Anti-biofilm effect of 405-nm LEDs against Listeria monocytogenes in simulated ready-to-eat fresh salmon storage conditions

•405 nm LED illumination inhibited the growth of L. monocytogenes cells in biofilm.•LED illumination inactivated planktonic cells but not cells detached from biofilms.•LED illumination failed to inhibit pre-formed biofilm cells.•Illuminated pre-formed biofilm cells were more susceptible to sanitizer treatment.

The objective of this study was to evaluate the anti-biofilm effect of 405-nm light-emitting diodes (LEDs) against Listeria monocytogenes in salmon exudate at 4, 15, and 25 °C, and to compare the susceptibility of LED-illuminated and non-illuminated pre-formed biofilm cells to sanitizer treatment. For the biofilm-forming scenario, stainless-steel (SS) or acrylic (AC) coupons in sterilized salmon exudate were inoculated with L. monocytogenes and then illuminated with 405-nm LEDs (26 ± 2 mW/cm2) at each temperature for 8 h. For the pre-formed biofilm scenario, L. monocytogenes biofilms were pre-formed onto each coupon at 25 °C for 24 h and subsequently illuminated at each temperature, followed by treatment with 200 ppm quaternary ammonium compound (QAC) for 10 s to compare the sensitivity of LED-illuminated biofilm cells to the sanitizer treatment. Regardless of illumination temperature, the results showed that 405-nm LED illumination significantly (P < 0.05) reduced both planktonic and biofilm cell populations on SS and AC coupons during biofilm formation. There were no significant (P ≥ 0.05) changes in the planktonic and biofilm cell populations, for the pre-formed biofilm scenario, in response to LED illumination at 4 and 15 °C. However, significant biofilm cell reductions were observed on SS and AC coupons in response to LED illumination at 25 °C for 8 h. Regardless of coupon type, LED-illuminated biofilm cells were found to be more sensitive to QAC treatment under the pre-formed biofilm scenario than non-illuminated cells. These results indicate that 405-nm LED illumination may be effective in controlling L. monocytogenes during the biofilm formation process, and at inducing sensitivity to sanitizer treatment in pre-formed biofilm cells. Thus, this study suggests the potential of LED technology in controlling L. monocytogenes biofilms during the processing and storage of ready-to-eat salmon, minimizing the chance of cross-contamination from contaminated surfaces.