Proteolysis in meat tenderization from the point of view of each single protein: A proteomic perspective

Enzymatic hydrolyzation of Cordyceps militaris mushroom extracts and its effect on spent hen chicken

OBJECTIVE

This study was aimed to investigate the effect of fresh and dried hydrolyzed Cordyceps militaris (CM) mushroom with proteolytic enzymes; bromelain (CMB), flavorzyme (CMF), and mixture of bromelain: flavorzyme (CMBF) on quality properties of spent hen chicken.

METHODS

Mushroom extract (CME) were combined with three proteolytic enzyme mixtures that had different peptidase activities; stem bromelain (CMB), flavorzyme (CMF), and mixture of stem bromelain:flavorzyme (CMBF) at (1:1). The effect of these hydrolysates was investigated on spent hen breast meat via dipping marination.

RESULTS

Hydrolyzation positively alters functional properties of CM protease. in which bromelain hydrolyzed group (CMB) displayed the highest proteolytic activity at 4.57 unit/mL. The antioxidant activity had a significant increment from 5.32% in CME to 61.79% in CMB. A significantly higher emulsion stability index and emulsification activity index compared to CME were another result from hydrolyzation (p<0.05). Texture properties along with the shear force value and myofibrillar fragmentation index were notably improved under CMB and CMBF in fresh condition. Marination with CM mushroom protease that was previously hydrolyzed with enzymes was proven to also increase the nucleotide compounds, indicated by higher adenosine 5'-monophosphate (AMP) and inosine 5'-monophosphate (IMP) in hydrolysate groups (p<0.05). The concentration of both total and insoluble collagen remained unchanged, meaning less effect from CM protease.

CONCLUSION

This study suggested the hydrolyzation of CM protease with bromelain or a mixture of bromelain:flavourzyme to significantly improve functional properties of protease and escalate the taste-related nucleotide compounds and texture profiles from spent hen breast meat.

Genome-wide scans identify biological and metabolic pathways regulating carcass and meat quality traits in beef cattle

Genome association studies (GWAS) provides knowledge about the genetic architecture of beef-related traits that allow linking the target phenotype to genomic information aiding breeding decision. Thus, the present study aims to uncover the genetic mechanism involved in carcass (REA: rib eye area, BF: backfat thickness, and HCW: hot carcass weight) and meat quality traits (SF: shear-force, MARB: marbling score, and IMF: intramuscular fat content) in Nellore cattle. For this, 6910 young bulls with phenotypic information and 23,859 animals genotyped with 435 k markers were used to perform the weighted single-step GBLUP (WssGBLUP) approach, considering two iterations. The top 10 genomic regions explained 8.13, 11.81, and 9.58% of the additive genetic variance, harboring a total of 119, 143, and 95 positional candidate genes for REA, BF, and HCW, respectively. For meat quality traits, the top 10 windows explained a large proportion of the total genetic variance for SF (14.95%), MARB (17.56%), and IMF (21.41%) surrounding 92, 155, and 111 candidate genes, respectively. Relevant candidate genes (CAST, PLAG1, XKR4, PLAGL2, AQP3/AQP7, MYLK2, WWOX, CARTPT, and PLA2G16) are related to physiological aspects affecting growth, carcass, meat quality, feed intake, and reproductive traits by signaling pathways controlling muscle control, key signal metabolic molecules INS / IGF-1 pathway, lipid metabolism, and adipose tissue development. The GWAS results provided insights into the genetic control of the traits studied and the genes found are potential candidates to be used in the improvement of carcass and meat quality traits.

Muscle Hypertrophy Is Linked to Changes in the Oxidative and Proteolytic Systems during Early Tenderization of the Spanish Breed "Asturiana de los Valles"

For fresh meat consumers, eating satisfaction is of utmost importance and tenderness is one of the most important characteristics in this regard. Our study examined beef of different animal biotypes of the autochthonous breed "Asturiana de los Valles" (AV) to determine if early postmortem oxidative and proteolytic processes may influence the final tenderness of the product. This meat-specialized breed shows different biotypes depending on the frequency of a myostatin mutation "mh" that induces double-muscling or muscular hypertrophy (mh/mh, mh/+, +/+). Samples from the longissimus dorsi muscles of yearling bulls were analyzed during the first 24 h postmortem. Changes in the redox balance of muscle cells were significant in the first hours after slaughter; total antioxidant activity was higher in the mh/mh biotype and it followed the shortening of the sarcomeres, a key parameter in understanding meat tenderness. The two proteolytic systems studied (proteasome and lysosome) followed distinct patterns. Proteasome activity was higher in the (mh/+) biotype, which correlated with higher protein damage. Lysosome proteolysis was increased in the more tender biotypes (mh genotypes). Autophagic activation showed significant differences between the biotypes, with (mh/mh) showing more intense basal autophagy at the beginning of the postmortem period that decreased gradually (p < 0.001), while in the normal biotype (+/+), it was slightly delayed and then increased progressively (p < 0.001). These results suggest that this type of catalytic process and antioxidant activity could contribute to the earlier disintegration of the myofibers, particularly in the mh/mh biotypes, and influence the conversion of muscle into meat.

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.

