BIOCHEMICAL COMPOSITION OF FISH ppt.pptx

ppt about fish

1. BIOCHEMICAL COMPOSITION OF FISH

2. The nutritive and medicinal value of fish has been recognized from time immemorial . Fresh fish provides an excellent source of protein for human diet. This protein is of high digestibility, biological and growth promoting value for human consumption . Nutritional studies have proved that fish proteins rank in the same class as chicken protein and are superior to milk, beef protein and egg albumen. Fish proteins comprise all ten amino acids in desirable strength for human consumption, namely Lysine ( high concentration), arg inine , histidine,leucine , isoleucine , valine , threonine , methionine, Phenylalanine and tryptophan. This accounts for high biological value of fish flesh.Fish flesh therefore becomes a valuable supplement to human diet for people who are habitually taking cereals ,

3. Starchy roots and sugar as their principal diet.Besides proteins fish flesh also offers minerals , iodine , vitamins and fat. Over and above all , fish flesh cooks easily,offers a palatable taste and flavour and is easily digestible.

4. Fish is consumed either as a preparation from freshly caught fish or from those that have been preserved in some form. However, fish in fresh condition makes a difference. The nutritional value, the look, the flavour and even the biochemical composition do not remain normal and undergo changes during preservation processes and storage. Also , same species of fish may show variation in biochemical composition of its flesh depending upon the fishing ground , fishing season, age and sex of the individual ; fat and water content being most affected.

5. The principal biochemical contents of fish are proteins, fats and water. Protein constitutes about 20%, fat and water vary widely and one varies inversely as the other. Beside these there are minerals ,vitamins and enzymes. Carbon- di - oxide does not occur in the composition except as glycogen ( C6 H10 O5) in the liver. Water content varies from 55 to 83%. This is really high as compared to birds and mammals.

6. PROTEINS Proteins occur in fish as : (i)Myosin , myogen , myoalbumin and globulin – all intracellular components of muscle fibres (ii) collagen and connective tissue fibres . (iii ) Phospo proteins and nucleo proteins. The connective tissue amounts to only 3-5% thus rendering the fish protein more digestible than meat. About 90-95 % of fish protein is assimilated by human. These proteins either simple or conjugated.The latter are characterized by a substance to which a protein molecule is attatched viz. nucleo protein has chromatin as the substance.

7. Simple proteins are either soluble in water or in salt solutions, acids and alkalies ( globulins). Electrophoresis of soluble proteins shows that proteins are species specific. Protein exists as monomolecular solution with characteristic hydrophilic properties.The digestibility coefficient and biological value of proteins varies from species to species. Pelagic species particularly Sardine,Herring , Mackarel , tuna etc have high amino acid concentrations particularly that of histidine which is responsible for high meaty concentration of their flesh. The protein nitrogen amounts to 2-3 % of their muscle weight.

8. The protein is contained chiefly in the skeletal muscles – the fish flesh which constitutes about 50-60 % of the total weight of fish. Red muscle and white muscle differ in exclusive presence of myoglobin in the former. Also the red meat has more of glycine , leucine , arginine and phenylaamine,whereas white meat has more of lysine, aspartic acid and glutamic acid.The protein content of the muscle extractable by soluble fractionation is generally classified into three groups 1) Albumin fraction comprising 16-22% present in sarcoplasm and interstitial fluid extractable with weak salt solution ( ionic strength less than 0.3) 2)Protein fraction comprising 75% present in contractile elements, extractable with strong electrolyte solutions ( ionic strength 0.3 ) 3) Stroma comprising 3% present in myocommata,cell membranes and connective tissue extractable with difficulty. The above three kinds of muscle proteins are considered not really pure types but mixtures , as more modern techniques of electrophoresis and ultracentrifugation have revealed a number fractions occuring in each.

9. Albumin is shown to consist of six components.One protein fraction of contractile elements is shown to consist of myosin , actin , actomyosin or tropomyosin fractions. Myosin is extractable by selective dyalysis or ultracentrifugation in the presence of ATP. The myosin is obtained as the supernatant part . Myosin is concentrated in the unisotropic A-bands made up of myosin filaments. The actin fraction is separable by acetone method in which the muscle is first dehydrated in acetone and this fraction is extracted with the salt solution of moderate strength. It is believed to represent a product of interaction between actin and myosin proteins during the extraction process.

