Ppm NaOCl Research Articles

Rugose Morphotype in Salmonella Typhimurium and Salmonella Heidelberg Induced by Sequential Exposure to Subinhibitory Sodium Hypochlorite Aids in Biofilm Tolerance to Lethal Sodium Hypochlorite on Polystyrene and Stainless Steel Surfaces.

Salmonella biofilms act as a continuous source for cross-contamination in the food processing environments. In this study, a stable rugose morphotype of Salmonella was first induced by sequential exposure to subinhibitory concentrations (SICs) of sodium hypochlorite (NaOCl) (ranging from 50 to 300 ppm over 18-day period) in tryptic soy broth. Then, rugose and smooth morphotypes of Salmonella Typhimurium ATCC 14028 and Salmonella Heidelberg ATCC 8326 were characterized for biofilm forming abilities on polystyrene and stainless steel surfaces. Rugose morphotype of both ATCC 14028 and ATCC 8326 exhibited higher Exopolysaccharide (EPS) formation than smooth morphotype (p ≤ 0.05). Also, the SICs of NaOCl (200 or 300 ppm in broth model) increased the biofilm formation ability of rugose morphotype of ATCC 8326 (p ≤ 0.05) but decreased that of ATCC 14028. The 2-day-old Salmonella biofilms were treated with biocidal concentrations of 50, 100, or 200 ppm NaOCl (pH 6.15) in water for 5, 10, or 20 min at room temperature. The biofilm reduction in CFU/cm2 for the rugose was lower than the smooth morphotype on both surfaces (p ≤ 0.05) by lethal NaOCl in water. Scanning electron micrographs on both polystyrene and stainless steel surfaces demonstrated that the rugose morphotype produced a denser biofilm than the smooth morphotype. Transmission electron micrographs revealed the cell wall roughness in rugose morphotype, which may help in tolerance to NaOCl. The gene expression data indicate that the expression of biofilm regulator (csgD), curli (csgA, csgB, and csgC), and cellulose (bcsE) was significantly increased in rugose morphotype when induced by sequential exposure of NaOCl SICs. These findings reveal that the rugose morphotype of S. Typhimurium and S. Heidelberg produced significantly denser biofilm on food contact surfaces, which also increased with sequential exposure to SICs of NaOCl in the case of S. Heidelberg, and these biofilms were more tolerant to biocidal NaOCl concentrations commonly used in the food processing plants.

Poly (ether sulfone) membrane surface modification using norepinephrine to mitigate fouling

Here we report on the efficacy of poly(norepinephrine) (PNE) coatings to mitigate membrane fouling. We modified 30 kDa poly(ether sulfone) (PES) ultrafiltration (UF) membranes using a facile dip-coating method. Norepinephrine (NE) is a dopamine (DA) analog, having an additional OH group on the ethyl chain. Like dopamine, it polymerizes in mildly oxidizing conditions, and creates robust coatings. PES membranes were modified with 2 g L−1 NE up to 24 h, and then characterized by contact angle measurement, AFM, FTIR, SEM, and XPS. The coating was confirmed by XPS, showing an increase in N1s and decrease in S2p signals. AFM results showed that the PNE coatings were quite smooth, and the contact angles of modified membranes decreased significantly compared to the as-received (AR) membrane, confirming that membrane wettability increased. The ultrapure water permeability of modified membranes increased relative to the AR membrane, and the modification enhanced anti-fouling properties against model foulants (BSA, SA, and SRNOM), and two treated municipal wastewaters. The modified membranes exhibited less energy consumption and lower fouling resistance as compared to the AR membrane. For both treated municipal wastewaters, optimum performance was exhibited with the 3-hr modification. The PNE coatings did not have a significant impact on foulant rejection. Both the two- and the three-mechanism fouling models were able to provide accurate descriptions of measured flux decline; however, the parameters of the three-mechanism model have greater physical significance because pore constriction is considered explicitly. The PNE layer was stable in 0.1 M HCl and 100 ppm NaOCl (3-day treatments) but was removed by 0.01 M NaOH.

