Postmortem Muscle Research Articles

Effects of pre-slaughter fasting on antemortem skeletal muscle protein degradation levels and postmortem muscle free amino acid concentrations in broiler chickens

This study investigated the effects of pre-slaughter fasting time on the relationship between skeletal muscle protein degradation levels at slaughter and chicken meat quality after 48 h of postmortem aging. Twenty-four broiler chicks at 0 d of age were used in this study until 28 d of age. At 27 d of age, the chickens were assigned to 4 treatment groups: 0 h of fasting (0H), 8 h of fasting (8H), 16 h of fasting (16H), or 24 h of fasting (24H). They were slaughtered at 28 d of age. Blood samples were collected before fasting and immediately before slaughter. Plasma Nτ-methylhistidine concentration, an index of skeletal muscle protein degradation level, and muscle free amino acid concentration were analyzed. Antemortem changes in individual plasma Nτ-methylhistidine concentrations were significantly increased in 8H, 16H, and 24H compared to that in 0H (P < 0.05). After 48 h of postmortem storage, the glutamic acid content in the pectoralis major muscles increased with fasting time (P < 0.05), and the umami taste of chicken soup in the fasting groups (8H, 16H, 24H) was higher than that in the 0H group (P < 0.05). The antemortem changes in plasma Nτ-methylhistidine concentrations were correlated with glutamic acid content in the pectoralis major muscles (r = 0.57, P < 0.05) and umami taste (r = 0.66, P < 0.05). These results suggest that skeletal muscle protein degradation levels at slaughter are related to postmortem chicken meat quality, especially glutamic acid content and umami taste.

87 Mitochondria: Life, Death, and the In-Between

Abstract Skeletal muscles exhibit considerable variation in their metabolic and contractile properties, which allows them to accomplish diverse functions in the living animal. Mitochondria content and function are key features driving oxidative capacity, and hence, the energy producing capacity of muscle fibers. In turn, these intrinsic muscle properties also influence postmortem muscle metabolism and the events that occur as living muscle becomes meat. This period is critical to the development of meat quality attributes. Yet, there is much that remains poorly understood regarding the conversion of muscle to meat. Considering that oxygen supply is removed at harvest, early efforts to understand postmortem metabolism primarily focused on glycolytic capacity. More recently, efforts have been redirected to mitochondria; not only are they critical for energy production, but mitochondria also influence calcium dynamics, apoptosis signaling, and reactive oxygen species production. These functions have been implicated in the development of meat quality attributes, including color variation, protein degradation, and tenderness. Defining the mitochondrial contributions to postmortem metabolism and meat quality is complex due to the heterogeneous nature of muscle fibers and the changes in cellular conditions (e.g., temperature, pH) that occur postmortem. Nonetheless, evidence supports that mitochondria retain at least some capacity for energy production early postmortem, indicating they are structurally intact and functional. Both inherent muscle characteristics as well as factors related to slaughter and processing appear to impact the subsequent decline in functional and structural integrity of mitochondria. Unraveling the structural and functional changes that occur in mitochondria postmortem will advance our understanding of early postmortem metabolism and meat quality development.

Dietary supplementation of Eucommia leaf extract to growing-finishing pigs alters muscle metabolism and improves meat quality.

The objective of this study was to investigate the influence of dietary supplementation of Eucommia ulmoides leaf extract (ELE) on muscle metabolism and meat quality of pigs with and without pre-slaughter transportation. In a 43-day feeding experiment, a total of 160 pigs with an initial body weight 60.00±2.00 kg were randomly assigned into four groups in a completely randomized design with 10 replicates. Pigs in groups A and C were fed a basal diet and pigs in groups B and D were fed a basal diet supplemented with 0.5% ELE. Pigs were slaughtered with (group B and D) or without (group A and C) pre-slaughter transport. Muscle chemical composition, postmortem glycolysis, meat quality and muscle metabolome were analyzed. Dietary ELE supplementation had no effect on the proximate composition of porcine muscle, but increased free phenylalanine, proline, citruline, norvaline, and the total free amino acids in muscle. In addition, dietary ELE increased decanoic acid and eicosapentaenoic acid, but decreased heptadecanoic acid, oleic acid, trans-oleic acid, and monounsaturated fatty acids in muscle. Meat quality measurement demonstrated that ELE improved meat water holding capacity and eliminated the negative effects of pre-slaughter transport on meat cooking yield and tenderness. Dietary ELE reduced muscle glycolytic potential, inhibited glycolysis and muscle pH decline in the postmortem conversion of muscle to meat and increased the activity of citrate synthase in muscle. Metabolomics analysis by liquid chromatographic tandem mass spectrometric showed that ELE enhanced muscle energy level, regulated AMP-activated protein kinase (AMPK) signaling, modulated glycogenolysis/glycolysis, and altered the metabolism of carbohydrate, fatty acids, ketone bodies, amino acids, purine, and pyrimidine. Dietary ELE improved meat quality and alleviated the negative effect of preslaughter transport on meat quality by enhancing muscle oxidative metabolism capacity and inhibiting glycolysis in postmortem muscle, which is probably involved its regulation of AMPK.

