Fish Products and By-product

FISH PRODUCTS AND BY-PRODUCTS

Landed fish fetches maximum price when sold in fresh condition worthy of human consumption. 

For several reasons including non-availability of a ready market, non-nearness of market, lack of facilities for fast transport or refrigerated transport etc., an appreciable amount of fish is preserved for long term storage. 

This preserved fish is also meant for human consumption as food. But there are yet other utilizations of fish in which protein, fat and other useful contents in the body of fish are processed into a number of valuable products and by-products for a variety of usage 

1. Fish liver oil

This is one of the most important products of fish. 

It is highly useful medicinely because of its vitamin contents, yet is actually obtained from liver which is a part of the offal discarded during dressing of landed fish. 

Huge amount of otherwise waste liver of fish forms a very economic raw material for many cottage and large scale commercial industries engaged in the manufacture of fish liver oil. 

There is also an added advantage of simultaneous production of a by-product-the fish meal.

Fish liver contains protein, water and fat, the last forming 55 to 75%, on an average. 

The fat carries with it vitamins A and D in considerable quantities. 

The fat of liver is the source of vitamin A & D rich liver oil. However. fat and vitamin A contents of liver vary from fish to fish and from season to season. 

Cod (Gadus morrhua and G. callarium) liver is rich in fat but poor in vitamin A content (ranging between 1000-3000 1.U. per gram). 

On the other hand, halibut (Psettodes spp.) and tuna (Thunnus spp.) have low fat but high vitamin A content (50000 to 300000 I.U. per gram), and sharks (Galeocerdo tigrinus, Carcharinus melanopterus. C. giganticus. Sphyrna blochii. S. malleus. Pristis cuspidatus etc.) have the highest fat and highest vitamin A content (15000 to 10.00.000 I.U. per gram). 

Also in case of sharks of large size, single liver size is also large measuring from a few kg to 200 kg. forming excellent raw material. 

For preparation of quality liver oil it is necessary, however, that the liver be in good condition. i.e. there is no decomposition of fat into fatty acids or rancidity of fat has taken place due to oxidation, following death of fish.

Fish liver oil presents vitamin A and D in proportions most suitable for human needs.

 Therefore fish liver oil has been in medicinal use for a very long time as a prophylactic and curative. 

Its curative value however came to light with our growing knowledge about vitamin deficiency diseases. 

Fish liver oil. because of its high vitamin A and D contents can cure or prevent occurrence of diseases caused by the deficiency in the body of these two vitamins, such as rickets, Xeropthalmia. impaired vision and eye defects. abnormalities of skin, mucous membranes and vertebrae. 

In general, fish liver oil when taken will ensure good growth of bone and teeth, help mainatin a normal skin and vision and will develop more resistance to counter bacterial attack and so forth.

Methods of extraction of fish liver oil from liver:

The raw material i.e. the liver is used in fresh condition or in a preserved one (frozen, salted or formalin treated).

 This is necessary more to guard the protein and fat rather than the vitamin A content which is very stable.

 Oils of various grades crude oil for burning, high quality technical grade, edible oil for medicinal use or of intermediate grade-are produced depending upon what principle or method of extraction has been used. 

Oil is produced both by cottage industries as well as by large manufacturing factories. 

Chief known methods of extraction are given below; many other methods are not known at least in details as these are closely guarded secrets of the manufacturing units.

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I. Extraction of oil: 

a. Method of autofermentation: 

Livers are left to undergo decomposition for several days, macerated and exposed to sun in earthen pots. 

Oil released during disintegration is collected. Oil is crude and used for burning purposes or for making lights in curing yards by fishermen. The method is simple but crude.

b. Method of boiling: 

Livers are chopped into pieces and boiled. Released oil is collected. 

Method is simple, not requiring equipments. However yield is moderate because not all oil is extracted out of liver. 

Generally followed in small cottage scale industries is this method.

c. Method of steaming: 

Minced Livers are steamed (850 to 90°C) under 2 kg/sq-cm of pressure. 

Oil is collected from top layer. The method is a quick one and is good for operation on board of fishing vessels (trawlers etc.) where steam is readily available.

d. Method of chemical digestion: 

There are three main procedures:

i. Aquacide digestion: 

Fresh liver is mixed with a mixture of sodium bicarbonate and paraldehyde. 

The pulp is stirred with warm water, giving an emulsion of water and released oil. 

