Processing and Value Addition

Fish Products

Chitosan

Chitin is a white, hard, inelastic, nitrogenous, polysaccharide found in the outer skeleton of insects, crabs, shrimps and lobsters and in the internal structures of invertebrates. Chitosan is deacetylated chitin, and is polymer of ß (1-4) acetyl - D glucosamine. It has multifarious uses in the cosmetic, pharmaceutical and medical industries. It is even considered as a wonder drug of the twenty-first century due to its versatile utility.

Potential

Scope for chitin/chitosan production in India

The international shrimp industry from harvest through various processing operations produces a vast amount of potentially recoverable proteinaceous by-products in the form of shrimp heads and shells which is one of the major raw materials for chitin/chitosan production. Shells of other crustaceans viz. crabs, lobsters, squilla, cuttle fish bones also could be profitably utilised.

In India, it is estimated that more than one lakh tonne of shrimp processing waste is being wasted annually which could be gainfully utilised for manufacturing chitin a high value industrial product. Another raw material for chitin is squilla. It is estimated that a potential of around 50,000 tonne of squilla is available of which nearly 5,000 tonne is being thrown back into the sea. This is an important trawl by catch especially in Mangalore and could be used for chitin/chitosan production. Crab shells and lobster shells are also raw materials for chitin/chitosan production. The estimated availability of crab shells is 30,000 - 40,000 tonne in the Indian waters.

Important properties of chitosan

•  Medical grade micronised chitosan is biodegradable, non allergic, haemostatic, non toxic and wound healing accelerator.

•  Chitosan films are flexible, tough, transparent, clear and oxygen permeable with good tensile strength.

•  Chitosan could be used to make single and bipolymer membranes , non woven fabrics and sponges for surgical applications.

•  It is resistant to alkali, digestive enzymes and urine.

•  Chitosan also could be cross linked.

Uses of Chitosan

i) Clarification and Purification

The property of long chain molecules of dissolved Chitosan to wrap the solid particles suspended in liquids and to bring them together and agglomerate makes it suitable as a coagulant aid. It is used in treatment of sewage effluents, purification of drinking water etc.

ii) Chromatography

The presence of free amino acid hydroxyl groups in chitosan is a good chromatographic support.

iii) Paper and Textiles

The high molecular weight, poly cationic linear film forming and hydrogen bonding ability makes chitosan an ideal polymer applicable in the paper industry.

The chelating ability, adhesive property and ionic bond forming characteristic of chitosan find potential application in textiles. Fabric seized with chitosan have good stiffness, improved dye uptake, added lustre and improved laundering resistance.

iv) Photography

Due to the resistance of chitosan to abrasion, optical characteristic film forming ability and behaviour with silver complexes chitosan has important application in photography.

v) Food and Nutrition

Chitosan supplemented chick feed and fish feed improved the weight gain in chicken and fish.

vi) Agriculture

It has potential application in agriculture such as germination and culturing to enhance self protection against pathogenic organisms in plants and suppress them in soil, to induce chitinase activity, in encapsulation of fertilizers, in liquid fertilizers and in controlled release of herbicides.

vii) Medical and Pharmaceutical

• bacteriostatic agent
• drug delivery vehicle
• enzyme immobilization
• film / membrane for dialysis
• artificial skull sponge for mucosal haemostatic agent wound dressing
• anti cholesteremic material
• anti sore composition
• antibillirubinemia agent
• preparation of self regulated drug delivery system
• sustained release / direct compression matrix tablets.

The Process

Technology

Central Institute of Fisheries Technology (CIFT) Kochi has the distinction of perfecting the technology for chitin and chitosan production in the country. The institute is imparting training to entrepreneurs who are interested in setting up such units. They also provide technical support on a turn key basis.

Raw material

Dried/wet shells of prawns, squilla, crabs, lobsters etc., could be utilised. The shells thus used should be thoroughly free from sand and extraneous matter, so as to reduce the ash content of the final product to less than 2%.

Deproteinisation

The shells are boiled with 3% sodium hydroxide for 30 minutes in a mild steel vessel to remove protein stuck to head and shell. The boiled raw material is allowed to cool and it is washed with water to remove all traces of alkali (could be tested with a pH paper).

