Inactivation of Escherichia coli O157:H7 on inoculated alfalfa seeds with ozonated water under pressure

Alfalfa seeds inoculated with Escherichia coli O157:H7 (similar to10(5) CFU/g) were subjected to low hydrostatic pressure. Seeds immersed in ozonated water at 4C were held at 8 and 12 psi ozone pressure for 2, 4, 8, 16, 32, and 64 min. Alternatively; seeds were continuously sparged with ozone for up to 64 min and then held at 12 psi for 5 min. Controls consisted of sparging and pressurization with air. Thirty-two minute treatments of continuous ozone sparging followed by pressurization of seeds at 12 psi for 5 min were repeated with the addition of four surfactants (Tween 20, Tween 80, SPAN 20, and SPAN 80) in the treatment water. Enumeration of E. coli O157:H7 on treated, untreated, and control seeds was done on tryptic soy agar supplemented with 50 mug/mL of nalidixic acid. The reduction in population of E. coli O157:H7 on seeds treated with the 8 and 12 psi hydrostatic pressure in ozonated water ranged from 0.74 - 1.56 log(10) CFU/g and 0.72 - 1.62 log(10) CFU/g, respectively. Control treatments carried out with air pressurization of seeds resulted in maximum population reductions of 1.55 log(10) and 1.83 log(10) CFU/g for 8 and 12 psi, respectively. For seeds treated with continuous ozone sparging (2 - 64 min) followed by pressurization at 12 psi for 5 min, the highest reduction was 2.03 log(10) CFU/g. Reductions were, however, not significantly different (P > 0.05) from control treatment (with air) which reduced the populations by 0.57 - 2.19 log(10) CFU/g. The presence of surfactants during continuous sparging of water followed by pressurization at 12 psi was not beneficial. None of the treatments adversely affected the germination of the seeds.