To ensure the absence of allergens after cleaning, agri-food companies check with swabs. The principle is to pass the cotton (or other material such as polyurethane) on the surface to capture the rest of allergens. Verification of the absence of micro-organisms can also be done with swabs. Following this sampling, the swab will be analyzed for the presence of allergens.
Professor Godefroy's team from the PARERA platform studied the stability of milk allergens and gluten on 5 different types of swabs for 7 days under different temperature conditions.
The gluten remained detectable on swabs for 7 days on polyurethane and cotton. For milk, the conclusions are the same except that the samples had to be stored in the fridge.
The article cn be found here.