Role of muscle endopeptidases and their inhibitors in meat tenderness

Intense degradation of myosin light chain isoforms in Spanish dry-cured ham

One of the main biochemical changes that take place during the processing of dry-cured ham is the degradation of the muscle protein fraction, mainly due to the action of muscle enzymes. In the present study, the isolation and tentative identification of 137 fragments from myosin light chain 1 (MLC 1), together with 88 fragments originated from myosin light chain 2 (MLC 2), have been achieved for the first time in Spanish dry-cured ham, proving the intense proteolysis experienced by myofibrillar proteins after dry-cured processing. This study was carried out by use of proteomic technology for peptide identification, and the possible enzymes contributing to the degradation of these proteins were also further discussed.

Regulatory polymorphisms in the bovine Ankyrin 1 gene promoter are associated with tenderness and intramuscular fat content

Background

Recent QTL and gene expression studies have highlighted ankyrins as positional and functional candidate genes for meat quality. Our objective was to characterise the promoter region of the bovine ankyrin 1 gene and to test polymorphisms for association with sensory and technological meat quality measures.

Results

Seven novel promoter SNPs were identified in a 1.11 kb region of the ankyrin 1 promoter in Angus, Charolais and Limousin bulls (n = 15 per breed) as well as 141 crossbred beef animals for which meat quality data was available. Eighteen haplotypes were inferred with significant breed variation in haplotype frequencies. The five most frequent SNPs and the four most frequent haplotypes were subsequently tested for association with sensory and technological measures of meat quality in the crossbred population. SNP1, SNP3 and SNP4 (which were subsequently designated regulatory SNPs) and SNP5 were associated with traits that contribute to sensorial and technological measurements of tenderness and texture; Haplotype 1 and haplotype 4 were oppositely correlated with traits contributing to tenderness (P < 0.05). While no single SNP was associated with intramuscular fat (IMF), a clear association with increased IMF and juiciness was observed for haplotype 2.

Conclusion

The conclusion from this study is that alleles defining haplotypes 2 and 4 could usefully contribute to marker SNP panels used to select individuals with improved IMF/juiciness or tenderness in a genome-assisted selection framework.

Genetic markers as one of tools for production of tenderness meat in cattle

Meat tenderness is one of the major characteristic quality of beef not only for consumers but for breeders of beef cattle too. Selection of cattle focussed on an increment of meat tenderness is complicated because this trait has large variability not only between different breeds but between individuals of equal breed too. Similarly a measurement of meat tenderness is expensive because it make after slaughter of animal and ageing of meat post mortem. Therefore it was developed a several methods, by the help of which is possible increase tenderness of meat. However still exist variance in values of meat tenderness which are caused by distinctness genetic base of animal. By using molecular genetic methods was described the most significant candidate genes (CAPN1, CAST) coding formation of the calpains-calpastatin proteolytic system, which exercise an influence on tenderness. The single nucleotide polymorphisms (SNPs) in these genes were using to design commercially genetic marker panels GeneSTAR Tenderness and Igenity Tender-GENE. By help this commercially test is possible to make genotyping and selection of animals for production of tenderness beef meat in meat industry.

Skeletal muscle fiber type and myofibrillar proteins in relation to meat quality

Although numerous studies have reported the relationships among muscle fiber characteristics, lean meat content and meat quality, controversial perspectives still remain. Conventional histochemical classifications may be involved in a high level of error, subjectivity and it could not clearly explain variety of myofibrillar protein isoforms. Therefore, more information is needed on how different factors, such as species, breeds, gender, nutrient conditions, physiological state of animals, and environment factors, affect ultimate meat quality in order to evaluate these uncertainness. Unfortunately, there is little information that completely covers with relationship among the muscle fiber types, myofibrillar proteins and enzymatic proteolysis. In addition to the perspective of postmortem metabolism, protein quality control in skeletal muscle and proteolytic degradation of muscle proteins during postmortem period could help to clarify this relationship. Therefore, the present review will focus on muscle fiber types, typing methods, muscle proteins and meat quality, and will summarize aspects of enzymatic view of proteasome.

Characterization of peptides released by in vitro digestion of pork meat

The main objective of this work was to identify and characterize the peptides generated by simulated gastrointestinal digestion of pork meat (longissimus dorsi) by the sequential action of pepsin and pancreatin. The obtained hydrolysate was analyzed by liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer equipped with a nanoelectrospray ionization source (nano LC-ESI-MS/MS). Using this technique 51 different peptides were identified in the hydrolysate, corresponding to fragments of the main structural muscle proteins and some well-known sarcoplasmic proteins. To the best of our knowledge, this constitutes the highest number of peptides identified in pork meat digests. Peptide fragment size ranged from six to sixteen amino acids, being rich in proline residues and thus making them more resistant to further degradation by digestive enzymes. The present study constitutes a clear evidence of the extensive degradation that pork muscle proteins would undergo after gastrointestinal digestion, giving rise to a wide variety of short peptides. So, the use of in vitro digestion contributes to a better knowledge about the generation of peptides from diets with high protein quality.

