Preparation of Incurred Samples Containing Egg-derived Protein and the Pilot Study for Proficiency Test

In allergen testing of food products, external quality assessment (EQA) programs are essential to ensure high-precision detection and the reliability of results across testing laboratories. However, conventional spiked samples may not sufficiently reflect the nature of processed foods. Therefore, this study examined the applicability of EQA programs using actual food samples that reflect real-world conditions. Twenty-four commercially available food samples were screened using the ELISA method. A coleslaw dressing (CoD) containing 33.1 μg/g of egg-derived protein which is closest to the labeling reference value of 10 μg/g, was selected. The CoD was diluted with egg-free CoD, resulting in a mean concentration of 10.4±0.6 μg/g (RSD 5.3%).Based on this result, approximately 2 kg of an incurred sample (Sample 1) was prepared for a sample in the pilot study for the EQA program, targeting a concentration of 10 μg/g, and its homogeneity and stability were confirmed. A conventional spiked sample (Sample 2) was also prepared with equivalent quality. A pilot study for the EQA program was conducted with 22 institutions. By using two kinds of ELISA kits, the average concentration was 11.9 μg and 9.7 μg for Sample 1 and 8.6 μg/g and 9.3 μg/g for Sample 2. The performance evaluation using robust statistical methods indicated that nearly all measurement results from the institutions fell within the control limits, suggesting that the incurred sample is beneficial as a test material for the EQA program. These results suggest that EQA programs using incurred samples can contribute to improving the reliability of egg allergen testing in food safety management.