pH inactivation of phosphofructokinase arrests postmortem glycolysis

Investigation of guanidino acetic acid and rumen-protected methionine induced improvements in longissimus lumborum muscle quality in beef cattle

This study examined the impact of dietary guanidino acetic acid (GAA) and rumen-protected methionine (RPM) on beef quality in Simmental bulls. For 140 days, forty-five bulls (453.43 ± 29.05 kg) were randomly divided into control (CON), 0.1% GAA (GAA), and 0.1% GAA + 0.1% RPM (GAM) groups with 15 bulls in each group and containing 3 pen with 5 bulls in each pen. Significant improvements in eye muscle area, pH48h, redness (a*) value, and crude protein (CP) content of longissimus lumborum (LL) muscles were observed in the GAA and GAM groups (P < 0.05). Conversely, the lightness (L*) value, drip loss, cooking loss, and moisture contents decreased (P < 0.05). Additionally, glutathione (GSH) and glutathione peroxidase (GSH-PX) concentrations of LL muscles in GAM were higher (P < 0.05), while malondialdehyde (MDA) content of LL muscles in GAA and GAM groups were lower (P < 0.05). Polyunsaturated fatty acids (PUFA) profiles were enriched in beef from GAM group (P < 0.05). The addition of GAA and RPM affected the expression of genes in LL muscle, such as HMOX1, EIF4E, SCD5, and NOS2, which are related to hypoxia metabolism, protein synthesis, and unsaturated fatty acid synthesis-related signaling pathways. In addition, GAA and RPM also affected the content of a series of metabolites such as L-tyrosine, L-tryptophan, and PC (O-16:0/0:0) involved in amino acid and lipid metabolism-related signaling pathways. In summary, GAA and RPM can improve the beef quality and its nutritional composition. These changes may be related to changes in gene expression and metabolic pathways related to protein metabolism and lipid metabolism in beef.

Dynamic changes of protein lactylation and their correlations with the glycolytic process during the postmortem acidification of broiler breast

This experiment aimed to reveal the dynamic changes of protein post-translational lactylation modifications and their correlations with the glycolytic process in broiler breast muscle within 48 h of postmortem acidification. The experiment involved 12 male AA broilers, 42 days old, with similar body weights (2.8 ± 0.05 kg). The breast fillets (Pectoralis major) were collected after slaughter, and samples were taken at various time points: 0, 15 min, 30 min, 45 min, 60 min, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, 24 h, 36 h, and 48 h postmortem. The results showed that the rate of glycogen decline in the muscle was highest at 45 min postmortem, and glycogen levels tended to stabilize at 8 h postmortem. The lactate content in the breast reached its highest level at 4 h postmortem and began to decrease, stabilizing at 24 h postmortem. Additionally, the glycolytic potential increased gradually in the first 4 h postmortem, decreased rapidly from 4 to 8 h. Similarly, lactylation modification levels were highest at 8 h postmortem, but stabilized at 12 h postmortem. During this process, the protein expression of the enzymatic lactylation modifier p300 showed no significant difference, while the content of the nonenzymatic lactylation substrate lactoylglutathione significantly decreased at 8 h and 24 h postmortem. Correlation analysis found that lactylation levels were negatively correlated with glycogen content, glucose content, glycolytic potential, and pH value, while positively correlated with lactate content. Besides, there was a positive correlation between lactylation levels and the protein expression of hexokinase, phosphoglycerate kinase 2, phosphoglucomutase 1, and triosephosphate isomerase. Additionally, lactylation levels were positively correlated with the activities of lactate dehydrogenase and phosphofructokinase. In summary, our experiment elucidated the dynamic changes in the entire glycolytic pathway in broiler pectoral muscle during acidification. During this process, lactylation modifications may participate in the glycolysis process by regulating the protein expression and activity of glycolytic enzymes.

Analysis of phosphofructokinase-1 activity as affected by pH and ATP concentration

A key player in energy metabolism is phosphofructokinase-1 (PFK1) whose activity and behavior strongly influence glycolysis and thus have implications in many areas. In this research, PFK1 assays were performed to convert F6P and ATP into F-1,6-P and ADP for varied pH and ATP concentrations. PFK1 activity was assessed by evaluating F-1,6-P generation velocity in two ways: (1) directly calculating the time slope from the first two or more datapoints of measured product concentration (the initial-velocity method), and (2) by fitting all the datapoints with a differential equation explicitly representing the effects of ATP and pH (the modeling method). Similar general trends of inhibition were shown by both methods, but the former gives only a qualitative picture while the modeling method yields the degree of inhibition because the model can separate the two simultaneous roles of ATP as both a substrate of reaction and an inhibitor of PFK1. Analysis based on the model suggests that the ATP affinity is much greater to the PFK1 catalytic site than to the inhibitory site, but the inhibited ATP-PFK1-ATP complex is much slower than the uninhibited PFK1-ATP complex in product generation, leading to reduced overall reaction velocity when ATP concentration increases. The initial-velocity method is simple and useful for general observation of enzyme activity while the modeling method has advantages in quantifying the inhibition effects and providing insights into the process.

