Multiomics correlation analysis on the mechanism of flavor substance formation during the processing of "Huanong 53" black tea

A comprehensive investigation was conducted using targeted metabolomics, transcriptomics, and GC-MS techniques to study the dynamic changes in volatile and non-volatile metabolites, as well as gene transcription levels, in five processing stages of 'Huanong 53 ' black tea ( Camellia sinensis). A total of 2062 metabolites were identified, with flavonoids (428) and amino acids and their derivatives (194) being the main categories. The types and contents of flavor characteristic components of black tea changed most significantly during the withering and fermentation stages. Key elements of tea aroma composition, including linalool, benzeneacetaldehyde, and geraniol were found to correspond significantly with specific transcripts annotated as linalool synthase, aromatic aminotransferase, and geraniol diphosphate synthase, respectively. Throughout processing, a decrease in catechins and concomitant increase in oxidized catechin dimers, such as theaflavin (TF), was positively correlated with down-regulated flavonoid pathway gene expression and up-regulated expression of putative TF biosynthetic genes, including laccases, polyphenol oxidase, and a wide range of peroxidases. This study provides a comprehensive perspective on the changes in metabolites during black tea processing, and contributes to the research on improving black tea quality and the suitability of tea varieties for processing.