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A recently identified broiler myopathy known as wooden breast (WB) is predominantly found in the pectoralis major muscle of fast-growing broiler hybrids and is causing significant losses to the poultry industry. The aim of this study was to investigate the effects of WB syndrome on raw meat texture, purge loss and thermal properties of intramuscular connective tissue of pectoralis major muscle in the early post-mortem period. Results showed that WB muscles at 1d postmortem was associated with significantly increased stiffness and significantly increased purge loss compared to normal muscles (NB). However, at 3d postmortem, these parameters did not differ between the two groups. Insoluble and total collagen content was significantly higher in WB muscles compared to NB muscles, and the extractability of intramuscular connective tissue (IMCT) was also higher and remained stable in the early postmortem period. These were coincided with significantly lower protein content in the sarcoplasmic protein fraction and myofibrillar protein fraction of WB muscles compared to NB muscles (P < 0.05). The IMCT of these two groups showed different thermal properties, as the enthalpy of denaturation (ΔH) was significantly lower in WB muscles compared to NB muscles. The WB syndrome had a great effect on the texture and connective tissue properties of the meat compared to normal muscle, with a tendency for having a lower water holding capacity and higher raw meat hardness

Over the recent decades,protein oxidation in muscle foods has gained increasing research interests as it is known that protein oxidation can affect eating quality and nutritional value of meat and aquatic products. Protein oxidation occurs during freezing/thawing and frozen storage of muscle foods, leading to irreversible physicochemical changes and impaired quality traits. Controlling oxidative damage to muscle foods during such technological processes requires a deeper understanding of the mechanisms of freezing-induced protein oxidation. This review focus on key physicochemical factors in freezing/thawing and frozen storage of muscle foods, such as formation of ice crystals, freeze concentrating and macromolecular crowding effect, instability of proteins at the ice-water interface, freezer burn, lipid oxidation, and so on. Possible relationships between these physicochemical factors and protein oxidation are thoroughly discussed. In addition, the occurrence of protein oxidation, the impact on eating quality and nutrition, and controlling methods are also briefly reviewed. This review will shed light on the complicated mechanism of protein oxidation in frozen muscle foods.

As a result of agri-food production, large quantities of organic waste are produced in the form of press cakes (by-products of plant-based drink production), and a huge quantity of these by-products is generally discarded, leading to environmental problems. This research aims to evaluate the effects of fermentation of Ultrasound (US) treated okara (soy press cakes) on protein oxidation level, techno-functional, texture and sensory properties of the meat analogues. Okara samples were fermented by applying L. plantarum P1 and L. acidophilus 308 strains. The meat analogues were produced by adding 3% and 6% fermented okara to the matrices. Fermented okara and matrices were maturated at temperatures 4 °C or 18 °C, separately. The effects of fermentation conditions, the amount of okara, and the dough maturation temperature, as well as the interaction effect on protein oxidation level, techno-functional, sensory, and textural properties of meat analogues were analysed. The results indicated that okara is a suitable source of fibre, plant-based proteins, and essential amino acids, and demonstrated the potential of the application of fermentation to improve water-holding capacity and sensory properties of meat analogues, as well as to reduce hardness and protein oxidation levels. The study recommended that the optimum condition for producing meat analogues was the application of 6% okara in the matrices fermented by L. plantarum P1, when the matrices and okara are maturated at 4 °C for 2 h. The research finally concluded that the use of fermentation process on US-treated okara makes it a suitable component of meat analogues.

International audience; A total of 436 young cattle from 15 cattle breeds were reared in as similar conditions as possible to evaluate the impact of breed on sensory quality of beef from longissimus muscle determined by sensory analysis. Two statistical methods for processing the sensory data were compared. The analysis of variance with or without the panelist effect gave similar conclusions indicating that the robustness of the results was not dependent on the method chosen. The 4 meat descriptors (tenderness, juiciness, beef flavor and off-flavor) placed breeds into 5 groups using an unsupervised classification (hierarchical ascending classification). Aberdeen Angus, Highland and Jersey, that have a high lipid content in the muscle studied, differed from the other breeds in that they had a higher beef flavour. The dual-purpose and rustic breeds, Simmental, Casina and Marchigiana, produced significantly less juicy and less tender meat than that from breeds selected for meat production. Overall, despite significant differences previously identified for animal, carcass, muscle and beef traits for the same animals, differences in sensory scores between most of the breeds were small, with only significant differences between the few breeds that had extreme sensory profiles (such as Simmental and Pirenaica).

