Actomyosin from fish

Most of the early work on this subject was done by extracting actomyosin from fish fillets following frozen storage and thawing. On the other hand, many studies designed to determine the mechanisms of denaturation have involved frozen solutions or suspensions of isolated protein preparations. 

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. 

Actin. Rabbit muscle G-actin is globular with a molecular weight of 4.2 X 104. In the presence of salts it is polymerized into F-action (34). The principal properties of fish actin (35-37,40, 43,44), including amino acid composition (41), are similar to rabbit actin, but fish actin is more readily extracted from wet muscle by salt solutions as a viscous solution of actomyosin (22,35,36,45). 

Myosins isolated from various frozen stored fish muscles had slightly lower ATPase activity than those from fresh muscles (94, 95). A decrease in ATPase activity was found also with isolated carp myosin when stored at -20°C (82) the rate of decrease was faster than with actomyosin isolated from the same fish. As with actomyosin, the decrease in ATPase activity was preceded by a temporary rise in activity M50% the pre-freezing value). 

These figures have been compared with those obtained for rabbit acto-myosin and myosin (Hamoir, 1955). These last values differ notably from one author to another especially in the case of actomyosin, but they always remain lower than our determinations. The viscosity numbers determined by Kerekjarto (1952) for rabbit actomyosin and myosin at 15° C., which seem to be the most reliable, are, respectively, 0.32 and 0.17 ( 0.01). Both figures are definitely lower than our values carried out at higher temperature. In the case of actomyosin, this difference appears to be due to the structure of the solutions. Recent determinations (Hamoir, 1955) suggest that fish and rabbit actomyosins have approximately the same intrinsic viscosity at = 0. The axial ratio of these particles seems therefore not to differ notably. In view of this relationship, more accurate determinations are necessary in order to determine if the different viscosities observed in the presence of ATP are really due to a different shape of the particles. 

In conclusion, fish and rabbit actomyosins are very similar from the... 

Viscosity. The reduced viscosity of the protein extracted from frozen-stored fish muscle (44,54) and of the soluble fraction of the frozen-stored solutions of isolated actomyosin decreases with increasing time of storage (51, 52). 

ATPase. Myosins isolated from various frozen-stored fish muscles exhibit specific activities for ATPase that are slightly lower than the specific activities of myosin from fresh muscles (73,74). The decline of ATPase activity also occurs with myosin isolated from carp, when storage is conducted at — 20°C (64). Like carp actomyosin, the decline is preceded by a temporary rise in activity. 

Sucrose and sorbitol are commonly used in frozen surimi processing. However, sucrose imparts a sweet taste to surimi products, which is undesirable to the consumer (Sych et al., 1990 Auh et al., 1999 Sultanbawa and Li-Chan, 2001). Thus, the use of other cryoprotectants to reduce sweetness but exhibit the equivalent cryoprotective effect is required. Auh et al. (1999) used highly concentrated branched oligosaccharide mixture (HBOS) as cryoprotectant in fish protein. An addition of HBOS resulted in the remainder Ca -ATPase activity of actomyosin extracted from Alaska pollock after freeze-thawing the best stabilization effect of HBOS was observed at a concentration of 8%. Sych et al. (1990) studied the cryoprotective effects of lactitol dehydrate, polydextrose, and palitinit at 8% (w/w) in cod surimi in comparison with an industrial control (sucrose/sorbitol, 1 1). The... 

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