Assessing the impact of ultrasound on the rate and extent of early post-mortem glycolysis in bovine Longissimus thoracis et lumborum

The rate of pH decline, early post-mortem, has been identified as a key factor that impacts the tenderness of meat, and manipulating this rate of pH decline is highly relevant to ensure consistent high quality meat. Ultrasound is a potential intervention in early post - mortem muscle that may have an impact on the rate of glycolysis through its ability to alter enzyme activity. Following a variety of different ultrasound treatments frequencies (25 and 45 kHz) and durations (15, 30 and 45 min), it was found, when analysed in muscle, that ultrasound treatment duration, specifically the 30 min treatment, and interaction between treatment duration and frequency, had a significant impact on the rate of pH decline, post - treatment. Frequency did not have a significant effect on the rate of pH decline, post - treatment, in muscle. Ultrasound did not have a significant permanent effect on the activity of glycolytic enzymes present in bovine Longissimus lumborum et thoracis muscle, where no significant differences were observed on the rate of pH decline and rate of change of reducing sugars, glycogen and lactic acid, when analysed in an in vitro glycolytic buffer. It seems that the impact observed in intact muscle is not as a consequence of a permanent change in enzymatic activity, instead indicating an impact on conditions in the muscle which enhanced enzyme activity.

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.

Skeletal Muscle Metabolism Is Dynamic during Porcine Postnatal Growth

Skeletal muscle metabolism has implications for swine feed efficiency (FE); however, it remains unclear if the metabolic profile of skeletal muscle changes during postnatal growth. To assess the metabolic changes, samples were collected from the longissimus dorsi (LD, glycolytic muscle), latissimus dorsi (LAT, mixed muscle), and masseter (MS, oxidative muscle) at 20, 53, 87, 120, and 180 days of age from barrows. Muscles were assessed to determine the abundance of several metabolic enzymes. Lactate dehydrogenase (LDHα) decreased in all muscles from 20 to 87 d (p < 0.01), which may be attributed to the muscles being more glycolytic at weaning from a milk-based diet. Pyruvate carboxylase (PC) increased in all muscles at 53 d compared to the other time points (p < 0.01), while pyruvate dehydrogenase α 1 (PDHα1) increased at 87 and 180 d in MS compared to LD (p < 0.05), indicating that potential changes occur in pyruvate entry into the tricarboxylic acid (TCA) cycle during growth. Isolated mitochondria from each muscle were incubated with 13C-labeled metabolites to assess isotopomer enrichment patterns of TCA intermediates. Citrate M + 2 and M + 4 derived from [13C3]-pyruvate increased at 87 d in LAT and MS mitochondria compared to LD mitochondria (p < 0.05). Regardless of the muscle, citrate M+3 increased at 87 d compared to 20, 53, and 120 d, while 180 d showed intermediate values (p < 0.01). These data support the notion that pyruvate metabolism is dynamic during growth. Our findings establish a metabolic fingerprint associated with postnatal muscle hypertrophy.

The impact of ultrasound treatment on glycolytic enzymes when applied to crude extracts from early post-mortem bovine muscle

The rate of pH decline post - mortem and its interaction with temperature influences the final tenderness of meat, and therefore, the manipulation of the rate of pH decline is a strategy of interest in order to obtain consistent high quality meat. Ultrasound is a potential early post - mortem carcass intervention, which may alter the rate of glycolysis based on its ability to alter enzyme activity. In this study, homogenates (prepared from early post-mortem Longissimus thoracis et lumborum muscle) were subjected to different ultrasound intensities (0 %/60 %/100 % amp) and treatment durations (15/ 30 min). The effect of these treatments on the inherent activity of the glycolytic enzymes was investigated using an in vitro glycolytic buffer model system. It was found that ultrasound treatment intensity and duration had a significant interactive effect on the rate of pH decline, and on reducing sugars and lactic acid concentrations, specifically following the 100 % amp ultrasound for 30 min treatment and between 30 and 240 min incubation. No significant differences in pH or metabolites content were observed between treatments after 1440 min of incubation. No effect of ultrasound intensity or treatment duration was observed on the degradation of glycogen. Under the reported conditions of this trial, it can be concluded that the application of ultrasound has limited potential to have an impact on the glycolytic pathways in bovine muscle.

Impact of cooking temperature on pork longissimus, and muscle fibre type, on quality traits and protein denaturation of four pork muscles

Variations in pork quality impact consumer acceptance, and fibre type differences between muscles contribute to this variation. The aim was to investigate the influence of variations in muscle fibre types and protein denaturation peaks across four pork muscles and the influence of ageing and cooking temperature on longissimus quality traits. The longissimus, masseter, cutaneous trunci, and psoas major from 13 carcases were removed 1-day postmortem and subjected to 0- or 14-days ageing (d0, d14). Quality traits, protein denaturation peak temperature (DSC), fibre diameter and fibre type proportions were measured. Cook loss for longissimus was similar on d0 and d14, but was higher on d14 for masseter, cutaneous trunci, and psoas major. Warner-Bratzler shear force was highest, and ultimate pH was lowest, for longissimus, and similar among cutaneous trunci, masseter, and psoas major. Masseter had lowest L* and highest a* and longissimus and cutaneous trunci had highest L* and lowest a*. The DSC temperature peaks for longissimus occurred at lower temperatures relative to the other muscles. Fibre diameter was largest for type-IIb fibres relative to type-IIa and type-I. Longissimus and cutaneous trunci had predominantly type-IIb glycolytic (71%, 51% respectively), masseter had predominantly type-IIa intermediate (50%) and psoas major had predominantly type-I oxidative (48%) fibres. The glycolytic longissimus had the lowest DSC temperature peaks and the lowest quality meat. Masseter had the highest proportion of type-I fibres but was generally similar in quality traits to psoas major, and also similar to cutaneous trunci which had more glycolytic fibres than masseter.