As soon as the emulsion breaks, oil forms a floating layer on the top from where it is collected.

ii. Alkali digestion: 

Minced liver is mixed with caustic soda (1 to 2% by weight of liver mass) or sodium bicarbonate (2 to 5% by weight). 

It is then steamed at 82°-88°C with constant stirring. 

The pulp is then centrifuged to separate oil which is collected.

iii. Enzyme-alkali digestion: 

In this process minced liver is brought to pH level of 1.2 to 1.5 by the addition of hydrochloric acid solution.

 Now commercial pepsin (0.5% by weight of the liver) is mixed and the pulp digested at 43°-49°C. 

Then the pH is raised by the addition of an alkali (sodium bicarbonate) until a level of 9 is reached. 

Temperature is also increased to 80°C. After complete digestion the oil is run off from the top.

e. Method of solvent extraction: 

This is an expensive method, but the yield is higher. However. 

It has not been adopted for commercial production. The method consists in, first.

 dehydration of the minced liver with the application of an anhydrous salt, generally sodium sulphate. 

When the moisture has been removed, the pulp is mixed with the solvent-ethylene dichloride being commonly used. 

Later on, the solvent is subject to distillation process and the oil is separated out.

 Any free fatty acid coming along during solvent extraction of oil is removed during refinement.

II. Refinement of oil: 

First, the oil collected after extraction from liver is left to stand so that water and any debris present in it settles down. 

Pure oil is now removed from top layer, filtered and then centrifuged. 

The oil thus obtained is congealing oil and has stearine present in it. 

To obtain non-congealing oil, it is cooled and stored at 10°C when stearine is separated out. 

The oil is again filtered while still cool (in a chill-room).

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III. Standardization of Vitamin A potency in the extracted oil: 

Since the liver oil is mostly used in medicine for its richness in vitamin A content, it is subject to rigorous estimation for the same.

Following three methods are in vogue:

a. Biological estimation: 

The standardization involves feeding with oil to experimental albino rats (five weeks old) raised on vitamin A deficient food. 

The response in growth is matched against a similar response in a case in which such albino rats have been fed on cod liver oil with known potency of vitamin A. 

This is how the potency or vitamin A is estimated.

b. Colorimetric estimation with tintometer:

 In this process of standardization, the oil is dissolved in chloroform, and then chloroformic solution of antimony trichloride is added to it. 

A blue colour develops. The intensity of this colour is read on tintometer, and is the measure of vitamin A potency.

c. Photoelectric Spectrophotometric estimation: 

The standardization uses the principle of characteristic and selective absorption of a certain zone of ultraviolet region of the spectrum. 

The extent of absorption is related directly to the concentration of vitamin A.

 The intensity of absorption is measured with photoelectric unit and can be read on its galvanometer. 

For this. simply the oil is dissolved in a suitable solvent and then the solution is kept in the path of ultra violet rays. 

Prototype of fish liver-oil manufacturing plant

The plant is designed on steam extraction principle. 

It consists of three parts: a disintegrator, a steaming tank and an oil separator. 

The disintegrator is a large tank to hold large amounts of chopped liver. 

It is fitted with a mincing device so that finally the liver is turned into a pulp. 

The pulp is then pumped through a large pipe to the steaming tank. 

Water is added here. Steam is circulated through conducted pipes in the tank. 

The digested liver is then brought down to the oil separator unit where it is subject to centrifugation. 

The debris is processed to get a by-product-the fish manure or an animal feed. 

The yield of oil is maximum, and the quality of oil is also good. 

The oil may, however, have a fishy odour and taste. 

This may be deodorized during refinement. 

Refined oil may be blended with other vegetable oils for flavour or capsulated into concentrates of vitamin A. 

Simple model of fish liver-oil extractor for use in small scale cottage industry

A simple model has been proposed by Saha in 1956. 

It consists of an all purpose tank (100 cm in height and 45 cm in diameter). 

It has two sections. A lower one serving as a boiler and an upper one the extractor-cum-separator. 

The bottom of the latter fits into the mouth of the former, the two sections soldered together. 

Two steam pipes 1.27 cm in diameter leave the boiler, and entering the extractor section from above run to its bottom, ending 3.8 cm above the bottom. 

There is a water inlet fitted into the boiler. 

One "window-tube" of glass tube is fitted in each section to read the level of water in the boiler or the level of the oil in the extractor. 

