University of Haifa scientists in Israel have identified a new species of bacteria that can grow at low temperatures,spoiling raw milk even when it is refrigerated.
The researchers say that the bacteria called chryseobacterium oranimense, which can grow at cold temperatures, secretes enzymes that have the potential to spoil milk.
Milk can be contaminated with many different bacteria from the teat of the cow, the udder, milking equipment and the milking environment, said Dr. Malka Halpern from the University of Haifa, Israel.
Milk is refrigerated after collection to limit the growth of microbes. During refrigeration, cold-tolerant, or psychrotolerant, bacteria that can grow at 7 degree Celsius dominate the milk flora and play a leading role in milk spoilage.
Although we have not yet determined the impact on milk quality of C. oranimense and two other novel species (C. haifense and C. bovis) that were also identified from raw milk samples, the discovery will contribute to our understanding the physiology of these organisms and of the complex environmental processes in which they are involved.
There is still a lot to learn about the psychrotolerant bacterial flora of raw milk, Halpern added.
Some people believe the health benefits resulting from the extra nutrient content of raw milk outweigh the risk of ingesting potentially dangerous microbes, such as Mycobacterium bovis, which can cause tuberculosis.
Because of these risks, many countries have made the sale of unpasteurised milk illegal.
The research is published in International Journal of Systematic and Evolutionary Microbiology.