Water reconditioning by high power ultrasound combined with residual chemical sanitizers to inactivate foodborne pathogens associated with fresh-cut products

The suitability of high power ultrasound (HPU, 20 kHz, 0.28 kW/l) combined with residual chemical sanitizers for water reconditioning was studied. A synergetic disinfection effect was observed when HPU was combined with peroxyacetic acid (PAA) or a commercial mix of organic acids and phenolic compounds (OA/PC). In recycled water (RW) with a chemical oxygen demand (COD) of 500 mg O₂/l, PAA inactivated 2 log units of Escherichia coli O157:H7 at concentrations of 3.2, 6.4, 16 mg/l after 7 min, 2 min, 29 s, respectively. The OA/PC or HPU treatments alone needed 26 min treatments to achieve the same reduction. The addition of TiO₂ (5 g/l) to HPU (sonocatalysis) did not improve E. coli O157:H7 inactivation. However, when HPU was combined with a residual concentration of PAA (3.2 mg/l), the total inactivation of E. coli O157:H7 and Salmonella (6 log unit reductions) occurred after 11 min, but for Listeria monocytogenes only 1.7 log reductions were detected after 20 min. When HPU was combined with OA/PC, a synergistic effect for the inactivation of E. coli O157:H7 was also observed, but this sanitizer significantly modified the physical-chemical quality characteristics of the RW. These results show that the residual PAA concentration that can be found in the wash water combined with HPU could result in an environmentally friendlier and toxicologically safer strategy for water reconditioning of the fresh-cut industry. The use of the sanitizer alone requires higher concentrations and/or longer contacts times. Even though the residual PAA in combination with HPU was adequate for water reconditioning, it is not appropriate for the process wash water because this wash water must be instantaneously disinfected.     

Photocatalytic TiO2 coating of plastic cutting board to prevent microbial cross-contamination

Kitchen cutting boards are one common source of microbial cross-contamination in foods. In this study, a method was developed to create an antimicrobial coating on HDPE cutting board using UV-activated TiO₂ nanoparticles (NPs). The antimicrobial efficacy of the developed coatings was tested against E. coli O157: H7 for 3 h at 0.5 ± 0.05 mW/cm² UVA light intensity. In addition, the effect of NP loading (0.0125, 0.0625, and 0.125 mg/cm²), and surface treatment of coatings by oxygen plasma for 1–15 min on the bactericidal efficacy was investigated. Further, the bactericidal efficacy of the TiO₂ coated cutting board on repeated use (i.e. 1, 2, 3 and 5 times) was also evaluated. The results showed that by increasing the NP loading from 0 to 0.125 mg/cm² has increased the log reduction from 0.37 to 1.18 CFU/cm². However, no significant difference (P > 0.05) in the reduction was observed between NP loadings at 0.0625 and 0.125 mg/cm². Oxygen plasma treatment of the coated surfaces for 5–15 min significantly increased (P ≤ 0.05) the log reduction compared to control sample without plasma treatment. Under the tested conditions, TiO₂ coating with 0.0625 mg/cm² NP loading followed by oxygen plasma treatment for 5 min was found to achieve the greatest reduction up to 2.67 log CFU/cm². Also, the coated-surfaces were found to retain the original bactericidal property even after up to 5 times washing treatment. The developed TiO₂ coating on cutting board showed promise to mitigate the risk of microbial cross-contamination by providing a stable antimicrobial activity for extended use. Plasma treatment further enhanced the bactericidal property of the developed coatings without affecting physical stability.     

Reduction of Escherichia coli O157:H7 and Salmonella enteritidis on mung bean seeds and sprouts by slightly acidic electrolyzed water

