Inactivation of Ecoli On Alfalfa Seeds with Ozonated Water and Heat Treatment

Inactivation of Escherichia Coli 0157:H7on Inoculated Alfalfa Seeds with Ozonated Water and Heat Treatment

March 2002
Journal of Food Protection: Vol. 65, No. 3, pp. 447­451.
Ratna R. Sharma, Department of Agricultural and Biological Engineering, ThePennsylvania State University, University Park, Pennsylvania 16802; Ali Demirci,Department of Agricultural and Biological Engineering and Life SciencesConsortium, The Pennsylvania State University, University Park, Pennsylvania16802; Larry R. Beuchat, Center for Food Safety and Department of Food Scienceand Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia30223-1797; William F. Fett, U.S. Department of Agriculture, AgriculturalResearch Service, Eastern Regional Research Center, Plant Science and TechnologyResearch Unit, 600 East Mermaid Lane,
Wyndmoor, Pennsylvania 19038, USA

Alfalfa seeds inoculated with a five-strain mixture of Escherichia coli  O157:H7were immersed in water containing 4, 8, 10, and 21 ppm of ozone for 2, 4, 8, 16,32, and 64 min at 4°C. Direct ozone sparging of seeds in water was used as analternative mode of ozone treatment.  Ozone-spargedseeds were also subsequently exposed to heat treatment at 40, 50, and 60°C for3 h.  Populations of E. coli O157:H7on untreated and treated seeds were determined by spread plating diluted sampleson tryptic soy agar supplemented with 50 g/ml of nalidixic acid.  Since E. coli O157:H7 was released from inoculated seedsduring treatment with ozone, the rate of release of cells from inoculated seedssoaked in 0.1% peptone water for up to 64 min was also determined. The overallreduction of E. coli O157:H7 on seeds treated with ozonated water withoutcontinuous 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 to90.5%). Treatment with higher ozone concentrations enhanced inactivation, butcontact time longer than 8 min did not result in significantly higher reductions(P > 0.05).  For seeds treated byozone sparging, a 1.12-log10 CFU/g (92.1%) reduction was achieved using a 2-mincontact time, and a 2.21-log10 CFU/g (99.4%) reduction was achieved with a64-min contact time. The corresponding reductions for control seeds were 0.71log10 CFU/g (79.5%) and 2.21 log10 CFU/g (99.4%), respectively. Treatment of ozone-sparged seeds at 60°C for 3 h reduced the populationto an undetectable level by direct plating (4 to 4.8 log10 CFU/g), althoughsurvivors were detected by enrichment. Ozone did not have a detrimental effecton seed germination percentage.