Optimal conditions for beef tenderization through radiofrequency heating with cold air

High-temperature (15-37°C) aging can shorten the tenderizing time of beef; however, the use of constant temperature heating can lead to microbial spoilage. This study tested radiofrequency (RF) tenderization (RF-T) to find the appropriate conditions for the aging-like effect of beef without microbial spoilage. After subjecting beef to 22 h RF-T with four different cooling temperatures (15, 5, -10, and -20°C), the proliferated aerobic bacteria on the surface showed a concentration of 6-6.2 log CFU/g at -10 and -20°C, lower than 7-7.5 log CFU/g at 15 and 5°C. When beef was treated with 25 W/kg RF heating power for 48 h RF-T, the estimated reduction rate of the sliced shear force (SSF) and the increase rate of glutamic acid based on the weight before RF-T were 22.6% and 1.51-fold, which were greater than 19.6% and 1.37-fold with 20 W/kg, and 11.0% and 1.11-fold with 15 W/kg. The optimal specific RF heating power was calculated as 30 W/kg from the results' extrapolation. When processed for 48 h under optimal conditions (30 W/kg specific RF heating power, -20°C cooling air), the tenderization rate and the increased rates of free amino acids based on the weight before RF-T of beef reached over 20% and 1.5-fold with 5.22 log CFU/g aerobic bacteria, which was lesser than the Korean regulation value of 6.7 log CFU/g (5 × 106  CFU/g). Therefore, RF-T could be proposed as a promising high-temperature tenderization method with lowered risk of microbial spoilage. PRACTICAL APPLICATION: We showed that lowering the chamber temperature during RF-T was effective in surface drying and inhibiting aerobic bacteria. RF-T for 24-48 h with 30 W/kg specific RF heating power had an aging-like effect given tenderization and increase in FAAs. Moreover, by providing the matching circuit and impedance during RF-T, this method could be industrially reproducible.

High-pressure processing of beef increased the in vitro protein digestibility in an infant digestion model

Beef is an ideal protein source for use as a complementary food in infants. Considering the limited protein-digesting capacity of infants, it is required to enhance protein digestibility while minimizing the deterioration of beef quality. Thus, this study aimed to determine the effects of high-pressure processing (HPP) on the physicochemical properties and in vitro digestibility of beef proteins in an infant digestion model. HPP at 200 and 300 MPa decreased the tryptophan fluorescence intensity of the myosin and actin fractions relative to that at 0.1 MPa (P < 0.05). Compared to treatment at 0.1 and 100 MPa, HPP at 300 MPa decreased α-helix and β-turn contents in the myosin and actin fractions (P < 0.05), whilst increasing the β-sheet content (P < 0.05). Beef actomyosin content decreased (P < 0.05) during HPP at 200 and 300 MPa (c.f., 0.1 and 100 MPa). After in vitro digestion of beef, HPP at 200 and 300 MPa increased the α-amino group content and the abundance of proteins below 3 kDa in the digesta (P < 0.05). However, due to the considerable lipid oxidation at 300 MPa, HPP at 200 MPa is ideal for improving the protein digestibility of beef when incorporated into complementary foods for infants.

The potential mediation of hypoxia-inducible factor-1α in heat shock protein 27 translocations, caspase-3 and calpain activities and yak meat tenderness during postmortem aging

The present study aimed to characterize the influence of hypoxia-inducible factor-1α on heat shock protein 27 and cytochrome c translocation, yak meat microstructure destruction, and endogenous enzymes activities, refining the understanding of the tenderization process after slaughter. Postmortem yak longissimus thoracis et lumborum muscles were incubated with 0.9% saline or hypoxia-inducible factor-1α stabilizer dimethyloxaloylglycine at 4 °C for 6, 12, 24, 72, and 120 h. Results showed that hypoxia-inducible factor-1α activation promoted heat shock protein 27 migration and cytochrome c release, facilitating (P < 0.05) caspase-3 activity by mediating the heat shock protein 27/caspase-3 interaction but did not exert (P > 0.05) significant effects on the calpain-1 activity. Additionally, hypoxia-inducible factor-1α activation contributed to the mitochondrial apoptosis cascade, leading to a higher (P < 0.01) apoptosis rate. Therefore, these observations indicate that hypoxia-inducible factor-1α affects caspase-3 activity and tenderness of postmortem muscle through distinct regulatory mechanisms, possibly, in part, with heat shock protein 27 and cytochrome c mediation.

Effect of boiling on texture of scallop adductor muscles and its mechanism based on label-free quantitative proteomic technique

The mechanism behind textural changes in scallop adductor muscle during boiling was investigated through proteomic analysis, determination of water holding capacity (WHC) and oxidative indices, as well as observation with scanning electron microscopy and multiphoton nonlinear optical microscopy. The hardness and shear force showed the trend of first rising and then falling in 45 min-boiling time. The results suggested that short-time boiling caused the oxidation, denaturation and aggregation of proteins, resulting in the transverse contraction of myofibers and lateral cross-linked aggregation of muscle fibers and a rise in WHC, which led to the increase in hardness and shear force. While long-time boiling caused the progressive degradation of structural proteins such as fibrillin-1, collagen alpha-2(I) chain, myosin heavy chain, basement membrane-specific heparan sulfate proteoglycan core protein, and paramyosin, resulting in a loose myofibril network and the decrease in WHC, which led to the decrease in hardness and shear force.

Degradation and evaluation of myofibril proteins induced by endogenous protease in aquatic products during storage: a review

Myofibril proteins degradation constitutes an important factor in quality deterioration, procedural activation or inhibition of endogenous protease potential regulates autolytic proteolysis-induced softening of post mortem fish muscle. Based on the brief introduction of myofibril proteins degradation in fish skeletal muscle, a detailed description of the main myofibril degradation properties and the distinct role played by endogenous proteases were proposed, which reflects the limitations and challenges of the current research on myofibril hydrolysis mechanisms based on the varied surrounding conditions. In addition, the latest researches on the evaluation method of myofibril proteins degradation were comprehensively reviewed. The potential use of label-free proteomics combined with bioinformatics was also emphasized and has become an important means to in-depth understand protein degradation mechanism.