Muscle proteolysis is differentially influenced by mitochondrial intactness

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

Dietary riboflavin supplementation improves meat quality, antioxidant capacity, fatty acid composition, lipidomic, volatilomic, and proteomic profiles of breast muscle in Pekin ducks

Our objective was to determine effects of supplemental dietary riboflavin on meat quality, antioxidant capacity, fatty acid composition, lipidomic, volatilomic, and proteomic profiling of duck breast muscle. The results showed that dietary riboflavin supplementation significantly increased growth performance, breast meat yield, intramuscular fat content, polyunsaturated fatty acid (PUFA), n3-PUFA, n6-PUFA, redness (a*), and pH24h, but decreased lightness (L*) and yellowness (b*). Furthermore, riboflavin supplementation significantly improved muscle antioxidant capacity based on various biochemical parameters. Lipidomic and volatilomic analyses revealed that riboflavin supplementation markedly increased breast meat phosphatidylglycerol and coenzyme Q contents and two favourable key odorants, citronellyl acetate and 3-(methylthio)-propanal. Proteomics analyses confirmed that riboflavin supplementation activated mitochondrial aerobic respiration, including fatty acid beta oxidation, the tricarboxylic acid cycle, and oxidative phosphorylation. In conclusion, supplementing duck diets with riboflavin enhanced breast meat quality, attributed to increases in antioxidant capacity and mitochondrial functions.

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.

Postmortem Metabolism and Pork Quality Development Are Affected by Electrical Stimulation across Three Genetic Lines

Variations in postmortem metabolism in muscle impact pork quality development. Curiously, some genetic lines are more refractile to adverse pork quality development than others and may regulate energy metabolism differently. The aim of this study was to challenge pork carcasses from different genetic populations with electrical stimulation (ES) to determine how postmortem metabolism varies with genetic line and explore control points that reside in glycolysis in dying muscle. Three genetic populations (GP) were subjected to ES (100 V or 200 V, 13 pulses, 2 s on/2 s off) at 15- or 25-min post-exsanguination, or no stimulation (NS). Genetic population affected relative muscle relative abundance of different myosin heavy chains, glycogen, G6P, and lactate concentrations. Genetic lines responded similarly to ES, but a comparison of ES treatment groups revealed a trend for an interaction between voltage, time of ES, and time postmortem. Higher voltage accelerated pH decline at 20 min up to 60 min postmortem. Trends in color and firmness scores and L* values were consistent with pH and metabolite data. These data show that genetic populations respond differently to postmortem perturbation by altering glycolytic flux and suggest differences in postmortem glycolysis may be partially responsible for differences in meat quality between genetic populations, though not entirely.

Biochar boosts nitrate removal in constructed wetlands for secondary effluent treatment: Linking nitrate removal to the metabolic pathway of denitrification and biochar properties

Constructed wetlands (CWs) amended with biochar have attracted much attention for nitrate removal treating secondary effluent. However, little is acknowledged about the linkage among the nitrate removal performance, microbial metabolic pathway of nitrate, and biochar properties. Herein, biochars pyrolyzed under 300 °C, 500 °C, and 700 °C (BC300, BC500, and BC700, respectively) were used in CWs to reveal the relationship. Results showed that CWs amended with BC300 (59.73%), BC500 (53.27%), and BC700 (49.07%) achieved higher nitrogen removal efficiency, compared with the control (39.51%). Metagenomic analysis showed that biochars could enrich the genes, which encoded key enzymes (adenosine triphosphate production, and electrons generation, transportation, and consumption) involved in carbon and nitrate metabolism. Further, biochar pyrolyzed under lower temperature, with higher oxygen content, molar O/C ratio, and the electron donating capacity, in CWs could obtain higher nitrate removal efficiency. Overall, this research offers new understandings for the promotion of denitrification in CWs amended with biochar.

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.

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.

Enhancement of denitrification in biofilters by immobilized biochar under low-temperature stress

Efficient removal of nitrate under low temperature is challenging because of the reduction of the microbial activity. This study successfully explored the promotion on the performance of denitrification utilizing the immobilized biochar in biofilters under low temperature (6 ± 2 °C). The results showed that the immobilized biochar increased the denitrification rate by 76.8% and decreased the nitrous oxide emissions by 82.5%. Mechanistic studies revealed that the immobilized biochar increased the activities of the denitrifying enzymes and three enzymes involved in glycolysis. Furthermore, the immobilized biochar elevated the activity of the electron transport system by 31.8%. Finally, structural equation model explained that the increase of nitrate reductase activity was a crucial factor to enhance the total nitrogen removal efficiency in biofilters with immobilized biochar. Overall, the use of immobilized biochar can be a novel strategy to enhance nitrogen removal and reduce greenhouse gas emissions in biofilters under low temperature.