Effects of Light and Oxygen Conditions on Nonenzymatic Metmyoglobin Reduction In Vitro

Previous research indicated that inherently present electron donors and carriers contribute to nonenzymatic metmyoglobin reduction. However, limited knowledge is currently available on how light and oxygen influence nonenzymatic metmyoglobin reduction. The objective of this study was to evaluate the effect of light and oxygen levels on nonenzymatic metmyoglobin reduction in vitro. Two experiments were conducted using equine metmyoglobin solution at pH 5.6 (represents typical postmortem muscle pH) with different electron donors and electron carriers in a 96-well plate. A gas blend of 80% oxygen and 20% carbon dioxide or a pure 99.9% nitrogen gas was bubbled in phosphate buffers and myoglobin solutions to create 2 oxygen levels (low oxygen [4%] and high oxygen [160%]). The desired dissolved oxygen content was measured using a NeoFox oxygen probe (atmospheric oxygen level was 20% oxygen). There were significant effects of electron donors, carriers, and light on nonenzymatic metmyoglobin reduction. Ascorbate and nicotinamide adenine dinucleotide reduced form (NADH) in the presence of methylene blue and ethylenediaminetetraacetic acid (EDTA) exhibited a greater nonenzymatic metmyoglobin reduction in light than dark. An increase in nonenzymatic metmyoglobin-reducing activity (P&amp;lt;0.0001) was observed for the combination of NADH+methylene blue+EDTA in the high-oxygen condition in comparison with the low-oxygen levels. The results indicate that light and oxygen levels increase nonenzymatic metmyoglobin reduction. Characterizing the cofactors required for nonenzymatic metmyoglobin reduction and understanding the conditions conducive to reduction enhance knowledge related to meat color changes.

Muscle proteolysis is differentially influenced by mitochondrial intactness

This study examined the potential influence of mitochondrial calcium sequestering ability on calpain-1 autolysis and proteolysis in vitro. We first tested whether mitochondria can sequester calcium in an in vitro setting. Isolated bovine mitochondria (0, 0.5, or 2 mg/mL) were incubated in a buffer containing varying calcium levels (0, 50, or 100 μM). An inverse relationship between mitochondrial content and measured free calcium was observed (P < 0.05), confirming that mitochondria can sequester calcium within the concentration range tested. In the first in vitro experiment, intact mitochondria (0, 0.5, or 2 mg/mL) were incorporated into an in vitro model simulating postmortem muscle conditions, and calpain-1 autolysis and proteolysis were evaluated over a 168-h period. Adding intact mitochondria to the in vitro model decreased calpain-1 autolysis and proteolysis during the first 4 h of incubation (P < 0.05), likely through reducing calcium availability. However, accentuated calpain-1 autolysis and proteolysis were observed at 24 h. To further explore these effects, mitochondrial integrity was evaluated at varying pH and calcium levels. Mitochondrial integrity decreased as pH declined (P < 0.05), especially in the presence of calcium. Based on these results, we conducted a second in vitro experiment involving disrupted mitochondria. Unlike intact mitochondria, which exerted a suppressive effect on calpain-1 autolysis and proteolysis early on, disrupted mitochondria increased both parameters at most time points (P < 0.05). Overall, it appears that intact mitochondria initially cause a delay in calpain-1 autolysis and proteolysis, but as their integrity diminishes, both processes are enhanced.

