Purpose: In order to assess the antimicrobial efficacy of the low residue PAA formulation, tests were conducted using various concentrations in the vapor apparatus against several species of Bacillus spores inoculated into beverage containers. Studies were also conducted to determine residue levels.
Methods: Bacillus spp. spores were spot-inoculated into 1 l containers, allowed to dry then treated using the FMC sterilant under various parameters of temperature, concentration and contact time. The sterilant was diluted and flash vaporized into a heated airstream applied to the container, and neutralized immediately afterwards using 50 ml neutralizing broth containing 0.5% sodium thiosulfate. Containers were then sonicated 5 minutes and vortexed 30s, and the fluid diluted and plated using APC Petrifilm.
Results: Complete reduction of the inoculum (approximately 6 log B. atrophaeus spores) was achieved using 4000 ppm PAA at 5 s contact, and at 8000 ppm PAA in 2s contact at 90°C. Similarly, complete reduction of the inoculum (approximately 6 log B. subtilis spores) was achieved using 4000 ppm PAA at 80°C for 5 s. B. cereus required additional concentration and temperature, but complete reduction was achieved in 5 s at 150°C and 20000 ppm PAA.
Residue tests showed little to no solid residue in tests comparing the new sterilant with standard grade 15% PAA and 35% hydrogen peroxide.
Significance: This novel sterilant effectively controlled organisms of concern, with little to no formation of residue in lab tests, compared with standard grade PAA and hydrogen peroxide. Pilot scale studies were also conducted and showed encouraging results.