Early Postmortem Metabolism and Protease Activation in Fast Glycolytic and Slow Oxidative Bovine Muscles

Muscle properties and metabolism influence muscle to meat conversion. Fiber type profile impacts glycolytic capacity as well as protein turnover rate in vivo. Our objective was to investigate protease content and activation during the early postmortem period using muscles with known divergent metabolism. Samples from longissimus lumborum (LL) and diaphragm (Dia) were taken from predominantly Angus steer carcasses (n = 6) at 1, 3, and 24 h postmortem and frozen. Myosin heavy chain (MyHC) isoforms, ATP, glycogen, glucose, glucose-6-phosphate (G6P), and lactate concentrations were determined. Procaspase-3, calpain-1, calpastatin, desmin, and troponin-T were assessed by immunodetection. Muscles showed contrasting MyHC profiles, with LL represented primarily by IIx and IIa isoforms (∼88%) whereas Dia contained mostly (80%) type I isoform. Glycogen degradation was more pronounced in LL and coincided with more rapid accumulation of glucose and lactate (P &lt; 0.01). Procaspase-3 content was influenced by muscle (m: P &lt; 0.01), being greater in Dia. Fragments indicating activation of procaspase-3 postmortem were not detected. Calpain-1 autolysis and intact calpastatin (135 kDa) content were influenced by muscle and time (m × t: P &lt; 0.01 and P &lt; 0.01, respectively). Calpastatin fragmentation postmortem was not associated with greater procaspase-3 content. In conclusion, fast glycolytic LL displayed faster protease activation and greater proteolysis during the first 24 h postmortem.

Inherent factors influence color variations in semimembranosus muscle of pigs

Variations in color, though a quality frustration, are common across the face of fresh and processed hams. Herein, we measured objective color across the semimembranosus (SM) muscle early postmortem and at 1440 min, then compared these differences against biochemical and metabolic characteristics responsible for pork quality development. Color (L*, a*) differed (P < 0.001) by zone and time but no interaction was evident. Lactate content and pH were highly correlated (R² = 0.92) at 30 min, but weakened (R² = 0.161412) by 1440 min. Lactate anaplerosis was not responsible for this lack of relationship. Glycolytic potential also differed across zone (P < 0.001) and time (P < 0.005). Differences in myoglobin expression and abundance, as well as mitochondrial DNA were notable (P < 0.05) across zone. These data suggest inherent differences in SM muscle are key determinants of ham color variation, while postmortem metabolism may play a lesser role in driving this quality attribute.

An early-postmortem metabolic comparison among three extreme acute heat stress temperature settings in chicken breast muscle

Normally, preslaughter acute heat stress could accelerate postmortem glycolysis and impair chicken breast (pectoralis major muscle) quality. However, previous studies indicated that it might be different when the acute heat stress temperature rises to an extreme range (above 35 °C). Therefore, this study's objectives were to compare the pH decline, glycolytic enzyme activity, and AMP-activated protein kinase (AMPK) phosphorylation at early postmortem among three extreme acute heat stress temperature settings: a control group (36 °C) and two experimental groups (38 °C and 40 °C). Although the temperature did not affect glycogen phosphorylase a and pyruvate kinase activity, there was a decrease in pH decline rate, phosphofructokinase-1 activity, and phospho-AMPK-α[Thr172] within 4 h postmortem when temperature increased from 36 to 40 °C. Temperature also affected hexokinase activity, with the 36 °C-group having the highest activity. The results of the current study, for the first time, indicated that postmortem metabolic rate in chicken breast muscle could be changed by acute heat stress temperature setting at extreme range.

miR-152 targets pyruvate kinase to regulate the glycolytic activity of pig skeletal muscles and affects pork quality

As a type of non-coding RNA, microRNAs are widely involved in the biological processes of animals. In the present study, the expression of miR-152 in glycolytic muscle fibers (Longissimus thoracis, LT) was lower than that of oxidative muscle fibers (Psoas major, PM). Using dual luciferase assay, miR-152 was shown to target muscle pyruvate kinase (PKM) to perform biological functions. Moreover, overexpression of miR-152 in primary porcine cells inhibited PKM gene expression and reduced lactic acid production in cells, whereas inhibition of miR-152 expression promoted PKM gene expression and increased lactic acid production. Correlation analysis showed that the expression of miR-152 was significantly positively correlated with the ultimate pH of LT after slaughter, while the expression of the PKM gene was significantly negatively correlated with the final pH of LT. In vivo and in vitro experiments discussed herein suggest that miR-152 may affect muscle pH by targeting the expression of the PKM gene. Our findings enrich the understanding of the genetic regulatory network that influences pork quality.

