Efficacy of Naturally Occurring Antimicrobials to Reduce Salmonella spp. Associated with Poultry at Various Stages of Processing

Salmonellae remain one of the leading causes of foodborne illnesses worldwide with poultry being recognized as a primary vehicle for salmonellosis. Despite considerable attention from the media and diligence by the industry to prevent product contamination, poultry remains responsible for about 50% of common-vehicle outbreaks. The efficacy of oxalic and fumaric acids, as naturally occurring antimicrobial agents for poultry processing, was evaluated by simulating on-line or post-chill dipping, water-immersion chilling, and soft scalding for reduction of Salmonella spp. attached to raw chicken skin. Skin samples were collected at different time periods to account for the natural variation observed in the industry and processed using the modified skin attachment model and thin agar layer plating technique for acid-injured cells. On-line or post-chill dipping (22ºC) with oxalic (0.5 to 2.0%) and fumaric (0.25 to 0.5%) acids showed the least quantitative reductions in Salmonella spp. compared to other applications. The greatest Salmonella reductions were achieved with 2.0% oxalic acid and 1.5% fumaric acid when applied for 3 min in a soft scalder treatment (53ºC), reducing initial Salmonella inoculum by 2.43 and 1.53 log, respectively. Simulated water-immersion chilling (3ºC) with 0.5% oxalic acid and 0.25% fumaric acid for 60 min resulted in Salmonella reductions of 2.25 and 0.72 log, respectively. Mutations in the fur, atp, or rpoS loci did not impact the survival of S. Typhimurium attached to broiler skins when treated with oxalic acid during dipping and scalding. The bactericidal effectiveness of fumaric acid as an antimicrobial agent was limited by its low water solubility and resulted in less than a 2-log Salmonella reduction on raw chicken skins at all tested applications. Fumaric acid's effectiveness in vitro was improved by the addition of acetic, oxalic, and lactic acids, and depended on the concentration of supplemented acid. The greatest antimicrobial effect was observed when 0.45% fumaric acid was coupled with 0.45 or 1.35% oxalic acid resulting in a 2.09-log and ≥6-log reduction in Salmonella, respectively. Variation was observed in the effectiveness of oxalic and fumaric acids to reduce Salmonella among three skin batches, even though no obvious difference was found among the batches that could explain variation in Salmonella reduction, including the variation in initial pH, fat and moisture content, thickness of epidermal layer as well as presence of channels and crevices on skins. This observation emphasized the importance of collecting samples from different flocks, days, and seasons for testing antimicrobial agents to best simulate the natural variation that occurs within the industry and more accurately assess the efficacy of antimicrobials.