EFFECTS OF ACETIC-ACID, LACTIC-ACID AND TRISODIUM PHOSPHATE ON THE MICROFLORA OF REFRIGERATED BEEF CARCASS SURFACE TISSUE INOCULATED WITH ESCHERICHIA-COLI O157-H7, LISTERIA-INNOCUA, AND CLOSTRIDIUM-SPOROGENES

The microbial profiles of inoculated beef carcass tissue (BCT) were mo nitored during prolonged refrigerated vacuum-packaged storage followin g antimicrobial treatment. An industrial spray wash cabinet was used t o deliver water (W), 1.5 and 3.0 degrees lactic (LA) or acetic (AA) ac id, or 12% trisodium phosphate (TSP) washes. Fresh unaltered bovine fe ces spiked with antibiotic-resistant strains of Escherichia coli O157: H7, Listeria innocua, and Clostridium sporogenes were used to inoculat e BCT prior to all treatments. The effect of treatments on bacterial p opulations was tracked by monitoring levels of specific-antibiotic-res istant (marked) bacteria along with mesophilic aerobic bacteria (APC), lactic acid bacteria (LAB), and pseudomonads for up to 21 days of sto rage at 5 degrees. Initial APC levels of approximately 5.6 log CFU/cm( 2) were reduced by 1.3 to 2.0 log CFU/cm(2) by LA, AA, and TSP treatme nts. Marked bacteria were reduced to <1.3 log CFU/cm(2), remaining tha t way throughout the 21-day storage. TSP treatments were not different in effectiveness from acids for controlling growth of E. coli O157:H7 and C. sporogenes, but were less effective for APC, L. innocua, or LA B. The aerobic bacteria, L. innocua, and LAB had counts greater than o r equal to 7 log CFU/cm(2) by 7 days in all but one case and by 14 day s all had counts >7 log CFU/cm(2) on the untreated controls and water- washed samples. Treatments generally added a degree of safety regardin g the foodborne pathogens and pathogen models used for the present stu dy when beef tissue was stored up to 21 days and in no case did the tr eatments appear to offer any competitive advantage to select microorga nisms on BCT.