Table of Contents
In modern animal husbandry and aquaculture, fishmeal, as a high-quality protein source, occupies a key position in feed formulation. It is rich in a variety of amino acids, vitamins and minerals required for animal growth, and has an irreplaceable role in enhancing the growth rate and immunity of farmed animals. The whole process of making fishmeal for feed is described in detail below.
Raw material selection and processing
Selection of raw fish species
Not all fish are suitable for making fishmeal. Usually, small high-protein fish, low-value fish with moderate fat content, such as sardines, herring, anchovies and so on, are chosen as raw materials. These fish are abundant in production, occupy a large proportion of fishery resources, and are relatively low in cost. At the same time, they have a high protein content, which can meet the protein content requirements for fishmeal production. In addition, like some deep-sea fish, though rich in nutrition, are generally not preferred as raw materials for large-scale fishmeal production due to their high fishing cost and relatively limited resources.
Freshness control of raw fish
Freshness is the key index to measure the quality of raw fish. In fresh fish, the protein, fat and other nutrients in the flesh have not been decomposed by microorganisms, which can ensure the high quality of fishmeal. When purchasing raw fish, we should judge the freshness by observing the appearance of the fish, the smell, the state of the eyes and other aspects. Fresh fish have glossy body surface, intact scales, full and prominent eyes and no odour. If the body of the fish shows discolouration, bad odour and loss of scales, it indicates that its freshness is not good enough to be used in the production of fishmeal. Once the raw fish is not fresh, it will not only reduce the nutritional value of fishmeal, but also produce harmful substances during processing, which will affect the quality and safety of the final product.
Cleaning and decontamination of raw fish
Before formal processing, the raw fish must be thoroughly cleaned and decontaminated. The purpose of cleaning is to remove sediment, microorganisms, parasites and other impurities attached to the surface of the fish to ensure the purity of fishmeal. When cleaning, the raw fish can be placed in flowing water, using mechanical mixing or manual brushing, comprehensive cleaning of all parts of the fish body. For some smaller, more impurity fish, you can also use multi-stage cleaning to further improve the cleaning effect. In addition to impurity is mainly for the internal organs of the fish body, gills and other easily deteriorated and affect the quality of fishmeal part. The internal organs and gills can be removed by manual or mechanical disembowelling, while attention should be paid to avoid breaking the fish gall bladder during the operation, because the bitter taste of the bile will affect the taste of fishmeal.
Steaming process
Purpose and principle of steaming
Steaming is an important part of fishmeal production process, its main purpose is to make the protein in the fish body denaturation and coagulation, destroy the enzyme system in the fish body, to prevent the protein from decomposition due to the action of enzymes in the subsequent processing, and at the same time also create favourable conditions for the subsequent pressing process. In the steaming process, the fish body absorbs heat, and the spatial structure of protein molecules changes from the original ordered state to a disordered state, thus losing biological activity. In addition, high temperature can kill most of the microorganisms on the surface and inside of the fish body, and improve the hygiene and safety of fishmeal.
Cooking equipment and parameter control
Common cooking equipment include steam cooking pot, continuous cooker and so on. Steam cooking pot has the characteristics of simple structure and convenient operation, which is suitable for small-scale fishmeal processing plant; continuous cooking machine has high production efficiency, which is suitable for large-scale industrial production. Regardless of the choice of equipment, it is necessary to strictly control the cooking temperature and time. Generally speaking, the cooking temperature should be controlled between 90 – 100°C, and the cooking time should be 15 – 30 minutes, depending on the type and size of the fish as well as the loading capacity. If the cooking temperature is too low or the time too short, the proteins cannot be denatured sufficiently, which will lead to difficulties in subsequent pressing and the quality of fishmeal can hardly be guaranteed; if the cooking temperature is too high or the time too long, although the proteins are denatured sufficiently, the fishmeal may have a burnt flavour, and the nutrients will be lost due to excessive heat.
Inspection of cooking effect
After steaming is completed, the steaming effect needs to be tested. This can be initially judged by observing the state of the fish body, which should show a uniformly cooked colour after steaming, with the muscle tissue becoming loose and easy to peel off from the fish bones. Simple physical tests, such as gently squeezing the fish by hand, can also be used to show that the steaming effect is good if water can be easily squeezed out and the fish flesh is smoothly separated from the fish bones. In addition, laboratory tests can also be used to analyse the degree of protein denaturation and microbial residues in the fish after cooking to further determine whether the cooking effect meets the requirements.
Pressing process
The role and principle of pressing
The main role of pressing is to separate the oil and water in the cooked fish body as much as possible, and at the same time, make the solid material get preliminary compaction. The principle is to use mechanical pressure to force the liquid components in the fish body to be discharged through the filter medium (such as filter mesh, filter cloth, etc.), while the solid material is retained. In this process, the oil and water in the fish body are squeezed out, which not only increases the protein content of the fishmeal, but also improves the storage stability of the fishmeal. Because too high oil content will lead to fishmeal is easy to oxidise and deteriorate in the storage process, affecting its quality and shelf life.
Selection and operation of pressing equipment
Commonly used pressing equipment include screw presses, hydraulic presses, and so on. Screw press pushes the material forward through the rotation of the screw shaft, exerts pressure on the material in the gradually narrowing space, and realises the separation of oil and water. Hydraulic presses, on the other hand, use the pressure generated by the hydraulic system to squeeze the material through the pressure plate. When choosing pressing equipment, comprehensive consideration should be made according to factors such as production scale, material characteristics and investment cost. In the operation process, attention should be paid to controlling the pressure and speed of pressing. If the pressure is too small, the oil and water separation is not complete; if the pressure is too large, it may lead to excessive crushing of solids, affecting the particle morphology of fishmeal. Generally speaking, the initial pressing pressure can be controlled at a low level, and then gradually increase the pressure until the desired pressing effect is achieved. The pressing speed should also not be too fast, so as not to cause material blockage or uneven pressing.