Formation of thaw loss cannot generally be avoided when meat is frozen and then thawed. Explanations have mainly focused on the damage to muscle fibers resulting from ice crystallization and the freezing-induced denaturation of myofibrillar proteins, the latter of which has, however, not received much research focus. This review discusses the relationship between myofibrillar protein denaturation and water-holding capacity of meat in freezing-thawing with the aim to improve the understanding the relative importance of protein denaturation in the formation of thaw loss. The contribution of decreased pH and high ionic strength in the unfrozen water in freezing is emphasized and we hypothesize that these two factors are causing protein denaturation and conformational changes within muscle fibers, and consequently loss of water-holding capacity. Slow freezing produces more thaw loss than fast freezing, and this is discussed here in relation to the impacts on myofibrillar protein denaturation induced by the freezing rate.

The aim was to study biophysical and chemical changes during low-temperature long-time (LTLT) heat treatment of pork by measuring cathepsin B+L activity, surface hydrophobicity of myofibrils, particle size of myofibrils and effect on meat toughness as indicated by Allo-Kramer shear force. Longissimus thoracis et lumborum muscles were divided into large pieces, vacuum packaged and cooked in water baths at 53, 58, 63, 68 and 73 °C for 1, 8 and 24 h. The results showed that the meat toughness was markedly lower at temperatures of 53 °C and 58 °C and decreased with increasing holding time. Myofibrillar surface hydrophobicity increased with temperature, but not with time, indicating aggregation and/or gelation phenomena took place. Treatments with the lowest shear force values generally had smaller particles and were associated with high cathepsin B+L activity. A mechanism by which these cathepsins might affect the aggregation dynamics and change the mechanical properties of meat is proposed.

Woody breast syndrome is characterized by degenerative changes at the muscle fiber level and accumulation of connective tissue between the fibers. This study explored effects of the syndrome on muscle properties by focusing on a comparison of the sarcomere lengths between normal and woody breast muscles, including cranial and middle parts, surface and deeper layers, electrically stimulated and nonstimulated muscles, and their combinations. Tensile strengths longitudinally and transversally to the muscle fiber direction in the cranial and middle parts of the muscles were determined. The overall sarcomere lengths of woody breasts were longer than normal muscles (1.93 μ m vs. 1.88 μm; P < 0.05). The surface layer had overall longer sarcomere lengths than the deeper layer (cranial surface vs. cranial deeper layer: 1.97 vs. 1.89 μ m; middle surface vs. middle deeper layer: 1.93 vs.1.84 μ m; P < 0.05). Compared with normal breast muscles, woody breast muscles had longer sarcomeres in the surface layer; however, sarcomere length did not differ in the deeper layer. Electrically stimulated chicken breasts generally had longer sarcomere lengths (2.00 vs. 1.82 μm; P < 0.001). There was no significant difference in tensile strength between normal and focal woody breast (mild local lesion, usually in the cranial end) samples when fiber direction or sample location was studied (P > 0.05), but there was a clear difference between normal and focal versus diffuse (severe woody breast lesion throughout the muscle) samples (P < 0.001). Tensile strength was much greater in diffuse woody breast muscles when extended longitudinally or transversely to the fiber direction. In conclusion, although this study did not show sarcomere lengths in living muscle, it suggests an imbalance in sarcomere lengths in different parts of the breast muscle, which may induce a reduction in the functionality and strength of the muscle.