Outlet taps, one each, is fitted in the bottom of the two sections. 

Another outlet tap is fitted high up in the extractor for removal of oil. 

The extractor has its conical mouth closed with a removable hopper, and on outlet tube for steam and also a socket for the thermometer. 

The whole unit can be easily fabricated with a 24 guage G.I. sheet at low cost. 

It is portable and handy also.

The working is simple. First boiler is filled 2/3rd with water. 

Now minced liver is introduced into the extractor through the hopper to fill half of it. 

Then water is added in a quantity 1/4th of the amount of liver. 

Now boiler is heated over a fire. The steam is conducted into the extractor, where it heats up the liver as well as stirrs it up. 

Uncondensed steam leaves through the outlet pipe. Periodically a thermometer is put on this tube to record the temperature reached.

 Steaming is carried out for 45 minutes and then discontinued. 

This is enough to extract all oil from liver. The unit is now allowed to cool down. 

The oil and water then separate away and their levels read on the window tube of the extractor. 

The oil can now be removed through the upper tap. by raising the water level by careful addition of water into the extractor until all oil is run off. 

Moisture of the oil is later removed with the help of anhydrous sodium sulphate.

 The liver debris is then removed from the extractor, and the latter washed with water. 

It is now ready to receive the second charge.

2. Fish body oil:

Fish body oil is different from fish liver oil. 

Fish body oil is the oil obtained from the entire body of fish and not from liver exclusively. 

Fish body oil is generally extracted from either oil sardines or from less edible varieties of fish or from offal and other wastes discarded from canneries or curing yards. 

On an average five kg of fish yields about half kg of fish body oil. 

The recovery however depends upon the fat content of fish. 

Fatty fish (oil sardines etc) yield more oil than non-fatty fish do. 

Fish body oil, as compared to fish liver oil, is poor in vitamin A and D contents and has less amount unsaponifiable matter. 

The body oil has in various proportions the glycerides of fatty acids of saturated and unsaturated groups. 

The uses of fish body oll depend upon these contents. Generally speaking, fish body. oils with low content are edible (used as cooking medium) and may serve as a source of vitamin A and D for medicinal purpose. 

But those with high iodine content find economic uses other than this. 

Some of the important uses are:

i. use in manufacture of paints and varnishes (the fish body oil is very suitable because it is a drying oil).

ii. use in dressing of leather and tanning of skin.

iii. use in the manufacture of cheap soaps such as laundary soap, insecticidal soap etc. 

iv. use in steel and iron industry, for tempering of steel (used as a quenching medium), concentration of low grade iron ores etc.

v. use in manufacture of chemicals such as alkyl halides, silicones and quaternary ammonium salts through the intermediate step of poly-unsaturated fatty alcohols. 

vi. use in the manufacture of cosmetics, lubricants, candles and cutting oils. 

vii. use in the manufacture of printing inks. water-proofing preparations and linolum (a substitue for rubber) and plastic.

viii. use as fungicides for citrus group of trees.

ix. for smearing the surface of boats for longer preservation etc.

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Method of extraction: 

There are two methods-the dry process and the wet process. 

In the former the fishes are grounded in a grinder, cooked and pressed to recover the oil, In the wet process, the fishes are minced. cooked with steam, and then pressed for oil recovery. 

The residue in both the cases is processed as a by-product-the fish meal. 

The oil collected as press-liquor has protein debris and lots of other impurities. 

These impurities consist largely of water soluble contents and non-fatty acids of the body tissues which come out alongwith the oil during pressing. 

The press-liquor is first filtered and then subject to refinement through following steps: 

(i) treatment with caustic soda to neutralize the acids 

(ii) treatment with super-heated steam and sodium carbonate to remove bad odour.

(iii) subject to aeration to bleach the unwanted dark colouration .

 (iv) subject to a temperature of 105°C to remove moisture.

 (v) subject to refrigeration to remove stearine content.

3. Fish Meal

After fish oils fish meal is the next most important product of fish. 

It is in fact ground, cooked and dried preparation of the body of fresh fish. 

Fish meal contains 55-70% protein. 2-15% oil/fat and 10-20% minerals. 

It is a highly nutritive product that makes an excellent poultry and animal feed, good for practically all classes of livestock. 

Egg and milk production is sufficiently increased by its use. 