Transferring bulk chemistry to interfacial synthesis of TFC-membranes to create chemically robust poly(epoxyether) films

Membrane technology is currently still excluded from separations in more aggressive feeds due to limited chemical robustness. To extent its applicability, a novel thin-film composite (TFC) membrane was synthesized via the homopolymerization of epoxide monomers, resulting in robust poly(epoxyether) top-layers with >90% rose bengal (MW = 1017 Da) and 70% methyl orange (MW = 327 Da) retention with reasonable water fluxes (>2 L m-2 h−1 bar−1). The superior chemical stability of this novel nanofiltration membrane type was proven via treatments in pH 1 and 500 ppm NaOCl (pH 4) for, respectively, 48 h and 2.5 h, after which an unchanged or even improved membrane performance was observed. Additionally, the synthesis of the thin top-layer occurred via an interfacial initiation of the polymerization (IIP), rather than via state-of-the-art interfacial polymerization (IP). This IIP approach allowed to convert well-known monophasic bulk epoxide polymerization (commonly used in e.g. the automotive and coating industry), into the synthesis of thin, yet cross-linked top-layers.

Impact of chlorophyllin-chitosan coating and visible light on the microbial contamination, shelf life, nutritional and visual quality of strawberries

Abstract The aim of this study was to evaluate the antimicrobial efficiency of photoactivated chlorophyllin-chitosan conjugate (Chl–CHS) against main foodborne pathogens (L. monocytogenes, E. coli) and strawberry plant pathogen (Botrytis cinerea) in vitro and to assess the impact of Chl-CHS coating and visible light on the microbial contamination, spoilage, nutritional and visual quality of strawberries. Photoactivated Chl–CHS (0.001–0.1%, light λ = 405 nm, 38 J/cm2) reduced the viability of L. monocytogenes by 7 log, E. coli – by 4.5 log in vitro. Moreover, it inhibited B. cinerea growth by 60%. Comparative analysis of strawberry decontamination techniques indicated that soaking of strawberries in 200 ppm NaOCl diminished the population of yeasts/microfungi by 0.6 log, whereas coating of strawberries with Chl–CHS and illumination with visible light (dose 76 J/cm2) inactivated yeasts/microfungi on the fruits by 1.4 log. Moreover, Chl–CHS coating in the presence of light prolonged the shelf-life of strawberries by 3 days without any negative impact on the visual quality and color, saving weight losses, water content and antioxidant activity. In conclusion, photoactivated Chl–CHS coating possessed significant antimicrobial activity. Such coatings might serve for the future development of new generation light-active edible antimicrobial coatings, so important for effective preservation of traditional and organic strawberry production.

Chlorine-resistant sulfochlorinated and sulfonated polysulfone for reverse osmosis membranes by coating method

In this work, sulfochlorinated polysulfone (SC-PSf), a functional polysulfone with chlorine resistance, was synthesized through metalation sulfochlorination of polysulfone (PSf). For endowing the required hydrophilicity of SC-PSf, the sulfonyl chloride groups on SC-PSf were partially hydrolyzed to sulfonic groups to produce sulfonated SC-PSf (SC-S-PSf). Thin film composite (TFC) membranes for reverse osmosis application were fabricated by coating solution of SC-S-PSf on porous PSf substrate and then crosslinked by piperazine (PIP) to form polysulfone-sulfamide (PSSA) skin layer. In order to enhance the spreadability of polymer solution on PSf supporting layer, tetrabutylammonium chloride (TBAC), a common surfactant, was added into the coating solution. A flawless membrane was acquired only by a single coating step and at dilute SC-S-PSf solution when TBAC was added into polymer solution. Through optimizing coating conditions, the NaCl rejection and water flux of PSSA membrane reached 96.9% and 17.8 L/m2h under brackish desalination conditions. Moreover, the PSSA membrane exhibited the long-term stability against chlorine during the operation condition of 2000 ppm NaOCl for 10 days. The salt rejection of PSSA only decreased by 1%. In contrast, the salt rejection of polyamide membrane decreased by 8% under the same condition.

Bactericidal efficacies of food additive grade calcium hydroxide toward Legionella pneumophila.

