Impact of RN genotype and ageing time on colour characteristics of the pork muscles longissimus dorsi and semimembranosus

Meat and nutritional quality comparison of purebred and crossbred pigs

Crossbreeding is an effective method of improving the efficiency and profit of production in commercial pig operations. To understand the effect of crossbreeding on meat and nutrient quality, a combination including three purebred (Duroc, D; Landrace, L; Yorkshire, Y) and two crossbred pig lines (Landrace × Yorkshire, LY; Duroc × (Landrace × Yorkshire), DLY) frequently used internationally were studied. The results showed that meat from the LY and DLY crosses had lower values for lightness L24h∗, shear force and epinephrine and higher values for drip loss, C18:1, insulin, glucagon and monounsaturated fatty acids than D, L and Y pigs. Moreover, LY had higher values for post mortem pH and lower values for a* and b* than the purebreds. In contrast, DLY had lower values for pH and higher values for a* and b* than the purebreds. Meat quality-related gene analysis showed that the CAST, IGF2 and MC4R gene expression levels in the LY and DLY pigs were significantly higher than those in the D, L and Y pigs. These results indicate that crossbreeding can alter the meat quality, nutritive value, energy metabolism and gene expression of pigs. Future research should focus on microRNA expression and DNA methylation that regulate gene expression and thus affect the meat quality.

Can calcium chloride injection facilitate the ageing-derived improvement in the quality of meat from culled dairy cows?

This study investigated whether the positive effects of ageing on tenderness of meat from culled dairy cows can be facilitated by CaCl₂. Injections of 250 mM CaCl₂ solution (10% wt/wt) were performed on Longissimus dorsi samples from 32 7-yrs old cows. Samples were vacuum packaged and aged for 0, 1, 3, 5 and 7 days. Ageing alone produced lighter and less red meat with lower shear force, higher myofibrillar fragmentation and tenderness scores but also elevated lipid oxidation. For most traits investigated, CaCl₂-injected meat exhibited similar ageing effects, but drip loss increased with age. The CaCl₂-injected meat had a lower shear force and myofibrillar fragmentation increased more rapidly, but drip loss, off-flavour scores, colour stability and oxidative stability were inferior to untreated meat. Overall, it was found possible to accelerate tenderisation of such meat with CaCl₂, but only at the cost of adverse effects in some other quality traits.

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 1. Microscopic analysis of muscles

Three porcine muscles (Longissimus thoracis, Semitendinosus, Masseter), known to have large differences in biochemical and histological traits, were fully characterized and the link between muscle structure and quality evaluated. The oxidative Masseter had more pigment, higher content of metmyoglobin, haem iron, protein and collagen, and was redder with higher fibre numbers, fibre circularity, pH and water holding capacity than the glycolytic Longissimus. Fibre type distribution showed predominance of type IIB in Longissimus and Semitendinosus white, type I in Semitendinosus red and IIA in Masseter. Type I fibres were larger than type IIB and IIA in Semitendinosus and Masseter, respectively, but not in the Longissimus, indicating that fibre size is muscle dependent. Muscle redness was positively correlated with type I fibre traits, haem iron and metmyoglobin, and negatively associated with type II fibre characteristics, non-haem iron and oxymyoglobin. Expressible juice had positive correlation with fibre size and negative with fibre number and connective tissue.

SNP variation in the promoter of the PRKAG3 gene and association with meat quality traits in pig

Background

The PRKAG3 gene encodes the γ3 subunit of adenosine monophosphate activated protein kinase (AMPK), a protein that plays a key role in energy metabolism in skeletal muscle. Non-synonymous single nucleotide polymorphisms (SNPs) in this gene such as I199V are associated with important pork quality traits. The objective of this study was to investigate the relationship between gene expression of the PRKAG3 gene, SNP variation in the PRKAG3 promoter and meat quality phenotypes in pork.

