Electrical stimulation affects metabolic enzyme phosphorylation, protease activation, and meat tenderization in beef

Identification of Candidate Genes and Pathways Linked to the Temperament Trait in Sheep

Temperament can be defined as the emotional variability among animals of the same species in response to the same stimulus, grouping animals by their reactivity as nervous, intermediate, or calm. Our goal was to identify genomic regions with the temperament phenotype measured by the Isolation Box Test (IBT) by single-step genome-wide association studies (ssGWAS). The database consisted of 4317 animals with temperament records, and 1697 genotyped animals with 38,268 effective Single Nucleotide Polymorphism (SNP) after quality control. We identified three genomic regions that explained the greatest percentage of the genetic variance, resulting in 25 SNP associated with candidate genes on chromosomes 6, 10, and 21. A total of nine candidate genes are reported for the temperament trait, which is: PYGM, SYVN1, CAPN1, FADS1, SYT7, GRID2, GPRIN3, EEF1A1 and FRY, linked to the energetic activity of the organism, synaptic transmission, meat tenderness, and calcium associated activities. This is the first study to identify these genetic variants associated with temperament in sheep, which could be used as molecular markers in future behavioral research.

Raw to charred: Changes of protein oxidation and in vitro digestion characteristics of grilled lamb

This study aimed to evaluate protein oxidation and in vitro digestion characteristics of lamb that was grilled from raw to charred (0-30 min). Results showed that protein oxidation was aggravated with the time of grilling, indicated by a significant linear increase in carbonyl groups and a linear decrease in sulfhydryl groups. Proteins had the highest simulated gastric and gastrointestinal digestibility at 10-15 min of grilling. Newly formed specific peptides were continuously released during the grilling process. The identified peptides were mainly derived from creatine kinase, phosphoglycerate kinase, actin and myosin light chain. Protein oxidation was closely related to digestive characteristics, and grilling for >15 min would aggravate protein oxidation and reduce its digestibility. Therefore, at 220 °C lamb should not be grilled for longer than 15 min.

Overview of omics applications in elucidating the underlying mechanisms of biochemical and biological factors associated with meat safety and nutrition

Over the years, significant technological discoveries have facilitated the improvement of meat-related research. Recent studies of complex and interactive factors contributing to variations in meat safety are increasingly focused on data-driven omics approaches such as proteomics. This review highlighted omics advances in elucidating the biochemical and biological actions on meat safety. Also, the impacts of the nutritional characteristics of meat and meat products on human health are emphasized. Future perspectives should explore multi-omics and in situ investigations to elucidate the implications in microbiological studies, including nutritional and health-related assessments. Also, creating meat safety assessment and prediction models based on biomarkers of meat safety traits will help to mitigate application constraints, thereby evaluating meat quality more accurately. This could provide a scientific basis for increasing the meat industry's profitability and producing high-quality meat and meat products for consumers. SIGNIFICANCE OF THE REVIEW: This review highlighted omics advances in elucidating underlying mechanisms of biochemical and biological factors associated with meat safety. Also, the impacts of meat proteins on human health are emphasized. Future perspectives should explore multi-omics and in situ investigations to elucidate the implications in microbiological studies, including nutritional and health-related assessments. Also, creating meat safety assessment and prediction models based on biomarkers of meat safety traits will help to mitigate application constraints, thereby evaluating meat quality more accurately. This could provide a scientific basis for increasing the meat industry's profitability and producing high-quality meat and meat products for consumers.

Molecular Changes of Meat Proteins During Processing and Their Impact on Quality and Nutritional Values

Meats are rich in lipids and proteins, exposing them to rapid oxidative changes. Proteins are essential to the human diet, and changes in the structure and functional attributes can greatly influence the quality and nutritional value of meats. In this article, we review the molecular changes of proteins during processing, their impact on the nutritional value of fresh and processed meat, the digestibility and bioavailability of meat proteins, the risks associated with high meat intake, and the preventive strategies employed to mitigate these risks. This information provides new research directions to reduce or prevent oxidative processes that influence the quality and nutritional values of meat.

