Date of Award:

5-2026

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Taylor S. Oberg

Committee

Taylor S. Oberg

Committee

Prateek Sharma

Committee

Robert Ward

Abstract

Cheese is popular for its rich sensory notes and desirable physical attributes; however, the late blowing gas defect in cheddar cheese disrupts its appearance and can undermine its commercial value, for example if the late gas defect is severe, the block can crumble upon cutting, increasing cutting losses from 10% (non-defective) up to 50% (Donnely et al., 2014).

Paucilactobacillus wasatchensis cannot survive pasteurization (McMahon, D. J., et al., 2020); therefore, it enters the cheese as a contaminant during the cheesemaking process. Cheesemaking occurs in three stages: (1) curdling of milk by acidification through starter cultures, (2) separation of curd from whey, and (3) aging, during which the pH of the cheese drops to approximately 5.1. Paucilactobacillus wasatchensis exhibits marginal growth at acidic pH values between 5.0 and 4.0 (Ortakci et al., 2015), which slows its proliferation but does not entirely inhibit it. The organism is also metabolically versatile, capable of utilizing lactose, gluconate, fructose, N-acetylglucosamine (NAG), ribose, and galactose as carbon sources (McMahon et al., 2020). These physiological traits allow Pa. Wasatchensis to persist and slowly grow during cheese aging, contributing to late gas defect formation.

Late gas defect in Cheddar cheese is driven by metabolic reactions and is associated with various microorganisms, including Clostridium species and Paucilactobacillus wasatchensis. This research focused on the metabolic interaction between the recently identified contaminant Pa. Wasatchensis and the starter culture Lactococcus lactis. Excess gas production resulting from this interaction leads to the formation of internal slits and cracks, packaging inflation, and difficulties in automated slicing. All of these factors reduce product quality, consumer acceptance, and ultimately the financial performance for cheese producers (Donnely et al., 2014).

Our project investigates this phenomenon by analyzing the metabolic pathways involved in this interaction. Our results show that Paucilactobacillus wasatchensis utilizes ornithine which is a compound produced and transported by L. Lactis through the arginine deiminase pathway — to generate excess gas during cheese maturation. This adds to the basis for understanding and mitigating late blowing defects in cheddar cheese. Our study demonstrates the significance of this microbial interaction and paves the way toward developing strategies to control and reduce these defects, thereby preserving both product quality and market competitiveness.

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