New frontiers in understanding drip loss in pork: recent insights on the role of postmortem muscle biochemistry

Alfalfa Silage Diet Improves Meat Quality by Remodeling the Intestinal Microbes of Fattening Pigs

Because the demand for pork is increasing, it is crucial to devise efficient and green methods to improve the quality and quantity of meat. This study investigated the improvement in pork quality after the inclusion of alfalfa meal or alfalfa silage in pig diet. Our results indicated that alfalfa silage improved meat quality more effectively in terms of water-holding capacity, drip loss, and marbling score. Besides, an alfalfa silage diet can affect the level of fatty acids and amino acids in pork. Further, alfalfa silage was found to improve meat quality by remodeling intestinal microbiota and altering the level of SCFAs, providing a viable option for improving meat quality through forage.

Effects of Dietary Nano-Zinc Oxide Supplementation on Meat Quality, Antioxidant Capacity and Cecal Microbiota of Intrauterine Growth Retardation Finishing Pigs

As nano-zinc oxide (Nano-ZnO), a new type of nanomaterial, has antioxidant and intestinal protection effects, we hypothesized that dietary Nano-ZnO could modulate poor meat quality, oxidative stress and disturbed gut microbiota in the finishing pig model of naturally occurring intrauterine growth retardation (IUGR). A total of 6 normal-born weight (NBW) and 12 IUGR piglets were selected based on birth weight. The pigs in the NBW group received a basal diet, and IUGR pigs were randomly divided into two groups and treated with basal diet and 600 mg/kg Nano-ZnO-supplemented diet. Dietary Nano-ZnO ameliorated IUGR-associated declined meat quality by lowering the drip loss_48h, cooking loss, shearing force and MyHc IIx mRNA expression, and raising the redness (a*), peak area ratio of immobilized water (P₂₂), sarcomere length and MyHc Ia mRNA expression. Nano-ZnO activated the nuclear factor erythroid 2-related factor 2-glutamyl cysteine ligase (Nrf2-GCL) signaling pathway by promoting the nuclear translocation of Nrf2, increasing the GCL activities, and mRNA and protein expression of its catalytic/modify subunit (GCLC/GCLM), thereby attenuating the IUGR-associated muscle oxidative injury. Additionally, the composition of IUGR pigs' cecal microbiota was altered by Nano-ZnO, as seen by changes in Shannon and Simpson indexes, the enhanced UCG-005, hoa5-07d05 gut group and Rikenellaceae RC9 gut group abundance. The UCG-005 and hoa5-07d05 gut group abundance were correlated with indicators that reflected the meat quality traits and antioxidant properties. In conclusion, Nano-ZnO improved the IUGR-impaired meat quality by altering water holding capacity, water distribution and the ultrastructure of muscle, activating the Nrf2-GCL signaling pathway to alleviate oxidative status and regulating the cecal microbial composition.

Towards the discovery of goat meat quality biomarkers using label-free proteomics

This study aimed to identify for the first time protein biomarkers of meat quality traits from Longissimus thoracis (LT) muscle of goats (Capra hircus). Male goats of similar age and weight reared under extensive rearing conditions were used to relate the LT muscle proteome with multiple meat quality traits. The early post-mortem muscle proteome analyzed using label-free proteomics was compared among three texture clusters built using hierarchical clustering analysis. Twenty-five proteins were differentially abundant and their mining using bioinformatics revealed three major biological pathways to be involved: 10 muscle structure proteins (MYL1, MYL4, MYLPF, MYL6B, MYH1, MYH2, ACTA1, ACTBL2, FHL1 and MYOZ1); 6 energy metabolism proteins (ALDOA, PGAM2, ATP5F1A, GAPDH, PGM1 and ATP5IF1), and two heat shock proteins: HSPB1 (small) and HSPA8 (large). Seven other miscellaneous proteins belonging to pathways such as regulation, proteolysis, apoptosis, transport and binding, tRNA processing or calmodulin-binding were further identified to play a role in the variability of goat meat quality. The differentially abundant proteins were correlated with the goat meat quality traits in addition to multivariate regression models built to propose the first regression equations of each quality trait. This study is the first to highlight in a multi-trait quality comparison the early post-mortem changes in the goat LT muscle proteome. It also evidenced the mechanisms underpinning the development of several quality traits of interest in goat meat production along the major biochemical pathways at interplay. SIGNIFICANCE: The discovery of protein biomarkers in the field of meat research is an emerging topic. In the case of goat meat quality, very few studies using proteomics have been conducted with the aim of proposing biomarkers. Therefore, this study is the first to quest for biomarkers of goat meat quality using label-free shotgun proteomics with a focus on multiple quality traits. We identified the molecular signatures underlying goat meat texture variation, which were found to belong to muscle structure and related proteins, energy metabolism and heat shock proteins along with other proteins involved in regulation, proteolysis, apoptosis, transport and binding, tRNA processing or calmodulin-binding. We further evaluated the potential of the candidate biomarkers to explain meat quality using the differentially abundant proteins by means of correlation and regression analyses. The results allowed the explanation of the variation in multiple traits such as pH, color, water-holding capacity, drip and cook losses traits and texture.

