WO1997022265A1

WO1997022265A1 - Fish feed and process for preparing the same

Info

Publication number: WO1997022265A1
Application number: PCT/SE1996/001653
Authority: WO
Inventors: Erik Jönsson; Kristine Nilsson
Original assignee: Sveriges Stärkelseproducenter, (Förening Upa)
Priority date: 1995-12-15
Filing date: 1996-12-13
Publication date: 1997-06-26
Also published as: SE9504489L; SE505003C2; SE9504489D0; AU1155597A

Abstract

Fish feed in the form of pellets is described. The fish feed has been made quick-sinking by coating the surface of the pellet with a cold-water-soluble starch. A process for preparing the fish feed is also described, in which a fish feed mixture of prior-art type is extruded to a pellet, the surface of which is then coated with a cold-water-soluble starch.

Description

FISH FEED AND PROCESS FOR PREPARING THE SAME

The present invention relates to a quick-sinking fish feed in the form of pellets, a process for preparing the same, as well as a process for increasing the sinking speed of fish feed. Breeding of fish, preferably salmonids, i.e. salmon of various kinds, takes place, after setting out, in open seawater. The fish is kept confined in large net bags, and foddering takes place by feed pellets being distri¬ buted at regular intervals on the marked-off surface of water. The fish eats the feed pretty soon after the dis¬ tribution, as a rule when the feed begins to sink.

The size of the pellets depends on the size of the fish. Just after setting-out, in the so-called s olt stage, pellets having a diameter of about 2-3 mm are fed. The mesh size of the enclosing net is greater than the diameters of the pellets.

The greater part of all fish feed is at present produced by so-called extrusion. Fish feed contains a large amount of protein and fat, since these nutritive substances are the best sources of energy for the fish. Fish feed may have, for instance, the following approxi¬ mate contents of nutritive substances:

46% by weight protein 26% by weight fat 12% by weight carbohydrates

8% by weight ashes

8% by weight water

The ratio of protein to fat may vary depending on age and size of the fish to be fed. The fat content usually is slightly more than 30%.

It has been found that pellets, the diameter of which is < 4 mm, have difficulty in sinking, especially in the cold time of the year when the density of water is at its maximum. The reason why the feed does not sink is its low intrinsic weight and the too high surface ten¬ sion. If the fish does not have time to catch the feed, the pellets will be moved by the waves of the sea through the meshes out into the free water. This is on the one hand an economic problem and, on the other hand, an envi¬ ronmental problem.

NO Patent Specification 911,946 discloses a method of modulating the sedimentation speed of dry fish feed pellets by admixing to the pellets a surface-active agent, selected among certain fatty acid esters having an HLB value (hydrophilic-lipophilic balance) of not less than 12 so as to increase the sedimentation speed of the pellets and certain fatty acid esters having an HBL value of less than 8 to decrease the sedimentation speed of the pellets.

The present invention provides a new and simple pro¬ cess of pronouncedly increasing the sinking speed of fish feed in the form of pellets of the above-mentioned type, whereby they are not affected by the waves of the sea. The problem is solved by coating the surface of fish feed pellets with a cold-water-soluble starch which has the capability of quickly absorbing cold water and swell¬ ing. This results in a quicker wetting of the surface, while the starch has the capability of forming "lumps of gel", which in turn increase the weight of the feed pel¬ let.

The invention thus provides a quick-sinking fish feed in the form of pellets, which is characterised in that the surface of the pellet is coated with a cold- water-soluble starch.

The invention also provides a process for increasing the sinking speed of fish feed in the form of pellets, said process being characterised in that the surface of the pellet is coated with a cold-water-soluble starch. Finally, a process for preparing a quick-sinking fish feed in the form of pellets is provided, a mixture of protein, fat, carbohydrates and optionally one or more additives selected from the group consisting of vitamins, minerals, colorants, being extruded to a pellet, said process being characterised in that the surface of the pellet is coated with a cold-water-soluble starch. Fish feed generally comprises protein in the form of e.g. fish meal, fat, carbohydrates and optionally other additives, selected among vitamins, minerals, colorants etc.

