Fish sarcoplasmic proteins

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. 

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). 

Other Proteins. Since Reay and Dyer discovered that denaturation of myofibrillar proteins is of such profound importance, little attention has been given to the water-soluble proteins including enzymes and other proteins in the sarcoplasm, subcellular organelles, and cell membranes. Recently reports have appeared on the freeze denaturation of enzymes. These studies involved enzymes such as catalase, ADH, GDH, LDH, and MDH from sources other than fish (88,89,90) and attention was given to the effectiveness of various cryoprotective substances (89, 90). Comparable studies with enzymes from fish muscle are few in number (91). Studies on fish muscle proteins must be extended to this area if a complete picture of the freeze denaturation of fish muscle is to be obtained. It should be noted that freeze stable enzymes might have important effects during frozen storage of fish (92,93). 

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

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. 

Enzymes have also been used in the preparation of protein ingredients from animal wastes. Mohr (1980) described the use of proteolytic enzymes in the preparation of protein concentrates from fish offal. Fish protein waste was ground with protease and incubated to yield a concentrated fish protein, which was then dried. Generally, the contractile and connective tissue proteins are hydrolysed most efficiently. Sarcoplasmic proteins tend to aggregate and resist enzyme attack. The proteins are broken down into peptides and individual amino acids, and the longer the hydrolysis continues the higher the yield of hydrolysates but the greater the peptide breakdown. For many food applications peptide breakdown needs to be carefully controlled. 

Proteins. Protein hydrolysates have already been mentioned as new marine-derived ingredients, but of a type that must be considered an additive for a specific use and not as an integral part of the food. The proteins present in fish muscle are usually divided into three fractions the sarcoplasmic proteins, the myofibrillar proteins and the connective tissue proteins. 

Okazaki, E. Nakamura, K. Factors affecting texturization of sarcoplasmic proteins of fish by high pressure treatment. Bull. Jpn. Soc. Fish. 1992, 58, 2197—2206. 

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]. 

Figure B3.1.1 A 15% SDS-polyacrylamide gel stained with Coomassie brilliant blue. Protein samples were assayed for the purification of a proteinase, cathepsin L, from fish muscle according to the method of Seymour et al. (1994). Lane 1, purified cathepsin L after butyl-Sepharose chromatography. Lane 2, cathepsin L complex with a cystatin-like proteinase inhibitor after butyl-Sepharose chromatography. Lane 3, sarcoplasmic fish muscle extract after heat treatment and ammonium sulfate precipitation. Lane 4, sarcoplasmic fish muscle extract. Lanes M, low-molecular-weight standards aprotinin (Mr 6,500), a-lactalbumin (Mr 14,200), trypsin inhibitor (Mr 20,000), trypsinogen (Mr 24,000), carbonic anhydrase (Mr 29,000), gylceraldehyde-3-phosphate dehydrogenase (Mr 36,000), ovalbumin (Mr 45,000), and albumin (Mr 66,000) in order shown from bottom of gel. Lane 1 contains 4 pg protein lanes 2 to 4 each contain 7 pg protein.

MALDI-TOF/TOF MS to successfully study the carbonylation of sarcoplasmic and myofibrillar proteins from fish subjected to metal-catalyzed oxidation (98). 

The proteins in the sarcoplasmic fraction are excellently suited to distinguishing fish species as each species has a characteristic band pattern when separated by the isoelectric focusing method. 

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]. 

PDA detection of sarcoplasmic fish proteins by reversed phase has been used as a rapid means to identify the source fish [45]. This was similar to earlier reports using a single wavelength (280 nm) for species identification, but PDA detection provided additional information, particularly with closely related fish species. The identification was made by combining the information from the chromatographic patterns obtained at several wavelengths. 

Much work has been reported on dried and whole fish. Tg s in frozen fish such as cod, tuna, mackerel, sea bream and bonita have been determined using DSC [98 ]. This work is normally carried out with a view to determining the safe storage conditions for these products. Both dried fish muscle and extracted protein fractions showed glass transitions. The 2 s of muscle and myofibrillar proteins from red-muscle fish tended to be lower than those from white-muscle fish. There was no difference in the Tg of sarcoplasmic reticulum. The myofibrillar proteins are responsible for the contractile mechanisms in muscle. These are predominantly... 

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