Characterization of pulsed light for microbial inactivation

Abstract

Pulsed light is an emerging technology that can serve as an alternative to current antimicrobial interventions in the food industry. The first objective of this study was to define the spectrum and energy characteristics of pulsed light. The second objective was to establish the germicidal response of Escherichia coli , Salmonella enterica subsp. enterica ser. Typhimurium, Listeria monocytogenes , Bacillus cereus (vegetative cells and endospores), Aspergillus niger spores, and Penicillium roqueforti spores were evaluated following pulsed light treatments. Microorganisms were treated using three different broad-spectrum xenon gas flashlamps (Type A: 380–1100 nm, Type B: 235–1100 nm, and Type C: 190–1100 nm) for up to 15 pulses. All microorganisms experienced a significant interaction of flashlamp type × treatment duration (P < 0.0001). Additionally, E. coli was treated with pulsed light with flashlamp type B using light filters to block ultraviolet light and selectively deliver visible (VIS; 380–740 nm), near-infrared (NIR; 700–1080 nm), and VIS-NIR (400–1080 nm) radiation to the cells. The filter type × treatment duration interaction was significant (P < 0.0001). The VIS, NIR, and VIS-NIR filter treatments achieved modest reductions of 0.72, 0.19, and 0.83 Log 10 CFU/mL, respectively, after 75 consecutive pulses. To visualize physical effects on cell structures, transmission electron microscopy (TEM) images were obtained for E. coli following 15 pulse treatments of the three flashlamp types and the type B flashlamp with VIS-NIR filter placement. TEM imaging indicated that damage to cell morphology following treatment by broad-spectrum radiation was negligible. These results indicate that microbial sensitivity to pulsed light treatment differs for species and is predominantly attributed to the ultraviolet portion of the spectrum. • Pulsed light treatment susceptibility differs for Gram -, Gram +, and spores/fungi. • Microbial inactivation by pulsed light is predominantly attributed to UV light. • Visible and near-infrared radiation contribute negligibly to microbe inactivation. • Pulsed light treatment imparts negligible effects to Escherichia coli morphology.