Publications

  • Min-Jeong Kim · Marta Mikš-Krajnik · Amit Kumar · Hyun-Gyun Yuk
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    ABSTRACT: The objective of this study was to evaluate the antibacterial effect of 405 ± 5 nm light emitting diode (LED) on Escherichia coli O157:H7, Salmonella Typhimurium and Shigella sonnei. Its antibacterial mechanism was also investigated by determining the permeability of bacterial membrane and DNA degradation. Bacterial strains in phosphate-buffered saline were exposed to 405 ± 5 nm LED to a final dose of 486 J/cm2 (7.5 h) at 4 C. The inactivation curves were fitted by Weibull model to compare the sensitivities of pathogens to the LED illumination by calculating the decimal reduction times (tR). The bacterial sensitivity to bile salts and NaCl by LED illumination was also determined. LIVE/DEAD® BacLight™ staining as well as comet assay and DNA ladder analysis were carried out to determine the bacterial membrane integrity and DNA degradation, respectively. Results showed that LED illumination inactivated 1.0, 2.0, and 0.8 log CFU/ml for E. coli O157:H7, S. Typhimurium, and S. sonnei for 7.5 h, respectively. The comparison of tR values demonstrated that S. Typhimurium was found to be the most (P < 0.05) susceptible strain to LED illumination. Regardless of the bacterial strain, the sensitivity of illuminated bacterial cells to bile salts and NaCl considerably increased compared to non-illuminated controls. Furthermore, LIVE/DEAD® assay clearly showed that LED illumination resulted in loss of bacterial membrane permeability. On the other hand, no DNA degradation was observed by both comet assay and DNA ladder analysis. Therefore, these results suggest that the antibacterial effect of 405 ± 5 nm LED might be partly attributed to the physical damage to bacterial cell membrane. This study proposes that 405 ± 5 nm LED under refrigerated conditions may be effective to control the pathogens on foods.
    Food Control 05/2016; 59:99-107. DOI:10.1016/j.foodcont.2015.05.012 · 2.82 Impact Factor
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    ABSTRACT: A mathematical model integrating 11 first-order differential equations describing the dynamics of the aerobic composting process of sewage sludge was proposed. The model incorporates two microbial groups (mesophiles and thermophiles) characterized by different capacities of heat generation. Microbial growth rates, heat and mass transfer and degradation kinetics of the sewage sludge containing straw were modeled over a period of 36days. The coefficients of metabolic heat generation for mesophiles were 4.32×10(6) and 6.93×10(6)J/kg, for winter and summer seasons, respectively. However, for thermophiles, they were comparable for both seasons reaching 10.91×10(6) and 10.51×10(6)J/kg. In the model, significant parameters for microbial growth control were temperature and the content of easily hydrolysable substrate. The proposed model provided a satisfactory fit to experimental data captured for cuboid-shaped bioreactors with forced aeration. Model predictions of specific microbial populations and substrate decomposition were crucial for accurate description and understanding of sewage sludge composting. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Waste Management 06/2015; DOI:10.1016/j.wasman.2015.05.036 · 3.16 Impact Factor
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    ABSTRACT: The objective of this study was to evaluate performance of the commercial kit based on loop-mediated isothermal amplification (LAMP) in comparison with the International Organization for Standardization method for detecting uninjured and sublethally injured Salmonella cells artificially inoculated at levels of 100 and 101 CFU/25 g on raw duck wing, raw mung bean sprouts, and processed fishballs. Injured cells were prepared by a heat treatment for duck wings and fishball samples and a chlorine treatment for bean sprout samples. Additionally, a validation study was performed on naturally contaminated food samples sold in Singapore. A total of 110 samples of each commodity were analyzed in this study. Regardless of inoculum levels, the detection by the commercial LAMP kit showed 100% sensitivity and specificity for both inoculated and uninoculated samples compared with the International Organization for Standardization method, with the exception of bean sprout samples. Only 20% of bean sprout samples inoculated with 100 CFU/25 g injured Salmonella cells were positive by using the commercial LAMP-based kit. However, all negative samples became positive following a secondary enrichment in Rappaport-Vassiliadis medium with soy broth or after concentration by centrifugation. These results suggest that secondary enrichment or centrifugation should be considered as an additional step to increase the sensitivity of the commercial LAMP-based kit with low numbers of injured target cells in samples with high background microflora (such as mung bean sprouts). The validation study also showed that the commercial LAMP-based kit provided 91% sensitivity and 95% specificity for naturally contaminated samples. Thus, this study demonstrates that the commercial LAMP-based kit might be a cost-effective method, as this system could provide rapid, accurate detection of both uninjured and injured Salmonella cells on raw duck wings, raw mung bean sprouts, and processed fishballs in less than 26 h.
