Protein concentrates myofibrillar

Considerable effort has been devoted to the improvement of functional properties of fish protein concentrate. Spinelli et al. (44) conducted a study to determine the feasibility of modifying myofibrillar fish proteins by partially hydrolyzing them... 

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. At high salt concentrations ( . . 0.6 M KC1), actin and myosin combine to form actomyosin filaments giving a highly viscous solution. Actomyosin retains the ATPase activity of myosin and demonstrates "super-precipitation" on the addition of ATP (24,34). As expected, there are differences between actomyosins of rabbit and fish with respect to solubility (10,22,35,36), viscosity (46) and ultracentrifugal behavior (477. Since actomyosin is the most readily available form of myofibrillar proteins from fish muscle, its behavior relative to deterioration during frozen storage has been most frequently studied. 

Much research has been devoted to working out optimum parameters of producing different protein concentrates from fish and krill (Lanier, 1994). While the products have high nutritional value and many are tasteless and odorless, some, manufactured in denaturing conditions, lack the desired functional properties. A good example is the fish protein concentrate obtained by hot azeotropic isopropanol extraction. On the other hand, a concentrate of myofibrillar proteins known as surimi, produced mainly from fish and to a lesser extent from poultry and meat, is highly functional. 

Grant (58), single-cell protein concentrates by McElwain et al. (59), and fish protein by Groninger and Miller (60) and Chen et al. (61). Succinylated fish myofibrillar protein had rapid rehydration and good dispersion characteristics at neutral pH (60). Succinylation of fish protein concentrate improved its emulsifying capacity and emulsion stability (61). 

Modification of fish proteins by proteolytic enzymes to increase their solubilities illustrates a variety of techniques and approaches. Basically, three general enzymic methods have been used to prepare fish proteins or hydrolysates with altered solubilities and other functionalities. These methods include (a) the enzymic solubilization of fish protein concentrate prepared by hot solvent extraction of fish, (b) the enzymic modification of myofibrillar proteins extracted from fish with 0.6M NaCl, and (c) the proteolysis of whole fish to prepare biological fish protein concentrate (FPC). 

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... 

Other studies included the investigation of the stabilizing effect of sorbitol on hen egg white lysozyme and the use of the self-diffusion coefficient, D, to follow the solution and aggregative properties of lysozyme at different pH, temperature, and protein and salt concentrations. The properties of frozen ovalbumin solutions were studied by NMR relaxation spectroscopy. It is known that the functional properties of muscle proteins are affected by protein interactions with ions, and NMR was used to assess protein/water, protein/salt, and protein/protein interactions in myofibrillar protein solutions. Previous X-ray and NMR studies on collagen and peptides were reviewed by Mayo and, more recently, such types of system were characterized by high-resolution H and C NMR. °0 The structure, hydration state, and nature of the interactions between water and gelatin were determined by time domain NMR. ... 

Soluble proteins make up 25-30% of the total protein in muscle tissue. They consist of ca. 50 components, mostly enzymes and myoglobin (cf. Table 12.5). The high viscosity of the sarcoplasm is derived from a high concentration of solubilized proteins, which can amount to 20-30%. The glycolytic enzymes are bound to the myofibrillar proteins in vivo. 

Water holding capacity also remains high when freezing is performed rapidly. Under these conditions the formation of large ice crystals is suppressed and damage to membranes and the irreversible change in myofibrillar proteins caused by temporary high salt concentrations are avoided. 

Myofibrillar proteins were prepared from fresh pork according to the method reported by Yang et al 12). One percent actinase E or papain was incubated with myofibrillar proteins in distilled water (pH7.0) at 37°C for 24-48h. After incubation, ethanol was added into the reaction mixture at the final concentration of 80 % in order to stop the enzyme reaction and remove unhydrolyzed proteins. This solution was centrifuged at 2,000xg for lOmin. The supernatant was concentrated by evaporation at 45 C. 

Antioxidative activities of the hydrolysates from porcine myofibrillar protein were measured in a linolenic acid oxidation system The hydrolysates at the concentration of 0.02, 0.2 and 2% exhibited antioxidative activities. All hydrolysates exhibited stronger antioxidative activity, as the concentration was higher in the production of hydroperoxides. On the other hand, the addition of 0.2% hydrolysate suppressed the production of TEARS most strongly, and the antioxidative activity in the addition of 2% hydrolysate was lower than that of 0.2% in the method of TEARS. It is well known that 2-thiobarbituric acid (TEA) reacts with aldehyde compounds including malondialdehyde (MDA) formed by Upid peroxidation. Two percent hydrolysates contained a lot of amino confounds including free amino acids and peptides. Therefore, the production of aldehyde compounds seems to be accelerated by amino-carbonyl reaction between hydrolysate and lipid in lipid peroxidation system including 2% hydrolysate. This might be the reason why the antioxidative activity of 2% hydrolysate was lower than that of 0.2 % hydrolysate in the method of TEARS. 

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