Modelling of energy metabolism and analysis of pH variations in postmortem muscle

A kinetic model structure was developed to describe the major variations in energy metabolism and to gain further understanding of pH changes in postmortem muscle experimentally observed with an in vitro glycolytic system. Comparison with experiments showed that the model could describe the kinetics of major metabolites and pH under varied conditions. Optimized model parameters definitively and consistently showed the observed effects of mitochondria, indicating a desirable level of model complexity. Simulation and analysis of pH variations based on the model suggested that phosphofructokinase activity has the strongest impact on the rate and extent of postmortem pH decline. Postmortem pH is also influenced by rates of ATP hydrolysis and glycolysis, and to a much lesser extent, pH buffering capacity. Other reactions, including those mediated by creatine kinase, adenylate kinase, and AMP deaminase, have minimal effects on postmortem pH decline.

Dark-cutting beef: A brief review and an integromics meta-analysis at the proteome level to decipher the underlying pathways

Comprehensive characterization of the post-mortem muscle proteome defines a fundamental goal in meat proteomics. During the last decade, proteomics tools have been applied in the field of foodomics to help decipher factors underpinning meat quality variations and to enlighten us, through data-driven methods, on the underlying mechanisms leading to meat quality defects such as dark-cutting meat known also as dark, firm and dry (DFD) meat. In cattle, several proteomics studies have focused on the extent to which changes in the post-mortem muscle proteome relate to dark-cutting beef development. The present data-mining study firstly reviews proteomics studies which investigated dark-cutting beef, and secondly, gathers the protein biomarkers that differ between dark-cutting versus beef with normal-pH in a unique repertoire. A list of 130 proteins from eight eligible studies was curated and mined through bioinformatics for Gene Ontology annotations, molecular pathways enrichments, secretome analysis and biological pathways comparisons to normal beef color from a previous meta-analysis. The major biological pathways underpinning dark-cutting beef at the proteome level have been described and deeply discussed in this integromics study.

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.

New Insights in Muscle Biology that Alter Meat Quality

Fresh meat quality is greatly determined through biochemical changes occurring in the muscle during its conversion to meat. These changes are key to imparting a unique set of characteristics on fresh meat, including its appearance, ability to retain moisture, and texture. Skeletal muscle is an extremely heterogeneous tissue composed of different types of fibers that have distinct contractile and metabolic properties. Fiber type composition determines the overall biochemical and functional properties of the muscle tissue and, subsequently, its quality as fresh meat. Therefore, changing muscle fiber profile in living animals through genetic selection or environmental factors has the potential to modulate fresh meat quality. We provide an overview of the biochemical processes responsible for the development of meat quality attributes and an overall understanding of the strong relationship between muscle fiber profile and meat quality in different meat species.

The role of histidine dipeptides on postmortem acidification of broiler muscles with different energy metabolism

It is generally held that the content of several free amino acids and dipeptides is closely related to the energy-supplying metabolism of skeletal muscles. Metabolic characteristics of muscles are involved in the variability of meat quality due to their ability to influence the patterns of energy metabolism not only in living animal but also during postmortem time. Within this context, this study aimed at establishing whether the concentration of histidine dipeptides can affect muscle postmortem metabolism, examining the glycolytic pathway of 3 chicken muscles (pectoralis major, extensor iliotibialis lateralis, and gastrocnemius internus as glycolytic, intermediate, and oxidative-type, respectively) selected based on their histidine dipeptides content and ultimate pH. Thus, a total of 8 carcasses were obtained from the same flock of broiler chickens (Ross 308 strain, females, 49 d of age, 2.8 kg body weight at slaughter) and selected immediately after evisceration from the line of a commercial processing plant. Meat samples of about 1 cm³ were excised from bone-in muscles at 15, 60, 120, and 1,440 min postmortem, instantly frozen in liquid nitrogen and used for the determination of pH, glycolytic metabolites, buffering capacity as well as histidine dipeptides content through ¹H-NMR. Overall results suggest that glycolysis in leg muscles ceased already after 2 h postmortem, whereas in breast muscle continued until 24 h, when it exhibited significantly lower pH values (P < 0.05). However, considering its remarkable glycolytic potential, pectoralis major muscle should have exhibited a greater and faster acidification, suggesting that its higher (P < 0.05) histidine dipeptides' content might have prevented a potentially stronger acidification process. Accordingly, breast muscle also showed greater (P < 0.05) buffering ability in the pH range 6.0–7.0. Therefore, anserine and carnosine, being highly positively correlated with muscle's buffering capacity (P < 0.001), might play a role in regulating postmortem pH decline, thus exerting an effect on muscle metabolism during prerigor phase and the quality of the forthcoming meat. Overall results also suggest that total histidine dipeptides content along with muscular ultimate pH represent good indicators for the energy-supplying metabolism of chicken muscles.