Effects of sweet potato vine silage supplementation on meat quality, antioxidant capacity and immune function in finishing pigs

Sweet potato vine, the byproduct of sweet potato, has a high nutritional value. Silage is an effective solution for nutrient preservation. This article explored the effects of sweet potato vine silage (SPVS) supplementation on meat quality, antioxidant capacity and immune function in finishing pigs. One hundred and eighty finishing pigs (Berkshire × Licha Black) with a body weight of 74.54 ± 3.32 kg were randomly divided into three groups. The three groups were separately fed basal diet (Ctrl), Ctrl supplemented with 2.5% SPVS (LSPVS) or 5% SPVS (HSPVS) on a dry matter basis. Results showed that the eye muscle area in the LSPVS group was significantly increased. The carcass weight in the HSPVS was significantly reduced compared with Ctrl. For the meat quality, only cooking loss in both HSPVS and LSPVS was reduced while other indexes had no significant differences. For the antioxidant capacity, the hepatic level of glutathione (GSH) peroxidase (GSH-PX) was significantly upregulated in LSPVS but downregulated in HSPVS. In the serum, HSPVS decreased GSH level and increased GSH-PX level. HSPVS significantly reduced hepatic interleukin-1β (IL-1β) levels and LSPVS significantly reduced IL-12 levels and increased IL-8 and IL-6 levels. Moreover, HSPVS and LSPVS promoted the secretion of immunoglobulin M (IgM) and IgG in the serum. Our data showed that low-dose SPVS supplementation improved carcass traits and high-dose SPVS supplementation increased immune function in finishing pigs, which provides a new alternative to improve animal health.

Effects of dietary adenosine and adenosine 5′-monophosphate supplementation on carcass characteristics, meat quality, and lipid metabolism in adipose tissues of finishing pigs

This study investigated the effects of adenosine (ADO) and adenosine 5'-monophosphate (AMP) supplementation on the growth performance, carcass characteristics, meat quality, and lipid metabolism in adipose tissues of finishing pigs. The pigs were allocated to three treatment groups: the control diet, 0.2%ADO diet, or 0.2%AMP diet. Compared with CON group (CON), both ADO and AMP groups increased in carcass straight length (P < 0.05) and decreased in drip loss (P < 0.05), while AMP group tended to increase in redness value (P = 0.05) and decreased in free amino acid content in longissimus thoracis (LT) muscle (P < 0.05). Additionally, ADO or AMP supplementation increased the ADO or AMP content in serum, adipose tissue, and LT muscle (P < 0.05), as well as the protein level of adenosine 2A receptor (A2a) in adipose tissue (P < 0.05). Moreover, both ADO and AMP groups showed an increase in the expression of lipolysis genes (ATGL and HSL) in adipose tissue (P < 0.05). Overall, AMP supplementation could improve meat quality, and ADO and AMP supplementation regulate the lipid metabolism of finishing pigs.

Bioimpedance-based Authentication of Defrosted Versus Fresh Pork at the End of Refrigerated Shelf Life

Correct food labeling is a legal requirement and helps consumers to make informed purchasing choices. Mislabeling defrosted meat as fresh is illegal in the EU. However, there are no standardized technologies to authenticate fresh versus defrosted meat. We address this by testing if bioimpedance-based measurements can separate defrosted meat from refrigerated-only meat at the end of shelf life, i.e., when also fresh meat shows deterioration. Pork sirloin samples from 20 pigs were first tested at 12 days postmortem ('fresh group'). This time point was chosen to represent a typical use-by date for refrigerated storage of fresh pork. Then, all samples were transferred to a -24°C freezer for 3 days and thawed for 2 days before final testing ('frozen-thawed group'). Bioimpedance analyses (BIA) were done in a frequency range of [10²-10⁶ Hz]. Weight, pH and electrode positioning were assessed to test for potential confounding effects. Statistics for treatment dependent differences were based on the established P_y parameter and phase angle, which were extracted from the BI spectra. We found that using bioimpedance testing with tetrapolar electrodes, P_y and phase angle allowed almost complete separation of fresh and previously frozen samples. However, within the whole sample population, there was some overlap between the spectra of fresh and frozen samples. Yet, based on P_y, only one fresh sample (5% of N_total=20) fell in the lowest P_y class with all the frozen samples. We used a multifactorial design that allowed to test the effects of potential confounding factors, such as electrode positioning and meat quality parameters. We found a relatively low explained variance for the P_y parameter, indicating that confounding effects from other factors or quality defects in fresh pork may affect the detection capacity of bioimpedance-based authentication of fresh pork. Our data, therefore, suggest that reliable fresh-label authentication with bioimpedance testing should be based on testing a small number of samples to represent a specific lot of pork that is to be inspected.

Water holding properties of Atlantic salmon

With global seafood production increasing to feed the rising population, there is a need to produce fish and fishery products of high quality and freshness. Water holding properties, including drip loss (DL) and water holding capacity (WHC), are important parameters in determining fish quality as they affect functional properties of muscles such as juiciness and texture. This review focuses on the water holding properties of Atlantic salmon and evaluates the methods used to measure them. The pre- and postmortem factors and how processing and preservation methods influence water holding properties and their correlations to other quality parameters are reviewed. In addition, the possibility of using modelling is explained. Several methods are available to measure WHC. The most prevalent method is the centrifugation method, but other non-invasive and cost-effective approaches are increasingly preferred. The advantages and disadvantages of these methods and future trends are evaluated. Due to the diversity of methods, results from previous research are relative and cannot be directly compared unless the same method is used with the same conditions.

