Removal of bacteria from beef tissue by spray washing after different times of exposure to fecal material

This study examined the effect of exposure time of beef-fat fascia to an inoculated fecal paste on the efficiency of removal of bacteria by spray washing or rinsing. Brisket fat (obtained <15 min postmortem) samples (10 by 10 by 2 cm) were inoculated, in the geometric center of their fascia surface, with four 0.64-cm diameter loops of a bovine fecal paste containing an inoculum (10(8) CFU/g) of streptomycin-resistant Escherichia coli ATTC 11370. Triplicate samples were spray washed with water (35 degrees C, 20.7 bar) and then rinsed with solutions of 2% acetic acid, 5% hydrogen peroxide, or 12% trisodium phosphate, or spray washed with water at 35 degrees C or 74 degrees C (20.7 bar), in an automated spray-washing cabinet for 12 s, after 0, 2, or 4 h of exposure to the inoculated fecal paste. The samples were analyzed for streptomycin-resistant bacterial counts. Washing or washing/rinsing at time 0 (immediately after exposure to the inoculated fecal paste) with trisodium phosphate; 35 degrees C water, hydrogen peroxide, acetic acid, and 74 degrees C water removed 3.04 +/- 0.40, 3.52 +/- 0.55, 3.62 +/- 0.67, 3.69 +/- 0.72 and 4.17 +/- 0.55 log CFU/cm(2), respectively. Applying the spray-washing treatments 2 or 4 h after exposure to the fecal paste resulted in significantly (P < 0.05) less removal (1.76 to 3.89 log CFU/cm(2) after 2 h and 0.94 to 2.58 log CFU/cm(2) after 4 h) of bacteria. Thus, the time of exposure to fecal contamination affected the attachment of bacteria to beef-carcass tissue, as indicated by the decreasing numbers of bacteria removed by spray washing with increasing time of exposure, regardless of the washing treatment. The most effective washing agent was 74 degrees C water at all washing times.