Min Suk Rhee

Prevalence and classification of pathogenic Escherichia coli isolated from fresh beef, poultry, and pork in Korea

Foodborne diseases occur worldwide, including through the consumption of contaminated meat. This study was conducted to investigate the prevalence of Escherichia coli contamination in fresh beef, poultry, and pork, and to determine whether any isolated E. coli possessed genes associated with pathogenicity. Three thousand meat samples were collected from 2004 to 2006 and were tested for the presence of E. coli. Two hundred and seventy-three E. coli isolates were obtained from beef, poultry, and pork, resulting in an overall isolation rate of 9.1%. Of these isolates, 201 were obtained from 1350 pork samples (14.9%), followed by 41 of 900 poultry samples (4.6%) and 31 of 750 beef samples (4.1%). A total of 39 pathogenic E. coli isolates from the three meat types were categorized into three virulence groups, namely enterotoxigenic E. coli (43.6%), enterohemorrhagic E. coli (EHEC) (35.9%; 22.6% of beef, 7.3% of poultry, and 2.0% of pork), and enteropathogenic E. coli (20.5%). Fourteen strains were identified as belonging to the EHEC, which included O18, O136, O119, O86, O8, O111, O15, O128, and O6. This study demonstrated that pathogenic E. coli are found in meat in Korea, and could act as a transmission vehicle for human infection as suggested by the occurrence and classification of pathogenic E. coli in retail meats. Furthermore, the data from this study could be used in the risk assessment of foodborne illnesses linked to meat consumption.

Antimicrobial Effects of Mustard Flour and Acetic Acid against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica Serovar Typhimurium

ABSTRACT This study was designed to investigate the individual and combined effects of mustard flour and acetic acid in the inactivation of food-borne pathogenic bacteria stored at 5 and 22°C. Samples were prepared to achieve various concentrations by the addition of acetic acid (0, 0.5, or 1%) along with mustard flour (0, 10, or 20%) and 2% sodium chloride (fixed amount). Acid-adapted three-strain mixtures of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica serovar Typhimurium strains (106 to 107 CFU/ml) were inoculated separately into prepared mustard samples stored at 5 and 22°C, and samples were assayed periodically. The order of bacterial resistance, assessed by the time required for the nominated populations to be reduced to undetectable levels against prepared mustards at 5°C, was S. enterica serovar Typhimurium (1 day) < E. coli O157:H7 (3 days) < L. monocytogenes (9 days). The food-borne pathogens tested were reduced much more rapidly at 22°C than at 5°C. There was no synergistic effect with regard to the killing of the pathogens tested with the addition of 0.5% acetic acid to the mustard flour (10 or 20%). Mustard in combination with 0.5% acetic acid had less bactericidal activity against the pathogens tested than did mustard alone. The reduction of E. coli O157:H7 and L. monocytogenes among the combined treatments on the same storage day was generally differentiated as follows: control < mustard in combination with 0.5% acetic acid < mustard alone < mustard in combination with 1% acetic acid < acetic acid alone. Our study indicates that acidic products may limit microbial growth or survival and that the addition of small amounts of acetic acid (0.5%) to mustard can retard the reduction of E. coli O157:H7 and L. monocytogenes. These antagonistic effects may be changed if mustard is used alone or in combination with >1% acetic acid.

Resistance of Enterobacter sakazakii (Cronobacter spp.) to environmental stresses.

Aim:  To gain a better understanding of the survival and persistence of Enterobacter sakazakii in severe environments.

Effect of low voltage electrical stimulation and temperature conditioning on postmortem changes in glycolysis and calpains activities of Korean native cattle (Hanwoo)

The combined effects of low voltage electrical stimulation (LVES) and temperature conditioning during early postmortem (PM) ageing on glycolytic rates and calpains activities of Korean native cattle (Hanwoo) were determined. M. longissimus was taken after splitting course, divided into three pieces and temperature conditioned at 2, 16, and 30°C for 3 h PM. The PM glycolytic rates, calpains and calpastatin activities were measured at 1, 3, 9, and 24 h PM. Although both LVES and the 30°C treatment accelerated glycolytic rates and resulted in improved enzyme activities, LVES was more effective for the improvement of enzyme activities than the 30°C treatment. Among tested Rigor-values (R-value; R(248), R(250), and R(258)), R(258) showed the highest correlation with pH (r=0.814, P<0.01), glycogen content (r=0.784, P<0.01) and μ-calpain (r=0.838, P<0.01) and selected as a suitable parameter to predict glycolytic rate. The high correlation coefficients between μ-calpain activity and metabolic rate parameters suggest that the change in the enzyme activity is closely related to glycolytic rates. The LVES in combination with the 30°C treatment until 3 h PM was the best treatment to accelerate the glycolytic rate and to improve the calpains activities in Hanwoo tissue.

Effects of supercritical carbon dioxide treatment against generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7 in marinades and marinated pork

This study was conducted to evaluate the effects of supercritical carbon dioxide (SC-CO(2)) treatment on soy sauce and hot-pepper paste marinades, as well as in marinated pork products, for the inhibition of generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7. SC-CO(2) was more effective at destroying foodborne pathogens when it was applied to the marinades than the marinated products. SC-CO(2) treatment at 14MPa and 45°C for 40min resulted in a greater reduction in soy sauce (2.52-3.47logCFU/cm(2)) than in hot-pepper paste marinade (2.12-2.72log CFU/cm(2)). In the case of the marinated pork, when SC-CO(2) was applied at 14MPa and 45°C for 40min, the reduction levels of L. monocytogenes were 2.49 and 1.92logCFU/cm(2) in soy sauce and hot-pepper paste marinated pork, respectively. The results should be useful in the meat industry to help increase microbial safety and assure the microbial stability of marinades and marinated products.

