Foreword
Aquaculture is the fastest growing food industry in the world. According to the 1998 report of the Food and Agriculture Organization of the United Nations (FAO), the People's Republic of China is the world's largest producer of aquatic products. To make aquatic animals grow faster, you must first understand their nutritional needs and learn about feed production techniques. Of course, genetics, physiology, biochemistry and farming techniques are also important. Aquatic feed technology has progressed rapidly over the past 20 years. For example, aquafeed production has almost completely changed from steam granulation to extrusion curing. One of the many strengths of extrusion is the ability to make a floating feed so that the farmer can estimate how much feed the fish eats based on the amount of feed remaining on the surface. Overfeeding not only causes waste, increases production costs, but also pollutes the environment. Although extrusion will reduce the utilization of certain nutrients in the feed, it is still the first choice for farms. Farmers can see the feeding situation of the fish with their own eyes, so that they can better feed and master the fish. This article describes the aquafeed production process and makes some suggestions.
Source: United Nations Food and Agriculture Organization (FAO)
1 Aquatic Feed Factory Design
The feed ingredients are stored in the crushing shop silo or raw material warehouse through the receiving system. Feed ingredients can be comminuted separately and then batch-blended with vitamin premixes, mineral premixes, feed additives and liquid materials (this pre-mixing comminution system is common in North America). The system requires more storage bins, and the transportation and storage are not as good as the raw materials before the crushing. The raw materials can also be pulverized in batches (this post-crushing system is common in Europe), and then the vitamin premix, the mineral premix, the feed additive and the liquid raw materials are batch-mixed and stirred together. The post-grinding system is ideal for handling high-oil raw materials such as fishmeal and poultry lower feet. Such raw materials can also be mixed with cereal raw materials such as wheat and solvent-extracted oil mash, which can alleviate the trouble of pulverizing the high-oil-containing raw materials. The post-grinding system is provided with a buffer chamber for storing the pulverized material, sent from the buffer chamber to the mixer, and then formed. This system is used by most aquaculture feed mills because the feed mill uses a variety of by-products as feed ingredients, and it is not as easy to smash the various raw materials as the crushed mix. After batching, the raw materials of the batch are pulverized, stirred, and then sent to a silo in the workshop for granulation or extrusion.
When processing shrimp feed, the pulverized raw material discharged from the silo of the workshop is subjected to a two- or three-layer pre-modulator, the purpose of which is to lengthen the residence time of the material and add steam before granulation. The steam contains heat and water, and the heat raises the temperature to the temperature conditions required for the binder such as starch and wheat gluten to function. Without proper time, temperature and moisture, starch cannot be gelatinized and gluten cannot be formed. Shrimp is slowly fed at the bottom of the water, so the shrimp feed should be as stable as possible and stay in the water for a long time without disintegration. Figure 2 shows the effect of shrimp feed immersion time on water stability index (WSI) (Cheng Zongjia et al., 2002). The longer the feed is immersed, the greater the loss of feed. Figure 3 shows the effect of material moisture and process water temperature on shrimp feed WSI made with a meat grinder (Cheng Zongjia et al., 2002). It is clear from Fig. 3 that the shrimp feed prepared by the ground meat mechanism at 100 ° C and 40% moisture has the highest WSI.
The raw material processed by the pre-modulator is pressed into pellets in a granulator and then passed through a granulation cooker where more steam reaches the surface of the shrimp feed to enhance ripening. Finally the granules are dried by a dryer/cooler to a suitable moisture (less than 10%) for safe storage.
Most fish feeds are either floating or slow-feeding and are made by extrusion techniques. The extrusion process is also the same as granulation. The raw materials from the silo are placed in the extruder, and the suitable processing conditions are created by suitable casing, screw and shear lock configuration to make fish feed. After the material is extruded into a certain shape and cut into a certain size, it is sent to a drying/cooling machine for drying and cooling. The biggest benefit that farms can get from extrusion processing
It is to improve feed efficiency. Extrusion processed fish feed has better durability and water stability than steam granulated or cold extruded products. Extrusion is also beneficial for making fish feeds that add a lot of oil to some formulas, such as high-energy salmon and salmon feed. For this type of fish, high-energy feed can save diet protein and improve feed efficiency. The feed efficiency of the young rainbow trout feed can reach 1.0g feed/g weight gain, and the feed efficiency of the whole production cycle is about 1.2g feed/g weight gain. In the United States, the rainbow trout market weight is usually about 0.75kg.
After the feed is dried/cooled, the ground is removed by sieving. If it is necessary to apply grease to the granules, it should be sprayed hot after the granules are discharged from the dryer. Then, the pellet feed is sent to the bulk warehouse for shipment to the factory or loaded into the package for shipment.
2 crushing
Most of the raw materials used in the production of aquafeeds are crushed (reduced particle size). The purpose of the comminution is to obtain materials suitable for making high quality feeds and most suitable for animal digestion (Martin, 1983). Stevens (1961) pointed out that raw material pulverization has the following reasons: pulverization can increase the exposed surface area of ​​the material; make the material easier to digest; easy to transport during processing; pulverization can improve the uniformity of mixing, which is especially important for young animals with small feed intake Crushing also aids in granulation and extrusion.
The production of fish and shrimp feed, especially shrimp feed, requires the comminution of raw materials, so that the pelletized feed produced has better water stability and can improve animal performance. Palaniswamy and A1i (1991) conducted a study to reduce the particle size of the raw materials to 500, 420, 300, 250, 210, 50 μm (micron, the same below), and the results showed that the water stability of the obtained pellet feed was preferably 210 μm. Penaeus indicus (Penaeusindicus) has the fastest growth rate, the best feed conversion rate and the highest digestibility when fed with a diet with a raw material size of 210 μm. Obaldo et al. (1998) reduced the raw material granules of a shrimp diet from 603 μm to 586, 52 l, 408, 272, 124, 69 μm, and found that feeds made from 124 μm of raw material particles improved the water stability of the granules, granules. Persistence, starch gelatinization rate, live weight and weight gain of shrimp. Granular feeds with poor water stability produce a lot of debris, which not only causes waste, increases production costs, but also pollutes the environment. However, the crushing of raw materials increases power consumption and moisture and powder loss during production, which increases production costs.
The hammer mill and roller mill are used to coarsely grind the grain to make 300-1200 μm crumb, which is very efficient. When a high-fat or high-oil raw material is processed by a hammer mill, the sieve plate is easily clogged. When smashing high-fat raw materials such as fishmeal and poultry lowering feet, some grains can be pulverized better. When the pulverizer is processed, a sieve should be added to the pulverization process, and the coarse granules are returned to the pulverizer for further pulverization, so that the desired particle size can be stably obtained.
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