Association of polymorphisms in candidate genes with colour, water-holding capacity, and composition traits in bovine M. longissimus and M. semimembranosus

The objective of this study was to determine the association of single nucleotide polymorphisms (SNP) in selected candidate genes with sensory and technological meat quality traits in commercial cattle. SNP in seven candidate genes were genotyped in 130 crossbred Bos taurus cattle using PCR-RFLP. Reported associations between calpastatin (CAST) and Warner-Bratzler shear force and carboxypeptidase E (CPE) and intra-muscular fat were not confirmed. However, SNP in CAST, amp-activated protein kinase, gamma-3 subunit (PRKAG3), growth hormone receptor (GHR) and stearoyl coA desaturase (SCD) genes were significantly associated with colour traits (p<0.05). The PRKAG3 SNP was additionally associated with cook loss in M. longissimus thoracis et lumborum (p<0.05) and tended towards association in M. semimembranosus (p<0.1). An association with pH was identified for the SCD SNP (p<0.001). The GHR polymorphism was influential on moisture and intra-muscular fat in M. semimembranosus and protein content in both muscles (p<0.05). Only CPE was associated with sensory traits (flavour in M. longissimus, p<0.01).

Proteome changes during meat aging in tough and tender beef suggest the importance of apoptosis and protein solubility for beef aging and tenderization

Within a population of Charolais young bulls, two extreme groups of longissimus thoracis muscle samples, classified according to Warner-Bratzler shear force (WBSF) of 55 degrees C grilled meat, were analyzed by 2D-electrophoresis. Muscle analyses were performed on 4 bulls of the "tender" group (WBSF=27.7+/-4.8 N) and 4 bulls of the "tough" group (WBSF=41.2+/-6.1 N), at 3 post-mortem times: D0, samples taken within 10 min post-mortem; D5 and D21, samples kept at 4 degrees C under vacuum during 5 and 21 days. Proteins of muscle samples were separated in two fractions based on protein solubility in Tris buffer: "soluble" and "insoluble". Proteins of both fractions were separated by 2D-electrophoresis. Evolution of spots during the 3 post-mortem times was analyzed by hierarchical classification (HCA). Three clusters of proteins presenting similar evolution profiles provided accurate classification of post-mortem times and showed the translocation of some chaperone proteins and glycolytic enzymes from the soluble fraction to the insoluble fraction between D0 and D5. Cellular structure dismantlement and proteolysis was observed at D21. Effect of group ("tender" vs "tough") on spot intensities was tested by ANOVA. At D0, higher quantity of proteins of the inner and outer membrane of mitochondria was found in the tender group suggesting a more extensive degradation of mitochondria that may be related to the apoptotic process.

Naturally generated small peptides derived from myofibrillar proteins in Serrano dry-cured ham

A proteomic approach has been carried out to investigate the extensive proteolysis occurring in the processing of Serrano ham. In this study, a total of 14 peptide fragments derived from myosin light chain I and titin have been identified for the first time. Nine of these peptides originated from myosin light chain I protein, with the loss of dipeptides at the N-terminal position observed in some of them. This suggests that dipeptidyl peptidases are involved in the generation of dipeptides, which contribute to the generation of the characteristic taste associated with Serrano ham. The other five peptides came from the PEVK region of the titin protein. This region is believed to confer elasticity to the sarcomere as well as the ability to bind calpains. The hypothetical action of mu-calpain and calpain 3 enzymes over this region would make these enzymes potentially responsible for protein breakdown during the early dry-curing stage.

Variation in bull beef quality due to ultimate muscle pH is correlated to endopeptidase and small heat shock protein levels

