Cold acclimation reprograms the flavor metabolome of fresh tea leaves to enhance sensory quality: Insights from metabolomics, GC-O, and transcriptomics.

The enhanced sensory quality of early spring tea is empirically associated with pre-harvest cold exposure, yet the chemical and mechanistic basis for this enhancement requires further clarification. In this study, we investigated the metabolic changes in tea leaves under cold acclimation (4/0 °C) compared to mild cooling (15/11 °C) using metabolomics, HS-SPME/GC × GC-Q-TOF-MS, gas chromatography-olfactometry (GC-O), and transcriptomic analyses. Results indicated that cold acclimation induced the accumulation of key non-volatile tastants, notably soluble sugars and γ-aminobutyric acid (GABA), driven by the activation of starch hydrolysis and polyamine degradation pathways. This provides the material basis for the sweetness and umami attributes of the tea infusion. Concurrently, volatilomic and GC-O analyses confirmed a shift in the aroma profile. The odor activity values (OAVs) and perceived sensory intensities of specific floral and sweet compounds, including trans-β-ionone, linalool, and (Z)-jasmone, were increased. This aroma development was closely linked to the accumulation of lipid precursors, the activation of jasmonic acid (JA) biosynthesis, and the subsequent upregulation of terpene synthases. Transcriptomic analysis and subsequent molecular validation verified that these carbon, nitrogen, and lipid fluxes are coordinated by transcriptional modules (e.g., CsERF21-CsAMY2), alongside a feedback loop that fine-tunes the signaling response. These findings demonstrate that cold acclimation acts as a natural pre-conditioning step that reprograms the raw leaf matrix, optimizing the chemical precursors essential for tea flavor. Ultimately, these metabolic markers and gene modules offer valuable targets for breeding high-quality tea cultivars and optimizing pre-harvest agricultural practices.