Inactivation of Escherichia Coli O157 On Inoculated Alfalfa Seeds with Ozonated Water Under Pressure

Inactivation of Escherichia Coli O157:H7

on Inoculated Alfalfa Seeds with Ozonated Water Under Pressure1

Journal of Food Safety, Vol. 22 No.2, July 2002

RATNA R. SHARMA2 and ALI DEMIRCI2,3,4

2Department of Agricultural and Biological Engineering

3Life Sciences Consortium

The Pennsylvania State University

LARRY R. BEUCHAT

Center for Food Safety and Department of Food Science and Technology

University of Georgia

AND

WILLIAM F. FETT

United States Department of Agriculture

Agricultural Research Service

Eastern Regional Research Center

Food Safety Intervention Technologies Research Unit

Received for Publication December 21, 2001

Accepted for Publication March 27, 2002

ABSTRACT

Alfalfa seeds inoculated with Escherichia coli O157:H7 (~105 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 μg/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 log10 CFU/g and 0.72 – 1.62 log10 CFU/g, respectively. Control treatments carried out with air pressurization of seeds resulted in maximum population reductions of 1.55 log10 and 1.83 log10 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 log10 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 log10 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.

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