Comparative evaluation of different modalities for measuring in vivo carnosine levels

Carnosine is an endogenous di-peptide (β-alanine -L- histidine) involved in maintaining tissue homeostasis. It is most abundant in skeletal muscle where its concentration has been determined in biopsy samples using tandem mass spectrometry (MS-MS). Carnosine levels can also be assessed in intact leg muscles by proton magnetic resonance spectroscopy (1H-MRS) or in blood and urine samples using mass spectrometry. Nevertheless, it remains uncertain how carnosine levels from these distinct compartments are correlated with each other when measured in the same individual. Furthermore, it is unclear which measurement modality might be most suitable for large-scale clinical studies. Hence, in 31 healthy volunteers, we assessed carnosine levels in skeletal muscle, via 1H-MRS, and in erythrocytes and urine by MS-MS. While muscle carnosine levels were higher in males (C2 peak, p = 0.010; C4 peak, p = 0.018), there was no sex-associated difference in urinary (p = 0.433) or erythrocyte (p = 0.858) levels. In a linear regression model adjusted for age, sex, race, and diet, there was a positive association between erythrocyte and urinary carnosine. However, no association was observed between 1H-MRS and erythrocytes or urinary measures. In the relationship between muscle versus urinary and erythrocyte measures, females had a positive association, while males did not show any association. We also found that 1H-MRS measures were highly sensitive to location of measurement. Thus, it is uncertain whether 1H-MRS can accurately and reliably predict endogenous carnosine levels. In contrast, urinary and erythrocyte carnosine measures may be stable and in greater synchrony, and given financial and logistical concerns, may be a feasible alternative for large-scale clinical studies.

[The Structural Features of Skeletal Muscle Titin Aggregates]

Titin is a multidomain protein of striated and smooth muscles of vertebrates. The protein consists of repeating immunoglobulin-like (Ig) and fibronectin-like (FnIII) domains, which are β-sandwiches with a predominant β-structure, and also contains disordered regions. In this work, the methods of atomic force microscopy (AFM), X-ray diffraction, and Fourier transform infrared spectroscopy were used to study the morphology and structure of aggregates of rabbit skeletal muscle titin obtained in two different solutions: 0.15 M glycine-KOH, pH 7.0 and 200 mM KCl, 10 mM imidazole, pH 7.0. According to AFM data, skeletal muscle titin formed amorphous aggregates of different morphologies in the above two solutions. Amorphous aggregates of titin formed in a solution containing glycine consisted of much larger particles than aggregates of this protein formed in a solution containing KCl. The "KCl-aggregates" according to AFM data had the form of a "sponge"-like structure, while amorphous "glycine-aggregates" of titin formed "branching" structures. Spectrofluorometry revealed the ability of "glycine-aggregates" of titin to bind to the dye thioflavin T (TT), and X-ray diffraction revealed the presence of one of the elements of the amyloid cross β-structure, a reflection of ~4.6 Å, in these aggregates. These data indicate that "glycine-aggregates" of titin are amyloid or amyloid-like. No similar structural features were found in "KCl-aggregates" of titin; they also did not show the ability to bind to thioflavin T, indicating the non-amyloid nature of these titin aggregates. Fourier transform infrared spectroscopy revealed differences in the secondary structure of the two types of titin aggregates. The data we obtained demonstrate the features of structural changes during the formation of intermolecular bonds between molecules of the giant titin protein during its aggregation. The data expand the understanding of the process of amyloid protein aggregation.

Effect of housing system on carcass composition, meat quality, digestive morphometry, and leg bone dimensions of Ross 308 parent broilers

The aim of the present study was to compare the effects of 2 Ross 308 parent broiler housing systems (SLS-slat-litter system vs. LS-litter-based system) in terms of carcass composition, meat quality traits (chemical composition, texture, physicochemical properties), as well as biometric traits of the digestive system and leg bones. The weight of the eviscerated carcass and the proportion of carcass components were determined at the end of the reproductive period (60 wk of life) following slaughter. The lengths and diameters of the individual intestinal segments, the weight of selected internal organs, the acidity (pH24) and electrical conductivity (EC24), as well as the color (L*, a*, b*) of breast and thigh muscles were assessed. The basal chemical composition of the breast and thigh muscles was also determined, texture analysis of the pectoralis major muscle and measurements of the femur and tibia of parent broilers were also carried out. The housing system differentiated the birds in terms of percentage of breast muscle (SLS-27.4% vs. LS-26.0%) and intramuscular fat content in the breast muscle (SLS-1.1% vs. LS-0.7%), spleen weight pH of the breast and thigh muscles and EC of the thigh muscles (SLS-9.3 mS/cm vs. LS-7.0 mS/cm). Differences were also found between the study groups in the color of the breast and thigh muscles. The housing system affected the results of the texture analysis of the pectoralis major muscle. The birds differed significantly (P < 0.05) in terms of gumminess (SLS-11.1 N vs. LS-16.0 N), springiness, chewiness (SLS-17.6 N × cm vs. LS-23.4 N × cm) and cohesiveness parameters. The housing system did not affect the lengths and diameters of the individual intestinal segments, except for the length of the terminal intestine. There was no significant effect of the housing system on the tibia and femur dimensions analyzed. This study provided information about differences in certain carcass characteristics, meat quality, and the digestive system of Ross 308 parent broilers in relation to the maintenance system.