Integrated proteomic, phosphoproteomic, and N-glycoproteomic analyses of the longissimus thoracis of yaks

Yaks (Bos mutus) live in the Qinghai–Tibet plateau. The quality of yak meat is unique due to its genetic and physiological characteristics. Identification of the proteome of yak muscle could help to reveal its meat-quality properties. The common proteome, phosphoproteome, and N-glycoproteome of yak longissimus thoracis (YLT) were analyzed by liquid chromatography-tandem mass spectrometry-based shotgun analysis. A total of 1812 common proteins, 1303 phosphoproteins (3918 phosphorylation sites), and 204 N-glycoproteins (285 N-glycosylation sites) were identified in YLT. The common proteins in YLT were involved mainly in myofibril structure and energy metabolism; phosphoproteins were associated primarily with myofibril organization, regulation of energy metabolism, and signaling; N-glycoproteins were engaged mainly in extracellular-matrix organization, cellular immunity, and organismal homeostasis. We reported, for the first time, the “panorama” of the YLT proteome, specifically the N-glycoproteome of YLT. Our results provide essential information for understanding post mortem physiology (rigor mortis and aging) and the quality of yak meat.

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A total of 2650 proteins were identified in yak longissimus thoracis.

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Common proteins were involved mainly in myofibril structure and energy metabolism.

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Phosphoproteins were associated with myofibrils, energy metabolism, and signaling.

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N-glycoproteins were engaged mainly in ECM organization, immunity, and homeostasis.

Proteomic Studies on the Mechanism of Myostatin Regulating Cattle Skeletal Muscle Development

Myostatin (MSTN) is an important negative regulator of muscle growth and development. In this study, we performed comparatively the proteomics analyses of gluteus tissues from MSTN^+/− Mongolian cattle (MG.MSTN^+/−) and wild type Mongolian cattle (MG.WT) using a shotgun-based tandem mass tag (TMT) 6-plex labeling method to investigate the regulation mechanism of MSTN on the growth and development of bovine skeletal muscle. A total of 1,950 proteins were identified in MG.MSTN^+/− and MG.WT. Compared with MG.WT cattle, a total of 320 differentially expressed proteins were identified in MG.MSTN cattle, including 245 up-regulated differentially expressed proteins and 75 down-regulated differentially expressed proteins. Bioinformatics analysis showed that knockdown of the MSTN gene increased the expression of extracellular matrix and ribosome-related proteins, induced activation of focal adhesion, PI3K-AKT, and Ribosomal pathways. The results of proteomic analysis were verified by muscle tissue Western blot test and in vitro MSTN gene knockdown test, and it was found that knockdown MSTN gene expression could promote the proliferation and myogenic differentiation of bovine skeletal muscle satellite cells (BSMSCs). At the same time, Co-Immunoprecipitation (CO-IP) assay showed that MSTN gene interacted with extracellular matrix related protein type I collagen α 1 (COL1A1), and knocking down the expression of COL1A1 could inhibit the activity of adhesion, PI3K-AKT and ribosome pathway, thus inhibit BSMSCs proliferation. These results suggest that the MSTN gene regulates focal adhesion, PI3K-AKT, and Ribosomal pathway through the COL1A1 gene. In general, this study provides new insights into the regulatory mechanism of MSTN involved in muscle growth and development.

Seasons affect the phosphorylation of pork sarcoplasmic proteins related to meat quality

OBJECTIVE

Sarcoplasmic proteins include proteins that play critical roles in biological processes of living organisms. How seasons influence biological processes and meat quality of postmortem muscles through the regulation of protein phosphorylation remain to be investigated. In this study, the phosphorylation of sarcoplasmic proteins in pork longissimus muscle was investigated in four seasons.

METHODS

Sarcoplasmic proteins were extracted from 40 pork carcasses (10 for each season) and analyzed through ProQ Diamond staining for phosphorylation labeling and Sypro Ruby staining for total protein labeling. The pH of muscle, contents of glycogen and ATP were measured at 45 min, 3 h, and 9 h postmortem and the water (P2b, P21, and P22) was measured at 3 h and 9 h.

