The role of collagen in the quality and processing of fish

Abstract

Collagen in the muscles of fish constitutes the main component of the connective tissue membranes joining individual myotomes and is responsible for the integrity of the fillets. The content of collagen in fish muscles is from about 0.2 to 1.4% and in squid mantel about 2.6%. Fish and invertebrata collagens contain slightly more essential amino acids than intramuscular bovine connective tissue collagen. The invertebrata collagens are exceptionally rich in sugars linked mainly O-glycosidically to hydroxylysine residues. During maturation of fish the proportion of collagen to total protein in the muscles increases while the extent of crosslinking does not change significantly. The thermal properties of fish collagens depend significantly on the content of hydroxyproline and proline residues which in turn is correlated to the temperature of the habitat. Generally the shrinkage temperature of fish skin collagens is about 20 degrees C lower than that of mammalian hide collagens. In several species of fish the weakening of the connective tissues post mortem may lead to serious quality deterioration that manifests itself by disintegration of the fillets, especially under the strain of rough handling and of rigor mortis at ambient temperature. Thermal changes in collagen are the necessary result of the cooking of fish, squid, and minced fish products and contribute to the desirable texture of the meat. However, they may lead to serious losses during hot smoking due to a reduction in the breaking strength of the tissues when heating is conducted at high relative humidity. Because of the high viscosity of gelatinized collagen, it is not possible to concentrate the fish stickwaters, a proteinaceous byproduct of the fish meal industry, to more than 50% dry matter. Better knowledge of the contents and properties of fish collagens could be helpful in rationalizing many aspects of fish processing.

Nutritional Composition of Cultured Sturgeon (Acipenserspp.)

“…Mean hydroxyproline content fell within the upper third of the range (22-98 mg/ 100 g) reported by Sikorski et al (1984) for numerous fish species. Furthermore, it was very similar to that found in carp by Kimura et al (1988) as regards Type I collagen, which is the type predominating in fish in general and in sturgeon specifically (Sato et al, 1989).…”

Characteristics of the flesh and quality of products of catfishes

“…Its thickness seems to be relatively similar amongst the species (Yamaguchi et al, 1976) although such comparisons have not been made on fish of the same age and it is known that thickness of connective tissue should increase with aging (Bremner, 1992). Sorne early studies suggest that the collagen content in the flesh of catfish: 7% could be the highest amongst fish species (Sikorski et al, 1984). From the hydroxyproline content of the flesh, it also seems that collagen content of cultured African catfish is lower than that of wild catfish (Hoffman et al, 1993) but this could probably be related to age differences.…”

“…It is probably the consequence of a larger proportion of intermolecular cross-links within collagen. Finally, the susceptibility to thermal denaturation of catfish collagen seems to be higher than that of other species (Yamaguchi et ul., 1976;Sikorski et al, 1984) and this is associated with its low proportion of hydroxyproline.…”

Dietary leucine improves flesh quality and alters mRNA expressions of Nrf2-mediated antioxidant enzymes in the muscle of grass carp ( Ctenopharyngodon idella )

“…The enhancement of fish firmness by leucine may be linked to the increase of collagen content. Collagen is the major constituent of fish connective tissues (Sikorski et al, 1984). In general, firmness of fish muscle is directly related to its collagen content (Suarez et al, 2005).…”