High microbial populations on mung beans and its sprouts are the primary reason of a short shelf life of these products, and potentially present pathogens may cause human illness outbreak. The efficiency for inactivating Escherichia coli O157:H7 (E. coli O157:H7) and Salmonella enteritidis (S. enteritidis), which were artificially inoculated on mung bean seeds and sprouts, by means of slightly acidic electrolyzed water (SAEW, pH 5.0 to 6.5) generated through electrolysis of a mixture of NaCl and hydrochloric acid solution in a non-membrane electrolytic chamber, was evaluated at the different available chlorine concentrations (ACCs, 20–120 mg/l) and treatment time (3–15 min), respectively. The effect of SAEW treatment on the viability of seeds was also determined. Results indicate that the ACC had more significant effect on the bactericidal activity of SAEW for reducing both pathogens on the seeds and sprouts compared to treatment time (P < 0.05). The seeds and sprouts treated with SAEW at ACCs of 20 and 80 mg/l resulted in a reduction of 1.32–1.78 log₁₀ CFU/g and 3.32–4.24 log₁₀ CFU/g for E. coli, while 1.27–1.76 log₁₀ CFU/g and 3.12–4.19 log₁₀ CFU/g for S. enteritidis, respectively. The germination percentage of mung bean seeds was not significantly affected by the treatment of SAEW at an ACC of 20 mg/l for less than 10 min (P > 0.05). The finding of this study implies that SAEW with a near-neutral pH value and low available chlorine is an effective method to reduce foodborne pathogens on seeds and sprouts with less effects on the viability of seeds.     

The bactericidal activity of acidic electrolyzed oxidizing water against Escherichia coli O157:H7, Salmonella Typhimurium,and Listeria monocytogenes on raw fish,chicken and beef surfaces

The bactericidal efficacy of acidic electrolyzed oxidizing water (AC-EW) (pH = 2.30, free chlorine = 38 ppm) and sterile distilled water (DW) on three pathogens (Escherichia coli O157:H7 Salmonella Typhimurium, and Listeria monocytogenes) inoculated on raw trout skin, chicken legs and beef meat surfaces was evaluated. The decontaminating effect of AC-EW and DW was tested for 0 (control), 1, 3, 5 and 10 min at 22 °C. AC-EW significantly (P < 0.05) reduced the three pathogens in the inoculated samples compared to the control and DW. The level of reduction ranged between ca.1.5–1.6 logs for E. coli O157:H7 and S. Typhimurium in the inoculated foods. However, AC-EW exhibited less bactericidal effect against L. monocytogenes (1.1–1.3 logs reduction). AC-EW elicited about 1.6–2.0 log reduction in the total mesophilic count. Similar treatment with DW reduced pathogens load by ca. 0.2–1.0 log reduction and total mesophiles by ca. 0.5–0.7 logs. No complete elimination of the three pathogens was obtained using AC-EW possibly because of the level of organic matter and blood moving from food samples to the AC-EW solution. This study demonstrates that AC-EW could considerably reduce common foodborne pathogens in fish, chicken and beef products.     

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.     

Resistances to UV-C irradiation of Salmonella Typhimurium and Staphylococcus aureus in wet and dried suspensions on surface with egg residues

To clarify the effects of food sediments on ultraviolet-C (254 nm) sanitation in food-related environments, we examined the resistance of pathogenic bacteria (Salmonella Typhimurium and Staphylococcus aureus) cells, in wet and dried suspensions adhered with 1.5-15% w/v egg albumen, 1.5-15% yolk or 3.0-30% whole egg solutions, against UV-C irradiation. Bacterial suspensions (0.1 ml of 8 log CFU/ml) were put on 47 mmφ glass dishes and dried at room temperature (20-24 °C) for 180 min in a bio safety cabinet with ventilation. Viable S. Typhimurium and S. aureus cells in distilled water decreased during the drying period from 7.2 to 3.2 and from 8.0 to 6.5 log CFU/dish, respectively,. On the other hand, the bacteria cells were protected from drying by egg compounds, even by the lowest concentration. The UV-C treatment (0.16 mW/cm² for 10 min) showed a clear bactericidal effect in the absence of egg compounds. However, the bactericidal effect was inhibited by 15% yolk and 30% whole egg. Results in this study suggested that the small food sediment protect bacteria on the surfaces from dryness and UV-C irradiation and it might introduce cross contamination.     

