Marta Miks-Krajnik

Food Science

Ph.D.
22.74

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.
    No preview · Article · May 2016 · Food Control
  • Marta Mikš-Krajnik · Y.-J. Yoon · Dike O. Ukuku · H.-G. Yuk
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    ABSTRACT: The purpose of this investigation was to identify and quantify the volatile chemical spoilage indexes (CSIs) for raw Atlantic salmon (Salmo salar) fillets stored under aerobic storage conditions at 4, 10 and 21 °C in relation to microbial and sensory shelf lives. The volatile organic compounds (VOCs) were analyzed with SPME-GC-MS technique. Through multivariate chemometric method, hierarchical cluster analysis (HCA) and Pearson's correlations, the CSIs: trimethylamine (TMA), ethanol (EtOH), 3-methyl-1-butanol (3Met-1But), acetoin and acetic acid (C2) were selected from the group of 28 detected VOCs. At the moment of microbiological shelf life established at total viable count (TVC) of 7.0 log CFU/g, the CSIs achieved levels of 11.5, 38.3, 0.3, 24.0 and 90.7 μg/g of salmon for TMA, EtOH, 3M-1But, acetoin and C2, respectively. Pseudomonas spp. was found as major specific spoilage organism (SSOs), suitable for shelf life prediction using modified Gompertz model at the cut-off level of 6.5 log CFU/g. H2S producing bacteria and Brochothrix thermosphacta were considered as important spoilage microorganisms; however, they were not suitable for shelf life estimation. Partial least square (PLS) regression revealed possible associations between microorganisms and synthetized VOCs, showing correlations between Pseudomonas spp. and 3Met-1But and aldehydes synthesis, lactic acid bacteria were linked with EtOH, C2 and esters, and B. thermosphacta with acetoin formation.
    No preview · Article · Feb 2016 · Food Microbiology
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    ABSTRACT: Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. The aim of this study was to develop a rapid and accurate detection methodology for low levels of healthy and sanitizer-injured Salmonella on mung bean sprouts using real-time PCR coupled with either immunomagnetic separation (PCR-IMS) or centrifugation (PCR-cen). Initially, three parameters of IMS; specificity/sensitivity, bacterial concentration and bead incubation time were optimized. Secondly, limit of detection (LOD) was determined for the optimized PCR-IMS and PCR-cen. These two methods were compared against PCR alone (PCR) and the standard culture method (ISO) for their ability to detect Salmonella using inoculated and uninoculated sprouts. Under optimum IMS conditions (105 CFU/ml for 30 min), capture efficiency of Salmonella in sprout suspensions was lower than 40%, most probably due to the non-specific binding of the background microbiota. PCR-IMS and PCR-cen had a similar LOD at 103 CFU/ml, which was one log unit lower than PCR. Enrichment of 10 h was sufficient to detect 100% of the inoculated sprouts with both PCR-IMS and PCR-cen, which was significantly faster compared to PCR and the ISO method. Moreover, the validation study using uninoculated sprouts revealed that PCR-IMS and PCR-cen were equally effective on Salmonella detection, showing 98.3% accuracy. These results suggest that PCR-cen would be the effective and less costly method for the detection of both healthy and sanitizer-injured Salmonella on mung bean sprouts.
    No preview · Article · Jan 2016 · International journal of food microbiology
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    ABSTRACT: The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typhimurium and Salmonella cocktail on mung bean sprouts was evaluated to select an optimum broth for detection. Results showed that S. Typhimurium multiplied faster and reached a higher population in buffered peptone water (BPW), Salmonella AD media (AD) and ONE broth-Salmonella (OB), compared with other broths. Healthy and 90% sanitizer-injured Salmonella at low concentrations increased by 4.0 log CFU/ml in these three broths. However, no Salmonella growth was observed in lactose broth (LB). Further investigation showed that during incubation, pH of LB dropped from 6.7 to 4.2, due to production of lactic (66 mM) and acetic acids (62 mM) by lactic acid bacteria that were identified as dominant microbiota in bean sprouts. Though no cell membrane damage was detected by propidium monoazide combined with real-time PCR, it was found that LB inhibited Salmonella growth, especially from low inoculum levels. This study suggests that in consideration of effectiveness and cost, BPW would be a suitable enrichment broth to use for isolating and detecting Salmonella on mung bean sprouts, while using LB might cause false negative results in Salmonella detection by either PCR or standard cultural method. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Dec 2015 · Food Microbiology
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    ABSTRACT: Food safety and food security are interrelated concepts with a profound impact on the quality of human life. Food security describes the overall availability of food at different levels from global to individual household. While, food safety focuses on handling, preparation and storage of foods in order to prevent foodborne illnesses. This review focuses on innovative thermal and non-thermal technologies in the area of food processing as the means to ensure food security through improving food safety with emphasis on the reduction and control of microbiological risks. The antimicrobial efficiency and mechanism of new technologies to extend the shelf life of food product were also discussed.
    No preview · Article · Oct 2015 · Cosmos: journal of the Singapore National Academy of Science
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    ABSTRACT: This study determined the effects of temperature (4 and 25 °C), pH (5.3, 7.3, and 8.3), and nutrient availability (TSB and 20 times diluted TSB (1/20 TSB)) on Salmonella Enteritidis biofilm formation and its resistance to chlorine treatment (pH 6.8, 50 ppm for 1 min). The results showed that biofilm density was significantly higher (P < 0.05) at 25 °C or in 1/20 TSB, regardless of pH and bacterial strains. Moreover, 1/20 TSB significantly enhanced the chlorine resistance of biofilms formed at 25 °C, especially for S. Enteritidis with rdar morphotype, with an average reduction of 1.52 log CFU/cm2 compared to that of biofilm in TSB with 4.07 log reduction. All biofilms formed at 4 °C were very sensitive to chlorine treatment. In most cases, acidic pH sensitized biofilms to chlorine treatment compared with neutral and alkaline pHs. The further analysis of cellulose production of biofilms indicated that it had a positive impact on biofilm resistance to chlorine treatment. This study suggests that environmental stress conditions encountered in food processing plant might alter S. Enteritidis biofilm resistance to sanitizer treatment possibly by acting on the cellulose production.
