Meat sarcoplasmic proteins

Meat, sarcoplasmic proteins extracted in bidistilled deionized water, myofibrillar extracted in 0.6 M NaCl/0.01 M phosphate buffer, 0.5% polyphosphates, pH 6.0, Biorad SDS sample buffer Meat adulterated with chicken egg white... 

The sacroplasmic proteins myoglobin and hemoglobin are responsible for much of the color in meat. Species vary tremendously in the amount of sacroplasmic proteins within skeletal muscle with catde, sheep, pigs, and poultry Hsted in declining order of sarcoplasmic protein content. Fat is also an important component of meat products. The amount of fat in a portion of meat varies depending on the species, anatomy, and state of nutrition of the animal. The properties of processed meat products are greatiy dependent on the properties of the fat included. Certain species, such as sheep, have a relatively higher proportion of saturated fat, whereas other species, such as poultry, have a relatively lower proportion of saturated fat. It is well known that the characteristic davors of meat from different species are in part determined by their fat composition. 

Of probably greater importance is the effect of local concentration gradients. For example, analysis for a given constituent in the entire meat mass does not reflect the real concentration at a given point. For example, DNA is localized in the nuclei and lipid is localized predominantly in the adipose cells. Another factor of potential influence in reaction schemes for nitrite is the fact that polar-nonpolar interfaces are present as a result of structural compartmentalization. In an adipose cell, the lipid is contained as the body of the cell, but it is surrounded by a thin layer of sarcoplasmic protein. Therefore, large surface areas are involved. 

In contrast to milk, where samples are primarily derived from cows, meat analysis has to be performed in samples of a widely different animal origin including cattle, lamb, swine, poultry, and fish. Muscle is a complex matrix with a pH of 5.7, composed of muscle fibers, various types of connective tissue, adipose tissue, cartilage, and bones. Sarcoplasmic proteins such as myoglobin, and glycolytic enzymes are soluble in water while the myofibrillar proteins such as myosin and actin are soluble in concentrated salt solutions (14). The connective tissue proteins, collagen and elastin, are insoluble in both solvents. 

Meat proteins include sarcoplasmic, myofibrillar, and connective tissue proteins. Among the sarcoplasmic proteins are heme pigments and enzymes, which influence the color, smell, and structure of meat. Myofibrillar proteins and collagen are able to retain and hold water in meat structure and to emulsify fat. Therefore they influence the rheological properties of meat products. 

Basically, there are three major groups of proteins in muscle tissue (a) the sarcoplasmic proteins of the muscle cell cytoplasm, (b) the myofibrillar proteins, soluble at high ionic strengths, that make up the myofibril or contractile part of the muscle, and (c) the stromal proteins comprised largely of the connective tissue proteins, collagen, and elastin. The myofibrillar proteins and the stromal proteins are fibrous and elongated they form viscous solutions with large shear resistance. These properties coupled with other lines of indirect evidence indicate that the physical properties of the myofibrillar and stromal proteins are directly related to the texture and tenderness of meat (34). 

Sebranek (1988) has reviewed the effects of heat on denaturation of the proteins. Dehydration by heat denatures the muscle proteins, particularly the sarcoplasmic proteins. This induces a rather dramatic change in meat color. The heme pigments, which provide most of the color of fresh meat, serve as a general indication of doneness or temperature history. In the case of cured products, heme pigments react to form nitric oxide hemochro-mogen, which contributes the characteristic pink cured meat color (Pearson and Tauber, 1984). 

CE has also been successfully apphed to the study of muscle proteins, and some of these applications have been recently reviewed. - - Methods for the determination of muscle proteins were based on CZE, SDS-CE, or isoelectric focusing (CEIF). Meat species identification was carried out by analyzing sarcoplasmic or myofibrillar proteins by a replaceable polymer-filled SDS-CE method (Table 30.8). However, the analysis of sarcoplasmic protein profiles allowed better differentiation among beef, pork, and turkey meat (Figure 30.8). The importance of sample preparation in the established method was highlighted since sarcoplasmic proteins extracted by simply homogenizing meat with cold bidistilled water were most useful for meat species identification when protein profiles were examined by linear discriminant analysis. On the other hand, myofibrillar proteins extracted with 0.6 M NaCl/0.01 M phosphate buffer with 0.5% polyphosphates (pH 6.0) were not useful for raw meat species identification, although they may be of importance in the identification of heat-processed meats. ... 

FIGURE 30.8 CE-SDS electropherograms of sarcoplasmic proteins extracted from beef, pork and turkey meat. (From Cota-Rivas, M. and Vallejo-Cordoba, B., J. Cap. Elec., 4, 197, 1998. With permission.)... 