Combined effect of acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) on the microbial reduction of fresh-cut cilantro

In the present study, the disinfection efficacy on fresh-cut cilantro of the combination of strongly acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) was evaluated, in comparison with single slightly acidic electrolyzed water (SAEW) and single AcEW treatments. The populations of E. Coli O78 on inoculated cilantro treated by AlEW 5 min + AcEW 5 min, was not detected while 3.43 and 3.73 log₁₀ CFU/g in the AlEW 2.5 min + AcEW 2.5 min and AcEW 2 min + AlEW 2 min + AcEW 2 min treatments respectively. Our results implied that the bactericidal abilities of the combination of AlEW and AcEW treatments were higher than that of single AcEW and SAEW, which also was demonstrated microscopically by scanning electron microscopy (SEM). Moreover, the efficacy of combination of AcEW and AlEW in reducing natural micro flora on fresh-cut cilantro was also evaluated compared with single AcEW and SAEW. The results showed that the combination of AlEW and AcEW had stronger sterilization ability than single AcEW and SAEW. Considering the utilizations of AlEW and disinfection efficacy, we suggest that the combination of AlEW and AcEW may also be a better choice in fresh-cut produce.     

Effects of water hardness and pH on efficacy of chlorine-based sanitizers for inactivating Escherichia coli O157:H7 and Listeria monocytogenes

The effects of hardness and pH of water used to prepare electrolyzed oxidizing (EO) water and bleach solutions on the bactericidal activity of sanitizer prepared from the water were examined. EO water and bleach solutions were prepared with hard water of 0, 50, 100, and 200 mg/l as CaCO₃ at pH 5, 6, 7, and 8. Increased water hardness tended to increase free chlorine and oxidation–reduction potential (ORP) and decrease pH of EO water. Chlorine levels also increased with water pH. Water hardness and pH only had minor effect on the pH of bleach solutions. Increasing hardness to 50 mg/l increased antimicrobial effect of EO water against Escherichia coli O157:H7, but reduced when water hardness further increased to 100 mg/l or higher. Water pH had no effect on EO water produced against E. coli O157:H7. Water hardness had no significant effect on bactericidal activity of EO water against Listeria monocytogenes but elevated water pH decreased bactericidal activity of EO water produced against L. monocytogenes. Bleach solution prepared using hard water at 200 mg/l or at pH 7 or higher had significant lower efficacy in inactivating E. coli O157:H7, but had no effect on the inactivation of L. monocytogenes. Results indicate that increasing the hardness or pH of water used to prepare EO water or bleach solutions will decrease the bactericidal activity of sanitizers prepared from the water.     

Virucidal effect of high power ultrasound combined with a chemical sanitizer containing peroxyacetic acid for water reconditioning in the fresh-cut industry

The use of chlorine-based sanitizers is widespread throughout the fresh produce industry in the process water to maintain microbial safety of produce, avoid cross-contamination and recycle water. In this study, alternative disinfection technologies were investigated due to the negative reports showing chlorine instability in the presence of organic matter and the undesirable by-product residues. Tsunami^® (15.2% peroxyacetic acid and 11.2% hydrogen peroxide) and high-power ultrasound (HPU, 0.56 kW/l, 20 kHz), alone or in combination, were evaluated in lettuce process water analyzing their ability to reduce MNV during either produce washing or water recycling. PAA concentrations of 6.4, 12.8 and 16 mg/l as well as HPU were insufficient for application in the produce washing tank where a rapid MNV inactivation is required. In contrast, a complete rapid inactivation of MNV (7.4 log TCID₅₀) was recorded when 80 mg/l of PAA was used. For recycled water reconditioning, HPU was applied and no virus reduction was observed. Two PAA concentrations (6.4 and 12.8 mg/l) that can be found in the recycled water were also tested. The MNV inactivation was faster at 12.8 mg/l than at 6.4 mg/l of PAA with 2.6 and 2 log reductions after 20 min contact. One additional log reduction was achieved 20 and 40 min later, respectively. MNV inactivation fitted the Bipashic model well. A contact time of 95 and 115 min would be required to obtain the complete elimination of MNV (4.4 log TCID₅₀) by 6.4 and 12.8 mg/l of PAA. PAA efficacy was not enhanced by the combination with HPU in contrast to the inactivation of pathogenic bacteria tested in other studies. This indicates that viruses are more resistant to this hurdle technology than pathogenic bacteria such as Escherichia coli O157:H7, Salmonella and other HPU conditions such as higher frequencies and combination of HPU with other physical treatments need to be explored.     

