The inactivation of Escherichia coli O157:H7 ATCC 35150 and methicillin-resistant S. aureus ATCC 33591 by a light emitting diode (LED) was investigated in the present study. Various wavelengths of LEDs (365, 385, and 405 nm) were used individually or combined with folic acid (LEDF), and inactivation curves were analyzed using the Weibull model to compare the bactericidal effects. Reduction levels of pathogens by combination treatment of LED and 100 μM folic acid were significantly higher than those by individual LED treatment for the wavelength used in this study. It was confirmed that the reactive oxygen species produced by folic acid degradation accelerated the bactericidal effect of LEDs. When applied in apple juice, the same trend was observed by 405 nm treatment, although the inactivation rates were higher than those of buffer due to the low pH of apple juice. Moreover, injured cells were not observed except 30 J/cm2 LED, LEDF and 36 J/cm2 LEDF treatments. Mode of inactivation by LEDF was suggested as DNA damage along with membrane damages. Moreover, it was validated that genes related to antimicrobial resistance would be mutated by LEDF treatment. Therefore, LEDF can be used effectively to control foodborne pathogens in apple juice.
Keywords: Apple juice; E. coli; Folic acid; Inactivation kinetics; LED; MRSA.
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