As mentioned above, the main part of the fish feed is present in the form of pellets which are prepared by so-called extrusion. The extrusion is principally carried out in the following manner:

The dry ingredients are mixed. Immediately before or during the extrusion, part of the fat and water are added, such that the fat content during extrusion is between about 15 and 20% by weight and the water con¬ tent is slightly above 20% by weight. In the extruder, the material is subjected to vigorous mechanical working in combination with high pressure and high temperature. This treatment results in an expanded feed of high melt- ability. At the end of the extruder there is arranged a nozzle, through which the material passes, and after that, a rotary cutter which cuts the material to a suit¬ able size. By varying the size of the nozzle and the speed of the cutter, the size of the feed pellets can be adapted to the fish to be fed. Immediately after extru¬ sion, the pellets are dried, whereupon the remaining amount of fat is added, either by immersion in a hot oil bath or by spraying. Finally the pellets are cooled. So far, the preparation of the pellets according to the invention conforms with the preparation of pellets that are known hitherto.

With a view to providing the pellets according to the invention, the surface of the pellets is to be coat- ed with a cold-water-soluble starch. This can take place either simultaneously with the completing supply of fat after extrusion, or in a separate stage after that. The actual coating operation can be carried out in different ways. During so-called coating, the pellets are coated with a suspension of starch particles in oil. A further method is so-called dusting, in which the pellets are shaken together with particulate starch.

There are different manners of physically modify¬ ing starch for the purpose of obtaining solubility in cold water. The selection of method of preparation and starch raw material is not decisive of the function of the starch product in the invention.

When a plant produces starch molecules, these are successively stored around a centre, the so-called hilum, and form a firmly packed granule consisting of amorphous and crystalline regions. The molecular composition of the starch is heterogeneous. Normal starch is composed of two types of molecules. The one, amylose, is essentially linear and consists of 100-10000 glucose units. The other type of molecule, amylopectin, is considerably bigger and very much branched. Amylopectin consists of about 100,000 glucose units. Normal starch consists of about 20% amy¬ lose which forms the amorphous parts in the granule, and about 80% amylopectin which forms the crystalline regions. In order to make starch in granular form hydra- tise and swell, water and heat are required. The access to water is decisive of the temperature at which the starch dissolves.

In drum drying, the starch is preboiled, thereby swelling and being dissolved. Subsequently, the product is dried on drum driers to an amorphous powder. This powder can be ground down to various grain sizes and then has the property of swelling when treated with cold liquids.

For further improvement of the water absorbency of the starch product, it can be modified chemically before drum drying. Suitable modifications are esterification and etherification, see "Specifications for identity and purity of certain food additives" issued by JECFA, Joint FAO/WHO Expert Committee on Food Additives.

The amount of cold-water-soluble starch on the sur¬ face of the pellets can be within a range of 1-5%, pre- ferably 2-3%, based on the weight of the pellet.

The invention will now be described with reference to the following, non-limiting Examples.

EXAMPLE 1

Feed pellets consisting of 60% fish meal (protein) 30% fat, 3% binder (starch) and the balance being vita¬ mins, minerals and colorants, were prepared by extrusion in conventional manner.

As cold-water-soluble starch use was made of an esterified, drum-dried starch product. The pellets were coated with starch in a coating operation.

5-15% of the cold-water-soluble starch was added to fish oil. A suspension was formed by stirring and heating in a water bath to about 60°C.

Fish feed pellets in the size of 3 mm were supplied to a net basket. The basket was placed in a vessel. The oil suspension prepared as described above was poured over the pellets. The basket with the pellets is retained in the vessel during continuous stirring for 2 min. Sub¬ sequently, the basket is removed and excessive oil sus- pension is shaken off. The pellets are removed from the basket and spread on an absorbing base for air drying.

A re-checking indicates an absorption of starch of about 1-2% based on the weight of the pellets.

EXAMPLE 2 The same starting products as in Example 1 were used, but the starch was applied by so-called dusting.

Fish feed pellets were placed in a mixing vessel. 2% cold-water-soluble starch, based on the weight of the pellets, was added by dusting. The vessel was shaken for 5 min, whereupon the pellets were moved to plastic bags to be stored. EXAMPLE 3

The sinking speed of pellets according to the inven¬ tion was examined in two different ways. Water-soluble starch was applied by the above-described coating tech- nique. The pellets had a size of 3 mm. The results ac¬ counted for are an average value from 10 measurements.

