The lipid composition and biochemistry of freshwater fish.

Effects of variation in essential fatty acids in fish feeds on nutritive value of freshwater fish for humans

The fish processing industry is a major exporter of seafood and marine products in many countries. About 70% of the fish is processed before final sale. Processing of fish involves stunning, grading, slime removal, deheading, washing, scaling, gutting, cutting of fins, meat bone separation and steaks and fillets. During these steps significant amount of waste (20-80% depending upon the level of processing and type of fish) is generated which can be utilized as fish silage, fishmeal and fish sauce. Fish waste can also be used for production of various value added products such as proteins, oil, amino acids, minerals, enzymes, bioactive peptides, collagen and gelatin. The fish proteins are found in all parts of the fish. There are three types of proteins in fish: structural proteins, sacroplasmic proteins and connective tissue proteins. The fish proteins can be extracted by chemical and enzymatic process. In the chemical method, salts (NaCl and LiCl) and solvents (isopropanol and aezotropic isopropanol) are used, whereas during the enzymatic extraction, enzymes (alcalase, neutrase, protex, protemax and flavorzyme) are used to extract proteins from fish. These fish proteins can be used as a functional ingredient in many food items because of their properties (water holding capacity, oil absorption, gelling activity, foaming capacity and emulsifying properties). They can also be used as milk replacers, bakery substitutes, soups and infant formulas. The amino acids are the building blocks of protein. There are 16-18 amino acids present in fish proteins. The amino acids can be produced from fish protein by enzymatic or chemical processes. The enzymatic hydrolysis involves the use of direct protein substrates and enzymes such as alcalase, neutrase, carboxypeptidase, chymotrypsin, pepsin and trypsin. In the chemical hydrolysis process, acid or alkali is used for the breakdown of protein to extract amino acids. The main disadvantage of this method is the complete destruction of tryptophan and cysteine and partial destruction of tyrosine, serine and threonine. The amino acids present in the fish can be utilized in animal feed in the form of fishmeal and sauce or can be used in the production of various pharmaceuticals. The fish oil contains two important polyunsaturated fatty acids called EPA and DHA or otherwise called as omega-3 fatty acids. These omega-3 fatty acids have beneficial bioactivities including prevention of atherosclerosis, protection against maniac–depressive illness and various other medicinal properties. Fish oil can also be converted to non-toxic, biodegradable, environment friendly biodiesel using chemical or enzymatic transesterification.

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Fish Processing Wastes as a Potential Source of Proteins, Amino Acidsand Oils: A Critical Review

Characteristics of the fatty acid composition and biochemistry of some fresh-water fish oils and lipids in comparison with marine oils and lipids.

Bacterial decomposition of butterfish and smelts in small sealed jars containing seawater and other solutions, for periods ranging from 65 to 205 days, results in a large increase in concentrations of dissolved bicarbonate, carbonate, and ammonia (plus volatile amines). Accompanying this is a rise in pH and the precipitation of Ca(++) ion from solution. The Ca(++) is not precipitated as CaCO(3) but instead as a mixture of calcium fatty acid salts or soaps with from 14 to 18 carbon atoms. This can be explained by the thermodynamic instability of CaCO(3) relative to Ca soaps in the presence of excess free fatty acid. It is suggested that some ancient CaCO(3) concretions, especially those enclosing fossils of soft-bodied organisms, may have formed rapidly after death in the form of natural Ca soap (adipocere) which was later converted to CaCO(3).

https://science.sciencemag.org/content/sci/159/3811/195.full.pdf

Calcium Carbonate Concretions Formed by the Decomposition of Organic Matter

The fatty acid composition of body lipids was determined by GLC for 14 species of saltwater fish, three species of freshwater fish and four species of shellfish. In addition, liver lipids of two species and egg lipids of one species were analyzed for comparison with the fish body lipids. The various species ranged from lean to fatty and contained from 0.7~15.5% oil in the tissues. Certain major fatty acids were found to vary widely among the species, as follows: 1.6~8.0% myristic, 9.5~33.4% palmitic, 2.0~11.2% palmitoleic, 5.2~29.1% oleic, 0.7~10.5% eicosenoic, 5.0~21.5% eicosapentaenoic, 0.2~11.6% docosenoic and 5.9~26.2% docosahexaenoic acids. Analyses of two separate mullet-oil samples illustrated the wide differences that are possible for a single species caught during different seasons. Significant differences in the amt of particular fatty acids were found in comparing freshwater-fish analyses with analyses for marine fish. Oysters and scallops showed large amt of pentaenoic and hexaenoic acids in their oils.

R. W. Nelson

Papers

Fatty acid composition of oils from 21 species of marine fish, freshwater fish and shellfish.