Date of Award

8-2014

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

Cheng-An Hwang

Third Committee Member

Balunkeswar Nayak

Abstract

Toxoplasma gondii is one of the leading causes of foodborne illness related hospitalizations and death in the United States. The risk of T. gondii infection is especially a concern for pregnant women and immunocompromised individuals. This study had two main objectives to: 1) develop a rapid and simple detection method based on oligonucleotide-functionalized gold nanoparticles (AuNPs) optical properties and 2) study processing interventions that can be utilized to successfully eliminate T. gondii contamination.

Currently, cat and mouse bioassays are the standard methods for T. gondii detection. This study aimed to develop a rapid and specific optical sensing method for the detection of T. gondii by DNA sandwich hybridization with AuNPs. This method requires less than an hour for detection after the DNA preparation. The AuNp-DNA hybridization was confirmed through gel electrophoresis and the aggregation was corroborated with spectrophotometric data. The colorimetric properties of this specific detection method of T. gondii offer a significant advantage over the traditional cat and mouse bioassays in terms of time, cost and simplicity.

This study also determined the effectiveness of using peroxyacetic acid (50, 100 ppm, 1%), lactic acid (2%), chlorine dioxide (1, 3, 5, 10, 15 ppm) and chlorine (100, 150, 200 ppm) washes to remove T. gondii oocysts inoculated on the surface of blueberries. Results indicate that peroxyacetic and lactic acid washes are more effective in removing T. gondii oocysts from blueberry surface than ClO2 NaClO and water washes. Peroxyacetic acid removed just over 5 log of the 5.2 log inoculated oocysts while water washes only remove 4.7 log. Interventions targeting the oocyst stage of T. gondii are imperative for controlling T. gondii contamination of fruits and other produce. The use of peroxyacetic acid and lactic acid washing could be a viable method of controlling T. gondii oocysts contamination on blueberries.

Other processing interventions such as freezing and irradiation were also studied. Freezing was shown to be an effective method in controlling T. gondii tissue cysts in contaminated meat products at -20°C for 24h. Low dosages of irradiation 0.2-0.6 kGy were studied in their effectiveness of controlling T. gondii. Doses of 0.6 and 0.4 kGy control oocysts and tissue cysts respectively. Product quality analyses on low dosage irradiation with blueberries has not previously been studied and therefore the color, texture and total anthocyanins were analyzed in this study and no significant differences were found between irradiated and non-irradiated blueberries.

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