    Journal of food protection 06/2015; 78(6):1203-1207. DOI:10.4315/0362-028X.JFP-14-535 · 1.80 Impact Factor
  • Shing Yee Tan · Marta Mikš-Krajnik · Shan Yu Neo · Alice Tan · Gek Hoon Khoo · Hyun-Gyun Yuk
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    ABSTRACT: The increasing occurrence of outbreaks associated with consumption of contaminated fresh produce suggests the need for effective sanitizing treatments on these commodities. In this study, six sanitizers including acid electrolyzed water (AcEW, 5 min), acidified sodium chlorite (ASC, 1200 ppm, 3 min), cetylpyridinium chloride (CPC, 1%, 3 min), chlorine (200 ppm, 3 min), ozonated water (2 ppm, 5 min) and sodium dichloroisocyanurate (NaDCC, 150 ppm, 10 min) were tested against natural microflora and inoculated Salmonella spp. on peeled turnips (Jicama). Among these sanitizers, ASC was found to be the most effective sanitizer, resulting in the reduction of 2.09 and 2.13 log CFU/cut-turnip in aerobic mesophilic count and yeasts and molds, respectively, as well as 3.91 log CFU/turnip reduction in Salmonella spp. Storage study was performed to evaluate the effect of aerobic or vacuum packaging as well as storage temperature on the microbiological and physical quality changes of ASC-treated shredded turnips. The results indicated that treated turnip kept in aerobic conditions at 4 �C for up to 9 days maintained a microbial count of less than regulatory limits (5 log CFU/g) and retained the colour and firmness. This study suggests that ASC treatment followed by aerobic storage at 4 �C would be the best handling practice for improving microbiological safety and maintaining good physical quality of commercially produced shredded turnips.
    Food Control 02/2015; 54:216-224. · 2.82 Impact Factor
  • Marta Mikš-Krajnik · Yong-Jin Yoon · Hyun-Gyun Yuk
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    ABSTRACT: Volatile organic compounds (VOCs) of naturally aerobically spoiled chicken breast at ambient temperature were analyzed to identify volatiles that can be used as spoilage markers. The headspace solid-phase micro-extraction (HS-SPME) technique coupled with gas GC/MS running in Fast Automated Scan/SIM Type (FASST) mode was applied using 4 SPME fibers of different polarity. All of fibers were able to detect the sulfides methanethiol (MeSH), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS), the alcohols ethanol (EtOH), 1- and 2-butanol, and 1-butanol isomers, and free fatty acids (FFAs) in the range of C2 to C5. Principal component analysis (PCA) revealed that spoilage in chicken meat is 2-step process. Initially, an increase in amounts of alcohols and FFAs was observed (primary spoilage), followed by an increase in the sulfide content (secondary spoilage). The most promising volatile spoilage markers for chicken breast were EtOH and 3-methyl-1-butanol, followed by acetic acid (C2) and sulfides.
