Protein changes in frozen fish

Abstract

Storage of frozen fish brings about a decrease of extractability of myofibrillar proteins. There is also deterioration of the texture and functional properties of the flesh. In model systems, aggregation of myosin, actin, tropomyosin, and whole myofibrils have been described. These changes are caused by concurrent action of partial dehydration due to the freezing out of water, exposure of the proteins to inorganic salts which are concentrated in the remaining nonfrozen fluid, interactions with free fatty acids liberated from phospholipids and with lipid oxidation products, and cross-linking by formaldehyde produced in some species of fish as a result of enzymic decomposition of trimethylamine oxide. The extent of protein alterations increases with time and temperature of storage as well as with advanced disintegration of the tissues and intermixing of their components. The role played by the individual factors and the significance of different types of bonds, i.e., hydrophobic adherences, ionic bonds, and covalent cross-links in particular cases are not yet fully disclosed. Retardation of the deteriorative changes of proteins in frozen fish is possible by avoiding high storage temperatures and oxidation of lipids, removing hematin compounds and other constituents promoting cross-linking reactions, and by adding cryoprotectors like sugars, several organic acids, amino acids, or peptides.

Protein Structural Changes During Preparation and Storage of Surimi

“…Most of the alterations oeeur in the myosin-actomyosin system. Myosin upon standing in solutions tends to aggregate (Sikorski et al, 1976). The properties of actin do not change signifieantly during prolonged frozen storage of fish (Connell, 1960).…”

“…Freezing of surimi is done commercially with the addition of sucrose (4%), sorbitol (4%) and polyphosphates (0.2%), which protect fish myofibrillar proteins during long periods of frozen storage (Lee, 1984). Sikorski et al, 1976).…”

“…Factors causing protein denaturation include partial dehydration, inorganic salts, lipids and fatty acids and the action of formaldehyde (Sikorski et al, 1976). The degree of protein denaturation during frozen storage is affected by many factors such as the state of rigor at the time of freezing, treatment before freezing, quantity and composition of free amino acids, and adenosine-nucleotides and their derivatives (Park et al, 1997).…”

“…Protein denaturation lS a complex phenomenon involving alterations of the secondary and tertiary structure of proteins due to breakage of the bonds that contribute 21 to the stability of the native protein conformation without rupture of the covalent linkages between carbon atoms in the polypeptide chains (Sikorski et al, 1976).…”

Freezing / Thawing and Cooking of Fish

“…Denaturation can be defined as a loss of functionality caused by changes in the protein structure due to the disruption of chemical bonds and by secondary interactions with other constituents (Sikorski et al, 1976). Structural and spatial alterations can cause a range of textural and functional changes, such as the development of toughness, loss of protein solubility, loss of emulsifying capacity, and loss of water holding capacity (Miller et al, 1980;Awad et al, 1969;Dyer, 1951).…”