INACTIVATION KINETICS OF LISTERIA-INNOCUA IN SKIM MILK IN A CONTINUOUS-FLOW PROCESSING SYSTEM

Thermal inactivation of Listeria innocua in raw skim milk determined under continuous flow conditions was compared to results from the capillary tube method at 65, 68, and 70 degrees C. A laboratory scale pasteurizer (LSP) was used to generate kinetic data under isothermal, continuous-flow conditions. Inactivation was monitored by sampling at various locations along the hold tubes. D-(65 degrees C-), D-(68 degrees C-) and D-(70 degrees C-)values for L. innocua M1 were 11.5, 3.5, and 1.6 sec, respectively, when determined by the LSP system and 16.5, 3.9, 1.5 sec, respectively, when determined by the capillary tube method. Decimal reduction times for the two methods were predicted to be coincident at 69 degrees C. Z(D)-values for the capillary tube and LSP systems were significantly different. The data suggest that the mechanism of thermal destruction may be different between batch and continuous flow processes.