Myofibril degradation and structural changes in myofibrillar proteins of porcine longissimus muscles during frozen storage

The effect of frozen time and the temperature on myofibril degradation and the structure of myofibrillar proteins of porcine longissimus muscles were investigated. With extended frozen time and increased temperature, the muscle fibres became broken; the muscle cells became irregularly arranged; and the fragmentation index value, number of ionic bonds, and number of hydrogen bonds of the samples significantly decreased. Meanwhile, the myofibril fragmentation index value, number of hydrophobic interactions, and number of disulphide bonds significantly increased (P < 0.05). After 12 months of storage, the intensities of I760/I1003, I850/I830, I1450/I1003, and I2945/I1003 in the samples frozen at -8 °C were reduced by 4.36 %, 1.28 %, 1.86 %, and 0.74 %, respectively. A reduction in the maximum absorption peak and a red shift were observed in the ultraviolet spectrum. Therefore, frozen storage resulted in significant damage to the tissue microstructureand caused accelerated protein degradation, and the loss of protein structural integrity.

Effect of packaging thickness and muscle type on ultrasound-assisted beef quality

High-intensity ultrasound (HIU) can modify muscle structure, leading to improvements in tenderness. However, factors such as packing type and muscle complexity may attenuate the acoustic cavitation. In this research, the effect of packing thickness (40.6-70 μm) on the quality of bovine Gluteus medius and Biceps femoris treated with HIU (37 kHz, 90 W/cm2, 40 min) was evaluated. The hardness of G. medius decreased significantly as the thickness of the packing bag decreased. The wide interfibrillar and intermyofibrillar spaces corroborated the tenderizing effect. These effects are related to damage of cell structure and changes in the collagen content (3.37 ± 0.1 µg/mL). In addition, the HIU decrease the variability in the water holding capacity of the muscle produced by the use of low thickness bags during storage. The trained sensory panel described the sonicated samples in 50.8 μm bags as less hard and juicier. Contrarily, in B. femoris no significant effects were reported in the variables evaluated. B. femoris is a white muscle, with a high amount of collagen (3.59 ± 0.1 µg/mL) and little intramuscular fat. Consequently, the effect of the HIU on muscle quality is associated with the composition of the muscle fibers and the thickness of the packing bag. HIU application is recommended to improve the quality of leg muscles whenever low-thickness bags (50.8 μm or less) are used.

Muscle, season, sex, and carcass weight affected pork texture, collagen characteristics, and intramuscular fat content

In this study, pigs from 3 supply chains were slaughtered in an Australian summer and winter (n = 20 for each supply chain). The pigs were from 2 sexes (female and castrated male) and 2 carcass weight groups (high: 95.0 to 100.0 kg and low: 75.0 to 80.0 kg). From each carcass, the Biceps femoris (BF), Longissimus thoracis et lumborum (LTL), and Triceps brachii (TB) were excised at 24 h postmortem, vacuum packed, frozen at 24-48 h and transported to the lab. Cooking loss, Warner-Bratzler shear force (WBSF) and texture profile analysis (adhesiveness, chewiness, cohesiveness, hardness, resilience, and springiness) were measured in LTL and BF. pH, collagen content, and solubility and intramuscular fat (IMF) content were determined for all muscles. Results showed that BF was tougher than LTL, and winter samples were tougher than summer ones (P < 0.05). The TB had higher pH, collagen, and IMF content than BF and LTL (P < 0.05). Collagen solubility was higher in castrated male and winter samples. pH, collagen solubility, and IMF content were significantly (P < 0.05) related to chewiness and hardness in pork BF and LTL. pH and IMF were also related to cooking loss, while collagen solubility and IMF were related to WBSF (P < 0.05). The relationships of pH and IMF with pork texture were predominantly driven by the LTL, while the relationships between collagen solubility and texture were predominantly driven by the BF. Collagen solubility and IMF of pork BF and TB were related to those of LTL, but the correlations were not strong enough for prediction. Pork texture and chemical components were affected by muscle, seasons, sex and carcass weight. pH, collagen solubility, and IMF-affected pork texture.