Treatment of pressing products
The products obtained after pressing mainly include press liquor (containing fish oil and water) and press cake (mainly solid materials, including fish meat, fish bones, etc.). The press liquor needs to be further separated from oil and water, which can be done by gravity settling, centrifugal separation and other methods. Gravity settling uses the difference in density between oil and water to gradually float the oil layer and sink the water layer, and then separates the oil and water through a liquid separation device. Centrifugal separation, on the other hand, makes use of the centrifugal force generated by high-speed rotation to separate oil and water quickly. The separated fish oil can be used as an important by-product for the production of fish oil health products, biodiesel, etc. The press cake then enters the subsequent drying process to further remove water and make fishmeal.
Drying
Purpose and importance of drying
Drying is an indispensable link in the process of fishmeal production, and its main purpose is to reduce the moisture content in the press cake to the level of safe storage, and the moisture content of fishmeal is generally required to be controlled at less than 10%. Reducing the moisture content can effectively inhibit the growth and reproduction of microorganisms, prevent mould and deterioration of fishmeal in the storage process, and extend the shelf life of fishmeal. At the same time, drying can also make the particles of fishmeal looser, which is convenient for subsequent crushing and packaging. If the drying is not thorough, the moisture content in the fishmeal is too high, which will lead to lumps, moulds and other problems in the storage process, seriously affecting the quality and use value of fishmeal.
Selection and characteristics of drying methods
Common drying methods include spray drying, vacuum drying, convection drying and so on. Spray drying is the liquid or slurry material through the nozzle into a mist, and hot air full contact, in an instant to complete the drying process. This drying method is fast and efficient, which can make the fishmeal keep better nutrient composition and particle form, but the equipment investment is larger and the energy consumption is higher. Vacuum drying is drying in a vacuum environment, by reducing the pressure, so that the moisture in the material at a lower temperature boiling evaporation. The advantage of vacuum drying is that it can be dried at a lower temperature to reduce the loss of nutrients, which is suitable for temperature-sensitive materials, but the drying time is relatively long and the production efficiency is low. Convection drying is the use of hot air and materials in direct contact, through heat conduction and convection of heat transfer to the material, so that the moisture in the material evaporation. Convection drying equipment is simple and easy to operate, but the drying process is prone to uneven drying of materials.
Optimisation and control of drying parameters
No matter which drying method is chosen, the drying parameters need to be optimised and controlled. Take spray drying as an example, the parameters that need to be controlled include inlet temperature, outlet temperature, feed speed, atomisation pressure and so on. The inlet temperature is generally controlled at 180 – 220 ℃, and the outlet temperature is about 80 – 100 ℃. Too high an inlet temperature may lead to overheating of the fishmeal surface and destruction of nutrients; too low an inlet temperature will result in low drying efficiency. The feeding speed and atomising pressure should be adjusted according to the performance of the equipment and the characteristics of the material to ensure that the material can be evenly sprayed into a mist and fully contacted with the hot air to achieve rapid drying. In the drying process, it is also necessary to monitor the moisture content of fishmeal in real time, and adjust the drying parameters in time according to the changes in moisture content to ensure that the moisture content of the dried fishmeal meets the requirements.
Crushing and quality inspection
The purpose and method of crushing
After drying, the fishmeal will usually form blocks or larger particles, which need to be crushed to make it a uniform powder, so as to facilitate better mixing and use in the feed. The main methods of crushing are mechanical crushing, such as the use of hammer mills and ball mills. Hammer mill through the high-speed rotation of the hammer head on the material impact crushing, with high crushing efficiency, particle size adjustment is convenient. Ball mill, on the other hand, uses the impact and grinding effect of grinding media (such as steel balls) to crush materials into fine powder. In the crushing process, the particle size of fish meal should be controlled according to the requirements of feed production. Generally speaking, the particle size of fishmeal used for livestock and poultry feed is required to pass through 80 – 100 mesh screen; the particle size of fishmeal used for aquatic feed is required to be even finer, and usually needs to pass through 100 – 120 mesh screen.
Quality inspection
Conduct quality inspection of fishmeal to ensure that it meets the relevant quality standards. The quality inspection items mainly include protein content, fat content, moisture content, ash content, amino acid composition, health indicators (such as heavy metal content, microbial content, etc.).
Packaging
Qualified fishmeal should be packed in time to prevent moisture absorption, oxidation and pollution. The choice of packaging materials is crucial, and should have good sealing, moisture resistance and light shielding. Commonly used packaging materials are plastic woven bags, composite plastic bags, aluminium foil bags and so on. Plastic woven bags are less expensive and stronger, but the moisture-proof performance is relatively poor, generally applicable to short-term storage or moisture-proof requirements are not high occasions. Composite plastic bags are made of a variety of materials composite, with good moisture resistance and sealing, is currently a commonly used material in fishmeal packaging. Aluminium foil bags, on the other hand, have excellent moisture-proof, light-shielding and barrier properties, which can effectively extend the shelf-life of fishmeal, but the cost is relatively high, and they are commonly used in the packaging of high-end fishmeal. In the process of packaging, attention should be paid to controlling the weight of packaging and sealing quality to ensure that the packaged fishmeal will not have leakage, moisture absorption and other problems during storage and transportation.
In summary, the production of fishmeal for feed needs to go through raw material selection and processing, cooking, pressing, drying, crushing, packaging and other links, each link has an important impact on the quality of fishmeal. Only by strictly controlling the process parameters and operation specifications of each link can we produce high-quality fishmeal to meet the demand for high-quality protein raw materials in animal husbandry and aquaculture.
