Duck Eggs and Food Safety
Duck eggs are widely consumed as a source of animal protein and contain nutrients including protein, fat, vitamins, and minerals. However, eggs can become contaminated with microorganisms during production, transportation, storage, and retail handling.
One important foodborne pathogen is Salmonella sp. The bacterium can contaminate animal-derived foods and may reach consumers through inadequate cooking or poor handling. The eggshell normally acts as a physical barrier against microorganisms, but cracks or damage can reduce that protection. Environmental contamination can also occur even when the eggshell remains intact.
The researchers from the Politeknik Kesehatan Kemenkes Kalimantan Timur examined duck eggs sold by nine vendors at Segiri Central Market. They selected 27 eggs, with three eggs from each vendor: one with a clean shell, one with a dirty shell, and one with a visible crack. Each category therefore contained nine samples.
One Sample Tested Positive for Salmonella
Laboratory testing detected Salmonella sp. in one of the 27 samples, equivalent to 3.7 percent of the tested eggs.
The positive sample came from the cracked-eggshell group. All nine clean eggs and all nine dirty eggs tested negative for Salmonella sp. Overall, 26 samples, or 96.3 percent, were negative in the specific Salmonella test.
The researchers noted that a cracked shell may reduce the egg's physical protection and provide an opportunity for microorganisms from the surrounding environment to reach the inside of the egg.
However, the finding does not establish that cracked eggs statistically have a higher risk of Salmonella contamination. The study was descriptive, included only nine samples in each shell-condition category, and did not use an inferential statistical test to determine whether shell condition was associated with Salmonella detection.
Seven Eggs Exceeded the Microbial Limit
The researchers also measured Total Plate Count, or TPC, to estimate the overall number of viable microorganisms detected under the laboratory testing conditions.
TPC results varied considerably among the samples. The highest countable value was recorded in a clean-shell egg at 2.22 × 10⁶ colony-forming units per gram (CFU/g). The highest countable value in the cracked-shell group was 7.0 × 10⁵ CFU/g, while the dirty-shell group reached 3.0 × 10⁵ CFU/g. Some dirty and cracked eggs produced results classified as “Too Many To Count,” meaning the number of colonies exceeded the practical counting range.
When the results were compared with the 1 × 10⁴ CFU/g limit used in the study under BPOM Regulation No. 13 of 2019, seven of the 27 samples, or 25.9 percent, did not meet the standard.
The seven samples consisted of:
- 1 of 9 clean eggs that exceeded the limit
- 2 of 9 dirty eggs that exceeded the limit
- 4 of 9 cracked eggs that exceeded the limit
The remaining 20 samples, or 74.1 percent, met the standard used in the study.
Clean-Looking Eggs Can Still Carry High Microbial Loads
One of the important findings from the research by Virliana Mertasari and colleagues is that consumers cannot determine an egg's microbial quality simply by looking at its shell.
The clean-shell group actually contained the highest countable TPC result. This means a visually clean egg can still have a substantial microbial load as a result of contamination occurring during production, transportation, storage, or handling.
At the same time, the researchers caution against assuming that dirty or cracked eggs always contain more microorganisms. The microbial condition can vary depending on when and how contamination occurred, as well as storage and handling conditions.
Supri Hartini and the other researchers from the Politeknik Kesehatan Kemenkes Kalimantan Timur also distinguish between TPC and Salmonella testing. TPC provides an indication of the general viable microbial load, whereas specific Salmonella testing determines whether the particular foodborne pathogen is detected. Therefore, a high TPC result does not automatically mean that an egg contains Salmonella, and a low TPC result cannot be used to conclude that Salmonella is absent.
Implications for Consumers, Vendors, and Future Research
The findings have practical implications for food safety at traditional markets. Egg safety requires attention not only to the appearance of the shell but also to handling, storage, sanitation, and cooking practices.
For consumers, the researchers recommend hygienic handling of eggs, appropriate storage, and avoiding raw or inadequately cooked eggs. Proper cooking is particularly important because contaminated eggs can serve as a vehicle for foodborne infection.
For future research, Virliana Mertasari, Supri Hartini, Tiara Dini Harlita, and Lamri recommend examining larger numbers of eggs and vendors. Future studies could also measure storage duration, storage temperature, egg source, handling practices, sanitation conditions, and the degree of shell cracking or dirtiness. Additional testing for bacteria such as Escherichia coli and Staphylococcus aureus could provide a broader picture of the microbiological quality of duck eggs.
The researchers ultimately reported that one of 27 duck egg samples from Segiri Central Market tested positive for Salmonella sp., while seven samples exceeded the microbial limit applied in the study. Because the research used a descriptive design without inferential statistical analysis, the results do not establish a statistically significant relationship between eggshell condition and microbial contamination.
Author Profiles
Virliana Mertasari — Politeknik Kesehatan Kemenkes Kalimantan Timur. The article does not state her academic degree or specific field of expertise.
Supri Hartini — Politeknik Kesehatan Kemenkes Kalimantan Timur and corresponding author. The article does not state her academic degree or specific field of expertise.
Tiara Dini Harlita — Politeknik Kesehatan Kemenkes Kalimantan Timur. The article does not state her academic degree or specific field of expertise.
Lamri — Politeknik Kesehatan Kemenkes Kalimantan Timur. The article does not state his academic degree or specific field of expertise.
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