Improving the Safety and Postharvest Quality of Field-grown Organic Leafy Greens: Assessment of Good Agricultural/Production Practices Along the Farm-to-Fork Continuum

The long-term goal of this project is to improve the profitability of organic leafy green farms by developing and implementing commercially feasible technology and operational production/handling programs to assure the safety and quality of organic leafy greens. The mechanisms by which Escherichia coli O157:H7 attach to and internalize organic leafy greens and attach to harvesting equipment surfaces were studied. Rapid attachment was seen in 5 minutes, with cut surfaces having greater attachment than intact. Strains that expressed curli and were more hydrophobic, attached at higher numbers compared to non-expressing strains. Wild type and cellulose deficient strains persisted better than curli deficient and curli and cellulose deficient mutants on spinach cultivars. In vitro studies showed that growth regulators may interfere with bacterial biofilm formation. A contaminated tool used to core iceberg lettuce cross-contaminated as many as 75 lettuce heads. Low level chlorine (1.3 ppm free chlorine) washes prevented cross-contamination from field-contaminated lettuce to non-contaminated lettuce. Environmental factors and agricultural practices that affect leafy green safety and quality were evaluated. Survival of E. coli in different compost teas and biostimulants was studied in the lab and field, through foliar application using different spray systems. Different spray applicators showed that big drops held higher bacterial numbers up to 24 h; however, no organisms were detected after day 10. Irrigation water samples from Yuma, AZ were collected and analyzed for indicator organisms, quality parameters, E. coli O157:H7, Salmonella, hepatitis A virus, and norovirus. Salmonella was detected in 2 sediment samples. Generic E. coli (<1-27.2 MPN/100ml) and coliforms (131.4->2419.6 MPN/100 ml) were identified.  Efficacies of post-harvest interventions (plant compounds, organic sanitizers, antimicrobial edible films) against pathogens were tested in vitro and on organic lettuce and spinach. In vitro studies showed complete reductions of test microbes with many plant compounds, while up to 3 log reductions were achieved with some plant compounds and organic sanitizers on leafy greens. Antimicrobial edible films were also very effective, showing 3 logs to complete reductions of E. coli O157:H7 and S. enterica in packaged leafy greens. An aggressive outreach/education program for stakeholders (leafy green growers and processors; manufacturers of natural antimicrobials and organic sanitizers; and consumers) was started. These groups have been informed regularly on the results of this project at stakeholder meetings. Information generated is being used in extension and microbiology courses. Numerous media outlets have provided coverage/stories on this project to reach a wide variety of audience.

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