HK1023912B - Method for continuous production of dry feed for fish and shell fish - Google Patents

Description

Continuous production method of dry feed for fish and shellfish

Technical Field

The invention relates to a method for the direct production of dry feed for fish and shellfish (Crustacea) on the basis of fresh fish raw material.

Background

Presently, rearing of various fish and shellfish is a rapidly expanding business, and a growing trend is expected in many countries. Different types of fish and shellfish require different types of feed, but generally high levels of fish protein and fish oil are required for many types of fish and shellfish. Fresh fish or fresh fish waste has previously been used to produce fresh fish feed. One breaks down the fish or fish waste into small pieces, mixes them with various dry additives such as cereal products, various protein additives such as fish meal or animal blood meal, and then granulates the mixture. The moisture content of the resulting pellets was 40%. However, the shelf life of feeds with such high water content is limited.

Most fish feed found on the market today is produced from various dry materials, wherein the fish protein is present in the form of fish meal. During the production of fish meal, fresh fish or fish waste is heated to about 90 ℃ so as to release water and fish oil. During this heating the protein is denatured, i.e. its various functional qualities are destroyed. After heating, the fish material is mechanically separated in several steps, first of all free moisture and oil are removed from the fish material in a sieve, after which further dewatering and defatting are carried out in a screw press. The water from the sieve and the press is clarified in a decanter, and the solid phase separated in the decanter is added to the filter cake. The aqueous phase from the decanter is separated in a separator into fish oil and fish juice. In order to obtain the best possible separation of the fat, the temperature is kept around 90 ℃ during these processing steps. After separation, the fish juice is concentrated to a dry matter content of 35-40% by evaporation in a falling film evaporator. Mixing the concentrated fish juice with the filter cake, and drying the mixture in a directly or indirectly heated dryer until the water content is 6-10%. The total production time to finished fish meal is around 3-4 hours, while fish meal and fish oil are subjected to a number of thermal effects during conventional production.

The fat content in the finished fish meal should be below 12% according to international standards, but this content is usually still somewhat lower. In order to reduce the thermal effect, so-called LT (low temperature) -powders are currently sold. The powder is dried under vacuum at a temperature of 75-80 deg.C.

When producing fish feed from fish meal, various processes are used, wherein the shaping of the pellets is carried out in a granulator, such as the California type, or through a hot extruder, wherein the material is cooked. The most modern method is by extrusion. In both processes, a dry mix having the desired composition of fish meal and fish oil, or various protein sources, cereals and vitamins, pigments and other materials is started. If the shaping is carried out by means of extrusion, water is added to the dry feed mixture in order to obtain a homogeneous composition. To force the starch in the grain to gelatinize, steam is introduced into the mixture. During the subsequent extrusion, a high pressure was built up in the product mixture, while the temperature rose to about 120 ℃. When the pressure of the product after passing through the extruder is reduced and part of the water evaporates when the formed pellets expand, the pellets obtain a porous structure which can absorb oil. Upon subsequent coating with oil, the fat content of the feed product may increase to 20-30%. The water content after extrusion is still high, 20-30% and the increasing part of the oil is dried by hot air at a temperature of 50-100 ℃. The moisture content of the finished product is less than 10%.

As the pellet formation is carried out in the pelletizer, the mixture is rolled through a die plate, a circular disk having a plurality of tapered openings. The feed mixture is pressed through the openings by rollers having a high pressure and the formed pellets are pressed into a firm and solid product. The stability of the particles depends on the strength of the particles when pressed together. The fat content of the feed mixture during shaping should not be too high, since too high an oil content would weaken the compression force. The particles will be firm after compression, i.e. the ability of the particles to take up oil during subsequent coating will be limited. The maximum fat content of the granules, when they have sufficient mechanical strength, is about 18%.

Fish meal is first produced from fresh fish material according to current technology. The production of fish meal generally requires low levels of fat in the fish meal. To do this, attempts have been made to reduce the amount of fish oil in fish raw materials during the production of fish meal.

In contrast, in the production of fish feed, it is desirable to produce a product with a high fat content, during which process a large amount of fat is added to compensate for the low fat content in fish meal.

