High pHu Research Articles

Label-free quantitative proteomic analysis reveals muscle contraction and metabolism proteins linked to ultimate pH in bovine skeletal muscle

The purpose of this research was to investigate the causes and consequences of pHu variations in beef cattle. A group of 176 Nellore beef cattle was evaluated and classified into two different pHu groups: High (≥6.0, N = 17) and Normal (<5.8, N = 159). Plasma concentrations of cortisol and adrenocorticotropic hormone, lactate and glycogen muscular content, meat color, shear force and Longissimus thoracis muscle proteomic profile were evaluated and compared between pHu groups. Muscle glycogen content, meat color and shear force statistically differed between pHu groups. Label-free quantitative proteomic analysis revealed ten differentially abundant proteins between pHu groups, involved in metabolic processes and muscle contraction, which also were significantly correlated with pHu. Thirty-six and 31 proteins were exclusively present in Normal and High pHu group, respectively, which were related to TCA cycle, cortisol production, calcium regulation, and antioxidant function. The MYH7, UGP2, H2AFJ and VDAC3 were identified as potential indicators of pHu variations. CALM and NNT appeared to be interesting proteins to understand the metabolic pathways behind pHu. Data are available via ProteomeXchange with identifier PXD009320.

Association of ultimate pH and stress-related blood variables in cattle

The objective of this study was to investigate the relationship between ultimate pH (pHu) and stress-related blood variables. Of 50 cattle in total, blood samples from 6 cattle which exhibited high (≥6.10) pHu (dark-cutting) were collected, along with the same number of low pHu and intermediate pHu cattle (5.40–5.80; 5.80–6.10, respectively) to determine the concentration of plasma cortisol, glucose, lactate, creatine kinase, lactate dehydrogenase, haptoglobin and serum amyloid A protein. Compared to cattle with low pHu, high pHu cattle showed higher plasma cortisol, glucose, lactate, creatine kinase and lactate dehydrogenase levels at exsanguination. But the concentration of haptoglobin and serum amyloid A protein showed no significant differences among three pH groups. These results imply that measuring plasma cortisol, glucose, lactate, creatine kinase, or lactate dehydrogenase levels at exsanguination may be useful to identify the dark-cutting beef condition.

Carbon monoxide packaging shows the same color improvement for dark cutting beef as high oxygen packaging

In this study, carbon monoxide (CO) modified atmosphere packaging (MAP) was used to increase redness (a*) and lightness (L*) values of dark cutting beef (ultimate pH (pHu)≥6.10), compared to normal pHu beef and intermediate pHu beef (pH: 5.40–5.79; pH: 5.80–6.09, respectively) during 20 d chilled storage. Compared with HiOx-MAP, CO-MAP exhibited similar color improvement effects (increased L*, a*, b* values) for all pHu beef groupings. The metmyoglobin (MetMb) content was lower under CO-MAP than that of HiOx-MAP in normal pHu beef, but opposite effects were observed in dark, high pH beef. This result could not be explained by MetMb reducing ability (MRA) and lipid oxidation, as both parameters were higher in CO-MAP beef than either normal or high pHu beef, compared with HiOx-MAP. In conclusion, CO-MAP was effective to maintain the cherry red color for dark cutting beef, but the color improvement mechanisms might be different with HiOx packaging methods.

Performance, carcass traits, meat quality and amino acid profile of different Japanese quails strains.

Poultry production is considered one of the prospective opportunities to accomplish sustainable and quick production of superior protein to challenge the growing mandate for animal protein. Therefore, this study was aimed to explore the difference on growth performance, carcass traits, meat quality and amino acid profile of different Japanese quails strains. A total of 480 quail chicks of four different plumage colors (120 of each white, golden, gray and brown) were collected after hatching. At 6week of age, birds were stunned and decapitated to determine the physical meat quality, thiobarbituric acid reactive substances and amino acid profile. White quails had the highest weight of slaughter, carcass, dressing, carcass yield, liver, gizzard, heart and spleen (197.27g, 169.27g, 91%, 82%, 6.63g, 6.53g, 2.27g and 0.40g, respectively). Also, they had the highest PhU, lightness, yellowness and water holding capacity with the lowest level of redness, cooking losses and thiobarbituric acid in pectoral (6.28, 46.40, 12,46, 22.17, 9.20, 19.21 and 0.44, respectively) and thigh muscles (6.37, 42.30, 11.51, 26.01, 10.12 and 0.93, respectively). Moreover, they possessed the highest level of all essential (11.68 and 10.16g/100g protein in pectoral and thigh muscles, respectively) and non essential amino acids (13.27 and 12.54g/100g protein in pectoral and thigh muscles, respectively). Therefore, the current study revealed that white quails had the heaviest body weight with the best carcass traits and meat quality.

