Color stability and cooked muscle color were evaluated in relation to myoglobin content, oxygen consumption rate, pH, lipid oxidation, oxygen penetration depth, metmyoglobin reductase activity, Hunter L*- a*- b*- values, discoloration, and degree of doneness for the M. Infraspinatus (IF), M. Triceps brachii (TB), M. Teres major (TM), M. Rectus femoris (RF), M. Vastus lateralis (VL), M. Semimembranosus (SM), M. Biceps femoris (BF), M. Semitendinosus (ST), M. Gluteus medius (GM), as well as the M. Psoas major (PM), and M. Longissimus lumborum (LL). Steaks from these muscles were segmented into a low oxygen dark, low oxygen light, high oxygen, and PVC overwrap packaging environment for six days of retail display. There were no major differences in pH, oxygen consumption rate, or myoglobin reductase acitivity between shelf-life days and packaging environments for the muscles used in the study. The VL, TB, ST, SM, and the GM had higher levels of lipid oxidation in the later days of shelf-life storage and were higher (P < 0.05) in high oxygen packaging compared to the other three treatments. Oxygen penetration depth was greater (P < 0.05) over all storage days for the high oxygen treatment in the TB and LL as compared to the other treatments. Hunter CIE a* and b* values significantly decreased across all muscles for the high oxygen and PVC treatments. Discoloration increased significantly as storage days increased in the high oxygen and PVC treatments for the TB, SM, VL, BF, IF, GM, PM, and TM. Degree of doneness was higher (P < 0.05) for the PM, TB, and SM muscles in a high oxygen atmosphere as compared to the low oxygen light and low oxygen dark treatments. Aerobic reducing ability tended to decrease as retail shelf-life day increased. A high oxygen environment increased rancidity, oxygen penetration depth, redness values, and degree of doneness (P < 0.05) when compared to a low oxygen light and low oxygen dark modified atmosphere package.

Master of Science / Department of Animal Sciences and Industry / Travis G. O'Quinn / The objectives of this study were to evaluate the extent marbling compensates for reduced beef palatability at elevated degrees of doneness and to determine the relationship of residual moisture and fat in cooked steaks to beef palatability, specifically beef juiciness. Paired strip loins (IMPS # 180) were collected to equally represent five quality treatments [Prime, Top Choice (modest and moderate marbling), Low Choice, Select, and Select Enhanced (110% of raw weight)]. Steaks were grouped into sets of three consecutively cut steaks and randomly assigned a degree of doneness (DOD): very-rare (VR; 55°C), rare (R; 60°C), medium-rare (MR; 63°C), medium (M; 71°C), well-done (WD; 77°C), or very well-done (VWD; 82°C). Samples were subjected to consumer and trained sensory evaluation, Warner-Braztler shear force (WBSF), slice shear force (SSF), pressed juice percentage (PJP) evaluation, and raw and cooked proximate analysis. There were no (P > 0.05) interactions for consumer sensory ratings, indicating increased DOD had the same negative impact regardless of marbling level. There was a quality treatment × DOD interaction (P < 0.05) for percentage of steaks rated acceptable by consumers for juiciness. Increased marbling extended the point in which steaks became unacceptable for juiciness. Similarly, there was a quality treatment × DOD interaction (P < 0.05) for trained juiciness ratings. When cooked to MR and lower, Prime was only rated 8 to 18% higher (P < 0.05) than Select for trained juiciness ratings but was rated 38 to 123% higher (P < 0.05) than Select when cooked to M and higher. Besides cook loss, combined cooked moisture and fat percentage was more highly associated (P < 0.01) to consumer juiciness (r = 0.69) and trained initial (r = 0.84) and sustained (r = 0.85) juiciness ratings than all other objective evaluations. For regression analysis, cooked moisture and fat percentages, alone, were poor indicators of consumer and trained juiciness ratings. However, when combined, the regression equations explained 45, 74, and 69% of the variation in consumer, trained initial, and trained sustained juiciness ratings, respectively. These results indicate that increased marbling levels only offer “insurance” for juiciness of steaks that are cooked at high degrees of doneness, but not for other palatability traits. Additionally, cooked residual moisture and fat percentages when combined are a good indicator of sensory juiciness ratings.

