Fish proteins extractability

Figure B3.1.1 A 15% SDS-polyacrylamide gel stained with Coomassie brilliant blue. Protein samples were assayed for the purification of a proteinase, cathepsin L, from fish muscle according to the method of Seymour et al. (1994). Lane 1, purified cathepsin L after butyl-Sepharose chromatography. Lane 2, cathepsin L complex with a cystatin-like proteinase inhibitor after butyl-Sepharose chromatography. Lane 3, sarcoplasmic fish muscle extract after heat treatment and ammonium sulfate precipitation. Lane 4, sarcoplasmic fish muscle extract. Lanes M, low-molecular-weight standards aprotinin (Mr 6,500), a-lactalbumin (Mr 14,200), trypsin inhibitor (Mr 20,000), trypsinogen (Mr 24,000), carbonic anhydrase (Mr 29,000), gylceraldehyde-3-phosphate dehydrogenase (Mr 36,000), ovalbumin (Mr 45,000), and albumin (Mr 66,000) in order shown from bottom of gel. Lane 1 contains 4 pg protein lanes 2 to 4 each contain 7 pg protein.

Lipids are often a nuisance in extraction of proteins. For example, in preparing leaf protein concentrate a protein-lipid complex is formed frequently affecting the protein extraction efficiency (16). Nutritionally, the complex is disadvantageous because it resists digestion by proteases (17). Shenouda and Pigott (18) found that the formation of protein-bound lipids can cause a low efficiency of extraction of protein from fish. Hydro-phobic bonding probably plays an important role in protein-lipid interactions. Mohammadzadeh-k et al. (19) reported protein interaction with completely apolar compounds such as aliphatic hydrocarbons. 

Biological products were developed traditionally, before recombinant proteins, as extracts or derivatives of the actual protein from the human body or nature. This approach continues today and Table 15 lists 18 such products, mostly blood derivatives for therapeutic use. Albumin is obtained for cardiovascular volume conditions. A fish protein is harvested for osteoporosis. Igs extracted from blood are available for immunodeficiency conditions, viral infections (hepatitis-B and vaccinia), hemolytic anemia in newborns, and idiopathic thrombocytopenic purpurea. Antihemophilic products are still derived from blood. An antiglobulin is produced for kidney transplant rejection. A collagen product and two botulinum toxin products are used for various facial wrinkle problems and cervical dystonia. A bacterial antigen is formulated to enhance immunity to treat a cancer. 

Much research has been devoted to working out optimum parameters of producing different protein concentrates from fish and krill (Lanier, 1994). While the products have high nutritional value and many are tasteless and odorless, some, manufactured in denaturing conditions, lack the desired functional properties. A good example is the fish protein concentrate obtained by hot azeotropic isopropanol extraction. On the other hand, a concentrate of myofibrillar proteins known as surimi, produced mainly from fish and to a lesser extent from poultry and meat, is highly functional. 

It was pointed out before that studies on marine fish from India indicate that the proteins from them are about 93% digestible by man (Qureshi, 1951). The United States Fish and Wildlife Service has studied the nutritive value of the proteins extracted from the flesh of 17 species of fish. It was found that these marine proteins were equally effective in promoting growth in rats. As compared with proteins from beef round they were comparable in growth promoting effectiveness (Nilson, Martinek, and Jacobs, 1947). Earlier studies had indicated that the growth-promoting... 

Methods. Early investigations relevant to technological analyses of the freezing operations involved determining the amount of protein extractable in salt solutions, such as 5% NaCl or 0.6M KC1. Proteins extracted in this manner were defined as native or undenatured. Then a question arose concerning the mechanism by which denaturation occurs. Unfortunately, denatured proteins are difficult to study because of their insolubility thus information about the state of proteins in fish had to be gained from the soluble protein fraction. 

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). 

