Effects of protein oxidation on the texture and water-holding of meat : a review

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.Peer reviewe

Oxidation increases myofibrillar protein net charge

In order to study the effect of oxidation on the charges of myofibrillar proteins, extracted myofibrils were incubated with different concentrations of the oxidant NaClO (0, 1, 5, and 10 mM) at 5 ºC overnight. Isoelectric focusing gel showed that the isoelectric point (pI) of oxidized proteins were lower compared to non-oxidized ones. The lower pI values of oxidized proteins indicated that oxidation increased overall net negative charge of proteinsPeer reviewe

Muscle structure, sarcomere length and influences on meat quality : A review

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.Peer reviewe

Ca2+-induced binding of calpain-2 to myofibrils: Preliminary results in pork longissimus thoracis muscle supporting a role on myofibrillar protein degradation

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On the origin of thaw loss : Relationship between freezing rate and protein denaturation

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.Peer reviewe

Effect of LTLT heat treatment on cathepsin B and L activities and denaturation of myofibrillar proteins of pork

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Mimicking myofibrillar protein denaturation in frozen-thawed meat : Effect of pH at high ionic strength

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EFFECT OF PROTEIN OXIDATION ON PARTICLE SIZE OF MYOFIBRILS

In order to study the effect of protein oxidation on the structure of myofibrils, extracted myofibrils from porcine longissimus dorsi muscle were incubated with different concentrations of the oxidant NaClO (0, 5, 10, 20 and 40 mM) at 5 ºC for 16 h. Increasing concentrations of NaClO led to a greater loss of free thiols and a larger particle size (in terms of D(v, 0.1), D(v, 0.5), D(v, 0.9), D(3, 2) and D(4, 3)) of myofibrils. Light microscope imaging showed that the myofibrils oxidized in 40 mM NaClO were less broken as compared to the non-oxidized group (0 mM NaClO). The increased structural integrity of myofibrils is likely caused by oxidation-induced protein cross-links, which resulted in a larger particle size when the myofibrils were subjected to homogenization

Myofibrillar protein gel properties are influenced by oxygen concentration in modified atmosphere packaged minced beef

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.Peer reviewe

Changes of Raw Texture, Intramuscular Connective Tissue Properties and Collagen Profiles in Broiler Wooden Breast during Early Storage

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 postmortem period (1–3 days). Results showed that the presence of the WB muscles condition at 1 day postmortem was associated with significantly increased stiffness (27.0 N vs. 23.1 N) and significantly increased purge loss (1.8% vs. 1.0%) compared to normal breast (NB). However, on 3 days postmortem, these parameters did not differ between WB and NB groups. Insoluble and total collagen content was significantly higher in WB muscles compared to NB muscles, and the extractability of intramuscular connective tissue (IMCT) of WB was also higher (0.42% vs. 0.37%) compared to NB and remained stable in the early postmortem period. There was 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 purge loss and higher raw meat hardness