Myosin light chain 1 release from myofibrillar fraction during postmortem aging is a potential indicator of proteolysis and tenderness of beef

LF-NMR determination of water distribution and its relationship with protein- related properties of yak and cattle during postmortem aging

The water distribution have a profound influence on meat quality, and proteins play a critical role in water distribution. The water distribution detected with proton NMR and its relationship with protein related properties were investigated. Three populations of water were detected: bound water (T21, P21), immobilized water (T22, P22), and free water (T23, P23). The decreased T22 and T23 indicated an increase in water-holding capacity in both muscles from 3 days of aging. The P22 in cattle was higher than that in yak and the P23 in cattle was lower than that in yak, suggesting that cattle exhibited a greater water-holding capacity compared to yak. Moreover, postmortem aging affected muscle protein oxidation, denaturation, and degradation. Correlation analysis suggested that protein oxidation and denaturation caused muscle water loss and protein degradation could allow the muscle to retain water. It provides a basis for the optimization of quality of meat and products.

Investigation of changes in proteomes of beef exudate and meat quality attributes during wet-aging

This study was performed to evaluate the effects of wet-aging (3, 7, 14, 21, and 28 d at 2 °C) on beef (longissimus lumborum muscles) exudate proteome and meat quality changes. The pH, purge loss, and tenderness of beef increased with aging (P < 0.05), while color and lipid oxidative stabilities decreased, especially when long-term (14 and 21 d) aged meat were repackaged and displayed under retail condition (P < 0.05). Nineteen proteins changed significantly with aging (FDR < 0.05), in which most of them progressively accumulated in exudates over aging periods. Combined with partial least squares discriminant analysis, 16 proteins (including 9 structural proteins, 3 metabolic enzymes, 1 heat shock protein, 2 binding proteins, and KBTBD10 protein) were screened as characteristic proteins that could be used for potential meat quality indication. These findings offered novel insight into the utilization of exudates for meat quality assessment.

Distinct myofibrillar sub-proteomic profiles are associated with the instrumental texture of aged pork loin

Fresh pork tenderness contributes to consumer satisfaction with the eating experience. Postmortem proteolysis of proteins within and between myofibrils has been closely linked with pork tenderness development. A clear understanding of the molecular features associated with pork tenderness development will provide additional targets and open the door to new solutions to improve and make pork tenderness development more consistent. Therefore, the objective was to utilize liquid chromatography and mass spectrometry with tandem mass tag (TMT) multiplexing to evaluate myofibrillar sub-proteome differences between pork chops of different instrumental star probe values. Pork loins (N = 120) were collected from a commercial harvest facility at 24 h postmortem. Quality and sensory attributes were evaluated at 24 h postmortem and after ~2 weeks of postmortem aging. Pork chops were grouped into 4 groups based on instrumental star probe value (group A,x¯ = 4.23 kg, 3.43 to 4.55 kg; group B,x¯ = 4.79 kg, 4.66 to 5.00 kg; group C,x¯ = 5.43 kg, 5.20 to 5.64 kg; group D,x¯ = 6.21 kg, 5.70 to 7.41 kg; n = 25 per group). Myofibrillar proteins from the samples aged ~2 wk were fractionated, washed, and solubilized in 8.3 M urea, 2 M thiourea, and 1% dithiothreitol. Proteins were digested with trypsin, labeled with 11-plex isobaric TMT reagents, and identified and quantified using a Q-Exactive Mass Spectrometer. Between groups A and D, 54 protein groups were differentially abundant (adjusted P < 0.05). Group A had a greater abundance of proteins related to the thick and thin filament and a lesser abundance of Z-line-associated proteins and metabolic enzymes than group D chops. These data highlight that distinct myofibrillar sub-proteomes are associated with pork chops of different tenderness values. Future research should evaluate changes immediately and earlier postmortem to further elucidate myofibrillar sub-proteome differences over the postmortem aging period.

Comparative 3-Sample 2D-DIGE Analysis of Skeletal Muscles

The skeletal muscle proteome consists of a large number of diverse protein species with a broad and dynamic concentration range. Since mature skeletal muscles are characterized by a distinctive combination of contractile cells with differing physiological and biochemical properties, it is essential to determine specific differences in the protein composition of fast, slow, and hybrid fibers. Fluorescence two-dimensional difference gel electrophoresis (2D-DIGE) is a powerful comparative tool to analyze fiber type-specific differences between predominantly fast contracting versus slower twitching muscles. In this chapter, the application of the 2D-DIGE method for the comparative analysis of different subtypes of skeletal muscles is outlined in detail. A standardized proteomic workflow is described, involving sample preparation, protein extraction, differential fluorescence labeling using a 3-CyDye system, first-dimension isoelectric focusing, second-dimension slab gel electrophoresis, 2D-DIGE image analysis, protein digestion, and mass spectrometry.