High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris spores in orange juice

The spoilage of high acid fruit juices and nectars by Alicyclobacillus acidoterrestris is a major concern to juice manufacturers around the world since it is difficult to detect. In this study, thermosonication (ultrasound and heat, TS) and thermal inactivation of A. acidoterrestris spores in pretreated orange juice were carried out and resistance parameters were estimated. First, the effect of TS acoustic energy density (AED, 0.3–20.2 W/mL) on the inactivation at 75 °C was investigated. Then, the influence of TS temperature (70–78 °C) on the spore inactivation (AED = 20.2 W/mL) was studied. Next, we explored the effect of high pressure processing (HPP) pretreatment of juice on the 20.2 W/mL TS inactivation at the best temperature (78 °C). Lastly, the thermal inactivation of spores in juice heat shocked + 1 min sonicated vs. untreated juice was also investigated.Results of TS showed higher spore inactivation for higher AED (D_75°C-value of 49 min for 20.2 W/mL vs. 217 min for 0.33 W/mL). Lower D-values were obtained at higher temperatures (D_78°C-value of 28 min vs. D_70°C-value of 139 min at 20.2 W/mL). The TS D_78°C-value (at 20.2 W/mL) decreased further from 28 min to 14 min when the orange juice was previously submitted to 600 MPa for 15 min. Thermal treatment alone at 78 °C resulted in almost no spore inactivation, whereas the heat shock + ultrasound pretreatment of juice enhanced the thermal inactivation of spores (D_85°C-value decreased from 69 to 29 min). To conclude, HPP-assisted TS provided the best method for spore inactivation, indicating the benefit of high pressure and power ultrasound technology in addition to heat. TS required at least 8 °C lower temperatures than thermal treatments to achieve the same spore inactivation, which could enhance juice quality and energy savings.     

Modelling the shelf-life of minimally-processed fresh-cut apples packaged in a modified atmosphere using food quality parameters

The objective of the present study was to determine the shelf-life of minimally-processed fresh-cut apples treated with anti-browning agents under modified atmosphere packaging. Shelf-life is calculated by application of mathematical models with product quality attributes such as: pH; soluble solids content (SSC); CIELab color parameters; sensory evaluation; and microbial spoilage (Salmonella spp., Staphylococcus aureus, Sulfite-Reducing Clostridium, Enterobacteriacae, Escherichia coli, Aerobic mesophilic bacteria (AMB), yeast, mold, Listeria monocytogenes). Golden Delicious and Cripps Pink apple cultivars were individually treated with one of several anti-browning treatments and packaged in a modified atmosphere (N₂ = 90.5%; CO₂ = 2.5%; O₂ = 7%), and stored at 4 °C. The treatments were; 1) non-treated (control); 2) dipping in a mixture of ascorbic and citric acids for 3 min with and without ultrasound (40 kHz, 3 min) treatment; and 3) Ca-ascorbate with/without ultrasound (40 kHz, 3 min) treatment. Results revealed that Cripps Pink was the most suitable variety for minimally-processed fresh-cut product. All the investigated treatments were equally effective in improving the quality of the product compared to the control. Shelf-life predictive models were developed based on the following quality attributes: apple cultivar, anti-browning treatment, color parameters, sensory evaluation, pH, and SSC. Maximum growth rates for Enterobacteriacae and Aerobic mesophilic bacteria were 0.25 ± 0.02 log CFU/g/day and 0.46 ± 0.02 log CFU/g/day, respectively. In order to optimize fresh-cut production, these models can be useful tool for predicting the longest shelf-life time with monitoring microbial activity during production. All models are freely available on-line (“Anti-browning Apple Calculator – C.A.P.P.A.B.L.E.^©”; apple.pbf.hr or 31.147.204.87).     

Antimicrobial efficacy of vacuum impregnation washing with malic acid applied to whole paprika,carrots, king oyster mushrooms and muskmelons

