Inactivation of Cronobacter sakazakii by manothermosonication in buffer and milk

The inactivation of Cronobacter sakazakii by heat and ultrasound treatments under pressure at different temperatures [manosonication (MS) and manothermosonication (MTS)] was studied in citrate-phosphate pH 7.0 buffer and rehydrated powdered milk. The inactivation rate was an exponential function of the treatment time for MS/MTS treatments (35-68 degrees C; 200 kPa of pressure; 117 mu m of amplitude of ultrasonic waves) in both media, and for thermal treatments alone when buffer was used as heating media. Survival curves of C. sakazakii during heating in milk had a concave downward profile. Up to 50 degrees C, the lethality of ultrasound under pressure treatments was independent of the treatment temperature in both media. At temperatures greater than 64 degrees C in buffer and 68 degrees C in milk, the inactivating effect of MTS was equivalent to that of the thermal treatments alone at the same temperature. Between 50 and 64 degrees C for buffer and 50 and 68 degrees C for milk, the lethality of MTS was the result of a synergistic effect, where the total lethal effect was higher than the lethal effect of heat added to that of ultrasound under pressure at room temperature. The maximum synergism was found at 60 degrees C in buffer and at 56 degrees C in milk. A heat treatment of 12 min (60 degrees C) or 4 min of an ultrasound under pressure at room temperature treatment (35 degrees C; 200 kPa; 117 mu m) would be necessary to guarantee the death of 99.99% of C. sakazakii cells suspended in milk. The same level of C. sakazakii inactivation can be achieved with 1.8 min of a MTS treatment (60 degrees C; 200 kPa; 117 mu m). Damaged cells were detected after heat treatments and after ultrasound under pressure treatments at lethal but not at non-lethal temperatures. (C) 2011 Elsevier B.V. All rights reserved.