Morphological changes of mitochondria-related to apoptosis during postmortem aging of beef muscles.

This study aimed to investigate how postmortem muscle cells' mitochondria changed in morphology from three aspects: the outer membrane, cristae, and fission/fusion. Atomic force microscopy (AFM) results showed that mitochondria underwent a morphology transformation from normal to swelling and collapse. Meanwhile, the cleavage of OPA1, upregulation of OMA1, downregulation of Mic60 and transmission electron microscope micrographs revealed that mitochondrial cristae ruptured with an aging time extended. Additionally, the increased expressions of Fis1 and Drp1, and the AFM topographic images mutually confirmed mitochondrial fission. These results further proved from the perspective of mitochondrial morphology that the degree of mitochondrial damage increased with the postmortem aging time extended, which was consistent with the results of the release of cytochrome c caused by the increase of mitochondrial permeability transition pore opening and the decrease of mitochondrial membrane permeability, and further induced the apoptosis of postmortem muscle cells.

Protein Phosphorylation Induced by Pyruvate Kinase M2 Inhibited Myofibrillar Protein Degradation in Post-Mortem Muscle.

Myofibrillar protein degradation is primarily related to meat tenderness through protein phosphorylation regulation. Pyruvate kinase M2 (PKM2), a glycolytic rate-limiting enzyme, is also regarded as a protein kinase to catalyze phosphorylation. The objective of this study was to investigate the relationship between myofibrillar protein degradation and phosphorylation induced by PKM2. Myofibrillar proteins were incubated with PKM2 at 4, 25, and 37 °C. The global phosphorylation level of myofibrillar proteins in the PKM2 group was significantly increased, but it was sensitive to temperature (P < 0.05). Compared with 4 and 25 °C, PKM2 significantly increased the myofibrillar protein phosphorylation level from 0.5 to 6 h at 37 °C (P < 0.05). In addition, the degradation of desmin and actin was inhibited after they were phosphorylated by PKM2 when incubated at 37 °C. These results demonstrate that phosphorylation of myofibrillar proteins catalyzed by PKM2 inhibited protein degradation and provided a possible pathway for meat tenderization through glycolytic enzyme regulation.

Impact of sampling location and aging on the Longissimus thoracis et lumborum muscle proteome of dry-aged beef

This study aimed to explore the differences in the proteome and molecular pathways between two sampling locations (external, internal) of bovine Longissimus thoracis et lumborum (LTL) muscles at 0, 21, and 28 days of dry-aging (i.e. 3, 24, and 31 days post-mortem). It further assessed the impact of post-mortem aging on the meat proteome changes and the biological processes at interplay. Proteins related to defence response to bacterium and regulation of viral entry into host cell were identified to be more abundant on the external location before dry-aging, which may be associated to the oxidative conditions and microbial activity to which post-mortem muscle is exposed during dressing, chilling, and/or quartering of the carcasses. This highlights the relevance of sampling from interior tissues when searching for meat quality biomarkers. As dry-aging progressed, the meat proteome and related biological processes changed differently between sampling locations; proteins related to cell-cell adhesion and ATP metabolic processes pathways were revealed in the external location at 21 and 28 days, respectively. On the other hand, the impact of aging on the proteome of the interior meat samples, evidenced that muscle contraction and structure together with energy metabolism were the major pathways driving dry-aging. Additionally, aging impacted other pathways in the interior tissues, such as regulation of calcium import, neutrophil activation, and regeneration. Overall, the differences in the proteome allowed discriminating the three dry-aging times, regardless of the sampling location. Several proteins were proposed for validation as robust biomarkers to monitor the aging process (tenderization) of dry-aged beef: TTN, GRM4, EEF1A1, LDB3, CILP2, TNNT3, GAPDH, SERPINI1, and OMD.

