Chyer Kim

Roles of Oxidation-Reduction Potential in Electrolyzed Oxidizing and Chemically Modified Water for the Inactivation of Food-Related Pathogens

This study investigates the properties of electrolyzed oxidizing (EO) water for the inactivation of pathogen and to evaluate the chemically modified solutions possessing properties similar to EO water in killing Escherichia coli O157:H7. A five-strain cocktail (10(10) CFU/ml) of E. coli O157:H7 was subjected to deionized water (control), EO water with 10 mg/liter residual chlorine (J.A.W-EO water), EO water with 56 mg/liter residual chlorine (ROX-EO water), and chemically modified solutions. Inactivation (8.88 log10 CFU/ml reduction) of E. coli O157:H7 occurred within 30 s after application of EO water and chemically modified solutions containing chlorine and 1% bromine. Iron was added to EO or chemically modified solutions to reduce oxidation-reduction potential (ORP) readings and neutralizing buffer was added to neutralize chlorine. J.A.W-EO water with 100 mg/liter iron, acetic acid solution, and chemically modified solutions containing neutralizing buffer or 100 mg/liter iron were ineffective in reducing the bacteria population. ROX-EO water with 100 mg/liter iron was the only solution still effective in inactivation of E. coli O157:H7 and having high ORP readings regardless of residual chlorine. These results suggest that it is possible to simulate EO water by chemically modifying deionized water and ORP of the solution may be the primary factor affecting microbial inactivation.

Efficacy of Electrolyzed Oxidizing (EO) and Chemically Modified Water on Different Types of Foodborne Pathogens

This study was undertaken to evaluate the efficacy of electrolyzed oxidizing (EO) and chemically modified water with properties similar to the EO water for inactivation of different types of foodborne pathogens (Escherichia coli O157:H7, Listeria monocytogenes and Bacillus cereus). A five-strain cocktail of each microorganism was exposed to deionized water (control), EO water and chemically modified water. To evaluate the effect of individual properties (pH, oxidation-reduction potential (ORP) and residual chlorine) of treatment solutions on microbial inactivation, iron was added to reduce ORP readings and neutralizing buffer was added to neutralize chlorine. Inactivation of E. coli O157:H7 occurred within 30 s after application of JAW EO water with 10 mg/l residual chlorine and chemically modified solutions containing 13 mg/l residual chlorine. Inactivation of Gram-positive and -negative microorganisms occurred within 10 s after application of ROX EO water with 56 mg/l residual chlorine and chemically modified solutions containing 60 mg/l residual chlorine. B. cereus was more resistant to the treatments than E. coli O157:H7 and L. monocytogenes and only 3 log10 reductions were achieved after 10 s of ROX EO water treatment. B. cereus spores were the most resistant pathogen. However, more than 3 log10 reductions were achieved with 120-s EO water treatment.

Efficacy of Electrolyzed Oxidizing Water in Inactivating Salmonella on Alfalfa Seeds and Sprouts

Studies have demonstrated that electrolyzed oxidizing (EO) water is effective in reducing foodborne pathogens on fresh produce. This study was undertaken to determine the efficacy of EO water and two different forms of chlorinated water (chlorine water from Cl2 and Ca(OCl)2 as sources of chlorine) in inactivating Salmonella on alfalfa seeds and sprouts. Tengram sets of alfalfa seeds inoculated with a five-strain cocktail of Salmonella (6.3 x 10(4) CFU/g) were subjected to 90 ml of deionized water (control), EO water (84 mg/liter of active chlorine), chlorine water (84 mg/liter of active chlorine), and Ca(OCl)2 solutions at 90 and 20,000 mg/liter of active chlorine for 10 min at 24 +/- 2 degrees C. The application of EO water, chlorinated water, and 90 mg/liter of Ca(OCl)2 to alfalfa seeds for 10 min reduced initial populations of Salmonella by at least 1.5 log10 CFU/g. For seed sprouting, alfalfa seeds were soaked in the different treatment solutions described above for 3 h. Ca(OCl)2 (20,000 mg/liter of active chlorine) was the most effective treatment in reducing the populations of Salmonella and non-Salmonella microflora (4.6 and 7.0 log10 CFU/g, respectively). However, the use of high concentrations of chlorine generates worker safety concerns. Also, the Ca(OCl)2 treatment significantly reduced seed germination rates (70% versus 90 to 96%). For alfalfa sprouts, higher bacterial populations were recovered from treated sprouts containing seed coats than from sprouts with seed coats removed. The effectiveness of EO water improved when soaking treatments were applied to sprouts in conjunction with sonication and seed coat removal. The combined treatment achieved 2.3- and 1.5-log10 CFU/g greater reductions than EO water alone in populations of Salmonella and non-Salmonella microflora, respectively. This combination treatment resulted in a 3.3-log10 CFU/g greater reduction in Salmonella populations than the control (deionized water) treatment.

Ultraviolet spectrophotometric characterization and bactericidal properties of electrolyzed oxidizing water as influenced by amperage and pH.

