A rapid heating and cooling of milk significantly reduces the amount of harmful bacteria, extending the shelf life by several weeks, according to a study produced by Purdue University, West Lafayette, Ind.

Bruce Applegate, associate professor in the Department of Food Science for Purdue University, and collaborators from the University of Tennessee, Knoxville, Tenn., published findings that show increasing the temperature of milk by 10 degrees for less than a second eliminates more than 99% 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,” Applegate says.

The low-temperature, short-time (LTST) method 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 temperatures about 10°C, but still below the 70°C 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.”

The LTST chamber technology was developed by Millisecond Technologies (MST), New York.

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

Phillip Myer, an assistant professor of animal science at the University of Tennessee and a co-author of the paper, says the process uses the heat already necessary for pasteurization to rapidly heat milk droplets.

“The process significantly reduces the amount of bacteria present, and it doesn’t add any extra energy to the system,” Myer adds.

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 study was funded by the Agricultural Research Service of the U.S. Department of Agriculture, Washington, D.C., the Center for Food Safety Engineering at Purdue University and Millisecond Technologies.