Control of spoilage microbial load of trout fillets and fish contact surfaces by ozonated water. A case report

This study reports some results of application of ozonated water in improving hygienic conditions of food contact surfaces and trout fillets carried out by a small Italian trout and salmon breeding company located in north east of Italy. Processed trout were washed with ozonated water at 5 ppm O3 coming out a showerhead under 1 bar pressure for 1 and 5 minutes and immediately stored in ice. After 24h and after 4, 7 and 11 days of cold (4 and 7°C) storage, trout fillets were analyzed for total bacterial aerobic count (APC) and for Enterobacteriaceae. In addition, the same ozonated water at about 10 ppm, was employed to verify its antimicrobial activity on two target pathogens potentially contaminating fish contact surfaces and later the floor of processing rooms. In the case of trout fillets, the best conditions allowed to increase the trout fillet shelf-life from 4 to 11 days thanks the reduction when, compared to un-ozonated samples, target microbial population reached 6 log cfu/cm2 and 4 log cfu/cm2for APC and for Enterobacteriaceae, respectively. In the case of fish contact surfaces contaminated by target pathogens, results confirmed that the best antimicrobial activity was directly proportional to contact time and ozone concentration and inversely proportional to organic matter contaminating the surface. When antimicrobial assays were conducted on fish contacts surfaces, including floor of the processing room, the best experimental conditions employing ozonated water were able to kill almost all naturally contaminating microorganisms. In conclusion, the use of ozonated water in a fish processing plant is useful to improve microbial quality of the semi-processedproducts, reduce environmental microbial contamination and, in addition, to reduce the amount of drinkable water employed thank to the possibility to avoid the last washing step that always follows the final disinfection step.