Effects of slightly acidic electrolysed water spraying and ultraviolet C light-emitting diode irradiation combination on the inactivation kinetics of Escherichia coli biofilms on food contact surfaces

Abstract

In this study, we aimed to quantitatively investigate the effect of ultraviolet C (UVC)-light-emitting diode (LED) irradiation and slightly acidic electrolysed water (SAEW) treatment, alone or in combination, on elimination and inactivation mechanisms and the inactivation kinetics of E. coli O157:H7 biofilms formed on stainless-steel coupons. Although E. coli biofilms were inactivated significantly up to 2.36 log and 3.23 log, respectively, by both SAEW and UVC-LED disinfection treatment alone, a lesser reduction was seen with sprayed SAEW droplet treatment than with UVC-LED irradiation, possibly due to the interactions between extracellular polymeric substances and the constituents of biofilms and the chemical composition of SAEW. The inactivation kinetics of E. coli O157:H7 biofilms were evaluated using mathematical models to fit nonlinear reduction curves (Mean Sum of Squared Error (MSSE): 0.055–0.245; Root-mean-square deviation (RMSE): 0.236–0.495; R2: 0.943–0.985). For disinfection by a combination of spraying SAEW droplets and UVC-LED irradiation, inactivation synergy effect values and synergy ratios were calculated, where synergy effect values and synergy ratios were not time-dependent. The synergistic effect of the combined treatment showed the highest value of 1.2 log10 in the 14-min treatment condition, whereas the synergistic effect value of the 19-min treatment condition, which was the longest treatment time, was 0.9 log10. Our results established that the combination of sprayed SAEW droplets and UVC-LED irradiation could have a more efficient synergistic effect in biofilm reduction on SUS food contact surface materials than sprayed SAEW droplets or UVC-LED treatment alone. Further studies are required to simulate typical commercial conditions to develop reliable combined applications of SAEW and UVC-LEDs for food safety management.