Bio-based phenolic branched-chain fatty acid in wash water reduced populations of Listeria innocua on apple fruit

Abstract

Phenolic branched-chain fatty acid (PBC-FA) emulsion was produced by dissolving it in ethanol and mixing with water (pH 7). The resulting monodispersed emulsion droplets were approximately 200 nm in diameter. The stability of the emulsion was evaluated by storing it at 4 and 20 °C for 30 days. The antimicrobial activity of the PBC-FA emulsion was tested against Escherichia coli and Listeria innocua (8 log CFU/mL) by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using a microdilution method. The PBC-FA was effective against L. innocua with MIC and MBC of 14.1 μg/mL and caused membrane permeation as determined with SEM and Live/Dead cell assay, but was not effective against E. coli O157:H7 at the tested concentrations (5–250 μg/mL). We also evaluated PBC-FA emulsion's potential to be used as a wash against L. innocua inoculated on apples. The results showed that the 500 μg/mL PBC-FA emulsion with 5 % ethanol had equivalent antimicrobial activity (2–3 logs reductions) against L. innocua as the 20 μg/mL chlorine solution, a commonly used sanitizer. 500 μg/mL PBC-FA emulsion had better antimicrobial efficacy when organic matter (chemical oxygen demand: 9.0 g/L) was present compared to 20 μg/mL of chlorine. The effect of PBC-FA on the quality of the apples, was determined by measuring changes in color, firmness, and soluble solids content over a 14-day storage period at 20 °C. The quality of the apples was not affected by PBC-FA over the 14-day storage period, suggesting that PBC-FA emulsion can be used as a wash for apples without affecting their quality.