Food additive grade calcium hydroxide (FdCa(OH)2) in the solution of 0.17% was evaluated for its bactericidal efficacies toward Legionella pneumophila with or without sodium hypochlorite (NaOCl) at a concentration of 200 ppm total residual chlorine, at room temperature (RT) (25°C ± 2°C) and 42°C, either with or without 5% fetal bovine serum (FBS). Besides, FdCa(OH)2 in different concentration solutions were prepared in field water samples (hot spring and bath tab water) and evaluated for their bactericidal efficacies at 42°C. FdCa(OH)2 (0.17%) inactivated the L. pneumophila to the undetectable level (<2.6 log CFU/ml) within 5 min and 3 min, respectively, at RT and 42°C, with 5% FBS. At RT and 42°C, NaOCl inactivated L. pneumophila to the undetectable level within 5 min, without 5% FBS, but with 5% FBS, it could only inactivate this bacterium effectively (≥3 log reductions). Conversely, at RT and 42°C, the mixture of 0.17% FdCa(OH)2 and 200 ppm NaOCl could inactivate L. pneumophila to the undetectable level, respectively, within 3 min and 1 min, even with 5% FBS, and it was elucidated that FdCa(OH)2 has a synergistic bactericidal effect together with NaOCl. FdCa(OH)2 0.05% solution prepared in hot spring water could inactivate L. pneumophila to the undetectable within 3 min at 42°C. So, FdCa(OH)2 alone could show nice bactericidal efficacy at 42°C, even with 5% FBS, as well as in field water samples.

Influence of cold stress on the survival of Listeria monocytogenes Bug600 and ScottA in lethal alkali, acid and oxidative stress

The objective of this study was to determine the influence of cold stress (4 °C) on the survival of Listeria monocytogenes Bug600 and ScottA in lethal alkali, acid and oxidative stress in broth and in distilled water. Four distinct patterns were observed: (1) Survival of cold stressed L. monocytogenes was increased by 1–4 logs in lethal alkali stress (pH 12.3 NaOH or KOH); (2) Survival of cold stressed L. monocytogenes was decreased by 1–4 logs in lethal acid stress (pH 1.3 HCl or H3PO4); (3) Survival of cold stressed L. monocytogenes was increased by 1–4 logs in lethal oxidative stress (1500 ppm H2O2); and (4) No difference in survival of cold stressed L. monocytogenes was observed in lethal oxidative stress by chlorine (1000 ppm NaOCl) compared to control. These patterns were also consistently observed for survival of L. monocytogenes cells in lethal alkali, acid or oxidative stress after adaptation of cold stress at 4 °C in low nutrient conditions (1/10 TSBYE). These findings demonstrate that cold stressed cells of L. monocytogenes Bug600 and ScottA have greater tolerance to lethal alkali and some oxidative stresses that are commonly employed by the food industries to kill this foodborne pathogen.

Immunomagnetic separation combined with RT-qPCR for evaluating the effect of disinfectant treatments against norovirus on food contact surfaces

Despite the importance of preventing the spread of human norovirus (NoV), effective disinfectants are lacking. In this study, the efficacy of disinfectants against NoV on various non-porous surfaces was investigated by immunomagnetic separation (IMS) and quantitative real-time reverse transcription (RT-q)PCR. Monoclonal anti-NoV antibody-conjugated magnetic beads captured intact viral particles for RT-qPCR after the treatment of surfaces with disinfectants. Viral suspensions of approximately 5.97 log10 genomic copies were inoculated onto rubber, glass, stainless steel, ceramic tile, wood, and polyvinyl chloride surfaces. Various elution buffers were used to elute NoV from surfaces. Ethanol (50–70%), sodium hypochlorite (NaOCl, 100–1000 ppm), sodium metasilicate (SMS, 0.1% and 0.3%), and quaternary compounds (1000–2000 ppm) were investigated as disinfectants; the observed reductions were <1 log10, except for SMS (1.17 ± 0.21 to 2.71 ± 0.06 log10 reduction) and 700–1000 ppm NaOCl (1.04 ± 0.07 to 2.03 ± 0.05 log10 reduction). Ethanol and quaternary compounds exhibited low efficacy against NoV GII.4 on all surfaces. These results indicated that SMS is the most effective disinfectant and emphasized the need to develop suitable agents to inactivate NoV on surfaces.

Bactericidal Efficacy of Food Additive-Grade Calcium Hydroxide Against Salmonella Infantis on Eggshells.

