Influence of Illumination Temperature and Wavelength on Bactericidal Effect of Light Emitting Diodes

Introduction: The preservation of raw food products is of prime importance to the food industry because of their high propensity to pathogenic contamination. The current method of preservation, refrigeration, does not kill bacteria, but only inhibits their growth, with psychrotrophs such as Listeria monocytogenes retaining their ability to grow. Hence, another hurdle is needed to ensure the microbial safety of these foods.

Purpose: The aim of this study was to investigate the effect of temperature and wavelength of light emitting diodes (LEDs) on the inactivation of foodborne pathogens.

Methods: Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes or Staphylococcus aureus in tryptone soy broth were illuminated for 7.5 h with 10-W blue (461-nm), green (521-nm) and red (642-nm) LEDs at 20, 15 and 10°C. The distance between the LED and bacterial culture was 4.5 cm and the irradiances of the LEDs were 22.1 (461-nm), 15.97 (521-nm) and 25.48 mW/cm²(642-nm). D-values were calculated based on survivor curves and compared using ANOVA.

Results: Regardless of the bacterial strains, bacterial inactivation was observed with the range of 4.6 – 5.2 and 1.0 – 2.0 log reductions at 10 and 15°C during illumination with 461- and 521-nm LEDs, respectively. No bactericidal effect was observed during the 642-nm LED treatment and the illumination at 20°C with 461- and 521-nm LEDs. D-values for four pathogens at 10 and 15°C after the illumination of 461-nm LED ranged from 1.29 to 1.74 h, indicating insignificant (P > 0.05) difference among the pathogens, except for L. monocytogenes. Thus these results indicate that the bactericidal effect of LEDs was highly dependent on the wavelength and the illumination temperature.

Significance: These data suggest that 461- and 521-nm LEDs, in combination with refrigeration, have the potential to act as a novel food preservation technology.