Muscle proteome of crossbred cattle that received vitamin A at birth: impacts on meat quality traits

This study aimed to evaluate the skeletal muscle proteome of calves that received an intramuscular application of vitamin A at birth and its impacts on meat quality. Forty male crossbred calves were used from birth to feedlot finishing. On the day of birth, 20 calves were injected intramuscularly with a single dose of 300,000 IU of vitamin A and the other 20 animals received placebo (control). After weaning at 210 days, the animals of the two treatments were feedlot finished for 180 days. Longissimus muscle samples were collected for proteome analysis and meat quality assessment. There was a trend (P = 0.07) towards more tender meat in animals that received vitamin A compared to control (WBSF = 3.92 ± 0.16 kg vs. 4.23 ± 0.15). Meat color, pH and cooking loss were not affected (P > 0.05). Vitamin A treatment resulted in a more than 50% increase in intramuscular fat (IMF) content (P < 0.05) compared to control (4.10 ± 0.35% vs. 2.57 ± 0.27%). The intramuscular injection of vitamin A affected the post-mortem muscle proteome and the protein-protein interactions. A greater abundance of proteins involved in three main pathways were observed these being energy metabolism (GAPDH, ENO3, TPI1, CKM, and COX5A), muscle contraction (ACTB, ACTC1, ACTG1, ACTG2, ACTA1, ACTA2, ACTN1, ACTN2, ACTN3, TPM1, TPM2, TPM3, MYH1, PDLIM3, and TNNT3), protein binding, transport, and signaling (TUBA4A, VIM, TBA1B, and EEF1A2). A greater abundance of oxidative stress and cellular defense proteins (HSPA8 and DNAJC18) was specifically observed in the control treatment. Vitamin A upregulated key biological processes related to energy metabolism, which favored IMF accumulation during the finishing phase.

New insights into the function of lipid droplet-related proteins and lipid metabolism of salt-stimulated porcine biceps femoris: Label-free quantitative phosphoproteomics, morphometry and bioinformatics.

Lipid droplets (LD) are important multifunctional organelles responsible for lipid metabolism of postmortem muscle. However, the dynamics in their building blocks (cores and layers) and phosphorylation of lipid droplet-related proteins (LDRP) regulating meat lipolysis remain unknown at salt-stimulated conditions. LDRP extracted from cured porcine biceps femoris (1% and 3% salt) were subjected to label-free quantitative phosphoproteomic analysis and LD morphological validation. Results indicated that 3% salt curing significantly decreased triglyceride (TG) content with increase in glycerol and decrease in LD fluorescence compared to 1% salt curing. Comparative phosphoproteomics showed that there were significant changes in phosphorylation at 386 sites on 174 LDRP between assayed groups (p < 0.05). These differential proteins were mainly involved in lipid and carbohydrate metabolism. Curing of 3% salt induced more site-specific phosphorylation of perilipin 1 (PLIN1, at Ser81) and adipose triglyceride lipase (ATGL, at Ser399) than 1%, whereas the phosphorylation (at Ser600) of hormone-sensitive lipase (HSL) was up-regulated. Ultrastructure imaging showed that LD were mostly associated with mitochondria, and the average diameter of LD decreased from 2.34 μm (1% salt) to 1.73 μm (3% salt). Phosphoproteomics unraveled salt-stimulated LDRP phosphorylation of cured porcine meat provoked intensified lipolysis. Curing of 3% salt allowed an enhanced lipolysis than 1% by up-regulating the phosphorylation sites of LDRP and recruited lipases. The visible splitting of LD, together with sarcoplasmic disorganization, supporting the lipolysis robustness following 3% salt curing. The finding provides optimization ideas for high-quality production of cured meat products. This article is protected by copyright. All rights reserved.

Molecular mechanisms contributing to the development of beef sensory texture and flavour traits and related biomarkers: Insights from early post-mortem muscle using label-free proteomics

