Scientists have discovered new species of bacteria that can grow at low temperatures, potentially spoiling raw milk even when it is refrigerated.

According to research published in the November issue of the International Journal of Systematic and Evolutionary Microbiology, the microbial population of raw milk is much more complex than previously thought.

Malka Halpern, from the University of Haifa in Israel, says scientists have found many bacteria living in raw mile that have not been identified before.

"One of these bacteria, Chryseobacterium oranimense, can grow at cold temperatures and secretes enzymes that have the potential to spoil milk," he says.

"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."

New technologies are being developed to reduce the initial bacterial counts of pasteurized milk to very low levels. But most enzymes will be denatured at the high temperatures used during pasteurisation, which means they will stop working.

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