Transcriptome profiling analysis of muscle tissue reveals potential candidate genes affecting water holding capacity in Chinese Simmental beef cattle

Water holding capacity (WHC) is an important sensory attribute that greatly influences meat quality. However, the molecular mechanism that regulates the beef WHC remains to be elucidated. In this study, the longissimus dorsi (LD) muscles of 49 Chinese Simmental beef cattle were measured for meat quality traits and subjected to RNA sequencing. WHC had significant correlation with 35 kg water loss (r = − 0.99, p < 0.01) and IMF content (r = 0.31, p < 0.05), but not with SF (r = − 0.20, p = 0.18) and pH (r = 0.11, p = 0.44). Eight individuals with the highest WHC (H-WHC) and the lowest WHC (L-WHC) were selected for transcriptome analysis. A total of 865 genes were identified as differentially expressed genes (DEGs) between two groups, of which 633 genes were up-regulated and 232 genes were down-regulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment revealed that DEGs were significantly enriched in 15 GO terms and 96 pathways. Additionally, based on protein–protein interaction (PPI) network, animal QTL database (QTLdb), and relevant literature, the study not only confirmed seven genes (HSPA12A, HSPA13, PPARγ, MYL2, MYPN, TPI, and ATP2A1) influenced WHC in accordance with previous studies, but also identified ATP2B4, ACTN1, ITGAV, TGFBR1, THBS1, and TEK as the most promising novel candidate genes affecting the WHC. These findings could offer important insight for exploring the molecular mechanism underlying the WHC trait and facilitate the improvement of beef quality.

Effects of protein posttranslational modifications on meat quality: A review

Meat quality plays an important role in the purchase decision of consumers, affecting producers and retailers. The formation mechanisms determining meat quality are intricate, as several endogenous and exogenous factors contribute during antemortem and postmortem periods. Abundant research has been performed on meat quality; however, unexpected variation in meat quality remains an issue in the meat industry. Protein posttranslational modifications (PTMs) regulate structures and functions of proteins in living tissues, and recent reports confirmed their importance in meat quality. The objective of this review was to provide a summary of the research on the effects of PTMs on meat quality. The effects of four common PTMs, namely, protein phosphorylation, acetylation, S-nitrosylation, and ubiquitination, on meat quality were discussed, with emphasis on the effects of protein phosphorylation on meat tenderness, color, and water holding capacity. The mechanisms and factors that may affect the function of protein phosphorylation are also discussed. The current research confirms that meat quality traits are regulated by multiple PTMs. Cross talk between different PTMs and interactions of PTMs with postmortem biochemical processes need to be explored to improve our understanding on factors affecting meat quality.

Meat quality of Pulawska breed pigs and image of longissimus lumborum muscle microstructure compared to commercial DanBred and Naima hybrids

The objective of this article was the evaluation of selected properties of meat quality including the characteristics of longissimus lumborum (LL) muscle microstructure of Pulawska breed pigs and fatteners of the DanBred and Naima hybrids which are used in national meat production. Three genetic groups of fatteners were studied in the experiment: group I – DanBred hybrid; group II – Naima hybrid; and group III – the Pulawska breed. Pig fattening took place under the same environmental conditions from the starting weight of 30 kg ± 2 kg to 103–105 kg. For the analysis of muscle fibre characteristics and meat quality from each group, 30 animals were selected ( 1:1 ). Physico-chemical properties and ultrastructure were evaluated in samples collected from the LL muscle. A statistically significant impact (P<0.01) of a genetic group on pH45, content of water, protein and ash, as well as on the colour of meat, the number of STOs (slow-twitch oxidatives) and the diameter of FTG (fast-twitch glycolytic) muscle fibres, was found. Meat of the Pulawska breed, compared to DanBred and Naima, showed a statistically significant (P<0.01) higher (by 2.05 % and 2.49 %, respectively) nutritional value expressed as protein content and mineral components. Overall, these results imply better biological properties of Pulawska meat than DanBred and Naima hybrids. The higher STO and lower FTG found in muscles from Pulawska pigs might partially explain meat quality differences found between the breeds in the present study. The data of the current study indicated that meat quality characteristics and muscle microstructure of fatteners showed differences, and these differences may be used for alternative pork meat production for the consumer.

Meat color is determined not only by chromatic heme pigments but also by the physical structure and achromatic light scattering properties of the muscle

Meat color is important for consumer acceptability, with excessively dark meat often associated with consumer rejection. It is determined chromatically by pigment content (measured by hue and chroma) and achromatically by scattering of light by the microstructure (measured by lightness), the latter of which has received minimal research focus. This review discusses the individual components of the meat microstructure that cause differences in achromatic contributions to color. Differences in achromatic light scattering between light and dark extremes of meat color are most likely explained by structural attributes within the muscle cell. These differences are proposed to arise from variations in (a) transverse shrinkage of the structural lattice of the myofilaments, myofibrils, and muscles fibers, (b) longitudinal shrinkage of the sarcomere, and (c) different protein composition of the surrounding medium (sarcoplasm and extracellular space). These are discussed at a mechanistic level, in relation to six parameters of the muscle cell: (a) protein surface charge altering the myofilament spacing, (b) protein solubility, (c) sarcoplasmic protein binding to myofilaments and myofibrils, (d) integrity of the cytoskeleton and cell adhesion proteins, (e) sarcomere integrity and myofibrillar proteins, and (f) myosin denaturation and rigor bond modification. New data are presented to support the proposed role of structural elements in muscle causing achromatic light scattering and their contribution to the surface color of meat. In addition, the relationships between lightness and water holding capacity and pH are explored and the economic impact of dark meat for the meat industry is discussed.

