| Summary: | Ozone is an effective sanitizing agent against a broad spectrum of pathogenic and spoilage organisms. Optimization of treatment applications of ozonated water is needed for increased use in the food industry.
An experimental apparatus and process has been developed to digitally measure ozone concentrations in processing water at the point of product application. Two application methods were evaluated. Ozone concentrations were measured rapidly at the point of product application. Shrimp samples were either sprayed or soaked for 20, 40 or 60 seconds with similar volumes of water with dissolved ozone levels of 1, 2, or 3 ppm. Microbial destruction using aerobic plate counts (APC), and lipid oxidation using the TBARS test, was measured to determine an optimal treatment.
Lowering the water temperature to 10°C facilitated the production of elevated levels of dissolved ozone (dO<sub>3</sub>), whereas high chlorine levels reduced dO<sub>3</sub>. The soaking treatment resulted in greater bacterial reduction than the spray treatment of peeled shrimp, and application time had little effect at low concentrations of dO<sub>3</sub>.
Well handled shrimp samples were then treated within 24 h of harvest using the optimal treatment of soaking in 3 ppm for 60 s. Peeled shrimp were sampled at two day intervals to evaluate APC and rancidity and at 3 day intervals for bioamines (putrescine and cadaverine) using gas chromatography (GC). Sensory quality changes were evaluated using consumer sensory testing. A Listeria monocytogenes inoculation study was also conducted.
Treated shrimp took 16 days to reach bacterial loads of 10<sup>7</sup> CFU/g as compared to untreated shrimp which showed these levels at day 12. Day 12 and day 15 untreated shrimp were rejected by a majority of the consumer panel and treated shrimp were not, based on their odors of decomposition. These rejected untreated shrimp showed >2.6 ppm putrescine and >1.5 ppm cadaverine. Untreated shrimp reached spoilage levels of 10<sup>7</sup> CFU/g 4 days before treated samples during iced storage (12 vs. 16 days). Shrimp inoculated with L. monocytogenes serotype (1/2a) and L. monocytogenes serotype (4b) resulted in a >10<sup>4</sup> CFU/g reduction after treatment. As expected oxidative rancidity did not increase in any of these studies.
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