Effect of Storage Time and Temperature on the Recovery of Peanut, Milk, and Gluten Residue from Environmental Swabs

Food companies utilize environmental swabs in production facilities to validate cleaning procedures and ensure food products and food contact surfaces contain no detectable residues of unintentional food allergens. When swabs are sent to third-party laboratories as part of cleaning validation trials, the current recommendation is to ship swabs on ice with same-day shipping. However, with unforeseen delays, the temperature and duration of storage exert unknown effects on the recovery of allergen residues from swabs. The recovery of three allergenic food residues (peanut, milk, gluten) from Neogen Environmental Swabs following storage at specified temperatures and times was evaluated. Extracts of 25, 50, and 100 ppm (mg/L) peanut flour, nonfat dry milk (NFDM), and gluten (an additional 10 ppm (mg/L) spike was included for gluten) were prepared and spiked onto the swabs that were then stored at room temperature, 37 °C, 4 °C, and -20 °C for 0, 1, 3, 5, 7, 10, and 14 days. Subsequently, swabs were tested using two commercial ELISA methods (Neogen Veratox® and Morinaga) for each allergenic food. Higher and more stable recovery was obtained throughout the 14-day period across all three allergenic foods when tested using the Morinaga kits by comparison to the Veratox kits. For peanut and milk recovery from swabs analyzed using the Veratox kit, the greatest decrease in recovery was observed from day 0 to day 1. Gluten-spiked swabs tested with the Veratox kit did not demonstrate significant variability in recovery over time. Overall, higher recoveries were observed when swabs were stored at lower temperatures. These results indicate that swabs should be transported and stored at 4 °C or -20 °C until analysis. However, these results are limited to the Neogen Environmental Swabs and the ELISA kits evaluated in the current study. Further evaluation of additional protein targets, ELISA kits, and swab types is warranted to determine if these results are consistent for alternate targets, extractions, and swab types.