Inactivation of Bacillus subtilis spores on the surface of small spheres by dielectric barrier discharge (DBD) using relatively low AC high voltage (<10 kV0-p) for practical applications in the ...sterilization of small dried food was investigated. In this study the 6 and 10 mm gap distances were employed to place small dried foods inside the DBD, but a gap distance of more than 3 mm generally did not generate DBD at this applied voltage and atmospheric pressure. Therefore, the pressure was reduced to generate DBD and the relationship between discharge area rate and pressure was investigated using discharge area rate as the index. Low-pressure DBD (LPDBD) at 6 and 10 mm gap distances showed the maximum discharge area rates of 28% and 25% at 50 and 30 kPa, respectively. After 4 min treatment, B. subtilis spores on the surface of glass beads as the model of a small dried food were inactivated and the survival ratio decreased to 3.6 × 10−4 after the LPDBD treatment at 10 mm gap distance, and no viable cells were detected after the LPDBD treatment at 6 mm gap distance. Moreover, the humidification of the atmosphere was effective in improving the inactivation efficiency of LPDBD treatment, with which, B. subtilis spores were inactivated within 2 min of LPDBD treatment at 6 mm gap distance.
•Reducing the pressure allowed the generation of DBD in 6 and 10 mm gap distances using AC 10 kV0-p.•The relationship between the discharge area rate of PLDBD and pressure was concave down.•PLDBD treatment inactivated B. subtilis spores on the surface of glass beads.•The contribution of ozone produced by PLDBD to the inactivation of B. subtilis spores was small.•PLDBD treatment in humidified atmosphere inactivated B. subtilis spores within 2 min.
The engineering of pulsed electric field (PEF) reactors using carbon materials as the electrode was carried out to fundamentally eliminate the concern about the release of metallic ions into the ...treatment solution. PEF treatment using carbon cloth with a textile structure showed a strong inactivation effect on the inactivation Escherichia coli in a batch-type reactor. We also developed two continuous-flow-type PEF reactors: one allowed the treatment solution to flow parallel and the other perpendicular to the surface of the electrode. When the two reactors were compared, the latter showed higher sterilization capability. The effects of decreasing the flow rate of the treatment solution and increasing the electric field intensity on the inactivation of E. coli by PEF treatment were investigated. Although both improved the E. coli inactivation efficiency, the latter showed higher inactivation efficiency and a smaller increase in the temperature of the treatment solution. From the viewpoint of engineering for the pasteurization of liquid food, increasing the electric field intensity was more effective in the PEF treatment than decreasing the flow rate of the treatment solution. The continuous-flow-type PEF reactor with the carbon cloth electrode was applied to the pasteurization of sake, and although the sake yeast and Lactobacillus homohiochii in the sake were not inactivated to undetectable levels, they were significantly inactivated by continuous-flow PEF treatment.
•PEF treatment using carbon cloth as the electrode showed a strong inactivation effect.•A cross-flow reactor showed higher inactivation efficiency than a parallel-flow reactor.•Increasing the electric field intensity was effective for obtaining high inactivation efficiency.•Sake yeast and L. homohiochii in sake were significantly inactivated by continuous-flow PEF treatment.
In this study, a rotating nonthermal plasma (NTP) reactor was designed and its practical use for the inactivation of microorganisms on dried granular agricultural products such as black pepper was ...investigated. As the target microorganism to inactivate in the rotating NTP reactor, Aspergillus spores were artificially inoculated on whole black peppers. Inactivation treatments were carried out under several conditions. Rotating the NTP reactor facilitated the inactivation of the Aspergillus spores on the whole black peppers, and a decrease in the survival ratio of three orders (3 Log) was achieved after 4 min treatment. Using humidified gases for inactivation treatment in the rotating NTP reactor also facilitated the inactivation of the Aspergillus spores on the whole black peppers, and no viable spores of Aspergillus sp. were detected after 4 min treatment. The quality of the NTP- and dry-heat-treated whole black peppers was compared with that of untreated peppers in terms of the piperine content and antioxidative activity. The piperine contents of the NTP- and dry-heat-treated black peppers showed no significant difference, but the antioxidative activity in the NTP-treated peppers was higher than that in the dry-heat-treated peppers.
•A rotating non-thermal plasma (NTP) reactor was constructed and applied to the inactivation of Aspergillus sp. spores.•Rotating the NTP treatment reactor improved the inactivation efficiency of Aspergillus sp. spores.•The NTP treatment using humidified gases also enhanced the inactivation of Aspergillus sp. spores.•The antioxidative activity in NTP-treated whole black peppers remained relatively unaffected by the treatment.
