Blue 405 nm LED light effectively inactivates bacterial pathogens on substrates and packaging materials used in food processing

Abstract

This study investigates the antimicrobial effectiveness of 405 nm light emitting diodes (LEDs) against pathogenic Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, and Staphylococcus aureus, in thin liquid films (TLF) and on solid surfaces. Stainless steel (SS), high density polyethylene (HDPE), low density polyethylene (LDPE), and borosilicate glass were used as materials typically encountered in food processing, food service, and clinical environments. Anodic aluminum oxide (AAO) coupons with nanoscale topography were used, to evaluate the effect of topography on inactivation. The impact of surface roughness, hydrophobicity, and reflectivity on inactivation was assessed. A 48 h exposure to 405 nm led to reductions ranging from 1.3 (E. coli) to 5.7 (S. aureus) log CFU in TLF and 3.1 to 6.3 log CFU on different solid contact surfaces and packaging materials. All inactivation curves were nonlinear and followed Weibull kinetics, with better inactivation predictions on surfaces (0.89 ≤ R² ≤ 1.0) compared to TLF (0.76 ≤ R² ≤ 0.99). The fastest inactivation rate was observed on small nanopore AAO coupons inoculated with L. monocytogenes and S. aureus, indicating inactivation enhancing potential of these surfaces. These results demonstrate significant promise of 405 nm LEDs for antimicrobial applications in food processing and handling and the healthcare industry.

Figure 1

Inactivation of E. coli, L. monocytogenes, S. Typhimurium, P. aeruginosa, S. aureus in 1.2-mm thick liquid suspension by exposure to continuous 405 nm LEDs of an irradiance of approximately 0.5 mW/cm². Data points represent means and error bars represent one standard deviation (n = 3). The blue dotted line denotes the limit of detection (LOD). Asterisks denote data points that are significantly different from the others at the same 405 nm LED exposure doses (p < 0.05), whereas circles denote clusters of data points that are not significantly different within the circle (p > 0.05). Circles of different colors indicate data points are significantly different between two circles at the same 405 nm LED exposure doses (p < 0.05).

Figure 2

Experimental data and Weibull predicted inactivation curves for E. coli after exposure to continuous 405 nm LEDs of an irradiance of approximately 0.5 mW/cm² on: (a) stainless steel (SS); (b) food-grade borosilicate glass (glass); (c) plastic materials: high density polyethylene (HDPE) and low density polyethylene (LDPE); and (d) anodic aluminum oxide with different nanotopography: nanosmooth (NS AAO), small nanopore (15 nm AAO) and large nanopore (100 nm AAO). Points represent means and error bars represent one standard deviation (n = 3). Limit of detection (LOD) is denoted by the blue dotted line. Points represent means and error bars represent one standard deviation (n = 3). Different letters denote significant differences (p < 0.05); inactivation data for the different colors were analyzed together at the same cumulative dose.

Figure 3

Experimental data and Weibull predicted inactivation curves for L. monocytogenes after exposure to continuous 405 nm LEDs of an irradiance of approximately 0.5 mW/cm² on: (a) stainless steel (SS); (b) food-grade borosilicate glass (glass); (c) plastic materials: high density polyethylene (HDPE) and low density polyethylene (LDPE); and (d) anodic aluminum oxide with different nanotopography: nanosmooth (NS AAO), small nanopore (15 nm AAO) and large nanopore (100 nm AAO). Points represent means and error bars represent one standard deviation (n = 3). Limit of detection (LOD) is denoted by the blue dotted line. Points represent means and error bars represent one standard deviation (n = 3). Different letters denote significant differences (p < 0.05); inactivation data for the different colors were analyzed together at the same cumulative dose.

Figure 4

Experimental data and Weibull predicted inactivation curves for S. aureus after exposure to continuous 405 nm LEDs of an irradiance of approximately 0.5 mW/cm² on anodic aluminum oxide substrates with different nanotopography: nanosmooth (NS AAO); small nanopore (15 nm AAO) and large nanopore (100 nm AAO). Data points represent means and error bars represent one standard deviation (n = 3). Limit of detection (LOD) is denoted by the blue dotted line. Different letters denote significant differences (p < 0.05); inactivation data for the different colors were analyzed together at the same cumulative dose.

Figure 5

The 405 nm blue LED experimental set up. (a) Dimensions of the 405 nm blue LED panel. (b) Light intensity emission (in Candela) tested at the lamp surface, at 25 °C. (c) Lamp setup used in the bacterial inactivation experiments.