Modeling the inactivation of Listeria innocua in raw whole milk treated under thermo-sonication

Abstract

Abstract Ultrasound was used to study the inactivation of Listeria innocua and mesophilic bacteria in raw whole milk. Five systems were evaluated in an ultrasonic processor (24 kHz, 120 µm, 400 W). Tested amplitudes of ultrasonic waves were 0, 40, 72, 108 and 120 µm, with a constant temperature of 63 °C and treatment time of 30 min. The pH, acidity and color were measured. After 10 min of treatment, thermal pasteurization achieved a 0.69 log and a 5.3 log-reduction after 30 min. However, after using ultrasound at 60, 90 or 100% in combination with temperature, a 5 log-reduction was obtained after 10 min. Inactivation of mesophilic bacteria was similar to those for Listeria . The heat and the strongest thermo-sonication survival curves were best fitted using a Weibullian model, while an alternative four-parameter model was selected for the mildest thermo-sonication treatment (30%). As intensity of thermo-sonication increased, pH was slightly lower (6.64), acidity was increased (0.141%), and color of samples was whiter (92.37). Industrial relevance Thermo-sonication is an emerging technology that has shown positive effects in bacterial inactivation, reducing treatment times considerably. In the dairy industry, pathogenic microorganisms such as Listeria monocytogenes can be inactivated in milk using ultrasound, although inactivation patterns do not follow traditional first order kinetics. Thermo-sonicated milk has better color and similar physicochemical characteristics compared to conventional pasteurized milk, but the processing time is shorter. Industrially, thermo-sonication seems to be a viable option for pasteurization of milk; however, there are advantages to using conventional pasteurization in combination with ultrasound, as the results in this manuscript show. The possibility of using HTST processing in addition to ultrasound is also feasible, which could reduce treatment times even more.