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 tiss ue type, inoculation menstruum, bacterial level, or spray temperature affect removal of bacteria from beef carcass tissue during spray washi ng. For the first experiment, prerigor (15 min postexsanguination), po strigor (24 h postexsanguination), or postrigor frozen (-20 degrees, 7 days), thawed, lean beef carcass tissue (BCT) was inoculated with bov ine feces and subjected to spray washing (15 s, 56 degrees) with water or acetic acid. Spray washing with either compound resulted in bacter ial populations that were similar for prerigor and postrigor BCT; howe ver, remaining bacterial populations from spray-treated postrigor, fro zen BCT were significantly (P less than or equal to 0.05) less than fo r the other two tissue types. For the second experiment, prerigor, lea n BCT was inoculated with Escherichia coil O157:H7 suspended in bovine feces or physiological cal saline and spray washed (15 s, 56 degrees) with water or acetic acid. Bacterial populations were reduced to simi lar levels with acid sprays, regardless of menstruum. For the third ex periment, E. coli O157:H7 in feces was used to contaminate prerigor le an BCT to obtain different initial bacterial levels (7, 5, 3, and 1 lo g CFU/cm(2)). Spray washes (15 s, 56 degrees) with acetic acid reduced the level of the pathogen to 2.51 and 0.30 log CFU/cm(2) when initial bacterial levels were 7 and 5 log CFU/cm(2), and to undetectable leve ls when initial bacterial levels were 3 and 1 log CFU/cm(2). In a four th experiment, water or acetic acid (15 s), ranging from 30 to 70 degr ees was applied to beef tissue contaminated with E. coli O157:H7 in fe ces. Remaining bacterial populations were not different between the wa ter treatments or between the acid treatments at any temperature. Whil e variables such as bacterial level and inoculation menstruum may affe ct the efficacy of spray washing with organic acids, these results ind icate that tissue type or spray temperature do not.