Research on fatty acids (FA) is important because their intake is related to human health. NIRS can be a useful tool to estimate the FA of beef but due to the high moisture and the high absorbance of water makes it difficult to calibrate the analyses. This work evaluated near-infrared reflectance spectroscopy as a tool to assess the total fatty acid composition and the phospholipid fraction of fatty acids of beef using freeze-dried meat. An average of 22 unrelated pure breed young bulls from 15 European breeds were reared on a common concentrate-based diet. A total of 332 longissimus thoracis steaks were analysed for fatty acid composition and a freeze-dried sample was subjected to near-infrared spectral analysis. 220 samples (67%) were used as a calibration set with the remaining 110 (33%) being used for validation of the models obtained. There was a large variation in the total FA concentration across the animals giving a good data set for the analysis and whilst the coefficient of variation was nearly 68% for the monounsaturated FA it was only 27% for the polyunsaturated fatty acids (PUFA). PLS method was used to develop the prediction models. The models for the phospholipid fraction had a low R2 p and high standard error, while models for neutral lipid had the best performance, in general. It was not possible to obtain a good prediction of many individual PUFA concentrations being present at low concentrations and less variable than other FA. The best models were developed for Total FA, saturated FA, 9c18:1 and 16:1 with R2 p greater than 0.76. This study indicates that NIRS is a feasible and useful tool for screening purposes and it has the potential to predict most of the FA of freeze-dried beef. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

This study aims at providing new insight on protein denaturation in freezing-thawing. Freezing-thawing minced pork reduced water-holding of myofibrils and increased surface hydrophobicity. One additional freezing-thawing cycle at slow freezing rate caused appearance of a 160 kDa myosin-4 fragment in SDS-PAGE, further decreased water-holding of myofibrils and increased surface hydrophobicity. Fresh minced pork was exposed to either high salt (2 M KCl) only or high salt with lower pH to mimic conditions in freezing. Exposure to high salt only increased water-holding of myofibrils and hence did not reproduce myofibrillar protein changes in freezing. Exposure to combinations of lower pHs and high salt decreased water-holding and increased surface hydrophobicity, suggesting myofibrillar protein denaturation occurred by a comparable mechanism as in freezing-thawing. We propose that exposure to decreased pH combined with high solute concentrations in the unfrozen water of frozen meat is the primary cause of myofibrillar protein denaturation in frozen-thawed meat.

The most common consequences of protein oxidation include dimerization through cross-linking, modification of amino acid side-chain, and protein fragmentation. Amino acids with side-chains most prone to oxidative modification are the sulfur-containing amino acids Cys and Met, the aromatic amino acids Trp, Tyr, and Phe, as well as His, Pro, Lys, and Arg. Several factors are known to trigger protein oxidation reactions including reactive oxygen species and nonradicals. Protein oxidation often goes hand in hand with lipid oxidation; for example, lipid hydroperoxides can initiate protein oxidation. Carbonyls are generally used as markers of protein oxidation although carbonyls are derived only from Lys, Agr, and Pro. However, there is no universal analytical method to monitor protein oxidation. Protein oxidation in foods leads to impaired food functionalities, reduction of nutritional value, and changes in physiological functions. Thus controlling the conditions for processing and storage of protein-rich food and food ingredients is important. Protein oxidation may also be purposely employed for improved food structure, as for example enzymatic cross-linking of Cys and Tyr residues. The present chapter provides an overview of the consequences of protein oxidation in both animal-based and plant-based raw materials and products.

Publisher Copyright: © 2021 The Authors The subcellular distribution of calpain-1 and -2 and the proteolytical activity of myofibril-bound calpains in pork were investigated during 12 days cold storage. The content of sarcoplasmic calpain-1 decreased during storage while myofibril-bound calpain-1 content first increased (P < 0.05) to 17% of that of 12 h-sarcoplasmic calpain-1 on day 6 followed by a gradual decrease with subsequent storage, suggesting that calpain-1 gradually translocated from sarcoplasm to myofibrils during the initial 6 days of postmortem storage. Intact desmin decreased (P < 0.05) after incubation of myofibrils with 0.05 mM Ca2+, and this was more pronounced with 5 mM Ca2+ (P < 0.05). Ca2+ titration curves of day 6 myofibrils showed two distinct proteolytic activities becoming activated in the range 0.03 to 0.06 mM and 0.4 to 0.8 mM Ca2+, respectively. The results suggest that both calpain-1 and calpain-2 binds to myofibrils during storage and subsequently degrade structural proteins including desmin.

