Cyclocarya paliurus tea, also known as “sweet tea”, an herbal tea with Cyclocarya paliurus leaves as raw material, is famous for its unique nutritional benefits and flavor. However, due to the unique “bittersweet” of Cyclocarya paliurus tea, it is still unable to fully satisfy consumers’ high-quality taste experience and satisfaction. Therefore, this study aimed to explore metabolites in Cyclocarya paliurus leaves during their growth period, particularly composition and variation of sweet and bitter taste compounds, by combining multi-platform metabolomics analysis with an electronic tongue system and molecular docking simulation technology. The results indicated that there were significant differences in the contents of total phenols, flavonoids, polysaccharides, and saponins in C. paliurus leaves in different growing months. A total of 575 secondary metabolites were identified as potential active metabolites related to sweet/bitter taste using nontargeted metabolomics based on UHPLC-MS/MS analysis. Moreover, molecular docking technology was utilized to study interactions between the candidate metabolites and the sweet receptors T1R2/T1R3 and the bitter receptors T2R4/T2R14. Six key compounds with high sweetness and low bitterness were successfully identified by using computational simulation analysis, including cis-anethole, gluconic acid, beta-D-Sedoheptulose, asparagine, proline, and citrulline, which may serve as candidates for taste modification in Cyclocarya paliurus leaves. These findings provide a new perspective for understanding the sweet and bitter taste characteristics that contribute to the distinctive sensory quality of Cyclocarya paliurus leaves.

Cyclocarya paliurus tea, also known as "sweet tea", a health substitute tea with Cyclocarya paliurus leaves as raw material, is famous for its unique nutritional benefits and flavor. However, due to the unique "bittersweet" of Cyclocarya paliurus tea, it is still unable to fully satisfy consumers' high-quality taste experience and oral pleasure. The taste and sensory quality of Cyclocarya paliurus tea are mainly determined by secondary metabolites. Therefore, this study aimed to explore the metabolites in Cyclocarya paliurus leaves during their growth process, particularly the composition and variation of sweet and bitter taste compounds, by combining multi-platform metabolomics analysis with an electronic tongue system and molecular docking simulation technology. The results indicated that there were significant differences in the contents of total phenols, flavonoids, polysaccharides and saponins of C. paliurus leaves in different growing months, among which the bioactive components in leaves harvested in July were the highest, and the best balance between sweetness and bitterness was achieved. A total of 575 secondary metabolites were identified as potential active metabolites related to sweet/bitter taste using nontargeted metabolomics based on UHPLC-MS/MS analysis. Molecular docking technology was utilized to study the interactions between candidate metabolites and the sweet receptor T1R2/T1R3 and the bitter receptor T2R4/T2R14. Six key compounds with high sweetness and low bitterness were successfully identified by using computational simulation analysis, including cis-Anethole, Gluconic acid, beta-D-Sedoheptulose, Asparagine, Proline, and Citrulline, which may serve as candidates for taste modification in Cyclocarya paliurus leaves. These findings provide a new perspective for understanding the sweet and bitter taste characteristics metabolites that contribute to the distinctive sensory quality of Cyclocarya paliurus leaves.

Unmodified gold nanoparticles (AuNPs)-based aptasensing (uGA) assay has been widely implemented in the determination of many different targets, but there are few reports on protein detection using uGA. Here, we designed a uGA assay for protein detection including the elimination of interfering proteins. Positively charged protein can be absorbed directly on the surface of AuNPs to form “protein corona”, which results in the aggregation of AuNPs even without salt addition, thereby preventing target protein detection. To overcome this problem, we systematically investigated the effect of modifying the pH of the solution during the uGA assay. A probe solution with a pH slightly higher than the isoelectric points (pI) of the target protein was optimal for protein detection in the uGA assay, allowing the aptamer to selectively detect the target protein. Three proteins (beta-lactoglobulin, lactoferrin, and lysozyme) with different pI were chosen as model proteins to validate our method. Positively charged interfering proteins (with pIs higher than the optimal pH) were removed by centrifugation of protein corona/AuNPs aggregates before the implementation of actual sample detection. Most importantly, the limit of detection (LOD) for all three model proteins was comparable to that of other methods, indicating the significance of modulating the pH. Moreover, choosing a suitable pH for a particular target protein was validated as a universal method, which is significant for developing a novel, simple, cost-effective uGA assay for protein detection.

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.