Optimizing Extraction Polarity for Multifunctional Bioactivities and Phenolic Composition in Polygonum cuspidatum Sieb. et Zucc. Ultrasonic Extraction

Objective: This study aimed to optimize the extraction of bioactive compounds from Polygonum cuspidatum Sieb. et Zucc. (P. cuspidatum) by evaluating the effect of ethanol concentration. Methods: Ultrasonic extraction was performed using ethanol concentrations of 0%, 30%, 50%, and 70%, and the resulting extracts were assessed for their chemical composition and multifunctional bioactivities. Results: The 70% Ethanol extract exhibited the highest total polyphenol and flavonoid contents and demonstrated the most potent antioxidant, enzyme-inhibitory, and antimicrobial activities, with significant differences (p < 0.05) compared to other concentrations. Chemical analysis identified tannic acid, emodin, and a variety of phenolic compounds as the primary bioactive constituents. Structural analyses using Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared (FT-IR) Spectroscopy revealed that 70% Ethanol induced the most pronounced structural changes to the cell wall, while FT-IR analysis confirmed the presence of O-H, C=O, C=C, and C-O functional groups, providing a mechanistic basis for the superior extraction efficiency and bioactivity. Conclusions: Ethanol concentration is a critical determinant for maximizing the bioactivity of P. cuspidatum. Extraction with 70% ethanol is identified as the optimal condition, supporting the potential of this plant as a source of natural bioactive compounds.