Purpose: The objective of this study was to investigate the effect of LEDs of three different wavelengths and temperatures on the photodynamic inactivation of Campylobacter jejuni, Lactobacillus plantarum, Staphylococcus aureus and Vibrio parahaemolyticus.
Methods: A spectrometer and an irradiance meter were used to characterize the three (405, 460 and 520 nm) LEDs. Four bacterial strains in phosphate buffer saline were illuminated with each LED at 4, 10 and 25°C for 7 h. Inactivation curves were modeled using the modified Gompertz Model and the decimal reduction times (D-values) corresponding to the three LEDs were compared.
Results: The intensity of the three LEDs was approximately 120 mW/cm2. Illumination with 405 and 460 nm LEDs produced significant inactivation (P < 0.05) in the population of C. jejuni and V. parahaemolyticus (> 4 log), while L. plantarum and S. aureus showed relatively less susceptibility. The 520 nm LED brought about negligible inactivation. Of the three LEDs, 405 nm LED proved most effective as reflected by the D-values, which was generally 3 - 6 fold lower for the 405 nm LED compared to the 460 nm LED. Temperature had no significant effect (P > 0.05) on the photodynamic inactivation of C. jejuni. However, a significant inactivation was observed in L. plantarum with 460 nm LED at 25°C (D = 1121 J/cm2), and not at 4 and 10°C.
Significance: The results of this study demonstrate the antibacterial efficacy of LEDs were highly influenced by wavelengths and illumination temperatures, indicating that 405 and 460 nm LEDs would be suitable LEDs for food application.