Survival of Salmonella enteritidis During the Processing and Storage of Processed Duck Egg

YOU-MIN FU* AND TING SU

National Laboratories of Foods and Drugs, Department of Health, Executive Yuan

ABSTRACT

   Salmonella enteritidis CCRC 10744 from the Culture Collection and Research Center （CCRC） and S. enteritidis strain SEP from a patient specimen, were used for the survival test in the salted duck egg and the thousand-year egg during processing and storage. After inoculation of S. enteritidis at levels of 50-100 CFU∕egg yolk, the NaCl content of the egg yolk increased from 0.56％ to 0.98％ during processing of the salted egg. Similar growth curves were obtained for S. enteritidis CCRC 10744 and strain SEP. The viable cells increased to 107-108 CFU∕g in the first 2 days and maintained 107 CFU∕g by the end of the process. After processing, the salted eggs with S. enteritidis were stored at 25～30℃. Five eggs were examined every month, and both strains were found in most of the eggs even after 2 months storage. Similar procedure was followed for the thousand-year egg. During processing period, the pH value of the yolk increased from 6.5 to 10.3. The changes of viable cell count in the thousand-year eggs were similar as those in the salted egg. However, due to the final alkaline pH of the egg yolk, the viable counts in the thousand-year egg decreased to about 106 CFU∕g by the end of the process. After processing, the thousand-year eggs were also stored at 25～30℃. The viable cells of both strains decreased to roughly 105 CFU∕ g in the first month of storage. After 2 and 3 months' storage, S. enteritidis CCRC 10744 could still be found in 2 and 1 egg yolks of the 5 sampled eggs respectively, while strain SEP could be detected in all 5 eggs even after 2 or 3 months' storage.

   CCRC 10744 from the Culture Collection and Research Center （CCRC） and S. enteritidis strain SEP from a patient specimen, were used for the survival test in the salted duck egg and the thousand-year egg during processing and storage. After inoculation of S. enteritidis at levels of 50-100 CFU∕egg yolk, the NaCl content of the egg yolk increased from 0.56％ to 0.98％ during processing of the salted egg. Similar growth curves were obtained for S. enteritidis CCRC 10744 and strain SEP. The viable cells increased to 107-108 CFU∕g in the first 2 days and maintained 107 CFU∕g by the end of the process. After processing, the salted eggs with S. enteritidis were stored at 25～30℃. Five eggs were examined every month, and both strains were found in most of the eggs even after 2 months storage. Similar procedure was followed for the thousand-year egg. During processing period, the pH value of the yolk increased from 6.5 to 10.3. The changes of viable cell count in the thousand-year eggs were similar as those in the salted egg. However, due to the final alkaline pH of the egg yolk, the viable counts in the thousand-year egg decreased to about 106 CFU∕g by the end of the process. After processing, the thousand-year eggs were also stored at 25～30℃. The viable cells of both strains decreased to roughly 105 CFU∕ g in the first month of storage. After 2 and 3 months' storage, S. enteritidis CCRC 10744 could still be found in 2 and 1 egg yolks of the 5 sampled eggs respectively, while strain SEP could be detected in all 5 eggs even after 2 or 3 months' storage.

Key words: Salmonella enteritidis, duck egg, salted egg, thousand-year egg