A comparative study on the effectiveness of chlorine dioxide gas, ozone gas and e-beam irradiation treatments for inactivation of pathogens inoculated onto tomato, cantaloupe and lettuce seeds.

The increase in reported food-borne outbreaks linked with consumption of raw fruits and vegetables has motivated new research focusing on prevention of pre-harvest produce contamination. This study evaluates and compares the effectiveness of three non-thermal technologies, chlorine dioxide gas, ozone gas and e-beam irradiation, for inactivation of Salmonella enterica and Escherichia coli O157:H7 on pre-inoculated tomato, lettuce and cantaloupe seeds, and also their corresponding effect on seeds germination percentage after treatments. Samples were treated with 10mg/l ClO(2) gas for 3 min at 75% relative humidity, with 4.3mg/l ozone gas for 5 min and with a dose of 7 kGy electron beam for 1 min. Initial load of pathogenic bacteria on seeds was ~6 log CFU/g. Results demonstrate that all treatments significantly reduce the initial load of pathogenic bacteria on seeds (p<0.05). In particular, after ozone gas treatments 4 log CFU/g reduction was always observed, despite the seeds and/or microorganisms treated. ClO(2) and e-beam treatments were noticeably more effective against Salmonella on contaminated tomato seeds, where 5.3 and 4.4 log CFU/g reduction were respectively observed. Germination percentage was not affected, except for cantaloupe seeds, where the ratio was significantly lowered after ClO(2) treatments. Overall, the results obtained show the great applicability of these non-thermal inactivation techniques to control and reduce pathogenic bacteria contamination of seeds.