At physiological concentrations, AMP increases phosphofructokinase-1 activity compared to fructose 2, 6-bisphosphate in postmortem porcine skeletal muscle

Phosphofructokinase-1 (PFK-1) is the most important enzyme controlling postmortem glycolysis in living skeletal muscle and is the most likely candidate for regulation of postmortem glycolysis. We investigated the regulation of PFK-1 activity by F-2, 6-BP and AMP under simulated postmortem conditions in porcine skeletal muscle. Six pigs were harvested and longissimus lumborum samples were collected immediately post-slaughter. PFK-1 activity was assayed using increasing concentrations of F-2, 6-BP or AMP, added to the buffer adjusted to different pH. Both F-2, 6-BP and AMP increased PFK-1 activity with increasing buffer pH from 5.5 to 7.0. A concentration of 50 μM F-2, 6-BP was required to increase PFK-1 activity which is very high compared to physiological concentration in the porcine skeletal muscle. However, physiological concentrations (50-150 μM) of AMP resulted in increased PFK-1 activity compared to 1-2 μM F-2, 6-BP. Thus, AMP may play a greater role in dictating the rate and extent of postmortem muscle glycolysis and pH decline as compared to F-2, 6-BP.

Myosin heavy chain isoform and metabolic profile differ in beef steaks varying in tenderness

Our objective was to investigate possible differences in muscle fiber characteristics of beef longissimus lumborum (LL) steaks varying in tenderness (very tender vs. intermediate tender). Therefore, the relative abundance of myosin heavy chain (MHC) isoforms and activity/abundance of several glycolytic and oxidative enzymes were compared between the two steak groups. Greater (P < 0.05) content of MHC type IIa (MHC-IIa) and activities of phosphofructokinase (PFK) and glycogen phosphorylase (GP) were observed in the very tender steaks. Conversely, intermediate tender steaks had greater (P < 0.05) contents of MHC type I (MHC-I) and succinate dehydrogenase (SDH) and greater citrate synthase (CS) activity. Increased tenderness in the very tender steaks was associated with greater (P < 0.05) proteolysis as evaluated by desmin and troponin-T degradation. Further, mitochondrial calcium uniporter (MCU) was lower (P < 0.05) in the very tender steaks than steaks of intermediate tenderness. Collectively, shifting muscle characteristics toward a more glycolytic type appears to positively impact postmortem proteolysis and tenderization.

Exploring the Factors Contributing to the High Ultimate pH of Broiler Pectoralis Major Muscles Affected by Wooden Breast Condition

The elevated ultimate pH (pH u ) found in wooden breast (WB) meat suggests an altered muscular energetic status in WB but also could be related to a prematurely terminated post-mortem pH decline. The aims of this study were to explore the factors contributing to the elevated pH u and establish whether the occurrence of WB defect alters muscle post-mortem carbohydrate metabolism and determine if the contractile apparatus reflects such changes. A total of 24 carcasses from Ross 308 male chickens were obtained from a commercial producer and harvested using commercial processing procedures. Carcasses were categorized into unaffected (NORM) and WB groups (n = 12 each), and samples were collected from cranial bone-in pectoralis major (PM) muscles at 15 min and 24 h post-mortem for the determination of pH, glycolytic metabolites, adenonucleotides, buffering capacity, phosphofructokinase (PFK) activity, and in vitro pH decline. Twenty-four additional deboned PM samples (12 NORM and 12 WB) were collected from the same processing plant to assess muscle histology and sarcomere length at four different locations throughout the PM muscle. Data show that the reduced glycolytic potential of WB muscles only partially explains the higher (P < 0.001) pH u of WB meat, as residual glycogen along with unaltered PFK activity suggests that neither glycogen nor a deficiency of PFK is responsible for arresting glycolysis prematurely. The dramatic reduction in ATP concentrations in the early post-mortem period suggests a defective ATP-generating pathway that might be responsible for the reduced pH decline in WB samples. Further, the addition of excess of ATPase extended post-mortem glycolysis of WB meat in an in vitro glycolytic system. WB-affected samples have longer (P < 0.001) sarcomeres compared to NORM, indicating the existence of compromised energy-generating pathways in myopathic muscles that may have had consequences on the muscle contraction and tension development, as in vivo, also during the post-mortem period. Considering the overall reduced glycolytic potential and the myodegenerative processes associated with WB condition, we speculate that the higher pH u of WB meat might be the outcome of a drastically impaired energy-generating pathway combined with a deficiency and/or a dysfunction of muscle ATPases, having consequences also on muscle fiber contraction degree.

Mitochondrial oxygen consumption in early postmortem permeabilized skeletal muscle fibers is influenced by cattle breed

Functional properties and integrity of skeletal muscle mitochondria (mt) during the early postmortem period may influence energy metabolism and pH decline, thereby impacting meat quality development. Angus typically produce more tender beef than Brahman, a Bos indicus breed known for heat tolerance. Thus, our objectives were to compare mt respiratory function in muscle collected early postmortem (1 h) from Angus and Brahman steers (n = 26); and to evaluate the effect of normal and elevated temperature on mt function ex vivo. We measured mt oxygen consumption rate (OCR) in fresh-permeabilized muscle fibers from Longissimus lumborum (LL) at 2 temperatures (38.5 and 40.0 °C) and determined citrate synthase (CS) activity and expression of several mt proteins. The main effects of breed, temperature, and their interaction were tested for mt respiration, and breed effect was tested for CS activity and protein expression. Breed, but not temperature (P > 0.40), influenced mt OCR (per tissue weight), with Brahman exhibiting greater complex I+II-mediated oxidative phosphorylation capacity (P = 0.05). Complex I- and complex II-mediated OCR also tended to be greater in Brahman (P = 0.07 and P = 0.09, respectively). Activity of CS was higher in LL from Brahman compared to Angus (P = 0.05). Expression of specific mt proteins did not differ between breeds, except for higher expression of adenosine triphosphate (ATP) synthase subunit 5 alpha in Brahman muscle (P = 0.04). Coupling control ratio differed between breeds (P = 0.05), revealing greater coupling between oxygen consumption and phosphorylation in Brahman. Our data demonstrate that both Angus and Brahman mt retained functional capacity and integrity 1-h postmortem; greater oxidative phosphorylation capacity and coupling in Brahman mt could be related to heat tolerance and impact early postmortem metabolism.

