Comparison of activity, expression and S-nitrosylation of glycolytic enzymes between pale, soft and exudative and red, firm and non-exudative pork during post-mortem aging

Inhibition of pyruvate dehydrogenase accelerates anaerobic glycolysis under postmortem simulating conditions

This research aimed to explore the potential influence of mitochondria on the rate of anaerobic glycolysis. We hypothesized that mitochondria could reduce the rate of anaerobic glycolysis and pH decline by metabolizing a portion of glycolytic pyruvate. We utilized an in vitro model and incorporated CPI-613 and Avidin to inhibit pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC), respectively. Four treatments were tested: 400 μM CPI-613, 1.5 U/ml Avidin, 400 μM CPI-613 + 1.5 U/ml Avidin, or control. Glycolytic metabolites and pH of the in vitro model were evaluated throughout a 1440-min incubation period. CPI-613-containing treatments, with or without Avidin, decreased pH levels and increased glycogen degradation and lactate accumulation compared to the control and Avidin treatments (P < 0.05), indicating increased glycolytic flux. In a different experiment, two treatments, 400 μM CPI-613 or control, were employed to track the fates of pyruvate using [13C6]glucose. CPI-613 reduced the contribution of glucose carbon to tricarboxylic acid cycle intermediates compared to control (P < 0.05). To test whether the acceleration of acidification in reactions containing CPI-613 was due to an increase in the activity of key enzymes of glycogenolysis and glycolysis, we evaluated the activities of glycogen phosphorylase, phosphofructokinase, and pyruvate kinase in the presence or absence of 400 μM CPI-613. The CPI-613 treatment did not elicit an alteration in the activity of these three enzymes. These findings indicate that inhibiting PDH increases the rate of anaerobic glycolysis and pH decline, suggesting that mitochondria are potential regulators of postmortem metabolism.

S-nitrosoproteomics profiling elucidates the regulatory mechanism of S-nitrosylation on beef quality

This study aimed to quantitively profile the S-nitrosylation in beef semimembranosus (SM) with different treatments (nitric oxide donor or nitric oxide synthase inhibitor) by applying iodoTMT-based nitrosoproteomics. Results showed that 2096 S-nitrosylated cysteine sites in 368 proteins were detected in beef SM. Besides, differential SNO-modified proteins were screened, some of which were involved in crucial biochemical pathways, including calcium-releasing-related proteins, energy metabolic enzymes, myofibrils, and cytoskeletal proteins. GO analysis indicated that differential proteins were localized in a wide range of cellular compartments, such as cytoplasm, organelle, and mitochondrion, providing a prerequisite for S-nitrosylation exerting broad roles in post-mortem muscles. Furthermore, KEGG analysis validated that these proteins participated in the regulation of diverse post-mortem metabolic processes, especially glycolysis. To conclude, changes of S-nitrosylation levels in post-mortem muscles could impact the structure and function of crucial muscle proteins, which lead to different levels of muscle metabolism and ultimately affect beef quality.

Multi-omics in food safety and authenticity in terms of food components

One of the main goals of food science is to ensure the high quality and safety of food. The inspection technology for known hazards has matured, and the identification of unknown and potential food safety hazards, as well as the identification of their composition and origin, is a challenge faced by food safety. Food safety and authenticity require multi-omics methods to support the implementation of qualitative discrimination to precise quantitative analysis, from targeted screening to non-target detection, and from multi component to full component analysis to address these challenges. The present review aims to provide characterizations, advantages, the latest progress, and prospects of using omics (including genomics, proteomics, and metabonomics) in food safety and authenticity. Multi omics strategies used to detect and verify different standard biomarkers of food will contribute to understanding the basic relationship between raw materials, processing, foods, nutrition, food safety, and human health.