The Effects of Postmortem Time on Muscle Trout Biochemical Composition and Structure

Fish industry operators have to process fish that arrive at various postmortem times. Postmortem time constrains processing and impacts product quality, safety, and economic value. The objective identification of biomarkers is desirable to predict the postmortem day of aging and this requires a comprehensive longitudinal characterisation of postmortem aging. We analysed the postmortem aging process in trout over a 15-day window. Quantitative physicochemical measurements (pH, colour, texture, a_w, proteolysis, and myofibrillar protein solubility) performed on the same fish over time revealed the levels of protein denaturation, solubility, and pH, among other parameters, change very little when assessed by conventional chemical methods. Histological analyses were performed on thin sections and revealed fibre ruptures after 7 days of storage on ice. Ultrastructures were observed by transmission electronic microscopy (TEM) and revealed that sarcomere disorganisation occurred more often after 7 days of storage. Label-free FTIR micro-spectroscopy combined with a SVM model accurately predicted the postmortem time. Spectra-based PC-DA models also enable the identification of biomarkers corresponding to Day 7 and Day 15 postmortem. This study provides insights on postmortem aging and raises prospects for the rapid assessment of trout's freshness status from label-free imaging.

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.

First insights into the dynamic protein changes in goat Semitendinosus muscle during the post-mortem period using high-throughput proteomics

Proteomics plays a key and insightful role in meat research in the post-genomic era. This study aimed to unveil using a shotgun proteomics approach the temporal dynamic changes in early post-mortem proteome of goat Semitendinosus muscle. Therefore, the evolution and comparison of the muscle proteome over three post-mortem times (1, 8, and 24 h) was assessed. The temporal proteomics profiling quantified 748 proteins, from which 174 were differentially abundant (DAPs): n = 55 between 1 h versus 8 h, n = 52 between 8 h versus 24 h, and n = 154 between 1 h versus 24 h. The DAPs belong to myriad interconnected pathways. Binding, transport and calcium homeostasis, as well as muscle contraction and structure, exhibited an equivalent contribution during post-mortem, demonstrating their central role. Catalytic, metabolism and ATP metabolic process, and proteolysis were active pathways from the first hours of animal bleeding. Conversely, oxidative stress, response to hypoxia and cell redox homeostasis along chaperones and heat shock proteins accounted for the large proportion of the biochemical processes, more importantly after 8 h post-mortem. Overall, the conversion of muscle into meat is largely orchestrated by energy production as well as mitochondrial metabolism and homeostasis through calcium and permeability transition regulation. The study further evidenced the role of ribosomal proteins in goat post-mortem muscle, signifying that several proteins experiencing changes during storage, also undergo splicing modifications, which is for instance a mechanism known for mitochondrial proteins. Overall, temporal proteomics profiling of early post-mortem muscle proteome offers an unparalleled view of the sophisticated post-mortem biochemical and proteolytic events associated with goat meat quality determination.

Molecular Changes of Meat Proteins During Processing and Their Impact on Quality and Nutritional Values

Meats are rich in lipids and proteins, exposing them to rapid oxidative changes. Proteins are essential to the human diet, and changes in the structure and functional attributes can greatly influence the quality and nutritional value of meats. In this article, we review the molecular changes of proteins during processing, their impact on the nutritional value of fresh and processed meat, the digestibility and bioavailability of meat proteins, the risks associated with high meat intake, and the preventive strategies employed to mitigate these risks. This information provides new research directions to reduce or prevent oxidative processes that influence the quality and nutritional values of meat.

Application of Plant Proteases in Meat Tenderization: Recent Trends and Future Prospects

Papain, bromelain, and ficin are commonly used plant proteases used for meat tenderization. Other plant proteases explored for meat tenderization are actinidin, zingibain, and cucumin. The application of plant crude extracts or powders containing higher levels of compounds exerting tenderizing effects is also gaining popularity due to lower cost, improved sensory attributes of meat, and the presence of bioactive compounds exerting additional benefits in addition to tenderization, such as antioxidants and antimicrobial effects. The uncontrolled plant protease action could cause excessive tenderization (mushy texture) and poor quality due to an indiscriminate breakdown of proteins. The higher cost of separation and the purification of enzymes, unstable structure, and poor stability of these enzymes due to autolysis are some major challenges faced by the food industry. The meat industry is targeting the recycling of enzymes and improving their stability and shelf-life by immobilization, encapsulation, protein engineering, medium engineering, and stabilization during tenderization. The present review critically analyzed recent trends and the prospects of the application of plant proteases in meat tenderization.