Effects of electrical stimulation and pre-rigor conditioning temperature on aging potential of hot-boned beef M. longissimus lumborum

The objective of this study was to create various pH/temp decline rates in hot-boned bull beef M. longissimus lumborum (LL) through a combination of electrical stimulation (ES) and pre-rigor holding temperature. The relationship between the pre-rigor interventions, the activities of µ-calpain and small heat shock proteins (sHSP), and the impacts on meat product quality were determined. Paired LL loins from 13 bulls were hot-boned within 40 min of slaughter, immediately ES and subjected to various holding temperatures (5, 15, 25, and 35°C) for 3 hr. The rate of muscle pH decline, sarcomere length, shear force, and proteolysis of muscle proteins were measured. ES-25°C had a longer sarcomere length compared to non-electrical stimulation samples. ES-25°C and ES-35°C samples had lower shear force values, higher µ-calpain activity and higher desmin, troponin-T, and sHSP degradation. The above findings suggest that pH/temp decline rates created in hot-boned muscle impacted muscle protein proteolysis by increasing the activity of proteases and degradation of sHSP.

Effect of Season, Location, Filleting Regime and Storage on Water-Holding Properties of Farmed Atlantic Salmon (Salmo salar L.)

The effect of season, localization, filleting regime and storage on water-holding properties of Atlantic salmon (Salmo salar L.) was investigated. Salmon was sampled at two different slaughter facilities (in the north and south of Norway) in autumn and spring and divided in pre- and post-rigor groups, which were sampled before and after filleting. This gave a total of 16 groups that were analyzed for water-holding capacity (WHC), water content and pH. In addition, a storage trial was performed to assess the effect of all the design variables on drip loss and the composition of the drip loss during up to 18 days of storage. WHC was significantly affected by both rigor status and filleting, while water content was affected by localization and filleting. In addition, post-rigor filleting gave significantly decreased drip loss compared to pre-rigor filleting. However, storage time had the highest impact on the drip loss. Based on this, it is concluded that pre-rigor filleted salmon have excellent water-holding properties and a great potential for early processing (pre-rigor processing). It was however difficult to find a clear connection between the drip loss and the water-holding capacity of the muscle.

Quality of meat from three muscles of farmed fallow deer (Dama dama)

The quality of three muscles (supraspinatus, longissimus, semimembranosus) were studied in a group of 12 farmed fallow deer bucks (Dama dama) aged 28 months. The aim was to compare the selected quality traits of these muscles and to assess the extent to which these traits change after 14 days of being stored in vacuum packaging. Both the pH and the temperature were significantly affected by the muscle (P < 0.0001) and the time of storage (P < 0.0001). The supraspinatus muscle had the highest initial and final pH (pH0.5 h = 6.95; pH15d = 5.93), while m. semimembranosus showed the greatest drop in temperature (by 37.5°C) 24 h postmortem. The colour parameters differed among muscles. Only lightness (L*) was not influenced by the duration of storage (P = 0.081). The 14-day storage in a vacuum bag caused a decrease in the drip loss (P = 0.002), free water (%; P = 0.001), free water (cm2; P < 0.0001) and a cooking loss (P = 0.050). The duration of time in storage caused an increase in the dry-matter (P = 0.049) and crude-protein (P = 0.044) contents and a decrease of the water to protein ratio (W : CP; P = 0.014). There was a significant effect of muscle on the dry-matter (P < 0.0001) and crude-protein (P < 0.001) contents and W : CP (P < 0.0001). The highest contents of dry matter (P ≤ 0.01) and crude protein (P ≤ 0.01) were found in m. longissimus. The highest W : CP was observed in m. supraspinatus (W : CP24 h = 4.02; W/CP15d = 3.92). The results indicated a different technological quality of the analysed muscles, and, thus, a need to further explore the background of these differences in the early postmortem period and after meat maturation.

Influence of carcass weight on meat quality of commercial feedlot steers with similar feedlot, slaughter and post-mortem management

The effects of beef carcass weight on muscle pH/temperature profile and selected meat quality attributes were evaluated. Twenty-six carcasses from light (≤260kg, n=15) and heavy (≥290kg, n=11) feedlot steers were randomly allocated and stimulated with low voltage electrical stimulation (LVES) for 30s at 7min post-mortem (pm). Quality evaluations were carried out on samples from the Longissimus et lumborum (LL) muscle from the left side of each carcass. Heavier carcasses showed faster pH decline and slower (P<0.05) temperature decline at 45min, 3, 6, 12 and 24h pm. Heavier carcasses passed through the heat shortening window (i.e. at pH6, temperature was >35°C) but there was no sign of sarcomere shortening in any carcass. Significantly lower (P<0.05) shear force values were recorded in the heavier carcasses at 3days pm but at 14days pm, heavier carcasses had numerically lower but not significantly different shear force. Heavier carcasses produced numerically higher but not significant (P>0.05) drip loss at 3 and 14days pm as well as higher L* (meat lightness) (P<0.05) and C* (chroma) (P<0.05) values early (2days) pm. However, at 14days pm, there were no significant differences between the light and heavy carcasses in terms of L* and C*. No significant difference was observed between heavy and light carcasses in terms of H* at 2 and 14days pm. The study showed that heavier carcasses which favor slaughter house pricing can be produced and processed alongside lighter carcasses without significant detrimental effects on meat quality by using low voltage electrical stimulation (LVES).

