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Sequential Disinfection of
Escherichia coli O157:H7 Inoculated Alfalfa Seeds Before and During
Sprouting Using Aqueous Chlorine Dioxide, Ozonated Water, and Thyme Essential
Oil
Lebensmittel-Wissenschaft und-Technologie
Volume 36, Issue 2 , March 2003, Pages 235-243
N. Singha,
R. K. Singha
and A. K. Bhuniab
a Department of Food Science and Technology, University of Georgia,
Food Science Building, Athens, GA 30602-7610, USA
b Department of Food Science, Purdue University, West Lafayette, IN
47907-1160, USA
Abstract
Several outbreaks of human illness have been
documented in the United States associated with alfalfa sprouts. This
study was done to evaluate the efficacy of aqueous chlorine dioxide (ClO2)
(10, 25, and 50 mg/L), ozonated water (4.60, 9.27, and 14.3 mg/L) and thyme oil
(1.0, 2.5, and 5.0 mL/L), for 3, 5, and 10 min, respectively, alone or their
sequential washing (thyme oil followed by ozonated water and aqueous ClO2)
for eliminating Escherichia coli O157:H7 from alfalfa seeds prior and
during sprouting.
 Alfalfa
seeds were inoculated with a three-strain E. coli O157:H7 mixture and
dried to attain approximately 106 cfu/g of seed. No single washing
treatment was able to ensure complete elimination of E. coli O157:H7 from
alfalfa seeds. Germination of seeds was not adversely affected by any of the
treatments. A membrane-transferring surface-plating method was evaluated to
recover uninjured and injured E. coli O157:H7. Direct surface-plating on
selective media, Sorbitol MacConkey-cefixime-tellurite (SMac-CT) showed
significantly (P<0.05) low populations recovered, thus indicating
a large population of injured cells for each washing treatments in comparison to
membrane-transferring surface-plating method tryptic soy agar/membrane/Sorbitol-MacConkey
agar-cefixime-tellurite (TSA/M/SMac-CT). Regardless of different washing
treatments, populations of E. coli O157:H7 increased to 7.8–8.2log10 cfu/g
after sprouting (72 h). Results of this study also showed that sequential
washing treatments (as irrigation water) during sprouting process have greater
lethality than other sanitizer treatments alone.
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