S.A. Kim

Microbial contamination of food products consumed by infants and babies in Korea

Aims:  The objectives of this study were to investigate the microbiological safety of various foods intended for consumption by infants and babies.

Direct application of supercritical carbon dioxide for the reduction of Cronobacter spp. (Enterobacter sakazakii) in end products of dehydrated powdered infant formula.

The objective of this study was to develop a viable new method for inactivation of Cronobacter spp. that could be applied directly to dehydrated powdered infant formula (PIF) using supercritical carbon dioxide (SC-CO(2)). Samples inoculated with Cronobacter spp. were subjected to SC-CO(2) treatment under various conditions (temperature: 63, 68, and 73 degrees C; pressure: 15, 20, and 25 MPa; time: 10, 20, and 30 min). The survival of Cronobacter spp. was assayed, as were any changes in the quality of the treated PIF. Inactivation of Cronobacter spp. by SC-CO(2) was enhanced as temperature and pressure conditions increased (>6.32 log(10) cfu/g). In a validation assay using low-level inoculation (3.21 log(10) cfu/g), treatment at 73 degrees C and 15 MPa for 30 min, 20 MPa for 20 and 30 min, or 25 MPa for 20 and 30 min reduced Cronobacter spp. to undetectable levels, with no recovery of cell viability. There was no significant change in water activity, pH, and color of the treated PIF. Overall, the optimum conditions for elimination of Cronobacter spp. were determined to be 73 degrees C and 20 MPa for 20 min. These parameters for effective SC-CO(2) treatment are feasibly applicable to end product of dehydrated PIF. The results of our study may contribute to the development of an efficient method for improving the microbiological safety of PIF.

New decontamination method based on caprylic acid in combination with citric acid or vanillin for eliminating Cronobacter sakazakii and Salmonella enterica serovar Typhimurium in reconstituted infant formula.

The antimicrobial effects of natural compounds (caprylic acid, CA; citric acid, CTA; and vanillin, VNL) on the inactivation of Cronobacter sakazakii and Salmonella enterica serovar Typhimurium were examined in reconstituted infant formula. The samples were treated with: 1) CA, CTA, or VNL alone (0, 10, 20, 30, 40, 60, and 80 mM); 2) a combination of CA (10 and 20 mM) and CTA (15 and 30 mM); and 3) a combination of CA (10 and 20 mM) and VNL (15 and 30 mM), at mild feeding temperatures (40 °C and 45 °C), and the bacterial populations were assayed periodically (0, 5, 10, and 30 min). For both bacteria, the combined treatments had marked synergistic antimicrobial effects compared with the sum of the effects of each individual treatment. For example, there was no noticeable reduction (P > 0.05) in the population of C. sakazakii following an individual treatment with 20 mM CA or 30 mM CTA for 5 min at 40 °C, whereas the population was reduced to undetectable levels (reduction > 7.3 log CFU/ml) following treatment with a combination of CA and CTA (20 CA+30 CTA for 5 min at 40 °C). As the temperature increased, the bactericidal effect was stronger at all time points with a synergistic effect. In a validation assay using a low level inoculum (approximately 10³ CFU/ml) of desiccation-stressed bacteria in certain conditions, the combined treatments (e.g., CA 10 mM+CTA 30 mM for 5 min at 45 °C for C. sakazakii, and CA 10mM+VNL 15 mM for 10 min at 45 °C for S. Typhimurium) completely destroyed the bacteria with no recovery of cell viability. Disintegration of the membrane and changes in the cell structure or morphology, such as plasmolysis and membrane disruption, were detected by flow cytometry and electron microscopy, respectively. These methods use antimicrobials that could be applied as food additives in infant formula, which may help to eliminate bacteria.

Changes in microbial contamination levels and prevalence of foodborne pathogens in alfalfa (Medicago sativa) and rapeseed (Brassica napus) during sprout production in manufacturing plants

Samples were taken from three sprout processing plants at five different stages of production (a total of 20 investigations). Quantitative analyses comprised aerobic plate counts (APCs) and the measurement of coliforms and Bacillus cereus levels, whereas qualitative analyses involved assessing the levels of Escherichia coli and major foodborne pathogens (E. coli O157:H7, Listeria monocytogenes, Salmonella spp., and Staphylococcus aureus). The APC for alfalfa seeds (3·71–4·61 log CFU g−1) and rapeseed (4·25–5·11 log CFU g−1) increased by approximately 3 log CFU g−1 during sprouting, reaching 7·17–7·61 and 7·33–8·28 log CFU g−1, respectively, by the final stage of production. Similarly, increasing trends were noted in the level of coliforms (0·58–4·03 log CFU g−1 at the seed stage, increasing to 5·52–6·99 log CFU g−1 by the sprout stage). Bacillus cereus was detected in eight alfalfa (40%) and 14 rapeseed (70%) sprouts, and L. monocytogenes was isolated from one pregermination soaked alfalfa seed. A slight reduction in the level of bacterial contamination was noted after washing the sprouts with water prior to storage, indicating that improvements to the current washing protocol, or other efficient intervention methods, may be needed. Taken together, these results suggest that improved hygiene control during production and processing and a more sanitary environment are needed. The present study provides comprehensive information regarding the microbiological safety of seeds and sprouts during manufacturing.

Eight enrichment broths for the isolation of Campylobacter jejuni from inoculated suspensions and ground pork

Aims:  The efficiency of eight enrichment broths for the selective isolation of Campylobacter jejuni was compared to identify an optimal enrichment broth.