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

The activity, expression and S-nitrosylation of glycogen phosphorylase (GP), phosphofructokinase (PFK) and pyruvate kinase (PK) was compared between pale, soft and exudative (PSE) and red, firm and non-exudative (RFN) pork. The nitric oxide synthase (NOS) activity of RFN pork was higher than PSE pork (P < 0.05). Glycogen and lactic acid content were significantly different between PSE and RFN samples at 1 h postmortem (P < 0.05). Compared to PSE pork, RFN pork had lower activities and higher S-nitrosylation levels of GP, PFK and PK (P < 0.05). Moreover, GP expression in RFN pork was lower (P < 0.05) while no significant differences of PFK and PK expression were observed between these two groups. These data suggest that protein S-nitrosylation can presumably regulate glycolysis by modulating glycolytic enzymes activities and then regulate the development of PSE pork.

Muscle from grass- and grain-fed cattle differs energetically

Insufficient acidification results in dark, firm, and dry beef. While this defect is often indicative of a stress event antemortem, muscle tissue may change in response to feeding regime. Longissimus dorsi muscle samples from 10 grain-fed and 10 grass-fed market weight, angus-crossbred beef cattle were collected postmortem. Lower (P < .05) L* and a* values were recorded for steaks from grass-fed cattle. Higher (P < .05) ultimate pH values were noted in lean of grass-fed cattle compared to grain-fed cattle, yet differences in lactate, glycogen and glucose were not detected. Further, increased (P < .05) ultimate pH values and lower (P < .05) lactate accumulations were noted when samples from grass-fed cattle were subjected to an in vitro glycolysis system. Muscle from grass-fed beef possessed nearly two-fold more (P < .05) succinate dehydrogenase and (P < .001) myoglobin than that of grain-fed cattle. These data show lean from grass-fed beef has greater enzymes reflective of oxidative metabolism and suggest dark lean from grass-fed cattle may be a function of more oxidative metabolism rather than a stress-related event antemortem.

Glycolysis and pH Decline Terminate Prematurely in Oxidative Muscles despite the Presence of Excess Glycogen

Meat from oxidative skeletal muscle has a higher postmortem ultimate pH, which was originally thought to be a result from decreased antemortem glycogen stores. Therefore, we hypothesized that excess glycogen may not resolve the high ultimate pH of meat from oxidative muscles in ruminants and poultry. To test this hypothesis, an in vitro muscle glycolytic buffer system containing excess glycogen was used to compare glycolysis and pH decline of glycolytic and oxidative muscle from beef, lamb, chicken, and turkey. Glycogen concentration of both glycolytic and oxidative muscle homogenates was similar at 0 min and decreased significantly with time in all species tested. All homogenates contained residual glycogen at 1440 min, indicating glycogen was provided in excess. The ultimate pH of the oxidative muscle homogenates was significantly increased compared to the glycolytic muscle. The oxidative muscle also contained decreased lactate and decreased glucose 6-phosphate in all the species tested at 1440 min. Combined these data suggest that glycolysis and pH decline of oxidative muscles terminate prematurely at higher ultimate pH even in the presence of excess glycogen across livestock species. Additionally, the data indicated that the in vitro glycolytic buffer system can be used to study species specific meat quality problems in beef, lamb, chicken, and turkey.

Biochemical alterations in the Musculus triceps brachii and Musculus longissimus thoracis during early postmortem period in pigs

Muscle-to-meat-transition is influenced by alterations of the energy metabolism. Porcine Musculus triceps brachii (MT) consisted of more fast-twitch-glycolytic muscle fibers and samples, collected 0, 10 and 20 min after slaughter (p.m.), showed higher mitochondrial respiratory activities and ATP concentrations than Musculus longissimus thoracis (LT) samples. Enzyme activities in MT were higher at 0 min (glycogen phosphorylase (GP)), 10 min (GP, citrate synthase (CS)) and at 20 min p.m. (CS). However, LT results were higher at 0 min (lactate dehydrogenase (LDH)), 10 min (phosphofructokinase (PFK), LDH) and at 20 min p.m. (PFK, F₀F₁-ATPase (F₀F₁)). Between 0 min and 10 min p.m. CS activities decreased in LT and MT samples, PFK increased in LT and GP in MT samples. Between 10 min and 20 min p.m. PFK and LDH decreased in LT and GP in MT samples, whereas F₀F₁ increased in LT and CS in MT samples. The data indicate that muscles with different mitochondria contents show clearly different energy metabolism characteristics.