10. Planktophagus fish have higher proteins than do fish having other feeding habits. Lean fish have greater protein proportion than fat fish. Cultivated fish as compared to wild fish of the same species having comparable protein components. Besides proteins, there are some non-protein nitrogenous components. The principal ones include :

11. i) Peptides to which the fish owes much of its flavour . ii) Free amino acids of which histidine is important. Red muscle is rich in histidine than white one. iii)Volatile bases like trimethylamines , ammonia particularly in marine fishes ( viz. in red muscles of pelagic fishes like albacore and mackerels. iv ) Creatine , taurine , betaine , histamine, glycine , uric acids, carnosine , anserine etc. v) Nucleic acids.

12. FISH OILS These are chiefly triglyceride esters of fatty acids combined with small amounts of free fatty acids, some vitamins, sterols, hydrocarbons, phospholipids and colour substances. Oil content of marine and freshwater fish differ in relative proportion of various fatty acids . Marine fish oils contain larger quantities of C 18 ,C 20 and C 22 acids. In general , fish oil differ from vegetable oils in containing a wider variety acids particularly of the highly saturated groups. Besides, as pointed out by Swain ( 1952), the commonest fatty acids in fish oils has six double bonds which made them attain a degree of insaturation substantially higher than that of vegetable oils. Due to this characteristics, fish oil find large scale application in industries. Shark oil is rich in unsaponiable substances, whereas sardine oil and herring oil are poor in this.

13. MINERALS This constitutes 1 to 2% of fish flesh composition.The bulk is concentrated in fish bones.Some elements ( Boron,fluorine , bromine, lithium, strontium ) are present in greater concentration in marine fish than in fresh water fish. Mercury is present in fish in greater concentration than it is in outside water. The principal minerals are Ca, Mg, K, Na, P, Fe, S, Cl , Ca, Mn , I, . Besides traces of Sr , Zn, Ba , Al,Pb , Mo, Co, Ni, Hg, Cd are also present.

14. Phosphorus occurs in fish as phosphoproteins,phospholipids,complementary phosphoric acids, ( such as vitamin B1 and B12) , glycerophosphatides and adinosinopolyphosphates . The adinosinopolyphosphate is the active substance in muscle breakdown during freezing, and it is therefore subject of importance in fish preservation.

15. FAT Depending upon the fat content , the fish may be classified as oily or fat ( fat content more than 8% ), average fat content ( fat content between 1 to 8%). Although fat is distributed in all tissues , in some it is present in extraordinary amounts which is in far excess of the amount normally required for cell function. Such fats are called depot fats.The principal sites of the depot fat are muscle, head tissues, roe, milt , liver, skeletal tissue,subcutaneus connective tissue and viscera ( Pyloric caeca and mesenteries). Liver in fish is often the main site with large deposits. Brain shows the highest concentration of fats, and heart the lowest. Liver and kidney rank intermediate.

16. The fat content of fish flesh is a factor that determines the quality of fish and hence its price. A number of parameters governs its variation, these includes species difference, diet of fish, selective mobilization and distribution of lipids in the fat body, salinity and temperature of water etc. Fatty substances chiefly belong to either the glyceride group or the lipid group of fatty acids which differ in points of melting, oxidation, solidification and similar other properties . In fatty acids there are straight chain monocarboxylic forms containing an even number of carbon atoms. The chain length varies from 12 to 28 carbon atoms. In the glyceride group, the fatty acids occur on three – OH groups of the glycerol molecule producing a variety of combinations often complex fats ( triglycerides). There are some twenty fatty acids of which 16% make stable saturated fatty acids ( C n H 2n O 2 ) . These commonly include C 16 palmitic acids, C 14 ( myristic acid) and C 18 ( stearic acids) and arachidic , behenic and selachoceric . The remaining fatty acids forming a high content are unsaturated fatty acids with low melting point and which easily oxidise and polymerise ie ., rather unstable. These belong to C n H 2n-2 O 2 monoenoic acid series ( such as tetradeconic acids,zoomaric , oleic etc) to C n H 2n-4 O 2 ( such as linoleic ) to Cn H 2n -6 O 2 ( linolenic ) to C n H 2n-8 O 2 ( therapinic ) and C n H 2n-10 O 2 ( clupanodonic ).

17. VITAMINS Fish provides vitamin A, B, D all essential vitamins for human diet. Liver is particularly rich in Vitamin B12 and B complex includes thiamine ,riboflavin and nicotinic acid. The distribution of vitamins is however not uniform in the body. Vitamin B occurs more in liver, eyes, skin , roe,kidney , spleen, pyloric caeca and intestines. Also , the vitamin content varies from species to species.

