Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 25, 1996
Publication Date: N/A
Interpretive Summary: Surface contamination of meat animal carcasses by bacteria from the hide or digestive tract of the animal is undesirable but unavoidable during processing. To remove this contamination, beef processing plants spray wash carcasses with water or with water containing antimicrobials. A series of experiments was conducted with spray washes to determine if carcass tissue type, cell suspension, bacterial level, or spray temperature affect removal of bacteria on beef. First, three tissue types (pre-rigor, post-rigor, and post-rigor frozen) were contaminated with feces and spray washed (15 sec., 140 deg F) with tap water or 2% acetic acid (vinegar). Spray washing removed bacteria from all three tissue types by >99%, but more bacteria remained on the pre- and post-rigor tissue than on the frozen tissue. Secondly, Escherichia coli O157:H7 was inoculated into sterile feces or a salt solution, used to contaminate beef tissue, and spray washed (15 sec., 140 deg F) with tap water or vinegar. The cell suspension did not affect spray washing. Thirdly, beef tissue was contaminated with E. coli O157:H7 in sterile feces to obtain ten to ten million bacteria per cm2 on beef. Spray washes (15 sec., 140 deg F) with vinegar reduced the pathogen to zero levels when initial bacterial levels were 1,000 and 10 cells per cm2. Fourthly, tap water or vinegar (15 sec.) was heated from 80 to 190 deg F and applied to beef tissue contaminated with E. coli O157:H7. When subjected to vinegar or water (80 to 190 deg F), the pathogen was reduced by 99.9% and 99%, respectively, regardless of temperature. These experiments show that bacterial level affects spray washing greatly, but that tissue type, temperature, and cell suspension do not.
Technical Abstract: 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, pre-rigor, post-rigor, or post-rigor, frozen lean beef carcass tissue (BCT) was inoculated with bovine feces and subjected to spray washing (15 s, 56 deg C) with water or acetic acid. Spray washing with either compound resulted in bacterial populations that were similar for pre-rigor and post-rigor BCT. Remaining bacterial populations from post-rigor, frozen BCT were significantly less than the other two tissue types. For the second experiment, pre-rigor BCT was inoculated with Escherichia coli O157:H7 suspended in bovine feces or physiological saline and spray washed (15 s, 56 deg C) with water or acetic acid. Resulting bacterial populations were similar, regardless of menstruum. For the third experiment, BCT was contaminated with E. coli O157:H7 in feces to obtain 7, 5, 3, and 1 log10 CFU/cm**2. Spray washes (15 s, 56 deg C) with acetic acid reduced the level of the pathogen to undetectable levels when initial bacterial levels were 3 and 1 log10 CFU/cm**2. In a fourth experiment, water or acetic acid (15 s), ranging from 30 to 70 deg C was applied to beef tissue contaminated with E. coli O157:H7 in feces. Remaining bacterial populations were not different between the water treatments or between the acid treatments at any temperature.