Comparison of physiologically functional compounds in Sika deer Cervus nippon meats obtained from different regions in Japan

In Japan, the promotion of effective use of many wild deer as food resource has been conducted. However, they are not necessarily utilized effectively. Thus, we focused physiologically functional compounds to find characteristics of Sika deer meats (commercially available) obtained from different regions such as Hokkaido, Wakayama, Tokushima, and Miyazaki prefectures in Japan, making it a valuable resource for future studies and applications. The amount of carnosine, anserine, and balenine in muscle of deer from Wakayama prefecture was significantly lower than that in muscle of deer from other prefectures. The differences of amount of imidazole dipeptides in different prefectures seems to be caused by feed, rearing environment, and breed. The amount of carnitine in deer meat from Hokkaido was significantly lower than that in muscle of deer from other prefectures, while the amount of acetyl-carnitine in deer meat from Miyazaki prefectures was significantly higher than that from other prefectures. The amounts of glutamine, ornithine, and 3-methylhistidine in muscles of deer from Wakayama prefectures were significantly higher than those in muscle of deer from other prefectures. These results might be caused by differences in feeding habits, habitat, the muscle types, and subspecies of deer obtained from four regions in Japan.

Characterization of the dystrophin-associated protein complex by mass spectrometry

The dystrophin-associated protein complex (DAPC) is a highly organized multiprotein complex that plays a pivotal role in muscle fiber structure integrity and cell signaling. The complex is composed of three distinct interacting subgroups, intracellular peripheral proteins, transmembrane glycoproteins, and extracellular glycoproteins subcomplexes. Dystrophin protein nucleates the DAPC and is important for connecting the intracellular actin cytoskeletal filaments to the sarcolemma glycoprotein complex that is connected to the extracellular matrix via laminin, thus stabilizing the sarcolemma during muscle fiber contraction and relaxation. Genetic mutations that lead to lack of expression or altered expression of any of the DAPC proteins are associated with different types of muscle diseases. Hence characterization of this complex in healthy and dystrophic muscle might bring insights into its role in muscle pathogenesis. This review highlights the role of mass spectrometry in characterizing the DAPC interactome as well as post-translational glycan modifications of some of its components such as α-dystroglycan. Detection and quantification of dystrophin using targeted mass spectrometry are also discussed in the context of healthy versus dystrophic skeletal muscle.

Genetic parameter estimates for sensory and meat quality traits measured at 3 and 29 days of aging of beef from Canadian crossbred cattle

Genetic parameters were estimated for objective and subjective traits assessed after 3 and 29 days aging in meat samples of 1154 commercial beef cattle. Meat attributes [Warner-Bratzler shear force (WBSF), intramuscular fat (IMF), and pH] and sensory traits [flavor intensity (FI), off-flavor (OF), connective tissue (CT), overall tenderness (OT), sustained juiciness (SJ), and overall palatability (OP)] were available. The animal mixed model used included additive genetic and residual effects as random effects, contemporary group as fixed effect and genomic breed composition and slaughter age as covariates. Genetic parameters were estimated using airemlf90 software and single-step genomic BLUP. Heritability estimates for OT (3 and 29 d), OP (3 d) and OF (29 d) were of moderate magnitude ranging from 0.18 ± 0.07 to 0.31 ± 0.07. Heritabilities were negligible or of low magnitude for all other sensory traits with values ranging from 0.03 ± 0.05 to 0.14 ± 0.07. Among objectively measured traits, the estimate of heritability for meat pH was moderate at day 3 (0.20 ± 0.08) and negligible at 29 (0.00 ± 0.05). For IMF and WBSF the heritability estimates were 0.43 ± 0.09 and 0.54 ± 0.09, and 0.22 ± 0.07 and 0.19 ± 0.07 for day 3 and 29, respectively. Genetic correlations between days for each sensory trait tended to be of high and positive magnitude ranging from 0.54 ± 0.60 to 0.99 ± 0.28. Genetic and phenotypic correlations of subjectively assessed traits were consistent in direction and magnitude with WBSF (negative) and IMF (positive) suggesting that genetic selection based on objectively measured traits can be used for meat quality improvement and to increase consumer satisfaction. In addition, selection can be implemented using sensory traits collected after 3 days of aging.