Antimicrobial effect of vacuum impregnation (VI) applied to organic acid washing against Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on paprika fruit, carrots, king oyster mushrooms and muskmelons was investigated. Samples were treated with intermittent VI with 21.3 kPa and compared with dipping washing in 2% malic acid. The initial sample pathogen levels were approximately 10⁵–10⁷ CFU/cm². Enumerations of the three pathogens on paprika and carrots treated with VI washing were reduced to below the detection limit (= 1 log₁₀ CFU/cm²) after 3–5 min and 15–20 min, respectively. For each time point where populations of the three pathogens were reduced to below the detection limit by VI treatment, populations of 1.2–1.9 log CFU/cm² and 2.5 to 2.8 log CFU/cm² survived on paprika and carrots, respectively, when subjected to dipping treatment. After 20 min of dipping treatment, surviving populations of the three pathogens ranged from 3.5 to 4.1 and 3.3 to 4.4 log CFU/cm² on king oyster mushrooms and muskmelons, respectively. After 20 min of VI treatment, surviving populations of the three pathogens ranged from 3.0 to 3.6 log and 3.1 to 4.1 log CFU/cm², respectively, on king oyster mushrooms and muskmelons. Additionally, there were no significant (P ≥ 0.05) differences in pathogen reductions between dipping and VI treatment for both king oyster mushrooms and muskmelons. King oyster mushrooms (R_a = 6.02 ± 1.65 μm) and muskmelons (R_a = 11.43 ± 1.68 μm) had relatively large roughness values compared to those of paprika (R_a = 0.60 ± 0.10 μm) and carrots (R_a = 2.51 ± 0.50 μm). Scanning electron photomicrographs showed many deep protected sites in king oyster mushrooms and muskmelons with many microbes located deep in these sites following VI treatment. Instrumental color, texture and titratable acidity values of paprika and carrots subjected to VI washing treatment with 2% malic acid for 5 and 20 min were not significantly (P ≥ 0.05) different from those of untreated control samples during 7 day storage.     

Effects of high hydrostatic pressure on the inactivation of norovirus and quality of cabbage Kimchi

In Korea, cabbage Kimchi is potentially regarded as a high-risk food with respect to enteric norovirus (NoV). This study investigated the effect of high hydrostatic pressure (HPP) treatment (100–500 MPa for 5 min at room temperature) on the inactivation of murine norovirus-1 (MNV-1, initial inoculum of 5–6 log₁₀ PFU/ml) as a human NoV surrogate in the Kimchi. The effects of HHP treatment on the microbiological, physicochemical properties and sensory qualities of cabbage Kimchi were also examined. The MNV-1 in the Kimchi after 100, 200, 300, and 400 MPa were 5.6 (0.1 log reduction), 5.5 (0.2 log reduction), 5.4 (0.3 log reduction), and 4.2 (1.5 log₁₀ PFU/ml), respectively. Complete inactivation of MNV-1 was determined in the cabbage Kimchi by 500 MPa. One-log reduction of total aerobic bacteria and lactic acid bacteria was only determined in the 500 MPa HHP treated Kimchi. The pH values and acidity (%) in all HPP treated Kimchi were 4.4–5.7 and 0.4–0.7%, respectively. The Hunter colors ‘a’ (redness) and ‘b’ (yellowness) and mechanical texture (hardness) in HHP Kimchi were not different between 0 MPa and HHP (100–500 MPa) treated Kimchi significantly (P > 0.05) different although the HHP treated Kimchi turned to very slight darkness. All sensory scores in HHP treated Kimchi were determined as > 5 point (like) in 7 point-hedonic scale. The current study suggest that 500 MPa for 5 min could potentially be used for direct application in commercial Kimchi processing and distribution for complete MNV-1 inactivation without causing any deleterious overall quality changes.     

Combination effects of ultrasound and citral nanoemulsion against Shigella flexneri and the preservation effect on fresh-cut carrots

This present study evaluated the effect of ultrasound (US), citral nanoemulsion (CLON) and combined treatments on the inactivate effectiveness of Shigella flexneri in phosphate-buffered saline (PBS) and on the surface of fresh-cut carrots. In this study, CLON was produced by ultrasonic nanoemulsification. Results demonstrated that US + CLON treatment significantly (P < 0.05) improved the bactericidal effect against Sh. flexneri, especially 0.15 mg/mL of CLON combined with US (20 kHz, 345 W/cm²) treatment for 9 min decreased the number of Sh. flexneri by 8.55 log CFU/mL. The assay of reactive oxygen species (ROS) and malondialdehyde (MDA) levels indicated that US + CLON aggravated oxidative stress and lipid peroxidation in cell membranes. The leakage of cell constituents (proteins and nucleotide) demonstrated that the permeability and integrity of the cell membrane was significantly (P < 0.05) impaired. Field-emission scanning electron microscopy further showed that US + CLON exacerbates the disruption of the bacteria morphology. Confocal laser scanning microscopic and flow cytometry observed US + CLON treatment enhanced the changes of bacterial cell membrane integrity. Meanwhile, US + CLON was effective in reducing the presence of bacteria on the surface of fresh-cut carrots, and had no negative effects on the quality of fresh-cut carrots in terms of colour, hardness and weight during storage. Overall, this present study revealed ultrasound combined with CLON is a promising and viable cleaning method for improving the microbiological safety of fresh produce.     

