Author

Fatih Ortakci

Date of Award:

2015

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Donald J. McMahon

Abstract

This study sought to determine whether a recently isolated slow-growing nonstarter lactic acid bacterium, Lactobacillus wasatchii sp. nov., could be implicated in late gassy defect in Cheddar cheese. I demonstrated that Lb. wasatchii grows readily in the laboratory under cheese-like stress conditions of 5% salt and pH 5.2, and has the potential to survive pasteurization. Lactobacillus wasatchii can co-utilize ribose and galactose to maximize its growth. Due to being an obligatory heterofermentative, Lb. wasatchii produces CO2 whenever it ferments a hexose such as galactose.

A second investigation extended these findings by examining the growth and gas forming characteristics of Lb. wasatchii in Cheddar cheese. The optimum growth of Lb. wasatchii and highest levels of gas production were observed in cheese supplemented with ribose plus galactose, and stored at 12°C rather than 6°C. Lactobacillus wasatchii also grew readily and produced gas in Cheddar cheese even without added ribose and galactose, which corresponds with the ability of Lb. wasatchii to grow on starter cell lysate. A challenge still remains of how to easily enumerate Lb. wasatchii in cheese with a higher background population of other nonstarter lactic acid bacteria.

The third set of experiments explored the consequences on growth and gas production of Lb. wasatchii in Cheddar cheese made with Streptococcus thermophilus. Using St. thermophilus in cheesemaking results in galactose accumulation, which Lb. wasatchii then can utilize for growth, causing release of CO2 with the end result of having blown Cheddar cheese. Results showed Lb. wasatchii or similar nonstarter lactic acid bacteria are likely to be particularly problematic in cheesemaking involving starter or adventitious St. thermophilus.

From these observations, it was concluded that Lb. wasatchii is a contributor to late gassy defect in Cheddar cheese and may be widely present as part of the nonstarter lactic bacteria population but has been undetected up until now. The late gassy defect is more pronounced at temperatures used for accelerated ripening of cheese and when there are substantial residual levels of galactose in the cheese. Thus, researchers and cheese manufacturers now must consider slow-growing obligatory heterofermentative nonstarter lactic acid bacteria when dealing with late gassy defect in cheese.

Included in

Nutrition Commons

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