Modification-Specific Proteomic Analysis Reveals Cysteine S-Nitrosylation Mediated the Effect of Preslaughter Transport Stress on Pork Quality Development

This study aimed to explore the effects of preslaughter transport stress on protein S-nitrosylation levels and S-nitrosylated proteome in post-mortem pork longissimus thoracis (LT) muscle. Pigs (N= 16) were randomly divided into 3 h transport (high-stress group, HS) and 3 h transport followed by 3 h resting treatments (low-stress control group, LS). Results demonstrated that high transport stress levels induced nitric oxide (NO) overproduction by promoting NO synthase (NOS) activity and neuronal NOS (nNOS) expression, which thereby notably increased protein S-nitrosylation levels in post-mortem muscle (p < 0.05). Proteomic analysis indicated that 133 S-nitrosylation-modified cysteines belonging to 85 proteins were significantly differential, of which 101 cysteines of 63 proteins were higher in the HS group (p < 0.05). Differential proteins including cytoskeletal and calcium-handling proteins, glycolytic enzymes, and oxidoreductase were mainly involved in the regulation of muscle contraction and energy metabolism that might together mediate meat quality development. Overall, this study provided direct evidence for changes in S-nitrosylation levels and proteome in post-mortem muscle in response to preslaughter transport stress and revealed the potential impact of S-nitrosylated proteins on meat quality.

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.

Validation of protein biological markers of lamb meat quality characteristics based on the different muscle types

This work investigated the ability of 8 potential biomarkers (phosphoglycerate kinase-1 (PGK1), pyruvate kinase-M2 (PKM2), phosphoglucomutase-1 (PGM1), β-enolase (ENO3, myosin-binding protein-C (MYBPC1), myosin regulatory light chain-2 (MYLPF), troponin C-1 (TNNC1) and troponin I-1 (TNNI1)) to characterize meat quality by analyzing their relative abundance and enzymatic activity. Two different meat quality groups (Quadriceps femoris (QF) and Longissimus thoracis (LT) muscles) were selected at 24 h postmortem from 100 lamb carcasses. The relative abundance of PKM2, PGK1, PGM1, ENO3, MYBPC1, MYLPF, and TNNI1 was significantly different between LT and QF muscle groups (P < 0.01). Moreover, PKM, PGK, PGM, and ENO activity in LT muscle group was significantly lower than that in QF muscle (P < 0.05). Suggesting that PKM2, PGK1, PGM1, ENO3, MYBPC1, MYLPF, and TNNI1 can be used as robust biomarkers of lamb meat quality, providing the reference for understanding the molecular mechanism of postmortem meat quality formation in future.

Targeted energy metabolomics analysis of postmortem pork in an in vitro model as influenced by protein S-nitrosylation

For exploring the effect of protein S-nitrosylation on the energy metabolism of early postmortem pork (within 24 h postmortem), the six Longissimus thoracis (LT) muscle homogenates were treated with nitric oxide donor (NOR-3, (±)-(E)-4-Ethyl-2-(E)-hydroxyimino-5-nitro-3-hexenamide), nitric oxide synthase (NOS) inhibitor (L-NAME, Nω-nitro-L-arginine methyl ester hydrochloride) and control (0.1 M K₂HPO₄, pH 7.4) in the in vitro buffer system for 24 h, respectively. The western blotting result showed that NOR-3 treatment led to a greater level of protein S-nitrosylation (p < 0.05). However, S-nitrosylation levels had no significant difference between L-NAME and control groups (p > 0.05). In addition, results showed that 16 significantly differential energy metabolites were identified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and clearly separated among three groups in the principal component analysis. Four pathways (glycolysis, tricarboxylic acid cycle, purine metabolism and pentose phosphate pathway) related to energy metabolism were significantly influenced by different levels of protein S-nitrosylation. Furthermore, the correlation analysis of metabolites demonstrated that metabolites were in dynamic equilibrium with each other. These results indicate that protein S-nitrosylation can participate in and regulate energy metabolism postmortem pork through glycolysis and tricarboxylic acid (TCA) cycle.