Thermal inactivation of Salmonella Typhimurium on dressed chicken skin previously exposed to acidified sodium chlorite or carvacrol

Salmonella is a leading cause of foodborne illness and live poultry is a main reservoir of this pathogen, worldwide. Cross-contamination and transportation of contaminated poultry meat act as an important vehicle of Salmonella infections in humans. In this study, we assessed the effect of two antimicrobials; acidified sodium chlorite (ASC) and carvacrol followed by thermal treatment to inactivate Salmonella Typhimurium on dressed chicken skin. D-values (time in min for the pathogen to decrease by 90%) of Salmonella Typhimurium at 56, 60 and 64 °C on dressed chicken skin in the control samples, determined by linear regression, were 6.17, 3.16, 1.32 min, respectively. Two D-values calculated using a logistic model, ranged from 6.28 (D_1, major population, plus T_L) and 11.66 (D_2, heat-resistant subpopulation, plus T_L) min at 56 °C to 1.08 (D₁ plus T_L), and 2.07 (D₂ plus T_L) min at 64 °C. Pre-dipping in 100–300 ppm ASC or 0.02–0.06% carvacrol rendered the pathogen more sensitive to the lethal effect of heat. Thus, combination of antimicrobials with thermal inactivation was more effective in reducing heat resistance of the pathogen on dressed chicken surface. The model developed will assist poultry processors in estimating the time required for specific log reductions of Salmonella Typhimurium on chicken skin and thus, will contribute in designing acceptance limits at critical control points for chicken skins at lower times and temperatures for cooking.     

Reference organism selection for microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm

This study identified a reference organism for the establishment of microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm. Three different, predominant spoilage bacteria were isolated from spoiled liquid endosperm and identified through 16S rDNA sequencing, prior to propagation and eventual challenge studies. Basic Local Alignment Search Tool comparisons revealed that the isolated spoilage bacteria were Klebsiella sp., Staphylococcus sp., and Kluyvera sp (%Identity 97.34–97.82%). The isolates were propagated to mid-stationary growth phase (17 h) and thereafter suspended in liquid endosperm. The inactivation rates of the spoilage isolates in liquid endosperm subjected to plasma jet at 450 and 650 W input power settings were determined and compared to those of pathogens Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. Inactivation rates of all test organisms at 450 W (2.76–5.98 min) were significantly less (p < 0.05) than those at 650 W (1.86–3.11 min). In both power settings, S. enterica exhibited the significantly (p < 0.05) greatest resistance towards plasma treatment, while Staphylococcus sp. exhibited the least. Heat penetration studies in both power settings revealed that the temperature of the liquid endosperm did not significantly increase and did not reach bactericidal ranges (<30 °C) during plasma jet treatment, hence the observed inactivation were attributed to antimicrobial species generated by the plasma. Optical emission spectroscopy revealed that these antimicrobial species included atomic oxygen (777.41 and 844.67 nm) and ultraviolet radiation (200–280 nm). Thus, this study determined S. enterica as an appropriate target organism for the establishment of plasma jet process for coconut liquid endosperm, the inactivation rate of which shall be soon established in higher scale treatment process.     

Sublethal injury and recovery of Escherichia coli O157:H7 by high pressure carbon dioxide

A study was carried out to investigate possible sublethal injury caused by high pressure carbon dioxide (HPCD) to Escherichia coli O157:H7 suspended in phosphate-buffered saline (PBS, pH 7.00). The treatment pressure was 5 MPa, treatment temperatures were 25–37 °C and treatment time was 5–70 min. Only 1.21 log₁₀ cycles reduction was obtained in the nonselective medium, while a higher reduction of 5.18 log₁₀ cycles was obtained in the selective medium after treatment at 5 MPa and 25 °C for 50 min, indicating HPCD could induce sublethal injury of E. coli cells and these cells could not recover in the selective medium. The proportion of the sublethally injured E. coli cells in the survivors increased dramatically up to 72.4% with increasing the treatment time from 20 min to 30 min by HPCD at 5 MPa and 25 °C, and this proportion increased gradually with increasing the treatment time, up to 100% at 5 MPa and 25 °C for 60 min. The effect of recovery media, inhibitors of specific metabolic processes, Mg and Ca cations on the recovery of the sublethally injured cells was also investigated. When PBS, peptone water, tryptic soy broth (TSB) and carrot juice were used as recovery media, the maximum repair rate of the sublethally injured cells was found in TSB and the minimum was in PBS. The addition of inhibitors such as sodium azide, chloramphenicol, rifampicin and penicillin G showed that repair of most sublethally injured cells required energy, protein and RNA synthesis, but was not dependent on peptidoglycan synthesis. Moreover, Mg and Ca cations were also needed in the repair.     

