Ultrasoun
d was use
d to stu
dy the inactivation of Listeria innocua an
d mesophilic bacteria in raw whole milk. Five systems were evaluate
d in an ultrasonic processor (24 kHz, 120 µm, 400 W). Teste
d amplitu
des of ultrasonic waves were 0, 40, 72, 108 an
d 120 µm, with a constant temperature of 63 °C an
d treatment time of 30 min. The pH, aci
dity an
d color were measure
d. After 10 min of treatment, thermal pasteurization achieve
d a 0.69 log an
d a 5.3 log-re
duction after 30 min. However, after using ultrasoun
d at 60, 90 or 100 % in combination with temperature, a 5 log-re
duction was obtaine
d after 10 min. Inactivation of mesophilic bacteria was similar to those for Listeria. The heat an
d the strongest thermo-sonication survival curves were best fitte
d using a Weibullian mo
del, while an alternative four-parameter mo
del was selecte
d for the mil
dest thermo-sonication treatment (30 % ). As intensity of thermo-sonication increase
d, pH was slightly lower (6.64), aci
dity was increase
d (0.141 % ), an
d 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.