High pH in beef longissimus thoracis reduces muscle fibre transverse shrinkage and light scattering which contributes to the dark colour

Most studies have focused on myoglobin regarding meat colour development, with little focus on the contribution of muscle structure and light scattering. Our aim was to investigate the pH-dependent changes in muscle structure, on the light scattering properties of the meat. Beef longissimus thoracis muscles were segregated into light, medium or dark colour groups (n=18). ‘Dark’ muscles had a high ultimate pH (pHu), lower lightness (L*), redness (a*), higher myoglobin concentration and deoxymyoglobin content compared to other muscles. Reflectance confocal laser scanning microscopy (rCLSM) revealed ‘dark’ muscles had decreased global brightness (indicator of light scattering) and increased fibre width. In a secondary experiment, decreasing the homogenisation buffer pH from 6.10 to 5.40 induced a 17% shrinkage in high pHu muscle fibres, which increased light scattering by ~25%. In conclusion, rCLSM demonstrated that muscle structure contributes to the magnitude of light scattering by a pH dependent mechanism.

Assessment of the meat quality of lamb M. longissimus thoracis et lumborum and M. triceps brachii following three different Halal slaughter procedures

A total of fifteen male and fifteen female lambs were allocated to three groups of ten animals and subjected to: traditional Halal slaughter without stunning (TNS); slaughter following electric head-only stunning (EHOS) or; post-cut electric head-only stun (PCEHOS) and their meat quality was determined. Instrumental and sensory analyses were carried out on two muscles; M. longissimus thoracis et lumborum (LTL) and M. triceps brachii (TB). Additionally, the effects of sex and muscle type were also assessed. No differences were found among slaughter methods for pH, drip loss and shear force. TB had a higher pHu and was more tender than LTL. Muscles from EHOS and PCEHOS lambs discoloured more quickly than TNS muscles. There were no differences in the measured sensory attributes, with the exception of EHOS meat being tougher than PCEHOS and TNS meat. This study showed that the three slaughter methods had no substantial effect on lamb meat quality.

Effect of genotype, gender and feed restriction on growth, meat quality and the occurrence of white striping and wooden breast in broiler chickens

Due to their importance for the control of meat quality in broiler chickens, the present study aimed at identifying the factors associated with the occurrence of myopathies and characterizing the meat properties when affected by myopathies. To this aim, a total of 768 broiler chickens were reared until slaughter (46 d) to evaluate the effect of genotype, gender, and feeding regime (ad libitum vs. restricted rate, 80% from 13 to 21 d of age) on performance and meat quality. Standard broilers were heavier (3,270 vs. 3,139 g; P < 0.001) and showed lower feed conversion (1.56 vs. 1.61; P < 0.001) than the high-yield broilers. Males showed higher final live weight (3,492 vs. 2,845 g) and lower feed conversion (1.54 vs. 1.63) than females (P < 0.001). Feed restriction decreased final live weight (3,194 vs. 3,142 g; P < 0.01) and feed conversion (1.60 vs. 1.57; P < 0.01) compared to ad libitum feeding. At gross examination, feed restriction tended to increase white-striped breasts (69.5 vs. 79.5%; P < 0.10), whereas females showed less wooden breasts than males (8.0 vs. 16.3%; P < 0.05). White-striped fillets had higher pHu (5.87 vs. 5.83), and lower a* (−0.81 vs. −0.59) and b* color indexes (13.7 vs. 14.5) (P < 0.05), whereas wooden breast fillets exhibited higher cooking losses (25.6 vs. 22.1%) and AK-shear force (4.23 vs. 2.84 kg/g) compared with normal fillets (P < 0.001). At histological examination, 3.1% of pectoralis major were normal, 26.6% mildly degenerated, 45.3% moderately degenerated, and 25.0% severely degenerated. In conclusion, genotype had a moderate effect on growth without modifying myopathy occurrence. In contrast, gender and feed restriction affected performance, meat quality, and breast abnormalities.

