Author

Amanda Rioux

Date of Award

12-2007

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Vivian C.H Wu

Second Committee Member

Alfred Bushway

Third Committee Member

Brian Perkins

Abstract

Many potato farmers lose potatoes during storage due to the length of storage time and microbial contamination. During harvesting, potatoes may become injured and susceptible to microorganisms such as yeast and molds and bacteria. When in storage, bacteria and fungi that were potentially introduced during harvesting may contaminate some potatoes. As the potatoes are in such close contact during storage, the infection may spread throughout the entire storage facility. The first objective of this study was to develop a novel, simple gaseous chlorine dioxide (CIO2) method that could effectively control natural flora, yeast and mold, and Pseudomonas aeruginosa on potatoes during storage. Different treatments included the combination of: 2 g of sodium chlorite and 2 g of acid into sachet to generate 16 mg/1 after 2.5 hrs and 20 mg/1 after 5 hrs (low treatment), 3g of sodium chlorite and 3 g of acid to generate 24 mg/1 after 2.5 hrs and 30 mg/1 after 5 hrs (medium treatment), and 4 g of sodium chlorite and 4 g of acid to generate 32 mg/1 after 2.5 hrs and 40 mg/1 after 5 hrs (high treatment). Results were effective for yeast and mold, showing over a 5 log CFU/potato reduction after 5 hr of treatment with a 4 g treatment of gaseous CIO2. The natural flora study also showed over a 5 log CFU/potato reduction. For P. aeruginosa, there was a slight increase in the reduction after 5 hr of the 4 g treatment with almost a 6 log CFU/potato reduction. The lowest treatment tested (2 g at 2.5 hrs) had reductions of 1.7, 1.9, and 2.3, log CFU/potato for natural flora, yeasts and molds, and P. aeruginosa, respectively. Overall, gaseous CIO2 effectively killed natural flora, yeast and mold, as well as P. aeruginosa on potatoes for each treatment. As natural preservatives in food are desired, the second objective was to determine the antimicrobial effects of peel and tubers on common foodborne pathogens. Methods included using plain freeze dried potato juice that was tested at 50% (w/v) and 75% (w/v) concentrations with distilled water, as well as plain potato peel juice. These compounds were tested utilizing the agar diffusion assay or the log reduction method. Antioxidant levels were also studied to determine a correlation with the antimicrobial study using the DPPH (l,l-Diphenyl-2 picrylhydrazyl) method. The Russet potato peel treatment resulted in a complete 5 log CFU/ml reduction over time (24 hr) against Escherichia coli 0157:H7. The freeze dried potato juice from Russet potatoes at 75% (w/v) concentration, showed an inhibition zone of 13.3 mm against Salmonella Typhurmium. The freeze dried tuber juice of Katahdin potatoes at a 50% (w/v) concentration had an average zone of inhibition of 13.2 mm (triplicate) against S. Typhimurium. The antioxidant study showed that the potato peel resulted in slight antioxidant activity, whereas the tuber did not. Overall, potatoes showed antimicrobial activity, yet these studies may require further research such as different extraction methods. Antioxidants in potatoes may be further studied using quantitative methods.

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