US - A rapid heating and cooling of milk significantly reduces the amount of harmful bacteria present, extending by several weeks the shelf life of one of the most common refrigerator staples in the world, according to a Purdue University study.
Bruce Applegate, Purdue associate professor in the Department of Food Science, and collaborators from Purdue and the University of Tennessee published their findings in the journal SpringerPlus, where they show that increasing the temperature of milk by 10 degrees for less than a second eliminates more than 99 per cent of the bacteria left behind after pasteurisation.
“It’s an add-on to pasteurisation, but it can add shelf life of up to five, six or seven weeks to cold milk,” Mr Applegate said.
Pasteurisation, which removes significant amounts of harmful pathogens that can cause illness and eventually spoil dairy products, is considered a high-temperature, short-time method. Developed by Louis Pasteur in the 19th century, the treatment gives milk a shelf life of about 2-3 weeks.
The low-temperature, short-time (LTST) method in the Purdue study sprayed tiny droplets of pasteurised milk, which was inoculated with Lactobacillus and Pseudomonas bacteria, through a heated, pressurised chamber, rapidly raising and lowering their temperatures about 10 degrees Celsius but still below the 70-degree Celsius threshold needed for pasteurisation.
The treatment lowered bacterial levels below detection limits, and extended shelf life to up to 63 days.
“With the treatment, you’re taking out almost everything,” Mr Applegate said. “Whatever does survive is at such a low level that it takes much longer for it to multiply to a point at which it damages the quality of the milk.”
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