During extrusion, the feed mixture must have a certain moisture content in order for this processing step to be carried out in the most desirable way. The water content of fish meal has earlier been dried to about 10%, which has been detrimental to the colloidal binding and the nutritional value of the protein. The moisture content of the feed product is dried to a maximum of 10% by temperature effect after extrusion, which also has an effect on the quality of the protein.

Disclosure of Invention

It is an object of the present invention to produce fish feed directly from fresh fish raw material, avoiding the intermediate steps of producing fish meal.

WO 96/01058 suggests producing fish feed directly from fish raw material by mixing the intermediate product from fish meal production with a concentrated solution of fish juice to form a mixture product at a temperature of 20-120 ℃ and then drying the mixture. According to this specification, the feed produced consists purely of fish.

According to the present invention we propose a method for producing dry feed for fish and shellfish from fresh fish raw material, which comprises subjecting the raw material to mild treatment during all the processing steps for making said feed product, but at the same time fulfilling as much as possible the specific requirements which can be accommodated for different species of fish and shellfish.

The method according to the invention is mainly characterized in that: cooked (already pasty) vegetable carbohydrates are added to the fresh fish raw material during production, together with other additives such as minerals, vitamins and binders, to give a feed with a carbohydrate content of at least 5%. The water content in the fractions containing fish protein during all processing steps to make the feed pellets is over 10%, wherein the prepared dry feed contains 25-60% protein, 10-40% fat and 5-25% carbohydrate, wherein the feed contains 25-60% fish protein and up to 40% fish oil. According to the proposed method, the production of dry feed is performed in a manner that avoids the use of unnecessary drying steps, resulting in a feed product with a higher nutritional value. Since the moisture content is never below this value, the protein is preserved in a colloidal state.

The vegetable carbohydrate products consist of various types and amounts of cereals which are metabolized by the fish fed by the feed.

The proposed method is preferably carried out by: heating a fish feed obtained from raw fish material to a temperature at which pasteurisation/sterilisation takes place and separating the fish feed into at least two parts: a liquid phase and a solid phase. The solid phase containing fraction is dehydrated to a moisture content of at least 10% during a low thermal effect and the liquid fraction is concentrated to a moisture content of 20-80%. The concentrated liquid fraction is mixed with the dehydrated solid phase, fish oil and predetermined amounts of various carbohydrate-containing products, possibly with additional protein sources and other various additives. The obtained mixture is mixed together in the emulsification step to obtain a homogeneous mixture having a moisture content of 10-40%. The resulting mixture is granulated and the granules are dried in a final drying step with low thermal effect to a moisture content of 6-10%.

By means of this method, fish feed of high quality is obtained both in terms of bacterial content and functional quality, due to the open pasteurisation or sterilisation. Both bactericidal and enzymatic inhibition occur during this processing step. Since the dehydration of the solid phase and the concentration of the liquid fraction take place separately, various optimal conditions for these measures will be achievable.

According to the method of the invention, the production of feed takes place in a short time, and therefore has less temperature effect on the nutrients in the fish. The drying step according to the invention is completed within a few minutes, whereas the total drying time may be several hours during the conventional production of fish feed. According to the present invention, the temperature effect is minimized. The method also saves energy and equipment.

The separation of the fish material is usually performed in such a way that three fractions are obtained, namely fish oil, fish juice and a solid phase. The fish oil is separated in the form of a separate phase during the separation means that the fraction is not subjected to any further heat treatment, thereby avoiding the risk of compromising the quality of the fish oil. If appropriate, the separation is carried out in two steps, i.e. the fish material is first separated into a liquid and a solid fraction in a decanter, after which the liquid fraction is separated into fish juice and fish oil in a high-speed separator.

According to the invention, fish oil is emulsified into the mixture to be granulated. Fat is added in conventional feed production mainly by coating the prepared granules. This results in the fish oil being released immediately during feeding and collecting on the surface of the water.

If it is desired to produce a fish feed with a low ash content, the raw material of the fish is passed through a device called "deboner" in which the skeleton, skull bone and gill cover (lock) of the fish are removed.

If appropriate, the fish raw material may be finely divided before heating. Small particles transfer heat better and faster. If such fine grinding is performed, then an antioxidant should preferably be added prior to heating to avoid rancidity of the fat.

