Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

Robert M. Grodner

Abstract

Listeria monocytogenes has the potential to be a serious pathogen for the compromised health segment of our population (immunocompromised, young, elderly and the pregnant). While the infectious dose is generally believed to be high 1.0 $\times$ 10$\sp6$, infectious dosages of 1.0 $\times$ 10$\sp3$ have been reported. Listeria monocytogenes poses a threat because of several factors: ubiquity in nature, isolation from fresh/salt waters, soil, ruminates and 17% of the human population. Listeria monocytogenes can colonize surfaces within 20 minutes, evade sanitizing, and is capable of growth from 37$\sp\circ$C to below refrigeration temperature. Fish and seafoods are high in water activity and undergo minimal if any processing. Most fish, mollusk, crustacea and shellfish still undergo hand filleting, picking or shucking. Listeria monocytogenes has been isolated from blue crab processing plants, catfish viscera and 61% of frozen seafoods and in one survey 17% of food worker's hands. While widely found in nature, L. monocytogenes can colonize stainless steel, polyproylene, rubber, glass and iron surfaces and could serve as a contamination source. These factors could coincide under the right circumstances and cause an estuarine related listeriosis outbreak. The need for a simple process utilizing GRAS (Generally Recognized As Safe) substances to suppress L. monocytogenes proliferation needs to be established. Listeria monocytogenes in planktonic cultures and incubated catfish fillets were exposed to chemical dips. Linear relationships and chemical D-values for the reduction of L. monocytogenes in planktonic and dynamic systems were obtained. Hydrogen peroxide eliminated L. monocytogenes at low concentrations. Unacidulated sodium hypochlorite was not effective in reducing microbial populations in any system. Acetic, lactic acids and hydrogen peroxide lowered log counts by a minimum of 1.5. Acetic acid (2% at 65$\sp\circ$C dipped 30 seconds) was found to reduce natural flora and artificially incubated L. monocytogenes fillets up to twelve days. Treated fillets were found acceptable to a consumer panel. Listeria monocytogenes was found to adhere in a blood biofilm to common processing surfaces. Sanitizing surfaces with acetic acid (70$\sp\circ$C, 5% for 5 minutes) was effective in nearly sterilizing cutlery grade 4000 series stainless steel, polyethylene knife handles and polypropylene filleting boards.

ISBN

9780591288643

Pages

130

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