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Microbe Population in Raw Milk Changes During Processing

24 August 2016

US - Findings from a new study, reported in the journal mBio, may help food companies improve the quality of dairy products.

The microbial composition of raw milk has an impact on the quality, shelf life, and safety of processed milk and other dairy products. While harmful bacteria rarely reach the consumer, because they are destroyed during pasteurisation, other bacteria can cause spoilage issues or defects in the product, such as off-flavors in cheese, which can result in product being thrown away.

In the new study, researchers set out to identify the microbiota of raw milks collected for large-scale product manufacturing in California.

Bacteria varied by season and were highly diverse, but the milk also had a core microbiome composed of 29 different taxa, including Streptococcus, Staphylococcus, and unidentified Clostridiales.

Another important finding was what happened to the milk after it got into the dairy processing plant. "We saw this interesting shift of the types of bacteria that are dominant in the milk when it goes from the truck to silos where the milk is stored before pasteurisation," said Maria Marco, PhD, associate professor, Department of Food Science & Technology, University of California-Davis, and lead author of the paper. The effects of the processing facility outweighed the raw milk microbiome and the microbial composition changed distinctly within some, but not all silos, a short time after transfer.

By knowing the types of microbes present in foods, scientists can devise ways to manage or get rid of spoilage microbes, so they don't make their way into the final product and cause quality problems.

"This study was an exploratory mission to find out what types of bacteria are in our raw milk and what happens to them when they reach the built-environment," said Dr Marco. "We now need to tackle the bigger problem of how can we control those microbes in an effective way."

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