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Subpopulations of non-starter bacteria increase in the draining and matting conveyors during extended production shifts.

B. Selover



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Subpopulations of non-starter bacteria increase in the draining and matting conveyors during extended production shifts.
B. Selover*, J. Johnson, J. Waite-Cusic. Oregon State University Corvallis, OR.

Cheese production environments are susceptible to microbial contamination in places where the temperature, pH, and available water and nutrients are sufficient to support growth. Long production runs can also contribute to non-starter bacteria growing in production equipment. Sources of contamination could originate from incoming raw milk or from biofilms within the draining and matting conveyor (DMC) that are reduced, but not eliminated by sanitation. The objective of this study was to identify areas in a commercial cheese production facility where bacterial populations increase during the production day. Combinations of milk, whey, curd, and/or food contact surface samples were collected on at the beginning, middle, end of the day, and after sanitation on 15 production days. Samples were enumerated for bacterial subpopulations using MacConkey, m-Enterococcus, Acinetobacter Chromogenic, and Pseudomonas Isolation agars. Representative isolates with unique morphologies were identified using 16S rRNA Sanger sequencing. Bacterial counts from swabs inside the DMC were usually below detection limit (10 cfu/mL) after sanitation; however, all subpopulations increased over the 18 h production day. Bacteria were detected at low levels (<2.4 Log cfu/mL) at mid-day. Inside the DMC (near the weir) at the end of the production day, coliform counts reached 5.3 Log cfu/mL and Acinetobacter increased to 6.2 Log cfu/mL. Throughout the DMC, Pseudomonas and Enterococcus were detected at levels as high as 3.1 Log cfu/mL and were detected after CIP (Pseudomonas: 1.4 Log cfu/mL; Enterococcus: 2.6 cfu/mL). Klebsiella, Escherichia, Enterobacter, Pseudomonas, Acinetobacter, Enterococcus and Streptococcus were all identified by 16S rRNA sequencing in samples collected from the DMC at the end of the day. Coliforms and Enterococcus increased 3.4 Log cfu/mL and 1.2 Log cfu/mL, respectively, inside the DMC in the final 8 h of the production day. This sharp increase demonstrates the critical need to consider the time between sanitation events for these subpopulations and consider their impact on finished product quality.

Keywords: cheese, microbiology, processing.