Relationship between peptides and the change in quality characteristics of beef strip loin (M. longissimus lumborum) and tenderloin (M. psoas major)

Peptides in fresh and aged beef strip loin (M. longissimus lumborum) and tenderloin (M. psoas major) were quantified to investigate the relationship between proteolysis-induced peptides and beef quality characteristics. A total of 409 and 450 peptides were quantified from strip loin and tenderloin, respectively, and found to be significantly correlated to beef quality characteristics. Changes in redness and yellowness were significantly correlated to the peptides derived from G3P, ENOB, and KCRM in both muscles during 14 days of storage. The peptides produced from MYG, ENOB, HBA, PGK1, and TPIS were strongly associated with improved tenderness, while those derived from major myofibrillar proteins, such as MYH1, MYH2, ACTS, and DESM, were associated with changes in tenderloin color. These results improve our understanding of the association between peptides and changes in meat quality during cold storage, indicating that proteolysis-induced peptides can be indicators of the quality characteristics of fresh and aged meat.

The effect of modified atmosphere packaging at an early postmortem stage on lamb meat quality during subsequent aging

This study explores the influence of modified atmosphere packaging (MAP) on fresh lamb meat quality with respect to gas concentration, rigor state, and post-mortem aging time. A comparison was done for the quality characteristics of lamb Longissimus thoracis lumborum chops that had been packaged separately in air, 75%O2  + 25%CO2 MAP or 50%O2  + 50%CO2 MAP at 1, 6, and 24 h post-mortem and then stored for 6, 12, 24, 72, and 144 h post-mortem, and the quality of lamb chops had been evaluated at each post-mortem period separately. Chops packaged at 1 and 6 h post-mortem in MAP had reduced pH decline, less purge loss, and enhanced redness at early post-mortem storage times. Lamb color stability was evidently greater in 75%O2  + 25%CO2 MAP than in 50%O2  + 50%CO2 MAP during the early storage period when a* and R630/R580 were taken into account. Shear force values were lowest in lambs packaged at 1 h post-mortem with 75%O2  + 25%CO2 MAP at 12 h post-mortem and then increased until 72 h post-mortem, suggesting that rigor has been delayed by such a high O2 MAP. Thus, fresh lamb quality was maintained most effectively when packaged at 1 h post-mortem in 75%O2  + 25%CO2 MAP for consumption at 12 h post-mortem. The exact mechanisms and optimization of MAP based on Chinese retail conditions should be considered in future studies. PRACTICAL APPLICATION: In this study, three slaughter patterns in the meat industry involving boning immediately after dressing (hot-boning) and chilling for a short period (warm-boning) or overnight (cold-boning) are considered, as well as the behavior of non-immediate consumption after purchase. Modified atmosphere packaging provides an effective preservation of early post-mortem muscles with enhanced color stability, water holding capacity, and texture during refrigerated storage. This could provide new insights into how to process lamb muscles in the early post-mortem period to improve and stabilize lamb quality.

Assessment of mitochondrial DNA copy number variation relative to nuclear DNA quantity between different tissues

Mitochondrial DNA is a widely tested genetic marker in various fields of research and diagnostics. Nonetheless, there is still little understanding on its abundance and quality within different tissues. Aiming to obtain deeper knowledge about the content and quality of mtDNA, we investigated nine tissues including blood, bone, brain, hair (root and shaft), cardiac muscle, liver, lung, skeletal muscle, and buccal mucosa of 32 deceased individuals using two real-time quantitative PCR-based assays with differently sized mtDNA and nDNA targets. The results revealed that the quantity of nDNA is a weak surrogate to estimate mtDNA quantities among tissues of an individual, as well as tissues across individuals. Especially hair showed extreme variation, depicting a range of multiple magnitudes of mtDNA molecules per hair fragment. Furthermore, degradation can lead to fewer fragments being available for PCR. The results call for parallel determination of the quantity and quality of mtDNA prior to downstream genotyping assays.