Beef sensory quality comprises a suite of traits, each of which manifests its ultimate phenotype through interaction of muscle physiology with environment, both in vivo and post-mortem. Understanding variability in meat quality remains a persistent challenge, but omics studies to uncover biological connections between natural variability in proteome and phenotype could provide validation for exploratory studies and offer new insights. Multivariate analysis of proteome and meat quality data from Longissimus thoracis et lumborum muscle samples taken early post-mortem from 34 Limousin-sired bulls was conducted. Using for the first-time label-free shotgun proteomics combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), 85 proteins were found to be related with tenderness, chewiness, stringiness and flavour sensory traits. The putative biomarkers were classified in five interconnected biological pathways; i) muscle contraction, ii) energy metabolism, iii) heat shock proteins, iv) oxidative stress, v) regulation of cellular processes and binding. Among the proteins, PHKA1 and STBD1 correlated with all four traits, as did the GO biological process ‘generation of precursor metabolites and energy’. Optimal regression models explained a high level (58–71%) of phenotypic variability with proteomic data for each quality trait. The results of this study propose several regression equations and biomarkers to explain the variability of multiple beef eating quality traits. Thanks to annotation and network analyses, they further suggest protein interactions and mechanisms underpinning the physiological processes regulating these key quality traits. SignificanceThe proteomic profiles of animals with divergent quality profiles have been compared in numerous studies; however, a wide range of phenotypic variation is required to better understand the mechanisms underpinning the complex biological pathways correlated with beef quality and protein interactions. We used multivariate regression analyses and bioinformatics to analyse shotgun proteomics data to decipher the molecular signatures involved in beef texture and flavour variations with a focus on multiple quality traits. We developed multiple regression equations to explain beef texture and flavour. Additionally, potential candidate biomarkers correlated with multiple beef quality traits are suggested, which could have utility as indicators of beef overall sensory quality. This study explained the biological process responsible for determining key quality traits such as tenderness, chewiness, stringiness, and flavour in beef, which will provide support for future beef proteomics studies.

Proteomic analysis by mass spectrometry of postmortem muscle protein degradation for PMI estimation: A pilot study

The determination of the postmortem interval is a topic of great forensic interest. The possibility of using new technologies has allowed the study of postmortem decay of biomolecules in the determination of PMI. Skeletal muscle proteins are promising candidates because skeletal muscle exhibits slower postmortem decay compared to other internal organs and nervous tissues, while its degradation is faster than cartilage and bone. In this pilot study, skeletal muscle tissue from pigs was degraded at two different controlled temperatures, 21 °C and 6 °C, and analysed at predefined times points: 0, 24, 48, 72, 96, and 120 h. The obtained samples were analysed by mass spectrometry proteomics approach for qualitative and quantitative evaluation of proteins and peptides. Immunoblotting validation was performed for the candidate proteins. The results obtained appeared significant and identified several proteins useful for possible postmortem interval estimation. Of these proteins, PDLIM7, TPM1, and ATP2A2 were validated by immunoblotting at a larger number of experimental points and at different temperatures. The results obtained are in agreement with those observed in similar works. In addition, the use of a mass spectrometry approach increased the number of protein species identified, providing a larger panel of proteins for PMI assessment.

The potential mediation of hypoxia-inducible factor-1α in heat shock protein 27 translocations, caspase-3 and calpain activities and yak meat tenderness during postmortem aging

The present study aimed to characterize the influence of hypoxia-inducible factor-1α on heat shock protein 27 and cytochrome c translocation, yak meat microstructure destruction, and endogenous enzymes activities, refining the understanding of the tenderization process after slaughter. Postmortem yak longissimus thoracis et lumborum muscles were incubated with 0.9% saline or hypoxia-inducible factor-1α stabilizer dimethyloxaloylglycine at 4 °C for 6, 12, 24, 72, and 120 h. Results showed that hypoxia-inducible factor-1α activation promoted heat shock protein 27 migration and cytochrome c release, facilitating (P < 0.05) caspase-3 activity by mediating the heat shock protein 27/caspase-3 interaction but did not exert (P > 0.05) significant effects on the calpain-1 activity. Additionally, hypoxia-inducible factor-1α activation contributed to the mitochondrial apoptosis cascade, leading to a higher (P < 0.01) apoptosis rate. Therefore, these observations indicate that hypoxia-inducible factor-1α affects caspase-3 activity and tenderness of postmortem muscle through distinct regulatory mechanisms, possibly, in part, with heat shock protein 27 and cytochrome c mediation.

