Myofibrillar protein solutions

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. ... 

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. 

The myofibrillar proteins make up 50-60% of the total protein of muscle cells. Insoluble at low ionic strengths, these proteins dissolve when the ionic strength exceeds -0.3 and can be extracted with salt solutions. Analysis of isolated mammalian myofibrils86 shows that nine proteins account for 96% or more of the protein myosin, which constitutes the bulk of the thick filaments, accounts for 43% and actin, the principal component of the thin filaments, 22%. 

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. 

Among the above hypotheses, effects of lipids (4-17,59-62, 69-71,155-159), formaldehyde (160-166), and gas-solid interface TMJ appear to be very important in Gadoid fishes. Denaturation of myofibrillar proteins caused by free fatty acids and/or lipid peroxides must occur during frozen storage. To prove this, Jarenback and Liljemark have shown by electron microscopy that, in muscle stored frozen with added linoleic and linolenic hydroperoxides, myosin became resistant to extraction with salt solution (168). 

Effects of linoleic acid and linoleic acid hydroperoxides on the myofibrils and the solutions of myofibrillar proteins of cod muscle have been proved using the electron microscopy (80). Linoleic acid hydroperoxides were ten times more effective than linoleic acid in reducing the amount of the protein in KCl-extracts from the myofibrils incubated with the acid or its hydroperoxides. Linoleic acid seemed to prevent the dissolution of the myofibril frame work but appeared not to impair the extraction of myosin while hydroperoxides appeared to cause a retention of A-bands (myosin) in the myofibrils. 

The myofibrillar proteins of fish are those proteins soluble in 0.6M NaCl (14). These proteins have been modified with Rhozyme P-11 at an enzyme-to-protein ratio of 1 75 at 30 °C, pH 6.6 for 1 hr. The modified myofibrillar protein was quantitatively recovered as a hexametaphosphate complex at pH 3. Residual lipids were removed by solvent extraction of the complex. After a solution of the phosphate-protein complex was neutralized to pH 7, it was spray-dried or freeze-dried to yield a freely soluble product which was 93.5% protein, 0.15% lipid, and 1.4% phosphate. 

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). 

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... 

Recent studies highlighted the film-forming properties of fish and meat myofibrillar proteins [127-134]. Films formed from an aqueous solution were found to be water-insoluble and completely transparent, with good mechanical and gas barrier properties [53]. Their mechanical strength is close to that of PE films. The thermoplastic features of myofibrillar proteins [135,136] could also be tapped for industrial-scale production of these films using techniques commonly implemented to obtain synthetic thermoplastic polymers (e.g., extrusion or thermoforming). 

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. 

Animal proteins, such as milk casein, whey, albumin, collagen, gelatin, keratin, and myofibrillar, are also proposed as raw materials to form edible films (13-15). Extended stmctures formed by unfolding of protein molecules are required for film formation. Amorphous three-dimensional stmctures formed by noncovalent interactions among protein chains stabilize the films. At high water content, films are produced by casting of viscous solutions, and at low water content, films are produced by extmsion using thermoplastic properties of proteins (13). 

Introduction of additional negative charge into proteins by reaction with dicarboxylic anhydrides resulted in an increased solubility in neutral and weak alkaline aqueous solutions [11-13], A positive correlation between solubility and the ability of a protein to emulsify has been documented by some authors [59-62], An increase in protein solubility would encourage a rapid migration to and adsorption of the protein at the water-oil interface. The adsorption would, in turn, lower the interfacial tension between the water and the oil and stabilize the emulsion [63 J. In fact, improved emulsifying properties have been found after succinylation or citraconylation of a large number of food proteins such as myofibrillar fish proteins [10, fish protein... 

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