Growth of Escherichia coli and Listeria monocytogenes on radish microgreens washed with sodium hypochlorite during storage

Abstract

This study aimed to establish appropriate conditions for the washing and storage of radish microgreens by evaluating the effect of a sodium hypochlorite (NaOCl) wash on the growth of Escherichia coli and Listeria monocytogenes. Sodium hypochlorite (50, 100, 150 and 200 mg/L) was added to wash water and radish microgreens were treated for 5, 10, 15, 20, 25 and 30 min. Treatment with NaOCl (150 mg/L, 5 min) significantly reduced (2.3 log CFU/g) the populations of both bacteria (p<0.05). After washing, the levels of bacteria in NaOCl treated radish microgreens was evaluated during storage at 4°C, 10°C, 15°C and 20°C for 3 days. The growths of E. coli and L. monocytogenes increased rapidly at temperatures over 15°C and 10°C respectively, from day 1. We believed that NaOCl treatmentinduced injuries may have caused the release of exudate on microgreen surfaces, which could have facilitated the growth of the pathogens at temperatures >10°C. To validate this hypothesis, we inoculated microgreen extract with the pathogens and incubated it under the above mentioned conditions. The growth of pathogens in the microgreens extracts corresponded to that observed after NaOCl treatment. The results of this study suggest that NaOCl treatment (150 mg/L, 5 min) and subsequent storage at temperatures <5°C can effectively reduce the growth and survival of E. coli and L. monocytogenes on radish microgreesns.