Metabolic, proteomic and microbial changes postmortem and during beef aging

The purpose of this review is to provide an overview of the current knowledge about proteomic and metabolic changes in beef, the microbiological alteration postmortem and during aging, and observe the influence on beef quality parameters, such as tenderness, taste and flavor. This review will also focus on the different aging types (wet- and dry-aging), the aging or postmortem time of beef and their effect on the proteome and metabolome of beef. The Ca2+ homeostasis and adenosine 5'-triphosphate breakdown are the main reactions in the pre-rigor phase. After rigor mortis, the enzymatic degradation of connective tissues and breakdown of energy metabolism dominate molecular changes in beef. Important metabolic processes leading to the formation of saccharides, nucleotides, organic acids (e.g. lactic acid), creatine and fatty acids are considered in this context as possible flavor precursors or formers of beef flavor and taste. Flavor precursors are substrates for lipid oxidation, Strecker degradation and Maillard reaction during cooking or roasting. The findings presented should serve as a basis for a better understanding of beef aging and its molecular effects and are intended to contribute to meeting the challenges of improving beef quality.

Tandem mass tag labeling to assess proteome differences between intermediate and very tender beef steaks

Tenderness is considered as one of the most important quality attributes dictating consumers' overall satisfaction and future purchasing decisions of fresh beef. However, the ability to predict and manage tenderness has proven very challenging due to the numerous factors that contribute to variation in end-product tenderness. Proteomic profiling allows for global examination of differentially abundant proteins in the meat and can provide new insight into biological mechanisms related to meat tenderness. Hence, the objective of this study was to examine proteomic profiles of beef longissimus lumborum (LL) steaks varying in tenderness, with the intention to identify potential biomarkers related to tenderness. For this purpose, beef LL muscle samples were collected from 99 carcasses at 0 and 384 h postmortem. Based on Warner-Bratzler shear force values at 384 h, 16 samples with the highest (intermediate tender, IT) and lowest (very tender, VT) values were selected to be used for proteomic analysis in this study (n = 8 per category). Using tandem mass tag-based proteomics, a total of 876 proteins were identified, of which 51 proteins were differentially abundant (P < 0.05) between the tenderness categories and aging periods. The differentially identified proteins encompassed a wide array of biological processes related to muscle contraction, calcium signaling, metabolism, extracellular matrix organization, chaperone, and apoptosis. A greater (P < 0.05) relative abundance of proteins associated with carbohydrate metabolism and apoptosis, and a lower (P < 0.05) relative abundance of proteins involved in muscle contraction was observed in the VT steaks after aging compared with the IT steaks, suggesting that more proteolysis occurred in the VT steaks. This may be explained by the greater (P < 0.05) abundance of chaperonin and calcium-binding proteins in the IT steaks, which could have limited the extent of postmortem proteolysis in these steaks. In addition, a greater (P < 0.05) abundance of connective tissue proteins was also observed in the IT steaks, which likely contributed to the difference in tenderness due to added background toughness. The established proteomic database obtained in this study may provide a reference for future research regarding potential protein biomarkers that are associated with meat tenderness.

TMT-based quantitative proteomics reveals protein biomarkers from cultured Pacific abalone (Haliotis discus hannai) in different regions

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TMT-based proteomics was used to study and compare the muscle protein profiles of Pacific abalones between northern and southern China.

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729 differential abundance proteins were identified in different regions.

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Fatty acid synthase and other 3 proteins were identified as candidate biomarkers for identification of northern and southern abalone.

Due to latitude, the growth cycle of abalone in southern China is significantly lower than that in the northern regions. Therefore, it often occurs merchants use southern abalone to disguise as northern abalone. This study aims to explore the differences in the muscle proteome of Pacific abalone (Haliotis discus hannai) in different regions. A total of 1,569 proteins were detected and 729 proteins were identified as differential abundance proteins (DAPs) in Haliotis discus hannai cultured in Northern (Liaoning Province) and Southern (Fujian Province) China. Bioinformatics analysis revealed and Western blot verified that fatty acid synthase, troponin I, calpain small subunit 1, and myosin light chain 6 are candidate biomarkers for abalone cultured in different regions. This study provides a deeper understanding of how to distinguish which region abalone is harvested from to improve abalone quality controls, and prevent food fraud.