The bactericidal efficacy of food additive-grade calcium hydroxide [FdCa(OH)2] was evaluated for inactivation of Salmonella Infantis and Salmonella Enteritidis in liquid and Salmonella Infantis on contaminated eggshells. The activity of FdCa(OH)2 was also compared with that of sodium hypochlorite (NaOCl) containing 150 ppm chlorine (150 ppm NaOCl). FdCa(OH)2 solutions (0.1% and 0.2%) in the presence or absence of organic materials (5% calf serum [CS]) at pH 12.6 were used to inactivate Salmonella Infantis and Salmonella Enteritidis in a reaction tube or on eggshells artificially contaminated with Salmonella Infantis. Both 0.1% and 0.2% FdCa(OH)2 were capable of inactivating Salmonella Infantis and Salmonella Enteritidis in liquid at >3 log10 colony-forming units (CFU)/ml within 3 and 1 min of contact time, respectively, even in the presence of 5% CS. Additionally, 0.1% and 0.2% FdCa(OH)2 reduced bacterial levels on contaminated eggshells to >3 log10 CFU/ml, within 3 and 1 min, respectively, in the presence of 5% CS. Without CS, 0.1% and 0.2% FdCa(OH)2 could reduce bacteria on eggshells to >3 log10 CFU/ml within 1 min and 30 sec, respectively. In contrast, 150 ppm NaOCl solution could not inactivate bacteria on eggshells down to >3 log10 CFU/ml within 3 min contact time, either with or without CS, and no bacterial reduction was observed in redistilled water. The findings of the present study indicate that FdCa(OH)2 solution has high efficacy against foodborne bacteria and may be a good candidate for enhancement of biosecurity at farms and egg processing plants.

Synergistic effect of X-ray irradiation and sodium hypochlorite against Salmonella enterica serovar Typhimurium biofilms on quail eggshells

The present study investigated the synergistic bactericidal effects of combined X-ray irradiation (0.5, 1.0, 1.5, and 2.0 kGy) and sodium hypochlorite (NaOCl) (50, 100, 150, 200, and 300 ppm) treatment on the reduction of S. enterica serovar Typhimurium ATCC 14028 biofilms on quail eggshells. Additionally, the color change of the quail eggshells was measured by hunter color “L” (lightness), “a” (red/green), “b” (yellow/blue), and “ΔE” (total color difference). Additionally, the puncture force was tested to evaluate eggshell thickness after the combined treatments. The highest biofilm reduction values were observed as 4.6 log CFU/egg after X-ray (2.0 kGy) and NaOCl (300 ppm) treatment. Moreover, the synergistic reduction in values after combined treatment was evaluated, and the highest biofilm reduction value was 4.3 log CFU/egg by 2.0 kGy X-ray/50 ppm NaOCl (1.47 log higher than the sum of reduction values of the individual treatments). The color of the quail eggshell and puncture force were not significantly changed by combined treatments (p > 0.05 at both cases). Consequently, 2.0 kGy X-ray/50 ppm NaOCl was considered optimal for combination treatment for eliminating S. enterica ser. Typhimurium biofilms on eggshell without any color or thickness changes. Furthermore, combination treatment could be useful for improving microbiological safety in the quail egg industry.

Combined effect of sodium hypochlorite and gamma-irradiation for the control of Vibrio vulnificus in fresh oyster and clam

This study investigated the synergistic bactericidal effects of treatment with a combination of sodium hypochlorite (NaOCl) and gamma irradiation against Vibrio vulnificus on shucked oysters and clams. The V. vulnificus population decreased to 1.1–4.8 and 1.2–4.8 log10 colony forming units/g in oysters and clams, respectively, after treatment with a combination of NaOCl (20–80 ppm) and gamma irradiation (0.1–2.0 kGy). V. vulnificus was not detected on oysters or clams after exposure to 60–80 ppm NaOCl and then 2.0 kGy gamma irradiation, where a >2-log synergistic reduction in bacterial population was observed. Based on the Weibull model, 5D-values for 5-log reductions were calculated for treatment with 60 ppm NaOCl with 1.1 kGy irradiation and 80 ppm NaOCl with 0.9–1.0 kGy gamma irradiation. These results indicate treating V. vulnificus populations 5 logs in size with a combination of 60 or 80 ppm NaOCl and 0.9–1.1 kGy gamma irradiation could be a strategy used in post-harvest processing of seafood and distribution to enhance the microbial safety of molluscan shellfish.

Efficacy of Combination Treatment with Sodium Metasilicate and Sodium Hypochlorite for Inactivation of Norovirus on Fresh Vegetables.