In order to be able to control the final composition of the dry feed, the protein content, the fish oil content and the ash content of the finely ground fish raw material must be analyzed. Such analysis can be performed by using GSM (guided microwave spectrometry) or MIR (mid-infrared) systems. Both methods are fast enough to be used in a continuous system. The results of the analysis can be used to determine the amount of protein and fish oil that needs to be added to the fish feed.

The fish feed is preferably heated to 95 ℃ over a period of 120 seconds. This is done to sufficiently kill bacteria while minimizing the thermal effects on the fatty acids in the fish protein and fish oil.

The concentrated fish juice and fish oil and various additives are preferably mixed in a first mixing operation to a homogeneous emulsion. In a second mixing step the emulsion is mixed with the carbohydrate product and homogenized to a pasty mixture. In a third mixing step, the dehydrated solid phase, and possibly additional proteins and taste imparting substances, is added to the pasty mixture. The resulting mixture containing all the components was pelletized by passing through a semi-dry low pressure extruder.

The granules prepared according to the present invention may be coated with a taste-enhancing substance such as cuttlefish extract or other substances.

Drawings

The method according to the invention is further described with reference to the accompanying drawing, which shows a flow chart of the method according to the invention as an embodiment.

Finely grinding whole fish, fish waste or finely divided fish having a moisture content of 65-75% with added antioxidant, feeding into an indirectly operating scraped surface heat exchanger and heating to a predetermined extent.

After the desired heat treatment (which may also be a pasteurization or sterilization treatment) the fish material is fed to a separator, preferably a decanter with a horizontal axis, in the embodiment shown in the drawing the fish material is separated into two phases, one liquid and one solid. The liquid fraction is sent to a high-speed centrifugal separator and separated into fish juice and fish oil. A three-phase decanter may also be employed if desired.

Preferably, the fish-juice phase from the second separation step is evaporated in a falling-film evaporator or plate heat exchanger to a moisture content of 55-65%. If desired, the concentration can also be carried out by ultrafiltration. The solid phase from the first separation is dried rapidly and gently to a moisture content of 10-20%, which ensures that the functional quality of the protein can be preserved in an optimal manner.

Mixing the concentrated fish juice with fish oil and various trace components such as vitamins, pigments and emulsifiers at 60-90 deg.C. The mixture is emulsified to a homogeneous liquid phase and then mixed with a highly gelatinized cooked starch to form a paste-like mixture.

Mixing the semi-dry solid phase obtained after drying with the liquid phase which has been made into a paste-like mixture. The obtained mixture has a water content of 20-30% and contains 25-32% fish oil (based on dry matter) which is incorporated in the mixture.

The use of such a mixture simplifies the granulation process and can be carried out in an apparatus similar to that used to form soft granules (so-called wet or semi-dry granules). Where the mixture is pressed through an open disc with blades to form granules. This shaping process results in particles of the desired diameter and length. Granular feed products for smaller fish are usually produced by crushing the granules followed by sieving to the desired particle size.

The formed pellets are then dried to a moisture content of 6-10% to obtain a storage stable feed product. The shaped particles have sufficient mechanical strength to retain their shape during shipping and handling. They also have the correct sinking rate and fish oil is not released during feeding, since most of it is emulsified into the product.

If desired, a higher fish oil content can be obtained by coating after the particles have been formed.

Detailed Description

In the method according to this embodiment, the processing time from the transport of the raw material of fish into the apparatus until the formed particles are dried is as short as 30 minutes or less.

The method according to the invention is further described in the following examples of material balance of a feed production process.

The term "dry matter" refers below to dry matter without fat.

1000 kg of fish material (herring) with a fat content of 11.9%, 70.2% water and 17.9% dry matter were placed in a scraped surface heat exchanger Contherm^TMIs heated to 95 ℃ within 120 seconds and the fish meal is then sent to a decanter. The fish meal is here separated into two parts, of which 364 kg of the solid phase fraction contains 3.8% fat, 62.1% moisture and 34.1% dry matter. The solid phase fraction was sent to a dryer where 198 kg of water was evaporated. 166 kg of dry solids fraction contained 8.3% fat, 17.0% moisture and 74.7% dry matter.

