Sarcoplasmic protein

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. 

Actomyosin. Solubility. Studies have dealt with changes in the solubility of proteins during frozen storage of fish muscle or solutions of isolated actomyosin (33,51,52). Analysis by gel filtration of the salt extracts has shown that the actomyosin fraction decreases in solubility during frozen storage whereas the sarcoplasmic proteins remain essentially unchanged (53). 

Angsupanich and Ledward (1998) showed that oxidative stability of lipids in Atlantic cod (Gadus morhud) muscle decreased after treatment at a pressure higher than 400 MPa dne to the release of metal ions from complexes. Of the major muscle proteins, myosin denatured at 100-200 MPa, whereas actin and most sarcoplasmic proteins denatured at 300 MPa. High-pressure treated hsh was harder, chewier, and gummier than both the raw and cooked prodncts. 

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). 

Tappel (99) reported on the hydrolytic activity of various enzymes. They found that the relative hydrolysis of muscle proteins increased in the following order pepsin, Rhozyme A-4, ficin, papain, bromelain, protease 15, Rhozyme P-11, and trypsin. Wang et al. (100) observed that papain was twice as active as ficin towards elastin, a minor component of connective tissue. Ficin and bromelain had equal enzyme activity towards collagen, a major component of connective tissue. Kang and Rice (101) studied the effects of various tenderizing enzymes on water-soluble sarcoplasmic proteins, salt-soluble myofibrillar proteins, and the insoluble stromal proteins. Table VII tabulates the results of some of these studies. 

Author Material Sarcoplasmic proteins L-Myosin Actin Stroma... 

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). 

LeBlanc, E.L., Singh, S., and LeBlanc, R.C. 1994. Capillary zone electrophoresis of fish muscle sarcoplasmic proteins. J. Food Sci. 59, 1267-1270. 

Sarcoplasmic proteins (myoalbumin, globulin, and enzymes) which are soluble in neutral salt solutions of low ionic strength (<0.15 M). This fraction constitutes 25%-30% of the protein. 

The majority of sarcoplasmic proteins are enzymes participating in cell metabolism, such as the anaerobic energy conversion from glycogen to ATP. If the organelles within the muscle cells are broken, this protein fraction may also contain the metabolic enzymes localized inside the endoplas-matic reticulum, mitochondria, and lysosomes. 

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