Tenderness is considered a crucial attribute of postmortem meat quality, directly influencing consumers' preferences and industrial economic benefits. The degradation of myofibrillar proteins by endogenous enzymes within muscle fibers is believed to be the most effective pathway for meat tenderization. After animals are slaughtered and exsanguinated, there is a significant accumulation of reactive oxygen species (ROS), and a dramatic depletion of adenosine triphosphate (ATP) in muscle, leading to inevitable cell death. Caspases are activated in postmortem muscle cells, which disrupt the cell structure and improve meat tenderness through protein hydrolysis. In this review, we systematically summarized the three primary types of cell death studied in postmortem muscle: apoptosis, autophagy and necrosis. Furthermore, we emphasized the molecular mechanisms of apoptosis and its corresponding apoptotic pathways (mitochondrial apoptosis, death receptors, and endoplasmic reticulum stress) that affect meat tenderness during muscle conversion to meat. Additionally, factors affecting apoptosis were comprehensively discussed, such as ROS, heat shock proteins, calcium (Ca2+)/calpains, and Bcl-2 family proteins. Finally, this comprehensive review of existing research reveals that apoptosis is mainly mediated by the mitochondrial pathway. This ultimately leads to myofibrillar proteins degradation through caspase activation, improving meat tenderness. This review summarizes the research progress on postmortem muscle apoptosis and its molecular mechanisms in meat tenderization. We hope this will enhance understanding of postmortem meat tenderness and provide a theoretical basis for meat tenderization techniques development in the future.

AbstractPhosphoglycerate kinase 1 (PGK1) and pyruvate kinase M2 (PKM2) have been identified as the postmortem meat quality biomarkers. However, the precise molecular mechanism through which they affect and regulate the development of meat quality remains unclear. In this work, the high‐ and low‐activity groups (n = 10) were selected from 60 lamb muscles at 24 h postmortem based on the activity levels of PGK1 and PKM2. The metabolomic, proteomic, and transcriptomic analyses combined with deeply integrated multi‐omics analysis were used to elucidate the mechanisms by which PGK1 and PKM2 characterize meat quality. The results indicated that glycolysis played a crucial role in regulating PGK1 and PKM2 activity at the metabolome, proteome, and transcriptome levels. In glycolysis pathway, we identified several key components closely related to PGK1 and PKM2 activity, including differential metabolites (adenosine triphosphate, adenosine diphosphate, glucose‐6‐phosphate, nicotinamide adenine dinucleotide phosphate, fructose‐6‐phosphate, dihydroxyacetone phosphate, 3‐phosphoglycerate, NAD+ nicotinamide adenine dinucleotide, lactate, and pyruvate), different abundance proteins (lactate dehydrogenase B and fructose bisphosphate aldolase B), and differentially expressed genes (hexokinase and fructose‐1,6‐bisphosphatase 1). It was concluded that PGK1 and PKM2 may affect the formation of meat quality by regulating these critical substrates. Additionally, PGK1 and PKM2 could also affect the tricarboxylic acid cycle, oxidative phosphorylation, and muscle contraction in postmortem and then influence meat quality. This integrative omics study offers valuable insight into unraveling the molecular mechanisms underlying postmortem meat quality development.

The objective of this work was to investigate the influence of phosphoglycerate kinase-1 (PGK1) and pyruvate kinase-M2 (PKM2) activity on glycolysis, myofibrillar proteins, calpain system, and apoptosis pathways of postmortem muscle. The activity of PGK1 and PKM2 was regulated by their inhibitors and activators to construct the postmortem glycolysis vitro model and then incubated at 4 °C for 24 h. The results showed that compared to PGK1 and PKM2 inhibitors groups, the addition of PGK1 and PKM2 activators could accelerate glycogen consumption, ATP and lactate production, while declining pH value. Moreover, the addition of PGK1 and PKM2 activators could increase desmin degradation, μ-calpain activity, and caspase-3 abundance. Interestingly, troponin-T degradation was significantly increased both in PKM2 inhibitor and activator groups. It was suggested that PGK1 and PKM2 might be used as robust indicators to regulate meat quality by affecting the glycolysis, myofibrillar proteins, μ-calpain and apoptosis pathways in postmortem muscle.