Mechanism of textural properties changes of cooked chicken in early postmortem: Effect of protein degradation induced by calpain on heating shrinkage

Although the relationship between myofibrillar protein status and cooked meat quality is well documented, its underlying mechanism still need to be clarified. In this study, the effect of calpain-induced myofibrillar degradation on the cooked chicken quality was discussed by comparing the difference in muscle fiber's heat shrinkage state. In early postmortem, the protein around Z-line was degraded, which would cause the unstable Z-line and released into the sarcoplasm, according to WB results. This phenomenon will aggravate the lateral contraction of muscle fragments during the heating process. Then along comes a higher cooking loss and lower texture properties of meat. Above findings indicate that the Z-line dissociation caused by calpain in the early postmortem period is an essential reason for the quality difference of mature chicken. This study provided a fresh light on the mechanism underlying the impact of myofibril degradation in the early postmortem on the quality of cooked chicken.

iTRAQ-based proteomic analysis reveals the underlying mechanism of postmortem tenderization of refrigerated porcine Longissimus thoracis et lumborum muscle

The isobaric tags for relative and absolute quantitation (iTRAQ) technology was used for differential proteomic analysis of refrigerated porcine Longissimus thoracis et lumborum (LTL) muscle at different time points postmortem (45 min, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h and 96 h) to mechanistically elucidate the postmortem tenderization. Compared with the proteins identified in porcine LTL muscle at 45 min postmortem (control), 862 proteins were significantly expressed at 4 h, 8 h, 12 h, 24 h, 48 h, 72 h and 96 h postmortem. Moreover, clustering and path analysis showed that the quality traits of porcine LTL muscle, including pH, shear force, myofibril fragmentation index, correlated significantly with 2, 6 and 6 differentially expressed proteins, respectively, with the lowest or highest expression at 8 h or 12 h postmortem. Overall, the tenderness of refrigerated porcine LTL muscle might be significantly affected by changes in quality traits at 8 h and 12 h postmortem.

Proteomics in bovine semitendinosus muscle to assess emerging strategies based on papain injection and ultrasounds on meat tenderization process

The impact of papain and/or ultrasound treatments on tenderization of semitendinosus muscle through a proteomic approach was studied. Sixteen bovine muscles were submitted to the following treatments: aging at 3 °C (Control), papain injection (PI), ultrasound (US), PI followed by US (PIUS) and US followed by PI (USPI). pH, myofibrillar fragmentation indices (MFI), soluble collagen, texture profile and changes of myofibrillar proteins were investigated after 2, 24, 48 and 96 h of storage. The highest MFI and soluble collagen content were found in PI, PIUS and USPI samples while control samples showed the lowest values. PI samples showed the lowest WBSF and hardness values until 48 h of storage while at 96 h meat from USPI treatment showed WBSF value comparable to PI treatment. The lowest values of cohesiveness, gumminess and chewiness were found in PI samples during all storage times. Proteomic analysis revealed a different quantity and expression of proteins among tenderization treatments. US treatment did not exhibit a significant ability to degrade muscle proteins, while, all treatments containing papain, showed a greater ability to hydrolyse and degrade myofibrillar proteins. PI promoted intense proteolysis leading to an early tenderization process; on the contrary, in PIUS and USPI treatments the sequence of treatments was relevant on meat tenderization. Particularly, USPI treatment, after 96 h, reached the same improvement in tenderness of enzymatic treatment but with slower hydrolysing rate; this could be determinant to preserve textural structure.

Application of 2-D DIGE to study the effect of ageing on horse meat myofibrillar sub-proteome

Considering the high relevance of meat tenderness for consumer acceptability, the aim of this study was to investigate post-mortem changes in myofibrillar sub-proteome in steaks from longissimus thoracis et lumborum muscle of six Hispano-Bretón horses. Indeed, the ageing process that leads to meat tenderization has been scarcely studied in this species. Steaks (n = 24) were aged (4 °C) in the dark under vacuum for 0, 7, 14 and 21 days and the myofibrillar sub-proteome was extracted. Using 2-D DIGE minimal labelling, 35 spots that were differentially abundant between 0 and 21 days aged meat were detected. Of them, 24 were analysed by LC-MS/MS, identifying a total of 29 equine proteins. These were structural and metabolic proteins, and among them, four (Actin, Troponin T and Myosin binding proteins 1 and 2) were selected for Western blot analysis, reporting changes in their abundance after 0, 7, 14 and 21 days of ageing. Results revealed that they should be further studied as potential protein biomarkers of horse meat tenderization. Additionally, several protein fragments increased after ageing, as was the case of glyceraldehyde-3-phosphate dehydrogenase. Fragments of this protein were present in four protein spots, and their study could be useful for monitoring horse meat tenderization. SIGNIFICANCE: Tenderization during ageing has been widely studied in meat from several farm animal species; however, both research and standardized ageing practices are lacking for the particular case of horse meat. In this regard, this study presents novel proteomic findings related to post-mortem evolution of horse muscle proteins. Acquired knowledge would support the development and optimization of efficient ageing practices by horse meat industry.

Investigation of changes in proteomes of beef exudate and meat quality attributes during wet-aging

This study was performed to evaluate the effects of wet-aging (3, 7, 14, 21, and 28 d at 2 °C) on beef (longissimus lumborum muscles) exudate proteome and meat quality changes. The pH, purge loss, and tenderness of beef increased with aging (P < 0.05), while color and lipid oxidative stabilities decreased, especially when long-term (14 and 21 d) aged meat were repackaged and displayed under retail condition (P < 0.05). Nineteen proteins changed significantly with aging (FDR < 0.05), in which most of them progressively accumulated in exudates over aging periods. Combined with partial least squares discriminant analysis, 16 proteins (including 9 structural proteins, 3 metabolic enzymes, 1 heat shock protein, 2 binding proteins, and KBTBD10 protein) were screened as characteristic proteins that could be used for potential meat quality indication. These findings offered novel insight into the utilization of exudates for meat quality assessment.

