The water stability of aquatic pellet feed refers to the property that the composition is not dissolved and not lost after being immersed in water for a certain period of time. Generally, the dissolution rate is the loss rate, that is, the loss of feed in water per unit time. The percentage of feed quality. It can also be expressed by the minimum time that the feed does not collapse in the water. After the aquatic feed is put into the water, it is impossible to eat it all at once. This requires the feed to be maintained in the water for a period of time. During this time, it does not collapse or dissolve, and there is a certain degree of water stability. If the stability is poor, the aquatic product compound feed is easy to dissolve, swell and collapse in the water, and the feed can not be completely ingested by the aquatic animals, which not only reduces the utilization rate of the feed, but also causes the fish body to digest and absorb the feed and improve the feed coefficient. Affecting the economic benefits of the aquaculture industry will also cause deterioration of water quality, endangering the health of farmed animals and polluting the environment. Therefore, the water stability of feed is an important indicator of the quality of aquafeeds that is unique to aquafeeds.
1 Aquatic feed water stability requirements
Table 1 Basic requirements for water stability (dissolution rate) of various types of fishery compound feeds -
Aquatic animals are different from terrestrial animals and need to be eaten in water. Moreover, different aquafeeds require different stability in water. Ordinary carp fish, the pellet feed requires soaking in water for 5 min, the dissolution rate is ≤10%; the shrimps are fed in a feeding manner, and the shrimp pellet feed is required to be soaked in water for 120 min, and the dissolution rate is ≤12%.
The aquatic industry standard “General technical requirements for compound feed for fishery†stipulates the basic requirements for the dissolution rate of powdered compound feed, granular compound feed and expanded compound feed for fishing (see Table 1).
The aquatic industry standards for compound feeds such as squid, grass carp, tilapia, squid, and prawns also have different requirements for the dissolution rate, as shown in Table 2.
Table 2 Aquatic feed industry standards for water stability (dissolution rate) of feed products
It can be seen from Table 2 that the loss rate index of a single product is not completely consistent with the specifications specified in the “General Technical Requirements for Fishery Compound Feedsâ€. In actual production applications, this requires that the aquatic feed produced must meet the “fishingâ€. The provisions of the General Technical Requirements for Compound Feeds must be consistent with the water stability (dissolution rate) of individual feed products specified by the Aquatic Feed Industry Standard.
2 Constraints on the stability of aquatic feed water
There are many factors that restrict the stability of aquatic feed water, mainly in the following aspects:
2.1 The raw material composition of the feed formula
The raw material composition and ratio of aquatic pellet feed have a great influence on the stability of feed water, and the stability of different raw materials in water is different. The stability of the commonly used aquatic feed ingredients in the order of strength is: flour - cottonseed meal - wheat - fish meal - rapeseed meal - soybean meal - silkworm cocoon - bran - corn yellow powder - corn - rice bran. Even with the same raw materials, the water resistance of the final product varies depending on the source and treatment. Some people experimented with three kinds of typical rapeseed from different sources, and found that the water resistance time of the three was 25min, 50min, 150min respectively; the whole fat soybean powder was prepared by microwave, baking and extrusion, among which the extrusion The result is the best. In addition, the freshness and type of raw materials are also important factors affecting the quality of feed pellets. Generally, fresh and high-quality raw materials have strong bonding ability, and the prepared feed has good water resistance, especially protein feeds such as fish meal and peanut meal. Feeds produced from raw materials with high natural protein content have high pellet quality. Studies have found that animal protein materials have better granulation effects than vegetable protein materials.
2.2 The crushing size of raw materials
The comminution particle size determines the surface area of ​​the feed component. Fine particle size, large surface area, fast absorption of steam, good for quenching and tempering, good particle adhesion, high hardness and strong water stability. Different aquatic product types and feeding stages have different requirements on the crushing size of feed. The pulverization particle size must meet the needs of the farmed animals, and the pelletized feed produced should maintain a reasonable water stability. National or industry standards regulate the crushing size of raw materials for aquafeeds. The basic requirements for the crushing granularity of aquatic feed ingredients specified in the aquatic industry standard “General Technical Requirements for Fishery Compound Feeds†are shown in Table 3.