The effect of electrical stimulation on post mortem myofibrillar protein degradation and small heat shock protein kinetics in bull beef

This study aimed to determine the effect of electrical stimulation and ultimate pH (pHu) on shear force, myofibrillar protein degradation and small heat shock protein (sHSP) concentrations in M. longissimus lumborum (LL). The LL from both sides of carcasses (n=15) was excised with low voltage electrical stimulation (ES) applied to an LL muscle from one side, while the opposing LL muscle was not stimulated (NS). Muscles were categorised into low (pHu<5.8), intermediate (5.8≤pHu<6.2) and high pHu (pHu≥6.2) and aged for up to 28days post mortem at −1.5°C. High pHu meat tenderised faster which corresponded with the faster degradation of titin and desmin in this group compared with low and intermediate pHu meat. Electrical stimulation significantly affected the variable levels of αβ-crystallin and HSP20 with higher concentrations of these sHSP in ES muscles at later ageing timepoints compared with NS muscles.

Effects of pre-slaughter showering and ventilation on stress, meat quality and metabolite concentrations of broilers in summer.

Effects of pre-slaughter showering and ventilation on stress, meat quality and energy metabolism of broilers in summer were investigated. After transport, 84 Arbor Acres broilers were randomly divided into four treatment groups: (i) control group without ventilation and showering (C); (ii) 10 min ventilation without showering (VWS); (iii) 10 min showering without ventilation (SWV); (iv) 5 min showering and then 5 min ventilation (SV). Compared with the control group, plasma lactate dehydrogenase and creatine kinase activities in the other three treatment groups were (P < 0.05) lower; however, the plasma glucose level did not show any significant changes among all the groups. The breast meat in the SV group had significantly (P < 0.05) higher pHu , glycogen content, lower L*, ΔpH, drip loss, cook loss, R-value and lactate content than the control group; however, there was no significant difference in shear force values among all the groups. In conclusion, this study indicated broilers in the SV group showed a lower stress level and greater meat quality, which suggest that showering and ventilation after transportation may be a good measure to relieve stress caused by transport under high temperature and improve the meat quality of broilers.

Selecting broiler chickens for ultimate pH of breast muscle: Analysis of divergent selection experiment and phenotypic consequences on meat quality, growth, and body composition traits1

Genetic parameters for ultimate pH of pectoralis major muscle (PM-pHu) and sartorius muscle (SART-pHu); color parameters L*, a*, b*; logarithm of drip loss (LogDL) of pectoralis major (PM) muscle; breast meat yield (BMY); thigh and drumstick yield (TY); abdominal fat percentage (AFP); and BW at 6 wk (BW6) were estimated in 2 lines of broiler chickens divergently selected for PM-pHu. Effects of selection on all the previous traits and on glycolytic potential, pectoralis major muscle pH at 15 min postmortem, curing-cooking yield (CCY), cooking loss (CL), and Warner-Bratzler shear force (WBSF) of the PM muscle were also analyzed after 5 generations. Strong genetic determinism of PM-pHu was observed, with estimated h(2) of 0.57 ± 0.02. There was a significant positive genetic correlation (rg) between PM-pHu and SART-pHu (0.54 ± 0.04), indicating that selection had a general rather than a specific effect on energy storage in skeletal muscles. The h(2) estimates of L*, a*, and b* parameters were 0.58 ± 0.02, 0.39 ± 0.02, and 0.48 ± 0.02, respectively. Heritability estimates for TY, BMY, and AFP were 0.39 ± 0.04, 0.52 ± 0.01, and 0.71 ± 0.02, respectively. Our results indicated different genetic control of LogDL and L* of the meat between the 2 lines; these traits had a strong rg with PM-pHu in the line selected for low ultimate pH (pHu) value (pHu-; -0.80 and -0.71, respectively), which was not observed in the line selected for high pHu value (pHu+; -0.04 and -0.29, respectively). A significant positive rg (0.21 ± 0.04) was observed between PM-pHu and BMY but not between PM-pHu and BW6, AFP, or TY. Significant phenotypic differences were observed after 5 generations of selection between the 2 lines. The mean differences (P < 0.001) in pHu between the 2 lines were 0.42 and 0.21 pH units in the breast and thigh muscle, respectively. Breast meat in the pHu+ line exhibited lower L* (-5 units; P < 0.001), a* (-0.22 units; P < 0.001), b* (-1.53 units; P < 0.001), and drip loss (-1.6 units; P < 0.001) than in the pHu- line. Breast meat of the pHu+ line was also characterized by greater CCY (+6.1 units; P < 0.001), lower CL (-1.66 units; P < 0.01), and lower WBSF after cooking (-5.1 units; P < 0.001) compared to the pHu- line. This study highlighted that selection based on pHu can be effective in improving the processing ability of breast meat and reducing the incidence of meat quality defects without affecting chicken growth performance.