Quantitative proteomics insights into gel properties changes of myofibrillar protein from Procambarus clarkii under cold stress

The impacts of cold stress (4 ℃ for 0 h, 12 h, 24 h, 36 h and 48 h, respectively) on the components, structural and physical properties of myofibrillar protein (MP) gel from Procambarus clarkii were investigated. The physicochemical analysis indicated the secondary and tertiary structure of MP were unfolding to different degrees after cold stress when compared to the control. The MP gel hardness reached a maximum when the cold stress reached 24 h. Furthermore, the quantitative proteomics results indicated that 20 up-regulated differentially abundant proteins (DAPs) were detected in 24 h when compared to control, specifically include myosin light chain 1 (MLC1) and skeletal muscle actin 6. Additionally, the combined analysis confirmed that MLC1 and skeletal muscle actin 6 might play key roles in hardening shrimp meat under cold stress. The results could provide a theoretical reference for the changes in crayfish muscle quality during cold chain transportation.

Postmortem Muscle Protein Changes as a Tool for Monitoring Sahraoui Dromedary Meat Quality Characteristics

The effects of slaughter age (2 vs. 9 years) and postmortem time (6, 8, 10, 12, 24, 48 and 72 h) on the meat quality and protein changes of the longissimus lumborum muscles of the Algerian Sahraoui dromedary were investigated. Muscles of young dromedaries evidenced a slower acidification process and a significantly higher myofibrillar fragmentation index throughout the postmortem time. The SDS-PAGE of sarcoplasmic and myofibrillar proteins revealed that meat from young dromedaries was characterized by the lowest percentage of myoglobin (p < 0.001) and the highest percentage of desmin (p < 0.01). During postmortem time, a decrease was found for phosphoglucomutase (p < 0.01), α-actinin (p < 0.05) and desmin (p < 0.01) in meat from young dromedaries. Western blot revealed an intense degradation of troponin T in younger dromedaries, with an earlier appearance of the 28 kDa polypeptide highlighting differences in the proteolytic potential between dromedaries of different ages. Principal component analysis showed that meat from young dromedaries, starting from 24 h postmortem, was located in a zone of the plot characterized by higher levels of the myofibrillar fragmentation index, 30 kDa polypeptide and enolase, overall confirming greater proteolysis in younger animals. Data suggest that the investigation of the muscle proteome is necessary to set targeted interventions to improve the aging process of dromedary meat cuts.

Marine Biopolymers: Applications in Food Packaging

Marine sources are gaining popularity and attention as novel materials for manufacturing biopolymers such as proteins and polysaccharides. Due to their biocompatibility, biodegradability, and non-toxicity features, these biopolymers have been claimed to be beneficial in the development of food packaging materials. Several studies have thoroughly researched the extraction, isolation, and latent use of marine biopolymers in the fabrication of environmentally acceptable packaging. Thus, a review was designed to provide an overview of (a) the chemical composition, unique properties, and extraction methods of marine biopolymers; (b) the application of marine biopolymers in film and coating development for improved shelf-life of packaged foods; (c) production flaws and proposed solutions for better isolation of marine biopolymers; (d) methods of preparation of edible films and coatings from marine biopolymers; and (e) safety aspects. According to our review, these biopolymers would make a significant component of a biodegradable food packaging system, reducing the amount of plastic packaging used and resulting in considerable environmental and economic benefits.

Proteomic analysis to understand the relationship between the sarcoplasmic protein patterns and meat organoleptic characteristics in different horse muscles during aging

The study investigates the changes in meat organoleptic characteristics and sarcoplasmic proteins of 3 horse muscles during aging. Longissimus lumborum (LL), semimembranosus (SM) and semitendinosus (ST) muscles, were removed from 12 Italian Heavy Draft Horse carcasses and aged for 1, 3, 6, 9 and 14 days. The lowest values of hardness and chewiness were found in LL muscle. During aging, a decrease of hardness was observed in ST muscle reaching the lowest value at 14 days. 2DE revealed a decrease of 15 sarcoplasmic protein spots in all muscles. Muscle-differences were found at 14 days. An increase of tropomyosin spots was found in LL muscle while, ST was characterized by a rise of superoxide dismutase, phosphoglucomutase-1 and two isoforms of myoglobin. Principal component analysis applied to color, texture parameters and spots volume differentiated the muscles into three different clusters. Data revealed that myofibrillar, glycolytic and mitochondrial proteins are potential muscle-biomarkers to monitor post-mortem processes and meat quality characteristics in horse meat.

iTRAQ-mediated analysis of the relationship between proteomic changes and yak longissimus lumborum tenderness over the course of postmortem storage

To identify differentially expressed proteins associated with energy metabolism and tenderness during the postmortem aging of yak longissimus lumborum muscle samples, we collected tissue samples from yaks raised at different altitudes. At 12 h post-slaughter, we identified 290 differentially expressed proteins (DEPs) in these samples, whereas 436 such DEPs were detected after 72 h. Identified DEPs were clustered into four main functional categories: cell structural proteins, glycogen metabolic proteins, energy reserve metabolic proteins, and cellular polysaccharide metabolic proteins. Further bioinformatics analysis revealed that these proteins were associated with carbon metabolism, glycolysis, and the biosynthesis of amino acids. Our functional insights regarding these identified proteins contribute to a more detailed molecular understanding of the processes of energy metabolism in yak muscle tissue, and represent a valuable resource for future investigations.

