A rapid heating and cooling of milk significantly reduces the amount of harmful bacteria, extending its shelf life by several weeks.

New research shows that increasing the temperature of milk by 10 degrees Celsius for less than a second eliminates more than 99 percent of the bacteria left behind after pasteurization.

“It’s an add-on to pasteurization, but it can add shelf life of up to five, six, or seven weeks to cold milk,” says Bruce Applegate, associate professor of food science at Purdue University and coauthor of a new study in the journal SpringerPlus.

Pasteurization, which removes significant amounts of harmful pathogens that can cause illness and eventually spoil dairy products, is considered a high-temperature, short-time method. The treatment gives milk a shelf life of about two to three weeks.

The new low-temperature, short-time method in the current 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 temperatures about 10 degrees Celsius but still below the 70-degree Celsius threshold needed for pasteurization. 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,” Applegate says. “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.”

Millisecond Technologies, a company based in New York, developed the technology. Sensory tests compared pasteurized milk with milk that had been pasteurized and run through the new process. Panelists didn’t detect differences in color, aroma, taste, or aftertaste between the products.

The process uses the heat already necessary for pasteurization to rapidly heat milk droplets, says coauthor Phillip Myer, assistant professor of animal science at the University of Tennessee. “The process significantly reduces the amount of bacteria present, and it doesn’t add any extra energy to the system.”

The promise of the technology is that it could reduce waste and allow milk to reach distant locations where transport times using only pasteurization would mean that milk would have a short shelf life upon arrival. The process could be tested without pasteurization to determine if it could stand alone as a treatment for eliminating harmful bacteria from milk.

The Agricultural Research Service of the US Department of Agriculture, the Center for Food Safety Engineering at Purdue University, and Millisecond Technologies funded the work.

Source: Purdue University

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