Combined effects of chlorine dioxide, drying, and dry heat treatments in inactivating microorganisms on radish seeds

Bang, J.,Kim, H.,Kim, H.,Beuchat, L.R.,Ryu, J.H. Academic Press 2011 FOOD MICROBIOLOGY Vol.28 No.1

We determined the combined effectiveness of ClO<SUB>2</SUB> (200 and 500 μg/ml, 5 min), air drying [25 <SUP>o</SUP>C, 40% relative humidity (RH), 2 h], and mild dry heat (55 <SUP>o</SUP>C, 23% RH, up to 48 h) treatments in killing total aerobic bacteria (TAB), Escherichia coli O157:H7, and molds and yeasts (MY) on radish seeds. A 5.1-log reduction in the number of TAB was achieved on radish seeds treated with 200 or 500 μg/ml ClO<SUB>2</SUB> followed by air drying for 2 h and dry heat treatment for 48 h or 24 h, respectively. When radish seeds were treated with 200 and 500 μg/ml ClO<SUB>2</SUB>, air dried, and heat treated for 12 h and 6 h, respectively, the initial population of E. coli O157:H7 (5.6 log CFU/g) on seeds was reduced to an undetectable level (<0.8 log CFU/g). However, the pathogen was detected in 5-day-old sprouts. The reduction of MY (1.2-1.0 log CFU/g) on radish seeds under similar experimental conditions was not changed significantly during subsequent heat treatment up to 48 h. Results show that treating radish seeds with 500 μg/ml ClO<SUB>2</SUB>, followed by air dried at 25 <SUP>o</SUP>C for 2 h and heat treatment at 55 <SUP>o</SUP>C for 36 h achieved a >5-log CFU/g reduction of TAB and E. coli O157:H7. These observations will be useful when developing effective strategies and practices to enhance the microbiological safety of radish sprouts.

Survival and colonization of <i>Escherichia coli</i> O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity

Choi, S.,Bang, J.,Kim, H.,Beuchat, L.R.,Ryu, J.‐,H Blackwell Publishing Ltd 2011 Journal of applied microbiology Vol.111 No.6

<P><B>Abstract</B></P><P><B>Aims: </B> To determine survival and colonization of <I>Escherichia coli</I> O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity (r.h.).</P><P><B>Methods and Results: </B> Spinach leaves were inoculated with suspensions of <I>E.?coli</I> O157:H7 in distilled water (DW) and 0·1% peptone water (PW) and incubated at 4, 12 and 25°C and 43, 85 and 100% r.h. The number of <I>E.?coli</I> O157:H7 on leaves (5·6 or 1·9 log CFU per leaf) inoculated using DW as a carrier medium increased significantly at 25°C and 100% r.h. within 120 h but remained constant or decreased significantly under other test conditions. <I>E.?coli</I> O157:H7 on leaves (5·4 log CFU per leaf) inoculated using PW as a carrier increased significantly within 72 and 24 h, respectively, at 12 or 25°C and 100% r.h.; counts using a low inoculum (2·2 log CFU per leaf) increased significantly within 24 h at 25°C.</P><P><B>Conclusions: </B> <I>Escherichia coli</I> O157:H7 can colonize on spinach leaves at 12 or 25°C in a 100% r.h. environment. Organic matter in the inoculum carrier may provide protection and nutrients which enhance survival and colonization.</P><P><B>Significance and Impact of the Study: </B> Colonization of <I>E.?coli</I> O157:H7 on spinach leaves as affected by organic matter in the inoculum, temperature and r.h. was determined. These observations will be useful when developing strategies to prevent growth of <I>E.?coli</I> O157:H7 on pre‐ and postharvest spinach.</P>

Pathogenesis of Enterohemorrhagic <i>Escherichia coli</i> O157:H7 is mediated by the cytochrome P450 family in <i>Caenorhabditis elegans</i> animal model

Ryu, S.,Oh, S.,Park, M.R.,Lee, W.J.,Yun, B.,Choi, H.J.,Oh, M.H.,Oh, N.S.,Song, M.H.,Kim, Y. BUTTERWORTH-HEINEMANN 2019 FOOD CONTROL Vol.103 No.-