Impact of Extraction Method on the Detection of Quality Biomarkers in Normal vs. DFD Meat

The objective of this work was to demonstrate how the extraction method affects the reliability of biomarker detection and how this detection depends on the biomarker location within the cell compartment. Different extraction methods were used to study the sarcoplasmic and myofibrillar fractions of the Longissimus thoracis et lumborum muscle of young bulls of the Asturiana de los Valles breed in two quality grades, standard (Control) or dark, firm, and dry (DFD) meat. Protein extractability and the expression of some of the main meat quality biomarkers—oxidative status (lipoperoxidation (LPO) and catalase activity (CAT)), proteome (SDS-PAGE electrophoretic pattern), and cell stress protein (Hsp70)—were analyzed. In the sarcoplasmic fraction, buffers containing Triton X-100 showed significantly higher protein extractability, LPO, and higher intensity of high-molecular-weight protein bands, whereas the TES buffer was more sensitive to distinguishing differences in the protein pattern between the Control and DFD meat. In the myofibrillar fraction, samples extracted with the lysis buffer showed significantly higher protein extractability, whereas samples extracted with the non-denaturing buffer showed higher results for LPO, CAT, and Hsp70, and higher-intensity bands in the electrophoretic pattern. These findings highlight the need for the careful selection of the extraction method used to analyze the different biomarkers considering their cellular location to adapt the extractive process.

Quantitative proteomic analysis of beef tenderness of Piemontese young bulls by SWATH-MS

Quantitative proteomic approach is a suitable way to tackle the beef tenderness. Ten aged-beef samples from Longissimus thoracis of Piemontese breed classified as tender (n = 5) and tough (n = 5) meat were evaluated using SWATH-MS and bioinformatic tools for the identification of the proteins and pathways most influencing tenderness variability. Between the two textural groups, proteomic changes were mainly caused by 43 differentially abundant proteins (DAPs) arranged in reference patterns as displayed by the heat map analysis. Most of these DAPs were associated with energy metabolism. From the functional proteomic analysis, two clusters of proteins, including ACO2, MDH1, MDH2 and CS in one cluster and FBP2, PFKL, LDHA, TPI1 and GAPDH/S in the other cluster, suggest gluconeogenesis, glycolysis and citrate cycle as key pathways for Piemontese breed beef tenderness. These findings contribute to a deeper insight into molecular pathways related to beef tenderness.

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.

Early Postmortem Proteome Changes in Normal and Woody Broiler Breast Muscles

Early postmortem changes in the whole muscle proteome from normal broiler (NB) and woody broiler (WB) breasts at 0 min, 15 min, 4 h, and 24 h after slaughter were analyzed using two-dimensional gel electrophoresis (2DE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Elongation factor 2, EH domain-containing protein 2, phosphoglycerate mutase 1 (PGAM1), and T-complex protein 1 subunit gamma were differentially abundant in both NB and WB muscles during the early postmortem storage. Twenty additional proteins were differentially abundant among four postmortem time points in either NB or WB muscles. In the postmortem WB, changes in protein degradation were observed, including the degradation of desmin fragments, ovotransferrin chain A, and troponin I chain I. Additionally, a few glycolytic proteins in the WB might have undergone post-translational modification, including enolase, phosphoglucomutase-1, PGAM1, and pyruvate kinase. These changes in protein biomarkers highlight the impact of WB myopathy on postmortem proteome changes and increase our understanding of the relationship between WB conditions, postmortem biochemistry, and meat quality.

