Solvent Fractionation of Polygonum cuspidatum Sieb. et Zucc. for Antioxidant, Biological Activity, and Chromatographic Characterization

Abstract

This study investigated the natural bioactive compounds in Polygonum cuspidatum Sieb. et Zucc. (P. cuspidatum) by fractionating a 70% ethanol extract using n-hexane, chloroform, ethyl acetate, n-butanol, and water. The total polyphenol and flavonoid contents of each fraction were determined, and their antioxidant activities were evaluated using DPPH, ABTS, and FRAP assays. Additionally, the anti-diabetic potential was assessed via α-glucosidase inhibitory activity, while anti-obesity activity was evaluated using lipase inhibitory activity. The fractions were also tested for tyrosinase and elastase inhibitory activities to assess their skin-whitening and anti-wrinkle potential, and their antibacterial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa was determined using the agar diffusion method. Finally, bioactive compounds were identified and quantified using HPLC and GC-MSD. The results showed that the ethyl acetate fraction possessed the highest total polyphenol content (0.53 ± 0.01 g GAE/g) and total flavonoid content (0.19 ± 0.02 g QE/g). It also exhibited strong antioxidant activity, with the lowest DPPH radical scavenging IC₅₀ (0.01 ± 0.00 mg/mL), ABTS radical scavenging IC₅₀ (0.06 ± 0.00 mg/mL), and the highest FRAP value (6.02 ± 0.30 mM Fe²⁺/mg). Moreover, it demonstrated potent enzyme inhibitory activities, including tyrosinase inhibitory activity (67.78 ± 2.50%), elastase inhibitory activity (83.84 ± 1.64%), α-glucosidase inhibitory activity (65.14 ± 10.29%), and lipase inhibitory activity (85.79 ± 1.04%). In the antibacterial activity, the ethyl acetate fraction produced a clear inhibitory zone of 19.50 mm against Staphylococcus aureus, indicating notable antibacterial activity. HPLC-PDA and GC-MSD analyses identified tannic acid and emodin as the major bioactive constituents. These findings suggest that the ethyl acetate fraction of P. cuspidatum extract, rich in polyphenol and flavonoid compounds, is a promising natural source of bioactive ingredients for applications in the food, pharmaceutical, and cosmetic industries. Further research is needed to explore its mechanisms and therapeutic applications.

Keywords: Polygonum cuspidatum Sieb. et Zucc.; antioxidant activity; chromatographic analyses; enzyme inhibitory activity.

Figure 1

Chromatographic and photodiode array (PDA) spectral data of tannic acid: (a) HPLC chromatogram of the tannic acid standard solution showing 3 peaks; (b) chromatogram of the P. cuspidatum solvent fractions showing 13 peaks; (c) PDA spectrum of the tannic acid standard; and (d) PDA spectrum of the corresponding sample peak. The identical spectral profiles confirm the presence of tannic acid in the sample matrix.

Figure 1

Chromatographic and photodiode array (PDA) spectral data of tannic acid: (a) HPLC chromatogram of the tannic acid standard solution showing 3 peaks; (b) chromatogram of the P. cuspidatum solvent fractions showing 13 peaks; (c) PDA spectrum of the tannic acid standard; and (d) PDA spectrum of the corresponding sample peak. The identical spectral profiles confirm the presence of tannic acid in the sample matrix.

Figure 2

Chromatographic and photodiode array (PDA) spectral data of emodin: (a) HPLC chromatogram of the emodin standard solution showing 6 peaks; (b) chromatogram of the P. cuspidatum solvent fractions showing 8 peaks; (c) PDA spectrum of the emodin standard; and (d) PDA spectrum of the corresponding sample peak. The identical spectral profiles confirm the presence of emodin in the sample matrix.

Figure 3

Chemical structure of tannic acid, a representative hydrolyzable tannin characterized by multiple phenolic hydroxyl groups and a polyaromatic framework.

Figure 4

Chemical structure of emodin, a hydrophobic anthraquinone with a rigid tricyclic aromatic structure and weak polarity.

Figure 5

GC–MSD chromatograms profiles of P. cuspidatum solvent fractions (a) n-hexane fraction, (b) chloroform fraction, (c) ethyl acetate fraction, (d) n-butanol fraction, and (e) aqueous fraction.

Figure 6

Stepwise solvent fractionation scheme of the 70% ethanolic extract of P. cuspidatum. The dried extract was successively partitioned with n-hexane, chloroform, ethyl acetate, and n-butanol, resulting in the corresponding solvent fractions.