Low pressure plasma to decontaminate Listeria innocua in Taleggio PDO cheese: Feasibility and preliminary outcomes

Background: Foodborne Listeriosis is a major public health concern worldwide, leading to higher hospitalization and fatality rates in comparison to other microbial pathogens. Soft mould- and smear-ripened cheeses are very sensitive to infection with Listeria monocytogenes, and their rinds are particularly favourable sites for listerial multiplication. Unlike other technologies effective in controlling food pathogens, non-thermal low pressure plasma could impair listerial growth without or with limited effects on the sensory properties of cheese. Objectives: This study aimed at assessing the application of low pressure plasma processing for decontaminating Listeria innocua in rinds of Italian Taleggio PDO cheese. The effect of the plasma treatment on rind color was investigated as well, since this parameter represents a typical quality attribute of this soft smear-ripened cheese. Methods: The closely related non-pathogenic species L. innocua was employed instead of L. monocytogenes for artificial contamination of Taleggio rinds. Two L. innocua strains were mixed in equal ratios and spread (5.56 log10 CFU) on rinds. Samples were exposed to Ar-O2 low pressure plasma (85-145 W, 7 mbar) at different time intervals. Listeria was enumerated (ISO 11290-2:1988). Color measurements were performed with a tristimulus colorimeter and expressed in terms of CIELAB color space values. Results: Low pressure plasma treatment was effective for inhibiting L. innocua. The logarithmic reductions depended on the exposure time and the highest inactivation (1.33 Log10 CFU/g) was observed after 20 min treatment. The treated rinds complied with the product specification concerning rind color and showed a less yellow, higher color intensity.