RESULTS

A total of 21 bands were detected. Band 8 (heat shock cognate 71 kDa protein; heat shock 70 kDa protein 1B) had higher phosphorylation level in summer than that in other seasons at 45 min postmortem. The phosphorylation levels of 3 Bands were significantly different between fast and normal pH decline groups (p<0.05). The phosphorylation levels of 4 bands showed negative associations with immobilized water (P21) and positive association with free water (P22).

CONCLUSION

The phosphorylation levels of sarcoplasmic proteins involved in energy metabolism and heat stress response at early postmortem time differed depending on the seasons. These proteins include heat shock protein 70, pyruvate kinase, phosphoglucomutase-1, glucose-6-phosphate isomerase, and carbonic anhydrase 3. High temperatures in summer might result in the phosphorylation of those proteins, leading to pH decline and low water holding capacity.

Endogenous Proteolytic Systems and Meat Tenderness: Influence of Post-Mortem Storage and Processing

Meat proteolytic systems play a crucial role in meat tenderisation. Understanding the effects of processing technologies and post-mortem storage conditions on these systems is important due to their crucial role in determining the quality characteristics of meat and meat products. It has recently been proposed that tenderisation occurs due to the synergistic action of numerous endogenous proteolytic systems. There is strong evidence suggesting the importance of μ-calpain during the initial post-mortem aging phase, while m-calpain may have a role during long-term aging. The caspase proteolytic system is also a candidate for cell degradation in the initial stages of conversion of muscle to meat. The role of cathepsins, which are found in the lysosomes, in post-mortem aging is controversial. Lysosomes need to be ruptured, through aging, or other forms of processing to release cathepsins into the cytosol for participation in proteolysis. A combination of optimum storage conditions along with suitable processing may accelerate protease activity within meat, which can potentially lead to improved meat tenderness. Processing technologies such as high pressure, ultrasound, and shockwave processing have been reported to disrupt muscle structure, which can facilitate proteolysis and potentially enhance the aging process. This paper reviews the recent literature on the impacts of processing technologies along with post-mortem storage conditions on the activities of endogenous proteases in meat. The information provided in the review may be helpful in selecting optimum post-mortem meat storage and processing conditions to achieve improved muscle tenderness within shorter aging and cooking times.

Effects of protein posttranslational modifications on meat quality: A review

Meat quality plays an important role in the purchase decision of consumers, affecting producers and retailers. The formation mechanisms determining meat quality are intricate, as several endogenous and exogenous factors contribute during antemortem and postmortem periods. Abundant research has been performed on meat quality; however, unexpected variation in meat quality remains an issue in the meat industry. Protein posttranslational modifications (PTMs) regulate structures and functions of proteins in living tissues, and recent reports confirmed their importance in meat quality. The objective of this review was to provide a summary of the research on the effects of PTMs on meat quality. The effects of four common PTMs, namely, protein phosphorylation, acetylation, S-nitrosylation, and ubiquitination, on meat quality were discussed, with emphasis on the effects of protein phosphorylation on meat tenderness, color, and water holding capacity. The mechanisms and factors that may affect the function of protein phosphorylation are also discussed. The current research confirms that meat quality traits are regulated by multiple PTMs. Cross talk between different PTMs and interactions of PTMs with postmortem biochemical processes need to be explored to improve our understanding on factors affecting meat quality.

Structural Changes and Evolution of Peptides During Chill Storage of Pork

In this work, we investigated changes in protein structures in vacuum-packed pork during chill storage and its impact on the in vitro protein digestion. Longissimus dorsi muscles were vacuum packed and stored at 4°C for 3 days. Samples were subjected to Raman spectroscopy, in vitro digestion and nano LC-MS/MS. The 3 d samples had lower α-helix content, but higher β-sheet, β-turn, and random coil contents than the 0 d samples (P < 0.05). SDS-PAGE revealed significant protein degradation in the 3 d samples and the differences in digested products across the storage time. Proteome analysis indicated that the 3 d samples had the higher susceptibility to digestion. Increasing protein digestibility was mainly attributed to the degradation of myofibrillar proteins. Thus, exposure of more enzymatic sites in loose protein structure during chill storage could increase protein degradation in meat.