Effect of beef ultimate pH and large structural protein changes with aging on meat tenderness

This study investigated the effect of ultimate pH (pHu) in beef on the degradation of large structural proteins during refrigerated storage using SDS-PAGE. M. longissimus dorsi from bull carcasses were selected and classified into three groups: low pHu (≤5.79), intermediate pHu (5.80–6.19) and high pHu (≥6.2) muscles. Samples were then stored at −1.5°C for 1, 2, 7, 14, 21 and 28days. Meat tenderness was measured at each aging time. Depending on meat pHu, different protein patterns and degradation rates of structural proteins were found. Rapid changes of large structural proteins took place within 48h post mortem. Besides titin and nebulin, degradation of filamin was clearly revealed. Two more large protein bands corresponding to myosin family members also exhibited fast decline with storage time. It suggested that the fast degradation of these proteins is a key factor in the improvement of meat tenderness.

Factors influencing the occurrence of high ultimate pH in three muscles of lamb carcasses in Australia

Chilled lamb meat exported from Australia has, on occasions, been rejected by importing countries due to greening, after only 6 weeks of storage time. Greening is known to be more prevalent in high ultimate pH (pHu) beef meat (&gt;5.9). There are few data available for lamb carcasses in Australia on the occurrence of high pHu meat, which may have an impact on the understanding and control of quality and greening during storage. The aim of this project was to determine the prevalence of, and influencing factors for, high pHu meat in a range of muscle types in lamb carcasses in Australia. Muscle pHu data were collected from a total of 1614 carcasses from 78 lots at four lamb processing plants in Victoria and New South Wales in autumn and spring of 2013. The pHu of the knuckle (rectus femoris), rack (longissimus) and blade (infraspinatus) was measured and data on carcass and lot characteristics were recorded. Data were subjected to restricted maximum likelihood and generalised linear mixed model analysis. The mean pHu of the knuckle, rack and shoulder were 6.06, 5.79 and 6.12 respectively, and the main factors influencing muscle pHu and occurrence of dark-cutting were breed, season, electrical stimulation and carcass weight. Merino lambs had a higher pHu in the blade and knuckle than did other breeds (P &lt; 0.05, P &lt; 0.01 respectively). Lambs processed in autumn had a higher predicted pHu in the blade and knuckle and a higher percentage dark-cutting (DC; pHu &gt;6.0) for those muscles, than did those processed in spring (P &lt; 0.05). Carcasses that had been electrically stimulated had a higher %DC and a higher pHu in all three muscles (P &lt; 0.05). Carcass weight had a significant effect on the pHu of all three muscles (P &lt; 0.001), with heavier carcasses having a lower pHu and lower %DC. The pHu of the rack was not a reliable predictor for the pHu in other muscles of the lamb carcass. In conclusion, the high occurrence of DC in the muscles, particularly the blade and knuckle, suggests that these muscles may be at risk for producing greening in the vacuum bag during storage.

The in vitro digestibility of beef varies with its inherent ultimate pH.