<P><B>Abstract</B></P> <P>Foodborne pathogens, including enterohemorrhagic <I>Escherichia coli</I> (EHEC) O157:H7, may enter from the farm environment and foods via several different vectors and influence human health. Here, we employed <I>Caenorhabditis elegans</I> as a host model system and compared specific host responses during EHEC O157:H7 infection using whole-transcriptome analysis. To elucidate the immune pathways stimulated by EHEC O157:H7, we employed quantitative real-time polymerase chain reaction (qRT-PCR), transgenic worms, and RNAi. Whole-transcriptome analysis revealed that genes encoding the cytochrome P450 (CYP450) family were induced more than 10-fold during EHEC O157:H7 infection in <I>C. elegans</I> host models. Importantly, <I>C. elegans</I> mutants lacking CYP450 genes were highly susceptible to EHEC O157:H7 infection compared with wild-type N2 worms. Consistent with susceptibility tests, qRT-PCR results indicated that CYP450 loss-of-function mutations significantly affected the transcriptional induction of antimicrobial peptide genes, such as <I>clec-60</I>. Together, our results provide critical insights into host strategies for avoiding EHEC O157:H7 pathogenesis in the gastrointestinal tract via the cytochrome P450 family and highlights potential molecular targets for preventing the virulence of EHEC O157:H7 in foods.</P>

Coumarins reduce biofilm formation and the virulence of Escherichia coli O157:H7

Lee, J.H.,Kim, Y.G.,Cho, H.S.,Ryu, S.Y.,Cho, M.H.,Lee, J. G. Fischer 2014 Phytomedicine Vol.21 No.8

E. coli O157:H7 is the most common cause of hemorrhagic colitis, and no effective therapy exists for E. coli O157:H7 infection. Biofilm formation is closely related to E. coli O157:H7 infection and constitutes a mechanism of antimicrobial resistance. Hence, the antibiofilm or antivirulence approach provides an alternative to antibiotic strategies. Coumarin and its derivatives have a broad range of biological effects, and in this study, the antibiofilm activities of nine coumarins were investigated against E. coli O157:H7. Coumarin or umbelliferone at 50μg/ml was found to inhibit biofilm E. coli O157:H7 formation by more than 80% without affecting bacterial growth. Transcriptional analysis showed that coumarins repressed curli genes and motility genes in E. coli O157:H7, and these findings were in-line with observed reductions in fimbriae production, swarming motility, and biofilm formation. In addition, esculetin repressed Shiga-like toxin gene stx2 in E. coli O157:H7 and attenuated its virulence in vivo in the nematode Caenorhabditis elegans. These findings show that coumarins have potential use in antivirulence strategies against persistent E. coli O157:H7 infection.

Sanitizing radish seeds by simultaneous treatments with gaseous chlorine dioxide, high relative humidity, and mild heat

Bang, J.,Choi, M.,Son, H.,Beuchat, L.R.,Kim, Y.,Kim, H.,Ryu, J.H. Elsevier Science Publishers 2016 International journal of food microbiology Vol.237 No.-

<P>Sanitizing radish seeds intended for edible sprout production was achieved by applying simultaneous treatments with gaseous chlorine dioxide (ClO2), high relative humidity (RH, 100%), and mild heat (55 degrees C). Gaseous ClO2 was produced from aqueous ClO2 (0.66 ml) by mixing sulfuric acid (5% w/v) with sodium chlorite (10 mg/mL) in a sealed container (1.8 L). Greater amounts of gaseous ClO2 were measured at 23% RH (144 ppm after 6 h) than at 100% RH (66 ppm after 6 h); however, the lethal activity of gaseous ClO2 against naturally occurring mesophilic aerobic bacteria (MAB) on radish seeds was significantly enhanced at 100% RH. For example, when exposed to gaseous ClO2 at 23% RH, the number of MAB on radish seeds decreased from 3.7 log CFU/g to 2.6 log CFU/g after 6 h. However, when exposed to gaseous ClO2 at 100% RH for 6 h, the MAB population decreased to 0.7 log CFU/g after 6 h. Gaseous ClO2 was produced in higher amounts at 55 degrees C than at 25 degrees C, but decreased more rapidly over time at 55 degrees C than at 25 degrees C. The lethal activity of gaseous ClO2 against MAB on radish seeds was greater at 55 degrees C than at 25 degrees C. When radish seeds were treated with gaseous ClO2 (peak concentration: 195 ppm) at 100% RH and 55 degrees C, MAB were reduced to populations below the detectable level (<-0.7 log CFU/g) within 2 h without decreasing the seed germination rate (97.7%). The lethality of combined treatments against artificially inoculated Escherichia coli O157:H7 was also evaluated. When exposed to gaseous ClO2 at 100% RH and 55 degrees C for 6 h, the initial number of E. coli O157:H7 (3.5 log CFU/g) on radish seeds decreased to below the detection limit (0.7 log CFU/g) by direct plating but it was not eliminated from seeds. The germination rate of radish seeds was not significantly (P> 0.05) decreased after treatment for 6 h. The information reported here will be useful when developing decontamination strategies for producing microbiologically safe radish seed sprouts. (C) 2016 Published by Elsevier B.V.</P>

