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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

David R. Henning


The lactoperoxidase system, a naturally occurring antibacterial system in bovine milk, was evaluated as an additional food safety hurdle in a cheese that can support the growth of pathogenic microorganisms. Lactoperoxidase is not completely inactivated at pasteurization temperatures; however, its activity decreases with the increase in the processing temperature. Reduced lactoperoxidase activity results in the reduction of antibacterial effects on a gram negative coliform, Escherichia coli K-12. Lactoperoxidase activity was determined after activation and heat treatment at temperatures ranging from 62.8 to 76.7°C for 19 s. Though measurable activity was found at 73.9°C and below, minimum High Temperature Short Time pasteurization resulted in at least a 3 0% reduction in lactoperoxidase activity. For cheese making trials, milk was processed at 72.5 ± 0.5 °C for 19 s to satisfy the regulatory requirements for pasteurization. Eighteen lots of Queso Fresco, a soft variety of Mexican cheese, were manufactured after the inoculation of the processed milk with Escherichia coli K-12 ATCC 23716 at high and low inoculum levels (> 100,000 and

Library of Congress Subject Headings

Escherichia coil
Cheese -- Microbiology


Includes bibliographical references (pages 37-42)



Number of Pages



South Dakota State University


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