Good vibrations: A greener way to pasteurize milk

It also yields a fresher tasting product, university scientists say.

CHICAGO Many people like the taste of raw – as in unpasteurized – milk. The problem, of course, is that germs may infect raw milk, so food safety regulations require that commercial milk producers heat-treat their product. But food scientists at Louisiana State University think they’ve stumbled onto a tastier way to sterilize milk. They bombard it with sound waves.

At the Institute of Food Technologists’ annual meeting, July 19, LSU graduate student Marvin Moncada Reyes presented data showing that his team in Baton Rouge successfully used sonication to knock out coliform bacteria – indicators of possible fecal germs – that can taint unpasteurized dairy products. The novel process heated milk, initially stored at 4 °C, to about 55 °C. Moncada Reyes notes this temperature is well below what the Food and Drug Administration now requires for pasteurization: a brief 15-second heating to 76 °C.

Sonication’s gentler heat can have several advantages, Moncada Reyes argues. Some milk proteins begin to denature – alter or break down – at 63 °C, changing milk’s flavor by creating new volatile compounds and eliminating others. Indeed, he observes, today’s high-temperature pasteurization leads to “a cooked flavor” in supermarket milk. The LSU scientists measured flavor compounds in the milk they tested. Although values of two key chemicals measured – dimethyl amine and dimethyl sulfide –  differed little between raw and sonicated milk, the compounds’ concentrations were up to 40 times higher in conventionally pasteurized milk.

Using sound waves takes roughly half as much energy as high-temperature pasteurization to kill coliform and other bacteria that grow in an oxygenated environment, Moncada Reyes found. Indeed, he reported, sonication far surpassed the germ kill rate required by FDA. And although LSU’s experimental bench-top system is slow, Moncada Reyes sees no reason why it couldn’t be adapted to match the processing speed of current pasteurization systems. (Clearly, any commercialization of this process would be many years away.)

And because it takes less energy to pasteurize with acoustic waves, Moncada Reyes suspects milk processors could save money by switching to such a treatment. That should be very welcome news to an industry that has not seen wholesale prices keep pace with inflation.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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