Date of Award:

12-2024

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Sulaiman K. Matarneh

Committee

Sulaiman K. Matarneh

Committee

Kara J. Thornton-Kurth

Committee

Stephan van Vliet

Committee

Luis J. Bastarrachea

Committee

Taylor S. Oberg

Abstract

Of all the attributes that define beef's eating quality, tenderness stands out as one of the most important. Previous studies have shown that consumers are willing to pay a premium for beef that is guaranteed to be more tender and are more likely to purchase that product repeatedly. Yet, due to the influence of numerous internal and external factors, controlling and predicting tenderness remains to be difficult. However, among these factors, meat aging is the primary contributor to end-product tenderness, as it is recognized for breaking down muscle tissue via enzymes present within the muscle. The activity of these enzymes weakens the structural integrity of muscle proteins and, consequently, results in meat that requires less force to chew (i.e., tenderness). The calpains, caspases, and cathepsins are three of the main enzyme families that participate in meat aging; however, the calpains contribute the most to this process. Despite the current understanding of meat aging and the enzymes that participate, producing consistently tender products is still an issue within the meat industry. This means that the aging process is not fully understood and there are more controlling factors that remain undiscovered.

Previous studies have found that many biochemical characteristics within meat can contribute to the aging process. These include the predominant muscle fiber type and its associated attributes within different muscles, the integrity and function of cellular machinery such as the "powerhouse of the cell" (mitochondria), and whether or not the meat has been previously frozen/thawed. However, the influence of these factors on the enzymes contributing to aging and the overall structural changes within the tissue could help us further understand what ultimately affects meat tenderization and end-product tenderness. Therefore, the purpose of this project is to use biochemical methods to evaluate the internal characteristics of different muscles, the abundance of mitochondria, and how freezing storage influences aging and subsequent meat quality in beef, to better understand the processes that affect meat tenderization. This is an effort to provide foundational knowledge that will enhance meat palatability and reduce variations in beef tenderness. To accomplish this, we performed four independent studies. Our first study examined the progression of protein breakdown during aging between muscles with unique muscle fiber compositions and biochemical properties. The second study evaluated how different concentrations of mitochondria alter protein breakdown along with enzyme activity, utilizing an in vitro system containing all of the chemicals needed to recreate postmortem conditions. Our third study sought to test how freezing/thawing and then aging the meat influences enzyme activity compared to only aging the meat, while our final study looked into different freezing/thawing rates and their effects on the microstructure and overall quality of large sections of meat known as primals.

Overall, our results showed that meat aging is a complicated process but is largely influenced by the fiber type composition and accompanying biochemical properties within different muscles, mitochondrial abundance, and integrity, whether the meat had been previously frozen/thawed, and the rates to which freezing/thawing occurred. Moreover, this project provides a greater understanding of the biochemical aspects of meat aging and their importance when optimizing beef tenderness. However, further research is needed to evaluate different breeds and species of meat-producing animals.

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