Purpose: This study was conducted to develop an ozone based treatment followed by advanced oxidative process (AOP) to inactivate L. monocytogenes introduced onto and into apples destined for candy apple production and to determine the fate of L. monocytogenes during posttreatment storage.
Methods: A forced air ozone reactor was constructed that introduced antimicrobial gas through an airstream into a column of apples that had been surface and subsurface inoculated with L. monocytogenes. The AOP reactor combined hydrogen peroxide mist in a chamber illuminated with ultraviolet light at 254 nm and ozone generation at 174 nm. The optimized treatments were applied to decontaminate apples that were used to prepare candied apples. The fate of L. monocytogenes on the candied apples during storage at 4 or 22°C was assessed.
Results: The ozone treatment optimized with respect to air flow and treatment time resulted in 1.90 to 2.40 log CFU reduction of target bacteria throughout the apple bed, but negligible decrease in subsurface populations. AOP, using 6% hydrogen peroxide vapor introduced at 48°C, and ultraviolet illumination for 30 s supported a four log CFU reduction of Listeria on the surface and 0.86 log CFU of internal populations. When combined in a sequential process, residual levels did not undergo outgrowth in the produced candy apples stored at 4 or 22°C.
Significance: A sequential process based on ozone and AOP provided an effective prevention control intervention for apples and could be extended to other fresh produce.