Viability of sprout seeds as affected by treatment with aqueous chlorine dioxide and dry heat, and reduction of Escherichia coli O157:H7 and Salmonella enterica on pak choi seeds by sequential treatment with chlorine dioxide, drying, and dry heat

Choi, S.,Beuchat, L.R.,Kim, H.,Ryu, J.H. Academic Press 2016 FOOD MICROBIOLOGY Vol.54 No.-

<P>Germination rates of 11 types of sprout seeds (alfalfa, broccoli, kohlrabi, kyona, mustard, pak choi, red kohlrabi, red radish, red young radish, tatsoi, and violet radish) treated with ClO2 (200 mg/ml, 5 min) or dry-heat (80 degrees C/23% relative humidity [RH], 24 h) were determined. Pak choi, red radish, and tatsoi seeds showed highest tolerance to both ClO2 and dry-heat treatments. Next, pak choi seeds were inoculated with Escherichia coli O157:H7 (5.4 log CFU/g) or Salmonella enterica (4.8 log CFU/g) and sequentially treated with ClO2 (200 mg/ml, 5 min), drying (45 degrees C/23% RH, 24 h), and dry heat (80 degrees C/23% RH, 48 h). E. coli O157:H7 was inactivated, but S. enterica was not eliminated (>3.8 log CFU/g reduction). Pak choi seeds inoculated with the pathogens were treated with ClO2, drying, and dry heat and subsequently sprouted for 5 days. When seeds were not completely decontaminated, initial populations of E. coli O157:H7 and S. enterica on seeds (<1.0 log CFU/g) increased to >5.3 and >8.4 log CFU/g of sprouts, respectively. This study shows that sequential treatments of pak choi seeds with ClO2, drying, and dry heat are effective in reducing large numbers of E. coli O157:H7 and S. enterica without loss of seed viability. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Functionality improvement of fungal lignin peroxidase by DNA shuffling for 2,4-dichlorophenol degradability and H₂O₂ stability

Ryu, K.,Hwang, S.Y.,Kim, K.H.,Kang, J.H.,Lee, E.K. Elsevier Science Publishers 2008 Journal of biotechnology Vol.133 No.1

One of the major problems of wild-type lignin peroxidase (LiP) is its inactivity at the presence of excess H<SUB>2</SUB>O<SUB>2</SUB> and high concentration of aromatic compounds. Little is known about the substrate-binding site of LiP, and functionality improvement of LiP was not actively tried by genetic engineering and directed evolution. In order to improve LiPs functionality, we performed directed evolution with a colorimetric screening method. Finally, three types of LiP mutants were screened. The catalytic efficiency of the variants toward 2,4-dichlorophenol (DCP) degradation activity and the stability against H<SUB>2</SUB>O<SUB>2</SUB> was increased over the wild type. The K<SUB>m</SUB> value of the variants toward H<SUB>2</SUB>O<SUB>2</SUB> was increased, but K<SUB>m</SUB> value toward 2,4-DCP degradation was reduced. Overall, The K<SUB>cat</SUB>/K<SUB>m</SUB> values of the mutants toward 2,4-DCP was increased ca. 4-fold, and that toward H<SUB>2</SUB>O<SUB>2</SUB> was increased ca. 89-fold. Amino acid sequence analysis indicated that the most of the mutations were located on the enzyme surface. We expect that these results coupled with recombining mutation can be successfully applied to the molecular evolution cycles for screening of LiPs and other oxidative enzymes with improved functionality and stability.

