Nam Hee Kim

Response surface methodology-based optimization of decontamination conditions for Escherichia coli O157:H7 and Salmonella Typhimurium on fresh-cut celery using thermoultrasound and calcium propionate.

A combination of thermoultrasound (temperature: 50, 55, 60°C; time: 10, 15, 20 min with the frequency of 40 KHz) and calcium propionate (concentration: 1, 2, 3%, w/v) treatment was applied to decontaminate Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) from fresh-cut celery. Using a Box-Behnken experimental design, predictive quadratic equations were developed for treatment-based population reductions of E. coli O157:H7 (R(2)=0.98, p<0.001) and S. Typhimurium (R(2)=0.96, p<0.001), and verified using 10 randomly selected treatment conditions. Among three factors (temperature, time, and calcium propionate concentration), temperature represented higher significance for inactivation of pathogenic bacteria. No significant changes (p>0.05) were observed in the color and shear force resistance of the treated celery. The optimum treatment conditions were 60°C thermoultrasound with 2% calcium propionate for 15 min (E. coli O157:H7) and 59°C thermoultrasound with 2% calcium propionate for 17 min (S. Typhimurium). Scanning electron microscopy was used to confirm membrane disruption in the treated microbial cells in each optimal condition. The combined treatment of thermoultrasound and calcium propionate contributes to the effective inactivation (more than 5 log reduction) of E. coli O157:H7 and S. Typhimurium on fresh-cut celery. Furthermore, this treatment extends fresh storability without physical quality deterioration.

Microbiological diversity and prevalence of spoilage and pathogenic bacteria in commercial fermented alcoholic beverages (beer, fruit wine, refined rice wine, and yakju)

The present study examined 469 commercially available fermented alcoholic beverages (FABs), including beer (draft, microbrewed, and pasteurized), fruit wine (grape and others), refined rice wine, and yakju (raw and pasteurized). Samples were screened for Escherichia coli and eight foodborne pathogens (Bacillus cereus, Campylobacter jejuni, Clostridium perfringens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus, and Yersinia enterocolitica), and the aerobic plate count, lactic acid bacteria, acetic acid bacteria, fungi, and total coliforms were also enumerated. Microbrewed beer contained the highest number of microorganisms (average aerobic plate count, 3.5; lactic acid bacteria, 2.1; acetic acid bacteria, 2.0; and fungi, 3.6 log CFU/ml), followed by draft beer and yakju (P < 0.05), whereas the other FABs contained , 25 CFU/25 ml microorganisms. Unexpectedly, neither microbial diversity nor microbial count correlated with the alcohol content (4.7 to 14.1%) or pH (3.4 to 4.2) of the product. Despite the harsh conditions, coliforms (detected in 23.8% of microbrewed beer samples) and B. cereus (detected in all FABs) were present in some products. B. cereus was detected most frequently in microbrewed beer (54.8% of samples) and nonpasteurized yakju (50.0%), followed by pasteurized yakju (28.8%), refined rice wine (25.0%), other fruit wines (12.3%), grape wine (8.6%), draft beer (5.6%), and pasteurized beer (2.2%) (P < 0.05). The finding that spore-forming B. cereus and coliform bacteria can survive the harsh conditions present in alcoholic beverages should be taken into account (alongside traditional quality indicators such as the presence of lactic acid-producing bacteria, acetic acid-producing bacteria, or both) when developing manufacturing systems and methods to prolong the shelf life of high-quality FAB products. New strategic quality management plans for various FABs are needed.

Prevalence and classification of toxigenic Staphylococcus aureus isolated from refrigerated ready-to-eat foods (sushi, kimbab and California rolls) in Korea.

Aims:u2002 To investigate the presence of toxigenic Staphylococcus aureus in ready‐to‐eat (RTE) Korean foods and determine the distribution of genes related to various types of toxin production.

