Potentially Important Aroma Compounds in Dark Tea and Volatile Compound Changes During Primary Pile Fermentation: A Systematic Review and Meta-Analysis

Pile fermentation is essential to the characteristic aroma of dark tea, yet studies have reported inconsistent changes in individual volatile compounds, leaving unclear which compounds change consistently and retain potential odor relevance after fermentation. We systematically searched six English- and Chinese-language databases and included 11 studies of primary solid-state pile fermentation of dark tea. Within-study relative concentration percentiles and odor activity values (OAVs) were used to characterize post-fermentation relative abundance and potential odor contribution. Random-effects meta-analysis was applied to comparisons quantifiable both before and after fermentation, whereas detection-state transitions were summarized separately for zero and non-detect data. Eighteen compounds met the prespecified criterion for potentially important aroma compounds. After Benjamini-Hochberg false-discovery-rate correction, 10 compounds increased significantly and one decreased significantly. Detection-state evidence further showed that methoxy-substituted aromatic compounds predominantly changed from non-detectable or non-quantifiable before fermentation to quantifiable after fermentation. Integrating the three evidence streams identified alpha-ionone, terpinen-4-ol, (E)-2-octenal, 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, and 1,2,4-trimethoxybenzene as fermentation-enriched potentially important aroma compounds, whereas linalool was fermentation-depleted but retained potential odor relevance after fermentation. This cross-study synthesis identifies compound-level patterns shared across dark-tea pile-fermentation systems and provides prioritized candidates for targeted quantification and sensory validation.