Demineralisation

The deproteinised shells are transferred to a mild steel vessel lined with fiber glass and is treated with 3% hydrochloric acid. This is kept for 30 minutes with occasional stirring till the reaction is complete. The excess acid is decanted and the residue is washed till the p H is normal.

Removal of water

Excess water is removed using a screw press till the moisture is below 60%. The product thus obtained is called chitin.

Deacetylation of Chitin

It is the process of conversion of chitin to chitosan.

Chitin is heated at 90-95 0 C for about one and a half hour with 40% caustic soda in a mild steel vessel. Excess alkali is drained off and the mixture is washed with water several times till it is free from alkali. Eighty percent of the alkali, thus removed could be reused in subsequent cycles.

Removal of water

Excess water is removed in a screw press and the product thus obtained is wet chitosan.

Drying

The above product is sun dried for 6-8 hours or in drier till the moisture content is less than 5%. Care should be taken not to exceed the drier temperature beyond 60 0 C. Chitosan thus obtained is in the form of flakes.

Powdering and Packing

The chitosan flakes obtained could be powdered and packed in lots of 10,20,25 kg in HDP/ Polyethylene lined non woven sacks in a dry place. Chitin can be stored for one year whereas chitosan can be stored for nearly three months only.

Yield

Chitin represent 14-27% and 13-15% of the dry weight of shrimp and crab processing waste respectively and squilla yields 15% chitin. On a conservative basis the yield is estimated as

Dry raw material chitin             14% by wt

Chitosan                                   10% by wt.

Thus from 1000 grams of dry shell, we get a yield of 140 grams of chitin and 100 grams of chitosan.

Utilisation of Prawn shell waste

The shrimp processing industry in India turns out more than 1.25 lakh tonnes of head and shell waste per annum. Until recently, it was creating enormous environmental pollution problems. Nearly 7,000 tonnes of chitin can be produced from the prawn shell, which is thrown out as waste now. Another alternate source is the squilla, which is a by-catch in shrimp trawlers, which is now discarded. Chitin is extracted from the prawn shell, as this is the raw material for production of chitosan and glucosamine hydrochloride. Chitin is a macromolecular linear polymer of anhydro-N-acetyl D-glucosamine whereas chitosan is its deacetylated form. Glucosamine hydrochloride is produced by the hydrolysis of chitin by hydrochloric acid. During the extraction of chitin, the protein in the shell can also be recovered for use in animal feeds.

CIFT has developed technology for production of chitin, chitosan and glucosamine hydrochloride from prawn shell waste and the method is given below.

• Treat the washed prawn shell with 1.25 N hydrochloric acid (commercial) at room temperature for 2 hours so as to remove the calcium and phosphorous contents in the residue completely. Wash the residue free of acid.


• Boil the acid treated shell (demineralised shell) in about 3 per cent solution of sodium hydroxide (quantity just enough to immerse the shell) for about 30 minutes. Drain off the solution and repeat the treatment with the residue. Treatment with sodium hydroxide removes the protein content of the shells. Wash it free of alkali. The residue obtained is almost pure chitin.


• Treat the chitin at 95°C to 100°C with 1.1 solution of sodium hydroxide for 90 minutes. Wash with water till it is free from alkali and then dry to get the final product, chitosan.

The yield of chitosan is about 4% the weight of the fresh prawn shell and 2% of the dry shell.

Chitosan finds use as a sizing material for rayon and other synthetic fibres, cotton, wool etc. It may also be used in the preparation of cosmetics and Pharmaceuticals and also as a water-clarifying agent. Chitosan dissolves easily in dilute solutions of organic acids to give viscous solutions. It can be precipitated by neutralising the solution with alkali.

Studies have also shown the effectiveness of medical application of chitosan in the form of chitosan impregnated gauze and chitosan film for treatment of chronic wounds and external ulcers, to arrest/minimise bleeding in neurosurgery, as artificial skin and kidney membrane, in plastic surgery, as contact lens, in periodontal application etc.

The application of glucosamine hydrochloride is also as a dietary supplement, mainly in controlling arthritis. The demand is increasing day by day and it is estimated to be more than 2000 tonnes per month.

India has a potential of producing 10,000 tonnes of chitin per annum from the prawn shell itself. Other unutilized sources like squilla are also available. At present, the chitin /chitosan industry in India is utilizing only less than 20% of the shell waste with an earning of Rs.100 crores annually. This has solved the environmental problem significantly in addition to job and income generation. India has the potential of meeting the increasing demand of chitin/chitosan by utilizing the unutilized resources.

