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Yu Zhang

Document Type

Thesis - University Access Only

Award Date

1999

Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

David R. Henning

Keywords

Cheese Curing, Escherichia coli Survival, Microbial Death Model V

Abstract

The objective of this study was to mathematically describe the decline of viable Escherichia coli in the curing of American Type cheese. Pasteurized whole milk was inoculated with 100 to 1000 E. coli biotype I /ml and was used to manufacture Cheddar and Colby-like cheeses. Multiple regression design was employed to determine the effects of low to high levels of environmental parameter in typical cheese, such as moisture (34 to 40%), pH (5.0 to 5.6), curing temperature (4 to 13°C) and salt concentration (0.8 to 1.7%) on survival of E. coli during cheese storage. Fourteen batches of cheese were made and a total of 56 survivor curves representing different combinations of the four environmental parameters were generated during the four-month curing time. The identity of the bacterial isolates was checked by RAPD-PCR, which confirmed that the organism found in cheese milk were the same as the bacteria in the curing cheese. Enumerations of surviving cells showed several forms of declining curves, including classic first-order declines, lag phases and two-phase declines with shoulder. The linear primary models were tested for their ability to depict the data. Multiple regression and step wise regression analysis were employed to develop second-order polynomial models relating decline slope (E. coli number vs. time) to moisture, pH, temperature and salt concentration. Results indicated temperature had the most significant effects on models. The second-order polynomial model provided a rapid means of estimating the effects of the controlling factors on the decline of E. coli in the curing cheese.

Library of Congress Subject Headings

Cheese -- Microbiology
Escherichia coli

Description

Includes bibliographical references (pages 28-33)

Format

application/pdf

Number of Pages

62

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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