Date of Graduation

2007

Document Type

Thesis

Degree Type

MS

Committee Chair

Kristen E. Matak

Abstract

Through science, we can meet increasing consumer demand to make foods safer and healthier, both by increasing the safety by decreasing possible microbial contamination and by increasing the nutritive value of food by supplementation. This thesis focuses on two facets of food science: safety and value-added foods. The effectiveness of electron beam (e-beam) irradiation on the reduction of Salmonella enterica subsp. enterica serovar Montevideo in pureed tomatoes was tested, and growth parameters of the microalga Crypthecodinium cohnii for production of the omega-3 fatty acid docosahexaenoic acid (DHA) were evaluated. E-beam is a technology that uses ionizing radiation to destroy bacteria in a nonthermal manner. E-beam could be applied to fresh produce to improve microbial safety while simultaneously maintaining their “fresh” characteristics. D10-values were obtained for acid-resistant Salmonella Montevideo in tomatoes that were subjected to e-beam. Homogenized Roma tomatoes were adjusted to pH values of 3.4, 3.9, 4.4, or 4.9 and then inoculated with S. Montevideo. Samples were subjected to e-beam at 0 (control), 0.5, 1.0, 1.5, 2.0, and 2.5 kGy. The D10-values were calculated as the inverse reciprocal of the slope of the survivor curves. Salmonella Montevideo did not survive in the samples at pH 3.4 or 3.9. Microbial populations were reduced at all e-beam doses; there were significant reductions (P< 0.05) between the control and both pH 4.4 and 4.9 samples ebeamed at 1.5, 2.0, and 2.5 kGy. D10-values for S. Montevideo in samples at 4.4 and 4.9 were 1.07 and 1.50, respectively. The D10-values for acid-resistant Salmonella Montevideo are considerably higher than previously published D10-values for non-acid-resistant Salmonella, indicating that resistance to e-beam may increase with acidresistance. DHA, an omega-3 fatty acid (FA) found in fatty fish, has positive health benefits. While suggested amounts of DHA may be attained by consuming fish, this may increase exposure to environmental pollutants. The oil produced by Crypthecodinium cohnii, a marine alga, contains DHA as 30-50% of total FA’s. The media recommended by the ATCC for initial growth of C. cohnii is expensive and is unavailable for purchase; therefore, one objective of this study was to see if C. cohnii growth was affected by initial medium. Processing parameters for continuous cultivation of C. cohnii were also ascertained. C. cohnii (ATCC 30772) was initially grown in ATCC media 460 or simple media (9 g L-1 glucose, 2 g L-1 yeast extract, and 27.8 g L-1 salt) and then grown in standard media (25 g L-1 glucose, 5.5 g L-1 yeast extract, and 25 g L-1 salt) for the duration of the study. Optical density (OD), conductivity, pH, and dissolved oxygen (DO2) tension were measured. Results showed that C. cohnii grew equally in both media (P< 0.05) with no significant differences in pH, conductivity, or DO2 between the two media (P>0.05). The OD indicated a lag phase of growth for ~13 hr, followed by exponential growth until ~48 hr growth. The pH dropped during the exponential phase. These data indicate optimum retention in a pH-controlled bio-reactor is 48 hr. For continuous production, ideal flow rate would be 5.2 ml/min for a 15 L culture. Results of these studies and their continuations will improve food safety and quality in the production process; which in turn will help improve the health of America’s consumers.

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