Semester of Graduation

Spring 2019


Master of Science (MS)


School of Nutrition and Food Sciences

Document Type



Chlorine dioxide, a stronger oxidizing agent, is effective against a broad spectrum of microorganisms. This study evaluated the efficacy of chlorine dioxide on reducing Salmonella, E. coli O157:H7, and Listeria monocytogenes on sweet potato (aqueous ClO₂), strawberries and blueberries (gaseous ClO₂). Sweet potatoes inoculated with multi-strain cocktails of each bacterial pathogen (107 CFU/cm²) were treated with 5 ppm aqueous ClO₂ or water for 10, 20, and 30 minutes. Strawberries and blueberries spot inoculated with multi-strain cocktails of each bacterial pathogen (107 CFU/g) were treated with gaseous ClO₂ sachets (63 mg/l for strawberry and 30 mg/l for blueberry) for 1, 2, and 3 hours. Aqueous ClO₂ treatment significantly (P<0.05) outperformed water treatment after 20 minutes, reducing Salmonella by 2.14 log CFU/cm² compared to 0.93 log CFU/cm² for water treatment. Similar results were observed for Listeria monocytogenes with a 1.98 log CFU/cm² reduction after 30 minutes treatment with aqueous ClO₂ compared to 0.49 log CFU/cm² for water treatment. However, no significant difference in E. coli O157:H7 counts was observed between samples treated with aqueous ClO₂ and water after 30 minutes of treatment. Pathogens were not recovered from ClO₂ wash solutions while water treatment wash solutions had pathogen levels from 3.47 to 4.63 log CFU/ml. Gaseous chlorine dioxide (ClO₂) treatments on strawberries reduced E. coli O157:H7, Listeria monocytogenes, and Salmonella spp. levels by 2.0±0.83, 3.5±0.18, and 2.9±0.20 log CFU/g, respectively within 3 h. For blueberries, after three hours of treatment, levels of E. coli O157:H7, Listeria monocytogenes, and Salmonella spp. were reduced by 2.3, 2.1±0.28, and 2.2±0.63 log CFU/g, respectively. E. coli O157:H7 and Salmonella spp. reduction were similar for both strawberry and blueberry samples treated with ClO₂ gas, however, some variation was observed in reduction of Listeria monocytogenes between 2 and 3 h treatment. Control treatments reported insignificant reductions for all pathogens, averaging at 0.20 log CFU/g of pathogen reduction. The findings of these studies indicate that ClO₂ is effective in reducing pathogens on produce surfaces as well as controlling cross-contamination during post-harvest sanitation.

Committee Chair

Adhikari, Achyut