Blood haematology, muscle pH and serum cortisol changes in pigs with different levels of drip loss

Objective

An experiment was conducted to study the blood haematology, muscle pH, and serum cortisol changes in pigs with different levels of drip loss.

Methods

Two groups (low and high) of 20 animals were selected from 100 pigs based on drip loss. All [Duroc× (Large White×Landrace)] pigs were slaughtered according to standard slaughtering procedures. At exsanguinations, blood samples were taken for the haematological parameters and serum cortisol analysis. The muscle samples were taken from longissimus dorsi muscle to evaluate the muscle pH and drip loss.

Results

Haematological parameters of low drip loss group showed higher content of white blood cells and monocytes than high drip loss group (p<0.05). The low drip loss group had higher muscle pH at 45 min (p<0.05) and 24 h (p<0.001) post-mortem than the high drip loss group. However, there was no significant difference in serum cortisol levels (p>0.05).

Conclusion

Drip loss is mainly affected by the muscle pH decline after slaughter and also might be affected by white blood cells and monocytes.

Protein profile and physicochemical characteristics of meat of lambs fed diets supplemented with rapeseed oil, fish oil, carnosic acid, and different chemical forms of selenium

Abstract. The objective of this study was to evaluate the physicochemical characteristics of the longissimus muscle of lambs fed a control diet containing 3 % rapeseed oil (RO) (group I); an experimental diet with 2 % RO and 1 % fish oil (FO) (group II); or experimental diets with coupled addition of 2 % RO, 1 % FO, and 0.1 % carnosic acid (CA) (group III) without/with 0.35 ppm Se as selenized yeast (SeY) (group IV) or selenate (SeVI as sodium selenate, Na2SeO4) (group V). The results showed that dietary FO or SeVI affected the ultimate pH and meat color in comparison to lambs fed the control diet. The differences noted between diets in the case of muscle tissue were as follows: myosin HC (heavy chain) and LC1 (light chain), 150 kDa, α-actinin, 60 kDa, and TnT (troponin T), 30 kDa protein. The addition of FO to lamb diets resulted in a lower content of 30 kDa proteins, which are indicators of proteolysis. Considering the protein profile of drip loss, results showed effects of dietary administration of FO, CA, and Se (as SeY and SeVI) on the abundance of the following sarcoplasmic proteins: AMPDA (AMP deaminase), PGM (phosphoglucomutase), PK/PGI (pyruvate kinase/phosphoglucose isomerase), CK/PGAK (creatine kinase/phosphoglycerate kinase), ALD (aldolase), LDH (lactate dehydrogenase), PGAM (phosphoglycerate mutase), and TPI (triosephosphate isomerase). The lower content of TPI (in group II with comparison to groups III–V) and PGAM (in group II with comparison to group I and III) could be due to a higher ultimate pH in the group with FO addition, whereas lower contents of CK/PGAK, ALD, and LDH were attributed to Se addition. In comparison to the control diet, all experimental diets without SeVI decreased the content of the sum of all assayed amino acids ( ∑ AAs), indispensable amino acids ( ∑ IAAs), and dispensable amino acids ( ∑ DAAs) in the muscle. The highest ratios of  ∑ IAAs to  ∑ DAAs and  ∑ IAAs to  ∑ AAs were found in the muscle of lambs fed the diet containing RO, FO, and CA. The FO-supplemented diet with CA and SeVI increased the abundance of methionine in the muscle in comparison to the control diet and the FO-supplemented diet without/with CA.

Elucidating a molecular mechanism that the deterioration of porcine meat quality responds to increased cortisol based on transcriptome sequencing

Stress response is tightly linked to meat quality. The current understanding of the intrinsic mechanism of meat deterioration under stress is limited. Here, male piglets were randomly assigned to cortisol and control groups. Our results showed that when serum cortisol level was significantly increased, the meat color at 1 h postmortem, muscle bundle ratio, apoptosis rate, and gene expression levels of calcium channel and cell apoptosis including SERCA1, IP3R1, BAX, Bcl-2, and Caspase-3, were notably increased. However, the value of drip loss at 24 h postmortem and serum CK were significantly decreased. Additionally, a large number of differentially expressed genes (DEGs) in GC regulation mechanism were screened out using transcriptome sequencing technology. A total of 223 DEGs were found, including 80 up-regulated genes and 143 down-regulated genes. A total of 204 genes were enriched in GO terms, and 140 genes annotated into in KEGG database. Numerous genes were primarily involved in defense, inflammatory and wound responses. This study not only identifies important genes and signalling pathways that may affect the meat quality but also offers a reference for breeding and feeding management to provide consumers with better quality pork products.

