Parameters affecting the efficacy of spray washes against Escherichia coli o157:H7 and fecal contamination on beef

A series of progressive experiments was conducted with a model carcass washer using tap water and 2% acetic acid sprays to determine if tissue type, inoculation menstruum, bacterial level, or spray temperature affect removal of bacteria from beef carcass tissue during spray washing. For the first experiment, prerigor (15 min postexsanguination), postrigor (24 h postexsanguination), or postrigor frozen (-20°C, 7 days), thawed, lean beef carcass tissue (BCT) was inoculated with bovine feces and subjected to spray washing (15 s, 56°C) with water or acetic acid. Spray washing with either compound resulted in bacterial populations that were similar for prerigor and postrigor BCT; however, remaining bacterial populations from spray-treated postrigor, frozen BCT were significantly (P ≤ 0.05) less than for the other two tissue types. For the second experiment, prerigor, lean BCT was inoculated with Escherichia coli O157:H7 suspended in bovine feces or physiological saline and spray washed (15 s, 56°C) with water or acetic acid. Bacterial populations were reduced to similar levels with acid sprays, regardless of menstruum. For the third experiment, E. coli O157:H7 in feces was used to contaminate prerigor lean BCT to obtain different initial bacterial levels (7, 5, 3, and 1 log CFU/cm²). Spray washes (15 s, 56°C) with acetic acid reduced the level of the pathogen to 2.51 and 0.30 log CFU/cm² when initial bacterial levels were 7 and 5 log CFU/cm², and to undetectable levels when initial bacterial levels were 3 and 1 log CFU/cm². In a fourth experiment, water or acetic acid (15 s), ranging from 30 to 70°C was applied to beef tissue contaminated with E. colo O157:H7 in feces. Remaining bacterial populations were not different between the water treatments or between the acid treatments at any temperature. While variables such as bacterial level and inoculation menstruum may affect the efficacy of spray washing with organic acids, these results indicate that tissue type or spray temperature do not.