Source: Central Institute of Fishery Technology, Kochi

Collagen – Chitosan membrane from fish

1. Periodontal application

Tooth salvaging by periodontists is set to benefit from a new fish-derived membrane, which has emerged from a clinical trial as an appropriate bio-absorptive natural medium for surgical correction of periodontal defects.

Collagen-chitosan membrane is derived from collagen of fish air bladder and chitosan of prawn shell. Good haemostatic and healing properties, good ability for guided tissue regeneration, bio-absorbability and non-antigenic nature make this membrane unique among various GTR membranes.

A six-month experimental trial carried out as part of a research project at the Department of Periodontics, Thiruvananthapuram Dental College gave promising results. This is the first time that an artificial membrane was used for periodontal GTR applications. The Central Institute of Fishery Technology was instrumental in developing this novel membrane.

The membrane, which has been found to possess haemostatic and healing properties, when introduced to the gingival site, acts as physical barrier and closes out the margin of detachment between the soft and hard tissues. The membrane achieves this by providing a space in the gingiva to which healthy periodontal cells can migrate, thus providing for sustainable tissue regeneration.

Using films with 0.l mm thickness, faster GTR takes place and it is observed by the periodontists that the depth of tissue-tooth detachment can be reduced from 8 mm to 2 mm in 6 months, or in other words, achieve a 6 mm tissue regener ation. Radiography and re-entry measures supported these results.

The fish derived membrane could be a superior substitute for the synthetic teflon, which is the gold standard for GTR procedures. The problems with teflon mainly pertain to its high cost and non-bioabsorbability necessitating a second surgery after a few weeks to remove the non-bioabsorptive teflon once the soft tissue-hard tissue binding is complete.

The membrane also conforms to current concepts of eliminating inflammation and infection in the tooth/gum area as well as requirements of salvaging the tooth through guided tissue regeneration. The laboratory level technology for commercial exploitation is available from CIFT.

A novel method for the preparation of absorbable surgical sutures from fish gut has been developed at CIFT, Cochin. The development is a significant achievement in the light of the following facts:

• Fine grade surgical sutures are monopoly products of one or two multinational companies.


• Currently, the cost of a fine grade absorbable suture is around 150 to 300 rupees.


• Absorbable fine grade sutures are essential for microsurgeries and ophthalmic surgeries.

Source: Central Institute of Fishery Technology, Kochi

Surimi

When fish flesh is separated from bones and skin, it is called minced fish which forms the starting material for surimi production. Surimi is the Japanese term for minced fish. When minced fish is water washed to remove water soluble components and fats it becomes raw surimi. The raw surimi which is a wet concentrate of myofibrillar proteins possesses enchaned gel forming, water holding, fat binding capacities compared to the minced fish. These functional properties are reduced rapidly once it is frozen. In order to maintain the functional properties, the raw surimi is mixed with cryoprotectants such as sugars or alcohols and are quick frozen in blocks and stored. These compact blocks are convenient to handle and can be economically transported. This frozen surimi becomes the raw material for manufacture of surimi based products. The raw surimi is ground with salt and other ingredients, then extruded, fiberised or composite moulded depending upon the final products and finally heated to set the shape, develop the texture and pasteurize the products. The type of heat treatment used is altered to vary the flavour, texture and appearance desired in the final products and may include steaming, broiling, boiling and deep fat frying.

Surimi manufacturing process

The widely used technique for surimi manufacture is the modified version of rotary rinser/screw press method. This has evolved through successfull cooperation among fish technologists, processors and fishing companies. The factors that must be considered and controlled to ensure good quality surimi is given below:-

1. Freshness is the most important requirement as it affects the gel forming capacity of the surimi. The fish should always be kept at a temperature below 0 o C and processed within 2 days of catch.

2. The catch has to be sorted out for the target species and size manually. This sorting will improve processing speed and yield of fillets. Washing and scaling should be done simultaneously.

3. Filleting will influence the quality and quantity of mince. Filleting involves - decapitation evisceration and excision of the backbone yielding a boneless fillet. The presence of viscera gills, heart etc. will affect the quality of surimi and therefore should be removed.

