Hyemin Oh

Determination of Salable Shelf-life for Wrap-packaged Dry-aged Beef during Cold Storage

Abstract We investigated microbial and quality changes in wrap-packaged dry-aged beef after completion of aging and subsequent storage in a refrigerator. After 28 days of dry aging (temperature, 4°C; RH, approximately 75%; air flow velocity, 2.5 m/s), sirloins were trimmed, wrap-packaged, and stored at 4°C for 7 days. Analyses of microbial growth, pH, volatile basic nitrogen (VBN), 2-thiobarbituric acid-reactive substance (TABRS), and instrumental color, myoglobin, and sensory evaluation were conducted on days 0, 3, 5, and 7. The results show that the number of total aerobic bacteria (TAB), yeast, and lactic acid bacteria increased with an increase in storage days, whereas no change in the growth of mold was observed during 7 days of storage. Based on the legal standard for TAB count, the estimated shelf-life of wrap-packaged dry-aged beef was predicted to be less than 12.2 days. However, the shelf-life should be less than 6.3 days, considering the result of sensory quality (odor, taste, and overall acceptance). No significant change in visible appearance was also observed during 7 days of storage. The results suggest that the present quality indicators for meat spoilage (pH, VBN, and TBARS) should be re-considered for dry-aged beef, as its characteristics are different from those of fresh and/or wet-aged beef.

Rapid Detection of Escherichia coli in Fresh Foods Using a Combination of Enrichment and PCR Analysis

Abstract The objective of this study was to determine the minimum enrichment time for different types of food matrix (pork, beef, and fresh-cut lettuce) in an effort to improve Escherichia coli detection efficiency. Fresh pork (20 g), beef (20 g), and fresh-cut lettuce (20 g) were inoculated at 1, 2, and 3 Log CFU/g of Escherichia coli. Samples were enriched in filter bags for 3 or 5 h at 44.5°C, depending on sample type. E. coli cell counts in the samples were enriched in E. coli (EC) broth at 3 or 5 h. One milliliter of the enriched culture medium was used for DNA extraction, and PCR assays were performed using primers specific for uidA gene. To detect E. coli (uidA) in the samples, a 3–4 Log CFU/mL cell concentration was required. However, E. coli was detected at 1 Log CFU/g in fresh pork, beef, and fresh-cut lettuce after 5, 5, and 3-h enrichment, respectively. In conclusion, 5-h enrichment for fresh meats and 3-h enrichment for fresh-cut lettuce in EC broth at 44.5°C, and PCR analysis using uidA gene-specific primers were appropriate to detect E. coli rapidly in food samples.

Quantitative Microbial Risk Assessment of Campylobacter jejuni in Jerky in Korea

Objective The objective of this study was to estimate the risk of Campylobacter jejuni (C. jejuni) infection from various jerky products in Korea. Methods For the exposure assessment, the prevalence and predictive models of C. jejuni in the jerky and the temperature and time of the distribution and storage were investigated. In addition, the consumption amounts and frequencies of the products were also investigated. The data for C. jejuni for the prevalence, distribution temperature, distribution time, consumption amount, and consumption frequency were fitted with the @RISK fitting program to obtain appropriate probabilistic distributions. Subsequently, the dose-response models for Campylobacter were researched in the literature. Eventually, the distributions, predictive model, and dose-response model were used to make a simulation model with @RISK to estimate the risk of C. jejuni foodborne illness from the intake of jerky. Results Among 275 jerky samples, there were no C. jejuni positive samples, and thus, the initial contamination level was statistically predicted with the RiskUniform distribution [RiskUniform (−2, 0.48)]. To describe the changes in the C. jejuni cell counts during distribution and storage, the developed predictive models with the Weibull model (primary model) and polynomial model (secondary model) were utilized. The appropriate probabilistic distribution was the BetaGeneral distribution, and it showed that the average jerky consumption was 51.83 g/d with a frequency of 0.61%. The developed simulation model from this data series and the dose-response model (Beta Poisson model) showed that the risk of C. jejuni foodborne illness per day per person from jerky consumption was 1.56×10−12. Conclusion This result suggests that the risk of C. jejuni in jerky could be considered low in Korea.

