Post-lethality water bath treatments to control Listeria monocytogenes in vacuum packed Ricotta salata wedeges

Ricotta salata produced in Sardinia is a whey cheese largely exported in several countries, usually consumed grated or cut into wedges. In recent years a number of recalls due to Listeria monocytogenes contamination have been reported. Recontamination of unpackaged product from processing environment during post process manipulations cannot be completely avoided. Composition of Ricotta salata supports the growth of L. monocytogenes during refrigerated storage. Therefore, alternative strategies should be implemented to reduce the risk of L. monocytogenes to levels accepted by international health authorities. Water bath treatment of vacuum packed Ricotta salata was previously validated as an effective and economic method to reduce surface contamination with L. monocytogenes. The aim of the present study was to select the ideal temperature time combination for reducing of 5 log L. monocytogenes level in artificially contaminated Ricotta salata wedges. Nine temperature-time combinations, i.e. 75°C, 85°C and 90°C for 10 min, 20 min and 30 min each were tested. The efficacy of the treatment was assessed based on the immediate effect on L. monocytogenes counts and after 30 days of refrigerated storage. The optimum combination was assessed taking into account also sensory properties and the economic cost of the treatment. None of the temperature was effective when applied for 10 min, while 75°C up to 20 min were not suitable for the desired level of reduction. Treatment at 85°C and 90°C applied for 20 and 30 min are eligible as possible control strategies to extend the shelf-life of vacuum packed Ricotta salata wedges.