Comparison of muscle fiber characteristics and meat quality between newborn and adult Haimen goats

Goat meat is popular with consumers for its rich nutritional content. Muscle fiber characteristics have been shown to play a crucial role in determining the quantity and quality of meat. However, little is known about the temporal changes in muscle fiber characteristics and meat quality during growth in goats. In this study, muscle fiber type, fiber diameter, fiber cross-sectional area (CSA), glycolytic potential (GP), meat pH, and meat color were analyzed in the gastrocnemius (GAS), gluteus medius (GM), biceps brachii (BB), longissimus lumborum (LL) muscles from newborn (NHMG) and adult (AHMG) Haimen goats. The distribution of type I and type Π fiber in goats is not consistent across the four muscles and undergoes alterations with age. The diameter and CSA of the muscle fibers were similar among the four NHMG muscles. However, in AHMG, the LL muscle had the largest fiber in terms of both diameter and CSA, followed by BB, GM, and GAS muscles. Moreover, the CSA of type Π fibers was higher than that of type I fibers in both NHMG and AHMG. GP values ranged from 90 to 140 umol/g across the muscle and no significant differences were observed. AHMG had a higher pH level and a* value, but lower L* and b* values than NHMG. Overall, our findings enhance our understanding of the changes in muscle fiber type and meat quality during the growth in Haimen goats and provide a basis for future research on the development and transformation of muscle fibers in goats.

Effect of different free-range systems on the growth performance, carcass traits, and meat quality of Yangzhou geese

This study was conducted to investigate the effects of different free-range systems on the growth performance, carcass traits, and meat quality of geese. Grass pasture zones in the study area were selected, and 28 d-old male Yangzhou geese with similar body weights (1.57 ± 0.12 kg) were randomly allocated to one of three conditions: (A) free-range conditions in the apron area during 9:00 a.m.-4:00 p.m. (10-20 m from shed with grass pasture); (B) free-range conditions in the outer range from 9:00 a.m. to 4:00 p.m. (beyond 50 m from shed with grass pasture); and (C) barn system. Free range-reared geese had higher weight gain after 42 days of age than barn-reared geese, regardless of the range area. A lower feed conversion ratio was found in outer range-reared and apron area-reared geese from 28 to 63 days of age. In addition, the highest percentages of leg and breast muscle weights were observed in outer range-reared and apron area-reared geese, respectively. Finally, outer-range rearing resulted in a lower pH and lower moisture content. Therefore, these data suggest that the outer range system benefits growth performance and feed conversion ratio of geese and results in a higher percentage of leg muscle weight, lower pH, and lower moisture content.

Muscle of dark and normal beef differs metabolically

Reduction in muscle glycogen triggered by adverse antemortem handling events alters postmortem energy metabolism and results in a high ultimate pH and dark, firm and dry beef, often referred to as 'dark-cutting'. However, the relationship between atypical dark (AT) beef, postmortem energy metabolism and underlying tissue characteristics remains somewhat unclear. Cattle harvested in the US and Canada representing normal (pH < 5.6), AT dark (pH 5.6-5.8) and dark cutting (DC; pH > 5.8) beef were analyzed for tissue characteristics related to energy metabolism. Results show AT dark beef is more oxidative but similar to normal beef in glycolytic potential and nucleotide abundance. Mitochondria DNA content (P < 0.05, Canada; P < 0.005, US) and oxidative enzymes for DC and AT dark beef were greater (P < 0.01; Canada and US) compared to normal beef. Myoglobin tracked (P < 0.01) with color classification. These findings show both DC and AT beef are inherently more oxidative and raise the possibility that more oxidative muscle may be more prone to develop dark beef.

Effect of carnosine synthesis precursors in the diet on jejunal metabolomic profiling and biochemical compounds in slow-growing Korat chicken

The slow-growing Korat chicken (KR) has been developed to provide an alternative breed for smallholder farmers in Thailand. Carnosine enrichment in the meat can distinguish KR from other chicken breeds. Therefore, our aim was to investigate the effect of enriched carnosine synthesis, obtained by the β-alanine and L-histidine precursor supplementation in the diet, on changes to metabolomic profiles and biochemical compounds in slow-growing KR jejunum tissue. Four hundred 21-day-old female KR chickens were divided into 4 experimental groups: a group with a basal diet, a group with a basal diet supplemented with 1.0% β-alanine, 0.5% L-histidine, and a mix of 1.0% β-alanine and 0.5% L-histidine. The feeding trial lasted 70 d. Ten randomly selected chickens from each group were slaughtered. Metabolic profiles were analyzed using proton nuclear magnetic resonance spectroscopy. In total, 28 metabolites were identified. Significant changes in the concentrations of these metabolites were detected between the groups. Partial least squares discriminant analysis was used to distinguish the metabolites between the experimental groups. Based on the discovered metabolites, 34 potential metabolic pathways showed differentiation between groups, and 8 pathways (with impact values higher than 0.05, P < 0.05, and FDR < 0.05) were affected by metabolite content. In addition, biochemical changes were monitored using synchrotron radiation-based Fourier transform infrared microspectroscopy. Supplementation of β-alanine alone in the diet increased the β-sheets and decreased the α-helix content in the amide I region, and supplementation of L-histidine alone in the diet also increased the β-sheets. Furthermore, the relationship between metabolite contents and biochemical compounds were confirmed using principal component analysis (PCA). Results from the PCA indicated that β-alanine and L-histidine precursor group was highly positively correlated with amide I, amide II, creatine, tyrosine, valine, isoleucine, and aspartate. These findings can help to understand the relationships and patterns between the spectral and metabolic processes related to carnosine synthesis.

