Date of Award:

12-2025

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Taylor Oberg

Committee

Taylor Oberg

Committee

Prateek Sharma

Committee

Marie Walsh

Abstract

Consumer expectations govern what is acceptable when it comes to the flavor, texture, and color of the cheese. These quality attributes of cheese are all influenced by the pH of the cheese which is in turn controlled by the acid production of the starter lactic acid bacteria (SLAB) used to make cheese. Whatever the final pH of the cheese is, is what determines the quality of the cheese. Unfortunately, there are some Cheddar cheese manufacturers that have observed pH variation during the early aging of their cheeses. We hypothesize that the addition of thermophilic, fast-acid producing bacteria, like Streptococcus thermophilus, as a SLAB is causing the pH variation.

To test this hypothesis, both simulated and traditional Cheddar cheese productions were undertaken. The simulated cheese production was done with a benchtop biofermenter where the temperature profile of a traditional Cheddar cheese production was mimicked to determine the rates of acidification of commercial Cheddar cheese starter culture blends containing mixtures of mesophilic and thermophilic bacteria. It was found that these starter culture blends had statistically different rates of acidification during the post-cook and Cheddaring phases of the make. The starter culture blends containing thermophilic bacteria also showed a plateauing or increase in the pH at the end of the simulated cheese production which could have been mimicking the variation of the pH during the manufacturing of commercial Cheddar cheese.

The same commercial starter culture blends were used in their traditional Cheddar cheese productions. Over the course of the cheese production and the first six weeks of aging, pH measurements were taken. While the pH of the cheeses were found to not be significantly different during aging, the cheeses made with 100% S. Thermophilus did have a higher pH and all the cheeses made with thermophilic bacteria had an increase in their pHs from the time of salting to after pressing.

These results strongly suggest that the inclusion of thermophilic, fast-acid producing bacteria into Cheddar cheese starter culture blends is behind recent pH variation in commercial Cheddar cheese manufacturing.

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