This study aimed to investigate the effect of storage at -3 ?C on myofibrillar protein in fast or slow frozen pork. Five pork loins at 48 h post-mortem were subjected to either fast (cold metal plate/-80 ?C) or slow freezing (still air/-20 ?C) followed by storage at -3 ?C for 0, 1, 3, and 7 days before thawing. Freezing rate significantly influenced myofibrillar proteins within 3 days at -3 ?C, evidenced by higher thaw loss, higher surface hydrophobicity and reduced water-holding of myofibrils, and accelerated appearance of a myosin-4 fragment (160 kDa) in slow freezing. However, these observed differences disappeared after 7 days of storage at -3 ?C. The meat pH after thawing did not differ between fast and slow freezing rate. However, the pH values after thawing in both groups decreased with extended storage at -3 ?C. Our results suggest that the beneficial effects of fast freezing are gradually lost by holding at -3 ?C due to more extensive protein denaturation.

The objective was to characterize the effect of wooden breast (WB) myodegeneration on the metabolite profile of chicken meat by H-1 NMR and multivariate data analysis. The results displayed that the metabonome of chicken breast consisted predominantly of 30 metabolites, including amino acids, organic acids, carbohydrates, alkaloids, nucleosides and their derivatives. WB-affected samples showed higher leucine, valine, alanine, glutamate, lysine, lactate, succinate, taurine, glucose, and 5'-IMP levels, but lower histidine, beta-alanine, acetate, creatine, creatinine, anserine and nicotinamide adenine dinucleotide levels compared to normal fillets (p

In the past decades, metabolomics has been used to comprehensively understand a variety of food materials for improvement and assessment of food quality. Farm animal skeletal muscles and meat are one of the major targets of metabolomics for the characterization of meat and the exploration of biomarkers in the production system. For identification of potential biomarkers to control meat quality, studies of animal muscles and meat with metabolomics (MEATabolomics) has been conducted in combination with analyses of meat quality traits, focusing on specific factors associated with animal genetic background and sensory scores, or conditions in feeding system and treatments of meat in the processes such as postmortem storage, processing, and hygiene control. Currently, most of MEATabolomics approaches combine separation techniques (gas or liquid chromatography, and capillary electrophoresis)–mass spectrometry (MS) or nuclear magnetic resonance (NMR) approaches with the downstream multivariate analyses, depending on the polarity and/or hydrophobicity of the targeted metabolites. Studies employing these approaches provide useful information to monitor meat quality traits efficiently and to understand the genetic background and production system of animals behind the meat quality. MEATabolomics is expected to improve the knowledge and methodologies in animal breeding and feeding, meat storage and processing, and prediction of meat quality.

This study investigated the effects of cold storage at different temperatures (4, -0.5, -3, and -20 degrees C) on protein degradation and its relationship to structural changes of black carp muscle. At -0.5 and 4 degrees C, major structural changes occurred, including the formation of gaps between myofibers and myofibrils, breakage of myofibrils and myofibers, and degradation of sarcoplasmic reticulum. Gel-based proteomic analysis showed that these structural changes were accompanied by degradation of a series of myofibrillar proteins, including titin, nebulin, troponin, myosin, myomesin, myosin-binding protein, and a-actinin. Loss of extractable gelatinolytic and caseinolytic protease activities was also observed. At -3 and -20 degrees C, formation of ice crystals was the most noticeable change. The major proteins were degraded at different locations in the black carp muscle, and gelatinolytic and caseinolytic proteases appear to contribute to the degradation of those proteins.

