The Impact of Oxidative Stress on Postmortem Meat Quality

Tenderness is the primary factor to influence consumer palatability in fresh meat. The tenderization of muscle is dependent on proteolytic mechanisms, including calcium dependent, non-lysosomal endogenous enzymes such as calpains and proteasomes. These mechanisms have been indicated alongside apoptosis early postmortem as cascades of apoptotic events promote ideal conditions for postmortem tenderization. Recent literature has identified oxidative stress-mediated events to be linked to apoptotic activity. Oxidative stress is defined as the overwhelming production of reactive species compared to homeostatic, endogenous antioxidants present within muscle systems. These conditions exhaust antioxidant function and facilitate reactive species to alter protein, lipid, or nucleic morphology and functionality. Perhaps, the generation of oxidative stress can alter muscle tissue, resulting in changes in the overall quality of fresh meat postmortem. This study examined the impact of different levels of oxidative stress in vivo on postmortem muscle quality of lambs, with emphasis towards elements of proteolytic mechanisms responsible for meat tenderness. Lipopolysaccharides (LPS) are endotoxins used to induce acute stress for this experiment. Effects of inducing lambs with an injection of either a saline control, 50 ng of LPS per kg of bodyweight (LPS50), or 100 ng of LPS per kg of bodyweight (LPS100). Injections were administered every 72 hours across a nine-day immune challenge. Treatments used examined changes in biomarkers of oxidative stress (RNA Transcriptomics and isoprostanes), pre-harvest stress conditions (rectal temperature), free calcium concentration, proximate composition, color and lipid oxidation, and tenderness. In this study, lambs administered LPS50 tended to be more tender early postmortem, and had a greater degree of Troponin T degradation compared to control samples (P \u3c 0.05). The LPS-treated lambs exhibited noticeable upregulation of gene pathways responsible for cell growth, differentiation, degradation, and generation of oxidative species and antioxidants (Praw \u3c 0.05). While not significant, LPS treated samples exhibited more oxidative biomarkers present in muscle tissue (isoprostane content). The LPS treatments had no detrimental effects of color or lipid oxidation (P \u3e 0.05). Oxidative stress may impact early postmortem tenderization of meat. Key words: apoptosis, lamb, meat quality, oxidative stress, proteolysis, tenderization Advisor: Chris R. Calkin

Impact of Diet and Quality Grade on Shelf Life of Beef Steaks

Steers were fed a diet containing dry rolled corn, steam flaked corn, dry rolled corn with 30% dried distillers grains, or steam flaked corn with 30% dried distillers grains. Strip loins from upper 2/3 Choice and Select- grade carcasses were obtained to evaluate the effects of diet and quality grade on shelf life characteristics. Strip loins were aged for 2, 9, 16, or 23 days. Results suggest that steaks from cattle fed steam flaked corn (with or without dried distillers grains) and from cattle fed dried distillers grains (regardless of corn type) had higher levels of many unsaturated fatty acids, more discoloration, and greater lipid oxidation compared to the dry rolled corn treatments or the no dried distillers grains treatments, respectively. Feeding of dry rolled corn or diets without dried distillers grains maintained red color better during retail display. Choice- grade steaks had significantly higher levels of unsaturated fatty acids like 18:2 and total polyunsaturated fatty acids than Select- grade steaks but did not diff er in color stability or oxidation. These data indicate the longest shelf life will occur when cattle are fed diets containing dry rolled corn (versus steam flaked corn) or without dried distillers grains (versus with dried distillers grains) and that both steam flaked corn and distillers grains have a negative impact on shelf life. Quality grade did not affect color stability

Impact of Dietary Fat Source on Beef Tenderness

Steers were finished on either a corn control, 40% full-fat modified distillers grains plus solubles, 40% de-oiled modified distillers grains plus solubles, or 38% de-oiled modified distillers grains plus solubles plus 2% corn oil diet to evaluate the effects of dietary fat source on the mechanism of beef tenderization . Feeding modified distillers grains plus solubles increased polyunsaturated fatty acid content in the sarcoplasmic reticulum membrane and increased free Ca2+ concentration early postmortem. Steaks from cattle fed de-oiled modified distillers grains and de-oiled modified distillers grains plus corn oil were more tender at 2 d of aging when compared to corn control diet. These data indicate that feeding modified distillers grains plus solubles to cattle has the potential to increase beef tenderness early postmortem in comparison to corn diets

Impact of Myoglobin Oxygenation State on Color Stability of Frozen Beef Steaks

The objective of this study was to determine the impacts of myoglobin oxygenation level and frozen storage duration on frozen beef color. Strip loins were wet- aged for 4 or 20 days and were fabricated into steaks that were assigned a myoglobin oxygenation level (highly oxygenated, lowly oxygenated, or deoxymyoglobin) and packaging film (impermeable or permeable). Steaks were then frozen for 0, 2, 4, or 6 months of storage and analyzed for various beef color measurements. Highly oxygenated steaks had greater a* values (redness) and percent oxymyoglobin compared to the other treatments. Frozen storage beyond 4 months and oxygen impermeable packaging tended to have detrimental effects on beef color. Highly oxygenated steaks that are aged for 4 d displayed superior red color for extended storage with few undesirable effects