The Profiling of DNA Methylation and Its Regulation on Divergent Tenderness in Angus Beef Cattle

Beef is an essential food source in the world. Beef quality, especially tenderness, has a significant impact on consumer satisfaction and industry profit. Many types of research to date have focused on the exploration of physiological and developmental mechanisms of beef tenderness. Still, the role and impact of DNA methylation status on beef tenderness have yet to be elucidated. In this study, we exhaustively analyzed the DNA methylation status in divergent tenderness observed in Angus beef. We characterized the methylation profiles related to beef tenderness and explored methylation distributions on the whole genome. As a result, differentially methylated regions (DMRs) associated with tenderness and toughness of beef were identified. Importantly, we annotated these DMRs on the bovine genome and explored bio-pathways of underlying genes and methylation biomarkers in beef quality. Specifically, we observed that the ATP binding cassette subfamily and myosin-related genes were highly methylated gene sets, and generation of neurons, regulation of GTPase activity, ion transport and anion transport, etc., were the significant pathways related with beef tenderness. Moreover, we explored the relationship between DNA methylation and gene expression in DMRs. Some methylated genes were identified as candidate biomarkers for beef tenderness. These results provide not only novel epigenetic information associated with beef quality but offer more significant insights into meat science, which will further help us explore the mechanism of muscle biology.

A preliminary investigation of the contribution of different tenderness factors to beef loin, tri-tip and heel tenderness

The objective of this study was to identify the relative contribution of tenderness factors for three beef muscles with similar tenderness ratings. Longissimus lumborum (LL), tensor fascia latae (TF) and gastrocnemius (GC) were collected from 10 USDA low Choice beef carcasses and assigned to a 5 or 21 days aging period (n = 60). Sarcomere length, troponin-T degradation, collagen content, mature collagen crosslink density, intramuscular lipid content and trained panel analysis were measured. Correlation and multivariate regression analysis indicated each muscle has a specific tenderness factor that contributed to the overall tenderness evaluated by trained panelists. The equations indicated LL tenderness was driven by lipid content (P < .05); TF tenderness was driven by collagen content (P < .05). GC tenderness was driven by proteolysis (P < .01), and only collagen content can be casually used as an overall tenderness predictor for all three cuts.

Investigation of the Sarcoplasmic Proteome Contribution to the Development of Pork Loin Tenderness

The study objectives were to determine the extent to which the sarcoplasmic proteome explains variations in aged pork loin star probe value. Pork loins (n=12) were categorized by differences in star probe at 21 d post mortem from a larger set of loins. Loins were categorized into low star probe (LSP) group (n=6; star probe&lt;5.80 kg) and high star probe (HSP) group (n=6; star probe&gt;7.00 kg) based on 21-d star probe value with inclusion criteria of marbling score (1.0–3.0) and 24-h pH (5.69–5.98). Quality traits were measured at 1-, 8-, 14-, and 21-d aging. Desmin and troponin-T degradation, peroxiredoxin-2 abundance, calpain-1 autolysis, and sarcomere length were determined. Two-dimensional difference gel electrophoresis and mass spectrometry were used to identify proteins that differed in abundance due to category. Star probe values were lower (P&lt;0.01) in LSP at each day of aging compared with HSP. Greater pH values were observed (P&lt;0.05)in LSP compared with HSP at each day of aging. Marbling score was greater (P&lt;0.05) in LSP compared with HSP at each day of aging. Greater (P&lt;0.05) desmin and troponin-T degradation was detected in LSP chops at 14- and 21-d aging and 8-, 14-, and 21-d aging, respectively. Greater (P&lt;0.05) sarcomere length was determined in LSP compared with HSP at 1-,8-, and 21-d aging. Sarcoplasmic proteins from HSP chops had greater abundance (P&lt;0.10) of metabolic and regulatory proteins, whereas the LSP chops had greater abundance (P&lt;0.10) of stress response proteins. Star probe values were affected by pH, marbling score, protein degradation, sarcomere length, and sarcoplasmic proteome.

The associations between proteomic biomarkers and beef tenderness depend on the end-point cooking temperature, the country origin of the panelists and breed

Steaks of 74 animals from 3 young bull breeds (Aberdeen Angus, Limousin and Blond d'Aquitaine) were cooked at two end-point cooking temperatures (55 and 74 °C) and evaluated for tenderness by trained panelists from France (FR) and the United Kingdom (UK). Using principal component regressions, the tenderness scores of each breed, country origin of the panelists and cooking temperature were linked with the abundances of 21 protein biomarkers belonging to five biological pathways. Twelve regression equations were built and explained 68 to 95% of tenderness variability. A high dissimilarity in the retained biomarkers was observed among the equations and differences exist among breeds, cooking temperatures and country origin of the panelists. Among the 21 biomarkers, 6 proteins including structural (MyHC-I, MyHC-IIa, MyHC-IIx), oxidative stress (DJ-1, PRDX6) and proteolysis (CAPN1) were retained robustly in positive or negative directions in the tenderization process of Longissimus thoracis, regardless the breed, the end-point cooking temperature or the country origin of the panelist.

