The bactericidal activity of 0.5, 1,2,4, and 6% acetic, citric, lactic, malic, mandelic, propionic, or tartaric acid was determined against Salmonella typhimurium that were loosely or firmly attached to broiler chicken skin by using the skin-attachment model. Acid treatments were applied during a simulated chill (0°C/60 min), postprocess dip (23°C for 15 s), or scald (50°C for 2 min). For comparison, activity of the acid treatments when applied under these conditions were also determined against S. typhimurium in aqueous suspension. In general, bactericidal activity (mean reduction log CFU per skin) of all acids increased linearly with increasing concentration in all applications. The bactericidal activity of organic acids depended on concentration and method of application. When compared to freely suspended cells, it is clear that salmonellae both firmly and loosely attached to poultry skin have increased resistance to or are protected from organic acids. In general, concentrations of ≥4% of the acids were required to kill ≥2 log number of cells of S. typhimurium that were attached to broiler skin.

Color of broiler skin was evaluated after exposure to organic acids under various concentrations and simulated potential plant application conditions. Breast skin from chilled broiler carcasses was treated with acetic (AA), citric (CA), lactic (LA), malic (ML), mandelic (MN), propionic (PA), or tartaric (TA) acids at 0.5, 1, 2, 4, and 6% concentrations. Each acid and concentration was applied in simulated dip (23 C for 15 s), scalder (50 C for 2 min), and immersion chiller (1 C for 60 min) conditions. A tap water control was included with each application method. Objective color values of L* (lightness), a* (redness), and b* (yellowness) were measured before and after the treatments to calculate color differentials under a factorial arrangement of organic acids and concentrations. Skin lightness increased (P < 0.01) in simulated chiller as compared to dip and scalder applications. Skin redness was reduced significantly in scalder, and yellowness in dip and scalder applications, respectively. In simulated dip application, with the exception of PA, all acids decreased lightness and increased redness and yellowness values. Propionic acid had little affect on lightness and redness values, but decreased yellowness values. In simulated scalder application, with the exception of PA, all acids decreased lightness with increasing concentration. The redness values changed little in scalder application. However, yellowness values were increased with all acids, except for PA, which decreased yellowness values. In simulated chiller conditions, all acids, except for PA, decreased lightness and redness and increased yellowness values. Propionic acid increased lightness and decreased yellowness values significantly in chiller conditions. Alterations in skin color should be taken into account in the selection and application of organic acids as carcass disinfectants.

The efficacy of organic acid sprays for eliminating Escherichia coli O157:H7 and Listeria monocytogenes from beef trim used in a model ground beef production scheme was determined. Beef trim pieces with ca. 20% fat inoculated with E. coli O157:H7 or L. monocytogenes (ca. 3 log10 CFU/g) were utilized as controls or treated by spraying with 2 or 4% acetic and lactic acids. Propylene glycol (20%) was the carrier for each treatment. Following acid treatment, intact pieces were stored at 4°C for 12 or 24 h, ground, divided into 4 100-g retail packages and stored at 4°C for 0, 1, 2, or 4 days, at which time surviving populations of E. coli O157:H7 or L. monocytogenes were enumerated. High populations (&gt;2.6 log10 CFU/g) of the pathogens persisted in all treatments. The 2% acid spray reduced (P &lt; 0.01) the E. coli O157:H7 population by only 0.1 log10 CFU/g. The 2 and 4% acid sprays reduced (P &lt; 0.001) the L. monocytogenes populations by 0.36 and 0.44 log10 CFU/g, respectively. Storing beef trim intact prior to grinding resulted in lower populations of E. coli O157:H7, and storage following grinding did not affect populations of either pathogen. The acid treatments tested were only slightly effective as sanitizers for beef trim destined for ground beef production.

Two experiments (EXP), utilizing the skin attachment model (SAM), were conducted to determine the bactericidal activity of six potential carcass disinfectants [EXP 1: 20, 400, and 800 ppm sodium hypochlorite; EXP 2: 5% acetic acid (AA), 8% trisodium phosphate (TSP), and 1% sodium metabisulfite (SS)] during simulated scalder (50 C for 2 min), chiller (0 C for 60 min), or post-process dip (23 C for 15 s) application. Efficacies of treatments were determined against populations of Salmonella typhimurium that were "loosely" or "firmly" attached to chicken breast skin (10 cm diameter). For comparison, activity of the six disinfectants was also determined against S. typhimurium in aqueous suspension. All disinfectants except SS reduced numbers of freely suspended S. typhimurium by > or = 4.5 log10 cfu/mL. The sodium metabisulfite did not reduce populations of salmonellae. In both EXP, there were disinfectant by application interactions (P < 0.05) on activity against loosely and firmly attached cells. Sodium hypochlorite at 20 ppm had little activity regardless of application, whereas higher levels were more effective (P < 0.001), particularly in the chiller application, in which loosely and firmly attached populations were reduced by 2.3 to 2.5 and 1.3 to 1.9 log10 cfu per skin, respectively. In EXP 2, SS showed no activity regardless of application. Trisodium phosphate was similarly effective (reduction by 1.2 to 1.8 log10 cfu per skin) in all applications (P > 0.05). In contrast, AA activity was affected by the application method (P < 0.05). Against loosely attached cells, AA was most effective in the chiller application (2.5 log10 reduction), whereas against firmly attached cells, AA was effective only in the scalder application (2.0 log10 reduction). Attachment of S. typhimurium to poultry skin apparently increased the ability of the bacteria to resist various disinfectants, and efficacy was influenced by extent of attachment of bacteria to skin and method of disinfectant application.

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