In-depth characterization of the sarcoplasmic muscle proteome changes in lambs fed with hazelnut skin by-products: Relationships with meat color

This study investigated the effect of agro-industrial hazelnut skin by-products supplementation on lamb meat color variation and the changes in the sarcoplasmic muscle proteome during post-mortem storage (0, 4 and 7 days). Gel-based proteomics and bioinformatics approaches were applied to better understand the potential role of feeding strategies in modulating the mechanisms underpinning meat discoloration and post-mortem changes during storage. Therefore, twenty-two Valle del Belice male lambs were randomly assigned to two dietary treatments: control (C), lambs fed with maize-barley diet, and hazelnut skin (H), lambs fed hazelnut skin by-product as maize partial replacer in the concentrate diet. Hazelnut dietary treatment led to better lamb meat color stability as evidenced by the lowest decrease in redness and saturation index values. Proteomics and bioinformatics results revealed changes in the abundance of 41 proteoforms, which were mainly involved in glycolytic processes, responses to oxidative stress, and immune and endocrine system. The proteins allowed revealing interconnected pathways to be behind meat color variation as a consequence of using hazelnut skin by-products to sustainable feed lamb. The proteins can be used as potential predictors of lamb meat color variation. Accordingly, the regression equations developed in this paper revealed triosephosphate isomerase (TPI1) as a reliable candidate biomarker of color stability in lamb meat. SIGNIFICANCE: The use of agro-industrial by-products in animal feeding can be a potential sustainable strategy to reduce the environmental impacts of the food production chain and consequently improve animal welfare and product quality. The inclusion of hazelnut skin by-products in the animal's diet, due to the high concentration of polyphenols, represents an effective strategy to improve the oxidative stability of meat, with significant implications on color. The use of proteomics combined with bioinformatics on the sarcoplasmic proteome is a powerful approach to decipher the underlying mechanism. Accordingly, this approach allowed in this trial a deeper understanding of the molecular mechanisms involved in the post-mortem processes through the discovery of several biological pathways linked with lamb meat color variation. Glycolysis, followed by responses to oxidative stress, and other proteins involved in the immune and endocrine system were found as the major interconnected pathways that could act as potential predictors of lamb meat color stability. Candidate proteins biomarkers were further revealed in this study to be related with multiple meat color traits.

Application of 2-D DIGE to study the effect of ageing on horse meat myofibrillar sub-proteome

Considering the high relevance of meat tenderness for consumer acceptability, the aim of this study was to investigate post-mortem changes in myofibrillar sub-proteome in steaks from longissimus thoracis et lumborum muscle of six Hispano-Bretón horses. Indeed, the ageing process that leads to meat tenderization has been scarcely studied in this species. Steaks (n = 24) were aged (4 °C) in the dark under vacuum for 0, 7, 14 and 21 days and the myofibrillar sub-proteome was extracted. Using 2-D DIGE minimal labelling, 35 spots that were differentially abundant between 0 and 21 days aged meat were detected. Of them, 24 were analysed by LC-MS/MS, identifying a total of 29 equine proteins. These were structural and metabolic proteins, and among them, four (Actin, Troponin T and Myosin binding proteins 1 and 2) were selected for Western blot analysis, reporting changes in their abundance after 0, 7, 14 and 21 days of ageing. Results revealed that they should be further studied as potential protein biomarkers of horse meat tenderization. Additionally, several protein fragments increased after ageing, as was the case of glyceraldehyde-3-phosphate dehydrogenase. Fragments of this protein were present in four protein spots, and their study could be useful for monitoring horse meat tenderization. SIGNIFICANCE: Tenderization during ageing has been widely studied in meat from several farm animal species; however, both research and standardized ageing practices are lacking for the particular case of horse meat. In this regard, this study presents novel proteomic findings related to post-mortem evolution of horse muscle proteins. Acquired knowledge would support the development and optimization of efficient ageing practices by horse meat industry.

Early postmortem muscle proteome and metabolome of beef longissimus thoracis muscle classified by pH at 6 hours postmortem

The objective was to identify metabolome and proteome differences at 1 h and 1 d postmortem between longissimus thoracis (LT) muscle classified based on 6 h pH values. Twenty beef LT rib sections were sorted based on 6 h postmortem pH values into low (LpH; pH < 5.55; n = 9) and high (HpH; pH > 5.84; n = 8) pH classifications. Warner-Bratzler shear force (WBSF), desmin degradation, and calpain-1 autolysis were measured. Two-dimensional difference in gel electrophoresis (3-10, 4-7, and 6-9 pH range) and Tandem mass tagging (TMT) protein analyses were employed to determine how the sarcoplasmic protein profile varied across pH classification. Non-targeted metabolomic analyses were conducted on extracts prepared at 1 h and 1 d postmortem. The LpH classification had a lower WBSF value at 1 d postmortem, which was explained by greater calpain-1 autolysis and desmin degradation at 1 d postmortem. Proteome and metabolome analysis revealed a phenotype that promotes more rapid energy metabolism in the LpH group. Proteome and metabolome analyses identified energy production, apoptotic, calcium homeostasis, and proteasome systems influencing pH classifications that could explain the observed pH, proteolysis, and beef tenderness differences. SIGNIFICANCE: This study is the first to identify proteomic and metabolomic variations early (1 h and 1 day) postmortem that are linked to differences in early (6 h) postmortem pH values and to tenderness differences at 1 day postmortem. This study integrates postmortem biochemical features (protein degradation, proteome, and metabolome variations) to postmortem pH decline and eating quality of beef steaks. Potential biomarkers of more rapid postmortem metabolism linked to earlier tenderization in beef are suggested. Identification of these biochemical features will assist in predicting the eating quality of beef products.