Research on apoptotic mechanism and related pathways involved in postmortem grass carp (Ctenopharyngodon idellus) muscle

BACKGROUND

Apoptosis activation is an essential research to reveal the triggering mechanism of flesh quality deterioration. This study was aimed at explaining apoptotic mechanism of postmortem fish in terms of caspases activation, cytochrome c (cyt-c) release, B-cell lymphoma 2 (Bcl-2) and Bcl2-associated X (Bax) protein levels, transcriptional levels of its molecules, and apoptosis-inducing factor (AIF) translocation at 4 °C for 5 days.

RESULTS

Activation of caspase-9, caspase-8, caspase-3 and the release of mitochondrial cyt-c were observed during storage. The decreased Bcl-2 protein levels, increased Bax protein expressions and Bax/Bcl-2 ratio were major steps for inducing apoptosis. Collectively, transcriptional regulation of Fas ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), inhibitors of apoptosis proteins (IAPs), myeloid cell leukemia-1 (Mcl-1), c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) indicated that extrinsic apoptotic pathways (FasL/caspase-8/caspase-3) and intrinsic pathway [(JNK and p38 MAPK)/(Bcl-2, Bax and Mcl-1)/cyt-c/Apaf-1/caspase-9/caspase-3] were involved in apoptotic process. Mitochondrial AIF translocation to nuclear indicated that AIF mediated caspase-independent pathway.

CONCLUSION

Therefore, transcriptional and translational alterations of multiple signaling molecules acted important roles in regulating apoptosis activation in postmortem process. © 2022 Society of Chemical Industry.

Proteomics Unveils Post-Mortem Changes in Beef Muscle Proteins and Provides Insight into Variations in Meat Quality Traits of Crossbred Young Steers and Heifers Raised in Feedlot

Proteomics has been widely used to study muscle biology and meat quality traits from different species including beef. Beef proteomics studies allow a better understanding of the biological processes related to meat quality trait determination. This study aimed to decipher by means of two-dimensional electrophoresis (2D-PAGE), mass spectrometry and bioinformatics the changes in post-mortem muscle with a focus on proteins differentially expressed in the Longissimus thoracis (LT) muscle of immunocastrated young heifers and steers. Carcass traits, chemical composition, pH, instrumental color (L*, a*, b*), cooking loss and Warner-Bratzler shear force (WBSF) of meat from F1 Montana-Nellore cattle were also evaluated. Backfat thickness (BFT) and intramuscular fat content (IMF) were 46.8% and 63.6% higher in heifers (p < 0.05), respectively, while evaporation losses (EL) were 10.22% lower compared to steers. No differences (p > 0.05) were observed for tenderness evaluated by WBSF (3, 10, and 17 days post-mortem), pH, and color traits (L*, a* and b*) between the experimental groups. The study revealed several proteins to be differentially expressed proteins in heifers compared steers (p < 0.05). In heifers, proteins involved in nutrient transport (TF, ALB, and MB), energy metabolism (ALDOA, GAPDH, and PKM), and oxidative stress and response to stress (HSPA8 and CA3) were associated with a greater BFT and IMF deposition. The higher expression of these proteins indicated greater oxidative capacity and lower glycolytic activity in the LT muscle of heifers. In steers, there was greater abundance of protein expression related to muscle contraction and proteins of structure (ACTA1, TPM2 and TNNT3), energy metabolism (ENO1, ENO3, PYGM, PGM1 and TPI1) and ATP metabolism (ATP5F1B, PEBP1 and AK1), indicating greater glycogenolysis in LT muscle, suggesting a shift in the glycolytic/oxidative fibers of steers.

Effect of Animal Age, Postmortem Calcium Chloride Marination, and Storage Time on Meat Quality Characteristics of M. longissimus thoracis et lumborum of Buffalo Bulls

This study investigated the effect of animal age, calcium chloride marination, and storage time on meat quality characteristics of buffalo bulls to suggest a cost-effective method of improving buffalo meat quality. The current study was designed considering the importance of buffalo meat and the usage of meat from spent buffalo animals in local markets of South Asian countries. A total of 36 animals comprised of 18 young and 18 spent buffalo bulls were selected. After slaughtering and 24 h of postmortem chilling, striploins were separated and cut into 16 steaks and equally divided into two groups, i.e., either marinated with calcium chloride or not. Meat quality characteristics were recorded on 0, 2, 4, 6, 8, and 10 days of storage. The results showed that the pH value of young animals was higher than the value of spent animals and pH was increased over the storage time. Color b*, C*, and h* values were higher in spent animals as compared with the young animals; however, values of colors L* and h* were higher and a* was lower in marinated samples than the values of non-marinated samples. Color a* and C* values were increased and h* was decreased with lengthening the storage time. The meat cooking loss was higher in marinated and the water-holding capacity was higher in non-marinated meat samples. Shear force values were lower in young animals and marinated samples than the values of spent animals and non-marinated meat samples, respectively. Sensory characteristic scores of marinated samples were better than the non-marinated samples. In conclusion, calcium chloride marination can be used to improve the quality characteristics of buffalo meat.

