Purpose: This article reports on the anti-listerial properties of selected organic acids and salt derivatives in order to inform possible alternatives in food preservation and pathogen control.
Methods: The susceptibility of two Listeria monocytogenes strains was assessed against five organic acids and two acid-salt derivatives across a series of pH environments. Minimum inhibitory concentrations (MICs) of the acids were tested against the two strains by means of an agar-dilution method
Results: In general, ATCC 19117 was found to be more resistant to both organic acids and salts. High MIC levels (low susceptibility) were noted for potassium sorbate, sodium benzoate and lactic acids, while at pH 5 the isolates were susceptible to all the organic acids tested. A small increase in pH notably reduced antimicrobial activity against the organisms. At pH 7 the isolates all but lost susceptibility to benzoic, lactic, malic and sorbic acids. Although the activity of the majority of acids was linked to pH, some acids were not as closely related (e.g., potassium sorbate, sodium benzoate and citric acid) and this suggests that the type of organic acids plays a role in inhibition. The relatively high MICs reported for compounds that are conventionally used as preservatives against Listeria spp. raises concern.
Significance: The results suggest that the type of organic acid used to set pH, and not only pH alone, plays a role in determining inhibition. It was confirmed that a “one-size-fits-all” approach to preservation is not always effective. Furthermore, the need for microbiological data to sub-species level to inform the selection of preservatives was highlighted.