Test 1

20 pellets were applied very gently to the surface of a 4% salt solution. The temperature of the salt solu- tion is not allowed to exceed 7°C on the occasion of eva¬ luation. Also the pellets that are to be tested must be cold and are therefore taken directly from a refrigerator immediately before testing. As reference sample, use was made of the same type of pellets, however with no coating of starch.

It was then registered how many per cent of the pel¬ lets are still floating after 20, 40 and 60 s, respec¬ tively. The smaller amount that floats the better the result. The result is shown in Table 1 below.

Table 1

Remaining amount of feed that has not sunk

Time Reference Pellets containing esterified, pellets drum-dried starch product

20 s 100% 18%

40 s 96% 2%

60 s 82% 0%

Test 2

200 pellets according to the invention were released from a height of 10 cm into a 4% salt solution. The tem- perature of the salt solution is not allowed to exceed

7°C on the occasion of evaluation. Also the pellets that are to be tested must be cold and are therefore taken directly from a refrigerator immediately before testing. As reference sample, use was made of the same type of pellets, but with no coating of starch.

It was then registered how many pellets that are still floating after 5 s. The results are shown in Table 2 below.

Table 2

Remaining amount of pellets that has not sunk

Time Reference Pellets containing esterified, pellets drum-dried starch product

5 s 20% 2%

Claims

1. A quick-sinking fish feed in the form of pellets, c h a r a c t e r i s e d in that the surface of the pel¬ let is coated with a cold-water-soluble starch.

2. The fish feed as claimed in claim 1, c h a r ¬ a c t e r i s e d in that the starch has been made solu¬ ble in cold water by physical and/or chemical modifica- tion.

3. The fish feed as claimed in claim 2, c h a r ¬ a c t e r i s e d in that the starch is esterified or etherified starch.

4. The fish feed as claimed in one or more of claims 1-3, c h a r a c t e r i s e d in that the cold-water- soluble starch is present in an amount of 1-5% based on the weight of the pellet.

5. The fish feed as claimed in one or more of claims 1-4, c h a r a c t e r i s e d in that it contains, in addition to the starch, protein, fat, carbohydrates and optionally one or more additives selected from the group consisting of vitamins, minerals, colorants.

6. A process for increasing the sinking speed of fish feed in the form of pellets, c h a r a c t e r i s - e d in that the surface of the pellet is coated with a cold-water-soluble starch.

7. The process as claimed in claim 6, c h a r a c ¬ t e r i s e d in that the surface of the pellet is coated with starch which has been made soluble in cold water by physical and/or chemical modification.

8. The process as claimed in claim 7, c h a r a c ¬ t e r i s e d in that the surface of the pellet is coat¬ ed with esterified or etherified cold-water-soluble starch.

9. The process as claimed in one or more of claims 6-8, c h a r a c t e r i s e d in that the surface of the pellet is coated with a cold-water-soluble starch in an amount of 1-5% based on the weight of the pellet.

10. A process for preparing a quick-sinking fish feed in the form of pellets, a mixture containing pro- tein, fat, carbohydrates and optionally one or more additives selected from the group consisting of vita¬ mins, minerals, colorants, being extruded to a pellet, c h a r a c t e r i s e d in that the surface of the pel¬ let is coated with a cold-water-soluble starch.

11. The process as claimed in claim 10, c h a r ¬ a c t e r i s e d in that the surface of the pellet is coated with a suspension of the cold-water-soluble starch in oil.

12. The process as claimed in claim 10, c h a r - a c t e r i s e d in that the surface of the pellet is coated by dusting of particulate cold-water-soluble starch onto the surface.

13. The process as claimed in one or more of claims 10-12, c h a r a c t e r i s e d in that the surface of the pellet is coated with a cold-water-soluble starch in an amount of 1-5% based on the weight of the pellet.

14. The process as claimed in one or more of claims 10-13, c h a r a c t e r i s e d in that the starch has been made soluble in cold water by physical and/or che- mical modification.