Proteolysis and changes in meat quality of chicken pectoralis major and iliotibialis muscles in relation to muscle fiber type distribution

The proteolysis trends and meat quality of the chicken pectoralis major (PM) and iliotibialis (IL) muscles stored at 4°C for 7 d were investigated. After 7 d of storage, the purge loss was higher (P < 0.05) in PM than in IL muscle. The difference in the composition of muscle fibers between PM (100% fast type) and IL (88.85% fast and 11.15% slow types) resulted in differences in proteolysis. Fructose-bisphosphate aldolase, troponin I, myosin heavy chain, and malate dehydrogenase exhibited the same tendencies, but pyruvate kinase, creatine kinase, L-lactate dehydrogenase, and triosephosphate isomerase exhibited different tendencies in the 2 muscles. The activity of cathepsin B was higher in PM than in IL during storage (P < 0.05). These results indicate that the proteolysis trend and changes in meat quality during cold storage are dependent on the different muscle fiber characteristics.

Early postmortem degradation of actin muscle protein in Algerian Sahraoui dromedaries

The present study aimed to evaluate actin degradation during the early postmortem time in Longissimus Lumborum muscle according to Sahraoui dromedary's age. A sample of eight males, young (2 years old) and adult (8 years old) dromedaries, was used to investigate meat quality traits and actin proteolysis during the conversion of muscle to meat. Results demonstrated higher pH values in young compared to adult with a polyphasic pH drop profile. While, age did not affect drip loss (DL) and the values at 72 h postmortem varied from 5 to 9%. Western blot revealed that actin proteolysis occurred since 1 h postmortem and that it was affected by age and postmortem time. In particular, the 32 and 25 kDa actin fragments could be potential markers of ongoing meat tenderization.

Estimation of the proteome affecting changes in tenderness of yak meat during storage by label-free mass spectrometry

Background

Tenderness is the main quality of meat products. However, the meat tenderness formation is a complex biological process, and pathways and proteins that affect the tenderness of yak meat are unknown.

Methods

Label‐free proteomics method was used to explore the effects of differentially expressed proteins on the tenderness of yak skeletal muscle (tenderloin) during post‐mortem storage (0, 3, and 7 days) at 3 ± 1°C.

Results

The tenderness of yak skeletal muscle improved significantly during storage. A total of 91 differentially expressed proteins of yak skeletal muscle during post‐mortem storage were identified by the following comparisons: day 3 versus 0, day 7 versus 0, and day 7 versus 3. NDUFS6, CYCS, COX6A2, LDB3, HSPB7, TPM4, TAGLN, COL1A1, LUM, MYH11, ACTC1, and MYOZ1 proteins showed a significant difference during yak skeletal muscle post‐mortem storage. Furthermore, bioinformatics analyses revealed that the identified proteins were related to carbon metabolism, citrate cycle, glycolysis, oxidative phosphorylation, and RNA degradation.

Conclusion

The results of the present study could provide proteomic insights into changes in yak skeletal muscle tenderness during storage and may be a valuable resource for future investigations.

Application of iTRAQ Technology to Identify Differentially Expressed Proteins of Sauce Lamb Tripe with Different Secondary Pasteurization Treatments

Vacuum-packed sauce lamb tripe was subjected to secondary pasteurization by high-pressure processing (HPP) and heat treatment (HT), and iTRAQ technology was applied to investigate the differentially expressed proteins (DEPs). The analysis revealed 484 and 398 DEPs in the HPP and HT samples, respectively, compared with no treatment. These DEPs were sorted by texture results, and it was revealed that these DEPs acted in different biological processes with many structural proteins and protein subunits related to lamb tripe texture. The results verified by Western blot were consistent with the protein expression changes observed by proteomics. The bioinformatics analysis showed that the hardness and gumminess of the sauce lamb tripe after HT might be related to changes in the expression of CNN1 and FN1. The changes in the expression of TMP, FN1, YWHAG, TTN, collagen isoforms, and ARPC3 might be related to the improved springiness and chewiness of lamb tripe after HPP.

Postmortem Muscle Protein Changes as a Tool for Monitoring Sahraoui Dromedary Meat Quality Characteristics

The effects of slaughter age (2 vs. 9 years) and postmortem time (6, 8, 10, 12, 24, 48 and 72 h) on the meat quality and protein changes of the longissimus lumborum muscles of the Algerian Sahraoui dromedary were investigated. Muscles of young dromedaries evidenced a slower acidification process and a significantly higher myofibrillar fragmentation index throughout the postmortem time. The SDS-PAGE of sarcoplasmic and myofibrillar proteins revealed that meat from young dromedaries was characterized by the lowest percentage of myoglobin (p < 0.001) and the highest percentage of desmin (p < 0.01). During postmortem time, a decrease was found for phosphoglucomutase (p < 0.01), α-actinin (p < 0.05) and desmin (p < 0.01) in meat from young dromedaries. Western blot revealed an intense degradation of troponin T in younger dromedaries, with an earlier appearance of the 28 kDa polypeptide highlighting differences in the proteolytic potential between dromedaries of different ages. Principal component analysis showed that meat from young dromedaries, starting from 24 h postmortem, was located in a zone of the plot characterized by higher levels of the myofibrillar fragmentation index, 30 kDa polypeptide and enolase, overall confirming greater proteolysis in younger animals. Data suggest that the investigation of the muscle proteome is necessary to set targeted interventions to improve the aging process of dromedary meat cuts.