Effect of Nitric Oxide and Its Induced Protein S-Nitrosylation on the Structures and In Vitro Digestion Properties of Beef Myofibrillar Protein

This study aimed to investigate the effects of nitric oxide (NO) and its induced protein S-nitrosylation on the structures and digestion properties of beef myofibrillar protein (MP). The MP was treated with 0, 50, 250, 500, and 1000 μM concentrations of NO-donor S-nitrosoglutathione (GSNO) for 30 min at 37 °C. The results indicated that GSNO treatment significantly decreased the sulfhydryl contents whereas the carbonyl contents increased. Meanwhile, compared with the control group, the surface hydrophobicity, the intrinsic fluorescence intensity, and the α-helix content of proteins were decreased significantly with the enhancement of GSNO concentrations. In addition, 250 μM GSNO treatment increased the gastric digestibility of MP, while the gastrointestinal digestibility and the release of peptides were both inhibited by 500 and 1000 μM GSNO treatments. These data demonstrate that protein S-nitrosylation can affect the in vitro digestion properties of proteins by altering the physicochemical properties and structure of MP.

H2O2-induced oxidative stress improves meat tenderness by accelerating glycolysis via hypoxia-inducible factor-1α signaling pathway in postmortem bovine muscle

Reactive oxygen species (ROS) affect meat quality through multiple biochemical pathways. To investigate the effect of ROS on postmortem glycolysis and tenderness of bovine muscle, ROS content, glycolytic potential, glycolysis rate-limiting enzyme activities, expression of hypoxia-inducible factor-1α (HIF-1α), phosphatidylinositol 3-kinase (PI3K), serine-threonine kinase (AKT), phosphorylated AKT (p-AKT), and tenderness were determined in the H₂O₂ group and control group. Results showed that the H₂O₂ group exhibited significantly higher ROS content within 48 h, coupled with increased glycolytic potential, pH decline, hexokinase (HK), and phosphofructokinase activities (PFK) early postmortem. These were attributed to ROS-induced PI3K/AKT signaling pathway activation and resultant HIF-1α accumulation. Moreover, shear force in the H₂O₂ group reached the peak 12 h earlier and decreased obviously after 24 h, accompanied by a significantly higher myofibril fragmentation index (MFI). These findings suggested that ROS drive HIF-1α accumulation by activating PI3K/AKT signaling pathway, thereby accelerating glycolysis and tenderization of postmortem bovine muscle.

Antimicrobial mechanism of linalool against Brochothrix thermosphacta and its application on chilled beef

This work aimed to explore the antibacterial ability and potential mechanism of linalool against Brochothrix thermosphacta (B. thermosphacta), providing knowledge of the preservation of chilled beef with linalool. The results found that linalool had an encouraging inhibitory effect on B. thermosphacta with a minimum inhibitory concentration (MIC) of 1.5 mL/L. Results of FESEM and zeta potential combined with probe labeling confirmed that linalool destroyed the cell structure thereby causing the leakage of intracellular components (AKP, protein, nucleic acid and ion). In addition, linalool caused respiratory disturbance by measuring the key enzyme activities including PK, SDH, MDH and ATPase. Energy limitation also appeared under linalool stress as seen from changes in ATP content (decreased by 56.06% and 69.24% in MIC and 2MIC groups, respectively). The respiratory inhibition rate of linalool to B. thermosphacta was 23.58% and the superposing rate with malonic acid was minimal (35.52%), suggesting that respiratory depression was mainly caused by the TCA cycle. Furthermore, accumulation of ROS and increase in MDA content (increased by 71.17% and 78.03% in MIC and 2MIC groups, respectively) accompanied by decreased activities of detoxification enzymes CAT and POD suggested that oxidative stress contributed to the bactericidal mechanism. Finally, linalool has been shown to effectively inhibit quality deterioration of chilled beef during storage by measuring pH, TVB-N and TVC without affecting sensory acceptability. All these highlight the great promise of using linalool as natural preservative for food industry.