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Adsorption and desorption behavior of chymotrypsinogen A (CTRA), cytochrome c (cyt c) and lysozyme (LYZ) on potassium cation types of zeolite L (K-LTL) and ferrierite (K-FER) was ...investigated. K-FER with SiO2/Al2O3 ratio of 17.7 exhibited better protein adsorption ability than K-LTL with SiO2/Al2O3 ratio of 6.0. The adsorption of proteins on zeolites took place rapidly, and more than 80% of the applied proteins were adsorbed within 30min. The proteins tightly adsorb on zeolites because most of the adsorbed proteins were retained on zeolites after washings. Recovery of proteins adsorbed on zeolites was examined by using various concentrations of KCl solutions. In the presence of 1M KCl, more than 90% of CTRA and cyt c, and 100% of LYZ were recovered from K-LTL. The recovery rates of the proteins from K-FER were entirely low. This difference between the two zeolites would be due to that basic amino acid residues of the proteins electrostatically interacting with negative charges in the pores of K-FER are difficult to be exchanged with K+ cations in the KCl solution because the pores of K-FER are much smaller in size than those of K-LTL. We also confirmed that CTRA recovered from K-LTL retained 84% of the initial activity. Zeolites have the potential as the cation exchange adsorbent of proteins.
The agricultural fungicide procymidone can cause external genitalia abnormalities in rats but not monkeys or rabbits. To investigate the relevance of developmental findings in rats to humans, we ...conducted in vitro plasma protein binding studies, in vitro metabolism (biotransformation) studies using liver S9 fractions and hepatocytes, and in vivo metabolism and excretion studies using chimeric mice with humanized hepatocytes. On the basis of these results, we concluded that the metabolic and excretion profiles of procymidone in humans are similar to those in monkeys and rabbits but differ from those in rats. From the findings of this and previous studies, we judge the developmental toxicity potential of procymidone to be very low in humans.
Disinfection and sterilization against cold-tolerant microorganisms are very important for enhancing food safety and hygiene management under refrigeration conditions. We isolated Exiguobacterium sp. ...and Pantoea sp. from an immersion solution of packed tofu and evaluated their growth properties and sensitivities to various bactericidal methods. These microorganisms were classified as psychrotrophic bacteria, according to their ability to grow at 4 °C, with an optimum growth temperature of 30 °C. Exiguobacterium sp. and Pantoea sp. were more sensitive to heat and sodium hypochlorite than Escherichia coli (E. coli). Exiguobacterium sp. was sensitive to acetic acid and citric acid, while Pantoea sp. was relatively insensitive and E. coli was insensitive to these organic acids. All microorganisms used in this study were resistant to sodium hydroxide solution (pH 8.00). Exiguobacterium sp. showed resistance to ozonated water and UV; therefore, particular attention should be paid to the contamination of this microorganism in food factories. Both Exiguobacterium sp. and Pantoea sp. were inactivated by pulsed electric field (PEF) treatment that did not cause lethal damage to E. coli. The results obtained in this study suggest that the bactericidal methods targeting the fragile cell membrane with high permeability are effective for the inactivation of cold-tolerant microorganisms.
To estimate the metabolic profile of trans-permethrin in humans, a comparison of the in vitro metabolism of trans-permethrin in humans and rats was conducted using hepatic microsomes, and cytochrome ...P450 and UDP-glucuronyltransferase isoforms, which catalyze the metabolism of 3-phenoxybenzyl alcohol (PBalc) and 3-phenoxybenzoic acid (PBacid), respectively. In humans and rats, the major metabolic reaction of trans-permethrin in microsomal incubations was the cleavage of ester linkage to give PBalc, followed by oxidation to 4'-OH-PBalc, 4'-OH-PBacid, and PBacid. As to 4'-hydroxylation of PBalc, several CYPs were able to catalyze the reaction, and CYP2E1 was identified as a predominant isoform. PBacid and its conjugates (glucuronide and glycine) are major urinary metabolites of trans-permethrin in mammals. PBacid is also a metabolite of several pyrethroids, and has been used as a biomarker of human exposure to pyrethroids. Our study indicated that there was no difference in glucuronyltransferase activity of PBacid between humans and rats, and that only UGT1A9 can catalyze the glucuronidation of PBacid among human UGTs. Some UGT1A9 variants are known to have poor glucuronidation activity. From these results, it was assumed that deficiency or polymorphism of UGT1A9 might affect the profile of PBacid and its conjugates in urine collected from persons exposed to trans-permethrin or other pyrethroids. These results are helpful for understanding the metabolism of trans-permethrin in humans and determining methods for quantification of target analytes for assessment of human exposure to trans-permethrin and other pyrethroids that give PBacid and its conjugates as urinary metabolites.