    Food Science and Biotechnology 02/2015; 24(1):361-372. DOI:10.1007/s10068-015-0048-5 · 0.66 Impact Factor
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    Qianwang Zheng · Marta Mikš-Krajnik · Yishan Yang · Wang Xu · Hyun-Gyun Yuk
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    ABSTRACT: Conventional culture detection methods are time consuming and labor-intensive. For this reason, an alternative rapid method combining real-time PCR and immunomagnetic separation (IMS) was investigated in this study to detect both healthy and heat-injured Salmonella Typhimurium on raw duck wings. Firstly, the IMS method was optimized by determining the capture efficiency of Dynabeads(®) on Salmonella cells on raw duck wings with different bead incubation (10, 30 and 60min) and magnetic separation (3, 10 and 30min) times. Secondly, three Taqman primer sets, Sal, invA and ttr, were evaluated to optimize the real-time PCR protocol by comparing five parameters: inclusivity, exclusivity, PCR efficiency, detection probability and limit of detection (LOD). Thirdly, the optimized real-time PCR, in combination with IMS (PCR-IMS) assay, was compared with a standard ISO and a real-time PCR (PCR) method by analyzing artificially inoculated raw duck wings with healthy and heat-injured Salmonella cells at 10(1) and 10(0)CFU/25g. Finally, the optimized PCR-IMS assay was validated for Salmonella detection in naturally contaminated raw duck wing samples. Under optimal IMS conditions (30min bead incubation and 3min magnetic separation times), approximately 85 and 64% of S. Typhimurium cells were captured by Dynabeads® from pure culture and inoculated raw duck wings, respectively. Although Sal and ttr primers exhibited 100% inclusivity and exclusivity for 16 Salmonella spp. and 36 non-Salmonella strains, the Sal primer showed lower LOD (10(3)CFU/ml) and higher PCR efficiency (94.1%) than the invA and ttr primers. Moreover, for Sal and invA primers, 100% detection probability on raw duck wings suspension was observed at 10(3) and 10(4)CFU/ml with and without IMS, respectively. Thus, the Sal primer was chosen for further experiments. The optimized PCR-IMS method was significantly (P=0.0011) better at detecting healthy Salmonella cells after 7-h enrichment than traditional PCR method. However there was no significant difference between the two methods with longer enrichment time (14h). The diagnostic accuracy of PCR-IMS was shown to be 98.3% through the validation study. These results indicate that the optimized PCR-IMS method in this study could provide a sensitive, specific and rapid detection method for Salmonella on raw duck wings, enabling 10-h detection. However, a longer enrichment time could be needed for resuscitation and reliable detection of heat-injured cells.
    International Journal of Food Microbiology 06/2014; 186C:6-13. DOI:10.1016/j.ijfoodmicro.2014.06.005 · 3.16 Impact Factor
  • Marta Mikš‐Krajnik · Andrzej Babuchowski
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    ABSTRACT: Multicolor fluorescence in situ hybridization (FISH) has been applied to detect Lactococcus lactis and Propionibacterium freudenreichii cells in mixed populations in medium and skimmed milk, using epifluorescent microscopy. The 16S rRNA-targeted 18-mer oligonucleotide probes, specific for P. freudenreichii were designed and evaluated. Based on multiple alignments of designed sequences, eight 16S rRNA probes were selected for in vitro studies. The permeabilization protocol was optimized for simultaneous hybridization of propionibacteria and lactococci cells. The probes GLO62 (62-80), PEU64 (64-82) and PFX311 (311-329) were found specific for P. freudenreichii in analysis in vitro. L. lactis cells were labeled with LactV5 (822-840), (S-S-L.lact-0821-a-A-18) probe. The following combinations of oligonucleotide probes: LactV5/GLO62, LactV5/PEU64 and LactV5/PFX311, enabled differentiation of L. lactis and P. freudenreichii cells in culture media and in skimmed milk.This article is protected by copyright. All rights reserved.