Antibacterial Activity and Mechanism of Polygonum orientale L. Essential Oil against Pectobacterium carotovorum subsp. carotovorum

Infected by Pectobacterium carotovorum subsp. carotovorum (Pcc), the quality of Chinese cabbage could severely decline. Using chemical bactericides to control Pcc could cause food safety problems. Thus, we investigated the optimum extraction conditions, antibacterial activity, chemical compounds and antibacterial mechanism of Polygonum orientale L. essential oil (POEO) against Pcc in order to search a new way to control Pcc. The optimum extraction conditions of POEO (soaking time 2.6 h, extraction time 7.7 h and ratio of liquid to solid 10.3 mL/g) were optimized by response surface methodology. The minimum inhibitory concentration (MIC) of POEO against Pcc was 0.625 mg/mL. The control efficiency of protective activity of POEO against Pcc was 74.67~92.67%, and its curative activity was 76.00~93.00%. Then, 29 compounds were obtained by GC-MS; the prime compounds of POEO were phytol, phytone, n-pentacosane, 1-octen-3-ol and β-ionone. It was verified that, compared with control samples, POEO destroyed cell morphology. It increased surface potential, increased hydrophobicity, damaged cell walls, destroyed the integrity and permeability of cell membrane, reduced membrane potential (MP), and changed membrane protein conformation. It inhibited the activities of pyruvate kinase (PK), succinate dehydrogenase (SDH) and adenosine triphosphatase (ATPase). Briefly, the results of this study demonstrate that POEO showed effective inhibitory activity against Pcc, thus POEO could have potential application in controlling Pcc.

The effect of postmortem pH decline rate on caspase-3 activation and tenderness of bovine skeletal muscle during aging

This study aimed to investigate the effect of postmortem pH decline rate on caspase-3 activity and bovine muscle tenderness during aging. Protein denaturation, reactive oxygen species (ROS) levels, mitochondrial apoptosis factors, and shear force were assessed in bovine muscles with different pH decline rates. The results showed that, compared with the slow group, the fast pH decline group had a 1.79% and 1.39% higher sarcoplasmic protein denaturation at 6 and 12 h, respectively (p < .05), and a significantly or extremely significantly higher ROS levels at 6-24 (p < .05, p < .01). Moreover, the fast group had a 14.05%, 22.39%,18.34%, and 25.28% of higher mitochondrial dysfunction at 6, 12, 24, and 72 h, respectively (p < .05); a 16.71%, 23.39%, 17.05%, and 26.61% of lower cytochrome c reduction levels at 6, 12, 24, and 120 h, respectively (p < .05); a significantly increased caspase-3 activity and proportion of apoptotic nuclei at 12-168 and 24-168 h, respectively (p < .05); and a 5.70%, 7.24%, 12.16%, 10.10% and 10.49% decreased shear force at 12, 24, 72,120, and 168 h, respectively (p < .05). These results demonstrated that the fast postmortem pH decline enhanced caspase-3 activation and bovine muscle tenderization by mitochondrial dysfunction-induced apoptosis during aging. PRACTICAL APPLICATIONS: Beef tenderness has long been one of the most important concerns for consumers and the meat industry. To date, the postmortem aging process has been an effective way to improve the tenderness of chilled beef. However, changes in many of the elements in a cattle's muscle after slaughter might actually determine the final tenderness of the meat. The present study suggested that the fast postmortem pH decline could promote the activation of caspase-3 and improve the tenderness of beef during aging. This finding can provide a basis for the meat processing industry to produce beef with high tenderness. In the future, beef tenderness could even be improved by adjusting the glycolytic rate and pH of muscle for a short time after slaughter.