Association of calpain and calpastatin activity to postmortem myofibrillar protein degradation and sarcoplasmic proteome changes in bovine Longissiumus lumborum and Triceps brachii

The aim of this study was to determine the extent to which calpastatin (CASN) variants (based on two chromatographic peaks; CASN-P1 and CASN-P2) explain variation in μ-calpain autolysis, protein degradation, and changes in the sarcoplasmic proteome observed during postmortem aging of beef. The Longissimus lumborum (LL) and Triceps brachii (TB) muscles were obtained from six crossbred steers and samples prepared from day 0, 1 and 7 postmortem (pm). The decline of CASN activity during aging was due to decrease of CASN-P2 in both muscles. The CASN-P2:μ-calpain ratio at day 0 was greater for TB, which presented lesser calpain autolysis, myofibrillar protein degradation, and fewer sarcoplasmic proteome changes during aging. Changes in abundance of Heat shock protein 70 family in the sarcoplasmic fraction were positively associated to proteolysis during aging, with greater differences in LL.

Effect of nitric oxide on myofibrillar proteins and the susceptibility to calpain-1 proteolysis

This study was designed to investigate the nature of modification of myofibrillar proteins by nitric oxide (NO) and the extent to which S-nitrosylation alters their susceptibility to calpain-1 proteolysis. Isolated myofibrils from porcine semimembranosus muscle were incubated with the NO donor S-nitrosoglutathione (GSNO) at 0, 20, 50, 250, 1000 µM for 30 min at 37 °C and then incubated with purified calpain-1. GSNO treatment decreased the thiol content of myofibrillar proteins and increased their intensity and amount of S-nitrosylation. GSNO caused the formation of proteins cross-linkage through intermolecular disulfide. More desmin and titin (T2, the degraded fragment of original titin) were degraded by calpain-1 when myofibrils were incubated with 1000 µM GSNO. Incubation with 250 and 1000 µM GSNO suppressed calpain-1-catalyzed cleavage of troponin-T. The data suggest that NO could change the redox state of myofibrillar proteins and subsequently affect the extent of proteolysis by calpain-1 in a protein-dependent manner.

Mitochondrial Degeneration, Depletion of NADH, and Oxidative Stress Decrease Color Stability of Wet-Aged Beef Longissimus Steaks

Interrelationship between mitochondria and myoglobin function influence beef color. NADH level in postmortem muscle is an important determinant of mitochondrial activity and metmyoglobin reduction. Increased aging time promotes discoloration of steaks; however, the mechanism of this effect is not clear. The objective was to characterize the role of wet-aging in beef longissimus lumborum muscle mitochondrial function and to characterize the global metabolome to determine the mechanism of that can regenerate NADH. Beef longissimus lumborum muscles were randomly assigned to 3, 7, 14, 21, and 28 days aging periods. Surface color, biochemical, mitochondrial, and metabolite profiles were determined at each aging period and at the end of 6-day display. During 6-day display, sections aged for 28 days had 30.4% decrease in redness than sections aged for 3 days. Aging time decreased (P <0.05) muscle oxygen consumption, mitochondrial protein content, and antioxidant capacity. Metabolites such as fumaric acid, creatinine, and fructose, that can take part in glycolytic/TCA cycle and regenerate NADH decreased (P <0.05) with aging and display time. In support, NADH levels also decreased (P <0.05) with aging time, but aging time had no effect (P = 0.44) on NADH-dependent reductase activity. The results suggest that decreased color stability in aged beef can be attributed to increased mitochondrial damage, depletion of metabolites that can regenerate NADH, and increased oxidative stress. PRACTICAL APPLICATION: Beef aging time results in increased discoloration of steaks under retail display. The current research determines the fundamental basis of lower color stability in aged beef. The results indicate that mitochondrial degeneration, depletion of metabolites that produce NADH, and increased oxidative stress can limit shelf-life of aged steaks. Hence, application of post-harvest strategies to minimize mitochondrial damage and oxidative changes may have the potential to increase shelf-life of aged beef.

Methods for Extraction of Muscle Proteins from Meat and Fish Using Denaturing and Nondenaturing Solutions

The objective of the present study was to test two extraction methods including solutions with different ionic strengths on the extraction and separation of the myofibrillar proteins from meat and fish muscles of different species. Meat samples from longissimus thoracis muscle of beef and lamb, pectoralis major muscle of chicken, and dorsal white muscle of fish from sole (Solea solea), European hake (Merluccius merluccius), and sea bass (Dicentrarchus labrax) were analyzed. The extraction method using nondenaturing solution led to a major extraction of high molecular-weight proteins as myosin heavy chain, α-actinin, and desmin; on the contrary, the denaturing method provided a good protein extractability of proteins and fragments with low molecular-weight as actin, troponin-T, tropomyosin, and myosin light chain 1 and 2 proteins for the most meat and fish samples. The nondenaturing extraction method showed several advantages resulting in time and labour saving and in minimizing the use of toxic and polluting agents.

