Inactivation of microorganisms in milk and apple cider treated with ultrasound

Nonthermal technologies are emerging as promising alternatives to heat treatment for food processing. Ultrasound, defined as sound waves with a frequency greater than 20 kHz, has proven bactericidal effects, especially when combined with other microbial-reduction strategies such as mild heating. In this study, ultrasound treatment (sonifier probe at 20 kHz, 100% power level, 150 W acoustic power, 118 W/cm2 acoustic intensity) with or without the effect of mild heat (57 degrees C) was effective at reducing microbial levels in raw milk, Listeria monocytogenes levels inoculated in ultrahigh-temperature milk, and Escherichia coli O157:H7 in apple cider. Continuous flow ultrasound treatment combined with mild heat (57 degrees C) for 18 min resulted in a 5-log reduction of L. monocytogenes in ultrahigh-temperature milk, a 5-log reduction in total aerobic bacteria in raw milk, and a 6-log reduction in E. coli O157:H7 in pasteurized apple cider. Inactivation regressions were second-order polynomials, showing an initial period of rapid inactivation, eventually tailing off. Results indicate that ultrasound technology is a promising processing alternative for the reduction of microorganisms in liquid foods.