Physicochemical composition, fatty acid profile and sensory attributes of meat (longissimus lumborum muscle) from Nellore and Nellore-cross bulls

This study aimed to compare the physicochemical characteristics, fatty acid composition, and sensory attributes of the meat from three genetic groups: Nellore (Nell), ½ Nellore × ½ Angus (NeAn), and ¼ Nellore × ¼ Angus × ½ Senepol (NASe). Longissimus lumborum muscle from 30 slaughtered bulls with a body weight of 549 ± 32.5 kg was used. The water holding capacity was greater for the Nell and NeAn groups than for the NASe group. Meat samples from the NASe group exhibited a higher L* index than those from the NeAn group and lower a* and b* color indexes than those from the Nell group. The meat fatty acid profiles showed that the Nell group had higher concentrations of 12:0, 14:0, 18:1 t11, 14:1 c9, 16:1 c9, 18:1 c9, 18:1 c11, 18:2 c9, t11 (conjugated linoleic acid (CLA)), and 20:3 n-6 polyunsaturated fatty acid (PUFA) than the NeAn and NASe groups. The total saturated (ΣSFA), unsaturated (ΣUFA), and monounsaturated (ΣMUFA) fatty acid concentrations were higher and the ΣPUFA:ΣSFA ratio was lower in the Nell group than in the NeAn group. The Δ⁹-desaturase C16 activity was significantly higher in the Nell and NASe groups than in the NeAn group. The atherogenicity index (AI) tended to be lower in the crossbreeds than in the Nell breed. The NASe group presented meat with better tenderness, juiciness, and overall acceptance than the Nell and NeAn groups and was therefore the best genetic group for beef production of the tested groups.

Is beef quality affected by the inclusion of distiller grains in cattle diets?

This study aimed to analyze the effect of including increasing levels of distiller grains (DG) in beef cattle feeding diets on meat quality from an integral approach. To this end, we analyzed the meat from 36 yearling steers fed with four dietary treatments: 0DG (control corn-based diet), 15DG, 30DG, and 45DG (containing 15%, 30%, or 45% of DG on DM basis). Crude protein, ash, and fat contents of diets increased with DG level. The fatty acid profile of DG diets was reflected in the fatty acid profile of plasma samples. Feeding diets with DG had no effect on the biochemical parameters analyzed in plasma. In addition, it did not influence the water holding capacity, the muscle or fat color at 72 h post mortem or at retail display, or the contents of SFAs, MUFAs, and PUFAs in beef. The DG diets led to lower values of cooking loss. Meat from 15DG and 30DG showed greater percentage of troponin C and fragments of 30 to 27 kDa than meat from 45DG. Also, meat from 30DG showed the lowest values of Warner-Bratzler shear force. Hence, including up to 30% corn DG in beef cattle feeding diets had positive effects on meat quality.

Peptidomic analysis characterising proteolysis in thaw-aging of beef short plate

Recent studies have suggested that thaw-aging can improve sensory attributes of freeze-thawed meat. Acceleration of proteolysis is expected to promote tenderisation and improve taste; however, the details of protein degradation, including substrate proteins and cleavage sites, remain unclear. Here, we report a time course overview of the peptidome of beef short plates during thaw-aging. The accelerated degradation of key proteins for meat tenderisation, such as troponin T and desmin, was confirmed. Additionally, 11 cleavage sites in troponin T related to taste-active peptide generation were identified. Terminome analysis showed that the contribution of each protease varies depending on the substrate proteins and the thaw-aging period. Based on our results; proteases, not only calpains, but also others contributed to the degradation of myofibrillar proteins. The techniques employed indicate that meat proteolysis during thaw-aging is not constant but dynamic.

Proteomics discovery of protein biomarkers linked to yak meat tenderness as determined by label-free mass spectrometry

Tenderness is one of the most important qualities in meat. A proteomic approach is a suitable way to ensure meat tenderness. Thirty-six tenderloin samples from yak were classified as exhibiting high (n = 12) or low (n = 12) tenderness and were evaluated using label-free proteomics for the identification of the proteins and pathways most influential in tenderness variability. Between the two groups, proteomic changes were mainly caused by 33 differentially expressed proteins as displayed in reference patterns in heat maps. The expression of ENO2, SUCLG2, ETFDH, PGM1, TNNT3, TNNT1, HSDL2, GPI, ALAD, and COL1A1 proteins was very different between yak meats with high and low tenderness, and therefore, they are candidate biomarkers of yak meat tenderness. Furthermore, bioinformatics analyses revealed that the identified proteins are related to pentose phosphate, glycolysis, the citrate cycle, fatty acid metabolism, and the calcium signaling pathway.

Genes and proteins associated with ribeye area and meat tenderness in a commercial Nellore cattle population

Despite several studies on genetic markers and differently expressed genes related to ribeye area (REA) and tenderness traits in beef cattle, there is divergence in the results regarding the genes associated with these traits. Thirteen genes that had been associated or have biological functions that may influence such phenotypes were included in this study. A total of five genes for REA (IGF-1, IGF-2, MSTN, NEDD4, and UBE4A) and eight genes for meat tenderness (CAPN1, CAPN2, CAST, HSPB1, DNAJA1, FABP4, SCD, and PRKAG3) were selected from previously studies in beef cattle. Genes and its respective proteins expression were validated in a commercial population of Nellore cattle using quantitative real-time PCR (RT-qPCR) and advanced mass spectrometry (LC / MS-MS) techniques, respectively. MSTN gene was upregulated in animals with low REA. CAPN1, CAPN2, CAST, HSPB1, and DNAJA1 genes were upregulated in animals with tougher meat. The proteins translated by these genes were not differentially expressed. Our results could confirm the potential of some studied genes as biomarkers for carcass and meat quality in Nellore cattle.

