Date of Award:

5-2015

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Donald J. McMahon (Committee Chair), Jeffrey R. Broadbent (Committee Co-Chair)

Committee

Donald J. McMahon

Committee

Jeffrey R. Broadbent

Committee

Craig J. Oberg

Committee

Conly L. Hansen

Committee

David W. Britt

Abstract

Cheddar cheese is usually aged for 3 to 24 months at temperatures ranging from 5 to 13°C. Ripening at elevated temperatures hastens the process, reducing manufacturing costs and enabling manufacturers to bring the product to market more quickly. However, cheeses ripened at elevated temperatures sometimes exhibit late gassy defect that may cause a textural defect, commonly referred to as slit defect. This results in crumbling and
losses during cutting of as much as 50%, making slit defect a major economic issue in the cheese industry. Moreover, loose or blown cheese packages are unsuitable for sale in the supermarkets due to the consumer rejection.

Recently, a previously unnamed lactic acid bacterium was isolated from an aged blown USU Cheddar cheese. The bacterium is named Lactobacillus wasatchii sp. nov., after the Wasatch mountain range in Northern Utah. The current research demonstrates that Lb. wasatchii, whose presence was unsuspected before, is a likely cause of late gassy defect in Cheddar cheese. Three experiments were conducted to explore this problem.

The first experiment showed that Lb. wasatchii grows well on sugars available in cheese (ribose, galactose) under conditions that mimic cheese ripening, namely a high salt and low pH environment. It also survives high temperature short time pasteurization (72°C for 15 sec), which further implicates it in the late gassy defect in cheese.

A second experiment was conducted in which Cheddar cheese was manufactured with or without added Lb. wasatchii to cheese milk. Cheeses with added Lb. wasatchii had significantly higher gas formation compared to control cheeses, and the defect was greater at the elevated ripening temperature.

Finally, since cheesemakers often use a blend of starter cultures containing Streptococcus thermophilus to shorten the time required to make cheese, a third experiment was conducted to show that a gas-forming bacterium such as Lb. wasatchii can also produce gas in cheese made using St. thermophilus by utilizing accumulated galactose. Compared to control Cheddar cheese (no added Lb. wasatchii), cheese containing added Lb. wasatchii ripened at 12°C exhibited major textural defects and produced prodigious amounts of gas when St. thermophilus was included in the starter culture.

This research advances our understanding of late gassy defect in Cheddar cheese, implicating Lb. wasatchii as a likely contributor to late gas formation. Cheese manufacturers now must consider slow-growing, obligatory heterofermentative nonstarter lactic acid bacteria as a potential source of late gassy defect in Cheddar cheese.

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