4. The most common meat separator is a belt drum type. The diameter of the holes chosen for the roller greatly influences the subsequent leaching and dewatering process, yield and ultimately the quality of the surmi. As per the size and freshness of the fish the hole diameter is chosen and it generally ranges from 4-7 mm. In order to increase the efficiency of thermal separation the fillets should be placed in such a way that maximum surface area of the meat is in contact with the drum.

5. Leaching in fresh (non-salt) water is carried out to remove water soluble matter, lipids and blood. This improves the colour, flavour and the gel strength of surimi. Although the optimal time varies with the freshness of the raw material, water temperature and size of the meat particles, 15-20 minutes for the entire leaching process is usually regarded as appropriate for any commercial operation. Two washings are generally regarded adequate from the gel strength point of view. The pH of the wash water should be adjusted to 6.5 to 7.0 to ensure maximum functional performance of fish protein. The temperature of the wash water should be 3-10 o C to recue microbial proliferation and protein denaturation.

6. The amount of water required for washing will be (10-20) times the amount of mince, in shore based units. The final intermediate dewatering is carried out to keep the moisture content around 90%. The fine particles lost from the screens and screen press during intermediate dewatering can be recovered using centrifugation.

7. Refining of the partially dewatered and leached mince is carried out to remove the connective tissues, skin scale or any undesirable inclusions using a strainer. Of late, refining is done prior to final dewatering.

8. Final dewatering is done by screw press for reducing water content to about 80-94%.

9. Blending of cryoprotective agents helps to stabilise fish proteins from freeze denaturation and frozen storage.

Curing is the traditional, cheapest and oldest method offish preservation in our country. As such, curing remains the only cheap and acceptable method of making fish available to the rural poor, in the interior parts of the country. For the same reason, curing still continues to be an important method of fish processing, but, by and large, the people engaged in curing are a bit reluctant to adopt scientific methods of processing.

The CIFT Research Centre at Calicut has standardised method for preparing good quality cured fish, a brief outline of which is given below.

The fresh fish landed is immediately washed in clean seawater to remove slime, adhering dirt, etc. These are then taken to the fish-curing yard where very strict care is to be taken to maintain hygienic conditions and quality of material. Unlike in the traditional method, all further processing work should be done on carefully cleaned tables to avoid contamination with sand, dirt etc. It is advisable to use water chlorinated up to 10 ppm. for all these cleaning operations.

The dressed fish is then washed in good quality water and the water is allowed to drain completely. After complete draining, the fish is taken to the salting table where good salt is applied to the fish uniformly by hand. Care must be taken to keep the hands of workers clean for this operation. In general, the salt-to-fish ratio can be 1:4 (one part salt to four parts fish).

After salting, the fish is stacked in very carefully cleaned cement tanks and kept for at least 24 hours in these tanks. After this, the fish is taken out and just rinsed in fresh water to remove excess solid salt adhering to its surface. The salted fish is then dried in clean drying platforms. These can be either clean, raised cement platforms or bamboo lattices. Fish must be dried to a moisture content of 25% or below. At every stage, extreme care must be taken to maintain proper standards of hygiene.

Fish dried by this method is then dusted with a mixture of calcium propionate and fine powdered salt. This mixture can be made by intimately mixing three parts by weight of calcium propionate with 27 parts by weight of powdered salt. Care must be taken to see that the mixture is applied uniformly on all parts of the fish. After this, the fish can be packed in suitable weighed lots in sealed polythene bags for retail marketing. For wholesale marketing, the fish can be packed in polythene lined gunny bags. This type of packaging prevents excessive dehydration during storage as well as contamination with harmful bacteria. Generally one kg of this mixture is required for dusting ten kg of fish.

When the fish is soaked in water just before cooking to remove excess salt, this preservative mixture is also removed. This is thus a very safe, easy and effective method for preserving cured fish for a long time. Fish preserved by this method can be kept in very good condition for a minimum period of eight months.

Compared to the conventional cured product, which spoils within two months, this is thus a very good method of preservation.

1. The method is very simple and can be easily adopted by the common man.


2. It prevents contamination with halophylic and other harmful bacteria and enhances the storage life of the cured fish considerably.


3. The calcium propionate does not affect the colour, smell, or taste of the cured fish in any way.


4. It is comparatively a very cheap method. Considering the enhanced shelf life and increased price that can be realized by curing fish by this method, the slight increase in the cost of production can be treated as negligible.

Last updated: 16-1-2007