The prevalence of eating out and foodservice is increasing according to changes in dietary habits. Moreover, the demand of processed foods also has been increased at home and foodservice as it is convenient to use and can save the cooking time. Unfortunately, livestock products are responsible for a large number of foodborne illnesses each year, constituting a serious obstacle to the well-being of populations, and being the source of tremendous economic losses. These nutrition rich livestock products also can provide appropriate environment for the growth of foodborne pathogens. Especially, Campylobacter jejuni, Salmonella spp. and Listeria monocytogenes are high risk pathogens in the foods originated from poultry. Various livestock products including egg products and duck meat products are introduced in food market, but microbiological risk in in manufacturing process of various egg products and duck meat products associated with foodborne pathogens has not been reported. The objectives of this study were 1) to assess the levels of microbiological hazards of egg products at each production stage and to validate critical control points of HACCP plan in egg product plant, 2) to investigate effect of storage temperature on the survival and growth of high risk foodborne pathogens on ready-to-eat (RTE) egg products and smoked duck meats, and 3) to evaluate of the transfer of C. jejuni biofilm to foods and examine for its ability to resuscitate from biofilm and viable but non-culturable (VBNC) state of C. jejuni on foods.
The samples we used in this study were liquid whole eggs and seven different kinds of RTE egg products (cheese/tuna/tteokgalbi/pizza omelets, baked egg, steamed egg, and egg strips). Microbial quality of these samples was evaluated by counting the level of aerobic plate count and coliform and Escherichia coli count as well as L. monocytogenes and Salmonella spp. at the critical control points in manufacturing process. In pasteurized liquid whole eggs and RTE egg products, the levels of aerobic plate counts were ranged from 0 to 4.67 log CFU/g, which is higher than microbiological standard. No coliform group and E. coli were detected in the processed egg products except for liquid whole eggs and egg strips. No significant effect of pasteurizing step on reduction of microbial levels in liquid whole eggs. However, the level of microbial contamination was significantly reduced in baked eggs after baking steps and then maintained under the safe microbial level. No L. monocytogenes and Salmonella spp. were detected in samples from the final stages of processing plan.
After surface inoculation with the mixture of S. Typhimurium, L. monocytogenes and E. coli onto various RTE egg products (cheese/tuna/tteokgalbi/pizza omelets, baked egg, steamed egg), omelets and baked egg were vacuum packed and steam egg was packed under aerobic conditions, which were stored for 9 to 12 days at 4, 10 or 15°C. In addition, inoculated baked egg and steamed egg with the mixture of S. Enteritidis, L. monocytogenes and E. coli were vacuum and aerobic packed, respectively, which were stored at 10°C in order to compare the growth of foodborne pathogens in egg products as a function of strain. Refrigeration temperature at 4°C inhibited the growth of S. Typhimurium and E. coli, but allowed the growth of L. monocytogenes slowly. However, the growth of all strains was not prevented at 10°C and the growth of L. monocytogenes was faster than that of S. Typhimurium and E. coli except for steamed egg where the population of S. Typhimurium and E. coli were reduced. At 15°C, all pathogens grew well on all egg products during storage. In addition, more rapid growth of S. Enteritidis than S. Typhimurium was observed in egg products, indicating the greater risk of S. Enteritidis in processed egg products.
Inoculated smoked duck meats with the mixture of C. jejuni, S. Typhimurium and L. monocytogenes were vacuum packed and stored at 10, 15 or 24°C. The populations of C. jejuni decreased, while the growth of S. Typhimurium and L. monocytogenes was observed regardless of storage temperature. Especially, L. monocytogenes grew up to the maximum population density more rapidly than S. Typhimurium at 10 and 15°C, while the growth rates of L. monocytogenes and S. Typhimurium at 24°C were similar during storage time.
Transfer experiments were conducted from biofilms, which were grown on slide glass in brucella broth containing 0.16% agar for 9 days at 42°C, to smoked duck meats for 5 min, 1, 3 and 24h at room temperature and the efficiency of transfer (EOT) was calculated. Inoculated smoked duck meats with C. jejuni biofilm were stored for 24h at 10, 24 and 36°C. In addition, inoculated smoked duck meats with induced VBNC C. jejuni at 10°C were stored for 24h at 42°C.
The 5 min contact time between C. jejuni biofilm and smoked duck show higher EOT (0.92) than 24h contact time (EOT = 0.08) and the efficiency of transfer decreased as contact time increased. Furthermore, C. jejuni biofilm on smoked duck meats was not recovered at 10, 24 and 36°C as well as VBNC C. jejuni was not resuscitated at 42°C.
These results indicated that effective methods to prevent cross-contamination are needed for microbial control in liquid whole eggs processing plan, especially at the steps of filtering and pasteurization. Hygiene management at processing stage based on good manufacturing practice and HACCP is important to get safe and high quality products. In addition, temperature control during transportation and at retail markets should be emphasized to control the risk of pathogens on livestock products, since pathogens grew well on egg products and smoked duck meats at 10°C. Moreover, developments of effective hurdle techniques besides smoking for smoked duck meats are needed to reduce the risk of the product from the contamination and growth of S. Typhimurium and L. monocytogenes. Microbial criteria of C. jejuni is needed in poultry and processed poultry products due to the risk of its survival and low infectious dose, although the growth of C. jejuni was not observed in smoked duck during refrigerated storage. In addition, L. monocytogenes and Salmonella spp. in livestock products such as processed egg products and poultry products should be controlled as negative in consideration of their growth and survival at refrigerated temperature.