Combined use of ultrasound and natural antimicrobials to inactivate Listeria monocytogenes in orange juice

The presence of Listeria monocytogenes could seriously affect the safety of nonpasteurized fruit juices. High-intensity ultrasound combined with mild heat treatment and natural antimicrobials may be an alternative technology for fruit juice preservation. The response of L. monocytogenes in orange juice to combined treatments involving moderate temperature (45 degrees C, high-intensity ultrasound (600 W, 20 kHz, 95.2-mu m wave amplitude), and the addition of different levels of vanillin (0, 1,000, 1,500, and 2,000 ppm), citral (0, 75, and 100 ppm), or both was investigated to find the most effective inactivation treatment. Nonlinear semilogarithmic survival curves were successfully fitted by the Weibull model. The presence of vanillin or citral greatly increased the bactericidal effect of thermosonication and changed the distribution of inactivation times. When both antimicrobials were added together and ultrasound was applied, narrowest frequency shapes, skewed to the right, with low variances and death time means between 1.6 and 2.6 min, were obtained. Orange juices with 1,500 or 1,000 ppm of vanillin and 100 ppm of citral were pleasant for the consumers.