Evaluation of electrolyzed water as cleaning and disinfection agent on stainless steel as a model surface in the dairy industry

In the dairy industry, cleaning and disinfection of surfaces are important issues and development of innovative strategies may improve food safety. This study was aimed to optimize the combined effect of alkaline electrolyzed water (AEW) and neutral electrolyzed water (NEW) as alternative cleaning and disinfection procedure on stainless steel plates (SSP) with and without electropolishing. NEW at 10 ppm total available chlorine (TAC), achieved a ˃5 log CFU/mL reduction of milk spoilage bacterial suspension, grown in trypticase soy broth (8.7 log CFU/mL of each bacterial strain: Pseudomonas aeruginosa, Enterococcus faecalis and Micrococcus luteus) contacted for 30 s. An optimal design of experiments was used to assess the combined effect of cleaning with AEW, followed by disinfection with NEW (40 ppm TAC, contact time 3 min). Tested factors were contact time (10, 20 and 30 min), concentration of AEW (100, 200 and 300 mg NaOH/L), temperature (30, 40 and 50 °C), and surface type (304-2B SSP with or without electropolishing), using sixteen treatments with two replicates. The response variable was bacterial cells removal (log CFU/cm²). All main effects, two factors interactions and a quadratic term significantly influenced cells removal, and were modeled using a second order polynomial. Best cleaning procedures were significantly affected by surface roughness; electropolished SSP required 10 min, 100 mg/L AEW at 30 °C, whereas SSP without modification required 30 min, 300 mg/L AEW at 30 °C. From confirmatory tests cells removed were 3.90 ± 0.25 log CFU/cm² for electropolished SSP, and 3.20 ± 0.20 log CFU/cm² for SSP without modification. NEW is non-corrosive, and can be advantageously used for environmentally friendly cleaning and disinfection processes.     

Combining basic electrolyzed water pretreatment and mild heat greatly enhanced the efficacy of acidic electrolyzed water against Vibrio parahaemolyticus on shrimp

The objective of this study was to investigate the efficacy of acidic electrolyzed water (AEW) against Vibrio parahaemolyticus on shrimp. The shrimp was initially inoculated with V. parahaemolyticus(7-8 log CFU/g), and treated with AEW (AEW1 containing 51 mg/L of chlorine or AEW2 containing 78 mg/L of chlorine) or organic acids (2% AA and 2%LA) for 1 min or 5 min under different treated conditions. The effect of AEW was better than that of organic acids, the number of survival V. parahaemolyticus cells on shrimp was reduced by 0.9 log CFU/g after treatment for 5 min with AEW without vibration, while 1.0 log CFU/g bacteria cells reduced with vibration. No significant difference (p > 0.05) was observed between AEW and organic acids in the bactericidal activity with or without vibration. The effective order of temperatures on bactericidal activities of AEW was 50 °C > 20 °C > 4 °C, and a 3.1 log CFU/g reduction of V. parahaemolyticus cells on shrimp was detected with treatment of AEW at 50 °C. Mild heat greatly enhanced efficacy of electrolyzed water against V. parahaemolyticus. Basic electrolyzed water (BEW) (50 °C) pretreatment combined with AEW (50 °C) treatment remarkably reduced bacterial cells by 5.4 log CFU/g on shrimp after treatment for 5 min. There was a significant change in physicochemical properties (pH, ORP, ACC) of AEW, after it was used to wash shrimp (P < 0.05). This study suggests that BEW (50 °C) pretreatment followed by AEW (50 °C) treatment could be a possible method to effectively control V. parahaemolyticus contamination on shrimp.