Addressing cheese quality defects with emphasis on late blowing in aged white cheddar

Alexander Lampien

doi:10.7273/000005089

Cheese products are vulnerable to contamination by hazardous microorganisms that originate from dairy farms or processing environments. These organisms can cause foodborne illness or spoilage if proper critical control points are not in place. However, certain microorganisms are difficult to control due to their enhanced heat resistance, spore-forming capabilities, and biofilm forming abilities. Raw milk is a common entry point for these hazardous microorganisms into creameries, making farm management decisions regarding feed systems, housing systems, and milking systems critical to controlling milk quality.Contamination by hazardous microorganisms can result in several cheese defects depending on the type of cheese and the offending organism. Late blowing is one such defect which has been observed in Cougar Gold® cheese at the Washington State University creamery. Our investigation traced the cause of this defect to contamination by Paucilactobacillus wasatchensis, a non-starter lactic acid bacteria originating from silage. To better understand the heat tolerance of bacteria that cause late blowing, we conducted two studies. We inoculated sterilized whole milk with either Plb. wasatchensis or Propionibacterium freudenreichii ssp. shermanii cells at >8 logs and filled five aluminum thermal-death-time (TDT) disks with the inoculated milk. The TDT disks were submerged in preheated water baths at various temperatures depending on the bacteria. The time intervals for each bacteria and temperature were selected to achieve a reduction of >3 logs between the first and last disk. All removed disks were promptly placed into an ice bath, then sampled for plating and enumeration. Survivors were plotted against the treatment time at each temperature for both bacteria, and decimal-reduction values (D-values) were calculated from these curves. The D-values obtained in our study indicated that Plb. wasatchensis does not survive pasteurization, whereas P. shermanii can survive pasteurization. Therefore, post-pasteurization contamination by Plb. wasatchensis is the likely cause of late blowing observed in Cougar Gold®. Cheesemakers may prevent cheese defects like late blowing by monitoring milk quality, using proper cleaning and sanitation procedures, utilizing pasteurization, or employing additional critical control points like microfiltration or bactofugation, both of which have shown to be effective in the removal of spores and heat-resistant microorganisms.

Addressing cheese quality defects with emphasis on late blowing in aged white cheddar

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