Synergistic effect of sequential wash treatment with two different low-dosage antimicrobial washes in combination with frozen storage increases Salmonella Typhimurium and Listeria monocytogenes reduction on wild blueberries

Abstract To increase the safety of fruits and vegetables, including blueberries, this study developed an efficient and practical treatment strategy that implements multiple antimicrobial wash “hurdles” using industrial realistic treatment times in combination with freezing (at −17 °C for 1 week) against Listeria monocytogenes and Salmonella Typhimurium on blueberries. To note synergistic effects of the sequential antimicrobial washes, a portable conveyer belt equipped with a spraying system was used to spray multiple treatment solutions at low concentrations on blueberries. Bacterial enumeration was then subsequently conducted before and after freezing. The sequential spraying treatments with chlorine (100 ppm)-lactic acid (2%), and chlorine (200 ppm)-chlorine dioxide (15 ppm) resulted in reductions below the recoverable limit and ranged from 6.6 to 7.2log reductions. Furthermore, every combination of treatment (chlorine (200 ppm)-chlorine dioxide (15 min), chlorine (100 ppm)- lactic acid (2%), chlorine (100 ppm)- ozone (5 ppm), chlorine dioxide (10 ppm) – lactic acid (2%), chlorine dioxide (10 ppm)- ozone (5 ppm), and lactic acid (2%)- ozone (5 ppm) followed by freezing for 1 week resulted in >4 log CFU/g reduction of both pathogens. Therefore, the food safety margin of frozen fruits and vegetables can be increased by incorporating this sanitation strategy into the existing processing protocols.