The Relationship of Liver Abscess Scores and Early Postmortem Meat Tenderness

Acidosis is one of the most common nutritional disorders found in commercial feedlots. Cattle diets with high concentrations of starch can cause rapid production of acids in the rumen, disrupting microbial fermentation, causing liver abscess formation, and lowering livestock performance. This study was conducted to evaluate the relationship between the occurrence of liver abscesses and beef tenderness early postmortem. Results showed numerically lesser shear force values (greater tenderness) in loins from animals without liver abscesses, however, this was not statistically significant for slice shear force or Warner- Bratzler shear force. Although the effects of liver abscess occurrence in relation to meat quality are still unclear, results from this study provide a conceptual foundation for additional research to be explored on meat quality

Impact of Diet and Quality Grade on Shelf Life of Beef Steaks

Steers were fed a diet containing dry rolled corn, steam flaked corn, dry rolled corn with 30% dried distillers grains, or steam flaked corn with 30% dried distillers grains. Strip loins from upper 2/3 Choice and Select- grade carcasses were obtained to evaluate the effects of diet and quality grade on shelf life characteristics. Strip loins were aged for 2, 9, 16, or 23 days. Results suggest that steaks from cattle fed steam flaked corn (with or without dried distillers grains) and from cattle fed dried distillers grains (regardless of corn type) had higher levels of many unsaturated fatty acids, more discoloration, and greater lipid oxidation compared to the dry rolled corn treatments or the no dried distillers grains treatments, respectively. Feeding of dry rolled corn or diets without dried distillers grains maintained red color better during retail display. Choice- grade steaks had significantly higher levels of unsaturated fatty acids like 18:2 and total polyunsaturated fatty acids than Select- grade steaks but did not diff er in color stability or oxidation. These data indicate the longest shelf life will occur when cattle are fed diets containing dry rolled corn (versus steam flaked corn) or without dried distillers grains (versus with dried distillers grains) and that both steam flaked corn and distillers grains have a negative impact on shelf life. Quality grade did not affect color stability

Proteomic Analysis of Oxidized Proteins in Beef

To evaluate the effects of diet and quality grade on tenderness and oxidative damage to proteins, strip loins from USDA Upper 2/3rd Choice and Select- grade carcasses were obtained. Steers were fed either a diet containing dry rolled corn, steam flaked corn, dry rolled corn with 30% dried distillers grains with solubles, or steam flaked corn with 30% dried distillers grain with solubles. Results suggest that steaks from steers fed dry rolled corn are more objectively tender than steam flaked corn; in addition, steaks grading USDA Upper 2/3rd Choice steaks were more tender when compared to USDA Select quality grade. In contrast to previous research, no tenderness differences were detected between steaks from steers with or without dried distillers with solubles. Proteomic analysis revealed increased oxidative damage of myofibrillar proteins. Steaks graded as USDA Upper 2/3rd Choice steaks were determined to generally have increased oxidative damage to glycolytic, structural, and heat shock proteins, compared to USDA Select quality grade. While samples from steers fed dry rolled corn were more tender and had increased myofibrillar oxidative damage from steers fed DRC with distillers grains, steam flaked corn- related treatment displayed the inverse response. Overall, results support the relationship between marbling and tenderness, and suggest oxidative stress may be a factor involved in this difference

Effects of Relative Humidity on Meat Quality in Dry Aged Beef

During dry- aging, water is transferred from the interior to the meat surface and is subsequently evaporated to the surrounding environment. Th ere is a common belief in the meat industry that rapid drying creates a hard crust on the meat surface, which would act as a protective barrier against moisture loss, holding moisture on the inside of the product. Th is phenomenon is called case hardening. If this hypothesis is correct, drying at low relative humidity would be recommended in order to get case hardening and avoid excessive yield loss. Th is study was conducted to evaluate the effects of relative humidity on moisture loss and flavor in dry- aged beef. No case hardening effects occurred, even at 50% relative humidity. Results suggest lower relative humidity results in more rapid moisture loss at the beginning of the aging process without significantly affecting the total amount of moisture loss. Lower relative humidity tended to associate with more desirable flavor notes

Quality Effects on Beef from Cattle Fed High-Protein Corn Distillers Grains and Other Ethanol By-Products

The objective of this study was to evaluate the effects of feeding high protein corn distillers grains on fresh beef quality. Steers were fed one of five diets, either a corn control, high protein distillers grains plus solubles, dry distillers grains plus solubles, wet distillers grains plus solubles, or bran plus solubles diet. Strip loins were aged for 2, 9, or 23 days and placed under retail display conditions for 0 or 7 days. Dietary treatment had no effect on tenderness within each aging period. There were also no differences between treatments for proximate composition, free calcium in the muscle, and sarcomere length. Results suggest that feeding high protein distillers grains decreases color stability and increases lipid oxidation when compared to corn diets leading to reduced shelf life

The Influence of Diet and Oxidation on Calcium Retention of the Mitochondria in Fresh Beef

Feeding dried distillers grains (DG) may influence calcium flux postmortem by disrupting the stability of the sarcoplasmic reticulum (SR) membrane, thus leading to a higher post- rigor calcium leakage, resulting in greater activation of calpains and improved tenderness. Mitochondria provide the opportunity to study calcium flux in a controlled, tightly defined environment as a model system for the SR. Cattle were finished on diets containing either 0% DG or 50% DG. Feeding DG increased proportions of PUFA in the SR and mitochondrial membrane. Oxidized mitochondria retained less calcium than non- oxidized mitochondria. Mitochondria from cattle finished on corn tended to retain more Ca than mitochondria from cattle finished on DG. These findings suggest that feeding DG in the finishing diet can possibly increase meat tenderness through altered calcium flux