This study was conducted to analyze the flavor profile of six commercially available Chinese indigenous breeds of sheep meat and to distinguish them based on their flavor characteristics. Various techniques such as gas chromatography-mass spectrometry (GC-MS), electronic nose (E-nose), high performance liquid chromatography (HPLC) and electronic tongue (E-tongue) were employed to analyze both volatile and non-volatile compounds in the meat samples. The results showed that, a total of 28 volatile compounds in sheep meat were detected, with 1-octen-3-ol, 1-pentanol, hexanal, octanal, and nonanal identified as the major contributors to its aroma. Tan Sheep and Oula Sheep had significantly higher concentrations of 1-pentanol, nonanal, 1-octen-3-ol, 1-octanol, and hexanoic acid than other breeds. Sweet amino acids were the most abundant free amino acids, comprising 72–85% of the total FAAs, and inosinic acid was the most abundant ATP-related compound. Small-Tailed Han sheep had significantly higher levels of SFAAs, total FAAs, and AMP, while Tan sheep had significantly higher levels of UFAAs, and Oula Sheep had significantly higher levels of GMP. The response values of differential electronic sensors W5S, W1W, NMS, PKS, and SCS were found to be useful in discriminating between breeds of sheep meat. The fusion electronic sensory signals were used to train support vector machine and random forest models, both achieving 100% accuracy in discriminating between sheep breeds.

To study the effect of rigor state on physicochemical characteristics of Funiu white goat and Oula sheep meat batters. In this study, the effect of rigor state of Funiu white goat and Oula sheep silverside muscle on meat batter quality and physicochemical properties was determined. Results indicated that meat batters obtained from post-rigor meat had less water holding capacity and lower immobilized water than that obtained from pre-rigor meat. The gel network of meat batters produced with Funiu white goat muscle appeared denser and smoother compared with Oula sheep meat batters. Furthermore, meat batters produced with pre-rigor meat had higher hardness compared to that produced with post-rigor meat. Differences in response values were found for CPS (sensitivity to sweet taste) of meat batters made with meat in the three rigor states. Collectively, both Funiu white goat and Oula sheep meat in pre-rigor state were more suitable to minced meat product production compared to post-rigor meat based on gel properties.

The aim of this study was to identify the potential indicators of lamb meat quality by TMT and PRM-based proteomics combined with bioinformatic analysis. Lamb muscles were divided into three different meat quality groups (high, middle and low) according to tenderness (shear force, MFI value), colour (a* value, R630/580), and water-holding capacity (cooking loss, drip loss) at 24 h postmortem. The results showed that the abundance of phosphoglycerate kinase 1 (PGK1), β-enolase (ENO3), myosin-binding protein C (MYBPC1) and myosin regulatory light chain 2 (MYLPF) was significantly different in the three groups and could be used as potential indicators to characterize meat quality. Moreover, the postmortem processes of glycolysis, oxidative phosphorylation, and muscle contraction remarkably changed in different groups, and were the key biological pathways influencing meat quality. Overall, this study depicted the proteomic landscape of meat that furthers our understanding of the molecular mechanism of meat quality and provides a reference for developing non-destructive detection technology for meat quality.

SummaryThe objective of this study was to investigate the effect of chilling rate on heat shock proteins (HSP) abundance, myofibrillar proteins degradation and caspase‐3 activity of lamb muscle in postmortem. Eighteen longissimus dorsi (LD) muscles from lamb were treated under three different chilling rates—very fast chilling I (VFC‐I, 22.2 °C h−1), very fast chilling II (VFC‐II, 32.4 °C h−1) and control (1.44 °C h−1)—and stored at −1 °C, −1 °C and 4 °C for 120 h postmortem, respectively. The results showed that myofibril fragmentation index (MFI), the abundance of αβ‐crystallin and HSP20, as well as the degradation of HSP27, HSP70, troponin‐T and desmin under the VFC‐I and VFC‐II groups were higher than control. Notably, HSP90 abundance may not be affected by the chilling rate in the late postmortem aging. Additionally, with increasing of chilling rate for postmortem muscle could inhibit caspase‐3 activity. Overall, results indicated that chilling rate may affect the process of meat tenderization by changing the abundance levels of heat shock proteins, myofibrillar degradation and apoptotic pathway.

Understanding the pre- and post-rigor meat quality characteristics is crucial for the development of featured goat meat products. To evaluate the quality characteristics of goat meat in different rigor states, knuckle muscle in pre-rigor, rigor, and post-rigor states of Taihang and Huanghuai goats were used to analyze chemical characteristics, water mobility, and electronic sense. Results indicated that Taihang and Huanghuai goat meat samples were rich in protein and essential amino acids, especially Lys. Pre-rigor goat meat samples had lower content of free moisture and higher water holding capacity than post-rigor goat meat samples. Furthermore, Taihang and Huanghuai goat meat samples exhibited different odour characteristics. Aromatic constituents content of post-rigor goat meat samples were greater than those of pre-rigor goat meat samples. The sweetness and bitterness of post-rigor goat meat samples were higher than those of pre-rigor goat meat samples. In conclusion, Taihang and Huanghuai goat meat samples have different quality characteristics, which were regulated by rigor state through different texture and flavor profiles.