Animal carcasses and cuts of meat are usually differentiated and valued according to size and compositional attributes. An underappreciated variable of red meat is its inherent ultimate pH (pHu) value, which affects organoleptic and processing characteristics. This study tests the hypothesis that high pHu aged meat would be more digestible than low pHu unaged (fresh) meat. Longissimus dorsi muscles collected from 59 bull carcasses had pHu values of 5.6-6.9. These were aged for 21 days at -1.5 °C, then raw and cooked (72 °C) samples were enzymatically digested at 37 °C with pepsin (pH 1.9 for 90 min) followed by pancreatin (pH 8.0 for an additional 120 min) to simulate conditions in the stomach and small intestine, respectively. Meat proteins and peptides in the digests were separated by 1D SDS PAGE. Regardless of pHu, ageing or cooking, most sarcoplasmic and myofibrillar proteins were rapidly digested by pepsin, with concomitant release of products identified by LC-MS/MS as mainly myosin-1, -2 and -7, α-actinin-2 or -3 and tropomyosin beta and alpha chains. These products were resistant to further digestion for the entire 210 min duration of the incubation. In terms of rate and extent of digestibility of these resistant products, high pHu > low pHu (P < 0.001), whereas aged > unaged (P < 0.003), with the effect of cooking dependent on pHu and varying somewhat by protein. Overall, the digestibility of meat samples increased with increasing pHu (P < 0.001). Beef meat was highly digestible but could be further differentiated on the basis of its pHu and the ease of digestibility of proteins. Specific carcasses or cuts could be targeted to consumer groups in order to provide benefits and add value.

Effect of ultimate pH on postmortem myofibrillar protein degradation and meat quality characteristics of Chinese Yellow crossbreed cattle.

This paper describes the complex effects of postmortem ultimate pH (pHu) on Chinese Yellow crossbreed cattle quality during postmortem ageing and provides an explanation of how pHu affects beef tenderness. High pHu beef had the highest initial tenderness (P < 0.05) compared with other groups at 1 day postmortem. Intermediate and low pHu beef had similar initial WBSF at 1 day postmortem, but intermediate pHu beef had slower tenderization rate than low pHu beef (P < 0.05). Purge loss, cooking loss, L*, a*, and b* values decreased with increasing pHu during ageing (P < 0.05). Myofibril fragmentation index (MFI) was higher in high pHu beef than intermediate and low pHu beef throughout ageing (P < 0.05). Protein degradation studies found that desmin and troponin-T appeared degraded within 0.5 h postmortem for high and low pHu beef, compared to >2 days for intermediate pHu beef. Overall, Chinese Yellow crossbred cattle tenderness is related to pHu, which may be affected by proteolytic enzymatic activity. Therefore, pHu may be used to predict beef tenderness and other quality characteristics during postmortem ageing. To achieve consistent tenderness, different ageing times should be used, depending on pHu.

Early on-line classification of beef carcasses based on ultimate pH by near infrared spectroscopy

Prediction of ultimate pH (measured 48h post mortem; pHu) in beef from Visible–near infrared (VIS–NIR) spectra collected 20 to 40min post mortem was assessed. Spectra were collected from carcasses (cows: n=86, bulls: n=170, steers: n=363, and heifers: n=38) in a commercial hot boning abattoir under routine conditions. Partial Least Squares (PLS) models showed limited accuracy with RMSE for validation equal to 0.26, 0.20 and 0.36 for the All-animals, Non-bulls and Bulls models, respectively. The pHu–PLS-predicted values were used to segregate carcasses as normal (pHu<5.8) or high (pHu≥5.8) showing better performance, by correctly classifying at least 90% of high pHu carcasses. The Non-bulls model was equivalent to the current technology used in the abattoir to classify carcasses based on pHu. Thus near infrared spectroscopy (NIRS) could be used for on-line classification of beef carcasses based on pHu.

The development of meat tenderness is likely to be compartmentalised by ultimate pH

Bull Musculus longissimus dorsi (n=63) were categorised into high (pH≥6.2), intermediate (pH5.8–6.19) and low (≤5.79) ultimate pH (pHu) and aged up to 28days post mortem at −1°C. High pHu samples were acceptably tender at 1day post mortem and significantly more tender than low pHu meat at all ageing timepoints (p<0.05). Rapid autolysis of μ-calpain in high pHu meat was linked with the more rapid degradation of titin, nebulin and filamin in this pHu group. Desmin degraded faster in low pHu meat and was concurrent with an increase of cathepsin B levels. The results from this study support the hypothesis that beef tenderisation is pHu compartmentalised with tenderness in high and low pHu meat characterised by variable rate of degradation of high and low molecular weight myofibrillar proteins during ageing, which are in turn regulated by μ-calpain and cathepsin B activities.