636 kg of liquid fraction from the decanter contained 16.5% fat, 74.9% moisture and 8.6% dry matter. This fraction is sent to a high speed centrifuge and is divided into three fractions: fish oil, fish juice and sludge. The amount of fish oil was 97 kg, with a fat content of 99%. 423 kg of fish sauce contained 0.8% fat, 7.6% dry matter and 91.6% moisture. The amount of sludge fraction was 117 kg, containing 4.5% fat, 76.3% moisture and 19.2% dry matter. The sludge fraction and the fish juice fraction were again mixed and sent to an evaporator where 359 kg of moisture were evaporated. 180 kg of the concentrated fish juice fraction contained 4.8% fat, 65.0% moisture and 30.2% dry matter.

97 kg of fish oil was mixed with 180 kg of concentrated fish juice and 6 kg of micro ingredients in the emulsification step. 444 kg of emulsified liquid contained 26.8% fat, 32.9% moisture and 40.3% dry matter. In the next mixing step, i.e. the gelling step, 74 kg of cereal having a moisture content of 10% were added. From this second mixing step 518 kg of a feed mixture containing 17.4% fat, 22.4% moisture and 60.2% dry matter was obtained.

The mixture is further homogenized and granulated in a shaping apparatus. The formed pellets were dried in a vertical drier to remove 113 kg of moisture. 405 kg of granules containing 29.5% fat, 10% moisture and 60.5% dry matter were obtained. On dry matter, ash was 7.4%, protein was 37.4%, and carbohydrate was 15.7%.

Claims (14)

1. Method for the continuous production of dry feed for fish and shellfish based on fresh fish raw material, characterized in that vegetable carbohydrate products and other additives are added to the fresh fish raw material during the production of the feed until the carbohydrate content of the produced feed is 5-25%, wherein the additives are selected from minerals, vitamins and binders, and the moisture content of the fractions containing fish protein is higher than 10% during all processing steps to make feed pellets, wherein the produced dry feed contains 25-60% protein, 10-40% fat and 5-25% carbohydrate, and characterized in that the feed contains 25-60% fish protein and up to 40% fat in the form of fish oil.

2. A method according to claim 1, characterized in that:

-heating fish feed obtained from raw fish material to a temperature at which pasteurization/sterilization takes place;

-separating the fish material into at least two fractions, a liquid phase and a solid phase;

-subjecting the solid phase-containing fraction to dehydration under low thermal effect with a mutual water content of at least 10%;

-concentrating the liquid fraction to a moisture content of 20-80%;

-mixing the concentrated liquid fraction with the dehydrated solid phase, fish oil, a predetermined amount of starch-containing product containing carbohydrates, other protein sources and other various additives;

-mixing the obtained mixture in an emulsification step to obtain a homogeneous mixture having a moisture content of 10-40%;

-shaping the obtained mixture into granules;

drying the shaped granules in a final drying step with low thermal effect to a moisture content of 6-10%.

3. A method according to claim 1 or 2, characterized in that the fish material is separated into three fractions: fish oil, fish juice and solid phase.

4. The process according to claim 1 or 2, characterized in that the separation is carried out in two steps.

5. A method according to claim 1 or 2, characterized in that the raw material of fresh fish is finely divided before heating.

6. A method according to claim 5, characterized in that an antioxidant is added to the finely divided fish mixture.

7. A method according to claim 5, characterized in that the composition of the finely divided fish mixture is determined on the basis of protein, fish oil and ash using rapid methods such as NIR, MIR and GSM, the determination data of which are used to control the addition of other protein sources, oils and carbohydrates.

8. A method according to claim 1 or 2, characterized in that the mixture of fish is heated to 95 ℃ within 120 seconds.

9. A method according to claim 1 or 2, characterized in that in the first mixing operation, the concentrated fish juice, the fish oil and the additives are mixed into a homogeneous emulsion.

10. Process according to claim 9, characterized in that in the second mixing step the emulsion is mixed with the carbohydrate product and homogenized to a pasty mixture.

11. The method according to claim 10, characterized in that in a third mixing step the mixture is mixed with the dehydrated solid phase, possibly together with additional proteins and taste substances.

12. A method according to claim 11, characterized in that the obtained mixture containing the total components is shaped into granules by semi-dry low-temperature extrusion.

13. A method according to claim 1 or 2, characterized in that the obtained feed pellets are further coated with a taste imparting substance.

14. The method according to claim 13, characterized in that the taste-imparting substance is selected from the group consisting of extracts of cuttlefish and the like.