Purpose: Inoculation studies examined peroxyacetic acid (PAA) as an antimicrobial for whole, fresh apple packing.
Methods: Laboratory experiments used cocktails of generic and pathogenic Escherichia coli (E. coli); industrial-scale experiments used generic E. coli. Laboratory study (3 replications; 570 total apples) treatments included: inoculated untreated, and 5 s of direct contact with water or PAA (40, 60, or 80 ppm) followed by 10, 25, 40 or 60 s of additional exposure time to mimic industry conditions. At warehouse A, (2 replications; 720 total apples) treatments included: inoculated untreated, spray bar applications of water or PAA (40, 60, 80 ppm, average 2 s direct contact) and 80 ppm PAA (average 9 s direct contact). At warehouse B (3 replications; 1,020 total apples), treatments included: inoculated untreated, spray bar applications of water, soap followed by a water rinse, PAA (60 or 80 ppm, average 21 s direct contact), or soap followed by PAA (60 or 80 ppm, average 21 s direct contact). Samples were enumerated on violet red bile agar for generic E. coli and Cefixime-Tellurite sorbitol-MacConkey agar for E. coli O157:H7.
Results: For the laboratory study, treatment effects were observed; bacterial levels on apples treated with PAA (40, 60 and 80 ppm) were significantly lower (P < 0.01) than the inoculated control (0.7-1.4 log CFU/ml reduction). At warehouse A, only 80 ppm PAA with average 9 s direct contact time achieved a significant reduction (P < 0.01) of generic E. coli compared to the inoculated control (0.7 log CFU/ml reduction). At warehouse B, generic E. coli levels were significantly reduced (P < 0.01) by PAA (60 and 80 ppm, average 21 s of direct contact) with or without soap compared to the inoculated control (1.4-1.5 log CFU/ml reduction).
Significance: Industrial PAA spray bar concentrations and application times were identified that achieved a significant bacterial reduction on apples.