Changes in microbial contamination levels of porcine carcasses and fresh pork in slaughterhouses, processing lines, retail outlets, and local markets by commercial distribution

The objective of this study was to evaluate the changes in microbial contamination levels of each porcine carcass and fresh pork in a general distribution process. A total of 100 commercial pigs were sampled (six sampling sites per individual, total 600 samples) at four sequential stages: slaughterhouse (after carcass grading and boning), processing line, retail outlet, and local market. No significant differences were observed in the contaminant percentages among sampling sites and sample collection years (P>0.05) with the exception of Bacillus cereus. The contaminant percentage of B. cereus at 1st collection year was higher than these of 2nd collection year (28.31% vs. 12.26%, P<0.05). B. cereus and Listeria monocytogenes were the most frequently detected pathogenic bacteria in the slaughterhouse and markets, respectively. On the other hand, Escherichia coli O157:H7 and Yersinia enterocolitica were not detected in carcasses or pork collected from any carcass sites and pork samples. However, the frequency of pathogenic bacteria in end-products at local markets was not highly related to the initial contamination of porcine carcasses in the slaughterhouse. Thus, the improvement of microbial safety for pork end-products requires hygienic control of porcine carcasses and meat cutting during all operations in the slaughterhouse, processing line, retail outlet, and local market.

Survival of foodborne pathogenic bacteria (Bacillus cereus, Escherichia coli O157: H7, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, and Listeria monocytogenes) and Bacillus cereus spores in fermented alcoholic beverages (beer and refined rice wine)

Only limited information is available on the microbiological safety of fermented alcoholic beverages because it is still a common belief that such beverages do not provide a favorable environment for bacterial growth and survival. Thus, in this study, we examined the survival of major foodborne pathogens and spores in fermented alcoholic beverages. Foodborne pathogens (Bacillus cereus, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Staphylococcus aureus) and B. cereus spores (initial population, 3 to 4 log CFU/ml) were inoculated separately into three types of beer and refined rice wine, which were then stored at 5 and 22°C. Bacterial counts were assayed periodically for up to 28 days. Vegetative B. cereus counts decreased rapidly, whereas B. cereus spore counts remained constant (P > 0.05) for a long period of time in all beverages. Vegetative B. cereus cells formed spores in beer at 5 and 22°C, and the spores survived for long periods. Among vegetative cells, E. coli O157:H7 had the highest survival (only 1.49 to 1.56 log reduction during 28 days in beer at 5°C). Beer and refined rice wine supported microbial survival from several days to several weeks. Our results appear to contradict the common belief that pathogens cannot survive in alcoholic beverages. Long-term survival of pathogens (especially B. cereus and E. coli O157:H7) in beer and refined rice wine should be taken into consideration by the manufacturers of these beverages. This study provides basic information that should help further research into microbial survival in alcoholic beverages and increase the microbiological safety regulation of fermented alcoholic beverages.

Predictive model and optimization of a combined treatment of caprylic acid and citric acid for the reduction of Escherichia coli O157:H7 using the response surface methodology

Our recent previous study reported the outstanding synergistic bactericidal activity of a combination of two natural antimicrobials: caprylic acid (CA) and citric acid (CTA). In the present study, the response surface methodology was used with the central composite design to build a model based on four factors, i.e., the CA concentration, CTA concentration, temperature, and treatment time, for the reduction of Escherichia coli O157:H7. This model was used to determine the optimum conditions for desirable responses and to evaluate the effects of experimental factors. The ranges of the four variables used in the design were as follows: CA concentration (0.25, 0.50, 0.75, 1.00, and 1.25 mM), CTA concentration (0.25, 0.50, 0.75, 1.00, and 1.25 mM), temperature (25, 30, 35, 40, and 45°C), and time (1, 3, 5, 7, and 9 min). A second-order quadratic model of the effect of four variables was constructed and the experimental values agreed well with the values derived from model equation (R(2)=0.954). The adequacy of this model for predicting the magnitude of bacterial reduction was verified based on the validation data (R(2)=0.946). The optimum conditions for the combined treatment for microbial reduction were determined by ridge analysis, which were 1.0mM CA and 0.8mM CTA at 39.6°C for 5.4 min. The CA concentration and temperature were the most significant variables. This study provides a comprehensive understanding of the bactericidal effects of the combined CA and CTA treatment. A distinct advantage of the proposed method is its cost-effectiveness. This treatment could be used as a preservative in the food industry because the two components are natural products.

Use of caprylic acid to control pathogens (Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium) in apple juice at mild heat temperature

The aim of this study was to examine the effects of caprylic acid (CA) on pathogens in apple juice having intrinsic organic acids, and to determine any synergistic effects.

Microbial diversity and prevalence of foodborne pathogens in cheap and junk foods consumed by primary schoolchildren.

Aerobic plate counts (APC), coliforms, Bacillus cereus, Escherichia coli and eight foodborne pathogens were tested in 1008 cheap and junk foods, including candies, dried cakes, chewing gum, chocolate, dried and seasoned seafood, ice cream, and sugary foods. APCs were positive for 342 samples (33·9%), and the majority of the counts were 2–3 log CFU g−1 or ml−1 (average: 1·10 log CFU g−1 or ml−1). Most samples (97·3%) contained no coliforms (average: 0·07 log CFU g−1 or ml−1). Bacillus cereus was detected in 68 samples (average: 0·14 log CFU g−1 or ml−1). Escherichia coli and Listeria monocytogenes were detected in 6 and 1 samples, respectively, whereas other foodborne pathogens were not isolated. The highest bacterial counts were associated with dried and seasoned seafood products and dried cakes, suggesting that appropriate regulations of these food types should be considered. Cheap and junk foods were produced mainly in developing countries, but there were no significant differences in the bacterial counts among different countries of origin. The presence of foodborne pathogens may pose a risk for children. These results suggest that there is cause for deeper concern about the safety of these foods and that effective countermeasures should be established to improve their microbiological safety.