Effects of the Specific Wavelength and Intensity of Intense Pulsed Light (IPL) on Microbial Inactivation

This study aimed to determine the effects of the specific wavelength and intensity of IPL on microbial inactivation by applying IPL under various conditions with the same fluence. Nine different filters were used to obtain pulse light sources with various composition ratios in the ultraviolet (UV), visible light (VL), and infrared (IR) ranges, and the inactivation was compared among gram-positive bacteria, gram-negative bacteria, and yeast. When gram-positive bacteria were treated with a light source that accounted for 85.29% of the total wavelength in the UV range, a significant reduction of bacteria by 6 logs was achieved at the fluence of 2.16 J/cm2. However, it was noteworthy that even when UV accounted for only 11.66%, a 6-log reduction was achieved at 3.94 J/cm2. This study confirmed that the intensity of single pulses in IPL is as important as the UV range in microbial inactivation. Even if the proportion of UV in IPL is low, strong intensity of single pulses delivered to microorganisms can cause significant damage and increase inactivation. There was no significant difference in resistance to IPL between gram-positive and gram-negative bacteria, but yeast showed relatively higher resistance to IPL, and this tendency was more pronounced in IPL with higher UV content.