Effects of Growth Month Variations on Volatile Profiles, Anti-Glycation Capacity, and Antioxidant Activity of <em>Cyclocarya paliurus</em> Leaves: A SPME-GC-MS Study

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.