The aim of this study was to investigate the role of Ca

In this study, 154 pectoralis major breast muscles from three chicken age groups were separated into different severity levels of wooden breast condition by manual palpation to investigate the changes of lipid and protein oxidation and citrate synthase activity. TBARS values, carbonyl contents and loss of free thiol groups were greater (P < 0.05) in the superficial (ventral) part of severe wooden breast samples, whereas no clear change was found in the deep (dorsal) part. Mitochondrial citrate synthase activity declined with increasing severity of wooden breast myopathy. Both bird age and wooden breast degree showed significant main effects on these indicators, while no interaction effect was observed. Moreover, there were significant correlations between lipid and protein oxidation and citrate synthase activity. Here, we propose a hypothesis that lipid and protein damages and mitochondrial dysfunction is linked to the aggravation of the wooden breast myopathy.

This study aimed to determine the effect of frozen-then-chilled storage on free Ca2+, proteolytic enzyme activity of calpains and the proteasome, water-holding capacity and shear force of porcine longissimus thoracis et lumborum muscle. Pork loins were subjected to either chilled storage at 2 +/- 1 degrees C for 1, 2, 4, 6 and 9 days, or frozen then chilled storage (20 +/- 1 degrees C for 1 week followed by thawing overnight). Free Ca2+ increased with chilled storage in the non-frozen group. Frozen-then-chilled storage increased free Ca2+ concentration, followed by a faster decrease of calpain-1 activity and activation of around 50% of calpain-2. Proteasome activity was reduced by around 40% following freezing-thawing. Purge loss increased and water-holding capacity of myofibrils decreased in the frozen-thawed group, suggesting considerable denaturation of myofibrillar proteins. Shear force was not affected by freezing-thawing, and we speculate that the tenderizing effect of calpain activation was counteracted by loss of proteasome activity and substantial exudate loss.

In the past few yr, an emerging muscle abnormality termed wooden breast (WB) was found to affect broilers’ Pectoralis major muscles. Although different studies have been performed in order to evaluate the effect of WB on meat quality, there is no evidence concerning its impact on the proteolytic processes taking place during meat aging. Thus, this study aimed at investigating the effect of a 7-day storage of broiler breast fillets on free calcium concentration, calpain activity, and proteolysis. Both the superficial and the deep layers of the Pectoralis major muscles were considered. Although similar electrophoretic profiles were observed by comparing the corresponding sampling positions, an evident lack of a high-molecular weight protein band, ascribed to nebulin, was found in the superficial layer of the WB fillets at 10 h postmortem. Compared to normal fillets (NB), both the superficial and the deep layer of WB exhibited a significantly higher amount of free calcium at 168 h postmortem (96 and 88 vs. 20 and 53 μM; P ≤ 0.001). Casein zymograms evidenced the presence of μ/m-calpain and its autolyzed form migrating as a doublet within the gel. Interestingly, neither the occurrence of WB nor the intra-fillet sampling position exerted any relevant effect on calpain activity. Indeed, a significant reduction (P ≤ 0.05) in the unautolyzed μ/m-calpain activity coupled with a remarkable increase (P ≤ 0.05) in the autolyzed form activity was observed during storage. Concurrently, if compared to NB, a significantly larger (P ≤ 0.05) amount of desmin was detected in both the superficial and the deep layers of the WB samples at 10 h postmortem. Then, a sharp decrease of the intact desmin band coupled with a progressive accumulation of its 39-kDa degradation fragment was observed without any significant difference among groups. In conclusion, the increased hardness that typically affects the WB cases seemed not to be exclusively attributable to differences in the proteolytic processes taking place within the postmortem period.

International audience; The objective of this study was to determine the variation of the colour of longissimus thoracis muscle within and among fifteen European cattle breeds reared under comparable management conditions. A total of 436 unrelated purebred young bulls from fifteen European breeds (Aberdeen Angus, Highland, Jersey, South Devon, Danish Red, Holstein, Simmental, Asturiana de las Montanas (also known as Casina), Asturiana de los Valles, Avilena-Negra Iberica, Pirenaica, Marchigiana, Piemontese, Charolais and Limousin) were reared in five experimental research centres in the United Kingdom, Denmark, Spain, Italy and France. The pH of M. longissimus thoracis was measured at 24 h and after 10 days of ageing and colour at 48 h and 10 days. Two generalised linear models, Pearson correlations and a hierarchical cluster analyses were carried out. Lean meat colour differed significantly between breeds, and these fifteen European breeds could be grouped according to four classes of commercial interest: 'very bright and pale-red', 'bright and pale', 'red' and 'dark and dull red'. These groups were partially related to body size and carcass traits, fatness and muscle development and structure, and were controlled by differences in gene expression within each breed.

