlation between the changes of (Z)-3-hexenal and (E)-2-hexenal contents and related gene expression was analyzed. The results indicated that during oolong tea processing, one of the two compounds fell, while the other rose. Mechanical damage caused by tossing increased and reduced the contents of (Z)-3-hexenal and (E)-2-hexenal, respectively. Subsequent spreading contributed to the transformation of (Z)-3-hexenal into (E)-2-hexenal, resulting in an increase in the content of (E)-2-hexenal. The four selected genes all responded to mechanical stress and water deficit stress. The constructed phylogenetic tree indicated that CsHI was closely related to many germin-like proteins in plants such as tea (Camellia sinensis) and carrot (Daucus carota). This study provides a reference for clarifying the formation and transformation mechanism of volatile substances during oolong tea processing and improving the quality of oolong tea.

Digital PCR is an emerging analysis technology for absolute quantification after realtime-PCR. Through digital PCR, single DNA molecules are distributed into isolated reactions, and the product with fluorescence signal can be detected and analyzed after amplification. With the advantages of higher sensitivity and accuracy, digital PCR, independent of a standard curve, is developing rapidly and applied widely to the next generation sequencing and detection fields, such as gene mutation, copy number variation, microorganism, and genetically modified food. In this article, we reviewed the quantitative method and research progress of digital PCR technology in the main application fields.