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Low-level microbial contaminants in whey multiply rapidly on food contact surfaces under production conditions.

B. Selover



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Low-level microbial contaminants in whey multiply rapidly on food contact surfaces under production conditions.
B. Selover*, J. Waite-Cusic. Oregon State University Corvallis, OR.

As the time between sanitation events increases, bacteria can attach and grow on equipment and surfaces potentially developing biofilms that could impact dairy product quality. Prudent sanitation schedules should be implemented to mitigate biofilm development; however, scientific evidence is lacking to inform these decisions. The purpose of this study was to demonstrate the potential for naturally low levels of non-starter bacteria in Cheddar cheese whey to attach and develop biofilms on representative surfaces within the length of a typical production day (18 h). Whey was collected after cutting Cheddar cheese curds during normal production activities at the Oregon State University Creamery. Whey was rapidly cooled and held at 4�C until use. The whey was preheated to 35�C and pumped (1.1 L/h) through a lab-scale CDC bioreactor containing polypropylene and stainless steel coupons. Bulk whey from the bioreactor was sampled at 0, 12, 15, and 18 h and enumerated for starter lactic acid bacteria, coliforms, Acinetobacter and Pseudomonas. Coupons of each material were removed at 12, 15, and 18 h and analyzed for bacterial attachment and growth using standard enumeration methods and scanning electron microscopy (SEM). The experiment was replicated 3 times. Non-starter bacteria increased in whey from 1.8 Log cfu/mL to 6.4 Log cfu/mL in 18 h, while starter bacteria remained constant at 7.6 Log cfu/mL. After 18 h, coliform levels on coupons increased to 6.4 Log cfu/cm2, whereas Acinetobacter and Pseudomonas counts each increased to 4.9 Log cfu/cm2. Whey pH was effectively maintained at 5.9—6.4 throughout the experiment. Bacterial attachment occurred at about the same rate on both materials after 18 h. SEM showed even distribution of attached bacteria on stainless steel, whereas polypropylene harbored biofilms only in manufacturing defects (cracks, crevasses). These results demonstrate that naturally low levels of bacterial contamination in whey can lead to significant bacterial growth on manufacturing surfaces within an 18 h production shift. These findings can inform sanitation schedules for cheese and other dairy manufacturers.

Keywords: biofilm, whey, microbiology.