Effect of thermosonication, pulsed electric field and their combination on inactivation of Listeria innocua in milk

The impact of thermosonication (TS) and poised electric field (PEF), individually and combined, on the survival of Listeria innocua 11288 (NCTC) in milk was investigated. TS (400 W, 160 s) without pre-heating reduced L. innocua by 1.2 log(10) cfu mL(-1), while shorter treatment times produced negligible inactivation, suggesting TS to be a hurdle rather than in effective standalone treatment. PEF (30 and 40 kV cm(-1), 50 mu s) at 10 degrees C caused a reduction of L. innocua of 1.1 and 3.3 log cycles, respectively. The highest field strength (40 kV cm(-1)) combined with TS (80 s) led to 6.8 log(10) cfu mL(-1) inactivation. Milk pre-heated to 55 degrees C (over 60 s) prior to TS followed by PEF (30 and 40 kV cm(-1)) showed inactivation between 4.5 and 6.9 log(10) cfu mL(-1), the latter being comparable (P > 0.05) with thermal pasteurisation. The data indicate that I'S followed by PEF represents a valid alternative for L. innocua inactivation in milk. (C) 2008 Elsevier Ltd. All rights reserved.