Treatment of milk with low-frequency ultrasound significantly increased the total bacterial counts and the counts of enterococci, coliforms, and staphylococci. Warming diluted milk for about 12 min at 30 or 40 C increased the counts of some organisms, but the heat produced by ultrasonic treatment did not account entirely for its effect. The ultrasonic effect was related to the energy output of the generator and to the energy absorbed by the treated materials.
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