Characterization and discrimination of lamb with different breeds and muscle types using precursors and volatile compounds

The unique aromas of mutton stem from the chemical reactions between the characteristic precursors during cooking. This study aimed to establish the relationship of volatile compounds and aroma precursors (protein, fat, free amino acids and fatty acids) in lamb from different breeds and muscle types. Hong lamb was characterized by greater tenderness and water holding capacity, higher polyunsaturated fatty acids and higher essential/non-essential amino acids in comparison with Hu lamb. Aldehydes, such as heptanal, hexanal, octanal and nonanal were higher in Hong-ST compared with Hu-ST. Principal component analysis (PCA) showed that aroma precursors were closely related to volatile components of cooked lamb. Discriminant analysis results showed that precursors and volatile compounds could be used to identify the breeds and muscle types of lamb. These findings revealed the contributors of lamb aroma and might help understand the regulatory mechanism of aroma in lamb from different breeds and muscle types.

Mapping metal (Hg, As, Se), lipid and protein levels within fish muscular system in two fish species (Striped Bass and Northern Pike)

Current guidelines tend to limit fish consumption based on mercury (Hg) or monomethylmercury (MeHg) content in fish flesh, without considering the presence of antagonist chemical elements that could modulate Hg toxicity. However, it is difficult to assess the potential for antagonistic interactions of these elements since their covariation within muscle tissues is poorly known. Here we present the first study simultaneously mapping multiple metal(oid)s (Hg, As and Se), lipids and proteins in fish fillets in order to assess the magnitude of intra-organ variability of metals and the potential for antagonistic interactions. We mapped two fish species (Striped Bass and Northern Pike) with contrasting muscular structure with respect to the presence of white, intermediate and red muscles. In individual Striped Bass muscle tissues, metals varied on average by 2.2-fold. Methylmercury and selenium covaried strongly and were related to protein content as assessed by % N; arsenic was inversely related to these elements and was associated with the lipid fraction of the muscle. In Pike, no such relationship was found because the contents in proteins and lipids were less variable. Arsenic speciation revealed that arsenobetaine and arsenolipids were the only As species in those fish species, whereas the toxic inorganic As species (As³⁺) was under the detection limit. Arsenobetaine was related to % N, whereas arsenolipids covaried with % lipids. Elemental associations found with muscle lipids and proteins could help explain changes in bioaccumulation patterns within and between individuals with potential implications on fish toxicology, biomonitoring and human consumption guidelines.

Effects of Aging on Angiogenic and Muscle Growth-Related Factors in Naturally Aged Rat Skeletal Muscles

Background

This study explored the effects of aging on the expression of angiogenic and muscle protein synthesis factors, as well as the number of satellite cells affecting sarcopenia in naturally aged rat skeletal muscles.

Methods

We divided 16 Sprague-Dawley rats into young (12 weeks old, n=8) and old (24 months old, n=8) groups and compared muscle and body weight (BW) between them. We also analyzed the expression levels of angiogenic and muscle growth proteins in soleus (slow-twitch) and extensor digitorum longus (EDL; fast-twitch) muscles by western blotting and assessed the number of skeletal muscle satellite cells and myonuclei and mean fiber cross-sectional area (CSA) using by immunofluorescence staining.

Results

EDL/BW was significantly lower in old rats than in young rats (p=0.002). The vascular endothelial growth factor level in soleus muscles was significantly lower in old rats than in young rats (p=0.001). Hypoxia-inducible factor 1-alpha and fetal liver kinase 1 levels in EDL muscles were lower in old rats than in young rats (p=0.001). The mammalian target of rapamycin (mTOR), p70S6K, and 4E-BP1 levels were significantly lower in the soleus muscles of old rats than in those of young rats (p<0.01). Similarly, insulin growth factor-1, Akt, mTOR, and p70S6K levels were significantly lower in EDL muscles of old rats than in those of young rats (p<0.01). Additionally, myonuclei/fiber, Pax7/fiber, and mean fiber CSAs in both muscle types were significantly lower in old rats than in young rats (p<0.01).

Conclusion

These data suggest different regulation of indices of angiogenic and muscle growth with aging in different muscle types.

Comparison of beef quality influenced by freeze-thawing among different beef cuts having different muscle fiber characteristics

The association of muscle fiber characteristics (MFC) with freeze-thawed meat quality was investigated using four different cuts (loin, M. longissimus thoracis; tenderloin, M. psoas major; top round, M. semimembranosus; eye of round, M. semitendinosus) obtained from beef carcasses (n = 10; Hanwoo steer; 28 months of age). Tenderloin had higher (P < .05) composition of muscle fiber type I than the others. Its quality traits except cooking loss were not affected by freeze-thawing (P > .05). However, top round having lower type I and higher type IIX compositions showed lower water-holding capacity and larger discoloration (P < .01) than other beef cuts after freeze-thawing. Increased tenderness after freeze-thawing was observed only for loin (P < .01) which had relatively larger size of type I fibers. In conclusion, individual muscle has different susceptibilities to freezing due to their different MFC. Considering different MFC by meat type when freezing meat will help to prevent excessive deterioration of meat quality.