This study set out to determine if ultimate pH (pH(u)) affected the performance of intracellular small heat shock protein and endopeptidase dynamics in muscle during beef ageing. Longissimus dorsi muscles from 39 Angus or Limousin×Angus bulls were examined to see if pH(u) achieved at 22h post mortem (rigor) affected tenderness and water holding capacity of beef. Samples were segregated into three pH(u) groups termed high (pH>6.3), intermediate (5.7<pH<6.3) and low (pH<5.7) pH(u) beef. More than 30% of bull beef did not achieve acceptable tenderness at 8 days post mortem with this ageing regime. No significant differences in calpain or cathepsin enzyme levels due to meat pH were observed until after 22h post mortem, but low pH(u) beef had elevated caspase 3/7 activity soon after slaughter. At 22h post mortem, greater levels of μ-calpain enzyme were found in the high and intermediate pH(u) beef and cathepsin B levels were superior in the low pH(u) beef after 2 days post mortem. Different rates of desmin and troponin T protein degradation were also observed in aged bull beef. Both proteins were degraded within 6h post mortem for high pH(u) beef, but took >3 days post mortem for intermediate pH(u) beef. High levels of alpha β-crystallin (aβC) at 22h post mortem coincided with delayed muscle protein degradation for low pH(u) beef. Our results support the hypothesis that aβC shields myofibrils and buffers against endopeptidase degradation of beef structure during ageing.

Activity of aspargate (cathepsin D), cysteine proteases (cathepsins B, B + L, and H), and matrix metallopeptidase (collagenase) and their influence on protein and water-holding capacity of muscle in commercially farmed atlantic halibut (Hippoglossus hippoglossus L.)

Atlantic halibut (Hippoglossus hippoglossus L.) were commercially farmed in Helgeland, Norway (May 2004-May 2005). The average weight (Mb) of fish increased over the 12 month production cycle by approximately 73% for females and approximately 50% for males, although during the winter months (November-early May) Mb was unchanged in females and declined by 18% in males because of sexual maturation and sperm release. Periods of zero or negative growth were associated with up to 5.7% (females) and 17.9% (males) decline in fast muscle protein content. The activities of cathepsins B, B + L, H, and D showed a reciprocal relationship and were highly correlated with the changes in protein content. Water-holding capacity was measured as the liquid loss increased from 3-5% in November to 11-13% in May. Two general additive models (GAMs) showed that cathepsin B + L, cathepsin D, and collagenase explained 73.1% of the total variance in protein content, while cathepsin H was the largest contributor to liquid loss, explaining approximately 48.8% of the total variance. The results indicate that to obtain the best flesh quality Atlantic halibut should be harvested in the fall or early winter when the liquid loss and cathepsin activities are low and less likely to cause problems during secondary processing and storage.

Proteomic identification of actin-derived oligopeptides in dry-cured ham

An intense proteolysis of muscle proteins, mainly due to the action of endogenous proteolytic enzymes, has been reported to occur during the processing of dry-cured ham. This gives rise to an important generation of free amino acids and peptides of small size that contribute directly or indirectly to flavor characteristics of the final product. The nature and properties of the free amino acids generated during postmortem proteolysis have been well established. However, little is known about the identity of peptides generated during the processing of dry-cured ham. In the present paper, we describe the isolation (by ethanol precipitation followed by size exclusion and reverse phase chromatographies) and identification (by matrix-assisted laser desorption/ionization time-of-flight MS and collision-induced dissociation MS/MS) in a Spanish dry-cured ham of the following four oligopeptides: (A) TKQEYDEAGPSIVHR, (B) ITKQEYDEAGPSIVHRK, (C) DSGDGVTHNVPIYE, and (D) DSGDGVTHNVPIYEG. This is the first time that these peptide fragments have been reported in dry-cured ham at the end of processing. Sequence homology analysis revealed that the four peptides originated from muscle actin, indicating an extensive hydrolysis of this protein during dry-curing. Some of the cleavage sites corresponding to these fragments in actin were reproduced by other authors through the incubation of this myofibrillar protein in the presence of cathepsin D (EC 3.4.23.5), thus supporting a relevant action of this enzyme during the processing of dry-cured ham.

Effect of age, muscle type, and insulin-like growth factor-II genotype on muscle proteolytic and lipolytic enzyme activities in boars1

