Purpose: To evaluate the efficacy of a peroxyacetic acid (PAA)-based sanitizer against Salmonella and native microbiota in float tank water collected from a commercial walnut huller.
Methods: PAA (25, 50, and 80 ppm) was assessed against a five-strain cocktail of rifampicin-resistant Salmonella and, separately, the native microbiota in both fresh well and used float tank water (collected after 1h of hulling). Duplicate individual samples from each of three separate trials (n = 6 per treatment) were neutralized with Dey/Engley broth after 30, 60, 90, and 120 s of exposure to PAA. Appropriate dilutions were plated onto tryptic soy (TSA) and bismuth sulfite agars, both with rifampicin (Salmonella), TSA with cycloheximide (aerobic plate count (APC)), CHROMagar ECC (coliforms), and Rose Bengal chloramphenicol agar (fungi) and incubated at 37°C for 24h or 22°C for 96h for bacteria or fungi, respectively. Total dried solids and consumption of peroxyacetic acid were determined.
Results: Populations of Salmonella, APC, coliforms, and fungi were 5.9, 0.6, <–1.0, and <–1.0 log CFU/ml, respectively, in the well water and 5.9, 6.6, 5.9, and 6.0 log CFU/ml, respectively, in the used float tank water. Reductions of >5.0 log CFU/ml were observed for Salmonella within 120 or 30 s of exposure to 25 or 50 and 80 ppm PAA, respectively, in both well and used waters. Populations of APC, coliforms, and fungi were reduced 2.3, >5.0, and 2.6 log CFU/ml, respectively, after 30 s of exposure to ≥25 ppm PAA in used float tank water. Total dry solids were 37 to 126 times higher in the used float tank water. PAA (80 ppm) was consumed at a rate of 0 and 1.3 ppm/min in well and used float tank water, respectively.
Significance: Use of a PAA-based sanitizer may reduce the potential for microbial cross-contamination during walnut hulling by controlling microbial loads in float tank water.