Long-Term Effect of Alkaline, Organic Acid, or Hot Water Washes on the Microbial Profile of Refrigerated Beef Contaminated with Bacterial Pathogens after Washing†

Abstract

The effect of 2% (vol/vol) lactic acid, 2% (vol/vol) acetic acid, 12% (wt/vol) trisodium phosphate, water at 72°C and water at 32°C washes on bacterial populations introduced onto beef carcass surfaces after treatment was determined for up to 21 days at 4°C in storage in vacuum packaging. Beef carcass short plates were collected from cattle immediately after slaughter and subjected to the above treatments or left untreated (C). Short plates were then inoculated with low levels (ca. <2 log10) of Listeria innocua, Salmonella typhimurium, Escherichia coli O157:H7, and Clostridium sporogenes cells contained in a bovine fecal cocktail. In general, growth of these four bacteria and of aerobic bacteria, lactic acid bacteria, and pseudomonads was suppressed or not observed when lactic acid or acetic acid treatments were used. Bacteria introduced to trisodium phosphate-treated tissue underwent some growth suppression, but to a lesser extent than on acid-treated tissue, and in some cases grew as well as on untreated beef surfaces. Water washes at 72 or 32°C offered little growth suppression of pathogens during subsequent storage when these bacteria were introduced to beef tissue after treatment. The use of a final lactic or acetic acid wash during the Processing of beef carcasses offers some residual efficacy in suppressing pathogen proliferation during refrigerated storage, should these bacteria be introduced immediately after carcass processing.