Date of Award

2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Family and Consumer Sciences

First Advisor

Ibrahim, Salam A. Dr.

Abstract

In recent years, Escherichia coli O157:H7 has been a major foodborne pathogen associated with fresh produce. Many outbreaks of foodborne illnesses have raised concerns in the microbial safety of fresh produce. Several different treatment solutions are being used to decontaminate fresh produce, but still it is very difficult to guarantee the microbiological safety. Therefore, the development of effective treatment for reducing E. coli O157:H7 on fresh produce is needed. The objectives of this study were to investigate the effect of copper alone or in combination with lactic acid on the survival and growth of E. coli O157:H7 in laboratory medium and to evaluate the potential of copper and lactic acid solution to reduce the bacterial population of E. coli O157:H7 on the surface of lettuce and tomatoes. . Four strains of E. coli O157:H7 were individually inoculated into BHI broth containing different concentrations of copper (5, 10, 20 and 40 ppm), lactic acid (0.1, 0.2, and 0.25%), and their combinations. Samples were then incubated at 37 ºC for 8 hours. Bacterial growth was monitored at 0, 4 and 8 hours by measuring turbidity levels. At the end of the incubation, samples were plated on BHI agar to determine the E. coli population. Results showed that lactic acid at 0.2% or higher retarded the growth of bacterial strains. The growth inhibition was negligible when copper was used alone. xii However, significant growth inhibition (p < 0.05) was observed when 0.2% lactic acid was used in combination treatments of copper at 20 ppm and 40 ppm. The pH value of individual or combined samples was determined. Results showed that individual or combined treatments had little effect on pH (5.48-5.74) values (p < 0.05) indicating that acid is not the main inhibiting factor in this study. A four-strain mixture of E. coli O157:H7 was inoculated separately on lettuce and tomatoes, which were treated with copper and lactic acid solution. Log reductions of 3.39 and 3.93 were obtained for tomato and lettuce treated with combination of copper 40 ppm and 0.2% lactic acid respectively. The results showed higher log reduction when surfaces were rinsed with treatment solution containing 0.1% Tween 80. Hence, the treatment with copper and lactic acid was effective in reducing substantial populations of foodborne pathogens. This indicates its potential application to inhibit E. coli O157:H7 and could be used as natural ingredients for the decontamination of fresh produce surfaces.

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