Inactivation of Listeria monocytogenes and Salmonella spp. on cantaloupe rinds by blue light emitting diodes (LEDs)

Abstract

This study evaluated the potential of blue light-emitting diodes (LED) of wavelength 405 and 460 nm in combination with sodium chlorophyllin to inactivate Listeria monocytogenes and Salmonella spp. on cantaloupe rind. A cocktail culture of L. monocytogenes or Salmonella spp. strains was surface inoculated onto cantaloupe rinds to reach a final concentration of 4 log CFU/cm² and dip-treated in a 100 μM sodium copper chlorophyllin solution. The cantaloupe samples were then exposed to 405 or 460 nm LEDs at a total dose of 1210 J/cm² and 5356 J/cm², respectively, at 4 and 20 °C. Results showed that the antibacterial efficacy against both pathogens on cantaloupe rinds between LED alone and LED with the chlorophyllin were statistically similar with bacterial inactivation ranging from 1.1 to 3 log CFU/cm² in most of the cases or the difference was only minimal. A similar inactivation of 3 log CFU/cm² was obtained in the case of L. monocytogenes and Salmonella spp. when illuminated by 405 nm LEDs while the inactivation of L. monocytogenes was higher than Salmonella spp. when illuminated by 460 nm LED. The δ value, a modified Weibull model parameter defined as the time (h) taken to reduce the bacterial population by 90%, was computed to compare the inactivation rates of the conditions. It was inferred that illumination with 405 nm LED required a lower δ value than 460 nm LED illumination (P < 0.05) for the inactivation of L. monocytogenes at 20 °C and Salmonella spp. at 4 °C. Thus the findings of this study indicate a promising application of blue LEDs to inactivate these pathogens on the surface of cantaloupe, minimizing the risk of listeriosis and salmonellosis by consumption of cantaloupe.

Keywords: Blue light emitting diodes; Cantaloupe; Listeria monocytogenes; Salmonella; Sodium chlorophyllin (Na-Chl).