18. Eels and prawns are rich in vitamin A, whereas mackerel in vitamin D. Variation due to age, season and fishing region also occurs. Vitamin A, D, E are fat soluble and therefore present where fat is present particularly in the liver. These owe their origin in the fish food. Vitamin A reaches fishes after conversion from carotene which is abundant in the plankton (diatoms and flagellates ). The invertebrates do the conversion. The food chain being Plankton-invertebrate – fish. Tuna, halibut and cod are well known examples among marine fishes and pike, pikeperch and perch from freshwater fishes which accumulate vitamin A. The liver of hammerhead shark,dogfish,cod , pollock,tuna etc. is the raw material for manufacture of vitamin oils. Vitamins occur in two forms A1 and A2 groups. A1 is abundant in marine fishes and catadromous whereas wheras A2 in freshwater and anadromous fishes.

19. Vitamins of B group are water soluble. These include thiamine( B1), riboflavin ( B2), vitamin B6 and Vitamin B12. Other water soluble vitamins found in fishes are niacin , pantothenic acid , folic acid, chlorine and ascorbic acid(vitamin C).Red muscles contain greater quantities of vitamin B1, B2 ,B12 and pantothenic acid than do white muscles. On the other hand white muscles contain greater quantities of follic acid than do white muscles. The marine fishes of India are rich in vitamin B1, B2 and D. Niacin is rich in muscles of Indian Shad, Pomfret and Clarius magur in freshwater fish.

20. Chlorine known for its medicenal value in treating hunger edema in underfed patients is found in large quantities in fishes of Bengal.

21. NUTRITIONAL VALUE OF RAW FISH The nutritional value of fish meat is comparable and even higher than that of meat of cattle calf (veal) cow or ox ( beef), pig ( pork),lamb and sheep (mutton)and poultry.The flesh of fish has less stroma protein which is of low nutritive value. Fish flesh provides an excellent source of all essential amino acids in concentrations needed in human diet. The Indian pomfret ( Stromateus argentius ) and the Amazon Arapaima gigas are ranked high on the basis of their amino gram. About 300 g of raw fish flesh suffices to supply about half of the total protein and fat requirement and one –fourth of the calories needed in a balanced daily diet for adult human being.

22. Also this amount of raw fish in addition provides 50% of phosphorus, 30% of iron, 100% of vitamin A ( fat fish only), 30% of Vitamin B1 and vitamin B2 requirement and 50 to 100% of niacin requirement. Fish proteins is also highly nutritious as child food and it is easily tolerated by infants. The digestibility of fish is in the order of 96%, fairly high compared to digestibility of beef and poultry. The protein contents are easily and completely split up into unitary amino acids by the digestive enzymes ( particularly trypsin) so is also the case with several linkages between amino acids and proteins. Lean fish are recommended in convalescing patients.

23. Fish is an effective supplementary food where diet is principally plant oriented. Cereal and rice based diet is deficient in lysine, methionine and such diet may be made good by supplementing with fish. Fish also supplements very well peas, grams and other pulses for their proteins.

24. NUTRITIONAL VALUE OF PRESERVED FISH (FISHERY PRODUCTS) The nutritive value of preserved and processed and fishery products is generally lower than that of raw fish. This is due to loss of some of the nutritive value during various stages and processes of fish preservation. Exudation : Drip occurring in unfrozen fish is increased during freezing and defrosting and thawing. The drip is a free liquid containing 4% protein which is lost. Similar losses in protein also occur during pre-cooking in canning. Water soluble vitamins and minerals are also lost in the exudate .

25. Cooking : A cooking at 60 c causes loss in weight due to exudation of liquid. Underdone fish is more digestible than overdone or raw and fried fish. Broiling,boiling,baking and simmering have little effect but frying causes heavy loss of essential amino acids ( leucine,lysine,phenylalanine and valine ).Heating destroys creatine . Steam or pressure cooking causes loss in proteins and minerals.Broiling or deep fat frying renders fish less digestible due to formation of additional difficult to split linkages among amino acids and proteins

26. Canning : Canning does not affect protein and fat as to their nutritional value, nor does it destroy iodine, heat stable vitamins( such as vitamin A, vitamin D,B2 and niacin,pyridoxine , biotin,vitamin B12) and essential amino acids.On the other hand canning causes considerable losses in such vitamins as B1, pantothenic acid and vitamin c Salting and smoking : Curing of fish with salting or salting combined with smoking results in substantial loss of protein – about 1-5% due to salting and 8-30% due to smoking. Salting of course acclerates oxidative rancidity of fats which ultimately which ultimately reduces the digestibility of the fat of the product.

27. Freezing : Freezing and lypophilizing ( do not affect the amino acid contents but encourage rancidity of fat on the other hand and dessication and denaturation of fats on the other. Such undesirable look such as freezer burn and rusting reduce the acceptability of the product although no actual loss in nutritional value of proteins occur.Among the vitamins, vitamin E alone is destroyed by freezing.