How to screen raw milk for hygiene quality at the dairy for bacteria and somatic cell count

While it sounds like an obvious thing to do, checking the hygienic quality of milk before it flows into the processing plant is not a straightforward task. 

The traditional petri film method for testing bacteria takes about two days to get to a result, by which time the milk is already in production. Alternatively, a direct microscope count (DMC) and direct microscopic somatic cell count (DMSCC) involves the use of chemical reagents and a physical cell count resulting in a subjective test as counts will always vary between operators.  

The BacSomatic tests both bacteria and somatic cell count using a technology called flow cytometry, delivering results in just under ten minutes. 

When James Black, Quality Control and Assurance Manager at Dairy Farmers of America, heard about an opportunity to test the new solution, it sounded like an obvious thing to do.  “We were interested in participating in the trial because it offers a new way to test bacteria and somatic cells at once,” he says. “The biggest potential is as an alternative to the way tests are performed today with an analyst conducting physical counts, which can have subjectivity such as a DMC method.”

The small footprint of the handy and easy-to-use unit is also attractive for the relatively small laboratory at the plant where he is based. 

Taking the blindfold off dairy production
Not only is the BacSomatic more consistent than subjective tests, it delivers results for both bacteria count and somatic cells within ten minutes, which is way faster than the traditional petri film test.

This will give producers the ability to check raw milk deliveries as they arrive in tanker trucks, leading to gains downstream in dairy production with better products made more efficiently using a more consistent quality raw material.

“This could be a great tool for larger dairy plants for use as a means to accept or reject incoming milk,” says Black. 

Black made regular checks to keep track of how the new method was performing against the old, with typically one traditional test to 25 BacSomatic tests. He did not conduct a formal study as such, but the regular tests performed over several months painted a clear picture of the performance.

It would typically count a little more than the manual count, but this was not a surprise because the BacSomatic gives a higher definition based on an individual bacteria count (IBC), whereas the manual count or microscope methods look at colony forming units (CFU). 

The individual bacteria count approach also explains the much faster time-to-result. While colony-forming units are grown over a period of two to three days, the BacSomatic has incubation chambers that take about eight minutes to prepare the milk for counting, generating just enough bacteria to give a reliable prediction of levels in a sample. Following the incubation step, the actual test of individual bacteria takes about one and a half minutes. Likewise, the somatic cell count is very fast at about two and a half minutes. 

Ideal for large volume raw milk plants
Overall, the accuracy and speed of the BacSomatic makes it an excellent tool to decide how to best use incoming milk at the dairy.  Running the instrument on a daily basis was also a pleasure. “The experience of using the instrument was pleasing,” says Black. “There was a great collaboration with FOSS. The instrument is easy to use and maintain. It did not require much training for my operators to start using the instrument.”

Last, but not least, the BacSomatic brings the dairy sector up to date with a consistent instrument-based test for raw milk hygiene quality. “It is always nice to eliminate a subjective test such as the DMC method,” he concludes. 

Dairy Farmers of America (DFA) is a national milk marketing cooperative owned by and focused on nearly 8,000 dairy farm families in 48 states. The Cooperative’s core business is to market members’ milk, pay them a competitive price, deliver value and be a leader in the industry.

DFA is also one of the country’s most diversified manufacturers of dairy products, food components and ingredients, and is a leader in formulating and packaging shelf-stable dairy products.

Background: 
The road from traditional plate counting to rapid instrument-based tests at the dairy

Around 20 years ago, milk testing centers started using instruments based on a technology called flow cytometry. This counts individual bacteria in a milk sample. Today, flow cytometry instruments like the FOSS BactoScan handle literally thousands of samples every day at milk testing centers around the world. However, these large high-throughput instruments were too expensive and cumbersome for application at the dairy.

Most dairies have therefore continued with the traditional manual ‘plate count’ method (also performed using ‘petri-film’ in many parts of the world). Alternatively, some semi-automated analytical equipment solutions have proved much faster, but still involve unwanted handling of chemical reagents.

The BacSomatic analyser offers a new fully-automated way to check the hygienic-quality of raw milk. It’s a world’s first and has been achieved by a clever new design that fits the flow cytometry method used in larger milk testing instruments into a small box ideal for use at the dairy intake.