Injection of l-arginine or l-lysine before freezing delays the emulsifying and gelling properties deterioration of myofibrillar proteins of frozen porcine Longissimus lumborum muscle

This study aimed to investigate the effects of injecting l-arginine and l-lysine solution before freezing and after thawing on the emulsifying and gelling properties of myofibrillar proteins (MPs) of frozen porcine longissimus dorsi. The results showed that the pre-freezing injections were more effective in alleviating the decrease in emulsifying properties of MPs compared with the post-thawing injections, as evidenced by higher emulsion creaming index, oil droplet size, interfacial absorptive protein amount, and viscoelasticity. Additionally, the pre-freezing injections could effectively mitigate the damage to the gelling properties of MPs, as evidenced by the formation of a homogeneous and compact gel network with stronger water retention, strength and chemical forces, as well as a higher proportion of non-flowing water, whereas the post-thawing injections could not. These results demonstrated that the injection of l-arginine and l-lysine solution before freezing could delay freezing-induced damage to the emulsifying and gelling properties of MPs, keeping the processing characteristics of frozen porcine.

Association of blood APMAP content and meat quality trait in Rex rabbits

APMAP is single transmembrane arylesterase which plays a cardinal role in adipogenesis. In this experiment, three tissue and blood samples of Rex rabbits at 3 growing periods were selected. The expression levels of APMAP gene in different tissues were detected by real-time fluorescence quantitative PCR and the content of APMAP in the blood was detected by Elisa. The results showed that fat deposition, the expression of APMAP in muscle and the content of APMAP in the blood increased rapidly during the growth of Rex rabbits. The correlation analysis showed that the correlation coefficient between APMAP content in the blood and the expression level of APMAP gene in longissimus lumborum muscle was 0.75(p < 0.05); the correlation coefficients between APMAP content in the blood and intramuscular fat and 24-hour pH were 0.90 (p < 0.01) and 0.75 (p < 0.05), respectively. According to the analysis results, we inferred APMAP content in the blood in Rex rabbits may influence meat quality and the meat quality of high APMAP content in the blood in Rex rabbits is better. These results revealed APMAP content in the blood may be one of the important signs for meat quality traits of molecular markers.

Different effects of dietary β-hydroxy-β-methylbutyrate on composition of fatty acid and free amino acid, and fatty metabolism in the different muscles of broilers

In the study, 336 broiler chickens were selected to explore dietary effects of different β-hydroxy-β-methylbutyrate (HMB) levels (0 (control), 0.05, 0.10, and 0.15%) on the compositions of fatty acids and free amino acids, and lipid metabolism in the different muscles of broilers. In the breast muscle, dietary HMB supplementation hardly affected the free amino acid composition (P > 0.05). Compared to the control group, dietary 0.10 and 0.15% HMB supplementation decreased the content of C18:1n9c and thus the monounsaturated fatty acid (MUFA), and dietary 0.15% HMB supplementation increased the sum of saturated fatty acids (SFA) (P < 0.05). Moreover, compared to the control group, dietary 0.05 and 0.10% HMB increased the mRNA expression of proliferator activated receptor-γ and the activity of fatty acid synthase (FAS), and dietary 0.10% HMB increased the acetyl-CoA carboxylase activity (P < 0.05). In the leg muscle, dietary 0.10 and 0.15% HMB increased the MUFA content and decreased the polyunsaturated fatty acid (PUFA) content, the PUFA to SFA ratio, the mRNA expression of sterol regulatory element binding proteins-1c, and the activities of acyl-CoA oxidase 1 and acetyl-CoA synthetase (P < 0.05). Moreover, dietary 0.10% HMB decreased the activities of hydroxy-3-methylglutaryl-CoA synthase 1 and FAS in comparison to the control group (P < 0.05). Dietary 0.05% HMB decreased the contents of essential amino acids and nonessential amino acids (NEAA), and dietary 0.15% HMB decreased the NEAA content (P < 0.05). In summary, dietary 0.10% HMB supplementation had superior efficiency on lipogenesis in the breast muscle of broilers. However, dietary HMB supplementation, especially at the level of 0.05 and 0.15%, decreased meat nutritional values and the lipogenesis in leg muscles.