The objective was to characterize the effect of wooden breast (WB) myodegeneration on the metabolite profile of chicken meat by

The role of protein denaturation in formation of thaw loss is currently not well understood. This study investigated denaturation of myofibrillar and sarcoplasmic proteins of pork loins caused by freezing-thawing in relation to freezing rate. Compared to fast freezing, slow freezing caused 28% larger thaw loss, decreased water-holding capacity of myofibrils and increased surface hydrophobicity, indicating more pronounced denaturation of myofibrillar proteins. We here propose a model: In slow freezing protons are concentrated in the unfrozen water resulting in reduced pH in proximity of structural proteins causing protein denaturation. In parallel, large ice crystals are formed outside of muscle fibers resulting in transversal shrinkage. In fast freezing small ice crystals trap protons and cause less severe protein denaturation and reduced thaw loss. Differential scanning calorimetry and tryptophan fluorescence spectra indicated sarcoplasmic protein denaturation in drip due to freezing-thawing. However, sarcoplasmic protein denaturation was independent of freezing rate.

The aim of this study was to investigate the role of Ca2+ in the process of calpain-2 becoming associated to myofibrils and the potential of myofibril-bound calpain to degrade myofibrillar proteins. Different Ca2+ concentrations were applied to myofibrils mixed with partially purified calpain-2. Ca2+ induced binding of calpain to myofibrils in a concentration-dependent manner. The half-maximal Ca2+ requirements for binding of calpain-2 to myofibrils and for calpain-2 proteolysis of myofibrils were 0.60 mM and 0.29 mM, respectively. To investigate the proteolytic activity of myofibril-bound calpain, a mixture of myofibrils and calpain-2 was briefly incubated with Ca2+. Unbound calpain was removed by washing with a Ca2+-free buffer. The myofibril-bound calpain maintained proteolytic activity and degraded desmin when re-activated with Ca2+. In conclusion, the results suggest that an increase in Ca2+ will activate and induce binding of calpain to myofibrils. Subsequently, calpain is relatively tightly bound and proteolytically active.

The role of heat-denatured sarcoplasmic proteins in water-holding is not well understood. Here we propose a new hypothesis that in PSE-like conditions denatured sarcoplasmic proteins aggregate within and outside myofilaments, improving the water-holding of denatured myofibrils. The process is compartmentalized: 1) within the filaments the denatured sarcoplasmic proteins shrink the lattice space and water is expelled; and 2) between the myofibrils and in the extracellular space, the coagulated sarcoplasmic proteins trap the expelled water from interfilamental space. The effect of sarcoplasmic proteins on the water-holding of myofibrils following incubation for 1h at 21 to 44°C was investigated. Our results were consistent with the new hypothesis. Myofibrils without sarcoplasm had the poorest water-holding. With increasing amount of denatured sarcoplasmic proteins, the water-holding of heat-denatured myofibrils improved proportionally. X-ray diffraction was used to measure the lattice space between the filaments. Precipitated sarcoplasmic proteins shrank (P

Protein oxidation is considered an ongoing deteriorative process during storage of fresh and processed meat. Carbonyl compounds have traditionally been detected spectrophotometrically after derivatization with 2,4-dinitrophenylhydrazine (DNPH) to form protein-bound hydrazones with absorbance at 370 nm. Here we describe a novel DNPH-based method to quantify protein carbonylation in muscle and meat. The additional steps of the novel method aimed at increasing the protein solubility and inducing protein unfolding before labeling with DNPH. Compared to the traditional method, the new procedure reflected an increased protein carbonylation level measuring overall two to fourfold more carbonyls in muscles from different species as well as in soluble, salt-soluble and insoluble protein fractions. The study suggested that protein unfolding is a more important phenomenon than solubilization for increased DNPH labeling. The novel method resulted in three to fourfold larger carbonyl content determined in chicken, pork and beef (2.8, 3.6 and 3.1 nmol/mg of protein, respectively).