Effect of refrigeration on the collagen and texture characteristics of yak meat

To investigate the effect of refrigeration on the collagen and texture characteristics of yak meat, the changes in collagen content, solubility, shear force, hardness, cohesiveness, springiness, gumminess, and chewiness of yak meat at 4 ± 1 °C were measured. The results showed that the contents and solubility of collagen in yak meat significantly decreased (P < 0.05). The myofibrillar fragmentation index of yak meat significantly increased (P < 0.05). The shear force, hardness, cohesiveness, springiness, gumminess, and chewiness of yak meat significantly decreased (P < 0.05). Correlation analysis and histological structure analysis confirmed that myofibrillar fragmentation and collagen characteristics significantly affected the formation of yak meat texture during refrigeration. After 5 d of refrigerated storage, yak meat has a higher quality. The results provide a theoretical basis and data to support the deep processing and quality control of yak meat.

Effect of Postmortem Phases on Lamb Meat Quality: A Physicochemical, Microstructural and Water Mobility Approach

To investigate the effect of postmortem phases on lamb meat quality, the physicochemical quality, microstructure and water mobility of oyster cut, short loin, knuckle and silverside muscles from Small-Tail Han sheep were evaluated in the pre-rigor, rigor mortis and post-rigor phases. Pre-rigor lamb meat had higher pH and water holding capacity (WHC), whereas lower CIE L*, b*, hue angle values than rigor mortis and post-rigor meat (p<0.05). The Warner-Bratzler shear force (WBSF) values were higher in rigor mortis short loin and silverside than their pre-rigor and post-rigor counterparts, pre-rigor short loin had lower WBSF value than its post-rigor counterpart (p<0.05). Muscle fibers shrank laterally and longitudinally during the onset of rigor mortis. Rigor mortis and post-rigor lamb meat exhibited wide I-bands, dark A-bands, short sarcomeres and large inter-myofibrillar spaces. The shift of immobilized water to free water and repulsion from the intra-myofibrillar space to the extracellular space result in the increase of water loss in rigor mortis and post-rigor lamb meat. The results of the principal component analysis (PCA) indicated that rigor mortis and post-rigor lamb meat had similar quality properties but different from pre-rigor lamb meat. In conclusion, the lamb meat in the pre-rigor phase had good tenderness, color and WHC. The results of this research could provide some theoretical references for lamb meat production and processing.

Redox Proteomic Analysis Reveals Microwave-Induced Oxidation Modifications of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix)

To provide an insight into the oxidation behavior of cysteines in myofibrillar proteins (MPs) during microwave heating (MW), a quantitative redox proteomic analysis based on the isobaric iodoacetyl tandem mass tag technology was applied in this study. MPs from silver carp muscles were subjected to MW and water bath heating (WB) with the same time-temperature profiles to eliminate the thermal differences caused by an uneven energy input. Altogether, 422 proteins were found to be differentially expressed after thermal treatments as compared to that with no heat treatment. However, MW triggered a larger number of proteins and cysteine sites for oxidation. Myosin heavy chain, myosin-binding protein C, nebulin, α-actinin-3-like, and titin were found to be highly susceptible to oxidation under microwave irradiation. Notably, MW caused such modifications at cysteine site 9 in the head of myosin, revealing the enhancement mechanism of MP gelation by excess cysteine cross-linking during microwave processing. Furthermore, Gene Ontology and functional enrichment analyses suggested that the two thermal treatments resulted in some differences in ion binding, muscle cell development, and protein-containing complex assembly. Overall, this study is the first to report the redox proteomic changes caused by MW and WB treatments, thus providing a further understanding of the microwave-induced oxidative modifications of MPs.

Meat tenderness: advances in biology, biochemistry, molecular mechanisms and new technologies

Meat tenderness is an important quality trait critical to consumer acceptance, and determines satisfaction, repeat purchase and willingness-to-pay premium prices. Recent advances in tenderness research from a variety of perspectives are presented. Our understanding of molecular factors influencing tenderization are discussed in relation to glycolysis, calcium release, protease activation, apoptosis and heat shock proteins, the use of proteomic analysis for monitoring changes, proteomic biomarkers and oxidative/nitrosative stress. Each of these structural, metabolic and molecular determinants of meat tenderness are then discussed in greater detail in relation to animal variation, postmortem influences, and changes during cooking, with a focus on recent advances. Innovations in postmortem technologies and enzymes for meat tenderization are discussed including their potential commercial application. Continued success of the meat industry relies on ongoing advances in our understanding, and in industry innovation. The recent advances in fundamental and applied research on meat tenderness in relation to the various sectors of the supply chain will enable such innovation.

The effect of caspase-3 in mitochondrial apoptosis activation on degradation of structure proteins of Esox lucius during postmortem storage

This study aimed to investigate the effect of caspase-3 inhibitor in mitochondrial apoptosis activation on structure protein degradation during postmortem storage. Mitochondrial dysfunction, apoptotic factors, structure protein degradation and the myofibrillar rupture index between the control and caspase-3 inhibitor groups were determined. The results show caspase-3 inhibitor repressed the mitochondrial membrane permeability and mitochondrial swelling, as well as increased mitochondrial membrane potential, causing a decrease in the release of cytochrome c from mitochondria to cytoplasm and caspase-9/3 activities (P < 0.05). Subsequently, small myofibrillar proteins (desmin and troponin-T) were susceptible to degradation, initiating texture deterioration. By contrast, giant structure proteins (titin and nebulin) were degraded during later postmortem storage, predominantly contributing to fish softening. The results further suggest that caspase-3 is involved in degradation of structure proteins during postmortem through mitochondrial apoptosis pathways.