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.

Partial Purification of Peroxiredoxin-2 From Porcine Skeletal Muscle

Fresh meat quality is adversely affected by protein oxidation. However, a fundamental understanding of the diverse factors that influence protein oxidation in postmortem muscle remains elusive. Peroxiredoxin-2 (Prdx2), an antioxidant protein, is more abundant in tough meat based on instrumental tenderness; however, the role of Prdx2 in postmortem skeletal muscle is unknown. Therefore, the objective was to develop a method to purify Prdx2 from the diaphragm, psoas major, and longissimus lumborum. Proteins soluble at low ionic strength were extracted, dialyzed, clarified, and loaded onto a Q-Sepharose anion exchange column equilibrated with TEM (pH 7.4). In all preparations, Prdx2 eluted between about 75 and 115 mM NaCl. Immunoreactive fractions were dialyzed against TEM (pH 8.0), clarified, and loaded onto a DEAE-650S anion exchange column. In all preparations, Prdx2 eluted between approximately 55 and 75 mM NaCl. Immunoreactive fractions were concentrated and loaded onto a Superose-12 size exclusion column. Prdx2 was detected between 14 and 16 mL, and these fractions were concentrated and reduced with 0.5% 2-mercaptoethanol. A final pass over the Superose-12 column was conducted, and Prdx2 was detected in 2 peaks from 11–12 mL and 15–16 mL. Fractions 15–16 were pooled and retained for further experiments. The elution profile of Prdx2 in all 3 muscles was similar. The iden- tification of the primary protein was confirmed with liquid chromatography with tandem mass spectrometry. The purity of Prdx2 off the final Superose-12 column was approximately 33%, 52%, and 47% pure in the diaphragm, psoas major, and longissimus lumborum, respectively. This is the first report of a method to partially purify Prdx2 from skeletal muscle.

Contribution of Early-Postmortem Proteome and Metabolome to Ultimate pH and Pork Quality

This study's objectives were to identify how subtle differences in ultimate pH relate to differences in pork quality and to understand how early-postmortem glycolysis contributes to variation in ultimate pH. The hypothesis was that elements in early-postmortem longissimus thoracis et lumborum proteome and metabolome could be used to predict quality defects associated with pH decline. Temperature and pH of the longissimus thoracis et lumborum were measured at 45 min, 24 h, and 14 d postmortem. Quality measurements were made after 14 d of aging. Groups were classified as normal pH (NpH; x̄ = 5 . 59 [5.53–5.67]; NpH, n = 10) and low pH (LpH; x̄ = 5 . 42 [5.38–5.45]; LpH, n = 10) at 14 d postmortem. Metabolites from 45 min postmortem were identified using GC-MS. Relative differences between proteins were quantified with two-dimensional difference in gel electrophoreses, and spots were identified with MALDI-MS. Western blot analyses were used to measure phosphofructokinase, peroxiredoxin-2, and reduced and non-reduced adenosine monophosphate deaminase-2 at 45 min and 14 d postmortem. Ultimate pH classification did not affect 45-min-postmortem pH (P = 0.64); 14-d pH was different between groups (P &lt; 0.01). NpH had less purge loss (P &lt; 0.01), was darker (P &lt; 0.01), had lower star probe (P &lt; 0.01), and had less intact day-7 desmin (P = 0.02). More pyruvate (P = 0.01) and less lactate (P = 0.09) was observed in NpH, along with more soluble lactate dehydrogenase (P = 0.03) and pyruvate kinase (P &lt; 0.10). These observations indicate that differences in enzyme abundance or solubility may produce more pyruvate and less lactate. Fructose 6-phosphate was more abundant (P = 0.08) in the LpH group, indicating that phosphofructokinase may be involved in glycolytic differences. Furthermore, greater abundance of heat shock proteins, peroxiredoxin-2 (P = 0.02), and malate (P = 0.01) early postmortem all suggest differences in mitochondrial function and oxidative stability that contribute to quality differences. These results show that even subtle changes in ultimate pH can influence pork quality. The proteome and metabolome at 45 min postmortem are associated with variation in the extent of pH decline.