Graduate Thesis Or Dissertation
 

Bacterial inhibition by electrolyzed oxidizing water and application to disinfection of sprout seeds

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  • Alfalfa sprouts have been implicated in several salmonellosis outbreaks in recent years. Electrolysis of a NaCl solution generates, in the anode side of a two-chamber electrolyzer, acidic electrolyzed oxidizing (EO) water which contains Cl₂, HOC1, dissolved oxygen, and it is characterized by a low pH and a high oxidation reduction potential (ORP). The disinfectant effects of EO water against Salmonella enterica both in an aqueous system and on artificially contaminated alfalfa seeds were determined. EO water (pH 2.54 to 2.38, and ORP +1083 to +1092 mV) exhibited strong potential for the inactivation of S. enterica in an aqueous system (producing a reduction of at least 6.6 log CFU/ml). Treatment of artificially contaminated alfalfa seeds with EO water at a seed-to-EO water ratio of 1:100 for 15 and 60 min significantly reduced Salmonella populations by 2.04 and 1.96 log CFU/g, respectively (P < 0.05), while a Butterfield's buffer wash decreased Salmonella populations by 0.18 and 0.23 log CFU/g, respectively. Germination of seeds was not significantly affected (P > 0.05) by a treatment for up to 60 min in electrolyzed water. Further studies were undertaken to investigate whether •OH radical species are present in EO water or are formed when EO water reacts with iron ions. Electron spin resonance spectroscopy (ESR) coupled with the spin trapping technique was used for the detection of free radicals. The DMPO-OH spin adduct, characteristic to •OH radicals, was not observed. In the presence of DMPO (5,5-dimethyl-l-pyrroline-N-oxide), the reactions of EO water with Fe³⁺ and Fe²⁺ yielded the spin adduct DMPO-OH. However, the addition of •OH radical scavengers (ethanol, methanol, and mannitol) to the reaction mixture, did not reduce the DMPO-OH signal nor generated the characteristic DMPO-alkyl spin adducts. This indicated that the DMPO-OH signal was due to a nucleophilic addition of water to DMPO and not to trapping of OH radicals. Addition of DMPO to EO water, generated an ESR spectrum identical with that of 5,5-dimethyl-2-pyrrolidone- N-oxyl (DMPOX). Hypochlorous acid, generated in the anode chamber, is proposed to oxidize the spin trap DMPO with the formation of DMPOX.
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