Inactivation of refrigerator biofilm bacteria for application in the food service environment

Abstract

Refrigerator biofilm formation in food environments can result in spoilage and food safety problems. Biofouling of food contact surfaces are difficult to combat, and while there are significant risks involved with tolerating their presence, methods for their removal are not commonly available. In this study, biofilms were grown on plastic refrigerator trays. Cultures of mixed wild strains were started using kitchen scraps suspended in nutrient broth. Biofilms were allowed to mature with approximately 10⁹ CFU per tray test area. Spoilage species identified included Pseudomonas putida, Sphingobacterium multivorum, Citrobacter freundii and Proteus vulgaris. A series of 39 different treatment interventions were trialed during three different biofilm test runs. Results obtained from treatments ranged from a less than 1 log₁₀ reduction for light duty cleaning operations to over a 5 log₁₀ reduction involving more complex treatment methods. The latter included combinations of hot soapy water (75 °C), scrubbing, treatment with high pH (12.0) cleaners followed by acetic acid (vinegar) exposure and included pre- and post-treatment wiping with paper towels.