Microbiological safety of processed meat products formulated with low nitrite concentration — A review

Nitrite plays a major role in inhibiting the growth of foodborne pathogens, including Clostridium botulinum (C. botulinum) that causes botulism, a life-threatening disease. Nitrite serves as a color-fixing agent in processed meat products. However, N-nitroso compounds can be produced from nitrite, which are considered as carcinogens. Thus, consumers desire processed meat products that contain lower concentrations (below conventional concentrations of products) of nitrite or no nitrite at all, although the portion of nitrite intake by processed meat consumption in total nitrite intake is very low. However, lower nitrite levels might expose consumers to risk of botulism poisoning due to C. botulinum or illness caused by other foodborne pathogens. Hence, lower nitrite concentrations in combination with other factors such as low pH, high sodium chloride level, and others have been recommended to decrease the risk of food poisoning. In addition, natural compounds that can inhibit bacterial growth and function as color-fixing agents have been developed to replace nitrite in processed meat products. However, their antibotulinal effects have not been fully clarified. Therefore, to have processed meat products with lower nitrite concentrations, low pH, high sodium chloride concentration, and others should also be applied together. Before using natural compounds as replacement of nitrite, their antibotulinal activities should be examined.

Evaluation on Antimicrobial Activity of Psoraleae semen Extract Controlling the Growth of Gram-Positive Bacteria

This study investigated bacterial growth-inhibitory effect of 69 therapeutic herbal plants extracts on 9 bacterial strains using a disc diffusion assay. Especially, the antimicrobial activity of Psoraleae semen, which showed different activity on pathogenic Gram-positive and Gram-negative bacteria, was evaluated by MIC (minimal inhibition concentration) and biofilm formation assay. The effect of Psoraleae semen extract on bacterial cell membranes was examined by measurement of protein leakage (optical density at 280 nm) and scanning electron microscope (SEM). No clear zone was formed on discs containing Gram-negative bacteria, but Gram-positive bacteria exhibited clear zones. The MICs of Psoraleae semen extract were 8 μg/mL for Streptococcus mutans, and 16 μg/mL for Enterococci and Staphylococcus aureus. In addition, biofilm formation was inhibited at concentration 8-16 μg/mL. Protein leakage values and SEM images revealed that cell membranes of Gram-positive bacteria were impaired following exposure to the extract. Further, the extract inhibited the growth of Listeria monocytogenes in sausages. These results indicate that Psoraleae semen extract could be utilized as a natural antimicrobial agent against Gram-positive bacteria.

Identification of Pork Adulteration in Processed Meat Products Using the Developed Mitochondrial DNA-Based Primers

The identification of pork in commercially processed meats is one of the most crucial issues in the food industry because of religious food ethics, medical purposes, and intentional adulteration to decrease production cost. This study therefore aimed to develop a method for the detection of pork adulteration in meat products using primers specific for pig mitochondrial DNA. Mitochondrial DNA sequences for pig, cattle, chicken, and sheep were obtained from GenBank and aligned. The 294-bp mitochondrial DNA D-loop region was selected as the pig target DNA sequence and appropriate primers were designed using the MUSCLE program. To evaluate primer sensitivity, pork-beef-chicken mixtures were prepared as follows: i) 0% pork-50% beef-50% chicken, ii) 1% pork-49.5% beef-49.5% chicken, iii) 2% pork-49% beef-49% chicken, iv) 5% pork-47.5% beef-47.5% chicken, v) 10% pork-45% beef-45% chicken, and vi) 100% pork-0% beef-0% chicken. In addition, a total of 35 commercially packaged products, including patties, nuggets, meatballs, and sausages containing processed chicken, beef, or a mixture of various meats, were purchased from commercial markets. The primers developed in our study were able to detect as little as 1% pork in the heat treated pork-beef-chicken mixtures. Of the 35 processed products, three samples were pork positive despite being labeled as beef or chicken only or as a beef-chicken mix. These results indicate that the developed primers could be used to detect pork adulteration in various processed meat products for application in safeguarding religious food ethics, detecting allergens, and preventing food adulteration.

