Antimicrobial activity of electro-activated solutions produced from lactate and propionate anions against Bacillus cereus ATCC 14579 and its spores and their application in cooked rice.

Bacillus cereus is a spore-forming, toxin-producing bacterium responsible for the spoilage and contamination of a wide variety of foods, posing a risk to consumer health. Its spores are more resistant than vegetative cells and can survive in food production environments even after decontamination, representing a high food safety challenge. Thermal treatments of contaminated foods cause bacterial cell lysis and toxin release, while altering their organoleptic and nutritional properties. This is why non-thermal methods are increasingly favored to meet the demands of consumers seeking fresher and minimally processed products. The aim of this work was to study the antimicrobial activity of electro-activated solutions (EAS) produced from lactate and propionate anions against the vegetative cells and spores of B. cereus ATCC 14579. Anodic electro-activation of lactate and propionate anions in aqueous solutions (L-EA 750 and P-EA 750) and in a starchy film-forming suspension (L + FS-EA 750 and P + FS-EA 750) was performed at 750 mA for 45 min. The MIC/MBC of L-EA 750 and P-EA 750 against vegetative cells were 80% and ≤ 10%, respectively, whereas those of L + FS-EA 750 and P + FS-EA 750 were ≤ 10%. Under the same conditions, only P-EA 750 exhibited a sporicidal effect after ≤ 5 min of contact, with an MST/MSD ≤ 10%, while no other EAS was effective after 30 min. The growth profiles of the vegetative cells in broth generally corresponded with the results obtained on agar. More interestingly, L-EA 750, which showed no sporicidal effect on agar, inhibited spore germination in broth with a MIC/MBC of 90%, demonstrating that only the aqueous EAS can eradicate spores. P-EA 750 exhibited stable bactericidal and sporicidal activity, regardless of the medium. No synergistic effect was observed between combinations of EAS containing lactic and propionic acids, regardless of the ratios or the medium, for both physiological forms of B. cereus. Bactericidal action times of EAS ranged from a few seconds to 6 min. CO2 production by treated B. cereus and spores was significantly reduced compared to controls (P < 0.001). Conductivity of treated cells and spores ranged from 2.29 ± 0.26 to 5.46 ± 0.71 mS/cm, compared with 1.47 ± 0.05 to 1.70 ± 0.08 mS/cm for controls (P < 0.001). Efflux of Ca2+/K+ ions and intracellular macromolecules (nucleic acids and proteins), correlated with increased conductivity, indicated cell lysis. Fluorescence microscopy confirmed that most cells treated with P-EA 750 were damaged. SEM and TEM analyses revealed deformations, pore formation, membrane destruction, and loss of the protoplast and spore core content. This study demonstrates that aqueous electro-activated solutions, without additional technologies, can effectively control the proliferation of both vegetative cells and spores of B. cereus. Finally, the electro-activated solutions demonstrated their ability to inactivate the vegetative cells of Bacillus cereus in the rice suspension before refrigeration, representing a promising antimicrobial alternative for food processing.