Nonthermal processing of milk

Low frequency ultrasound at different intensities (24 kHz, 400 W, 120 [mu]m) plus heat (63 C) was used to inactivate Listeria innocua in milk; the most intense treatment was useful to pasteurization standards in shorter times. Inactivation kinetics did not follow a first order model; Weibullian and four parameters model better fitted survivor curves. Composition and physicochemical parameters of milk changed after sonication, but are still within reported ranges for processed milk; e.g., protein content remained at 3%. Butter fat content was shown to be an important hurdle in cell inactivation with ultrasound, as lower fat content resulted in faster and higher inactivation. Microscopy studies performed with Transmission (TEM) and Scanning Electron Microscopy (SEM) revealed that cell inactivation with ultrasound is caused by disruption of the cell membrane, pore formation and break-down of cells. With SEM fat globules showed smaller size (