Enrichment Broth for the Detection of Campylobacter jejuni and Campylobacter coli in Fresh Produce and Poultry

Although campylobacteriosis caused by Campylobacter jejuni and Campylobacter coli has been increasingly reported worldwide owing to the consumption of contaminated poultry and fresh produce, the current detection protocols are not selective enough to inhibit unspecific microbes other than these pathogens. Five antibiotics were separately added to Bolton broth, and the survival rates of 18 Campylobacter spp. and 79 non-Campylobacter spp. were evaluated. The survival rate of the non-Campylobacter spp. was the lowest in Bolton broth with rifampin (6.3%), followed by cefsulodin (12.7%), novobiocin (16.5%), and potassium tellurite and sulfamethozaxole (both 17.7%). Also the most effective concentration of rifampin was found to be 12.5 mg/L, which markedly inhibited non-Campylobacter strains while not affecting the survival of Campylobacter strains. After the Campylobacter spp. were enriched in Bolton broth supplemented with 12.5 mg/L rifampin (R-Bolton broth), CampyFood Agar (CFA) was found to be better in selectively isolating the pathogens in the enrichment broth than the International Organization for Standardization method of using modified charcoal cefoperazone deoxycholate agar (mCCDA) for this step. When applied to natural food samples-here, romaine lettuce, pepper, cherry tomato, Korean leek, and chicken-the R-Bolton broth-CFA combination decreased the number of false-positive results by 50.0, 4.2, 20.8, 50.0, and 94.4%, respectively, compared with the International Organization for Standardization method (Bolton broth-mCCDA combination). These results demonstrate that the combination of R-Bolton broth and CFA is more efficient in detecting C. jejuni and C. coli in poultry and fresh produce and thus should replace the Bolton broth-mCCDA combination.

Antibiotic Susceptibility, Genetic Diversity, and the Presence of Toxin Producing Genes in Campylobacter Isolates from Poultry

This study examined antibiotic susceptibility, genetic diversity, and characteristics of virulence genes in Campylobacter isolates from poultry. Chicken (n = 152) and duck (n = 154) samples were collected from 18 wet markets in Korea. Campylobacter spp. isolated from the carcasses were identified by PCR. The isolated colonies were analyzed for antibiotic susceptibility to chloramphenicol, amikacin, erythromycin, tetracycline, ciprofloxacin, nalidixic acid, and enrofloxacin. The isolates were also used to analyze genetic diversity using the DiversiLabTM system and were tested for the presence of cytolethal distending toxin (cdt) genes. Campylobacter spp. were isolated from 45 poultry samples out of 306 poultry samples (14.7%) and the average levels of Campylobacter contamination were 22.0 CFU/g and 366.1 CFU/g in chicken and duck samples, respectively. Moreover, more than 90% of the isolates showed resistance to nalidixic acid and ciprofloxacin. Genetic correlation analysis showed greater than 95% similarity between 84.4% of the isolates, and three cdt genes (cdtA, cdtB, and cdtC) were present in 71.1% of Campylobacter isolates. These results indicate that Campylobacter contamination should be decreased to prevent and treat Campylobacter foodborne illness.

Prevalence and Genetic Characteristics of Meatborne Listeria monocytogenes Isolates from Livestock Farms in Korea.

This study aimed to evaluate the prevalence of Listeria monocytogenes on livestock farms in Korea and determine their serotypes and genetic correlations. Twenty-five livestock farms in Korea (central: 15, south west: 7, south east: 3) were visited 2-3 times, and 2,018 samples (feces: 677, soil: 680, silage: 647, sludge: 14) were collected. Samples were enriched in LEB (Listeria enrichment broth) and Fraser broth media, and then plated on Palcam agar. The isolates were identified by PCR and 16S rRNA gene sequencing. Then, the serotypes, presence of virulence genes (actA, inlA, inlB, plcB, and hlyA), and antibiotic resistance were determined. Genetic correlations among the isolates were evaluated by analyzing the restriction digest pattern with AscI. Of the 2,018 samples, only 3 (0.15%) soil samples (FI-1-FI-3) from 1 farm in the south east region were positive for L. monocytogenes. Based on biochemical tests and multiplex PCR, the serotype of the isolates were 4ab (FI-1 and FI-3) and 3a (FI-2), which are not common in foodborne L. monocytogenes. The 3a serotype isolate was positive for all tested virulence genes, whereas the 4ab serotype isolates were only positive for hlyA, actA, and inlA. The isolates were resistant to all 12 tested antibiotics, especially FI-3. The genetic correlations among the isolates were 100% for those of the same serotype and 26.3% for those of different serotypes. These results indicate that the prevalence of L. monocytogenes on livestock farms in Korea is low; however, the isolates are pathogenic and antibiotic resistant.