Stability and Antimicrobial Potency Against Escherichia coli O157:H7 of Acidic Solutions Produced Following Anodic Electro-activation of Lactate, Propionate and Sorbate Anions

The objective of this work was to study the physico-chemical and antimicrobial effectiveness against Escherichia coli O157:H7 ATCC 43981 of different acidic solutions produced following anodic electro-activation of lactate, propionate and sorbate anions. Electro-activation was conducted in aqueous solutions and 2% starchy media under 250, 500, and 750 mA during 45 min, then stored under refrigerated (4 °C) or frozen (-20 °C) conditions for comparison. Analysis of the stability of pH and titratable acidity of the electro-activated solutions did not reveal any significant variation for 7 days storage. HPLC confirmed production of lactic, propionic and sorbic acids with an average concentration of 1 ± 0.15%. The acids concentrations were electric-current intensity dependent with highest values obtained with 750 mA. Antimicrobial analysis showed that refrigerated electro-activated solutions exhibited greater effectiveness than frozen ones. Results showed that electro-activated solutions containing lactic and sorbic acids in aqueous media partly lost their antimicrobial activity after freezing, a fact confirmed by increase of their MIC/MBC from 40%/60% to 60%/80%. In contrast, electro-activated solution containing propionic acid have maintained MIC/MBC ≤ 10% regardless of the storage conditions. In starchy media, electro-activated solutions containing lactic and propionic acid maintained a constant MIC/MBC of 40% under both storage conditions. The bactericidal action time of the electro-activated solutions was low and ranged from 1 min for propionic to 4 min for lactic acid containing solution, respectively. At equivalent concentrations, commercial lactic and propionic acid exerted only a bacteriostatic effect, with significantly weaker activity than electro-activated solutions. The antimicrobial effect of electro-activated solutions against E. coli was confirmed by CO 2 production test, alteration of membrane permeability through massive release of calcium (0.44 mg/L) and potassium ions (57.31 mg/L). Efflux of nucleic acids and proteins, measured at 260 nm and 280 nm, measured by the relative absorbance relatively to the absorbance of the initial electro-activated solution, indicated oxidative damage of cells. Live/Dead fluorescence microscopy confirmed cell death, while TEM/SEM microscopy clearly revealed structural damages (wrinkled cells, membrane lysis, and protoplasm leakage). These findings demonstrate that electro-activated solutions are highly effective and represent promising alternatives for food preservation and prevention of E. coli surface contamination of foods. • Electro-activated solutions (EAS) produced from organic anions. • EAS effective against Escherichia coli O157:H7. • EAS more effective than commercial organic acids. • EAS as antimicrobial agent. • EAS for enhanced food safety.