Effects of linseed oil supplementation duration on fatty acid profile and fatty acid metabolism-related genes in the muscles of Chinese crested white ducks

Meat rich in polyunsaturated fatty acids is considered beneficial to health. Supplementing the diet with linseed oil promotes the deposition of polyunsaturated fatty acids (PUFAs) in poultry, a conclusion that has been confirmed multiple times in chicken meat. However, fewer studies have focused on the effects of dietary fatty acids on duck meat. Therefore, this study aims to evaluate the effects of the feeding time of a linseed oil diet on duck meat performance and gene expression, including meat quality performance, plasma biochemical indicators, fatty acid profile, and gene expression. For this study, we selected 168 Chinese crested ducks at 28 days old and divided them into three groups, with 56 birds in each group. The linseed oil content in the different treatment groups was as follows: the control group (0% flaxseed oil), the 14d group (2% linseed oil), and the 28d group (2% linseed oil). Ducks in the two experimental groups were fed a linseed oil diet for 28 and 14 days at 28 and 42 days of age, respectively. The results showed that linseed oil had no negative effect on duck performance (slaughter rate, breast muscle weight, and leg muscle weight) or meat quality performance (pH, meat color, drip loss, and shear force) (P > 0.05). The addition of linseed oil in the diet increased plasma total cholesterol and high-density lipoprotein cholesterol levels (P < 0.05), while decreasing triglyceride content (P < 0.05). Furthermore, the supplementation of linseed oil for four weeks affected the composition of muscle fatty acids. Specifically, levels of α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid were increased (P < 0.05), while eicosatetraenoic acid content was negatively correlated with flaxseed oil intake (P < 0.05). qRT-PCR analysis further revealed that the expression of FATP1, FABP5, and ELOVL5 genes in the breast muscle, as well as FABP3 and FADS2 genes in the thigh muscle, increased after four weeks of linseed oil supplementation (P < 0.05). However, after two weeks of feeding, CPT1A gene expression inhibited fatty acid deposition, suggesting an increase in fatty acid oxidation (P < 0.05). Overall, the four-week feeding time may be a key factor in promoting the deposition of n-3 PUFAs in duck meat. However, the limitation of this study is that it remains unknown whether longer supplementation time will continue to affect the deposition of n-3 PUFAs. Further experiments are needed to explain how prolonged feeding of linseed oil will affect the meat quality traits and fatty acid profile of duck meat.

50 Years of the steric-blocking mechanism in vertebrate skeletal muscle: a retrospective

Fifty years have now passed since Parry and Squire proposed a detailed structural model that explained how tropomyosin, mediated by troponin, played a steric-blocking role in the regulation of vertebrate skeletal muscle. In this Special Issue dedicated to the memory of John Squire it is an opportune time to look back on this research and to appreciate John's key contributions. A review is also presented of a selection of the developments and insights into muscle regulation that have occurred in the years since this proposal was formulated.

Double-headed binding of myosin II to F-actin shows the effect of strain on head structure

Force production in muscle is achieved through the interaction of myosin and actin. Strong binding states in active muscle are associated with Mg·ADP bound to the active site; release of Mg·ADP allows rebinding of ATP and dissociation from actin. Thus, Mg·ADP binding is positioned for adaptation as a force sensor. Mechanical loads on the lever arm can affect the ability of myosin to release Mg·ADP but exactly how this is done is poorly defined. Here we use F-actin decorated with double-headed smooth muscle myosin fragments in the presence of Mg·ADP to visualize the effect of internally supplied tension on the paired lever arms using cryoEM. The interaction of the paired heads with two adjacent actin subunits is predicted to place one lever arm under positive and the other under negative strain. The converter domain is believed to be the most flexible domain within myosin head. Our results, instead, point to the segment of heavy chain between the essential and regulatory light chains as the location of the largest structural change. Moreover, our results suggest no large changes in the myosin coiled coil tail as the locus of strain relief when both heads bind F-actin. The method would be adaptable to double-headed members of the myosin family. We anticipate that the study of actin-myosin interaction using double-headed fragments enables visualization of domains that are typically noisy in decoration with single-headed fragments.