Small heat shock proteins and toughness in intermediate pHu beef

Bull M. longissimus dorsi (n=94) categorised into high (n=28), intermediate (n=14) and low (n=52) ultimate pH (pHu) were aged at −1.5°C for 28days. Shear force was higher and more variable (p<0.05) in intermediate pHu samples during ageing. Titin, filamin and desmin degradation was also less extensive in intermediate pHu samples compared to the other two pH categories. The extent of the decline of HSP20, HSP27 and αβ-crystallin concentrations during post mortem ageing was pHu related such that high pHu meat maintained the highest concentration of small heat shock proteins followed by intermediate and low pHu meat. μ-Calpain autolysis was slowest in intermediate pHu and cathepsin B activities remained consistently low during ageing in this group (p<0.05). Meat toughness in the intermediate pHu group may be attributed to the combination of a larger pool of sHSP with a sub-optimal cathepsin B activity and intermediary μ-calpain activities.

Post-slaughter changes in ATP metabolites, reducing and phosphorylated sugars in chicken meat

The formation of ATP breakdown products in chicken M. pectoralis major post-slaughter is reported. The concentrations of metabolites were followed in chicken breast throughout the carcass processing post-slaughter and during chilled storage. The concentration of glucose remains similar throughout the period whilst that of glucose-6-phosphate decreases linearly. Glucose and glucose-6-phosphate concentrations were inversely related to the pHu of the breast meat throughout chilled storage. Rapid post-mortem glycolysis and high pHu values suggest the occurrence of stress at and pre-slaughter. Whilst ATP, ADP and AMP were rapidly broken down, the concentration of IMP rose rapidly and remained high. Concentrations of inosine, ribose and hypoxanthine increased gradually post-slaughter but an initial increase in ribose phosphate was not sustained. Most of the potential ribose present in chicken meat, believed to be important for flavor formation, remains bound in the form of inosine and IMP. There is evidence that additional breakdown pathways for ribose and ribose-5-phosphate may deplete the concentrations of these precursors.

MEAT QUALITY OF LOCAL AND HYBRID RABBITS

pH, colour and oxidative status were evaluated to study the effect of rabbit genotype on meat quality. Commercial Hybrids, selected for high growth rate and a local population, characterized by slow growing, were used. Meat quality characteristics of L. lumborum and B. femoris muscles showed significant differences between genotypes. Local population had higher pHu values but lower pH fall values than Hybrids. Hybrids showed higher lightness values and TBARS contents than local population. Meat quality parameters were influenced by genotype. The differences between genotypes could be related to the different degree of maturity because the rabbits, in relation to the different growth rate, were slaughtered at the same weight but at different age.

Characteristics of cold-induced dark, firm, dry broiler chicken breast meat

1. A study was designed to characterise dark, firm, dry (DFD) breast meat resulting from cold exposure of broilers and compare its properties with normal breast meat from cold-stressed and control birds. 2. A total of 140 broilers were selected from 5- and 6-week-old birds exposed to cold temperatures ranging from −18 to −4°C, or a control temperature of +20°C for 3 h in an environmental chamber. Half of these birds were slaughtered immediately following the cold exposure and the other half were given 2 h of lairage. 3. Breast meat samples were categorised based on ultimate pH (pHu) and colour L* (lightness) values into normal (5·7 ≤ pHu ≤ 6·1; 46 ≤ L* ≤ 53) breast meat from control (control-normal) or cold-stressed (cold-normal) birds, and DFD (pHu > 6·1; L* < 46) breast meat, which only occurred in cold-stressed birds (cold-DFD). 4. Residual glycogen was not different between cold-DFD and control-normal breast meat. Lactate concentration was lower in cold-DFD compared with control-normal breast meat. Lactate concentration almost tripled for all the samples by 30 h post-mortem, which resulted in a drop in pH of normal meat, but did not have any effect on pH of DFD breast meat. Glycolytic potential at both 5 min and 30 h post-mortem was lower in DFD breast meat compared with the normal breast meat from both cold-stressed and control birds. 5. Cold-DFD breast meat was significantly darker, with higher pHu, lower cook loss, higher water-binding capacity and processing cook yield than cold-normal and control-normal breast meat, which were not different from each other.