Table 3 Basic requirements for crushing granularity of raw materials for aquatic products (SC/T1077-2004)
Note: The pulverization granularity of the open feed ingredients in the early stage of seedlings is respectively carried out according to the feed standard in response to the feeding target.
At the same time, for the corresponding breeding objects of aquatic feed, such as carp, blue carp, grass carp, group head carp, tilapia, rainbow trout, giant salamander and other farmed animals, the compound feed industry standard also stipulates the pulverization granularity of raw materials, and basic The requirements are not completely consistent. Please refer to the relevant standards for specific values.
2.3 feed processing
The key to feed molding is conditioning. Quenching and tempering is the action of high temperature and high pressure steam on the feed, gelatinizing the starch, denaturation of the protein, increasing its cohesiveness and plasticity, ensuring the fine structure of the feed, and having appropriate hardness, which is beneficial to improving the stability of the pellet feed in water. The quality of the quenching and tempering is related to the quenching time, temperature, pressure and moisture. The higher the steam pressure during quenching and tempering, the longer the quenching and tempering time, the higher the quenching temperature, the higher the gelatinization degree of the starch in the raw material. The better the sex, the better the water resistance. The study found that the moisture content of the mixed powder after quenching and tempering has a significant effect on the stability of the feed water. Within the allowable range, the greater the moisture content of the raw material, the better the water resistance of the product; however, the moisture is too large, which may cause blockage of the die hole and increase The difficulty of drying the pellets.
2.4 Impact of granulation process
The most widely used pellet feeder is the ring die pelletizer. The compression ratio of the ring mode (deep diameter/aperture) also has a certain influence on the stability of the fish feed water. The feed pellets which are compressed by the large ring mold have a high hardness and a tight structure, and the feed water resistance time is long, and vice versa.
2.5 starch gelatinization degree
The gelatinization process of starch is the process of ripening the feed, which is beneficial to the digestion and absorption of starch by animals, especially aquatic animals. The gelatinized starch has good cohesiveness, and the fully gelatinized starch can completely replace the special binder which is expensive and has no nutritional value in the feed formulation, so that the aquatic feed has good water stability. Generally, the gelatinization degree of the expanded floating feed starch is ≥90%, the gelatinization degree of the expanded and hydrated feed starch is ≥70%, and the gelatinization degree of the hard granular aquatic feed is about 30%.
2.6 Feed Cooling
Cooling reduces the temperature and humidity after granulation. The increased hardness of the cooled feed can effectively prevent the ingress of moisture, while the reduction of moisture can enhance the stability of the pellet feed in water.
3 Countermeasures to improve the stability of aquatic feed water
In order to improve the stability of aquatic feed water stability, in order to improve the stability of aquatic pellet feed in water, the following countermeasures are proposed:
3.1 Choosing the right feed material
Since some raw materials can improve the stability of feed water, the greater the proportion of their feed formulations, the better the stability of the product in water, and vice versa, the worse the stability in water. In the design of the formula, the selection of raw materials should follow the following principles: First, the same type of feed ingredients should be selected as much as possible in the water stability of raw materials, such as flour, corn and rice bran, should choose more flour; cotton aphid and rapeseed, should Choose cotton aphid; fishmeal and silkworm cocoons should choose more fishmeal. Second, for the same raw material, its water resistance and freshness are also different. Raw materials with good water resistance and freshness should be selected. Third, because animal protein raw materials have better granulation effect than vegetable protein raw materials, animal protein materials should be used as much as possible at the cost.
3.2 Suitable starch and crude fiber
Starch is easy to gelatinize under high temperature and high humidity conditions, which is good for bonding and is one of the important raw materials that affect the stability of aquatic feed water. Due to the high level of protein requirements for fish feed, there is a limit to the amount of starch raw materials used, and the proportion of addition should not be too large. Adding an appropriate amount of flour in the production has a good effect on improving the stability of the water in the pellet feed, but due to the high cost of adding the high-quality flour, the actual production generally adds 13%-15% of the secondary powder. Due to the poor viscosity of the coarse fiber and affecting the hardness and forming rate of the pellet, the crude fiber content in the aquafeed should be controlled at 3%-5%, which can improve the water resistance of the feed. The crude fiber content of herbivorous fish compound feed can be suitably higher, the fish feed is controlled within 8%, and the adult fish feed is controlled within 12%.