    Letters in Applied Microbiology 05/2014; 59(3). DOI:10.1111/lam.12278 · 1.75 Impact Factor
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    Arkadiusz Ratajski · Marta Miks-Krajnik · Ireneusz Białobrzewski
    International Journal of Food Science & Technology 01/2014; DOI:10.1111/ijfs.12265 · 1.35 Impact Factor
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    Qianwang Zheng · Marta Mikš-Krajnik · Yishan Yang · Wang Xu · Hyun-Gyun Yuk
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    ABSTRACT: Conventional culture detection methods are time consuming and labor-intensive. For this reason, an alternative rapid method combining real-time PCR and immunomagnetic separation (IMS) was investigated in this study to detect both healthy and heat-injured Salmonella Typhimurium on raw duck wings. Firstly, the IMS method was optimized by determining the capture efficiency of Dynabeads® on Salmonella cells on raw duck wings with different bead incubation (10, 30 and 60 min) and magnetic separation (3, 10 and 30 min) times. Secondly, three Taqman primer sets, Sal, invA and ttr, were evaluated to optimize the real-time PCR protocol by comparing five parameters: inclusivity, exclusivity, PCR efficiency, detection probability and limit of detection (LOD). Thirdly, the optimized real-time PCR, in combination with IMS (PCR–IMS) assay, was compared with a standard ISO and a real-time PCR (PCR) method by analyzing artificially inoculated raw duck wings with healthy and heat-injured Salmonella cells at 101 and 100 CFU/25 g. Finally, the optimized PCR–IMS assay was validated for Salmonella detection in naturally contaminated raw duck wing samples. Under optimal IMS conditions (30 min bead incubation and 3 min magnetic separation times), approximately 85 and 64% of S. Typhimurium cells were captured by Dynabeads® from pure culture and inoculated raw duck wings, respectively. Although Sal and ttr primers exhibited 100% inclusivity and exclusivity for 16 Salmonella spp. and 36 non-Salmonella strains, the Sal primer showed lower LOD (103 CFU/ml) and higher PCR efficiency (94.1%) than the invA and ttr primers. Moreover, for Sal and invA primers, 100% detection probability on raw duck wings suspension was observed at 103 and 104 CFU/ml with and without IMS, respectively. Thus, the Sal primer was chosen for further experiments. The optimized PCR–IMS method was significantly (P = 0.0011) better at detecting healthy Salmonella cells after 7-h enrichment than traditional PCR method. However there was no significant difference between the two methods with longer enrichment time (14 h). The diagnostic accuracy of PCR–IMS was shown to be 98.3% through the validation study. These results indicate that the optimized PCR–IMS method in this study could provide a sensitive, specific and rapid detection method for Salmonella on raw duck wings, enabling 10-h detection. However, a longer enrichment time could be needed for resuscitation and reliable detection of heat-injured cells.
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    Justyna Borawska · Marta Miks-Krajnik · Małgorzata Darewicz
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    ABSTRACT: The bacterial physiological state, type of interactions and changes in metabolism of Lactococcus lactis and Propionibacterium freudenreichii strains in co-culture were studied in skimmed milk in response to osmotic [3% (w/v) NaCl] and low temperature (10°C) stress during long-term incubation. Changes in the integrity of cell membrane were examined by LIVE/DEAD® BacLight™ staining, and culture viability and bacterial interactions studies were performed with the use of the plate count technique. The profiles of volatile organic compounds were assessed by static headspace-gas chromatography. During the stationary growth phase, the number of LIVE cells with intact membranes was reduced in the presence of NaCl in comparison with control conditions, and a longer adaptation phase was observed at 10°C.The viability of starter cultures was high at ~108 to 109 CFU/ml at the end of the experiment in all tested conditions. Our results point to the possibility of commensalisms interactions between lactic acid and propionic acid bacteria. Prolonged culture incubation contributed to the accumulation of acetoin, and it enhanced acetic acid and propionic acid synthesis during the stationary growth phase of propionic acid bacteria.
    African journal of microbiology research 07/2013; 7(29):3794-3801. DOI:10.5897/AJMR12.2219 · 0.54 Impact Factor
  • Marta Miks-Krajnik · Andrzej Babuchowski · Ireneusz Białobrzewski
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    ABSTRACT: The changes in the physiological state and metabolism of starter culture in 15kg Swiss–Dutch-type cheese blocks during two-stage ripening were studied. The analyses were performed on samples from three layers of cheese between the rind and the core. Cell membrane integrity, intracellular esterase activity and bacteria culturability were chosen as physiological state indicators. Cheese flavour development was determined by static headspace gas chromatography. During warm room ripening, the number of cells with intact cell membranes and displaying intracellular esterase activity increased. Lactic acid bacteria underwent resuscitation and regained their culturability. A lack of homogeneity within the cheese was noticed in relation to bacterial activity and the volatiles concentration.
    International Journal of Dairy Technology 06/2013; 66(4):562-569. DOI:10.1111/1471-0307.12079 · 1.10 Impact Factor
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    Mikš-Krajnik M.
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    ABSTRACT: Swiss-Dutch type cheeses are produced with the use of lactic acid streptococci: Lactococcus spp., Leuconostoc spp. and propionic acid rods: Propionibacterium spp. Starter cultures and the environment of ripening cheese create a very complex and dynamic system. Biotechnological processes occurring in the cheese matrix ripened in industrial conditions depend mainly on the physiological state of applied microorganisms. The metabolism of bacterial cells gives direction for biochemical and enzymatic changes conducted in cheese environment, which shape the desirable characteristics of the product.
