Doctor of Philosophy / Department of Animal Sciences and Industry / Michael E. Dikeman / The objectives were to determine the effects of packaging and injection-enhancement on beef sensory attributes, postmortem proteolysis, and color. Muscles from USDA Select, A-maturity carcasses were fabricated into 2.54-cm steaks on d 7 postmortem. In Experiment 1, longissimus lumborum (n=14 pairs) muscles were used. Packaging treatments were: vacuum packaging (VP); 80% O2/20% CO2 (HiO2); 0.4% CO/35% CO2/64.6%N2 (ULO2CO); 0.4% CO/99.6% CO2; 0.4% CO/99.6% N2; or 0.4% CO/99.6% Ar. In Experiment 2, longissimus lumborum (n=12 pairs); semitendinosus (n=12 pairs); and triceps brachii (n=24 pairs) muscles from one carcass side were injection-enhanced or non-enhanced. Steaks were packaged into VP, HiO2, or ULO2CO MAP. Steaks packaged in HiO2 MAP were in dark storage (2°C) for 4 d and all other steaks for 14 d. Steaks were displayed under fluorescent lighting for 7 d. Trained color panelists assigned color scores. Steaks for tenderness, cooked color, and sensory were cooked to 70°C. Steaks packaged in VP or ULO2 with CO MAP had little or no discoloration. Steaks packaged in HiO2 MAP discolored faster (P < 0.05) and more (P < 0.05) than steaks in other packaging treatments. Steaks packaged in HiO2 MAP were less tender (P < 0.05) than other treatments at the end of display, but had 10 d less aging due to shorter dark storage. Steaks packaged in HiO2 had the lowest (P < 0.05) a* values for internal cooked color of all treatments and exhibited premature browning. Enhanced steaks were more tender (P < 0.05) than non-enhanced steaks. Sensory panelists found that non-enhanced steaks packaged in ULO2CO MAP or VP were more tender (P < 0.05), had more (P < 0.05) beef flavor, and had less (P < 0.05) off-flavors than steaks packaged in HiO2 MAP. Off-flavors for steaks packaged in HiO2 MAP often were described as oxidative and rancid. Enhanced steaks had more (P < 0.05) off-flavors than non-enhanced steaks. Postmortem proteolysis measured by desmin degradation was not affected (P > 0.05) by packaging. Steaks packaged in ULO2 plus CO MAP had superior color stability, tenderness, and sensory attributes compared to steaks in HiO2 MAP.

<p>Postmortem aging has been extensively practiced as value-adding process due to the beneficial impacts on meat palatability. Meat tenderization occurred through proteolytic fragmentation of myofibrillar structural proteins via endogenous protease systems, which is considered as the primary drive to enhance major palatability attributes including tenderness, juiciness, and flavor. Recent theoretical framework proposes apoptosis, or programmed cell death, as the preceding step that initiates postmortem proteolysis. Whereas small heat shock proteins have been consistently recognized as meat quality biomarkers, probably due to their protective activities against proteolysis through anti-stress, anti-apoptotic, and chaperoning functionalities. To shed light on detailed mechanisms controlling postmortem proteolysis and consequential impacts on the development of fresh meat quality characteristics, postmortem proteolytic changes of small heat shock proteins, apoptotic factors, and myofibrillar structural proteins were profiled in postmortem skeletal muscles under different metabolic backgrounds and across species. </p> <p>In beef, three muscles, <i>longissimus lumborum</i> (LL), <i>semimembranosus</i> (SM), and <i>psoas major</i> (PM), have been selected to represent glycolytic, intermediate, and oxidative muscle types. Tenderness and water - holding capacity were determined, and proteolysis, apoptotic features, and small heat shock proteins were measured in 8 beef carcasses at 1, 2, 9, 16, and 23 days of aging. PM exhibited limited aging potential in quality developments shown by lower extents of shear force, water-holding capacity, and proteolytic changes, including calpain 1 autolysis, troponin T, and HSP27 compared to LL and SM. Conversely, LL had an increase in tenderization and water-holding capacity, which was accompanied with more extended calpain 1 autolysis, proteolysis and HSP27 degradation, compared with other muscles. The results of this study suggest that postmortem proteolytic changes of myofibrillar proteins, small HSPs and apoptotic factors occur in a muscle-specific manner, which is likely attributed to different rate and extent of meat quality developments of each muscle during aging. </p> <p>Callipyge lambs are a unique genetic background showing calpastatin over-expression, muscle hypertrophy in loin and hindquarter area, substantially compromised meat tenderization potential, and a shift of muscle fiber composition towards fast-glycolytic directions. Proteome and metabolome changes in muscles from callipyge mutation (+/C) and non-callipyge phenotype (+/+, C/+, and C/C) lambs were profiled to provide insight into the biochemical changes affecting meat quality attributes. M. longissimus thoracis from lambs with all four possible callipyge genotype (n = 4, C/+, C/C, +/C, and +/+) were collected after 3d aging and analyzed using mass-spectrometry based platforms. Among identified proteomes, cytochrome c (pro-apoptotic protein) was detected with significantly lower abundances in +/C. Anti-apoptotic HSP70, BAG3, and PARK7 were over-abundant in +/C, which could result in delayed apoptosis and possibly attributed to tougher meat in callipyge lambs. Eight glycolysis enzymes were overabundant in +/C lambs, whereas 3 enzymes involved in TCA cycle were overabundant in non-callipyge ones (C/C and/or C/+). Twenty-five metabolites were affected by genotypes (P < 0.05), including metabolic co-factors, polyphenols, and AA/short peptides.