Aquaculture, which now accounts for almost half of all the world’s food fish, is one of the fastest-developing sectors in the world. Aquaculture is growing, and there is an increasing demand for aquafeed. The aquafeed making industry is the most promising in the world. Two types of aquafeed processing technology can be used in feed pellet production: extrusion (can produce floating or sinking extruded aquafeeds) as well as pelleting (mainly produces sinking aquafeeds). What is extrusion? What is extrusion? Is pelleting or extrusion better? These questions will be answered by comparing the two technologies in this article.
Aquafeed: Introduction
Aquafeed pellets are made from a variety of ingredients that have been pelleted or extruded according to the compound diet. They are good in shape, full gelatinization, and high levels of protein. You can also divide fish feed into three types based on their buoyancy: floating, slow sinking, and sinking. Floating aqua feed can be used for Tilapia, Crucian, Ranidae, Weever, and sinking aquatic for Siganus Guttatus feed.
Fish feed’s nutrient component consists primarily of protein, starch (sinking and floating aquafeed each contain more than 10%), crude fat, crude ash, vitamins and minerals. Protein is a source of energy and helps build muscles. Vitamins and minerals can increase natural resistance and feed conversion rates. Starch can be gelatinized at high temperatures and high humidity. It can increase the stability and extrusion density extruded aquafeeds.
Extruded fish feed: Merit and demerit
Extruding technology has become a very popular and widespread method of producing various types of feed. Extruding technology is widely used in the production of various feed types. Fishes should be fed according their feeding habits. Feed should remain in water for a certain amount of time so that fish can eat. The above mentioned features can only be achieved by extruding technology. The extruded fish food has an incomparable superiority. It is low in pollution, high efficiency and high conversion. This plays a crucial role in improving the digestive utilization ratio.
Extrusion can be influenced by heat, humidity, pressure, and other mechanisms. These actions can increase starch gelatinization, soften and damage the fiber cell structure, and release some digestible substances, which in turn boosts digestion and utilization.
Extrusion can be facilitated by moderate heat treatment to passivate proteinase inhibitors (like antitryptase and urease), eliminate side effects, kill germs in raw materials, and modify the property of protein molecules to increase contact with enzymes in fish bodies. This makes fish feed more digestible.
Extruded feed can reduce the amount of cottonseed or gossypol, which has a better detoxification effect. It is easy to monitor and control fish feeding because of its stability in water for up to 12 hours.
Extruded aqua feed is no exception. There are always two sides to every situation. Extruded aqua feed is more popular than pelleted aqua food and it’s manufacturing process is accepted by many feed plants. However, the initial investment for production line is larger which scares many fish farmers or feed businesses.
Advantage and disadvantage of pelleted aquafeed
Pelletized feed offers a number of benefits in terms of production, including low investment costs, high yield, low unit cost, quick capital return, and low production charges. Pelletized feeds are also easier to transport, store and package than unprocessed grain feed and natural food. Pelleted feed is a low-cost feed that has a high feed coefficient. This makes pelleted feed a good choice for fish farmers. They not only grow well, but also produce mixed-culture fish (like silver carp or dace). Good growth.
Pelleted feed has its flaws, just like every coin has two sides. Because of the low profit per unit, it is difficult for feed plants to make money. Pelleted feeds are more likely to sink in litter after being poured into water. This is bad news for fishes as many of them end up at the bottom. Statistics show that between 10% and 15% of pelleted feed is wasted because it sinks quickly, polluting the water quality, which in turn affects the ecological environment.
Feed cost is also an issue. Many nutrients get dissolved in water, which results in lower original feed quality. This is a major problem with aqua feed technology.
Extrusion and Pelletting
- Extruded aquafeed pellet making process: grinding-mixing-extrusion-drying-coating-cooling
- Pelleted feed making process: grinding-mixing-pelleting-drying-coating-cooling
The only difference is evident and we will now introduce extrusion or pelleting.
Extrusion
Extrusion, a heating process that uses high temperatures for short periods of time (HTST), reduces the loss of nutrients and improves the digestibility of proteins and starches. The fish feed extruder is a machine that can be used to process floating or sinking aquafeed. Extrusion is more difficult than pelleting because it requires higher levels for moisture, heat and pressure. To allow the feed to expand as it leaves the die, temperatures must be higher than 100 Wet extrusion is one type of extrusion. Dry extrusion is another. Dry extrusion produces high temperatures by dissipating mechanical energy from heated surfaces like barrel and screw surface or through shear forces between wall, material and screw and matter. Preconditioning and steam injection are used to achieve the desired temperature for wet extrusion. The material is also subject to high pressure. The extrusion will occur due to the pressure difference between the extruder’s interior and the outside environment. The material is compressed through the die holes in the barrel of the extruder. As the superheated dough heats up, some of the water evaporates immediately and causes expansion. Wet and dry types of fish feed extruders are the most popular machines for pellet extrusion.
Pelleting
The process of reducing small particles to a larger solid using heat, moisture and pressure is called “pelleting”. These dense pellets, which sink quickly in water, are larger homogenous particles that have formed from small ingredients. The professional aquafeed pellet mill is called the ring die.
Ingredients characteristics, steaming or moisturizing before pelleting, die thickness, binders, etc. are the main factors that affect pelleting.
- The amount of fat, starch and fiber in the formula will have an impact on the quality of pelted feed. Certain ingredients can reduce the pellet’s resistance to water and crumbling.
- Fish feed formulas often include additives that are primarily used as pelleting aids. This helps to reduce fines and increase water stability.
- Steam can be added to the ingredients for starch gellatinization during pelleting. This is conducive to ingredient binding. A steam addition is usually made to the mash to raise its moisture to around 16% and the temperature to 85 before it passes through the pellet die.
As you can see, extrusion has higher levels of heat and moisture than pelleting. The mixture of finely ground ingredients may be precooked or conditioned with steam before being put into the extruder. Extruded feeds have a greater degree of starch gelatinization and are therefore more stable than pellets.
Wet and Dry Extrusion
Extrusion technology can produce different sizes and shapes of aquatic feed. Extrusion using steam preconditioning, is known as “wet extrusion”, and extrusion without steam conditioning is called “dry extrusion”.
Preconditioning is an important part of wet extrusion. It allows steam or water to be injected into the conditioner or extruder barrel. Preconditioning, cooking, and die shaping are the core of an extruder machine’s operation. High pressure and high temperature can kill salmonellosis, bacterial infections, and make pellets easy to digest. For large-scale production of high quality pellets, wet extruders are often used.
Dry extrusion uses lower moisture levels without the need for preconditioning. Dry extrusion is ideal for processing low-moisture and high-fat feed material in small to medium-sized production.
Wet and dry type extruders are both equipped with either one or two screws. Twin-screw refers to two identically long screws that are placed within the same barrel. Twin screw extruders are built on single screw extrusion machines, which are more complex than single screw extruders. Twin screw extruders cost more to maintain and are more expensive than single-screw ones. Hot fish feed Extruders can be either dry or wet type fish feed extruders. They are both single screw extruders that are simple to use and require little training.