Acetylation and Phosphorylation of Proteins Affect Energy Metabolism and Pork Quality

Preslaughter handling has been shown to significantly affect meat quality, but the mechanisms are not fully understood. In this study, we investigated protein phosphorylation and acetylation in pig muscles at early postmortem time and their associations with meat quality attributes. Thirty pigs were randomly assigned to traditional (TH, n = 15) or mild handling (MH, n = 15). Compared with TH, MH reduced the incidence of pale, soft, and exudative (PSE) or dark, firm, and dry (DFD) pork. MH induced 65 and 20 peptides that match with 39 and 12 proteins to be more highly phosphorylated and acetylated, respectively. Creatine kinase, β-enolase, α-1,4-glucan phosphorylase, tropomyosin, and myosin heavy chain isoforms 1, 4, and 7 were found to be simultaneously phosphorylated and acetylated, which may involve glycolysis, tight junctions, and muscle contraction. The phosphorylation and acetylation levels of differential proteins showed significant correlations with meat quality traits. These findings indicate that preslaughter MH can improve meat quality by regulating protein phosphorylation and acetylation involving energy metabolism in muscle.

Effects of phosphorylation on the activity of glycogen phosphorylase in mutton during incubation at 4 °C in vitro

The aim of this study was to assess the effects of the phosphorylation levels of glycogen phosphorylase on its activity in mutton sarcoplasmic protein samples during incubation at 4 °C. Samples of sarcoplasmic proteins from mutton longissimus thoracis muscles were prepared and separated into three treatment groups to obtain glycogen phosphorylase with different phosphorylation levels, which were (1) treated with protein kinase A, (2) treated with alkaline phosphatase, and (3) left untreated (control). Glycogen phosphorylase phosphorylation levels and activity as well as the levels of related endogenous substances were assessed. The results showed that phosphorylation of glycogen phosphorylase in mutton promoted its activity during incubation at 4 °C. The activity of glycogen phosphorylase was also influenced by other factors (glycogen, glucose, glucose 6-phosphate, ATP, etc.) in vitro. The combined effects of phosphorylation and endogenous substances on glycogen phosphorylase activity varied at different incubation times.

Characterization of the promoter region of the bovine IRX3 gene: roles of SREBF2 and PPARG

As a member of the Iroquois homeobox gene family, the IRX3 gene plays an important role in regulating the growth, development and fat deposition of chordates. In the present study, we found, using real-time PCR, that the bovine IRX3 gene was highly expressed in lung, kidney, heart, subcutaneous fat and longissimus dorsi muscle. We cloned the full-length sequence of the bovine IRX3 gene promoter and constructed eight series of 5′ deletion promoter plasmid luciferase reporter assays and then transfected them to 3T3-L1 and C2C12 cell lines to detect its core promoter regions. The results showed that the core promoter of bovine IRX3 was located within a −292/−42 bp region relative to the transcriptional start site. Furthermore, sequence analysis identified eight CpG islands in the promoter region. A chromatin immunoprecipitation assay in combination with site-directed mutation and siRNA interference demonstrated that SREBF2 and PPARG binding occurs in region −292/−42 and is essential in bovine IRX3 transcription. These results lay an important theoretical foundation for exploring the molecular regulation mechanism of the IRX3 gene in bovine fat deposition.