Beef tenderness and intramuscular fat proteomic biomarkers: muscle type effect

Tenderness and intramuscular fat content are key attributes for beef sensory qualities. Recently some proteomic analysis revealed several proteins which are considered as good biomarkers of these quality traits. This study focuses on the analysis of 20 of these proteins representative of several biological functions: muscle structure and ultrastructure, muscle energetic metabolism, cellular stress and apoptosis. The relative abundance of the proteins was measured by Reverse Phase Protein Array (RPPA) in five muscles known to have different tenderness and intramuscular lipid contents: Longissimus thoracis (LT), Semimembranosus (SM), Rectus abdominis (RA), Triceps brachii (TB) and Semitendinosus (ST). The main results showed a muscle type effect on 16 among the 20 analyzed proteins. They revealed differences in protein abundance depending on the contractile and metabolic properties of the muscles. The RA muscle was the most different by 11 proteins differentially abundant comparatively to the four other muscles. Among these 11 proteins, six were less abundant namely enolase 3 (ENO3), phosphoglucomutase 1 (PGK1), aldolase (ALDOA), myosin heavy chain IIX (MyHC-IIX), fast myosin light chain 1 (MLC1F), triosephosphate isomerase 1 (TPI1) and five more abundant: Heat shock protein (HSP27, HSP70-1A1, αB-crystallin (CRYAB), troponin T slow (TNNT1), and aldolase dehydrogenase 1 (ALDH1A1). Four proteins: HSP40, four and a half LIM domains protein 1 (FHL1), glycogen phosphorylase B (PYGB) and malate dehydrogenase (MDH1) showed the same abundance whatever the muscle. The correlations observed between the 20 proteins in all the five muscles were used to construct a correlation network. The proteins the most connected with the others were in the following order MyHC-IIX, CRYAB, TPI1, PGK1, ALDH1A1, HSP27 and TNNT1. This knowledge is important for understanding the biological functions related to beef tenderness and intramuscular fat content.

Thiamine accumulation and thiamine triphosphate decline occur in parallel with ATP exhaustion during postmortem aging of pork muscles

We aimed to clarify the mechanisms affecting postmortem thiamine and its phosphoester contents in major edible pork muscles, namely the longissimus lumborum (LL) in addition to vastus intermedius (VI). Metabolomic analysis by capillary electrophoresis-time of flight mass spectrometry revealed that the level of thiamine triphosphate (ThTP), approximately 1.8-fold higher in LL than in VI muscle at 0h postmortem, declined in the first 24hrs, resulting in an undetectable level at 168h postmortem in both muscles. In contrast, the thiamine content in both muscles increased after 24h postmortem during the aging process. The thiamine accumulation and ThTP decline progressed in parallel with a drastic reduction of the ATP level. The intermuscular differences in pH at 24h and in expression of thiamine transporter and thiamine pyrophosphokinase might result in delayed thiamine generation in LL. These results suggest that postmortem ATP exhaustion forced ThTP hydrolysis and further depyrophosphorylation of thiamine diphosphate in the porcine muscles, which resulted in thiamine accumulation.

Modelling postmortem evolution of pH in beef M. biceps femoris under two different cooling regimes

A model based on enzyme kinetics was developed to predict differences in postmortem pH change in beef muscles as affected by cooling rate. For the calibration and validation of the model, pH and temperature measurements were conducted at different positions in M. biceps femoris following conventional carcass cooling or faster cooling of the muscle after hot boning. The glycogen conversion, and, hence, the pH fall, was observed to significantly vary with position and cooling regime but only during the initial hours of cooling. Comparison of the cooling regimes indicated that fast cooling following hot boning avoids heat shortening induced by the combined effect of high temperature and low pH.

Effect of number of motor units and muscle fibre type on surface electromyogram

Reduction in number of motor units (nMU) and fast fibre ratio (FFR) is associated with disease or atrophy when this is rapid. There is a need to study the effect of nMU and FFR to analyse the association with ageing and disease. This study has developed a mathematical model to investigate the relationship between nMU and FFR on surface electromyogram (sEMG) of the biceps muscles. The model has been validated by comparing the simulation outcomes with experiments comparing the sEMG of physically active younger and older cohort. The results show that there is statistically significant difference between the two groups, and the simulation studies closely model the experimental results. This model can be applied to identify the cause of muscle weakness among the elderly due to factors such as muscle dystrophy or preferential loss of type F muscle fibres.

CE-TOF MS-based metabolomic profiling revealed characteristic metabolic pathways in postmortem porcine fast and slow type muscles

To determine key compounds and metabolic pathways associated with meat quality, we profiled metabolites in postmortem porcine longissimus lumborum (LL) and vastus intermedius (VI) muscles with different aging times by global metabolomics using capillary electrophoresis-time of flight mass spectrometry. Loading analyses of the principal component analysis showed that hydrophilic amino acids and β-alanine-related compounds contributed to the muscle type positively and negatively, respectively, whereas glycolytic and ATP degradation products contributed to aging time. At 168h postmortem, LL samples were characterized by abundance of combinations of amino acids, dipeptides, and glycolytic products, whereas the VI samples were characterized by abundance of both sulfur-containing compounds and amino acids. The AMP and inosine contents in the VI were approx. 10 times higher than those in the LL at 4h postmortem, suggesting different rates of inosine 5'-monophosphate (IMP) accumulation by adenylate kinase 7 and 5'-nucleotidase, and subsequent different production levels of IMP and hypoxanthine between these two porcine muscles.