Effect of washing with high pressure water spray on removal of Listeria innocua from Gorgonzola cheese rind.

Contamination of Gorgonzola cheese surface by Listeria is a difficult problem to solve by only applying good manufacturing practices. Treating of the cheese rind at the end of ripening may be a tool to improve cheese safety. The aim of this study was to evaluate the effect of a high pressure water spray washing technology in reducing Listeria load from Gorgonzola cheese rind without using oxidizing agents. The surface of Gorgonzola cheese was contaminated (up to 107 cfu g1 of scraped rind) with a mixture of four strains of Listeria innocua. The count of Listeria was made by scraping (2 mm depth) the rind of the cheese. The contaminated cheeses were then washed at different pressures, ranging from 1 to 5 MPa for 1 min. The lower the pressure, the lower was the removal of Listeria. A reduction of up to 99.89% was achieved washing the cheese at 5 MPa, followed by rinsing at 1 MPa for 1 min. Changing the inoculum size (102, 104, and 107 cfu g1), did not change the efficacy of Listeria removal, when the same water pressure was applied. The washing of Gorgonzola cheese with pressurized jet water, without adding any preservative to the water, can be considered a further important physical hurdle, in controlling pathogenic bacteria and improving cheese safety.