An analysis of the influence of various tenderising treatments on the tenderness of meat from Polish Holstein-Friesian bulls and the course of changes in collagen

The aim of the study was to analyse the influence of tenderising treatments applied to the carcasses of Polish Holstein-Friesian (PHF) bulls of Black-and-White variety on the process of meat tenderisation and to assess the role of collagen in this process. The research was carried out on m. longissimus thoracis et lumborum. The carcasses were subjected to high-voltage electrical stimulation (ES), conditioning (CD), and both treatments together (ES + CD). The carcasses which were only refrigerated were the control group. The content of collagen in meat, its solubility, the share of the polypeptide subunits α1(I)CB7 and α1(I)CB8 of type I collagen and α1(III)CB5 of type III collagen were also analysed. ES with and without CD significantly accelerated the meat tenderisation and increased collagen solubility. CD always caused the degradation of type I collagen subunits, especially the α1(I)CB7 subunit. However, CD had significantly lesser influence on the rate of meat tenderisation than ES.

Stress Effects on Meat Quality: A Mechanistic Perspective

Stress inevitably occurs from the farm to abattoir in modern livestock husbandry. The effects of stress on the behavioral and physiological status and ultimate meat quality have been well documented. However, reports on the mechanism of stress effects on physiological and biochemical changes and their consequent effects on meat quality attributes have been somewhat disjointed and limited. Furthermore, the causes of variability in meat quality traits among different animal species, muscle fibers within an animal, and even positions within a piece of meat in response to stress are still not entirely clear. This review 1st summarizes the primary stress factors, including heat stress, preslaughter handling stress, oxidative stress, and other stress factors affecting animal welfare; carcass quality; and eating quality. This review further delineates potential stress-induced pathways or mediators, including AMP-activated protein kinase-mediated energy metabolism, crosstalk among calcium signaling pathways and reactive oxygen species, protein modification, apoptosis, calpain and cathepsin proteolytic systems, and heat shock proteins that exert effects that cause biochemical changes during the early postmortem period and affect the subsequent meat quality. To obtain meat of high quality, further studies are needed to unravel the intricate mechanisms involving the aforementioned signaling pathways or mediators and their crosstalk.

Purified Dietary Red and White Meat Proteins Show Beneficial Effects on Growth and Metabolism of Young Rats Compared to Casein and Soy Protein

This study compared the effects of casein, soy protein (SP), red (RMP), and white meat (WMP) proteins on growth and metabolism of young rats. Compared to casein, the ratio of daily feed intake to daily body weight gain of rats was not changed by meat protein but reduced by SP by 93.3% ( P < 0.05). Feeding RMP and WMP reduced the liver total cholesterol (TC) contents by 24.3% and 17.8%, respectively ( P < 0.05). Only RMP increased plasma HDL-cholesterol concentrations (by 12.7%, P < 0.05), whereas SP increased plasma triacylglycerol, TC, and LDL-cholesterol concentrations by 23.7%, 19.5%, and 61.5%, respectively ( P < 0.05). Plasma essential and total amino acid concentrations were increased by WMP (by 18.8% and 12.4%, P < 0.05) but reduced by SP (by 28.3% and 37.7%, P < 0.05). Twenty-five liver proteins were differentially expressed in response to different protein sources. Therefore, meat proteins were beneficial for growth and metabolism of young rats compared to casein and SP.

Quantitative Proteomics and Phosphoproteomics Analysis Revealed Different Regulatory Mechanisms of Halothane and Rendement Napole Genes in Porcine Muscle Metabolism

Pigs with the Halothane (HAL) or Rendement Napole (RN) gene mutations demonstrate abnormal muscle energy metabolism patterns and produce meat with poor quality, classified as pale, soft, and exudative (PSE) meat, but it is not well understood how HAL and RN mutations regulate glucose and energy metabolism in porcine muscle. To investigate the potential signaling pathways and phosphorylation events related to these mutations, muscle samples were collected from four genotypes of pigs, wild type, RN, HAL, and RN-HAL double mutations, and subjected to quantitative proteomic and phosphoproteomic analysis using the TiO₂ enrichment strategy. The study led to the identification of 932 proteins from the nonmodified peptide fractions and 1885 phosphoproteins with 9619 phosphorylation sites from the enriched fractions. Among them, 128 proteins at total protein level and 323 phosphosites from 91 phosphoproteins were significantly regulated in mutant genotypes. The quantitative analysis revealed that the RN mutation mainly affected the protein expression abundance in muscle. Specifically, high expression was observed for proteins related to mitochondrial respiratory chain and energy metabolism, thereby enhancing the muscle oxidative capacity. The high content of UDP-glucose pyrophosphorylase 2 (UGP2) in RN mutant animals may contribute to high glycogen storage. However, the HAL mutation mainly contributes to the up-regulation of phosphorylation in proteins related to calcium signaling, muscle contraction, glycogen, glucose, and energy metabolism, and cellular stress. The increased phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II (CAMK2) in HAL mutation may act as a key regulator in these processes of muscle. Our findings indicate the different regulatory mechanisms of RN and HAL mutations in relation to porcine muscle energy metabolism and meat quality.