Factors that affect texture include moisture content, composition, variety or species, pH, product history (maturation or age), and sample dimensions. Texture is also dependeut on the method of dehydration and pretreatments. Purslow [55] stated that meat texture is affected by the structure of the solid matrix. He coucluded that it is important to have a fundamental understanding of the fracture behavior of meat and how it relates to the structure of the material. Stanley [83] stated that many researchers now believe that the major structural factors affecting meat texture are associated with connective tissues aud myofibrillar proteins. Moreover, two other components muscle membranes and water also deserve consideration not because of their inherent physical properties, but rather as a result of the indirect influence they have on the physical properties. It should be noted that sarcoplasmic proteins may be important for the same reason, although little information on their role is available. He suggested that these structures merit particular attention. 

Muscle proteins are an important component of meat and can be classified according to solubility as sarcoplasmic (water soluble), myofibrillar (salt soluble), or stromal (insoluble) proteins. The application of CE to the analysis of meat proteins has been predominantly for separation of sarcoplasmic proteins in aqueous extracts from fish, bovine, and chicken muscle. The sarcoplasmic proteins that are present are mainly metabolic enzymes and therefore their separation profiles are useful for the purpose of species identification. Some reports also exist of the simultaneous separation of sarcoplasmic and myofibrillar meat proteins using SDS-CGE. 

Lawrie (1985) classified meat proteins into three types salt-soluble (myofibrillar) proteins, water-soluble (sarcoplasmic) proteins, and insoluble connective tissue proteins. The myofibrillar proteins actin, myosin and actomyosin are the major proteins responsible for determining the heat stability of comminuted meat emulsions. 

Young et al. (1992) separated myofibrillar proteins from heart muscle, the masseter muscle and the cutaneus trunci muscle of ox. The meats were minced and then bowl-chopped with ice. The slurry formed was tumbled with further ice/water. A screening step was carried out to remove connective tissue and the majority of the fat. The filtrate was centrifuged in a continuous separator and at this stage the sarcoplasmic proteins were removed. Using this technique the remaining fat was deposited on the centrifuge spindle, and the myofibrillar fraction on the inside of the bowl. 

Muscle proteins have traditionally been grouped into three categories based on their solubility the sarcoplasmic proteins (consisting mainly of enzymes), myofibrillar proteins (actin, myosin, tropomyosin, troponin, etc.) and connective tissue (mainly collagen). The mixture of myosin, actin, tropomyosin, troponins and other myofibrillar proteins is called actomyosin (AM). Myofibrillar proteins contribute significantly to the technological properties of fish and meat [1-2,5-8]. 

Any dialogue on meat flavor development and deterioration requires a brief discussion of muscle structure. Muscle has a highly compact and complex multicellular structural organization (Figure 2). Individual muscle cells contain numerous mitochondria and nuclei. They also contain contractile elements as the bulk of their structure. While the sarcoplasm of muscle (the aqueous non-organellar component) is small compared to the cytoplasm of non-muscle cells, it does have a highly evolved system of membranes called the SR/L representing an acronym for sarcoplasmic reticulum/lysosomal membrane system (11). The SR/L surrounds each contractile element (Fig. 9-13 in 12 Fig. 7-10 in 13). The close proximity of the SR/L to the contractile proteins situates the proteins in a location that is optimal for their hydrolysis by lysosomal hydrolases (12, 13). 

Stanley (1983) stated that many researchers now believe the major structural factors affecting meat texture are associated with connective tissues and myofibrillar proteins. Therefore, he suggested that these structures merit particular attention. He concluded that two other components, muscle membranes and water, also deserve consideration, not because of their inherent physical properties, but rather as a result of the indirect influence they have on the physical properties. It should be noted that sarcoplasmic... 

Although the primary radicals formed in the sarcoplasmic fluid of the muscle tissue, in the myofibrillar proteins of the muscles, and in the lipids of the intercellular and depot fats are expected to be similar to those formed in dilute aqueous solutions, in polypeptides, and in meat triglycerides, respectively, the radical yields and reactivities are affected by density and solute concentration... 

Meat is mainly muscular tissue of dead animal. It has a complex fibrillar structure containing several kinds of protein and other molecules, which are suspended in sarcoplasmic fluid and held together by tissue containing fat and blood vessels. 

In a muscle tissue (Fig lb), the fiber cells are thin and elongated as opposed to the polygonal cells in plants. The major myofibrillar proteins, myosin and actin, form the myofilament bundles in the sarcoplasm of the fiber cell. Bundles of fiber cells form the muscle tissue. Connective tissue distributed between individual (endomysium) and bundles of fiber cells (perimysium) as well as around the whole muscle (epimysium) holds the cells and the muscle tissue together. Majority of lipids is located in the adipose tissue depots associated with the connective tissue between the bundles of fiber cells in poultry and red meat as well as fish muscle [2]. 

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