Sequential disinfection of Escherichia coli O157 : H7 inoculated alfalfa seeds before and during sprouting using aqueous chlorine dioxide, ozonated water, and thyme essential oil

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 10(6) 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 (Pless than or equal to0.05) 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 7.8-8.2log(10)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. (C) 2002 Swiss Society of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.