A comparative analysis of phosphoproteome in ovine muscle at early postmortem in relationship to tenderness

BACKGROUND

Tenderness is considered to be the most important quality characteristic of meat as it is the main cause of unacceptability of meat. Post-translational modification regulates protein functions that involve in postmortem changes in muscle and meat quality formation. Specifically, phosphorylation was proved to regulate postmortem glycolytic rates and meat tenderisation. However, the relationship between protein phosphorylation and meat tenderness remains unclear. This study examined the phosphoproteomes found in ovine muscle with different degrees of tenderness over time (at 0.5 h, 4 h, and 24 h postmortem).

RESULTS

This study detected five, eight and nine phosphoprotein spots (>two-fold change, P < 0.05) at each respective time point. The different phosphoproteins found included glyceraldehyde-3-phosphate dehydrogenase, tropomyosin α-1 chain, pyruvate kinase, myosin binding protein H, glycogen phosphorylase, α-actinin-3, and an uncharacterised protein (GN, myosin-binding protein C2, MYBPC2). Most of the different phosphoproteins maintained sarcomeric functions, or were involved in glycometabolism.

CONCLUSION

Phosphorylation levels of multiple proteins that are involved in glycolysis, muscle contraction or sarcomeric structure integrity were identified in ovine muscles with different tenderness. The differential phosphorylation of these proteins explains in part the difference in meat tenderness. © 2017 Society of Chemical Industry.

Dephosphorylation enhances postmortem degradation of myofibrillar proteins

Protein degradation is primarily responsible for postmortem meat tenderization, which might be affected by phosphorylation. The objective of this study was to investigate the effect of phosphorylation on myofibrillar proteins degradation in muscle during postmortem. Here we modulated the phosphorylation status of protein by protein kinase inhibitor and phosphatase inhibitor, and the effect of these inhibitors on myofibrillar protein degradation was evaluated. Generally, myofibril fragmentation index of samples with lower phosphorylation level was higher. Troponin T and heat shock protein 27 were degraded faster in protein kinase inhibited (low phosphorylation level) muscle, compared with the other two groups, while the degradation of desmin was not affected by inhibitors. Meanwhile, myosin heavy chain, actin and tropomyosin showed limited degradation in postmortem muscle. This study showed that dephosphorylation enhances the degradation of some myofibrillar proteins, indicating that protein phosphorylation may play an important role in postmortem meat tenderization.

Phosphorylation of myofibrillar proteins in post-mortem ovine muscle with different tenderness

BACKGROUND

Tenderness is one of the most important quality attributes especially for beef and lamb. As protein phosphorylation and dephosphorylation regulate glycolysis, muscle contraction and turnover of proteins within living cells, it may contribute to the conversion of muscle to meat. The changes of myofibrillar protein phosphorylation in post-mortem ovine muscle with different levels of tenderness were investigated in this study.

RESULTS

The protein phosphorylation level (P/T ratio) of the tender group increased from 0.5 to 12 h post mortem and then decreased. The P/T ratio of tough group increased during 24 h post mortem, increasing faster from 0.5 to 4 h post mortem than from 4 to 24 h post mortem.The global phosphorylation level of tough meat was significantly higher than tender meat at 4, 12 and 24 h post mortem (P < 0.05). Protein identification revealed that most of the phosphoproteins were proteins with sarcomeric function; the others were involved in glycometabolism, stress response, etc. The phosphorylation levels of myofibrillar proteins, e.g. myosin light chain 2 and actin, were significantly different among groups of different tenderness and at different post-mortem time points (P < 0.05).

