Effects of different withering times on the biosynthesis of carotenoids and their derived volatiles in post-harvest tea leaves

Abstract Carotenoids are important fat-soluble pigments in tea plants, influencing leaf color and acting as precursors of aromatic compounds. Withering, a key initial step in tea processing, triggers various metabolic changes. However, variations in carotenoids and their derived volatiles (CDVs) during the withering stage remain insufficiently studied. In this work, six major carotenoids, abscisic acid (ABA), chlorophylls, and CDVs, were profiled by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS), and the expression of key biosynthetic genes was evaluated via transcriptome and quantitative real-time polymerase chain reaction (RT-qPCR) analysis. The results revealed that total carotenoid content declined overall during withering, while individual carotenoid levels changed dynamically—decreasing initially, peaking at 9 h, and then varying again. Ten CDVs, primarily alcohols, were detected, showing an initial decrease followed by an increase at 12 h. Expression of carotenoid biosynthetic genes (CsLCYb, CsLCYe, CsBCH, CsZEP, and CsVDE) and degradation genes (CsCCD1 and CsCCD4) was significantly altered and correlated with metabolite profiles. Genes related to ABA, chlorophylls, and gibberellin (GA) biosynthesis also exhibited withering-responsive expression patterns. This study systematically describes alterations in carotenoid metabolism during withering—covering precursors, gene expression, and end products—offering a theoretical basis for optimizing withering duration to improve tea quality.