Integrative Analysis of Metabolomic, Proteomic and Genomic Data to Reveal Functional Pathways and Candidate Genes for Drip Loss in Pigs

The aim of this study was to integrate multi omics data to characterize underlying functional pathways and candidate genes for drip loss in pigs. The consideration of different omics levels allows elucidating the black box of phenotype expression. Metabolite and protein profiling was applied in Musculus longissimus dorsi samples of 97 Duroc × Pietrain pigs. In total, 126 and 35 annotated metabolites and proteins were quantified, respectively. In addition, all animals were genotyped with the porcine 60 k Illumina beadchip. An enrichment analysis resulted in 10 pathways, amongst others, sphingolipid metabolism and glycolysis/gluconeogenesis, with significant influence on drip loss. Drip loss and 22 metabolic components were analyzed as intermediate phenotypes within a genome-wide association study (GWAS). We detected significantly associated genetic markers and candidate genes for drip loss and for most of the metabolic components. On chromosome 18, a region with promising candidate genes was identified based on SNPs associated with drip loss, the protein "phosphoglycerate mutase 2" and the metabolite glycine. We hypothesize that association studies based on intermediate phenotypes are able to provide comprehensive insights in the genetic variation of genes directly involved in the metabolism of performance traits. In this way, the analyses contribute to identify reliable candidate genes.

The c.-360 T>C mutation affects PGAM2 transcription activity and is linked with the water holding capacity of the longissimus lumborum muscle in pigs

The phosphoglycerate mutase 2 (PGAM2) gene encodes a key enzyme in the glycolytic process. This study examined a functional mutation in the PGAM2 gene and evaluated its relationship with water holding capacity (WHC). RT-qPCR analysis showed the PGAM2 mRNA level was significantly higher in the low-WHC group than in the high-WHC group (P<0.05). The c.-360 T>C mutation was identified through sequencing and found to have opposite allele distributions in the two groups. The allele was further genotyped in 170 Duroc×Large White×Yorkshire crossbred pigs using allele-specific PCR. The CC genotype was associated with lower WHC and higher PGAM2 mRNA levels, whereas the TT genotype corresponded to a higher WHC and lower PGAM2 mRNA levels (P<0.05). A luciferase activity assay also showed that the CC-genotype promoter had higher activity than the TT-genotype promoter (P<0.05). In conclusion, we discovered the c.-360 T>C mutation in the PGAM2 gene, which is a promising marker for improving pork WHC.

Comparative Proteomic Profiling of Divergent Phenotypes for Water Holding Capacity across the Post Mortem Ageing Period in Porcine Muscle Exudate

Two dimensional Difference Gel Electrophoresis (2-D DIGE) and mass spectrometry were applied to investigate the changes in metabolic proteins that occur over a seven day (day 1, 3 and 7) post mortem ageing period in porcine centrifugal exudate from divergent meat quality phenotypes. The objectives of the research were to enhance our understanding of the phenotype (water holding capacity) and search for biomarkers of this economically significant pork quality attribute. Major changes in protein abundance across nine phenotype-by-time conditions were observed. Proteomic patterns were dominated by post mortem ageing timepoint. Using a machine learning algorithm (l1-regularized logistic regression), a model was derived with the ability to discriminate between high drip and low drip phenotypes using a subset of 25 proteins with an accuracy of 63%. Models discriminating between divergent phenotypes with accuracy of 72% and 73% were also derived comparing respectively, high drip plus intermediate phenotype (considered as one phenotype) versus low drip and comparing low drip plus intermediate phenotype (considered as one phenotype) versus high drip. In all comparisons, the general classes of discriminatory proteins identified include metabolic enzymes, stress response, transport and structural proteins. In this research we have enhanced our understanding of the protein related processes underpinning this phenotype and provided strong data to work toward development of protein biomarkers for water holding capacity.

Genome-wide association analyses for meat quality traits in Chinese Erhualian pigs and a Western Duroc × (Landrace × Yorkshire) commercial population

BACKGROUND

Understanding the genetic mechanisms that underlie meat quality traits is essential to improve pork quality. To date, most quantitative trait loci (QTL) analyses have been performed on F2 crosses between outbred pig strains and have led to the identification of numerous QTL. However, because linkage disequilibrium is high in such crosses, QTL mapping precision is unsatisfactory and only a few QTL have been found to segregate within outbred strains, which limits their use to improve animal performance. To detect QTL in outbred pig populations of Chinese and Western origins, we performed genome-wide association studies (GWAS) for meat quality traits in Chinese purebred Erhualian pigs and a Western Duroc × (Landrace × Yorkshire) (DLY) commercial population.

METHODS

Three hundred and thirty six Chinese Erhualian and 610 DLY pigs were genotyped using the Illumina PorcineSNP60K Beadchip and evaluated for 20 meat quality traits. After quality control, 35 985 and 56 216 single nucleotide polymorphisms (SNPs) were available for the Chinese Erhualian and DLY datasets, respectively, and were used to perform two separate GWAS. We also performed a meta-analysis that combined P-values and effects of 29 516 SNPs that were common to Erhualian, DLY, F2 and Sutai pig populations.

RESULTS

We detected 28 and nine suggestive SNPs that surpassed the significance level for meat quality in Erhualian and DLY pigs, respectively. Among these SNPs, ss131261254 on pig chromosome 4 (SSC4) was the most significant (P = 7.97E-09) and was associated with drip loss in Erhualian pigs. Our results suggested that at least two QTL on SSC12 and on SSC15 may have pleiotropic effects on several related traits. All the QTL that were detected by GWAS were population-specific, including 12 novel regions. However, the meta-analysis revealed seven novel QTL for meat characteristics, which suggests the existence of common underlying variants that may differ in frequency across populations. These QTL regions contain several relevant candidate genes.