3.3 The use of adhesives
At present, there are many types of adhesives used on the market, but different adhesives have different effects. When choosing a binder, you should pay attention to: 1 Consider the feeding habits of the farmed animals and the stability requirements of the bait water. Generally, the fish and shrimps with slow food intake need higher water stability, while the fish and shrimps that feed fast need lower water stability. 2 consider the nature, suitability and cost of the adhesive; 3 consider the interaction between the binder and the feed to see if it will destroy the nutrients, such as when there are divalent and trivalent cations, Cellulose, alginate, etc. will precipitate and reduce the adhesion; 4 consider the nutritional value of the binder and the impact on the growth and survival rate of the fish and shrimp. Practice has shown that agricultural and sideline products (such as wheat gluten, rice gluten, α-starch, secondary powder, etc.) have good cohesiveness, which can make aquatic feeds obtain good water stability; attapulgite and bentonite stick It has good compatibility and contains a certain amount of mineral elements, which can be applied to low-cost feed with low stability in water. It can produce special synthetic aquatic feed such as prawns, and can use chemically synthesized polymer binder with strong adhesion; The use of fresh brown algae, fresh fish and shrimp paste is also very cost-effective.
3.4 Appropriate pulverization particle size
It is generally required that the pulverization particle size of all fish feed ingredients should meet the basic requirements for the pulverization particle size of the aquatic feed ingredients listed in Table 3, and different aquatic animal feeds should also meet the feed standards of the corresponding feeding objects. If a hammer mill is used in production, more sieves with a mesh diameter of 0.8mm, 1.0mm, 1.2mm, and 1.5mm are selected; if a "cycle crushing" process or a micro-pulverization plus a classifier is used to reduce the crushing size, The effect is better. At the same time, in order to avoid the micro-grinding of the raw materials, the fluidity is poor, and the arching and dust are spread in the batching bin, and the processing process of “first batching and then crushing†can be adopted.
In order to achieve a suitable crushing particle size for the feed ingredients, it is first necessary to use suitable crushing equipment and processes. Whether the product size is suitable or not depends largely on whether the selected crushing equipment is suitable. Different types of crushing equipment are suitable for products with different crushing particle size requirements and different raw material characteristics. If the pulverizing equipment is not properly selected, not only the product particle size can not be guaranteed, but also the negative impacts such as pulverization output, power consumption, screen breakage speed and high material temperature will be unbearable for manufacturers. When the particle size difference between the raw material and the product is large, two different types of pulverizers are used in series in one production line, that is, the secondary pulverization process after coarse pulverization and fine pulverization can increase the output, reduce the energy consumption, and the product granularity is more Guarantee. Secondly, it is necessary to adjust the pulverization process parameters in time. For the production line with large variation range of pulverization size and high frequency of production variety change, in the operation process, it should be adapted to the pulverization through various adjustment methods such as processing flow, mesh size, feed amount, air volume and rotation speed. The change in particle size is required. The pore size of the sieve is the main factor determining the size of the pulverization. It should be changed with the change of the raw materials of the formulation and needs to be determined by experiments. The third is to standardize the detection of granularity. The crushing particle size is one of the important processing quality indicators of feed products, and standardized testing is a necessary measure to ensure this quality index. Each production variety should be sampled and tested after the mixing process or at the finished product, and the particle size measurement should be carried out according to industry standards. The measurement data is used to determine whether the particle size is qualified, and necessary adjustments are made in time.
3.5 Control the quality control
The feed mill mostly uses steam for quenching and tempering, that is, the steam is directly introduced into the prepared material for hydrothermal treatment. Therefore, to control the speed of feeding, it is important to choose the time, temperature, pressure and moisture for quenching and tempering.
