Abstract: Objective: This study aims to elucidate the effect of varietal differences in selenium (Se) enrichment levels on the volatile metabolite profile of oolong tea and to explore the potential metabolic pathways through which Se regulates the synthesis of tea aroma compounds. Methods: Five oolong tea cultivars (Rougui, Shuixian, Queshe, Jinguanyin, and Huangguanyin) were included in this study. The Se content of the tea leaves was determined using inductively coupled plasma mass spectrometry (ICP-MS). Non-targeted metabolomics analysis of volatile compounds was conducted using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), followed by qualitative and quantitative analysis of volatile components employing multivariate statistical methods. Results: Under identical ecological and cultivation conditions, significant differences in selenium content were observed among the five oolong tea cultivars, in the descending order of Queshe > Shuixian > Jinguanyin > Rougui > Huangguanyin. A total of 615 volatile compounds were identified, with hydrocarbons, terpenoids, alcohols, esters, and aldehydes being the predominant classes, collectively accounting for 80% of the total volatile components. Through pairwise comparisons using the cutoff of variable importance in the projection (VIP) > 1 and P < 0.05, 82 differential aroma compounds were selected. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that these differential compounds significantly affected terpenoid and polyketide metabolism. Furthermore, 17 key aroma compounds were identified based on their odor activity values (OAV > 1), including linalool and its oxides, geraniol, α-ionone, and β-ionone. Correlation and absolute quantitative analysis confirmed that tea selenium content was significantly positively correlated with C13-norisoprenoids (β-ionone) (r = 0.97, P < 0.001) and (E)-2-nonenal (r = 0.89, P < 0.05). Conclusion: Varietal differences in selenium enrichment levels, determined by genetic characteristics, may influence the aroma quality of oolong tea by regulating the synthesis of C13-norisoprenoid aroma compounds derived from carotenoid metabolism. This study provides a theoretical basis for breeding tea cultivars with high Se accumulation capacity and for the simultaneous Se fortification and quality improvement of tea.

Key words: oolong tea; selenium enrichment levels; varietal differences; aroma components; carotenoids; metabolic pathways