Date of Award

Spring 5-13-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Vivian C.H. Wu

Second Committee Member

Benildo G. de los Reyes

Third Committee Member

Cheng-An Hwang

Abstract

The objective of this study was to evaluate the effectiveness of gaseous chlorine dioxide and ozone treatment to reduce Shiga toxin-producing Escherichia coli (STEC), Salmonella species, and Listeria monocytogenes on baby-cut carrots, lowbush blueberries, and beefsteak tomatoes using a scaled-down foundational version of an industrial realistic closed-circulation treatment system.

Gaseous chlorine dioxide was generated and circulated in-chamber for either 2.5 or 5.0 h using a dry-media system. Equal parts of dry ClO2 precursor were combined to make 0.03, 0.06, and 0.12 mg ClO2/g produce for a 2.5 h exposure and 0.04, 0.07, and 0.15 mg ClO2/g produce for a 5.0 h exposure time. Ozone was generated through corona-discharge of a dry oxygen feed and either 0.4 or 0.8 mg O3/g produce concentrations were used to treat the produce-mass for 2.5 and 5.0 h. All treatments consisted of 2 kg of produce and pathogen reduction was determined by comparison of treated produce against an untreated control through bacterial enumeration using the Thin Agar Layer method which is selective agar overlaid with a thin-layer of trypticase soy agar (TSA). Each produce model was visually inspected for signs of bleaching due to treatment and antimicrobial treatment residue was measured using rinse water.

Treatment of tomatoes was most effective as the 5.0 h exposure reduced levels of all three pathogens (≥ 7.0 log CFU/g) below the detection limit (

These results indicated that gaseous antimicrobials can be suitable treatments, at low doses, for produce models in a storage setting as a step in hurdle intervention. During storage, most produce commodities have already been exposed to treatment intervention (e.g. chlorine wash) and this next step can further reduce the microbial load present; thus increasing safety and shelf-life.

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