Comparing Organic Acids and Salt Derivatives as Antimicrobials Against Selected Poultry-Borne Listeria monocytogenes Strains14 December 2012
From their in-vitro investigations, researchers in South Africa raise concerns over the relatively high concentrations reported for compounds that are conventionally used as preservatives against Listeria spp. raise concern. The degree of inhibition varied by both product and pH, and the two Listeria isolates also differed in their susceptibility to the treatments.
In the journal, Foodborne Pathogens and Disease, Dr Jan F.R. Lues and Maria Magdalena Theron of the Central University of Technology in Bloemfontein in Free State Province, South Africa, report on the anti-listerial properties of selected organic acids and salt derivatives in order to suggest possible alternatives in food preservation and pathogen control in the poultry meat processing industry.
They assessed the susceptibility of two Listeria monocytogenes isolates against five organic acids (lactic, acetic, malic, citric and propionic) and two acid-salt derivatives (sorbic acid [potassium salt] and benzoic acid [sodium salt]) 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.
In general, strain CC60 was found to be more resistant than strain CC77 to both organic acids and salts. At pH values of 7 and above, high MIC levels (low susceptibility) were noted for potassium sorbate, sodium benzoate and lactic acids, whereas susceptibility at lower pH increased reaching pH5 where the isolates were susceptible to all the organic acids tested.
A small increase in pH notably reduced antimicrobial activity against the organisms. At pH7, the isolates just about 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. raise concern, according to Lues and Theron. They add that their 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, added the researchers, and they highlighted the need for microbiological data to the sub-species level to inform the selection of preservatives.
Lues J.F.R. and M.M. Theron. 2012. Comparing organic acids and salt derivatives as antimicrobials against selected poultry-borne Listeria monocytogenes strains in vitro. Foodborne Pathogens and Disease, 9(12):1126-1129. doi:10.1089/fpd.2012.1220
Further ReadingYou can view the full report by clicking here.