Effect of temporary freezing on postmortem protein degradation patterns

BackgroundA precise determination of time since death plays a major role in forensic routine. Currently available techniques for estimating the postmortem interval (PMI) are restricted to specific time periods or cannot be applied for individual case-specific reasons. During recent years, it has been repeatedly demonstrated that Western blot analysis of postmortem muscle protein degradation can substantially contribute to overcome these limitations in cases with different background. Enabling to delimit time points at which certain marker proteins undergo distinct degradation events, the method has become a reasonable new tool for PMI delimitation under various forensic scenarios. However, additional research is yet required to improve our understanding of protein decomposition and how it is affected by intrinsic and extrinsic factors.Since there are temperature limits for proteolysis, and investigators are confronted with frozen corpses, investigation of the effects of freezing and thawing on postmortem protein decomposition in the muscle tissue is an important objective to firmly establish the new method. It is also important because freezing is often the only practical means to intermittently preserve tissue samples from both true cases and animal model research.MethodsSets of dismembered pig hind limbs, either freshly detached non-frozen, or thawed after 4 months of freeze-storage (n = 6 each), were left to decompose under controlled conditions at 30 °C for 7 days and 10 days, respectively. Samples of the M. biceps femoris were regularly collected at predefined time points. All samples were processed via SDS-PAGE and Western blotting to identify the degradation patterns of previously characterized muscle proteins.ResultsWestern blots show that the proteins degrade predictably over time in precise patterns that are largely unaffected by the freeze-and-thaw process. Investigated proteins showed complete degradation of the native protein band, partly giving rise to degradation products present in distinct time phases of the decomposition process.ConclusionThis study provides substantial new information from a porcine model to assess the degree of bias that freezing and thawing induces on postmortem degradation of skeletal muscle proteins. Results support that a freeze–thaw cycle with prolonged storage in frozen state has no significant impact on the decomposition behavior. This will help to equip the protein degradation–based method for PMI determination with a robust applicability in the normal forensic setting.

The potential of metabolomics in meat science: Current applications, trends, and challenges

Metabolites are the final products of metabolism and provide insights into the biochemical balance of tissue systems. A cascade of reactions involving proteins, carbohydrates, and lipids affects meat color, tenderness, and flavor, specifically, metabolites that are key biomolecules in biochemical reactions associated with attainment of acceptable meat quality. Bioinformatics platforms, such as Kyoto Encyclopedia of Genes and Genomes (KEGG) databases and MetaboAnalyst, are utilized to help understanding the role of differentially abundant metabolites and characterizing their roles in cellular function/metabolism. However, the inability to identify all metabolites using a single platform and limited metabolite libraries specifically for meat/food remains a challenge. Therefore, the advances in metabolite separation, easy-to-use data processing, increased resolution of mass-spectrometry, and data analysis will help to make inferences or develop biomarkers related to meat quality. This review discusses how metabolomics can be exploited to characterize meat quality, the challenges, and current trends. SignificanceMetabolites play an important role in attaining consumer-preferred meat quality traits and nutritive value of foods. Visual appearance of fresh foods, such as muscle foods, are utilized by consumers to assess the quality at the retail market before making purchases. Similarly, tenderness and flavor of meats influence eating satisfaction and re-purchase decisions. Inconsistencies in meat quality lead to enormous economic losses to the food industry. For instance, consumers often associate a bright-cherry red color with freshness, and the US beef industry loses $3.74 billion annually due to discoloration during storage. Both pre-and post-harvest factors influence the extent of meat quality changes. Metabolomics offer robust tools to get a snapshot of small molecules such as acids, amino acids, glycolytic- and tricarboxylic acids, fatty acids, and sugars present in post-mortem muscle tissue and their role in meat quality. Further, using bioinformatics platforms enables characterizing the role of differentially present metabolites in meat quality as well as identifying biomarkers for desirable quality traits such as tender meat or color-stable carcasses. Innovative applications of metabolomics can be exploited to elucidate the underpinnings of meat quality and to develop novel strategies to enhance marketability of retail fresh meats.

First insights into the dynamic protein changes in goat Semitendinosus muscle during the post-mortem period using high-throughput proteomics

