Wet steam method for reducing attached cells of Salmonella and Listeria monocytogenes on Hass avocado

The consumption of avocados and their products has been linked to outbreaks of illness caused by Salmonella enterica and Listeria monocytogenes. These pathogens have been isolated from avocados collected from farms and markets. After contact with the avocado epicarp, the cells of Salmonella and L. monocytogenes can become loosely attached (LA) by suspension in a film of water and attraction by electrostatic forces, or strongly attached (SA) by physical and irreversible attachment mechanisms. Attached cells may have greater resistance to agents used to decontaminate the fruit. The effect of applying wet steam (WS) to the epicarp of Hass avocados on the reduction LA and SA counts of Salmonella and L. monocytogenes was evaluated as a function of the exposure time. The inoculated avocados were washed and exposed to WS for 30, 45, and 60 s inside a treatment chamber. Salmonella was found to be more susceptible to WS than L. monocytogenes. The efficacy of steam in reducing LA and SA cell numbers was similar for both pathogens. Steaming avocados for 60 s reduced LA Salmonella and L. monocytogenes cells by 4.6 and 4.8 log CFU/avocado, whereas SA cells were decreased by 5.2 and 4.4 log CFU/avocado, respectively.•Steaming the avocados for 60 s produced the greatest reduction in loosely and strongly attached cells for both pathogens.•Wet steam treatment efficiently eliminated the loosely and strongly attached cells of both pathogens.•The Listeria monocytogenes attached cells showed greater resistance to steam treatment than Salmonella.