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 monitored during prolonged refrigerated vacuum-packaged storage following antimicrobial treatment. An industrial spray wash cabinet was used to deliver water (W), 1.5 and 3.0 degrees lactic (LA) or acetic (AA) acid, or 12% trisodium phosphate (TSP) washes. Fresh unaltered bovine feces spiked with antibiotic-resistant strains of Escherichia coli O157:H7, Listeria innocua, and Clostridium sporogenes were used to inoculate BCT prior to all treatments. The effect of treatments on bacterial populations was tracked by monitoring levels of specific-antibiotic-resistant (marked) bacteria along with mesophilic aerobic bacteria (APC), lactic acid bacteria (LAB), and pseudomonads for up to 21 days of storage 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 treatments. Marked bacteria were reduced to <1.3 log CFU/cm(2), remaining that 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 LAB. The aerobic bacteria, L. innocua, and LAB had counts greater than or equal to 7 log CFU/cm(2) by 7 days in all but one case and by 14 days all had counts >7 log CFU/cm(2) on the untreated controls and water-washed samples. Treatments generally added a degree of safety regarding the foodborne pathogens and pathogen models used for the present study when beef tissue was stored up to 21 days and in no case did the treatments appear to offer any competitive advantage to select microorganisms on BCT.