Housekeeping Proteins in Meat Quality Research: Are They Reliable Markers for Internal Controls in Western Blot? A Mini Review

Advancements in technology and analytical methods enable researchers to explore the biochemical events that cause variation in meat quality. Among those, western blot techniques have been successfully used in identifying and quantifying the key proteins that have critical functions in the development of meat quality. Housekeeping proteins, like β-actin, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and tubulins are often used as internal controls in western blots to normalize the abundance of the protein of interest. However, there are increasing concerns about using housekeeping proteins for western blot normalization, as these proteins do not demonstrate any loading differences above the relatively small total protein loading amounts of 10μg. In addition, the interaction between these housekeeping proteins and programmed cell death processes highlights the concerns about using the housekeeping protein as the internal control in meat quality research. Moreover, recent proteomic research has indicated that the abundance of some housekeeping proteins, like β-actin, GAPDH, and tubulin, can be altered by preslaughter stress, dietary supplementation, sex, slaughter method, genotype, breed, aging period, muscle type, and muscle portion. Furthermore, these housekeeping proteins could have differential expression in meat with differing color stability, tenderness, and water holding capacity. Therefore, this review aims to examine the realities of using housekeeping proteins as the loading control in meat quality research and introduce some alternative methods that can be used for western blot normalization.

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.

Antimicrobial Activity and Proposed Action Mechanism of Linalool Against Pseudomonas fluorescens

In this study, linalool, one of the principal components of essential oils, was used as an antibacterial agent to investigate the antibacterial activity and mechanism of linalool against Pseudomonas fluorescens. The reduction in membrane potential (MP), leakage of alkaline phosphatase (AKP) and the release of macromolecules, including DNA, RNA and protein confirmed that damage to cell wall membrane structure and leakage of cytoplasmic contents were due to the linalool treatment. Furthermore, the decrease of enzyme activity, including the succinate dehydrogenase (SDH), malate dehydrogenase (MDH), pyruvate kinase (PK), and ATPase indicated that linalool could lead to metabolic dysfunction and inhibit energy synthesis. In addition, the activity of respiratory chain dehydrogenase and metabolic activity of respiration indicated that linalool inhibits cellular respiration. These results revealed that linalool had strong antibacterial activity against P. fluorescens via membrane damage, bacterial metabolic and oxidative respiratory perturbations, interfering in cellular functions and even causing cell death. It was suggested that linalool may be a new potential source as food antiseptics in food systems.

Antibacterial Activity and Mechanism of Linalool against Shewanella putrefaciens

The demand for reduced chemical preservative usage is currently growing, and natural preservatives are being developed to protect seafood. With its excellent antibacterial properties, linalool has been utilized widely in industries. However, its antibacterial mechanisms remain poorly studied. Here, untargeted metabolomics was applied to explore the mechanism of Shewanella putrefaciens cells treated with linalool. Results showed that linalool exhibited remarkable antibacterial activity against S. putrefaciens, with 1.5 µL/mL minimum inhibitory concentration (MIC). The growth of S. putrefaciens was suppressed completely at 1/2 MIC and 1 MIC levels. Linalool treatment reduced the membrane potential (MP); caused the leakage of alkaline phosphatase (AKP); and released the DNA, RNA, and proteins of S. putrefaciens, thus destroying the cell structure and expelling the cytoplasmic content. A total of 170 differential metabolites (DMs) were screened using metabolomics analysis, among which 81 species were upregulated and 89 species were downregulated after linalool treatment. These DMs are closely related to the tricarboxylic acid (TCA) cycle, glycolysis, amino acid metabolism, pantothenate and CoA biosynthesis, aminoacyl-tRNA biosynthesis, and glycerophospholipid metabolism. In addition, linalool substantially affected the activity of key enzymes, such as succinate dehydrogenase (SDH), pyruvate kinase (PK), ATPase, and respiratory chain dehydrogenase. The results provided some insights into the antibacterial mechanism of linalool against S. putrefaciens and are important for the development and application of linalool in seafood preservation.

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.