Rapid heating and cooling of milk reduces the amount of harmful bacteria present, extending its shelf life by several weeks, a team of researchers has found.

Increasing the temperature of milk by 10 degrees Celsius for less than a second eliminates more than 99% of the bacteria left behind after pasteurization, according to a study by Bruce Applegate, associate professor in Purdue University's Department of Food Science. He worked with scientists from the University of Tennessee on the research. “It’s an add-on to pasteurization, but it can add shelf life of up to five, six or seven weeks to cold milk,” he says.

Bruce Applegate of Purdue University developed a process that could greatly extend milk's shelf life. Image credit: Purdue Agriculture Communication/Tom Campbell.Bruce Applegate of Purdue University developed a process that could greatly extend milk's shelf life. Image credit: Purdue Agriculture Communication/Tom Campbell.Pasteurization removes significant amounts of harmful pathogens that can cause illness and eventually spoil dairy products. It is considered a "high-temperature, short-time" method. The treatment gives milk a shelf life of about two to three weeks.

The low-temperature, short-time (LTST) method used in the Purdue study sprayed tiny droplets of pasteurized milk, which was inoculated with Lactobacillus and Pseudomonas bacteria, through a heated, pressurized chamber, rapidly raising and lowering their temperature but still below the 70C threshold required for pasteurization. The treatment lowered bacterial levels below detection limits and extended shelf life to up to 63 days.

Sensory tests compared pasteurized milk with milk that had been pasteurized and run through the LTST process. Panelists did not detect differences in color, aroma, taste or aftertaste between the products.

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