Recently, a paternally expressed quantitative trait nucleotide (QTN) in the regulatory sequence of the IGF-II gene with effects on muscle growth and fat deposition was discovered in the pig. This QTN is also known as the IGF-II intron3 G3072A mutation. The aim of the current study was to determine the effects of age, muscle type, and IGF-II genotype (Apat, mutant allele vs. Gpat, wild-type allele) on muscle proteolytic and lipolytic enzyme activities. At approximately 4, 8, 16, and 26 wk of age, boars (n = 6 to 15 per genotype x age group) were slaughtered and mu- and m-calpain (CALP), calpastatin (CAST), cathepsins (CATH) B+L and H, acid lipase, and phospholipase activities were measured in Longissimus thoracis et lumborum, Semimembranosus, and Triceps brachii muscle samples taken soon after slaughter. Activities of CATH B+L and H, mu- and m-CALP, and acid lipase were not affected by the IGF-II genotype. Activity of CAST was greater (P < 0.005) and m-CALP:CAST was less (P < 0.05) in Apat animals. Because CAST activity and m-CALP:CAST are known to be related to protein degradation, satellite cell fusion, or both, it is likely that differences in proteolytic enzyme activities are involved in the greater percentage of muscle mass in Apat animals. Age and muscle type influenced proteolytic and lipolytic enzyme activities (P < 0.05), except for mu- and m-CALP (no effect of muscle) and acid lipase (no effect of age). The same pattern in mu-CALP, CAST, and m-CALP:CAST with age was found during growth for the 3 muscles, although clear differences (P < 0.05) between muscles existed. In general, and in agreement with previous reports, greater enzyme activities were found in the more oxidative Triceps brachii muscle compared with the other 2 muscles. A remarkable increase (P < 0.05) from 16 to 26 wk of age in mu-CALP, CAST, mu-CALP:CAST, and CATH H and a large decrease (P < 0.05) in acid phospholipase and m-CALP:CAST was found. For m-CALP and CATH B+L, a gradual decrease (P < 0.05) was found with age. Although age effects on enzyme activities could only partly be interpreted biologically in relation to the muscle growth rate, this study showed that proteolytic and lipolytic enzyme activities change during growth.

Changes in caspase activity during the postmortem conditioning period and its relationship to shear force in porcine longissimus muscle1

The objective of this study was to investigate the protease family caspases in skeletal muscle and their potential contribution to postmortem proteolysis and meat tenderization. Ten Large White gilts were slaughtered, and samples of LM were taken at 0, 2, 4, 8, 16, 32, and 192 h after slaughter and immediately snap frozen in liquid nitrogen. Samples were subsequently analyzed for caspase 3/7 and caspase 9 activity, protein levels of known caspase substrates, alpha II spectrin and poly (ADP-ribose) polymerase (PARP), as well as, at 192 h, shear force. Specific degradation products of alpha II spectrin and PARP, which are known indicators of caspase activity, and apoptosis were detected on immunoblots of muscle samples taken over the postmortem period. The relationships between the changes observed in caspase activities and protein levels of PARP and spectrin across the entire postmortem conditioning period were investigated (n = 70). Protein levels of alpha II spectrin cleavage products across the conditioning period were found to correlate positively to caspase 3/7 activity (r = 0.38, P = 0.003) and caspase 9 activity (r = 0.32, P = 0.012), indicating that caspase-mediated cleavage was occurring in situ. There was a negative relationship between shear force and the 0 to 32 h ratio of caspase 3/7 (r = -0.62, P = 0.053) and caspase 9 activities (r = -0.68, P = 0.044). In addition, there was also a negative relationship between shear force and the level of the caspase-generated alpha II spectrin 120 kDa degradation product (r = -0.75, P = 0.012). The findings of this study indicate that changes in caspase activity and caspase-mediated cleavage take place in muscle during the conditioning period, and this could be associated with the development of tender meat.

Trends in Postmortem Aging in Fish: Understanding of Proteolysis and Disorganization of the Myofibrillar Structure

Postmortem tenderization is caused by enzymatic degradation of key structural proteins in myofibrils as well as in extracellular matrix, and of proteins involved in intermyofibrillar linkages and linkages between myofibrils and the sarcolemma. The function of these proteins is to maintain the structural integrity of myofibrils. Current data indicate that calpains and cathepsins may be responsible for degradation of these proteins. Other phenomena occurring in cells postmortem (pH drop, sarcoplasmic Ca2+ increase, osmotic pressure rise, oxidative processes) may act in synergy with proteases. Our understanding of the underlying mechanisms of muscle degradation should be improved for an accurate evaluation of the postmortem muscle changes and consequently of the fish quality.

Genetic and environmental effects on the muscle structure response post-mortem

This paper reviewed the mechanisms by which glycolytic rate and pre-rigor stretching of muscle impact on meat quality. If muscle is free to shorten during the rigor process extremes in glycolytic rate can impact negatively on meat quality by inducing either cold or rigor shortening. Factors that contribute to variation in glycolytic rate include the glycogen concentration at slaughter and fibre type of the muscle. Glycolysis is highly sensitive to temperature, which is an important factor in heavy grain fed carcasses. An alternative solution to controlling glycolysis is to stretch the muscle pre-rigor so that it cannot shorten, thus providing an insurance against extremes in processing conditions. Results are presented which show a large reduction in variance (both additive and phenotypic) in tenderness caused by pre-rigor stretching. Whilst this did not impact on the heritability of shear force, it did reduce genotype differences. The implications of these results on the magnitude of genotype effects on tenderness is discussed.