EFFECT OF THE LACTOPEROXIDASE SYSTEM ON LISTERIA-MONOCYTOGENES BEHAVIOR IN RAW-MILK AT REFRIGERATION TEMPERATURES

Activity of raw milk lactoperoxidase-thiocyanate-hydrogen peroxide (LP) system on four Listeria monocytogenes strains at refrigeration temperatures after addition of 0.25 mM sodium thiocyanate and 0.25 mM hydrogen peroxide was studied. The LP system exhibited a bactericidal activity against L. monocytogenes at 4 and 8-degrees-C; the activity was dependent on temperature, length of incubation, and strain of L. monocytogenes tested. D values in activated-LP system milk for the four strains tested ranged from 4.1 to 11.2 days at 4-degrees-C and from 4.4 to 9.7 days at 8-degrees-C. The lactoperoxidase level in raw milk declined during a 7-day incubation, the decrease being more pronounced at 8-degrees-C than at 4-degrees-C and in control milk than in activated-LP sysem milk. The thiocyanate concentration decreased considerably in activated-LP system milk at both temperatures during the first 8 h of incubation. LP system activation was shown to be a feasible procedure for controlling development of L. monocytogenes in raw milk at refrigeration temperatures.