In recent years, fresh vegetables have frequently been associated with the foodborne transmission of enteric viruses, such as human norovirus (NoV). Therefore, several studies have focused on developing methods to inactivate foodborne viruses for preventing outbreaks of foodborne illnesses. Sodium hypochlorite (NaOCl) is commonly used as a disinfectant, but results in undesirable effects on the appearance and taste of foods and can generate toxic byproducts when it exceeds the allowable concentration. Here, we evaluated the efficacy of a range of NaOCl concentrations (50-1000 ppm) for reducing the amounts of human NoV (NoV GII.4) on lettuce (Lactuca sativa), celery (Apium graveolens L.), and white cabbage (Brassica oleracea ssp. capitata). In addition, the combination treatment of NaOCl and sodium metasilicate (SMS, 0.1-0.5%) pentahydrate was evaluated for its ability to decrease the populations of NoV GII.4 in the three food samples. An immunomagnetic separation procedure combined with reverse transcription quantitative polymerase chain reaction was used for virus detection. For lettuce, celery, and cabbage, the NoV GII.4 recovery rates were 57.3% ± 6.5%, 52.5% ± 1.7%, and 60.3% ± 3.9%, respectively, using a glycine/NaCl elution buffer (0.25 M glycine/0.14 M NaCl, pH 9.5). The reductions of NoV GII.4 were 3.17, 3.06, and 3.27 log10 genomic copies/μL for lettuce, celery, and cabbage, respectively, at 1000 ppm NaOCl, while a reduction of ∼3 log10 genomic copies/μL was obtained when the samples were treated with a combination of 100 ppm NaOCl and 0.4% SMS pentahydrate. Taken together, these results demonstrated that combined treatment with NaOCl and SMS pentahydrate was an efficient strategy to reduce the concentration of NaOCl for control of NoV GII.4 contamination in fresh vegetables.

Membrane fouling, chemical cleaning and separation performance assessment of a chlorine-resistant nanofiltration membrane for water recycling applications

Abstract The effectiveness of hypochlorite cleaning for fouling mitigation of a prototype chlorine-resistant nanofiltration (NF) membrane was assessed for direct filtration of a secondary treated effluent. The chlorine resistance and separation performance of the prototype NF membrane were also compared to commercial NF and reverse osmosis membranes. The prototype chlorine resistant NF membrane did not show any changes in permeability and conductivity rejection after exposing a NaOCl solution for up to 5 × 104 ppm-h. By contrast, a considerable deterioration in rejection was observed for the other two commercial membranes. Direct filtration of a secondary treated effluent by the prototype NF membrane resulted in a progressive permeability reduction by up to 25% after 10 h of filtration. The membrane permeability was fully restored by hypochlorite cleaning with a 2000 ppm NaOCl solution for 1 h. Effective permeability recovery by hypochlorite cleaning was demonstrated with multiple hypochlorite cleaning cycles. Membrane fouling and hypochlorite cleaning were also simulated using solutions containing a model foulant (sodium alginate, humic acids or bovine serum albumin). Among them, an insufficient permeability recovery was observed for membrane fouling caused by humic acids. Further research is recommended to develop an improved hypochlorite cleaning protocol to control various membrane fouling.

Evaluation of the efficiency of cleaning method in direct contact membrane distillation of digested livestock wastewater

This study investigated effects of physical and chemical cleaning methods on the initial flux recovery of fouled membrane in membrane distillation process. A laboratory scale direct contact membrane distillation (DCMD) experiment was performed to treat digested livestock wastewater with 3.89 mg/L suspended solids, 874.7 mg/L COD, 543.7 mg/L nitrogen, 15.6 mg/L total phosphorus, and pH of 8.6. A hydrophobic PVDF membrane with an average pore size of 0.22 um and a porosity of 75 % was installed inside a direct contact type membrane distillation module. The temperature difference between feed and permeate side was maintained at 40oC with the feed and permeate stream velocity of 0.18 m/s. The results showed that the permeate flux decreased from 22.1 L*m-2*hr-1 to 19.0 L*m-2*hr-1 after 75 hours of distillation. The fouled membrane was cleaned first by physical flushing and consecutively by chemicals with NaOCl and citric acid. After the physical cleaning the flux was recovered to 92 % as compared with the initial clean water flux of the virgin membrane. Then 94 % of the flux was recovered after cleaning by 2,000 ppm NaOCl for 90 minutes and finally 97 % of flux recovered after 3 % citric acid for 90 minutes. SEM-EDS and FT-IR analysis results presented that the foulants on the membrane surface were removed effectively after each cleaning step. The contact angle measurement showed that the hydrophobicity of the membrane surface was also restored gradually after each cleaning step to reach nearly the same hydrophobicity level as the virgin membrane.

