Post-Harvest UV-C Treatment of Microgreens for Inactivation of Salmonella enterica, Escherichia coli O157:H7 and Listeria monocytogenes

There is a high risk of transfer of foodborne pathogens to the edible part of microgreens when seeds, irrigation water or soilless substrates are contaminated. Post-harvest sanitizer treatments are generally not preferred due to the fragility of microgreens. In this study, the effectiveness of post-harvest UV-C treatment was evaluated against Salmonella enterica, Shiga toxin-producing Escherichia coli O157:H7, and Listeria monocytogenes in sunflower and radish microgreens. Agricultural perlite soaked with plant nutrient solution was artificially contaminated with foodborne pathogens at a concentration of 105–106 CFU/g to serve as the soilless substrate. UV-C was applied to harvested microgreens uni- and bidirectionally with doubled exposure at varying distances (10, 20, and 30 cm) and exposure times (5, 10, 20, 30, 60, and 120 s). UV-C doses ranged from 0.03 to 2.07 kJ/m2, depending on treatment distance and exposure time. The survival of pathogens in treated microgreens was also determined at 4 °C for 14 days. The highest pathogen inhibition was achieved with bidirectional UV-C treatment at a 10 cm distance for 120 s (p < 0.05), yielding reductions of up to 3.1, 3.0, and 2.0 log CFU/g for S. enterica, E. coli O157:H7, and L. monocytogenes, respectively. Pathogen inhibition decreased significantly with increasing distance (p < 0.05). During subsequent refrigerated storage after UV-C treatment, pathogen populations increased by 0.3–1.7 log CFU/g. These results demonstrate that UV-C treatment can significantly reduce pathogen populations on microgreens as a post-harvest treatment strategy but cannot fully address food safety concerns about these immature seedlings.