Aims: The objective of this research was to determine the antimicrobial activity of conventional and high-intensity ultrasound-assisted (HI-US) solvent-extracted Thai spices, including ginger (Zingiber officinale Rose), fingerroot (Bosenbergia pandurata Holtt) and turmeric (Curouma longa Linn).
Methods and results: Extracts were obtained using hexane, isopropanol and a 7 : 3 isopropanol : hexane mixture as solvents with and without HI-US. The antimicrobial activity of the extracts was assayed against four strains each of Listeria monocytogenes and Salmonella Typhimurium DT 104 using an agar dilution assay. Application of HI-US did not alter antibacterial activity against S. Typhimurium, but antilisterial activity of some HI-US spice extracts decreased. Solvent type affected antimicrobial efficacy of extracts with hexane producing the least antimicrobial activity. Fingerroot extracted with isopropanol-hexane and without HI-US had the best antilisterial effect while HI-US-isopropanol fingerroot extract had the greatest antimicrobial efficacy against S. Typhimurium.
Conclusions: Application of HI-US reduced time of extraction to 5 min, compared with the 24 h required for conventional extraction and maintained antimicrobial activity against Salmonella but slightly reduced activity against Listeria.
Significance and impact of the study: HI-US in combination with proper solvent selection may offer a new tool to optimize extraction of spice essential oil for use as antimicrobial agents, and reduce processing time and costs.