Honors Program


Document Type


Date of this Version

Spring 3-11-2020


Humphrey, J. 2020. Effect of Storage Time and Temperature on the Recovery of Milk and Peanut Residue from Environmental Swabs. Undergraduate Honors Thesis. University of Nebraska-Lincoln.


Copyright Jessica Humphrey 2020.


Environmental swabs of shared processing equipment are commonly utilized by the food industry during cleaning validation studies. Some of these swabs are sent to 3rd party laboratories for evaluation. However, the recovery of protein residues of allergenic foods between the time of swabbing and time of testing has yet to be systematically studied.

The objective of this study was to determine the recovery of allergen residues (peanut and milk) from swabs held at different holding times and temperatures. Commercial ELISAs (enzyme-linked immunosorbent assays) were evaluated to determine allergen residue recovery from swabs inoculated with known amounts of peanut and Non-Fat Dry Milk (NFDM). For each allergen, 100, 50, and 25 ppm peanut flour or NFDM were prepared and each spiked onto Neogen Environmental Swabs (Product No. 8432S) which were stored at room temperature (RT), 37, 4, and -20°C for 0, 1, 3, 5, 7, 10, and 14 days. Subsequently, swabs were tested using the commercial Veratox® for Peanut and Veratox® for Total Milk Allergen Quantitative ELISA Test kits from Neogen Corp. (Lansing, MI) and the Peanut Protein ELISA kit from Morinaga Institute of Biological Science, Inc. (Japan).

While both allergens were detected by ELISA on day 14 at all four storage temperatures, the percentage recovery decreased from day 0 to14 with the greatest decrease occurring from day 0 to 1. For swabs spiked with peanut and tested with the Veratox for Peanut ELISA kit, the largest decrease was observed at RT and 37 °C (3-6-fold decrease in recovery). However, only a 2-fold decrease in recovery was observed with peanut swabs stored at 4 °C and -20 °C, with the highest recovery observed from swabs stored at -20 °C. When peanut spiked swabs were analyzed using the Morinaga peanut ELISA kit, less variation in recovery was observed from day 0 to 14 at all four storage temperatures and at all three spike levels. For all swabs, there was a less than 2-fold decrease in recovery from days 0-14. For swabs spiked with NFDM, the percent recoveries decreased between 2-3-fold when stored at RT and 37 °C and ~2-fold when stored at 4 °C and -20 °C. The apparent recovery of peanut and NFDM decreases when the swabs are stored for extended times at higher temperatures but were minimally affected when stored at 4 or -20 °C. These results indicate that testing laboratories and the food industry should transport swabs at 4 or -20 °C. However, these results are limited to the Neogen Environmental Swabs and the evaluated test kits. Further evaluation of additional protein targets and ELISAs is warranted to determine if these results are consistent for alternate targets and extractions.