Inactivation of Alicyclobacillus acidoterrestris spores in apple juice by supercritical carbon dioxide

We investigated the lethal effect of supercritical carbon dioxide (SC-CO(2); temperature: 65, 70 degrees C, pressure: 80, 100, 120 bar, time: 10-40 min) on Alicyclobacillus acidoterrestris spores (10(6)-10(7)spores/ml) suspended in apple juice. A. acidoterrestris spores were completely inactivated by SC-CO(2) to undetectable levels in above 65 degrees C, 100 bar for 40 min and 70 degrees C, 80 bar for 30 min. The SC-CO(2) did not affect (p>0.05) the pH and Brix of apple juice. In electron microscopic observations, the surface and internal morphological changes and extraction of intracellular materials of the treated spores were observed. Our results indicate that SC-CO(2) can effectively kill A. acidoterrestris spores in apple juice with no changes to the quality of the juice and also provides a complementary understanding of inactivation action of SC-CO(2).

Inhibitory effect of caprylic acid and mild heat on Cronobacter spp. (Enterobacter sakazakii) in reconstituted infant formula and determination of injury by flow cytometry

The combined effects of caprylic acid and mild heat were investigated to ascertain their impact on Cronobacter spp. (E. sakazakii) in reconstituted infant formula. Samples containing a mixture of 3 strains of Cronobacter spp. (10(7) to 10(8) CFU/ml) were prepared with various concentrations of caprylic acid (5, 10, 20, and 30 mM) and were then heated to 45, 50, and 55 degrees C. The inhibitory effect of the combined treatment resulted in a synergistic effect, in which Cronobacter spp. numbers were reduced much more rapidly with increased temperatures and concentrations of caprylic acid. When samples were treated with 30 mM caprylic acid, the time required to reduce Cronobacter spp. cell numbers to an approximate reduction of 7.8 log CFU/ml was 60 min at 45 degrees C, 20 min at 50 degrees C, and 10 min at 55 degrees C. In the validation assay using a low population of Cronobacter spp. (approximately 10(3) log CFU/ml), no recovery of injured cells was observed after samples were treated with 10 mM caprylic acid for 20 min at 55 degrees C, 20 mM caprylic acid for 10 min at 50 degrees C and 55 degrees C, and 30 mM caprylic acid for 10 min at 45 degrees C to 55 degrees C. To determine the bactericidal mechanism of caprylic acid, membrane integrity was examined by fluorescent staining followed by flow cytometry and confocal microscopy. Increased cellular inactivation was associated with increased propidium iodide staining, indicating damage to the cell membrane of Cronobacter spp.. Overall, these data indicate that the addition of this natural antimicrobial agent to infant formula may have potential use for controlling microbes prior to consumption at lower heating temperatures. The study also provides a complementary understanding of the mode of action of caprylic acid on Cronobacter spp.

The influence of pork quality traits and muscle fiber characteristics on the eating quality of pork from various breeds

The purpose of this study was to compare parameters associated with pork quality, muscle fiber, and eating quality among various breeds, and to examine if differences in eating quality were associated to pork quality and muscle fiber characteristics. For carcass and pork quality, although there were significant differences among breeds, the values of parameters in all pigs were assigned a normal quality class, a likely outcome of the similarity in the area percentage of type I and IIB fibers. For eating quality, pork loins from Berkshire pigs were more tender and full of pork flavor than Landrace and Yorkshire pigs. Except juiciness and mouth coating, over 20% of the variability in the eating quality parameters can be explained by pork quality traits and muscle fiber characteristics using multiple regression analysis. Furthermore, differences in muscle pH(24h), cooking loss, shear force, and NPPC marbling score could explain a large proportion of variation in eating quality parameters associated with the texture of pork.

Potential use of supercritical carbon dioxide to decontaminate Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium in alfalfa sprouted seeds.

We sought to develop a method of decontaminating alfalfa sprouts of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium without altering the seed germination capability using supercritical carbon dioxide (SC-CO(2)). Samples were treated with SC-CO(2) at 10, 15, or 20 MPa and temperatures of 35, 40, or 45 degrees C for 5, 10, or 15 min. The germination percentage was measured after three days of germination. Generally, treating seeds with SC-CO(2) at higher pressures, temperatures, or for longer treatment times resulted in greater microbial reductions than treatments at lower pressures, temperatures, or for shorter treatment times. SC-CO(2) treatment clearly reduced the microorganism levels in alfalfa seeds; in particular, treatment at 20 MPa and 45 degrees C for 15 min reduced levels of the three pathogens by >7.0 log colony forming units (CFU)/g. However, SC-CO(2) treatment at a high pressure and high temperature, especially treatment at 20 MPa and 40 or 45 degrees C, impaired the seed germination capability in some cases. Without impairing the germination capability, the maximum reduction level of E. coli O157:H7 was 3.51 CFU/g with SC-CO(2) treatment at 15 MPa and 35 degrees C for 10 min. Maximum reductions of L. monocytogenes and S. typhimurium were 2.65 and 2.48 log CFU/g, respectively, with treatment at 10 MPa and 45 degrees C for 5 min. Therefore, our results indicate that SC-CO(2) treatment can be used to effectively improve alfalfa seed safety.

Combined effect of organic acids and supercritical carbon dioxide treatments against nonpathogenic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and E. coli O157:H7 in fresh pork.

Aims:  To evaluate the effectiveness of organic acids and supercritical carbon dioxide (SC‐CO2) treatments as well as their combined effect for the reduction of nonpathogenic Escherichia coli and three pathogenic bacteria in fresh pork.