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

Abstract
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.