Purpose: The objective of this research was to evaluate geraniol-loaded polymeric nanoparticles (GPNs) to reduce Escherichia coli O157:H7 and Salmonella Typhimurium inoculated onto produce surfaces.
Methods: For each sample, unwashed cantaloupe, spinach, and tomato surfaces were portioned into three 10 cm2 pieces. Samples were spotted with a cocktail of rifampicin-resistant S. enterica Typhimurium LT2 and E. coli O157:H7 ATCC 700728 and held to allow inoculum attachment. Treatments of GPNs (0.5 wt.% delivered concentration, prepared by flash nano-precipitation), unencapsulated geraniol (0.5 wt.%), and 200 ppm HOCl (pH 7.0) were applied via immersion for 2 min. Untreated inoculated samples were prepared. Following immediate enumeration of pathogens, samples were packed and stored aerobically at 5°C. Changes in pathogen numbers were quantified by selective/differential enumeration after 3, 5, 7, and 10 days’ storage. On day 5 of incubation, a set of identically prepared and treated samples was transferred to 15°C to simulate post-packing temperature abuse; changes in pathogen numbers were assayed at 7 and 10 days’ total storage. Pathogen numbers were analyzed for differences in numbers as a function of treatment application and time of storage (N=3; P<0.05).
Results: Immediately following inoculation and treatment, pathogen numbers were 1.5-6.1 log CFU/cm2 across treatments for all produce. At day 10, pathogen numbers were 1.0-5.8 log CFU/cm2 across treatments for cantaloupes and tomatoes and 1.8-3.0 log CFU/cm2 for chlorine-treated and untreated spinach, yet numbers for GPN- and unencapsulated geraniol-treated spinach were below detection (0.5 log CFU/cm2). During 15°C storage, pathogen loads increased across treatments for cantaloupes and decreased for GPN-treated tomatoes and spinach.
Significance: Results suggest GPNs can be utilized for the post-harvest decontamination of produce from contaminating enteric pathogens.