Results

PRKAG3 gene expression was found to correlate with a number of traits relating to glycolytic potential (GP) and intramuscular fat (IMF) in three phenotypically diverse F1 crosses comprising of 31 Large White, 23 Duroc and 32 Pietrain sire breeds. The majority of associations were observed in the Large White cross. There was a significant association between genotype at the g.-311A>G locus and PRKAG3 gene expression in the Large White cross. In the same population, ten novel SNPs were identified within a 1.3 kb region spanning the promoter and from this three major haplotypes were inferred. Two tagging SNPs (g.-995A>G and g.-311A>G) characterised the haplotypes within the promoter region being studied. These two SNPs were subsequently genotyped in larger populations consisting of Large White (n = 98), Duroc (n = 99) and Pietrain (n = 98) purebreds. Four major haplotypes including promoter SNP’s g.-995A>G and g.-311A>G and I199V were inferred. In the Large White breed, HAP1 was associated with IMF% in the M. longissmus thoracis et lumborum (LTL) and driploss%. HAP2 was associated with IMFL% GP-influenced traits pH at 24 hr in LTL (pHULT), pH at 45 min in LTL (pH₄₅LT) and pH at 45 min in the M. semimembranosus muscle (pH₄₅SM). HAP3 was associated with driploss%, pHULT pH₄₅LT and b* Minolta. In the Duroc breed, associations were observed between HAP1 and driploss% and pHUSM. No associations were observed with the remaining haplotypes (HAP2, HAP3 and HAP4) in the Duroc breed. The Pietrain breed was monomorphic in the promoter region. The I199V locus was associated with several GP-influenced traits across all three breeds and IMF% in the Large White and Pietrain breed. No significant difference in promoter function was observed for the three main promoter haplotypes when tested in vitro.

Conclusion

Gene expression levels of the porcine PRKAG3 are associated with meat quality phenotypes relating to glycolytic potential and IMF% in the Large White breed, while SNP variation in the promoter region of the gene is associated with PRKAG3 gene expression and meat quality phenotypes.

Analysis of acid-soluble glycogen in pork extracts of two PRKAG3 genotypes by 1H liquid-state NMR spectroscopy and biochemical methods

Meat extracts with acid-soluble glycogen (macroglycogen) from M. longissmus dorsi of carriers and noncarriers of the PRKAG3 mutation (RN(-) and rn(+) genotype) were analyzed by both (1)H liquid-state NMR spectroscopy and a biochemical method. The (1)H NMR analysis revealed that shorter polymers (dimers, trimers, etc.) of α-1,4-linked glucose were generated 24-48 h post-mortem. This is not possible to elucidate with the biochemical method, by which only the total amount of hydrolyzed glucose residues is determined. The shorter polymers were primarily formed in carriers of the PRKAG3 mutation, suggesting different post-mortem glycogen degradation mechanisms in the two genotypes.

Skeletal muscle proteomics in livestock production

Proteomics allows studying large numbers of proteins, including their post-translational modifications. Proteomics has been, and still are, used in numerous studies on skeletal muscle. In this article, we focus on its use in the study of livestock muscle development and meat quality. Changes in protein profiles during myogenesis are described in cattle, pigs and fowl using comparative analyses across different ontogenetic stages. This approach allows a better understanding of the key stages of myogenesis and helps identifying processes that are similar or divergent between species. Genetic variability of muscle properties analysed by the study of hypertrophied cattle and sheep are discussed. Biological markers of meat quality, particularly tenderness in cattle, pigs and fowl are presented, including protein modifications during meat ageing in cattle, protein markers of PSE meat in turkeys and of post-mortem muscle metabolism in pigs. Finally, we discuss the interest of proteomics as a tool to understand better biochemical mechanisms underlying the effects of stress during the pre-slaughter period on meat quality traits. In conclusion, the study of proteomics in skeletal muscles allows generating large amounts of scientific knowledge that helps to improve our understanding of myogenesis and muscle growth and to control better meat quality.

The significance of diet, slaughter weight and aging time on pork colour and colour stability

The objective of the present study was to investigate the effect of a diet with a low content of digestible starch, slaughter weight and subsequent aging time on meat colour and colour stability. Pork colour was determined as the extent of blooming of M. longissimus thoracis (LT) and M. semimembranosus (SM) after 1, 2, 4, 8 and 15 days postmortem and as colour stability during a subsequent storage period in air for 6 days. Compared to the control diet, the experimental diet resulted in a significantly lower postmortem muscle temperature (1°C; p<0.0001). Moreover, high slaughter weight (110kg) resulted in a higher postmortem temperature in LT (p<0.001) compared to low weight (85kg). Independent of feeding strategy and slaughter weight, the extent of blooming decreased during the first 2-4 days of aging in LT, however, the effect was more pronounced in meat from experimentally fed pigs and pigs with high slaughter weight. This effect was not seen in SM, where a gradual increase in blooming took place throughout the aging period. The colour stability was found to be superior in aged pork from experimentally fed pigs. The discoloration rate was faster in SM compared to LT. In conclusion, the present study shows that the diet composition can be used as a tool to control meat colour and colour stability in pork.