CONCLUSIONS

These findings provide valuable insights into the molecular basis of convergent evolution of meat quality traits in Chinese and Western breeds that show divergent phenotypes. They may contribute to genetic improvement of purebreds for crossbred performance.

Effects of a dietary antioxidant blend and vitamin E on growth performance, oxidative status, and meat quality in broiler chickens fed a diet high in oxidants

The aim of the study was to determine the effects of a dietary antioxidant blend (AB) and vitamin E on performance, oxidative status, and meat quality. Cobb 500 male broilers (n = 1,200, d 0) were randomly distributed into 6 treatments with 10 replicate pens. Treatments included 1) HO: high oxidant diet, vitamin E at 10 IU/kg, 3% oxidized soybean oil, 3% polyunsaturated fatty acid (PUFA) source; 2) VE: the HO diet with vitamin E at 200 IU/kg; 3) AOX: the HO diet with AB at 135 mg/kg; 4) VE+AOX: the HO diet with vitamin E at 200 IU/kg and AB at 135 mg/kg; 5) SC: standard control; and 6) PC: positive control, the SC diet with AB at 135 mg/kg. From d 0 through d 21, high oxidant diet treatment birds had greater BW, ADG, and ADFI than the SC birds; the AOX birds had better G:F on d 10 and 42, and from d 0 to 42 than SC birds (P < 0.05). The plasma TBA reactive substance level was lower in the AOX birds than the VE treatment birds in all phases (P < 0.05). High oxidant diet treatment birds had greater α-1-acid glycoprotein levels on d 10 than SC and PC birds (P < 0.05). The AOX, PC, and SC birds had a greater level of uric acid than the HO and VE+AOX birds on d 10. Superoxide dismutase expression in the liver was less with the HO treatment compared with the SC treatment on d 7 (P < 0.05). The vitamin E concentration in the breast muscle was greatest in the VE birds, whereas vitamin A concentration was greater in the PC birds compared with the SC birds on d 21 (P < 0.05). Compared with VE and AOX, the HO treatment had greater drip loss (P < 0.05). In conclusion, dietary addition of AOX was effective in improving growth, moderately restored the whole body antioxidant capability, and reduced drip loss.

Influence of high pre-rigor temperature and fast pH fall on muscle proteins and meat quality: a review

The impacts of accelerated pH decline combined with high muscle temperature on post-mortem muscle metabolism and subsequent meat quality attributes have been extensively studied. Traditionally, this phenomenon has been observed in pork muscles, primarily due to the relatively fast post-mortem glycolysis rate and its relationships to stress susceptibility of pigs before slaughter. However, the protein-denaturing condition of high temperature/rapid pH fall and subsequent PSE (pale, soft and exudative)-like abnormal meat quality characteristics have been observed in muscles from other species such as beef, lamb, venison and even poultry. Various pre-rigor conditions including the application of electrical stimulation, hot-boning, and/or pre-rigor carcass chilling temperatures in various muscles, in conjunction with carcass stretching/hanging methods, can also contribute to muscle-protein denaturation pre-rigor. This review considers the influence of a faster than normal pH fall at a higher than normal pre-rigor temperature on glycolysis, post-mortem muscle proteins and subsequently meat quality attributes. Gaps in current knowledge are identified and recommendations made for additional research.

A genetical genomics approach reveals new candidates and confirms known candidate genes for drip loss in a porcine resource population

In this study lean meat water-holding capacity (WHC) of a Duroc × Pietrain (DuPi) resource population with corresponding genotypes and transcriptomes was investigated using genetical genomics. WHC was characterized by drip loss measured in M. longissimus dorsi. The 60K Illumina SNP chips identified genotypes of 169 F2 DuPi animals. Whole-genome transcriptomes of muscle samples were available for 132 F2 animals using the Affymetrix 24K GeneChip® Porcine Genome Array. Performing genome-wide association studies of transcriptional profiles, which are correlated with phenotypes, allows elucidation of cis- and trans-regulation. Expression levels of 1,228 genes were significantly correlated with drip loss and were further analyzed for enrichment of functional annotation groups as defined by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways. A hypergeometric gene set enrichment test was performed and revealed glycolysis/glyconeogenesis, pentose phosphate pathway, and pyruvate metabolism as the most promising pathways. For 267 selected transcripts, expression quantitative trait loci (eQTL) analysis was performed and revealed a total of 1,541 significant associations. Because of positional accordance of the gene underlying transcript and the eQTL location, it was possible to identify eight eQTL that can be assumed to be cis-regulated. Comparing the results of gene set enrichment and the eQTL detection tests, molecular networks and potential candidate genes, which seemed to play key roles in the expression of WHC, were detected. The α-1-microglobulin/bikunin precursor (AMBP) gene was assumed to be cis-regulated and was part of the glycolysis pathway. This approach supports the identification of trait-associated SNPs and the further biological understanding of complex traits.