Pork loins were stored at 5 °C for 14 days to investigate the effect of oxygen concentration in modified atmosphere packaging (MAP) on shear force and oxidation of lipids and proteins. The modified atmosphere contained 0 to 80% O2, 20% CO2, and balanced with N2. The results showed that shear force and thiobarbituric acid-reactive substances (TBARS) values increased with increasing oxygen concentration. Protein oxidation when measured as loss of free thiol groups, was greater in meat packaged under oxygen (20–80%). Myosin heavy chain (MHC) cross-linking, another marker of protein oxidation, was greater in MAP with 80% oxygen than 0% and 20% oxygen. Desmin degradation was not affected by the presence of oxygen, suggesting that the mechanism of oxygen-induced toughening of meat is through protein oxidation leading to cross-linking of structural proteins rather than through inactivation of proteolytic enzymes leading to reduced proteolysis.

Lard from pork back fat was dry fractionated based on crystallization temperature, resulting in fractions with a ratio of saturated to unsaturated fatty acids of 1.10 and 0.61. Lean minced pork was mixed with the saturated and unsaturated fat fraction and stored in modified atmosphere (80% O2 and 20% CO2) at 5 °C for 2, 5, 7, 9, and 12 days under light to investigate the effect on oxidative stability of lipids and proteins. The saturated fat group developed higher TBARS values and lower levels of free thiol groups during storage, indicating that the unsaturated fat fraction in minced pork promoted increased oxidative stability of both lipids and proteins. A higher content of α-tocopherol in the unsaturated fat fraction suggests that the differences in oxidative stability is causatively linked to the balance between the fatty acid composition and content of antioxidants. The TBARS values and free thiol content were negatively correlated, suggesting a relationship between lipid and protein oxidation.

Protein oxidation readily occurs in postmortem muscle during storage and processing. Over the past decade new analytical methods have been developed and new aspects of protein oxidation in meat have been studied, such as the reaction mechanism, and impacts on eating quality and nutritional value. It is now evident that amino acid side chains in myofibrillar proteins undergoes modifications due to oxidative stress. In turn this will lead to formation of new protein-protein cross-links in structural proteins, however, also the overall level of fixed-charge groups attached to the peptide backbones is modified. Meat texture and water-holding are important quality attributes and they are affected by the oxidation of structural proteins. Different mechanisms have been suggested to explain the oxidation-induced quality changes, focusing mainly on reduced proteolysis and formation of cross-links. This review explores the current understanding of protein oxidation in fresh meat in relation to texture and water-holding. The consequences of protein oxidation at molecular level in relation to oxidation-induced cross-linking and changes in net charges of myofibrillar proteins, and the impacts on texture and water-holding are discussed.

Hypochlorous acid (HClO) is a strong oxidant that is able to mediate protein oxidation. In order to study the effect of oxidation on charges, aggregation and water-holding of myofibrillar proteins, extracted myofibrils were oxidized by incubation with different concentrations of HClO (0, 1, 5, and 10 mM). Loss of free thiols, loss of histidine and formation of carbonyls were greater with increasing oxidation level and the particle size increased. Water-holding in the 5 and 10 mM HClO groups were greater than in the non-oxidized control. Isoelectric focusing (IEF) showed that the isoelectric point (pI) of oxidized proteins were lower compared to non-oxidized ones. The lower pI values of oxidized proteins suggests that oxidation increased the overall net negative charge of myofibrillar proteins solubilized for IEF. Here we propose a hypothesis that oxidation-induced increase in net negative charges is the driving force for improved water-holding in myofibrils, whereas protein cross-linking and aggregation have an opposing effect by decreasing the water-holding.