To identify the primary component responsible in electrolyzed oxidizing (EO) water for inactivation, this study determined the concentrations of hypochlorous acid (HOCl) and hypochlorite ions (OCl-) and related those concentrations to the microbicidal activity of the water. The ultraviolet absorption spectra were used to determine the concentrations of HOCl and OCl- in EO water and the chemical equilibrium of these species with change in pH and amperage. EO water generated at higher amperage contained a higher chlorine concentration. The maximum concentration of HOCl was observed around pH 4 where the maximum log reduction (2.3 log10 CFU/ml) of Bacillus cereus F4431/73 vegetative cells also occurred. The high correlation (r = 0.95) between HOCl concentrations and bactericidal effectiveness of EO water supports HOCls role as the primary inactivation agent. Caution should be taken with standard titrimetric methods for measurement of chlorine as they cannot differentiate the levels of HOCl present in EO water of varying pHs.

Efficacy of Electrolyzed Water in the Inactivation of Planktonic and Biofilm Listeria monocytogenes in the Presence of Organic Matter

The ability of electrolyzed (EO) water to inactivate Listeria monocytogenes in suspension and biofilms on stainless steel in the presence of organic matter (sterile filtered chicken serum) was investigated. A five-strain mixture of L. monocytogenes was treated with deionized, alkaline EO, and acidic EO water containing chicken serum (0, 5, and 10 ml/liter) for 1 and 5 min. Coupons containing L. monocytogenes biofilms were also overlaid with chicken serum (0, 2.5, 5.0, and 7.5 ml/liter) and then treated with deionized water, alkaline EO water, acidic EO water, alkaline EO water followed by acidic EO water, and a sodium hypochlorite solution for 30 and 60 s. Chicken serum decreased the oxidation-reduction potential and chlorine concentration of acidic EO water but did not significantly affect its pH. In the absence of serum, acidic EO water containing chlorine at a concentration of 44 mg/liter produced a > 6-log reduction in L. monocytogenes in suspension, but its bactericidal activity decreased with increasing serum concentration. Acidic EO water and acidified sodium hypochlorite solution inactivated L. monocytogenes biofilms to similar levels, and their bactericidal effect decreased with increasing serum concentration and increased with increasing time of exposure. The sequential 30-s treatment of alkaline EO water followed by acidic EO water produced 4- to 5-log reductions in L. monocytogenes biofilms, even in the presence of organic matter.

Nonlinear Flexural Deflection of Thermoplastic Foam Core Sandwich Beam

Nonlinear flexural deflection behavior of foam core sandwich beams hasbeen experimentally investigated. The experimental data were compared with the predicted results obtained from a proposed analytical method and the finite element analysis. Sandwich beams with thermoplastic foam core and carbon/epoxy fabric faces were manufactured using the vacuum bagging process. To investigate the effect of the face thickness on the nonlinear flexural deflection, three types of specimens with different face thickness were prepared and tested using the four-point bending test method. Basic engineering data and nonlinear mechanical properties of the face sheet and the foam core were obtained from the tensile and shear tests. An analytical model wasproposed to predict the global nonlinear flexural deformation of the foam core sandwich beams. In the model, measured material nonlinear behavior of the foam core wasimplemented. The predicted global nonlinear deflection of the foam core sandwich beam using the proposed analytical model and the finite element analysis agreed well with the experimental data up to the local indentation failure point within some scattered range.

Composite Grid Structure with Near-Zero Thermally Induced Deflection

A cost-saving manufacturing process is proposed to construct a carbon/epoxy square grid structure with nearzero coefe cient of thermal expansion (CTE) in the three principal directions. Stacking sequences of the slotted joint rib and square tube are selected such that the individual member has near-zero CTE from an analysis using classical lamination theory. Pressureto bond ribs and tubesisprovided by thethermal expansion of silicon rubber. Experimental results have shown that thermally induced deformation of a carbon grid panel is much less than that of an aluminum honeycomb sandwich panel. A numerical test has demonstrated that thermally induced deformation of the composite square grid structure is almost zero.

Effects of Air Pressure, Orifice Size and Electrostatic Charge of Spray on Chemical Properties and Bactericidal Efficacy of Electrolyzed Oxidizing Water

Three-factor three-by-three-by-two-level factorial designs were adopted for studying the effects of air pressure, sprayer orifice size and electrostatic charge of a spray gun on pH, oxidation-reduction potential (ORP), electric conductivity and residual chlorine of electrolyzed oxidizing (EO) waters with either low ( 72 ppm) of chlorine. Results indicated that small orifice reduced more ORP and chlorine than large orifices. Electrostatic charge, in general, did not have significant effect. High air pressure spray retained more chlorine and yielded higher OPR than at low air pressure. High-chlorine EO water achieved at least 3 to 4 log10 CFU/mL reduction on Listeria monocytogenes populations when sprayed with the spray gun while sprayed with a commercial backpack sprayer or a poly-tank sprayer eliminated Listeria completely. These results demonstrated that although spraying reduced 20 to 97% of the chlorine in EO water, application of EO water through spraying still has good potential for reducing bacteria in food-processing operations.