Effects of Tau on the activity of triose phosphate isomerase (TPI) in brain cells

Tau is a main component of the aberrant paired helical filaments (PHF) found in Alzheimers disease (AD). It has also been reported to enhance oxidative stress, which is a major factor in the pathogenesis of neurodegenerative diseases. However, protective functions of Tau have recently been reported, including antagonizing apoptosis, in addition to its role in stabilizing microtubules. In this study, the interaction between Tau and triose phosphate isomerase (TPI) in a normal, nondisease state as well as in a neurodegeneration state was examined and demonstrated for the first time. More importantly, we also showed that Tau protects TPI against oxidative damage. An oxidative stress-induced decrease in the activity of TPI was attenuated in Tau-overexpressing cells, indicating that Tau protects TPI against oxidative damage. By contrast, the activity of TPI was decreased in Tau-transgenic (Tg) mice compared to non-Tg (NTg) mice even though protein levels were not changed in both groups. Some TPIs were found on the PHF in Tg mice, which explains the decrease in the activity of TPI. Taken together, we concluded that while Tau binds and protects TPI in normal cells, and conversely, the formation of PHF induced by Tau phosphorylation trap some TPI and trigger the functional loss of TPI in the development of neurodegenerative diseases. Our results provide new insights into understanding the in-depth involvement of Tau in the development of neurodegenerative disorders.

Microbiological Quality of Seasoned Roasted Laver and Potential Hazard Control in a Real Processing Line

Microbiological quality of laver, one of the edible seaweeds, has not been reported in a real processing line. Laver or supplements were collected from six manufacturers (A to F) to assess potential microbiological hazards and the critical control points in commercial processing lines. Aerobic plate counts (APC), coliform counts, Bacillus cereus, Staphylococcus aureus, and Vibrio parahaemolyticus were enumerated, and the presence of B. cereus, Listeria monocytogenes, Salmonella, S. aureus, and V. parahaemolyticus were confirmed during processing. The raw material, i.e., dried laver, had a high initial APC level (4.4 to 7.8 log CFU/g), which decreased gradually during processing (final products, 1.3 to 5.9 log CFU/g). Coliforms and B. cereus were not detected in any of the final products, but they were present in some raw materials and semiprocessed products in quantitative analysis. After enrichment for recovery of stress-injured cells, E. coli and foodborne pathogens were not detected in any samples, with the exception of B. cereus. Heat-injured and spore-forming B. cereus isolates were occasionally obtained from some of the raw materials and products after enrichment, thus B. cereus may be a potential microbiological hazard that should be controlled using strategic intervention measures. Secondary roasting (260 to 400°C, 2 to 10 s) significantly reduced the APC (maximum log reduction, 4.7 log CFU/g), and this could be a key intervention step for controlling microbiological hazards during processing (critical control point). When this step was performed appropriately, according to the processing guide for each plant, the microorganisms were inactivated more successfully in the products. This study provides scientific evidence that may facilitate the development of strategies for microbiological hazard control and hygienic management guidelines for real manufacturing plants.

Proteomic profiling of brain cortex tissues in a Tau transgenic mouse model of Alzheimer's disease.

Alzheimers disease (AD) involves regionalized neuronal death, synaptic loss, and an accumulation of intracellular neurofibrillary tangles and extracellular senile plaques. Although there have been numerous studies on tau proteins and AD in various stages of neurodegenerative disease pathology, the relationship between tau and AD is not yet fully understood. A transgenic mouse model expressing neuron-specific enolase (NSE)-controlled human wild-type tau (NSE-htau23), which displays some of the typical Alzheimer-associated pathological features, was used to analyze the brain proteome associated with tau tangle deposition. Two-dimensional electrophoresis was performed to compare the cortex proteins of transgenic mice (6- and 12-month-old) with those of control mice. Differentially expressed spots in different stages of AD were identified with ESI-Q-TOF (electrospray ionization quadruple time-of-flight) mass spectrometry and liquid chromatography/tandem mass spectrometry. Among the identified proteins, glutathione S-transferase P 1 (GSTP1) and carbonic anhydrase II (CAII) were down-regulated with the progression of AD, and secerin-1 (SCRN1) and V-type proton ATPase subunit E 1 (ATP6VE1) were up-regulated only in the early stages, and down-regulated in the later stages of AD. The proteins, which were further confirmed by RT-PCR at the mRNA level and with western blotting at the protein level, are expected to be good candidates as drug targets for AD. The study of up- and down-regulation of proteins during the progression of AD helps to explain the mechanisms associated with neuronal degeneration in AD.

