Abstract
Protecting fresh-packed produce microbiological safety against pre- and post-harvest microbial pathogen contamination requires innovative antimicrobial strategies. Although largely ignored in the scientific literature, there exists the potential for gross failure in food safety protection of fresh fruits and vegetables leading to opportunity for multiple produce contamination events to occur during production and post-harvest handling of food crops. The primary objective of this research was to determine the efficacy of plant-derived antimicrobial-loaded nanoparticles to reduce Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium on spinach leaf surfaces whilst simulating multiple pathogen contamination events (pre-harvest and post-harvest). Spinach samples were inoculated with a blend of E. coli O157:H7 and S. Typhimurium, each diluted to ~8.0 log10 CFU/mL. The inoculated samples were then submerged in solutions containing nanoparticles loaded with geraniol (GPN; 0.5 wt.% geraniol), unencapsulated geraniol (UG; 0.5 wt.%), or 200 ppm chlorine (HOCl; pH 7.0), with untreated samples serving for controls. Following antimicrobial treatment application, samples were collected for surviving pathogen enumeration or were placed under refrigeration (5°C) for up to 10 days, with periodic enumeration of pathogen loads. After 3 days of refrigerated storage, all samples were removed, aseptically opened and subjected to a second inoculation with both pathogens. Treatment of spinach surfaces with encapsulated geraniol reduced both pathogens to non-detectable numbers within 7 days of refrigerated storage, even with a second contamination event occurring 3 days after experiment initiation. Similar results were observed with the UG treatment, except that upon recontamination at day 3, a higher pathogen load was detected on UG-treated spinach vs. GPN-treated spinach. These data fill a research gap by providing a novel tool to reduce enteric bacterial pathogens on spinach surfaces despite multiple contamination events, a potential food safety risk for minimally processed edible produce.
Highlights
Foodborne diseases caused by bacterial enteric pathogens, including Salmonella and Shiga toxin-producing Escherichia coli (STEC) are repeatedly linked to the consumption of crosscontaminated foods, resulting in hospitalizations and fatalities
At 37◦C, the size of GPNs did not change during storage for the majority of particles, a second population of particles with a mean diameter of ∼37.36 ± 25.57 nm was detected at day 14 of storage
As with samples stored at 37◦C, the mean diameter of this second population of GPNs was initially observed at 14 days of storage, though it behaved more like GPNs stored at 50◦C in that its mean diameter did not increase over storage but rather decreased until a point at which it remained static thereafter
Summary
Foodborne diseases caused by bacterial enteric pathogens, including Salmonella and Shiga toxin-producing Escherichia coli (STEC) are repeatedly linked to the consumption of crosscontaminated foods, resulting in hospitalizations and fatalities. These result in substantial losses in wages, quality of life, and other financial costs (Scallan et al, 2011; Batz et al, 2012). Over the last 5 years, the U.S Centers for Disease Control and Prevention (CDC) reported five human disease outbreaks involving leafy green vegetables as vehicles transmitting Escherichia coli O157:H7, including two outbreaks in 2018 and one in 2019 involving romaine lettuce (CDC, 2018, 2019, 2020). Between 1973 and 2011, researchers identified 19 U.S outbreaks of foodborne disease involving cantaloupes, wherein Salmonella was the most commonly identified etiologic agent, causing 1,012 recorded disease cases and 38 fatalities, including one fetal death (Walsh et al, 2014). Burris et al (2021) recently discussed Salmonella capabilities to contaminate melon fruit through blossom contamination as well as internalization into cantaloupe flesh as drivers of melon transmission of the pathogen to consumers
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