Impact of pH on efficacy of peroxy acetic acid against Salmonella, Campylobacter, and Escherichia coli on chicken wings

Peroxy acetic acid (PAA) is widely used as an antimicrobial in poultry processing, specifically in the chiller. While the natural pH of PAA at the concentrations used is between 4.5 and 6.0, poultry processors adjust the pH to ≥8.0 to maintain product yield. The objective of this study was to evaluate 1) efficacy of PAA at different concentrations, pH, and contact times against Salmonella, Campylobacter, and Escherichia coli and 2) use of E. coli as a surrogate for Salmonella and Campylobacter to conduct validations studies for poultry processing. Fresh chicken wings (0.45 Kg) were inoculated with a cocktail of nalidixic acid–resistant Salmonella Typhimurium, rifampicin-resistant E. coli (5-strain cocktail), and gentamicin-resistant Campylobacter coli. Inoculated chicken wings were immersed in PAA solutions of 50, 250, and 500 ppm adjusted to pH 8.2 and 10.0 as well as nonadjusted PAA solutions for 10 s and 60 min. Treated chicken wings were rinsed in chilled buffered peptone water, serially diluted, and plated on Petrifilm APC for enumerating Salmonella and E. coli populations and spread plated on Campy Cefex Agar containing gentamicin (200 ppm) to enumerate Campylobacter. Immersion of chicken wings in 500 ppm of PAA (non–pH-adjusted) for 60 min resulted in greater microbial reductions (P ≤ 0.05) of Salmonella, Campylobacter, and E. coli populations of 2.56, 1.90, and 2.53 log CFU/mL, respectively. Higher concentrations and longer exposure times resulted in greater reductions (P ≤ 0.05) of Salmonella, E. coli, and Campylobacter populations, and increasing pH of PAA solution did not affect (P > 0.05) its efficacy. A high correlation (r = 0.93) was observed between E. coli (surrogate) and Salmonella populations suggesting that E. coli can be used as a surrogate for Salmonella for conducting validation studies for antimicrobial efficacy testing in poultry processing.