The objective of this study was to determine the influence of quality grade (QG) and degree-of-doneness (DOD) on thermophysical properties of beef strip steaks. The “Prime” eating experience must be marketed to compete with cheaper protein sources, and so palatability is a major concern with beef products. Thermal and physical properties help shed light on the impacts various components have on beef palatability, mainly tenderness and juiciness. Warner-Bratzler shear force (WBSF) and the textural property of springiness are both influenced by a combination of QG and DOD. This is also true for viscoelasticity and the degradation of myosin and sarcoplasmic protein. Although many factors contribute to beef palatability, intra-muscular fat (IMF) content is usually given the most credit when presented to the consumer. However, QG only impacted raw steak weight, cooking duration, cohesiveness, and moisture interactions. DOD influenced more properties including cooking duration and cook loss percent conductivity, various textural properties, protein degradation (even before cooking), and moisture interactions. Generally speaking, these textural properties resulted in less favorable values as DOD increased, but that was not only the case. Thermal properties and protein degradation values simply showed unique differences between DOD (including refrigerated and room-temperature sampling) and did not always follow a trend. These results show that although over-cooking can be mitigated with high IMF content for tenderness, DOD has more of an effect on many of the palatability characteristics. Furthermore, more research will need to be conducted to fully understand the differences between some of our more intricate tests between QG and DOD.

Master of Science / Department of Animal Sciences and Industry / Travis G. O'Quinn / The objective of this study was to evaluate the impact of quality grade on beef eating quality of top sirloin steaks when cooked to multiple degrees of doneness (DOD). Beef top sirloin butts (N = 60; 15 / quality grade) were collected to equally represent 4 quality grades [Prime, Top Choice (modest00 – moderate100), Low Choice, and Select]. Top butts were cut into six consecutive steaks, and then divided laterally to get a total of twelve steaks per top butt. Steaks were assigned to one of three DOD: rare (60°C), medium (71°C), and well-done (77°C). Steaks within DOD were assigned to consumer sensory analysis, trained sensory analysis, fat and moisture analysis, and Warner-Bratzler shear force (WBSF). There were no interactions (P > 0.05) for all consumer ratings of palatability traits, indicating increases in DOD had the same impact across all quality grades. There was a difference (P > 0.05) within quality grade for consumer ratings of juiciness (P > 0.05). Prime steaks had greater (P < 0.05) juiciness ratings than all other quality grades, except for Top Choice. As DOD increased, consumer ratings and the percentage of steaks rated acceptable for each palatability trait decreased (P < 0.05; rare > medium > well-done). There was a quality grade × DOD interaction (P < 0.05) for trained sensory panel juiciness scores. When cooked to medium, Prime and Top Choice steaks were rated higher (P < 0.05) for juiciness than Low Choice and Select steaks. Similar to consumer ratings, trained panel ratings of tenderness decreased (P < 0.05) as DOD increased (rare > medium > well-done). Lastly, there were no quality grade by DOD interactions (P > 0.05) for Warner-Bratzler shear force. These results indicate that regardless of the DOD steaks were cooked to, quality grade had minimal impact on the palatability of beef top sirloin steaks. Therefore, unless cooked to a medium DOD, it is unnecessary for consumers, retailers, and foodservice to pay premium prices for higher quality top sirloin steaks, as the same eating experience will be given.

Doctor of Philosophy / Department of Animal Sciences and Industry / John A. Unruh / Two experiments were conducted to evaluate the effects of exercise on feedlot cattle well-being, growth performance, and carcass characteristics (Experiments 1 and 2). Additionally, two experiments assessed the volatile compound profiles of beef in response to various postmortem processes (Experiments 3 and 4). Experiment 1 compared heifers (n=30) assigned to either a sedentary treatment or an exercise regimen 3 times/wk (20 min/d for the first 2 wk, 30 min/d for the next 2 wk, and 40 min/d for the final wk). Exercised heifers showed decreased blood insulin, daily gains, final body weights, and lower numerical yield grades in conjunction with decreased a* and b* color values of longissimus muscle lean. Experiment 2 exposed steers (n=419) to 1 of 4 treatments; not exercised (CON), or exercised 3 times/wk by animal handlers for 20-30 min for the first 10 wk (EARLY), the last 7 wk (LATE), or for the entire 116 d finishing period (ALL). EARLY treatment cattle exhibited a decrease in blood insulin while EARLY and ALL treatment cattle produced carcasses with decreased marbling scores in comparison to CON cattle. Experiment 3 assessed the volatile compounds generated by raw and cooked beef gluteus medius steaks (n=30) subjected to blade tenderization and aging times ranging from 5 to 61 d. Raw steaks aged longer than 19 d produced greater concentrations of heptanal, octanal, and nonanal than raw steaks aged 5 d, but cooked steaks showed no change in these compounds in response to aging. Additionally, blade tenderization reduced the concentrations of lipid oxidation and Maillard reaction products in cooked steaks. Experiment 4 investigated cross-sections, external, and internal locations of beef longissimus lumborum steaks (n=54) cooked to 63, 71, or 77 °C and aged for 5, 21, or 37 d. External locations generated aldehydes in greater amounts than internal locations while pyrazines are produced exclusively at external locations. Increases in degree of doneness increased all aldehydes, except nonanal, in steak cross-sections. Aldehydes, except hexanal and octanal, generated from external locations became similar to internal locations as aging times increased. Pyrazines from external locations were reduced by increased aging times.