Evaluation of factors influencing dairy biofilm formation in filling hoses of food-processing equipment

Biofilms in dairy-processing environments lead to increased opportunities for microbial contamination of processed products. The aim of this work is to investigate the influence of factors that can affect biofilm onset in a dairy-filling test hose. Bacterial composition (monoculture Pseudomonas fragi, polyculture), fat content of milk (1.5%, 3.5%), flow condition (laminar, turbulent), and contact material (PTFE, stainless steel 1.4404) were considered as factors at a constant low temperature of 5.5 +/- 0.5 degrees C. Biofilms were visualized by microscopy (CLSM) and analysed by counting viable cells, ATP-bioluminescence assay, and staining method for biomass quantification. The correlation between these methods was evaluated, since the chosen methods detect different characteristics of biofilms. Furthermore, enzymatic cleaning was applied after each experimental run. The results showed that the bacterial composition, material type, and fat content significantly affect the results of viable-cell counting (p <= 0.05). Flow conditions and material type both have significant influence upon biomass-quantification results (p <= 0.001). The highest positive Pearson correlation was estimated between the ATP-bioluminescence and biomass methods (0.550), while the lowest correlation was found between viable-cell counting and biomass quantification (0.345). Enzymatic treatment showed a good result for the cleaning of the PTFE-hose liner in the dairy-filling hose.