Proteomics plays a key and insightful role in meat research in the post-genomic era. This study aimed to unveil using a shotgun proteomics approach the temporal dynamic changes in early post-mortem proteome of goat Semitendinosus muscle. Therefore, the evolution and comparison of the muscle proteome over three post-mortem times (1, 8, and 24 h) was assessed. The temporal proteomics profiling quantified 748 proteins, from which 174 were differentially abundant (DAPs): n = 55 between 1 h versus 8 h, n = 52 between 8 h versus 24 h, and n = 154 between 1 h versus 24 h. The DAPs belong to myriad interconnected pathways. Binding, transport and calcium homeostasis, as well as muscle contraction and structure, exhibited an equivalent contribution during post-mortem, demonstrating their central role. Catalytic, metabolism and ATP metabolic process, and proteolysis were active pathways from the first hours of animal bleeding. Conversely, oxidative stress, response to hypoxia and cell redox homeostasis along chaperones and heat shock proteins accounted for the large proportion of the biochemical processes, more importantly after 8 h post-mortem. Overall, the conversion of muscle into meat is largely orchestrated by energy production as well as mitochondrial metabolism and homeostasis through calcium and permeability transition regulation. The study further evidenced the role of ribosomal proteins in goat post-mortem muscle, signifying that several proteins experiencing changes during storage, also undergo splicing modifications, which is for instance a mechanism known for mitochondrial proteins. Overall, temporal proteomics profiling of early post-mortem muscle proteome offers an unparalleled view of the sophisticated post-mortem biochemical and proteolytic events associated with goat meat quality determination.

Physicochemical Properties, Antioxidant Markers, and Meat Quality as Affected by Heat Stress: A Review.

Heat stress is one of the most stressful events in livestock life, negatively impacting animal health, productivity, and product quality. Moreover, the negative impact of heat stress on animal product quality has recently attracted increasing public awareness and concern. The purpose of this review is to discuss the effects of heat stress on the quality and the physicochemical component of meat in ruminants, pigs, rabbits, and poultry. Based on PRISMA guidelines, research articles were identified, screened, and summarized based on inclusion criteria for heat stress on meat safety and quality. Data were obtained from the Web of Science. Many studies reported the increased incidences of heat stress on animal welfare and meat quality. Although heat stress impacts can be variable depending on the severity and duration, the exposure of animals to heat stress (HS) can affect meat quality. Recent studies have shown that HS not only causes physiological and metabolic disturbances in living animals but also alters the rate and extent of glycolysis in postmortem muscles, resulting in changes in pH values that affect carcasses and meat. It has been shown to have a plausible effect on quality and antioxidant activity. Acute heat stress just before slaughter stimulates muscle glycogenolysis and can result in pale, tender, and exudative (PSE) meat characterized by low water-holding capacity (WHC). The enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) act by scavenging both intracellular and extracellular superoxide radicals and preventing the lipid peroxidation of the plasma membrane. Therefore, understanding and controlling environmental conditions is crucial to successful animal production and product safety. The objective of this review was to investigate the effects of HS on meat quality and antioxidant status.

Post-mortem muscle proteome of crossbred bulls and steers: Relationships with carcass and meat quality

This study investigated the skeletal muscle proteome of crossbred bulls and steers with the aim of explaining the differences in carcass and meat quality traits. Therefore, 640 post-weaning Angus-Nellore calves were fed a high-energy diet for a period of 180 days. In the feedlot trial, comparisons of steers (n = 320) and bulls (n = 320) showed lower (P < 0.01) average daily gain (1.38 vs. 1.60 ± 0.05 kg/d), final body weight (547.4 vs. 585.1 ± 9.3 kg), which resulted in lower hot carcass weight (298.4 vs. 333.7 ± 7.7 kg) and ribeye area (68.6 vs. 81.0 ± 2.56 cm2). Steers had higher (P < 0.01) carcass fatness, meat color parameters (L*, a*, b*, chroma (C*), hue (h°)) and lower ultimate pH. Moreover, lower (P < 0.01) Warner-Bratzler shear force (WBSF) were observed in steers compared to bulls (WBSF = 3.68 vs. 4.97 ± 0.08 kg; and 3.19 vs. 4.08 ± 0.08 kg). The proteomic approach using two-dimensional electrophoresis, mass spectrometry and bioinformatics procedures revealed several differentially expressed proteins between steers and bulls (P < 0.05). Interconnected pathways and substantial changes were revealed in biological processes, molecular functions, and cellular components between the post-mortem muscle proteomes of the compared animals. Steers had increased (P < 0.05) abundance of proteins related to energy metabolism (CKM, ALDOA, and GAPDH), and bulls had greater abundance of proteins associated with catabolic (glycolysis) processes (PGM1); oxidative stress (HSP60, HSPA8 and GSTP1); and muscle structure and contraction (TNNI2 and TNNT3). The better carcass (fatness and marbling degree) and meat quality traits (tenderness and color parameters) of steers were associated with higher abundance of key proteins of energy metabolism and lower abundance of enzymes related to catabolic processes, oxidative stress, and proteins of muscle contraction SignificanceSexual condition of cattle is known to be an important factor affecting animal performances and growth as well as the carcass and meat quality traits. The investigation of skeletal muscle proteome help a better understanding of the origin of the differences in quality traits between bulls and steers. The inferior meat quality of bulls was found to be due to the greater expression of proteins associated with primary and catabolic processes, oxidative stress, and muscle contraction. Steers had greater expression of proteins, from which several are known biomarkers of beef quality (mainly tenderness).