Heat treatment of meat at temperatures between 50 and 65 °C, for extended periods of time, is known as low-temperature long-time (LTLT) cooking. This cooking method produces meat that has increased tenderness and better appearance than when cooked at higher temperatures. Public concerns regarding this method have focused on the ability to design heat treatments that can reach microbiological safety. The heat treatment induces modification of the meat structure and its constituents, which can explain the desirable eating quality traits obtained. Denaturation, aggregation, and degradation of myofibrillar, sarcoplasmic and connective tissue proteins occur depending on the combination of time and temperature during the heat treatment. The protein changes, especially in relation to collagen denaturation, along with proteolytic activity, have often been regarded to be the main contributors to the increased meat tenderness. The mechanisms involved and the possible contribution of other factors are reviewed and discussed.

Minced beef was stored for 8 days and myofibrillar protein (MP) was extracted to investigate the effect of oxygen concentration (0, 20, 40, 60, and 80%) in modified atmosphere packaging (MAP) on heat-induced gel properties. Compression force of gels was lower when prepared from beef packaged in 0% oxygen, intermediate in 20 to 60% oxygen and greater in 80% oxygen. Total water loss of gels prepared from beef packaged with oxygen (20-80%) was higher and rheology measurements presented higher G' and G '' values. Additionally, gels from beef packaged without oxygen exhibited higher J (t) values during creep and recovery tests, demonstrating that oxygen exposure of meat during storage in MAP affect MP in such a way that heat-induced protein gels alter their characteristics. Generally, storage with oxygen in MAP resulted in stronger and more elastic MP gels, which was observed already at a relative low oxygen concentration of 20%. (C) 2017 Elsevier Ltd. All rights reserved.

The aim of this study was to investigate the relationship between the abundances of Bov-SERPINA3 inhibitors (able to form pseudo-irreversible complexes with their target enzymes) and meat tenderness in Rectus abdominis muscle from PDO Maine-Anjou cows. The experiment included 4 tender (TE) and 4 tough (TO) samples from 20 animals, based on Warner-Bratzler shear force measurements (WBSF) and sensory tenderness scores at 14 days post mortem (d p-m), taken at 24 h p-m. Western blotting revealed three Bov-SERPINA3 forms with MW of 114 (not yet identified), 75 and 45 kDa. The intensities of 75 and 45 kDa Bov-SERPINA3 bands were significantly lower in TE than TO group whereas no difference was observed for the 114 kDa band. The 45 and 75 kDa Bov-SERPINA3 were strongly correlated with both WB shear force (r=0.81 and r=0.75, respectively) and the 45 kDa was further significantly correlated with tenderness scores (r=-0.74).

The purpose of this study was to increase the knowledge on the relationship between proteolysis of myofibrillar proteins and the water-holding of meat. Myofibrils isolated from porcine longissimus thoracic et lumborum muscle were used as a model system. Myofibrils were incubated with either calpain-2, the proteasome or a lysosomal extract at 25 degrees C for 2 h. All three proteolytic systems improved the relative water-holding and generally there was a larger effect with increasing amount of enzymes in the incubation. The improved water-holding occurred in parallel to degradation of myofibrillar proteins. Desmin was degraded by calpain-2 as well as by lysosomal enzymes and a-actinin was released by the proteasome. We here propose a model in which degradation of proteins in and around the Z-disk allows overall swelling of the filament lattice and more specifically in the I band area. In conclusion, proteolytic degradation of myofibrillar proteins by calpain-2, the proteasome or lysosomal enzymes improves the water-holding of myofibrils.

The basic contractile unit of muscle, the sarcomere, will contract as the muscle goes into rigor post-mortem. Depending on the conditions, such as the rate of pH decline, the cooling rate and the mechanical restraints on the muscles, this longitudinal shortening will result in various post-mortem sarcomere lengths as well as lateral differences in the distances between the myosin and actin filaments. This shortening is underlying the phenomena described as rigor contraction, thaw rigor, cold shortening and heat shortening. The shortening in combination with the molecular architecture of the sarcomere as defined by the myosin filaments and their S-1 and S-2 units, the interaction with the actin filaments, and the boundaries formed by the 2-disks will subsequently influence basic meat quality traits including tenderness and water-holding capacity. Biochemical reactions from proteolysis and glycogen metabolism interrelate with the sarcomere length in a complex manner. The sarcomere length is also influencing the eating quality of cooked meat and the water-holding in meat products.