유착에 의한 AGS 및 Hep-G2 세포 표면 구조의 변화

박동규 ( D. K. Park ),전훈재 ( H. J. Chun ),박재홍 ( J. H. Park ),박철희 ( C. H. Park ),진윤태 ( Y. T. Jeen ),이홍식 ( H. S. Lee ),이상우 ( S. W. Lee ),엄순호 ( S. H. Um ),최재현 ( J. H. Choi ),김창덕 ( C. D. Kim ),류호상 ( H. S. Ryu 대한소화기학회 2002 대한소화기학회 춘계학술대회 Vol.2002 No.-

<목적> 최근 H. pylori 유착에 의한 세포 표면 구조의 변화에 관한 연구가 시도되어지고 있으나 actin 의 변화여부 및 그 특성에 관해서는 아직 명확히 정립되지 못한 실정이다. Rho GTPase는 세포 표면의 미세돌기인 microvilli, filopodia 및 membrane ruffle의 형성과 관련이 있으며, 최근 AGS 세포에서 H. pylori가 Rac activation에 의하여 membrane ruffle을 형성한다는 것과 Rac

An electric powertrain modelling of a full cell hybrid electric vehicle and development of a power distribution algorithm using H_[unknown] control

Ryu, J.-H.,Lee, H.-J.,Sunwoo, M.-H. Professional Engineering Publishing 2010 Proceedings of the Institution of Mechanical Engin Vol.224 No.8

<P>This paper presents an electric powertrain model of a parallel-type fuel cell hybrid electric vehicle (FCHEV) and its robust H-infinity controller for efficient power distribution between a fuel cell and a battery. The electric powertrain of the parallel-type FCHEV is composed of a fuel cell stack system, a d.c.-to-d.c. converter, and a battery. The fuel cell stack system is connected to the battery through the d.c.-to-d.c. converter, which is a key component for power distribution between the fuel cell and the battery. In this study, the electric powertrain model of the FCHEV was derived from the dynamic differential equations of the equivalent-circuit model that describes the electric powertrain. Using this model, the robust H-infinity controller was designed to control the power distribution between the fuel cell and the battery efficiently. Finally, the results of driving-cycle simulation verified the performance of the proposed robust H-infinity controller.</P>

Effect of ball-milling time on structural characteristics and densification behavior of W-Cu composite powder produced from WO₃-CuO powder mixtures

Ryu, S.S.,Park, H.R.,Kim, Y.D.,Hong, H.S. MPR Pub. Services 2017 International journal of refractory metals & hard Vol.65 No.-

<P>Understanding the microstructure of W-Cu nanocomposite powder is essential for elucidating its sintering mechanism. In this study, the effect of milling time on the structural characteristics and densification behavior of W-Cu composite powders synthesized from WO3-CuO powder mixtures was investigated. The mixture of WO3 and CuO powders was ball-milled in a bead mill for 1 h and 10 h followed by reduction by heat-treating the mixture at 800 degrees C in H-2 atmosphere with a heating rate of 2 degrees C/min to produce W-Cu composite powder. The microstructure analysis of the reduced powder obtained by milling for 1 h revealed the formation of W-Cu powder consisting of W nanoparticle-attached Cu microparticles. However, Cu-coated W nanocomposite powder consisting of W nanoparticles coated with a Cu layer was formed when the Mixture was milled for 10 h. Cu-coated W nanopowder exhibited an excellent sinterability not only in the solid-phase sintering stage (SPS) but also in the liquid-phase sintering stage (LPS). A high relative sintered density of 96.0% was obtained at 1050 degrees C with a full densification occurring on sintering the sample at 1100 degrees C. The 1 h-milled W-Cu powder exhibited a high sinterability only in the LPS stage to achieve a nearly full densification at 1200 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.</P>