Inactivation of L isteria monocytogenes in Milk by Multifrequency Power Ultrasound

Abstract

This study established the inactivation behavior of Listeria monocytogenes in nonfat, low-fat and full-cream milks treated with multifrequency Dynashock ultrasound. Inactivation in all samples was biphasic, with an inactivation lag phase where injury accumulated, prior to log-linear inactivation phase. L. monocytogenes exhibited shortest lag phase of 20.57 min in full-cream milk. L. monocytogenes exhibited slowest log-linear inactivation rate of −0.24 log colony-forming unit (cfu)/min in full-cream milk, and fastest inactivation rate of −0.37 log cfu/min in low-fat milk. Inactivation rate was slowest in full-cream milk at −0.24 log cfu/min, and fastest in low-fat milk at −0.37 log cfu/min. Corrected decimal reduction time was shortest in full-cream milk at 24.81 min, followed by those in nonfat and low-fat milk at 29.17 and 30.64 min, respectively. These results suggest the importance of careful consideration of microbial inactivation behavior in the establishment of food process schedules. Practical Applications The results reported in this study may be considered in the application of multifrequency power ultrasound-based processing of milk products against the tested reference microorganisms. Ultrasound processing may also be used in combination with other physical and/or chemical preservation methods to achieve a recommended level of lethality for safety and quality of the products.