Postmortem protein degradation is a key contributor to fresh pork loin tenderness

The objective of this study was to determine factors that influence tenderness independent of variation in pH, color, or marbling. To achieve the objective, 2 sample groups were chosen from a population of 159 pork loins aged 11 to 16 d. Predetermined ranges (ultimate pH, 5.54 to 5.86; marbling score, 1.0 to 3.0; percent total lipid, 1.61 to 3.37%) were defined for inclusion of individual loins in the study. The pork loins with the greatest ( = 12) and least ( = 12) Instron star probe values were assigned to 2 classification groups. The high star probe group had an average star probe that was 2.8 kg greater than the low star probe group (7.75 vs. 4.95 kg). Pork quality and sensory characteristics of pH, subjective and instrumental color values, cook loss, sensory tenderness, chewiness, juiciness, pork flavor, and off flavor were determined on fresh, never frozen pork chops. Lipid content, sarcomere length, myosin heavy-chain profile, and calpain autolysis were determined. Degradation of troponin-T, desmin, filamin, and titin were evaluated on the protein extracts from each sample. Pork loin pH, subjective color scores, Minolta L values, sarcomere length, and myosin heavy-chain composition were not different across groups. Chops from the low star probe group had a significantly greater marbling score (2.3 vs. 1.9) and lipid content (2.61 vs. 2.23%). Calpain-1 was completely autolyzed in both high and low star probe samples, demonstrating that calpain-1 potentially had been active in all samples. Low star probe whole-muscle protein extracts had more troponin-T ( < 0.01), desmin ( < 0.01), and filamin degradation ( < 0.01) than high star probe samples. Both classification groups showed degradation of titin. Remarkably, some high star probe samples still had observable intact bands of titin on SDS-PAGE gels. These results demonstrate that significant variation in instrumental tenderness is observed within a moderate pH range. Lipid content and proteolysis both appear to contribute to this variation.

Proteomic features linked to tenderness of aged pork loins

There is considerable evidence that the protein component of fresh pork makes a major contribution to tenderness. In particular, the proteomic profile can be linked to postmortem events including pH decline, tissue oxidation, and protein degradation. The objectives for this study were to determine differences in sarcoplasmic proteomes that contribute to tenderness variation in aged pork longissimus dorsi muscles (LM). A defined set of pork loins selected to be similar in pH, color, and lipid yet different in tenderness were used. Pork loins were assigned to tenderness groups based on their star probe values; a high star probe group (HSP; n=12 mean star probe 7.75 kg) and low star probe group (LPS; n=12 star probe 4.95 kg) Samples were selected for proteomic experiments based on star probe values, and selected samples were within specified ranges for ultimate pH (5.54-5.86), marbling score (1.0-3.0), and percent total lipid (1.61-3.37%). Two-dimensional difference in gel electrophoresis (2D-DIGE) and mass spectrometry were used to examine sarcoplasmic protein abundance and potential modifications. Proteins spots that were significantly different across groups were selected for identification. Results from 2D-DIGE showed that HSP samples had significantly more abundant metabolic, stress response, and regulatory proteins in the sarcoplasmic fraction compared with LSP samples. The stress response protein peroxiredoxin-2 was more abundant in HSP samples as determined by 2D-DIGE ( ≤ 0.01; 2 spots) and western blot assay ( = 0.02). Low star probe samples showed significantly more degradation of the structural protein desmin in 2D-DIGE ( < 0.01) and western blot assay ( < 0.01). These results demonstrate that extreme proteolytic differences influenced measured tenderness of LSP and HSP samples and that soluble desmin and peroxiredoxin-2 may be used as biomarkers to differentiate between tough and tender aged pork products.

Phosphorylation prevents in vitro myofibrillar proteins degradation by μ-calpain

Myofibrillar proteins degradation contributes to meat tenderisation during post-mortem ageing. Protein phosphorylation has been revealed to be associated with meat tenderness in recent years. This study was undertaken to determine the impact of myofibrillar proteins phosphorylation on the degradation susceptibility by μ-calpain. Myofibrillar proteins were first incubated with protein kinase A (PKA) or alkaline phosphatase (AP) to increase or decrease the phosphorylation level, following μ-calpain hydrolysis. Myosin heavy chain, actin, desmin and troponin T showed different levels of degradation in control, AP and PKA groups under different Ca²⁺ concentrations. Generally, more degradation products were detected with the increase of Ca²⁺ concentration. Compared to the control, the protein degradation was higher in AP-treated group and lower in PKA-treated group. This study shows that phosphorylation prevents proteolytic susceptibility of myofibrillar proteins to degradation by μ-calpain, indicating that protein phosphorylation plays an important role in meat tenderisation during post-mortem ageing.

