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Inactivation of Escherichia Coli
O157:H7 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. |