An assessment of L. monocytogenes transfer from wooden ripening shelves to cheeses: Comparison with glass and plastic surfaces

Food contact surfaces are subject to contamination by pathogens, which can lead to cross-contamination by transfer to other food products. However, the European regulation specifies that materials intended for safe food contact must not interfere with foodstuff characteristics. Considered a traditional and natural material, wooden boards are used as a "technological tool" during the cheese-ripening process. In France, wood is authorized for food-contact. The aim of this study was to determine the behavior of deliberately contaminated wooden surfaces in direct contact with foodstuffs. The model studied consisted of spruce ripening shelves experimentally inoculated with a well-known potential hazard throughout the production chain of some dairy products: Listeria monocytogenes. Then, the transfer from deliberately inoculated wood to cheese was analyzed and compared with plastic and glass inoculated surfaces. For this purpose, a protocol was developed and first-use spruce boards were inoculated with L. monocytogenes solution at a concentration of 105 CFU/cm(2) then the microbial transfer to pressed non cooked cheeses was studied. Factors such as cheese contact time, wood and cheese moisture contents, were tested. We compared the transfer rate with glass plates and plastic sheets with inclined meshes, commonly used throughout the cheese production chain, in the same conditions. The results showed a transfer yield below 3% (CFU/cm(2)) in the first hour of contact for all surfaces tested and was 0.55% for the wooden boards. No differences were found for drier cheeses or for higher wood moisture content. The wooden porous surface in contact with cheeses was not a factor that increased the L monocytogenes direct transfer rates. In conclusion, wooden shelves have the lowest transfer rate of L monocytogenes to pressed non-cooked cheeses compared to glass and polypropylene surfaces. This results contribute to the suitability of use of wooden material for direct contact with food.