CONCLUSION

Protein phosphorylation may influence meat rigor mortis through contractile machinery and glycolysis, which in turn affect meat tenderness.

Quantitative phosphoproteomic analysis of porcine muscle within 24 h postmortem

Protein phosphorylation can regulate most of the important processes in muscle, such as metabolism and contraction. The postmortem (PM) metabolism and rigor mortis have essential effects on meat quality. In order to identify and characterize the protein phosphorylation events involved in meat quality development, a quantitative mass spectrometry-based phosphoproteomic study was performed to analyze the porcine muscle within 24h PM using dimethyl labeling combined with the TiSH phosphopeptide enrichment strategy. In total 305 unique proteins were identified, including 160 phosphoproteins with 784 phosphorylation sites. Among these, 184 phosphorylation sites on 93 proteins had their phosphorylation levels significantly changed. The proteins involved in glucose metabolism and muscle contraction were the two largest clusters of phosphoproteins with significantly changed phosphorylation levels in muscle within 24 h PM. The high phosphorylation level of heat shock proteins (HSPs) in early PM may be an adaptive response to slaughter stress and protect muscle cell from apoptosis, as observed in the serine 84 of HSP27. This work indicated that PM muscle proteins underwent significant changes at the phosphorylation level but were relatively stable at the total protein level, suggesting that protein phosphorylation may have important roles in meat quality development through the regulation of proteins involved in glucose metabolism and muscle contraction, thereby affecting glycolysis and rigor mortis development in PM muscle.

BIOLOGICAL SIGNIFICANCE

The manuscript describes the characterization of postmortem (PM) porcine muscle within 24 h postmortem from the perspective of protein phosphorylation using advanced phosphoproteomic techniques. In the study, the authors employed the dimethyl labeling combined with the TiSH phosphopeptide enrichment and LC-MS/MS strategy. This was the first high-throughput quantitative phosphoproteomic study in PM muscle of farm animals. In the work, both the proteome and phosphoproteome were analyzed, and the large number of identified peptides, phosphopeptides and phosphorylation sites can greatly enrich the current farm animal protein database. The proteins involved in glycometabolism, muscle contraction and heat shock proteins (HSPs) showed significantly changed phosphorylation levels during PM meat development. This work indicated that PM muscle proteins underwent significant changes at phosphorylation level but were relatively stable at the total protein level, suggesting that protein phosphorylation may have important roles in meat development through the regulation of proteins involved in metabolism and muscle contraction, thereby affecting glycolysis and rigor mortis development in PM muscle. The work can promote the understanding of PM muscle metabolism and meat quality development, and be helpful for future meat quality control.

Effect of fasting on energy metabolism and tenderizing enzymes in chicken breast muscle early postmortem

Pre-slaughter fasting is a very important practice in the meat industry. The present study was designed to investigate the effect of fasting on energy metabolism and tenderizing enzymes in chicken muscle early postmortem. A total of 30 Yellow-feathered chickens were deprived of feed for 0 h, 12 h and 24 h before slaughter (n=10 each group). Breast muscles were removed and cut into 3 parts and stored at 0°C for 0 h, 3 h and 10 h. Samples were used for analyses of zymography, cathepsins, pH, glycogen/ATP/ADP/AMP, hormones and ultrastructure. Fasting caused the accelerated depletion (p<0.05) of glycogen, ATP and ADP before or immediately after slaughter, but no difference existed in ATP at 3 and 10 h (p>0.05). Fasting resulted in greater ultimate pH (p<0.05). Zymography indicated that fasting delayed the activation of μ/m-calpain (p<0.05), however, it accelerated the release of lysosomal enzymes (p<0.05). Fasting for 24 h resulted in greater ultrastructural changes and plasma corticosterone levels than fasting for 12 h and control groups. Therefore, fasting for no more than 12 h is acceptable in practice.