Cyclocarya paliurus leaves, commonly consumed as “sweet tea”, remain underutilized after spring harvest. This pilot study investigated harvest month-associated changes in bioactivity-related properties and volatile profiles of mature leaves collected from May to September (Q5–Q9) at one site in 2024. Aqueous extracts were analyzed for TPC, TFC, TP, TSC, DPPH and ABTS•+ radical scavenging activities, and inhibition of advanced glycation end-products (AGEs) formation in glucose/fructose-BSA models, with aminoguanidine as a positive reference. Dried leaf powders were profiled by SPME-GC-MS for tentative VOC annotation. TPC, TFC, TP, and TSC ranged from 28.04 to 28.87, 15.42 to 40.22, 2.14 to 2.51, and 23.15 to 25.30 mg/g, respectively. Q9 showed the strongest radical scavenging response, with the lowest DPPH and ABTS•+ IC50 values (0.119 and 0.131 mg/mL), while Q6 also exhibited relatively strong activity. Furthermore, Q6 and Q9 exhibited superior advanced glycation end-product (AGE) inhibitory responses, with Q9 being particularly effective in the fructose-BSA model. VOC profiles varied markedly by month, shifting from alkene/terpene predominance in Q5–Q6 to alcohol enrichment in Q7 and renewed alkene/terpene predominance in Q9. Integrated heatmap and Pearson correlation analyses identified clear temporal co-variations and pairwise associations between distinct VOC classes and bioactivity indices. Collectively, these results provide preliminary, site- and year-specific evidence that harvest month is associated with changes in the bioactivity-related properties and aroma-related phytochemical profiles of mature C. paliurus leaves, offering a cautious reference for harvest-stage-oriented utilization.

Cyclocarya paliurus leaves are widely consumed as “sweet tea”, yet mature leaves harvested after spring remain underutilized despite their potential health-promoting value. This study aimed to clarify how harvest month modulates volatile signatures and functional bioactivities of C. paliurus leaves across the growing season. Leaves collected from May to September (Q5–Q9) were extracted with water and characterized by spectrophotometric quantification of major non-volatile constituents (TPC, TFC, TP, and TSC), SPME–GC–MS profiling of volatile organic compounds (VOCs), DPPH radical scavenging assays, and BSA-based glucose/fructose glycation models; multivariate and correlation analyses were further applied to link chemical dynamics with bioactivities. Antioxidant capacity exhibited clear harvest-stage dependence, with Q9 and Q6 showing the strongest DPPH scavenging and the lowest IC₅₀ values (0.119 and 0.222 mg/mL, respectively). Anti-glycation activity displayed a similar temporal pattern: in both Glu–BSA and Fru–BSA systems, Q6 and Q9 consistently achieved the most pronounced inhibition of AGEs accumulation, exceeding 70% at weeks 3–4. VOCs underwent substantial seasonal remodeling, characterized by alkene predominance in Q6 (74.00%), alcohol enrichment in Q7 (38.90%), and a transient increase of alkanes in Q8 (22.32%), with ketones recurring at early and late stages. Correlation analysis and a three-phase schematic model collectively suggest that functional differentiation is driven by coordinated interactions between the non-volatile matrix (notably flavonoids) and stage-specific volatile signatures (e.g., alkenes and ketones). Overall, these findings provide a mechanistic basis for precision harvesting and stage-targeted utilization of mature C. paliurus leaves to optimize both bioactivity and aroma quality.