Towards the discovery of goat meat quality biomarkers using label-free proteomics

This study aimed to identify for the first time protein biomarkers of meat quality traits from Longissimus thoracis (LT) muscle of goats (Capra hircus). Male goats of similar age and weight reared under extensive rearing conditions were used to relate the LT muscle proteome with multiple meat quality traits. The early post-mortem muscle proteome analyzed using label-free proteomics was compared among three texture clusters built using hierarchical clustering analysis. Twenty-five proteins were differentially abundant and their mining using bioinformatics revealed three major biological pathways to be involved: 10 muscle structure proteins (MYL1, MYL4, MYLPF, MYL6B, MYH1, MYH2, ACTA1, ACTBL2, FHL1 and MYOZ1); 6 energy metabolism proteins (ALDOA, PGAM2, ATP5F1A, GAPDH, PGM1 and ATP5IF1), and two heat shock proteins: HSPB1 (small) and HSPA8 (large). Seven other miscellaneous proteins belonging to pathways such as regulation, proteolysis, apoptosis, transport and binding, tRNA processing or calmodulin-binding were further identified to play a role in the variability of goat meat quality. The differentially abundant proteins were correlated with the goat meat quality traits in addition to multivariate regression models built to propose the first regression equations of each quality trait. This study is the first to highlight in a multi-trait quality comparison the early post-mortem changes in the goat LT muscle proteome. It also evidenced the mechanisms underpinning the development of several quality traits of interest in goat meat production along the major biochemical pathways at interplay. SignificanceThe discovery of protein biomarkers in the field of meat research is an emerging topic. In the case of goat meat quality, very few studies using proteomics have been conducted with the aim of proposing biomarkers. Therefore, this study is the first to quest for biomarkers of goat meat quality using label-free shotgun proteomics with a focus on multiple quality traits. We identified the molecular signatures underlying goat meat texture variation, which were found to belong to muscle structure and related proteins, energy metabolism and heat shock proteins along with other proteins involved in regulation, proteolysis, apoptosis, transport and binding, tRNA processing or calmodulin-binding. We further evaluated the potential of the candidate biomarkers to explain meat quality using the differentially abundant proteins by means of correlation and regression analyses. The results allowed the explanation of the variation in multiple traits such as pH, color, water-holding capacity, drip and cook losses traits and texture.

Ferritin-dependent cellular autophagy pathway promotes ferroptosis in beef during cold storage

Ferroptosis plays a pivotal role in regulating various physiological processes and quality of post-mortem muscle. However, the molecular mechanisms underlying ferroptosis remain unclear. The study investigated how ferroptosis was induced in beef during cold storage. Results showed that the expression of autophagy-related genes, LC3, ATG5, ATG7, and NCOA4 in beef during cold storage promoted the degradation of ferritin heavy chains. Ferritin evoked ferroptosis by releasing free iron, inducing reactive oxygen species (ROS) accumulation and inhibiting the glutathione (GSH)-glutathione peroxidase 4 (GPX4) pathway. Furthermore, treatment of myoblasts with GSK 2656157 (autophagy inhibitor) showed that ferritin degradation was lower in the GSK 2656157-treated myoblasts than in the control, while GSH content and GPX4 activity were higher than the control (P < 0.05), and the contents of free iron, ROS and malondialdehyde, and apoptosis were lower than the control (P < 0.05). These results suggest that ferroptosis is induced by degradation of ferritin via the autophagic pathway.