Proteomic analysis of plasma from a Tau transgenic mouse

The neurofibrillary tangles (NFTs) formed by the accumulation of abnormal tau filaments have been shown to be involved in Alzheimers disease (AD) brain degeneration. In this study, a tau transgenic mouse (pNSE/htau23) model was used to monitor changes in protein levels and to search for novel biomarker candidates suitable for the early diagnosis of AD before onset of clinical symptoms. Plasma samples from 2‐month (n = 13, asymptomatic) and 4‐month (n = 7, symptomatic) tau transgenic mice were compared to the control group (n = 8) by 2‐dimensional gel electrophoresis (2‐DE) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Three proteins, ATP synthase, Adenosine kinase and Regucalcin showed significantly decreased levels in the plasma of tau transgenic mouse, which was further confirmed by Western blotting. This study suggests that these proteins could be used as candidate biomarkers for early diagnosis of AD in combination with previously discovered protein biomarkers.

Decontamination efficacy of neutral electrolyzed water to eliminate indigenous flora on a large-scale of cabbage and carrot both in the laboratory and on a real processing line

The decontamination efficacy of neutral electrolyzed water (NEW) was evaluated using shredded cabbages and carrots in both a scalable laboratory system (experiment I) and an actual processing line in a plant (experiment II). In experiment I, the antimicrobial effect of highly concentrated NEW (up to the maximum regulated level: 200ppm) was tested to determine the appropriate conditions for use in an actual plant test: (1) hypochlorous acid (HClO) concentration (100, 150, and 200ppm), (2) ratio of sample weight to NEW volume (1:5, 1:10, and 1:20), and (3) treatment time (5, 10, 20, and 30min), using 2kg of shredded cabbages and carrots. In experiment II, the feasibility of the NEW treatment was validated on an actual processing line (treatment unit: 20kg), including cutting, three washing steps (two air bubble washes for 5min each and 150ppm NEW for 5min at ratio of 1:10), rinsing (5min), and dehydration (5min). Overall, the microbial reductions tended to increase as the HClO concentration, ratio of sample to NEW, and treatment time increased. The results obtained from experiment I indicated that the maximum conditions (NEW 200ppm, 1:20, 30min) achieved 3.3-3.5 log CFU/g reductions in the coliform counts. After treatment with 200ppm NEW for >10min, however, there were noticeable color changes (color differences, DE>5.0) in both the shredded cabbages and carrots. In the experiment II, the microbial populations were not affected by cutting and two air bubble treatments, whereas washing with NEW greatly reduced both the aerobic plate counts (1.93-2.17 log CFU/g) and coliform counts (0.97-1.51 log CFU/g). More than 2 log CFU/g of indigenous flora were reduced from raw materials to final products with both shredded cabbages (2.05-2.48 log CFU/g) and carrots (2.34-2.76 log CFU/g). These results may provide useful recommendations for the practical application of highly concentrated NEW in the fresh-cut produce industry to improve the microbiological safety without quality deterioration.

Teriyaki sauce with carvacrol or thymol effectively controls Escherichia coli O157: H7, Listeria monocytogenes, Salmonella Typhimurium, and indigenous flora in marinated beef and marinade

An effective bactericidal cold-marinating method for beef products is described, exploiting the synergism between soy sauce and natural compounds (carvacrol, CV or thymol, TM) to reduce microbiological risks. Beef slices inoculated with Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium (3.1-3.5logCFU/g) were marinated in a teriyaki sauce with or without CV and TM (0.3 and 0.5%). After 1, 3, and 7days at 4°C, indigenous microflora population, color, lipid oxidation, marinade uptake, and pH of marinated beef and leftover marinade samples were examined. Teriyaki sauce alone did not reduce or inhibit any of the target pathogens or indigenous bacteria, while 0.5% CV- or TM-containing teriyaki sauce inactivated all inocula without recovery within 7days (p<0.05). The pathogens relocated from the beef into the leftover marinade (3.0-3.4logCFU/mL) were also completely inactivated. The treatment inhibited growth of indigenous aerobic bacteria (p<0.05) and inactivated coliform bacteria. Physicochemical parameters were not significantly affected (p>0.05).

Inactivation of Bacillus cereus spores in a tsuyu sauce using continuous ohmic heating with five sequential elbow-type electrodes.

The effect of ohmic heating (OH) in a pilot plant system which had a zig‐zag shaped (elbow‐type) ohmic heater with five sequential voltage electrodes was investigated on Bacillus cereus spores in a commercial tsuyu sauce.