Purpose: The overall purpose of this study was to evaluate design of equipment used to produce frozen dairy desserts for characteristics that might limit cleanability and allow survival of L. monocytogenes. We also evaluated the adherence, survival and resistance to sanitizers of L. monocytogenes in contaminated ice cream allowed to dry on stainless steel.
Methods: An expert on 3A and NSF sanitary standards examined equipment and highlighted several design issues that might result in difficult to clean niches. We also conducted experiments in which ice cream (5%, 10%, or 12% fat) was inoculated with a cocktail of L. monocytogenes strains, allowed to dry on stainless steel coupons and evaluated for L. monocytogenes survival and resistance to acid or chlorine-based sanitizers.
Results: We found sanitary design flaws such as rough finishes and surface irregularities that do not meet 3A or NSF standards and make these surfaces more difficult to efficiently clean and sanitize. When L. monocytogenes contaminated ice cream was allowed to dry on stainless steel coupons at 4°C, numbers of CFU remained at 7 log CFU for at least 12 weeks. Sanitizers had no detrimental effect on L. monocytogeneswhen used at a concentration and contact time (one minute) recommended by the manufacturer.
Significance: We find evidence that equipment used for frozen dairy desserts has design issues that might impair sanitization and provide harborage for L. monocytogenes. This is of potential concern because L. monocytogenes survives for extended periods in ice cream based soil, where it is more resistant to sanitizers.