Synergistic effect of a combination of ultraviolet–C irradiation and sodium hypochlorite to reduce Listeria monocytogenes biofilms on stainless steel and eggshell surfaces

The present study demonstrates the synergistic effect of treatment with a combination of ultraviolet (UV)C (300, 600, 1200, and 1800 mWs/cm2) irradiation and sodium hypochlorite (NaOCl) (50, 100, 150, and 200 ppm) on Listeria monocytogenes ATCC 19113 biofilms formed on stainless steel and eggshell surfaces. The synergistic effect was not dependent on the dose of UV–C irradiation or the concentration of NaOCl. Synergistic reductions of biofilms after UV–C/NaOCl treatment on stainless steel and eggshells were 0.95–3.68 log CFU/cm2 and –0.22 to 1.02 log CFU/cm2, respectively. The largest synergistic reductions of biofilms were 3.68 log CFU/cm2 using 1800 mWs/cm2 UV–C and 200 ppm NaOCl on stainless steel, and 1.02 CFU/cm2 using 600 mWs/cm2 UV–C and 50 ppm NaOCl on eggshells. The Hunter colors of L*, a*, and b* were not significantly (P > 0.05) changed on eggshell surfaces treated with all single and combined treatments. The results in this study indicate that the combination treatment of 1800 mWs/cm2 UV–C/200 ppm NaOCl could be feasible for use on stainless steel surfaces in industrial kitchens, facilities, and restaurants. In addition, the combination of 600 mWs/cm2 UV–C/500 ppm NaOCl could possibly be used in egg production, processing, and distribution processes to enhance food safety without causing changes to the eggshell surface color.

Inactivation of Cronobacter sakazakii in head lettuce by using a combination of ultrasound and sodium hypochlorite

The present study investigated the synergistic effects of combined ultrasound (37 kHz, 380 W for 5–100 min) and sodium hypochlorite (NaOCl) (50–200 ppm) on reducing Cronobacter sakazakii KCTC 2949 in head lettuce. Ultrasound was not enough to inactivate C. sakazakii (0.01–0.58 log-reduction), whereas NaOCl significantly (P < 0.05) reduced C. sakazakii (0.58–2.77 log-reduction). Despite the significant reduction in C. sakazakii with NaOCl treatment (200 ppm), the combination of 100 min ultrasound and 200 ppm NaOCl resulted in an additional 1.67 log-reduction of C. sakazakii (4.44 log-reduction = 2.77 + 1.67 log). Synergistic reductions on C. sakazakii were observed in most combined treatments, although the most synergistic reduction values were <1.0 log10 CFU/g. The highest synergistic value of reduction in head lettuce was 1.08 log10 CFU/g when treated with a combination of 100 min ultrasound and 200 ppm NaOCl. Moreover, the pH and °Brix after combined treatment with 5–100 min ultrasound and 50–200 ppm NaOCl did not significantly differ from any single treated lettuce. These results indicate that combined treatment with 100 min ultrasound and 200 ppm NaOCl could be a potential approach to reduce C. sakazakii on post-harvest leaf vegetable during processing and enhance the shelf-life during distribution and storage.

Low-Cost Potato Tissue Culture with Microwave and Bleach Media Preparation and Sterilization

Labor and equipment costs are the main expenses in potato micropropagation. To determine if we could reduce costs associated with media sterilization, a disinfectant, sodium hypochlorite (NaOCl), in combination with microwave heating, were assayed as media sterilants. Incorporating a common 5 % NaOCl household beach at a concentration of 9 ppm (active chlorine) in media sterilized with an autoclave or microwave oven controlled microorganism growth and maintained plantlet growth performance. Non-sterile 473 ml (16 oz.) clear deli containers were selected as an inexpensive replacement for traditional culture vessels and were effectively sterilized with a 50 ppm (active chlorine) NaOCl solution. Reuse of the non-sterile clear deli containers and alternate media water sources were also tested but this decreased plantlet growth performance. Comparison of a controlled growth chamber and ambient laboratory conditions was also investigated. Microorganism growth was significantly less in a controlled growth chamber (5 %) as compared to uncontrolled conditions (26–36 %).

