Effect of Extraction Solvents on Antioxidant and Antibacterial Activity of Zingiber montanum Rhizomes

Abstract

The Zingiber montanum rhizome has been utilized for its antiviral, immunomodulatory, anti-inflammatory, and antibacterial properties for a long time, particularly in Malaysia, Indonesia, and Thailand. Additionally, the rhizome has been a traditional ingredient in Asian cosmetic products. This study aimed to investigate the impact of different extracting solvents (hexane, dichloromethane, acetone, ethanol, methanol, 50% ethanol, and 75% ethanol) on the phenolic content, as well as the antioxidant and antibacterial activities of Zingiber montanum. The antioxidant activity was evaluated using two methods: 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and ferric-reducing antioxidant power (FRAP) assay, while antibacterial activity was tested against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa strains. The methanol extract demonstrated the highest phenolic content, while the ethanol extract exhibited a slightly lower amount. In the DPPH assay, the methanol extract showed an IC50 value of 36.89 ± 2.53 µg/mL, whereas the ethanol extract displayed a marginally higher value of 38.89 ± 0.27 µg/mL. In terms of ferric-reducing antioxidant power, the ethanol extract had slightly higher FRAP values (78.65 ± 4.73 mg AAE/g) than the methanol extract (76.09 ± 4.57 mg AAE/g). All extracts exhibited low activity against the three tested bacterial strains. Ethanol extract demonstrated the most antibacterial activity, with a clear zone ranging from 10.50 to 12.00 mm. The results suggest that ethanol is a suitable solvent for extracting Zingiber montanum rhizome for value-added materials application for cosmetic products.