Inactivation kinetics of slightly acidic electrolyzed water combined with benzalkonium chloride and mild heat treatment on vegetative cells, spores, and biofilms of Bacillus cereus.

Bacillus cereus can exist as vegetative cells, spores, and biofilms in food-processing environment, posing a big challenge for the food industry. The objective of this study was to examine the inactivation efficacy of slightly acidic electrolyzed water (SAEW) in combination with benzalkonium chloride (BAC) and mild heat treatment (50 and 60 °C) on B. cereus strains (ATCC 10987 and ATCC 14579). The inactivation efficacy of SAEW was found to be largely dependent on available chlorine concentration (ACC) level and exposure time as well as B. cereus strains and growth conditions. SAEW with ACC of 40 ppm reduced ATCC 10987 and ATCC 14579 vegetative cells to the non-detection limit within 30 s. and 1 min, respectively. Combination treatment with SAEW+60 °C for 10 min resulted in reductions of ATCC 10987 spores, ATCC 14579 spores, and ATCC 10987 biofilms at 0.76 logCFU/ml, 0.59 logCFU/ml, and 1.28 logCFU/cm2, respectively. While, treatment with SAEW+BAC + 60 °C for 10 min resulted in reductions of ATCC 10987 spores, ATCC 14579 spores, and ATCC 10987 biofilms at 1.91 logCFU/ml, 1.98 logCFU/ml, and 2.62 logCFU/cm2, respectively. The inactivation kinetics under different ACC of SAEW and in combination with BAC and mild treatment were determined by Weibull model. The calculated adjusted correlation coefficients (R2adj) and root mean sum of squared error (RMSE) values for all curves were found to be ranges from 0.95-0.99 and 0.04-0.23, respectively, indicating that the Weibull model precisely predicted the inactivation kinetics of B. cereus during SAEW in combination with BAC and mild heat treatments. These results suggest that SAEW in combination with BAC and mild heat may be used as an effective cleaning strategy against B. cereus in the food contact surfaces.

Effect of Electrolyzed Water on the Disinfection of Bacillus cereus Biofilms: The Mechanism of Enhanced Resistance of Sessile Cells in the Biofilm Matrix.

This study examined the disinfection efficacy and mechanism of electrolyzed water (EW) on Bacillus cereus biofilms. B. cereus strains, ATCC 14579 and Korean Collection for Type Cultures (KCTC) 13153 biofilms, were formed on stainless steel (SS) and plastic slide (PS) coupons. Mature biofilms were treated with slightly acidic EW (SAEW), acidic EW (AEW), and basic EW (BEW). SAEW (available chlorine concentration, 25 ± 1.31 mg L-1; pH 5.71 ± 0.16; and oxidation reduction potential, 818 to 855 mV) reduced ATCC 14579 biofilms on plastic slides to below the detection limit within 30 s. However, biofilms on SS coupons showed a higher resistance to the SAEW treatment. When the disinfection activities of three types of EW on biofilms were compared, AEW showed a higher bactericidal activity, followed by SAEW and BEW. In contrast, BEW showed a significantly ( P < 0.05) higher biofilm dispersal activity than AEW and SAEW. SAEW disinfection of the B. cereus biofilms was due to the disruption of the B. cereus plasma membrane. The higher resistance of biofilms formed on the SS coupon might be due to the higher number of attached cells and extracellular polymeric substances formation that reacts with the active chlorine ions, such as hypochlorous acid and hypochlorite ion of SAEW, which decreased the disinfection efficacy of SAEW. This study showed that the EW treatment effectively disinfected B. cereus biofilms, providing insight into the potential use of EW in the food processing industry to control the biofilm formation of B. cereus.

Assessment of Enterotoxin Production and Cross-Contamination of Staphylococcus aureus between Food Processing Materials and Ready-To-Eat Cooked Fish Paste.

This study evaluated Staphylococcus aureus growth and subsequent staphylococcal enterotoxin A production in tryptone soy broth and on ready-to-eat cooked fish paste at 12 to 37 °C, as well as cross-contamination between stainless steel, polyethylene, and latex glove at room temperature. A model was developed using Barany and Roberts's growth model, which satisfactorily described the suitable growth of S. aureus with R(2)-adj from 0.94 to 0.99. Except at 12 °C, S. aureus cells in TSB presented a lag time lower (14.64 to 1.65 h), grew faster (0.08 to 0.31 log CFU/h) and produced SEA at lower cell density levels (5.65 to 6.44 log CFU/mL) compare to those inoculated on cooked fish paste with data of 16.920 to 1.985 h, 0.02 to 0.23 log CFU/h, and 6.19 to 7.11 log CFU/g, respectively. Staphylococcal enterotoxin type A (SEA) visual immunoassay test showed that primary SEA detection varied considerably among different storage temperature degrees and media. For example, it occurred only during exponential phase at 30 and 37 °C in TSB, but in cooked fish paste it took place at late exponential phase of S. aureus growth at 20 and 25 °C. The SEA detection test was negative on presence of S. aureus on cooked fish paste stored at 12 and 15 °C, although cell density reached level of 6.12 log CFU/g at 15 °C. Cross-contamination expressed as transfer rate of S. aureus from polyethylene surface to cooked fish paste surface was slower than that observed with steel surface to cooked fish paste under same conditions. These results provide helpful information for controlling S. aureus growth, SEA production and cross-contamination during processing of cooked fish paste.