Synergistic effects of NaOCl and ultrasound combination on the reduction of Escherichia coli and Bacillus cereus in raw laver.

The current study investigated the synergistic effects of NaOCl (50-200 ppm)/ultrasound (37 kHz, 380 W for 5-100 min) combination on the reduction of Escherichia coli and Bacillus cereus in raw laver. The synergistic reductions were not dependent on concentrations of NaOCl and times of ultrasound. Synergistic reduction ranged from 0.1 to 0.5 log10 colony-forming units (CFU)/g and 0.1-1.1 log10 CFU/g, respectively, for E. coli and B. cereus, with the largest synergistic reduction in the combination of 200 ppm NaOCl and 60-min ultrasound. Moreover, significant differences of "L" (lightness), "a" (redness), and "b" (yellowness) were not observed in combined with 50-200 ppm NaOCl and 100-min ultrasound compared to those in raw laver treated by only 100-min ultrasound. The results in the current study indicate that the combined treatment of 200 ppm NaOCl and 60-min ultrasound could be regarded a potential optimum hurdle approach in the seaweed production, processing, and distribution process to enhance seaweed safety.

Preparation and characterization of chlorine resistant thin film composite polyamide membranes via the adsorption of various hydrophilic polymers onto membrane surfaces

The surfaces of the reverse osmosis (RO) membranes prepared by an interfacial polymerization method on the polysulfone supports in our lab were modified by the adsorption of the three hydrophilic polymers, poly(vinyl sulfonic acid) (PVSA), poly(ethylenimine) (PEI) and poly(vinyl alcohol) (PVA). Using the ‘salting-out effect’, these polymers, representative of anionic, cationic and neutral polymers, respectively, were used to investigate which adsorbed polymer is the most resistant to chlorine attack. The surface properties of the adsorbed RO membranes were characterized to confirm the adsorption by using contact angle measurement and scanning electron microscopy (SEM). The performance of chlorine-resistance RO membranes was measured through their evolution, before and after hypochlorite exposures in 3,450 ppm NaOCl solution for desired time points. This was determined in terms of pure water permeability and salt rejection. In order to determine the most dominant factor contributing to chlorine resistance, experiments were carried out under several conditions. The candidate factors included coating time, concentration of coating solution, ionic strength, and salt types. In general, as the coating time and concentration increased, the chlorine resistance increased for any salt used. Among the three materials, PVSA showed the greatest chlorine resistance of ca. 62,000 ppm·h, under the determined conditions, ionic strength (IS)=0.2 Mg and coating time of 60 s. The order of chlorine stabilities for the coating materials was determined to be PVSA, PEI, and PVA. It was found that the chlorine resistance of any polymer-coated membrane is superior to the pristine RO membrane. Open image in new window

NaOCl effect on biofilm produced by Staphylococcus aureus isolated from the milking environment and mastitis infected cows

Biofilms constitute a physical barrier, protecting the encased bacteria from detergents and sanitizers. The objective of this work was to analyze the effectiveness of sodium hypochlorite (NaOCl) against strains of Staphylococcus aureus isolated from raw milk of cows with subclinical mastitis and Staphylococcus aureus isolated from the milking environment (blowers and milk conducting tubes). The results revealed that, in the presence of NaOCl (150ppm), the number of adhered cells of the twelve S. aureus strains was significantly reduced. When the same strains were evaluated in biofilm condition, different results were obtained. It was found that, after a contact period of five minutes with NaOCl (150ppm), four strains (two strains from milk , one from the blowers and one from a conductive rubber) were still able to grow. Although with the increasing contact time between the bacteria and the NaOCl (150ppm), no growth was detected for any of the strains. Concerning the efficiency of NaOCl on total biofilm biomass formation by each S. aureus strain, a decrease was observed when these strains were in contact with 150 ppm NaOCl for a total period of 10 minutes. This study highlights the importance of a correct sanitation protocol of all the milk processing units which can indeed significantly reduce the presence of microorganisms, leading to a decrease of cow´s mastitis and milk contamination.