    No preview · Article · Oct 2015 · Food Microbiology
  • Min-Jeong Kim · Marta Mikš-Krajnik · Amit Kumar · Vinayak Ghate · Hyun-Gyun Yuk
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    ABSTRACT: This study investigated the antibacterial effect of 405±5nm light emitting diode (LED) on Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus, and examined its antibacterial mechanism by determining the bacterial membrane and DNA damages. A 405±5nm LED illuminated the Gram-positive pathogens until 486J/cm(2) at 4°C. Weibull model was used to calculate reliable life (tR) to compare bacterial sensitivities to LED illumination. The membrane damage was determined by NaCl and LIVE/DEAD® assay, while comet assay and DNA ladder analysis were conducted to determine DNA degradation. The illumination resulted in 1.9, 2.1, and 1.0 log reductions for B. cereus, L. monocytogenes, and S. aureus at 486J/cm(2), respectively. The comparison of tR values revealed that L. monocytogenes was identified as the most susceptible strain to LED illumination. The percentage of the bacterial sensitivity to NaCl remarkably increased in LED-illuminated cells compared to non-illuminated cells. Moreover, loss of membrane integrity was confirmed for LED-illuminated cells by LIVE/DEAD® assay, whereas no DNA breakage was indicated by comet assay and DNA ladder analysis. Thus, these findings suggest that the antibacterial effect of 405±5nm LED illumination on these pathogens might be due to physical damage to bacterial membrane rather than DNA degradation.
    No preview · Article · Sep 2015 · Journal of photochemistry and photobiology. B, Biology
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    ABSTRACT: A commercial loop-mediated isothermal amplification (LAMP) based system with bioluminescence, named as 3M™ Molecular Detection Assay (MDA), was validated for the detection of Listeria monocytogenes (3-strain cocktail) at low levels (100, 101, 102 CFU/100 cm2) inoculated on stainless steel (SS) and polyethylene (PE) surfaces, with and without (w/o) organic load (OL) of cold-smoked salmon homogenate by comparing with a standard ISO method as reference. The results of this study revealed that a commercial LAMP-based method performed equally effective compared with ISO method at inoculum levels of 100 and 102/100 cm2, showing 100% specificity and sensitivity, respectively. At 101 CFU/100 cm2, a slight reduction in the effectiveness of LAMP-based method was observed most likely due to the use of single enrichment step in the procedure of LAMP-based method. The LAMP-based method was shown to be rapid and reliable detection technique for L. monocytogenes present at low numbers on food processing surfaces, regardless of organic residues, and can be applicable in seafood industry.
    No preview · Article · Jul 2015 · Food Control
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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.
    No preview · Article · Jun 2015 · Waste Management
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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.
    No preview · Article · Jun 2015 · Journal of food protection
  • 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.
    No preview · Article · Feb 2015 · Food Control
  • 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.
    No preview · Article · Feb 2015 · Food Science and Biotechnology
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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.
    Full-text · Article · Jun 2014 · International Journal of Food Microbiology
  • Marta Mikš‐Krajnik · Andrzej Babuchowski
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    ABSTRACT: Unlabelled: Multicolour 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. Lactococcus lactis cells were labelled 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 Lc. lactis and P. freudenreichii cells in culture media and in skimmed milk. Significance and impact of the study: Results showed that three newly designed 16S rRNA-targeted oligonucleotide probes specific for Propionibacterium freudenreichii in combination with a probe specific for Lactococcus lactis can be used to differentiate lactic and propionic acid bacteria in mixed communities using multicolour fluorescence in situ hybridization (FISH), without applying permeabilization step. This is a first study on simultaneous detection of both bacterial species with FISH, which was found as rapid, useful and culture-independent tool for direct visualization of bacteria on single cell level. It might be applied in monitoring of mixed starter cultures in dairy industry.
    No preview · Article · May 2014 · Letters in Applied Microbiology
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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.
    Full-text · Article · Jan 2014
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    Arkadiusz Ratajski · Marta Miks-Krajnik · Ireneusz Białobrzewski

    Full-text · Article · Jan 2014 · International Journal of Food Science & Technology
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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.
    Full-text · Article · Jul 2013 · African journal of microbiology research
  • 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.
    No preview · Article · Jun 2013 · International Journal of Dairy Technology
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    M.H. Mikš-Krajnik
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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.
    Full-text · Article · Jan 2012 · Zywnosc: Nauka, Technologia, Jakosc
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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.
    No preview · Article · Aug 2010 · The Journal of Microbiology

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