Outbreaks of listeriosis associated with apples have led to increased research revealing the presence of Listeria species in apple processing environments. Listeria spp. were environmental sampled across separate facilities (A, B, and C) and from 9 controlled atmosphere (CA) apple storage rooms of apple processing facilities during 2021 and 2023. Out of f 300 samples, 6.3% (19) were positive for Listeria spp., with 65 isolates collected. The majority of positive samples came from floors below condenser units (9/19). Facility A had the highest number of positive samples - 11 total positives and the greatest diversity of Listeria spp. The highest rates of Listeria spp were recorded in Fall 2022 and Spring/Fall 2023. L. monocytogenes was the predominant species compromising 48 (74%) isolates. Three allelic types (AT) of L. monocytogenes were identified. Facility A had repeatedly sampled positive for L. monocytogenes contamination at one location in the same room but with different ATs, highlighting the utility of sigB allelic typing. These findings demonstrate, through the presence, distribution, and characterization of Listeria spp., the potential of CA apple storage rooms in spreading Listeria to the processing environment or on apples. Ozone is a potential alternative to chlorine due to its high oxidative potential but has limitations due to its volatility, hazardous off-gassing, and inconsistency. Nanobubble (NB) technology was explored to stabilize ozone in wash water and increase its antimicrobial effects. Submerging 0.5 kg of shredded Romaine lettuce in 80 L of 6 ppm ozone NBs for 90 s reduced E. coli O157:H7 populations by 0.8±0.20 log colony forming units (CFU)/g. When examining the application of 6 ppm ozone NBs in the context of a pilot-scale flume system for production of shredded lettuce, the addition of ozone NB into the final overhead rinse water, after washing in 10 or 20 ppm of chlorinated flume water for 90 s, did not significantly enhance the reduction of E. coli O157:H7 compared to tap water (p > 0.05). Furthermore, the application of ozonated NBs during centrifugal drying of shredded lettuce did not significantly differ from tap water in reducing E. coli O157:H7 populations (p > 0.05). Although there was a significant difference observed in microbial reduction between ozonated water applied before centrifugal drying and tap water (p < 0.05), the overall magnitude of this difference was minimal. These results suggest the application of ozone NBs as a sanitizer during pilot-scale processing may not be effective at inactivating E. coli O157:H7 on shredded Romaine lettuce.
Read