</p> <p>Pig production is facing increased public pressure regarding antibiotic usage restriction. Recently, dietary L-glutamine at cost effective level (0.2%) was identified as an effective antibiotic alternative in post-transport nursery pig diets. To evaluate carcass and meat quality characteristics in market-ready pigs when 0.2% dietary L-glutamine was applied as for early-life post-weaning and transport recovery, pigs (N=480) were weaned and transported in two replication trials in SPRING (April of 2017) vs. SUMMER (July of 2016), fed 3 different diets (Non: no antibiotic, Anti: 441 ppm chlortetracycline and + 38.6 ppm tiamulin, Gln: 0.20% L-glutamine) for 14 days after transport, and fed basal diet until reaching market weight. Pairs of <i>longissimus dorsi</i> (LD) and <i>psoas major</i> (PM) muscles from each carcass (n=10/diet/trial) were separated at 1 d and 7 d postmortem, respectively. Carcass yield and meat physical and quality attributes were evaluated. Overall impacts of Gln on physical attributes of carcasses and porcine muscles were minimal. No dietary effects were found in carcass, proximate composition, water-holding capacity, or shear force. Significant difference between trials were found in terms of productivity and pork/carcass qualities, where SPRING replicates showed increased body weight, faster pH decline, paler surface color, higher intra-muscular fat deposition, and improved tenderness and water-holding capacity as indicated by lower shear force values, thaw-purge loss, and cooking loss (P < 0.05).</p> <p>The pork and carcass quality results give rise to a postulation that different metabolism and animal growth might have been occured between the two production trials, consequentially differentiated meat quality development. In this regard, myofibrillar proteolysis, small heat shock proteins, and apoptotic factors were characterized during 7 d postmortem aging in porcine LD and PM muscles from both seasonal trials, combined with metabolomics profiles of 1d samples using the GC-TOF-MS/MS platform. Compared to SUMMER counterparts, SPRING muscles showed concurrence of more extended apoptosis, further calpain 1 autolysis, and increased structural protein degradation (P<0.05). SPRING muscles showed more ATP catabolism compounds and increase in carbohydrates, branched-chain amino acids, and 16-18 carbon fatty acids, which could be chemistry fingerprints of increased cellular oxidative stress, consequentially favoring onset of apoptosis and proteolysis. Meanwhile, SUMMER pigs showed increased stress-defending metabolites, such as ascorbic acid, antioxidant amino acids, and decreased inhibitory neuro-transmitter GABA, which may indicate elevated stress-defending activity in SUMMER pigs that possibly inhibited apoptosis and proteolysis. </p>

<p>Historically, the meat industry has struggled to provide consumers with consistent beef tenderness. Various post-harvest technologies have been used in industry; however, there is still a need to develop a natural and safe post-harvest processing system that can be used to create consistently tender products for consumers. In addition to postmortem aging being a time-consuming process, literature has suggested that it is not a sufficient method to achieve tenderization in certain cull cow muscles. This has resulted in the large supply of cull cow beef to be underutilized due to its inferior quality, specifically tenderness. Applying a combination of mechanical tenderization with additional postmortem aging may be an effective strategy to overcome deficiencies in beef tenderness. Recent studies have found that tumbling without brine addition can be successful at improving instrumental tenderness and consumer liking of tenderness of fresh beef loin. The physical disruptions of muscles, which likely occur during tumbling, may enhance activity of proteolytic enzymes and thus induce more tenderization. The overall objective of this thesis was to investigate the effects of fresh beef tumbling methods and postmortem aging times on the tenderness and proteolysis of loin muscles from both A maturity cattle and cull cows.</p> <p>The first chapter of this thesis is a literature review that will address the factors affecting tenderness and the methods used by the industry to improve tenderness, specifically focusing on meat tumbling and cull cow beef. The second chapter is a study that investigated the effects of fresh beef tumbling at different postmortem times on meat quality attributes and proteolytic features of loins. The results from this study suggest that early postmortem tumbling coupled with aging can synergistically impact the improvements of beef loin tenderness and proteolysis, shortening the necessary aging period. The third and final chapter of this thesis is a study that aimed to determine the effect of fresh beef tumbling and postmortem aging on the quality and proteolysis of loins from cull cows. The results from this study indicate that aging would be effective at improving the quality and palatability of cull cow beef loins, although tumbling could improve consumer liking of tenderness at earlier postmortem times.</p>