The protein of fish meal has high digestibility coefficient, and contains practically all the essential aminoacids.

 Minerals include calcium (about 5%) phosphorous (4%) and lodine. 

The fish meal is also very rich in vitamins which includes B. A, D, K and E. 

All this makes fish meal particularly important for growing cattles, for it promotes tissue and bone building. 

However, the nutritive value of fish meal depends upon several factors, the important among which include the type of fish used, the state of freshness of fish. the season of landing and the manner of preparation. 

A good fish meal with good keeping quality does not have more than 10% of moisture content. 

It should also have low fat and salt content. 

Fish meal accordingly is graded as superior or inferior quality. 

The raw materials include sardines, mackerels, sharks, ribbon fish, silver bellies and others. 

Shark and rays yield specially superior quality of fish meal. 

Fat and lean fishes require different processing ("reduction") for production of fish meal, because they have different proportions of fat and moisture. 

Whereas fat fish has 6% of fat. lean fish have only 1% of it. 

Moisture content is greater in lean fish than in fat fish. 

Fish meal is also obtained as by-products of canneries and fish oil industries. 

Peruvian anchovy, menhaden. herring and pilchard are commercially used for manufacture of fish meal by Peru and U. S. A. as the leading countries.

i. The method of preparation of fish meal for small scale production: 

The fish if small are treated whole. but if large, are minced after removal of entrails. Then the minced mass is cooked. 

The cooked mass is then pressed in screw presses to remove moisture. The cakes produced after pressing are dried in sun on clean platforms.

ii. The manufacture of fish meal on large scale : 

The manufacturing units deal with huge amounts of raw materials. 

The raw materials include beside entire landed fish of poor food value, mackerels and sardines, also wastes from filleting plants (of canneries) and curing yards.

 The raw materials are ground well to crush bone and flesh. The minced mass is then steam heated either by external application of steam (dry process) or by pressure-steaming through the mass (wet process). 

This is followed by hydraulically operated pressing which after extraction of oil and water leaves dry cakes ready for sac filling and marketing.

4. Others

1. Fish Flour (Hydrolyzed protein): 

This is a very superior quality of fish meal. produced under strict control and care. meant for human consumption. 

It is produced by a rather sophisticated solvent extraction process. 

Fish flour is considered an ideal protein source to supplement diet of both adults and infants. 

It may also be mixed with wheat or maize flour. 

It is also used to enrich bakery products such as bread, biscuits and cakes, soup and sweets. 

The product is manufactured in South Africa. Tropical Africa. Morocco, U. S. A. Chile and India.

The waste flesh of fish, particularly of shark and rays, is converted into high grade hydrolysed protein for human consumption. 

The product has high protein content (35%) which is very suitable for convaleasing patients struck with malnutrition, anaemia etc.

 The process is complicated, though not expensive, in its manufacture. 

Fish is minced and washed. It is then boiled with dilute acetic acid, at 80°C. 

The mass is again washed repeatedly, and then water is pressed out. 

Dry thread-like matter comes out after pressing. 

This matter is treated with petroleum to remove fat and to increase its keeping quality. 

The fat-free mass is then hydrolysed, preferably with alkali using caustic soda (10% at 80°C). 

The whole mass goes into liquid form when it is neturalized with acetic acid (85% strength). 

The liquid is then spray-dried to give a dry, cream-coloured, powder-like flour.

2. Fish Silage

This is yet another form of fish meal. 

It is liquid or semi-solid product and a highly nutritive animal feed. 

It is produced by an acid process. 

The raw material consists of fresh fish or fish offal. 

It is minced and mixed with either sulphuric acid (pH 2) or formic acid (pH 4-5) or both of them one after the other. 

Formic acid increases the keeping quality of the product. 

Acid also acts as a preservative. Fish silage is sometimes also obtained by fermentation with lactic acid bacterium, in molasses.

 However, its production is more preferred in temperate than in tropical regions. 

It is manufactured chiefly in Norway. Denmark and Europe.

3. Fish manure and guano

Fish manure and guano are inferior quality of fish meal products which are unfit as animal feed. 

Fish manure is a by-product of curing yards, fish glue industries and oil extracting plants in which trash fish or spoilt fish have been employed. 

The residue after extraction of oil or poorly cured fish including sun-dried fish, makes the manure. 