为探究包装方式和宰后不同时间包装对羊肉贮藏品质的影响,本研究对宰后1 h热分割羊肉和冷却成熟24h后的分割羊肉分别进行热收缩包装、真空包装、贴体包装、50％(体积分数,下同)O2+50％CO2气调包装,测定其在(2±2)℃贮藏过程中pH值、色泽、贮藏损失率、蒸煮损失率、离心损失率、剪切力、挥发性气味的变化.结果表明:与宰后24h包装相比,宰后1 h包装羊肉pH值在贮藏14d时更高,但其贮藏期间色泽较好,色泽稳定性更高,贮藏损失率更低.从整体来看,3种真空处理(热收缩包装、真空包装、贴体包装)羊肉嫩度均优于气调包装羊肉,且宰后l h包装时真空条件处理对羊肉嫩化效果最好,宰后24 h羊肉在贮藏前期气调包装对羊肉嫩化效果较好;而无论何时包装,热收缩包装和气调包装羊肉贮藏损失率均显著小于其他处理组(P＜0.05),在贮藏前期色泽及稳定性较好,但贮藏后期色泽稳定性下降明显,气调包装羊肉在14 d时已部分发绿,贮藏21d时挥发性气味变化显著.综上,宰后1 h包装有利于提高羊肉贮藏期间色泽及持水力,改善真空处理羊肉嫩度,宰后24h包装可提高50％O2+50％CO2气调包装羊肉贮藏前期的嫩度;其中热收缩包装和气调包装羊肉持水力高,贮藏前期色泽及稳定性好,真空包装、贴体包装羊肉品质变化相对稳定,适宜长期贮藏.

The protein is an ideal food matrix binding volatile compounds. However, the synergistic effects between the protein rheological behavior and protein-ligand interactions on the small molecule ligand retention are not fully reported. This study clarified how aldehydes bind to myosin during the constant thermal treatment. The results presented that the myosin unfolded at 25-64 degrees C and were cross-linked to generate polymers at 75-79 degrees C. The alpha-helix fractions of myosin turned into beta-turn and random coil fractions, regulating the rheological behavior and exposing more binding sites with aldehydes. The binding affinity of myosin with aldehydes was confirmed. Notably, the fluorescence quenching behaviors of myosin were increased (p < 0.05) with the increase of pentanal concentration and heating temperature. Synergistic effects between the rheological behavior of myosin and the myosin-aldehyde molecular interaction might predominantly contribute to the aldehyde retention. The hydrophobic interaction, amino acid residues, free sulfhydryl groups, and hydrogen bond might be the key (non)covalent linkages for myosin to bind aldehydes. Thr125, Pro128, Trp131, and Val187 might be key sites between myosin and pentanal, among which the chemical forces were the conventional hydrogen bond, alkyl, pi-alkyl, and alkyl hydrophobic among them, respectively.

The aim of this study was to investigate the effect of chilling rate (1.44, 22.2, and 32.4 °C/h) on the evolution of volatile and non-volatile compounds in raw lamb meat during refrigeration (1, 24, 72, and 120 h). Through orthogonal projection to latent structure-discriminant analysis, the calculation of odor activity values (OAV > 1) and taste activity values (TAV > 1) analysis, 1-octen-3-ol, (E, E)-2,4-decadienal, nonanal, hexanal, nona-3,5-dien-2-one, 2,3-octanedione, hexanoic acid, 1-nonen-4-ol, aspartate (Asp), Glutamic Acid (Glu), 5′-GMP, 5′-IMP, and 5′-AMP were regarded as differential flavor or taste compounds for raw meat undergone different chilling rates. With a rapid chilling rate at 24 h after slaughter, the contribution of 1-octen-3-ol decreased, but (E, E)-2,4-decadienal increased. Moreover, at 24 h post-mortem, the equivalent umami concentration of Asp, Glu, 5′-GMP, 5′-IMP and 5′-AMP in raw meat were significantly lower at a chilling rate of 1.44 °C/h than 32.4 °C/h (p < 0.05). Conclusively, under the rapid chilling rate, more fatty odor and umami compounds accumulated in 24 h aged meat.