Purpose: This study aimed to determine the effect of organic acids on the LED inactivation of foodborne pathogens and in the process, better understand the application and suitability of this novel technology.
Methods: LEDs with a peak wavelength of 461 nm were used to illuminate four foodborne pathogens – Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes and Staphylococcus aureus. These pathogens were placed in tryptone soya broth, whose pH was adjusted to 4.5 using citric, malic or lactic acid. Survivor curves were plotted and modelled using the Weibull Model. The D-values were subsequently calculated and compared using ANOVA.
Results: LED illumination significantly (P < 0.05) inactivated all four pathogens under the presence of the three acids, showing reductions of 2 – 5 log CFU/ml. Lactic acid was found to be the most effective in aiding the LED inactivation, while malic acid was found to be the least effective. This trend was reflected by the decimal reduction times (D-values) observed for these acids. For example, the D-values observed for E. coli O157:H7 were 3.66 ± 1.61, 4.05 ± 0.7 and 0.7 ± 0.14h using citric, malic and lactic acids respectively during the LED illumination, exhibiting significant (P < 0.05) difference among the D-values.
Significance: The results of this study suggest that the effectiveness of the LED treatment is likely to be different on foods of similar pH but having different predominant acids.