Electron Microscopy. Examination of fish proteins by electron microscopy conclusively shows that actomyosin aggregates during frozen storage (59,63,69). The change in structures of the extracted myofibrillar proteins and of the myofibril residues of frozen-stored cod muscle was studied by electron microscopy. The decrease in the number of actomyosin filaments and an increase in the number and size of large aggregate were found (69). Unfrozen carp actomyosin, either dissolved in 0.6M KC1 or suspended in 0.05M KC1, exists in a typical arrowhead... 

Tropomyosin and Troponin. Tropomyosin is apparently the most stable of the fish proteins during frozen storage. Tropomyosin can be extracted long after actin and myosin become inextractable (68). 

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... 

Figure 3. Relative curd strength (Brookfield viscometer readings) of gels prepared from 3% solutions of either fish protein concentrate extracted at high pH, succinylated FPC at various pH values, or raw skim milk. (A) Succinylated protein plus corn oil. (B) Succinylated protein. (C) Succinylated protein plus Ca2+. (D) High pH FPC extract plus corn oil. (E) High pH FPC extract. (F) Raw skim milk curd prepared with rennet. (75)...

Solubilization of Protein. Fish protein concentrate has high nutritional quality as determined both from its essential amino acid composition and from animal feeding experiments. Unfortunately, the concentrate is quite insoluble in water because of its denaturation by the solvent extraction method used in processing thus it contributes no functional properties to a food and must be used in bakery products primarily. A potentially useful method of solubilizing the protein is by proteolysis (9-12). As is the case with protein hydrolysates of casein and soybean protein, bitter peptides are formed during the hydrolysis. Papain and ficin produce more of these bitter peptides than does Pronase, for example (12). Pronase was found to produce a more brothy taste (13). A possible method of removing the bitter peptides is to convert the concentrated protein hydrolysate to plastein by further proteolytic enzyme action (14) to remove the bitter peptides. 

Modification of fish proteins by proteolytic enzymes to increase their solubilities illustrates a variety of techniques and approaches. Basically, three general enzymic methods have been used to prepare fish proteins or hydrolysates with altered solubilities and other functionalities. These methods include (a) the enzymic solubilization of fish protein concentrate prepared by hot solvent extraction of fish, (b) the enzymic modification of myofibrillar proteins extracted from fish with 0.6M NaCl, and (c) the proteolysis of whole fish to prepare biological fish protein concentrate (FPC). 

The effect of enzymic modification on the foaming and emulsification properties of fish proteins has been studied in several laboratories (8, 14, 28). Hermansson et al. (8) observed that solvent-extracted FPC modified with an alkaline bacterial protease yielded a whipped foam volume approximately 70% greater than untreated FPC. However, the stability of the foam from the enzyme-modified FPC was about 50% less than that of the untreated FPC. The foam volume of the enzyme-modified FPC was essentially equal to that of egg white, but the foam stability of the FPC hydrolysate was substantially less. 

Uses Solvent for coatings, paint removers, adhesives, resins, lacquers, industrial cleaners, pharmaceuticals prep, of methyl ethyl ketone petroleum octane booster extraction of fish protein ingred. in hydraulic brake fluids perfumes cosmetics ingred. synthetic flavoring agent in foods in paper/paperboard in contact with dry food Regulatory FDA 21CFR 172.515, 176.180 SARA 313 reportable Manuf./Distnb. Ashland http //www.ashchem.com, Atofina SA http //www.atofina.com, Chemcentral E-Chemicals http //www.e-chemicals.com, ExxonMobil... 

Stoddard solvent 1,1,2,2-Tetrachloroethane extraction, fish protein 2-Butanol extraction, gold Potassium cyanide... 

Solvents are also used in food processing. The largest uses are of aliphatic hydrocarbons, such as -hexane, which are important for oil seed extraction and purifying oils good solvency and ease of separation from the extracted oils (low boiling point) are key properties. Extraction is important in many other parts of the food industry to produce, for example, flavour extracts a variety of solvents from hydrocarbon to alcohols are used in such applications, but volumes are smaller. Isopropanol is used to extract fish protein from ground fish. Methylene chloride was used to extract caffeine from coffee, but has been largely superseded by liquid carbon dioxide. For all human food applications, food contact approval is vital if human consumption is involved. 

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