This manure is having a high content of nitrogen (5-7%), phosphates(P,O,, 4-6%) and lime (CaO. 4-6%). 

The fish manure is particularly useful in raising coffee, tea and tobacco crops.

Fish guano is the by-product of body oil extraction plants in which oil bearing species, particularly oil sardines are used as raw material. 

The product being already cooked during the processing for oil extraction decomposes quickly in the soil and mixes well. 

The nitrogen content of guano is very high (8-10%). and it has been found that guano is several times more effective than any animal manure.

4. Fish Sausage and ham

The product is commercially manufactured in Japan. U.S.S.R. and U.S.A. 

These are spiced pasted fish meat preparations very much popular in Japan. 

Fish ham differs from fish sausage in having small pieces of solid fish meat (pieces of one square cm) mixed with pasted fish meat. 

Spices and additives are added to improve taste, flavour and keeping quality.

 The product is finally packed in casings and bolled (at 85-90°C) to cook the meat. Spices include salt, sugar, chillies, corriander, onion, glutaminate, egg-white, hydrogenated vegetable oil etc. 

Additives include antiseptics (nitrofurazon, nitrofuryl acrylamide etc) and antioxidants (ascorbic acid; to prevent rancidity). 

Colouring agents may also be added. These products are. however, prepared from less valuable trash fish. 

Although sharks may be good raw material, these are not generally used because of high urea and T.M.A.O. content in their flesh.

5. Fish Glue

It is a kind of good glue obtained from trimmings, bones and skins of fish. 

These latter substances are washed, minced and steam heated. 

The mass is covered with plenty of water and the medium made acidic with acetic acid. 

It is cooked for 6-10 hours. The liquor is extracted and concentrated to form the glue. 

whereas the residue is used, after drying, as manure. 

Fish glue is considered a good adhesive, and is used for smearing the backs of glued stamps and labels. 

The glue obtained from cod is of superior quality and finds use in photo-engraving. When the product is of low quality it is utilized as adhesive for paper boxes. shoes and other things such as furniture where joining is required. 

U.S.A. is known for producing large amounts of fish glue.

6. Isinglass

Isinglass is a good substitute for gelatin. 

It swells in cold water but does not dissolve in it. 

At higher temperature it hydrolysis in water to produce strongly adhesive gelatin. 

Isinglass is used in confectionery as a substitute for gelatin; it is also used as an adhesive in the form of court plaster or other cements. But its chief use is in clarification of beer, vinegar etc.

Isinglass is in fact a collagen derived from the thin, inner silver shiny layer of the air-bladder of some fishes, particularly sturgeons, carps and catfishes. 

The air-bladders are collected, washed thoroughly: and then the outer thick and fibrous layer of the wall is separated from the inner layer which is exclusively isinglass raw material.

 Isinglass is then prepared from this layer. The Russian isinglass produced from sturgeons is considered to be a high grade isinglass.

7. Fish leather

The skin of some fishes such as cod, salmon, halibut, toad fish, sharks and rays yields good and ornamental leather. 

Fish leather particularly of sharks is used in making of shoes, wallets, bags, because the leather is durable, flexible and ornamental and can also be dyed in different colours.

The skin of larger individuals is collected. It is then soaked in brine and left for a day.

 Next day it is salted and again put in brine containing 10% hydrochloric acid. 

The skin is then taken out, drained and scraped on the surface, particularly in case of sharks to remove fine denticles. After this the skin is tanned by usual process.

8. Fish Caviar

U.S.S.R. is famous for the manufacture of caviar from sturgeons, which is the true caviar held in high esteem as a very delicious food. 

In fact, caviar is the processed and salted form of roe of any large sized fish, and it is served as an appetizer.

9. Fish Macaroni

The product is manufactured by the Mysore Institute of India. 

The fish Barbus carnaticus is minced and mixed with tapioca or sorghum flour in equal parts. 

The latter is partially gelatinized with hot water.

 Some wheat semoline is added, besides spicing with salt, chillies and tamarind.

 The paste is extruded and dried. The product has good keeping quality, and is cheap and easy to manufacture.

10. Fish Biscuits

The product is manufactured in Chile and Morocco. Fish flour is blended with biscuit mixture prior to baking.

11. Insulin

Fish is replacing cattles in providing raw material for the manufacture of insulin.

 The pancreas of shark is very rich in insulin. 

Whales also provide a considerable quantity of insulin.

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