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Effect of Thermoduric Bacteria on the Ripening Characteristics of Cheddar Cheese

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

Lloyd E. Metzger


Cheese defects in texture and body plague many cheese manufactures. For some, the appearance of defects can be traced to a specific cause. These include seasonal changes in milk supply, a change in processing conditions, and changes in bacterial quality. For others, occurrence is intermittent and hard to trace. Study 1 investigated the correlation between raw milk quality and finished cheese, in a commercial cheese plant. Three sampling trips took place, one each in summer, fall, and winter. Cheese was evaluated over a ripening period of 6 months. Study 2, was conducted on cheese made in the SDSU pilot plant. During the manufacture of this cheese, bacteria isolated from slit-defective cheese, some of which was thermoduric, was intentionally added to the cheese milk. To investigate the effects of salting level and cooling rate on defect behavior, two different levels of both of these factors were employed. Cheese was evaluated over a ripening period of 4 months. The results from study 1 showed that although thermoduric bacteria increase over the productions day, there were no correlated changes seen in chemical composition or proteolytic behavior. The results from this study indicate that sampling trips did not occur on days when defective cheese was produced. The results of study 2 showed that gassy and slit defects can occur without changes in chemical composition. There were no significant compositional differences observed between the control and thermoduric treated cheese. Differing cooling rates in the cheese did not result in chemical differences but differing salting levels did. The lower salt treatment resulted in an increased rate of primary proteolysis when compared to the higher salted cheese. The treatments factors of salt, bacteria content, and cooling temperature effected several organic acids and the concentration of sugars within the cheese block. An accelerated ripening treatment was utilized in both studies. Future work should focus on a single bacterium suspected of causing defects on an individual basis, rather than a cocktail. Flavor and texture analysis should be conducted to further detect changes through a production day and to determine if the added bacteria in study 2 affected these attributes.

Library of Congress Subject Headings

Cheddar cheese


Includes bibliographical references (pages 118-120).



Number of Pages



South Dakota State University


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