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The metabolites of tebufenozide, a model compound, formed by the yeast-expressed human CYP3A4 and CYP2C19 were identified to clarify the substrate recognition mechanism of the human ...cytochrome P450 (CYP) isozymes. We then determined whether tebufenozide metabolites may be predicted in silico. Hydrogen abstraction energies were calculated with the density functional theory method B3LYP/6-31G∗. A docking simulation was performed using FRED software. Several alkyl sites of tebufenozide were hydroxylated by CYP3A4 whereas only one site was modified by CYP2C19. The accessibility of each site of tebufenozide to the reaction center of CYP enzymes and the susceptibility of each hydrogen atom for metabolism by CYP enzymes were evaluated by a docking simulation and hydrogen abstraction energy estimation, respectively.
Zeolites adsorb microbial cells on their surfaces and selective adsorption for specific microorganisms was seen with certain zeolites. Tests for the adsorption ability of zeolites were conducted ...using various established microbial cell lines. Specific cell lines were shown to selectively absorb to certain zeolites, species to species.
In order to understand the selectivity of adsorption, we tested adsorption under various pH conditions and determined the zeta-potentials of zeolites and cells. The adsorption of some cell lines depended on the pH, and some microorganisms were preferentially adsorbed at acidic pH. The values of zeta-potentials were used for calculating the electric double layer interaction energy between zeolites and microbial cells. There was a correlation between the experimental adsorption results and the interaction energy. Moreover, we evaluated the surface hydrophobicity of bacterial cells by using the microbial adherence to hydrocarbon (MATH) assay. In addition, we also applied this method for zeolites to quantify relative surface hydrophobicity. As a result, we found a correlation between the adsorption results and the hydrophobicity of bacterial cells and zeolites. These results suggested that adsorption could be explained mainly by electric double layer interactions and hydrophobic interactions.
Finally, by using the zeolites Na-BEA and H-Y, we succeeded in clearly separating three representative microbes from a mixture of
Escherichia coli,
Bacillus subtilis and
Staphylococcus aureus. Zeolites could adsorb each of the bacterial cell species with high selectivity even from a mixed suspension. Zeolites can therefore be used as effective carrier materials to provide an easy, rapid and accurate method for cell separation.
A pulsed electric field (PEF) reactor that has two flow paths separated by a membrane was constructed for sake pasteurization. The treatment and cooling solutions were supplied to the flow paths in ...contact with a ground electrode and a high-voltage electrode, respectively. The characteristics of microbial inactivation in the continuous operation of the novel PEF treatment were investigated using the NaCl solution containing Escherichia coli as the model treatment solution and the NaCl solution as the cooling solution. The effects of the flow rate of the cooling and treatment solutions on the microbial inactivation efficiency and temperature of the treatment solution were investigated. In the PEF treatment at two different treatment solution flow rates, the lower flow rate could achieve effective inactivation, and the temperatures of the treatment solutions after PEF treatment were almost the same. Increasing the cooling solution flow rate was effective in preventing the increase in the temperature of the treatment solution during PEF treatment, but the temperature of the treatment solution remained at around 28 °C when the flow rate was increased. The effects of the electrical conductivity of the cooling solution on the microbial inactivation efficiency and temperature of the treatment solution were also investigated. It was demonstrated that increasing the electrical conductivity of the cooling solution increased not only the inactivation efficiency but also the temperature of the treatment solution after the PEF treatment, and determining the appropriate electrical conductivity of the cooling solution is essential for effective pasteurization. Finally, pasteurization of sake with the reactor using the obtained appropriate electrical conductivity and flow rate of cooling solution was demonstrated. The sake yeast and Lactobacillus homohiochii in sake were fully inactivated by PEF treatment, and the temperature of sake after PEF treatment was maintained below 40 °C.
•Cooling through a membrane was effective in controlling the temperature of sake.•The electrical conductivity of the cooling solution affected the inactivation efficiency.•Microorganisms in sake were completely inactivated by PEF treatment.•The temperature of sake after pasteurization by PEF was below 40 °C.
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