ANNEXURE I
Details of the process involved in Surimi production
The process - Raw surimi and surimi based products
When fish flesh is separated from bones and skin, it is called minced fish which forms the starting material for surimi production. 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. The process is explicity depicated in the flow diagram given below:-
FISH
Deheading and Gutting
Meat separation
MINCED MEAT
Washing
Straining
Dewatering
Raw Surimi
Mixing Cryoprotectants
Freezing into Blocks
FROZEN SURIMI
Grinding with Salt and Ingredients
Heat Processing
SURIMI BASED PRODUCTS
2. The 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 0o 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 3-10oC 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. The percentage of these additives are:-
Sugar - 4% Sorbitol - 4-5% Polyphosphate - 0.2-0.3% (cryoprotective additive) The actual quantities of the above ingredients/cryprotectants should be uniformly dissolved and dispersed using a blending apparatus. Quality filling and freezing into blocks, are done by automated machines. The equipment is operated in such a manner so as to obtain a block center at (-) 25oC or below. The blocks thus obtained are stored and shipped preferably at - 25oC. Surimi is normally traded in 10 kg. frozen blocks which are individually wrapped in waxed cardboard boxes. |
