title: Inactivation of Escherichia coli O157:H7 on inoculated alfalfa seeds with ozonated water and heat treatment.
abstract: Alfalfa seeds inoculated with a five-strain mixture of Escherichia coli O157:H7 were immersed in water containing 4, 8, 10, and 21 ppm of ozone for 2, 4, 8, 16, 32, and 64 min at 4 degrees C. Direct ozone sparging of seeds in water was used as an alternative mode of ozone treatment. Ozone-sparged seeds were also subsequently exposed to heat treatment at 40, 50, and 60 degrees C for 3 h. Populations of E. coli O157:H7 on untreated and treated seeds were determined by spread plating diluted samples on tryptic soy agar supplemented with 50 microg/ml of nalidixic acid. Since E. coli O157:H7 was released from inoculated seeds during treatment with ozone, the rate of release of cells from inoculated seeds soaked in 0.1% peptone water for up to 64 min was also determined. The overall reduction of E. coli O157:H7 on seeds treated with ozonated water without continuous sparging ranged from 0.40 to 1.75 log10 CFU/g (59.6 to 98.2%), whereas reductions for control seeds were 0.32 to 1.03 log10 CFU/g (51.7 to 90.5%). Treatment with higher ozone concentrations enhanced inactivation, but contact time longer than 8 min did not result in significantly higher reductions (P > 0.05). For seeds treated by ozone sparging, a 1.12-log10 CFU/g (92.1%) reduction was achieved using a 2-min contact time, and a 2.21-log10 CFU/g (99.4%) reduction was achieved with a 64-min contact time. The corresponding reductions for control seeds were 0.71 log10 CFU/g (79.5%) and 2.21 log10 CFU/g (99.4%), respectively. Treatment of ozone-sparged seeds at 60 degrees C for 3 h reduced the population to an undetectable level by direct plating (4 to 4.8 log10 CFU/g), although survivors were detected by enrichment. Ozone did not have a detrimental effect on seed germination percentage.
authors.affiliation: Department of Agricultural and Biological Engineering, The Pennsylvania State University, University Park, 16802, USA.
authors.forename: Ratna R
authors.initials: RR
authors.lastname: Sharma
authors.forename: Ali
authors.initials: A
authors.lastname: Demirci
authors.forename: Larry R
authors.initials: LR
authors.lastname: Beuchat
authors.forename: William F
authors.initials: WF
authors.lastname: Fett
mesh_terms: D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development*; D006358:Hot Temperature / Q000009:adverse effects*; D000455:Medicago sativa / Q000382:microbiology*; D010083:Oxidants, Photochemical; D010126:Ozone; D012639:Seeds / Q000382:microbiology; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D010083:Oxidants, Photochemical; D014867:Water; D010126:Ozone