New bacteria contaminates even refrigerated milk

November 17th, 2008 - 3:17 pm ICT by IANS  

London, Nov 17 (IANS) A new species of microbes, isolated by scientists, can contaminate raw milk even under refrigeration. Many countries have outlawed raw milk because of its potential contamination by harmful microbes. It then tastes bitter with a thick, sticky feel.

“When we looked at the bacteria living in raw milk, we found that many of them had not been identified before,” said Malka Halpern of University of Haifa, Israel.

“We have now identified and described one of these bacteria, Chryseobacterium oranimense, which can grow at cold temperatures and secretes enzymes that have the potential to spoil milk,” he added.

New technologies are being developed to reduce the initial bacterial counts of pasteurised milk to very low levels.

Most enzymes will be denatured at the high temperatures used during pasteurisation, which means they will stop working, according to a release of the Society for General Microbiology.

However, heat-stable enzymes made by cold-tolerant bacteria will still affect the flavour quality of fluid milk and its products. Because of this, research into cold-tolerant bacteria and the spoilage enzymes they produce is vital.

“Milk can be contaminated with many different bacteria from the teat of the cow, the udder, milking equipment and the milking environment,” said Halpern.

“Milk is refrigerated after collection to limit the growth of microbes. During refrigeration, cold-tolerant, or psychrotolerant, bacteria that can grow at 7°C dominate the milk flora and play a leading role in milk spoilage.”

The benefits and risks of drinking unpasteurised milk are being debated. Some people believe the benefits from extra nutrient content of raw milk outweigh the risk of ingesting potentially dangerous microbes, such as Mycobacterium bovis, which can cause tuberculosis, and Salmonella species.

The report was published in the November issue of the International Journal of Systematic and Evolutionary Microbiology.

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