(1) The feed rate of feed rate is fast and slow, which affects the time of starch gelatinization in the raw material. The feed rate is fast, the product yield is large, the raw starch gelatinization time is short, the cohesive force is poor, the product water stability is low, the feed rate is slowed down, the yield is reduced, but the starch gelatinization is sufficient, and the water resistance of the pellet material is improved. For the rated output of 1-2 t / h, with a mm 2.0mm ring die granulator, the output can be controlled at 0.8-1.0t / h, the motor speed is adjusted at 300-400r / min.
(2) The time of quenching and tempering is within a certain range. The longer the quenching and tempering time, the better the gelatinization degree of the starch in the raw material, and the higher the cohesiveness, the better the quality of the feed. The feed mill can use two or three multi-channel conditioners or two-axis differential conditioners to increase the time of quenching and tempering.
(3) The temperature of the quenching and tempering is higher, the better the water resistance of the feed, but the temperature is too high (above 100 ° C), the viscosity of the heat sensitive feed (skimmed milk powder, white sugar, etc.) increases, which easily leads to blockage of the die hole. And affect the appearance of the product. In the production, the appropriate temperature should be selected according to the characteristics of the raw materials and the stability of the feed water. Usually, the feed for fish is controlled at 80 ° C ~ 95 ° C.
(4) The moisture of the tempered and tempered water has the function of lubrication and gelatinization. To produce high quality aquafeeds, add appropriate steam (moisture) to the material. Generally, the moisture content of the raw materials before quenching and tempering is controlled at 12%-13%. The raw materials with excessive moisture content are generally not used for processing finished feed; when producing hard granular feed, the moisture content of the imported mold materials after quenching and tempering should be controlled at 17.0%～18.0. %between.
(5) Pressure tempering When granulating, the steam pressure has a great influence on the stability of the granular material in water. Generally, the higher the pressure, the longer the water resistance of the pellet feed. However, considering the safe production of boilers and reducing energy consumption, the steam pressure should be 0.35mpa~0.4mpa.
3.6 Good granulation off
The feed mill should select the ring mold according to the requirements of different aquatic feeds, the characteristics of the raw materials and the processing technology, and adjust the gap of the die roll and the position of the cutter. Conditional feed companies can also use the re-copying process to improve the stability of the feed in water.
3.7 Adopting post-maturing process
After the granulation of the feed, the post-aging is carried out, so that the hot granule feed just emerging from the mold is kept under high temperature and high humidity for a certain period of time, that is, the granulated hot granule feed is further incubated with the post-maturing equipment to further mature the starch, and the protein is fully denatured, and at the same time The cracks generated in the previous period are again pasted, and the starch on the surface of the pellet feed is completely gelatinized and hardened, and a protective film is formed, which is beneficial to further improve the stability of the pellet feed in water. The pellet feed is kept in the post-cooker for 5~12min, the temperature in the ripener is stable at 100~110°C, and the starch gelatinization rate can be increased from 33.3% to 53%.
3.8 regulate the cooling of
Usually, the temperature of the aquatic feed just discharged from the cooler is 6~9 °C higher than the room temperature, and the moisture after cooling is 12%~12.5%. In the production, the appropriate cooling time and air volume should be selected according to the characteristics of the materials, the particles and the type of the cooler. Generally, the temperature of the pellets after cooling cannot be higher than room temperature by 3~5 °C.
3.9 Production of Puffed Aquatic Feed
In order to further improve the water stability of the aquatic pellet feed, a puffed pellet feed machine can be used to produce the aquatic feed. To produce puffed pellets, the first thing is to control the quality of the quenching and tempering of the feed, that is, to control the temperature, time, moisture addition and starch gelatinization degree of the quenching and tempering, so that the state after quenching and tempering is most suitable for extrusion and puffing; secondly, the puffing is controlled. The degree of ripening, density, chalking rate, cooling temperature and moisture of the pellet feed, uniformity of the particles, consistency and water resistance. To achieve these requirements, it must be equipped with a reasonable steam supply and control system as well as quenching and tempering, extrusion, drying, cooling, screening equipment, and scientifically adjust the control parameters according to the different requirements of the product to produce high quality aquatic feed. .
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