Proteomic and peptidomic differences and similarities between four muscle types from New Zealand raised Angus steers

Four muscles from New Zealand-raised Angus steers were evaluated (musculus semitendinosus, m. longissimus thoracis et lumborum, m. psoas major and m. infraspinatus) to test their differences and common features in protein and peptide abundances. The ultimate goal of such a comparison is to match muscle types to products with targeted properties. Protein profiling based on two-dimensional electrophoresis showed that the overall profiles were similar, but, between muscle types, significant (p<0.05) intensity differences were observed in twenty four protein spots. Profiling of endogenous peptides allowed characterisation of 346 peptides. Quantitative analysis showed a clear distinction between the muscle types. Forty-four peptides were identified that showed a statistically significant (p<0.05) and substantial (>2-fold change) difference between at least two muscle types. These analyses demonstrate substantial similarities between these four muscle types, but also clear distinctions in their profiles; specifically a 25% difference between at least two muscles at the peptidomic level, and a 14% difference at the proteomic level.

Coherent correlation networks among protein biomarkers of beef tenderness: What they reveal

The development of proteomic biomarkers for meat tenderness remains an important challenge. The present study used Longissimus thoracis (LT) and Semitendinosus (ST) muscles of young bulls of three continental breeds (Aberdeen Angus, Blond d'Aquitaine and Limousin) to i) identify cellular pathways robustly related with meat tenderness, using potential protein biomarkers and ii) describe biochemical mechanisms underlying muscle to meat conversion. Correlation networks reveal robust correlations, i.e. present for at least two breeds, between potential meat tenderness biomarkers. For the two muscles of the three breeds, DJ-1 and Peroxiredoxin 6 were consistently correlated with Hsp20 and μ-calpain, respectively. For the three breeds, μ-calpain was related to Hsp70-8 in the LT muscle. Various correlations were muscle specific. For the three breeds, DJ-1 was correlated with Hsp27 for the ST, and with ENO3 and LDH-B for the LT muscle. Overall, in the LT, more correlations were found between proteins related to the glycolytic pathway and in the ST, with the small Hsps (Hsp20, 27 and αB-crystallin). Hsp70-Grp75 appeared involved in several relevant biological pathways. At the scientific level, results give insights in biological functions involved in meat tenderness. Further studies are needed to confirm the possible use of these biomarkers in the meat industry to improve assurance of good meat qualities.

Molecular characterization of porcine PGM1 gene associated with meat quality traits

Hwang, J. H., Kwon, S. G., Park, D. H., Kim, T. W., Kang, D. G., Ha, J., Kim, S. W. and Kim, C. W. 2015. Molecular characterization of porcine PGM1 gene associated with meat quality traits. Can. J. Anim. Sci. 95: 31–36. The PGM1 gene from four porcine breeds (Berkshire, Duroc, Landrace, and Yorkshire) is highly expressed in liver tissue at the transcriptional level. Single nucleotide polymorphisms (SNPs) of PGM1 were examined to analyze association with increased expression of PGM1 gene in the Berkshire liver. A Leu525 synonymous SNP of Chr6:137174682A>G (c.1575A>G) was identified and showed significant (P<0.05) differences to backfat thickness, drip loss, protein content, fat content, Warner–Bratzler shear force, and post-mortem pH24h. Therefore, it is concluded that PGM1 synonymous SNP is an important factor regulating meat quality.

Effect of low voltage electrical stimulation on protein and quality changes in bovine muscles during postmortem aging

This experiment was conducted to determine the influence of low voltage electrical stimulation (ES) on the tenderness development of beef round muscles. Eight steers were slaughtered, and ES applied to one side of each carcass within 90 min of exsanguination. Steaks from M. longissimus dorsi, semimembranosus, adductor, and gracilis were vacuum packaged and aged at 4 °C for 9 d. Star probe, sensory evaluation, Western blot assays of troponin-T and μ-calpain autolysis and 2D-DIGE were conducted. ES resulted in accelerated (P<0.05) pH decline of the longissimus in the first 24h postmortem. ES did not influence (P>0.05) proteolysis and tenderness, but did alter the predominance of metabolic proteins in the soluble fraction of muscle. Aging for 9 d improved tenderness (P<0.05). The data confirmed that low voltage ES at 90 min of exsanguination had no effect on proteolysis and tenderness development in the longissimus dorsi, semimembranosus, adductor or gracilis in beef.