A two-step approach to map quantitative trait loci for meat quality in connected porcine F(2) crosses considering main and epistatic effects

The aim of this study was to map QTL for meat quality traits in three connected porcine F(2) crosses comprising around 1000 individuals. The three crosses were derived from the founder breeds Chinese Meishan, European Wild Boar and Pietrain. The animals were genotyped genomewide for approximately 250 genetic markers, mostly microsatellites. They were phenotyped for seven meat quality traits (pH at 45 min and 24 h after slaughter, conductivity at 45 min and 24 h after slaughter, meat colour, drip loss and rigour). QTL mapping was conducted using a two-step procedure. In the first step, the QTL were mapped using a multi-QTL multi-allele model that was tailored to analyse multiple connected F(2) crosses. It considered additive, dominance and imprinting effects. The major gene RYR1:g.1843C>T affecting the meat quality on SSC6 was included as a cofactor in the model. The mapped QTL were tested for pairwise epistatic effects in the second step. All possible epistatic effects between additive, dominant and imprinting effects were considered, leading to nine orthogonal forms of epistasis. Numerous QTL were found. The most interesting chromosome was SSC6. Not all genetic variance of meat quality was explained by RYR1:g.1843C>T. A small confidence interval was obtained, which facilitated the identification of candidate genes underlying the QTL. Epistasis was significant for the pairwise QTL on SSC12 and SSC14 for pH24 and for the QTL on SSC2 and SSC5 for rigour. Some evidence for additional pairwise epistatic effects was found, although not significant. Imprinting was involved in epistasis.

Association and expression quantitative trait loci (eQTL) analysis of porcine AMBP, GC and PPP1R3B genes with meat quality traits

The aim of this research was to screen polymorphism and to perform association study of porcine AMBP (alpha-1-microglobulin/bikunin precursor), GC (group-specific component protein) and PPP1R3B (protein phosphatase 1, regulatory (inhibitor) subunit 3B) genes with meat quality traits as well as to unravel the transcriptional regulation of these genes by expression QTL (eQTL) study. For this purpose, Duroc × Pietrain F2 resource population (DuPi; n = 313) and a commercial breed Pietrain (Pi; n = 110) were used for association and only DuPi for expression and eQTL study. A SNP was identified in the genes AMBP (g.22229C>T), GC (g.398C>T) and PPP1R3B (c.479A>G), respectively. In DuPi SNP of AMBP was associated (P < 0.05) with meat colour, pH(1L), pH(24L), pH(24H) and conductivity(24L); SNP of GC showed tendency to association (P < 0.10) with pH24H, conductivity(1L) and thawing loss, and SNP of PPP1R3B was associated (P < 0.05) with meat colour, pH(1L), pH(24L), pH(24H) and shear force. In Pi SNPs of AMBP and GC was associated with pH(24H) and PPP1R3B SNP was associated with pH(24L). The mRNA levels in Longissimus dorsi muscle tissue of these three genes were evaluated by using qRT-PCR to identify association between gene expression and meat quality traits as well as to analyse eQTL. The mRNA expression of PPP1R3B associated with pH(24L) (P < 0.05). Expression of these three genes was higher in animals with low pH of muscle. Linkage analysis using QTL Express revealed ten trans-regulated eQTL on seven porcine autosomes. Suggestive eQTL [P < 0.05, CW (chromosome-wide)] were found for PPP1R3B on SSC3 and 13. These results revealed that genetic variation and gene expression of these genes are associated with the meat quality traits. These three genes could influence meat quality and could be potential positional, physiological and functional candidate gene for meat quality traits in pigs. However, the analysis of eQTL also suggested that we need to consider additional genes encoding for transcription factors (TF), via fine-mapping underlying the eQTL peaks, in order to understand interaction among these genes.

Investigation on interferon alpha-inducible protein 6 (IFI6) gene as a candidate for meat and carcass quality in pig

The aim of this research was to screen for polymorphism and to perform an association study of IFI6 with meat and carcass quality traits. A SNP (g.370A>G) was detected which was associated (P<0.05) with meat colour, pH 24h post mortem (p.m.) in ham, conductivity 45 min p.m. in loin and conductivity 24 h p.m. in ham, drip loss and carcass length in Duroc x Pietrain and with meat colour, muscle area and ham percentage in the Pietrain population. Highest expression of IFI6 mRNA was detected in skeletal muscle (longissimus dorsi) by qRT-PCR comparing different tissues. Both qRT-PCR and western blot revealed that the IFI6 gene and protein expressions were significantly (P<0.05) higher in skeletal muscle with low drip loss compared to that of high drip loss. IFI6 protein was localized in the myocytes membrane. Results suggested that IFI6 might play roles in meat and carcass quality and is a potential positional, physiological and functional candidate gene for improving meat quality traits in pigs.

Changes in water-holding capacity and textural properties of chicken gizzard stored at 4 degrees C

The water-holding capacity (WHC), and toughness (shear force) of chicken gizzard were evaluated during postmortem storage for 4.5, 7, 12, 24, 48, 72 and 96 h at 4 degrees C. Degradation of the cytoskeletal proteins desmin, talin and vinculin were monitored by sodium dodecyl sulfate--polyacrylamide gel electrophoresis and Western blotting during the same designated storage period. The WHC of the gizzards decreased significantly from 12 h to 72 h of storage, but by 96 h the WHC was restored to the level measured after storage for 12 h. The shear force value of the gizzards increased rapidly until 12 h and then decreased until 24 h, with a further slight decrease by 48 h. Degradation products of desmin, talin and vinculin appeared at 96 h, 12 h and 48 h postmortem, respectively. The intensity of immunolabeling for desmin, talin and vinculin after storage for 96 h decreased to 51%, 25% and 52% of the initial value. The appearance of desmin degradation products was accompanied by an increase in WHC. This suggests that the postmortem degradation of desmin is involved in the increase of WHC in chicken gizzard during storage at 4 degrees C, and talin and vinculin may be involved.