Somatic and germinal mosaicism in a Han Chinese family with laminopathies

"Laminopathies" refers to a wide spectrum of myopathies caused by mutations in the LMNA gene. These myopathies include limb girdle muscular dystrophy type 1B (LGMD1B) and dilated cardiomyopathy 1 A (DCM1A), which are both autosomal dominant neurogenetic diseases. There have been few studies on mosaicism in laminopathies. Herein, a Han Chinese family with laminopathies was enrolled in our study. Genetic analysis revealed that the proband carried a novel splice site mutation, c. 1158-3 C > T, in the LMNA gene due to her mother having de novo somatic and gonadal mosaicism. Reverse-transcription polymerase chain reaction (RT-PCR) analysis revealed reduced levels of LMNA mRNA in the proband, which were probably due to nonsense-mediated mRNA decay (NMD). Western blotting revealed reduced lamin A/C protein levels in the skeletal muscle tissue of the proband. In this family, the clinical phenotypes of the proband's mother were normal, and the c. 1158-3 C > T splicing mutation was identified in the blood sample of the proband's mother. Thus, the mutation could be easily considered to be nonpathogenic. Our study emphasizes the importance of mosaicism in the identification of pathogenic variants and genetic counseling.

Molecular mechanisms contributing to the development of beef sensory texture and flavour traits and related biomarkers: Insights from early post-mortem muscle using label-free proteomics

Beef sensory quality comprises a suite of traits, each of which manifests its ultimate phenotype through interaction of muscle physiology with environment, both in vivo and post-mortem. Understanding variability in meat quality remains a persistent challenge, but omics studies to uncover biological connections between natural variability in proteome and phenotype could provide validation for exploratory studies and offer new insights. Multivariate analysis of proteome and meat quality data from Longissimus thoracis et lumborum muscle samples taken early post-mortem from 34 Limousin-sired bulls was conducted. Using for the first-time label-free shotgun proteomics combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), 85 proteins were found to be related with tenderness, chewiness, stringiness and flavour sensory traits. The putative biomarkers were classified in five interconnected biological pathways; i) muscle contraction, ii) energy metabolism, iii) heat shock proteins, iv) oxidative stress, v) regulation of cellular processes and binding. Among the proteins, PHKA1 and STBD1 correlated with all four traits, as did the GO biological process 'generation of precursor metabolites and energy'. Optimal regression models explained a high level (58-71%) of phenotypic variability with proteomic data for each quality trait. The results of this study propose several regression equations and biomarkers to explain the variability of multiple beef eating quality traits. Thanks to annotation and network analyses, they further suggest protein interactions and mechanisms underpinning the physiological processes regulating these key quality traits. SIGNIFICANCE: The proteomic profiles of animals with divergent quality profiles have been compared in numerous studies; however, a wide range of phenotypic variation is required to better understand the mechanisms underpinning the complex biological pathways correlated with beef quality and protein interactions. We used multivariate regression analyses and bioinformatics to analyse shotgun proteomics data to decipher the molecular signatures involved in beef texture and flavour variations with a focus on multiple quality traits. We developed multiple regression equations to explain beef texture and flavour. Additionally, potential candidate biomarkers correlated with multiple beef quality traits are suggested, which could have utility as indicators of beef overall sensory quality. This study explained the biological process responsible for determining key quality traits such as tenderness, chewiness, stringiness, and flavour in beef, which will provide support for future beef proteomics studies.

Contribution of intramuscular connective tissue and its structural components on meat tenderness-revisited: a review

The tenderness of meat influences consumers' perceptions of its quality. Meat tenderness is a key quality characteristic that influences consumer satisfaction, repeat purchases, and willingness to pay higher prices for meat. Muscle fibers, connective tissues, and adipocytes are the main structural components of meat that contribute to its tenderness and texture. In the present review, we have focused on the role of connective tissue and its components in meat tenderness, specifically perimysial intramuscular connective tissue (IMCT) and its concept as an immutable "background toughness." The collagen contribution to cooked meat toughness can be altered by animal diet, compensatory growth, slaughter age, aging, and cooking. As well, progressive thickening of the perimysium leads to a progressive increase in shear force values in beef, pork, chicken, and this may occur prior to adipocyte formation as cattle finish in feedlots. Conversely, adipocyte accumulation in the perimysium can decrease cooked meat shear force, suggesting that the contribution of IMCT to meat toughness is complex and driven by both collagen structure and content. This review provides a theoretical foundation of information to modify IMCT components to improve meat tenderness.