Edible quality of soft-boiled chicken processing with chilled carcass was better than that of hot-fresh carcass

Soft-boiled chicken is widely popular with its flavor and texture. In a traditional view, the edible quality of soft-boiled chicken producing with hot-fresh carcass (without any chilled procedure after evisceration) was better than that of chilled carcass. Hot-fresh groups with 1, 2, or 4 hr and chilled groups with 24, 48, or 60 hr were used to clarify the view in this study. The results indicated that no significant difference in hardness, springiness, cohesiveness of texture profiles and b* value of skin color was observed between each group, although the highest L* value was obtained in hot-fresh 4 hr group. Higher contents of succinic acid were found in chilled groups when compared to that of hot-fresh groups, but there was no difference in lactic acid and pH values. Lower contents of adenosine 5'-monophosphate (AMP), guanosine 5'-monophosphate (GMP), inosine and hypoxanthine, and higher inosine-5'-monophosphate (IMP) (especially for hot-fresh 1 hr) were observed in hot-fresh groups. In addition, although no difference in umami amino acids and bitter amino acid was observed between each tested group, higher amounts of Asp, Met, Ile, Leu, Tyr, and Arg were observed in chilled groups, especially for chilled 60 hr. The finding indicated that the traditional view was lack of scientific evidence, and chilled carcass was suitable for soft-boiled chicken, substituting for the hot-fresh carcass.

Curcumin attenuates heat-stress-induced oxidant damage by simultaneous activation of GSH-related antioxidant enzymes and Nrf2-mediated phase II detoxifying enzyme systems in broiler chickens

The object of this study was to investigate the effect of curcumin on modulating the glutathione (GSH)-related antioxidant enzymes and antioxidant responses via NF-E2-related factor 2 (Nrf2) signaling pathway in heat-stressed broiler chickens. A total of 400 one-day-old male Arbor Acres broiler chicks was reared in an environmentally controlled room. At 21 d, broiler chicks were divided into 5 treatment groups and were fed one of 4 diets under 2 temperature conditions: 22°C + a basal diet (CON treatment); 34°C for 8 h (0900-1700) + a basal diet supplemented with 0, 50, 100, or 200 mg/kg curcumin (HS, CMN1, CMN2, and CMN3 treatments, respectively). The heat treatment lasted for 20 consecutive days. The results showed that heat stress significantly increased (P < 0.05) the weekly rectal temperature and average head and feet temperature. Compared to the HS treatment, feed conversion was significantly decreased (P < 0.05) in CMN1 and CMN2 treatments. CMN1 administration significantly improved (P < 0.05) the pH24 of muscle. The abnormal changes of serum malonaldehyde and corticosterone concentrations were prevented (P < 0.05) by curcumin. Mitochondrial GSH concentration in the liver was significantly increased (P < 0.05) in CMN1 and CMN2 treatments compared with the HS treatment. The CMN1, CMN2, and CMN3 supplementations significantly increased (P < 0.05) γ-GCL, GSH-Px, and GST activities. Curcumin significantly increased (P < 0.05) the expression of Nrf2, HO-1, and γ-GCLc in the liver as compared to the CON diet. The expression of Cu/ZnSOD and CAT were increased (P < 0.05) by feeding CMN2, respectively, as compared to the HS treatment. It was concluded that curcumin supplementation enhanced the resistance of broilers to heat stress, as evidenced by reversing the FC, increasing the GSH content and GSH-related enzyme activities, and inducing the expression of Nrf2 and Nrf2-mediated phase II detoxifying enzyme genes.

Physicochemical determinants of pH in pectoralis major of three strains of laying hens housed in conventional and furnished cages

1. Post-mortem decline in muscle pH has traditionally been attributed to glycogenolysis-induced lactate accumulation. However, muscle pH ([H⁺]) is controlled by complex physicochemical relationships encapsulated in the Stewart model of acid-base chemistry and is determined by three system-independent variables - strong ion difference ([SID]), total concentration of weak acids ([A_tot]) and partial pressure of CO₂ (PCO₂). 2. This study investigated these system-independent variables in post-mortem pectoralis major muscles of Shaver White, Lohmann Lite and Lohmann Brown laying hens housed in conventional cages (CC) or furnished cages (FC) and evaluated the model by comparing calculated [H⁺] with previously measured [H⁺] values. 3. The model accounted for 99.7% of the variation in muscle [H⁺]. Differences in [SID] accounted for most or all of the variations in [H⁺] between strains. Greater PCO₂ in FC was counteracted by greater sequestration of strong base cations. The results demonstrate the accuracy and utility of the Stewart model for investigating determinants of meat [H⁺]. 4. The housing differences identified in this study suggested that hens housed in FC have improved muscle function and overall health due to the increased opportunity for movement. These findings support past studies showing improved animal welfare for hens housed in FC compared to CC. Therefore, the Stewart model has been identified as an accurate method to assess changes in the muscle at a cellular level that affect meat quality that also detect differences in the welfare status of the research subjects.