    Zywnosc: Nauka, Technologia, Jakosc 01/2012; 80(1):45-59. DOI:10.15193/zntj/2012/80/045-059 · 0.31 Impact Factor
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    ABSTRACT: The focus of this study was to monitor the survival of populations and the volatile compound profiles of selected Lactobacillus strains during long-term incubation in milk. The enumeration of cells was determined by both the Direct Epifluorescent Filter Technique using carboxyfluorescein diacetate (CFDA) staining and the plate method. Volatile compounds were analysed by the gas-chromatography technique. All strains exhibited good survival in cultured milks, but Lactobacillus crispatus L800 was the only strain with comparable growth and viability in milk, assessed by plate and epifluorescence methods. The significant differences in cell numbers between plate and microscopic counts were obtained for L. acidophilus strains. The investigated strains exhibited different metabolic profiles. Depending on the strain used, 3 to 8 compounds were produced. The strains produced significantly higher concentrations of acetic acid, compared to other volatiles. Lactobacillus strains differed from one another in number and contents of the volatile compounds.
    The Journal of Microbiology 08/2010; 48(4):445-51. DOI:10.1007/s12275-010-0056-3 · 1.53 Impact Factor
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    Warmińska-Radyko I. · Sielawa H. · Mikš-Krajnik M.
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    ABSTRACT: The aim of the study was to assess usefulness of the LIVE/DEAD fluorescent staining method and gas chromatography to monitor the viability and metabolic activity of Propionibacterium strains in long-term cultures in milk. The effect of 4% NaCl addition and a temperature of 10°C on the growth of Propionibacterium freudenreichii ssp. freudenreichii 111, 109C, 108 strains was studied for 28 days. Bacterial cells were assessed in cultures by microscopic and plate counting methods in regular intervals. The cultures were additionally determined for the content of volatile fatty acids: C2 to C7. The total cell counts of all strains in cultures assessed by the microscopic method were noticed to be 1 to 5 logarithmic cycles higher in comparison to those determined with the plate counting method. In following days and weeks of culture, increasing discrepancies were observed between the results obtained using microscopic and plate methods. Both methods revealed similar trends in the viability of strains under control conditions and a little impact of NaCl addition on cell growth and decrease. The cultures run at a temperature of 10°C exhibited different course of growth and decline of the number of monitored populations depending on strain and method applied. Individual strains possessed different acid formation activity. From the beginning of incubation, the highest concentrations were reported for propionic and acetic acids, whereas the other acids in number from 4 to 6 appeared subsequently. The temperature of 10°C inhibited acids formation by all strains, whereas 4% addition of NaCl stimulated the acid-forming activity and during incubation under those conditions the contents of volatile acids were recorded to be the highest.
    Polish Journal of Food and Nutrition Sciences 01/2010; 60(4):363-368.
  • Warmińska-Radyko I. · Olszewska M. · Mikš-Krajnik M
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    ABSTRACT: The growth and metabolism of Lactococcus strains were studied in milk with an NaCl presence and at 10oC. The viability of bacteria was assessed by the LIVE/DEAD® BacLight™ assey and by plate counts. The gas-chromatography technique for the determination of volatile-free fatty acid profiles in milk was used. It was calculated that depending on the strain, conditions performed and incubation time, plate counts were from 0,5 to 6 log units lower than LIVE/DEAD counts. The LIVE/DEAD method allowed to exhibit a slight influence of selected factors on the growth of Lactococcus, providing delicate differences between live and dead cell counts at investigated conditions. It was shown that each strain contributed to the specific profile of volatiles of milk. Depending on the strain and conditions, from 3 to 9 acids were established. Production of acetic acid occurred early in the fermentation, whereas other acids were formed between day 28 and 42 of incubation.
    Milchwissenschaft 01/2010; 65(1):32-35. · 0.23 Impact Factor
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    Mikš-Krajnik M. · Warmińska-Radyko I.
    Medycyna weterynaryjna 05/2008; 64(4):623 – 628. · 0.20 Impact Factor
  • Polish Journal of Natural Science 12/2007; 22(4):733-741. DOI:10.2478/v10020-007-0063-y
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    Marta Miks-Krajnik · Wioleta Chajęcka-Wierzchowska

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