Temporal Dynamics of Phytochemicals in Selected Medicinal Plants Across Gandaki Province, Nepal

Many phytochemicals, including phenols and flavonoids, are valued for their anti-inflammatory, antioxidant, antibacterial, and anti-cancer properties. However, these compounds are susceptible to chemical degradation when exposed to heat, light, oxygen, or changes in pH. Understanding their stability over time is essential for ensuring the quality, safety, and efficacy of natural products. This study investigated temporal changes in phytochemical content and antioxidant activity in three commonly used medicinal plants in Nepal: Cinnamomum tamala (C. tamala) leaves, Curcuma longa (C. longa) rhizome, and Zanthoxylum armatum (Z. armatum) fruits. Standard Folin-Ciocalteu reagent method for TPC, AlCl₃ colorimetric method for TFC, and DPPH free radical scavenging assay for antioxidant activity were used. Results showed a significant decline in total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity over the 1-year storage period (p < 0.001). All three species showed decreases in TPC and TFC, but for C. tamala, the TFC reduction between 6 and 12 months was not significant (p = 0.0551), indicating partial stabilization. Antioxidant activity, measured as IC₅₀, decreased over time, compared with standard ascorbic acid values, indicating reduced capacity. Most changes were statistically significant across time points. Analysis of altitude revealed no substantial effect on TPC, TFC, or IC₅₀ for C. tamala and Z. armatum. Only C. longa exhibited a minor positive correlation between altitude and TFC (p = 0.045). In conclusion, storage duration markedly reduces the phytochemical content and antioxidant potential of these medicinal plants. These findings emphasize the importance of proper storage to preserve bioactive compounds and provide guidance for selecting high-quality plant materials. The results are relevant for optimizing the use of natural antioxidants in foods, spices, nutraceuticals, and pharmaceutical products.