Effectiveness of Surface Sanitizers against Salmonella spp. in Hydroponic Lettuce System

Margaret Moodispaw
Graduate (MS)
Sanja Ilic
Plant Pathology

Background: There has been an increase in hydroponic vegetable production, especially leafy greens, globally. However, there is a lack of specific practices to ensure food safety of hydroponic lettuce. Specifically, there are no validated sanitation protocols.
Objective: Determine the effectiveness of sanitizers to mitigate Salmonella spp. on contaminated surfaces in commercial leafy green hydroponic operations.
Methods: Commercial hydroponic surfaces (ABS plastic embedded with UV inhibitors, food grade UV stabilized PVC, and PVC) were inoculated with Salmonella spp. (~1x104 CFU/mL), and treated with sanitizers commonly used by the greenhouse industry. Pathogen were enumerated and surface swabs were collected from the edges and corners. A total of 13 treatments were tested, including the controls.
Results: Sanitizers Zerotol (5%), SaniDate 12.0 (200ppm), Virkon (1%), KleenGrow (2%), and GreenShield (5%) effectively eliminated Salmonella spp. population on all surfaces tested when applied for the label recommended contact time (5-10 minutes). These sanitizers eliminated (100% reduction achieved) Salmonella spp. from all surfaces. SaniDate 12.0 (100ppm) eliminated pathogen from ABS plastic with UV inhibitors but not on all other surfaces. Salmonella spp. was recovered after processing (2.91 ± 0.30 Log/cm2) or enrichment. Sodium hypochlorite (100ppm, 200ppm) and aqueous chlorine dioxide (10ppm, 50ppm) did not eliminate the pathogen, with 72.07-97.55% reduction rates. 
Conclusions: We have demonstrated that Salmonella spp. can be effectively removed from ABS plastic embedded with UV inhibitors, food grade UV stabilized PVC, and PVC using Zerotol (5%), SaniDate 12.0 (200ppm), Virkon (1%), KleenGrow (2%), and GreenShield (5%) when applied at the labeled rate for the recommended time. Although all sanitizers achieved 3 log reduction, sodium hypochlorite (100ppm, 200ppm), which is the most commonly used sanitizer, aqueous chlorine dioxide (10ppm, 50ppm), and SaniDate 12.0 (100ppm) were not effective in eliminating Salmonella spp. from all surface types. Ineffectiveness of chlorine-based sanitizers in ridding the hydroponic surfaces from the pathogen is significant due to their widespread use in industry. These findings are critical in the development of food safety guidelines for hydroponic growers. 
Acknowledgments: We thank CropKing for their continuous support. ODA Grant #GRT00049110.