Specially Requirements On The Quality Of Aqua Feed Processing

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Aquatic feed, as a kind of special animal food, has different requirements on its processing compared to common animal feed, since aqua feed is fed into water, especially floating fish feed granules that shall float on the water. So this also requires the aqua feed processing technology to be special. Now let’s see what are these special requirements on the quality of aqua feed processing.

  • Water stability (water resistance)
When aquatic feed is put into water, it is required to absorb water quickly, soften timely, dissolve less, not collapse and maintain prototype, which is water stability, often expressed by time unit h or min. Good water resistance can ensure that feed is fully utilized by aquatic animals and does not pollute water quality. The water resistance requirements of all kinds of aquatic feeds are as follows: common freshwater fish hard pellet feed, about 15mins; marine freshwater shrimp and crab feed, 120mins; marine freshwater fish and frog extruded feed, 8h.

aqua fee processing

  • Crushing granularity of feed raw materials
In view of the characteristics of small digestive tract and weak digestive and absorption function of fish and shrimp, the grinding fineness of feed raw materials and the contact area between feed and animal intestines are improved as far as possible in aqua feed processing technology, so as to improve the digestive utilization rate. In 1985, the digestibility of rainbow trout was measured by using white fish meal with different grinding sizes. The results showed that the grinding size of raw materials was 10-30 mesh and the digestibility was 11%. The grinding size was 30-50 mesh and the digestibility was 51%. The grinding size was 50-120 mesh and the digestibility increased to 73%. When the grinding size was larger than 120 mesh, the digestibility had no significant differences.

  • Mixing uniformity
Aquatic animals consume little food per day, so fish and shrimp need to obtain comprehensive nutrition from a small amount of diet. It is necessary to ensure that the nutrient composition of feed is uniform. Therefore, high quality mixing uniformity is needed in fish feed processing. Generally, the variation coefficients of feed mixing uniformity are as follows: livestock and poultry feed CV < 10%, premix CV < 5%, and aquatic feed requirement is the same as premix, which shows the importance of aquatic feed mixing uniformity.

  • Feed granules' curing degree
The curing process of aquatic feed processing includes pre-curing (i.e. conditioning curing) and post-curing (i.e. stable curing). In fact, Post-curing enhances feed curing. It can play an important role in granulation, bonding and gelatinization. The water resistance and palatability of well-cured feed were improved, and the utilization rate of protein, fat and carbohydrate in feed were improved.

(Further reading: MAKE AQUATIC FEED: PELLET FEED OR EXTRUDED PARTICLE FEED?)

Factors affecting fish feed coefficient

1. Rationality of feed form​ulation

The nutrient content of feed itself has great influence on feed coefficient. Protein and fat content are the two main nutritional indicators of feed, and the higher the content, the lower the feed coefficient, the better the digestion and absorption of fish. However, the diets with the same or similar contents differ greatly from the existing state and structure of their active ingredients. Taking barley, oat and wheat as examples, the protein digestibility of carp to the three kinds of grain feed is "barley > oat > wheat". This is mainly because the protein quality of wheat is worse than that of barley and oat, that is to say, the content of lysine and threonine in wheat is lower. The biological value of protein in feed calculated by essential amino acid index was 55 for wheat, 70 for oat and 73 for barley. In addition, the excessive content of essential nutrients in feed can also cause dyspepsia. For example, when protein content is too high, the accumulation of protein in fish body is almost unchanged, and the weight gain is not proportional to the protein content in feed. This not only causes the waste of protein, but also the metabolites of its protein also pollute the water quality. Therefore, the content of various nutrients in feed should have an optimum amount. Practice has proved that there should be an appropriate proportion between protein and non-protein in fish feed, and only when protein is sufficient, other nutrients can be effectively utilized. If there is a lack of nutrients in feed, it will also affect the utilization of other effective ingredients. Nutrient supplement in feed can increase feed utilization.

The nutritional needs of fish for feed have their own characteristics. For example, fish can make full use of protein and fat in feed, but cannot make good use of carbohydrates, and it is difficult to digest cellulose. Fish have different nutritional needs. Therefore, reasonable feed formulation should be formulated according to different fish. Only when the nutrients in the feed match the needs of fish, can the digestibility and absorptivity be improved and the feed coefficient be reduced. This means that feed coefficient is largely determined by the rationality of feed formulation.
 

aqua fish feed processing machine

2. Quality and processing of feed ingredients

The nutrient composition of feed materials varies greatly with the variety, origin, grade, foreign body content, storage conditions and storage period. Therefore, feed ingredients have a direct effect on the nutritional composition and quality of formulated feed. The quality of raw materials is good and the grade is high. The compound feed can reach the expected nutritional level. On the contrary, the nutrition of feed will change. In particular, the storage time of feed ingredients has great influence on the nutritional value of feedstuffs. Although the crude protein content of raw materials will not change during storage, the solubility and digestibility of protein will gradually decrease with the prolongation of storage period. When raw materials are stored at 24℃for 2 years, the protein digestibility will decrease by 8%. Other nutrients in raw materials will also have different degrees of efficiency reduction during storage. The loss of VE is the most serious. Fat is decomposed by lipase during storage, and it is easy to deteriorate. The quality of formula feed will be greatly reduced by using this kind of material.

In addition, due to the particularity of aquatic feed, the requirement on its processing technology is relatively high. The main technological indexes affecting the quality of feed processing are particle size, the pressure and temperature of conditioning steam. The results showed that the digestibility of feed processing granularity was 11% in 10-20mesh, 51% in 30-50mesh and 73% in over 50mesh. The fine grain size and large surface area of raw materials can obtain better conditioning effect, has high curing degree, more adequate gelatinization, good cohesion of particles, and is not easy to lose after entering water. Fish are easy to digest and absorb after feeding, and the feed coefficient is low. In the standard of feed processing, the requirement of crushing size of aquatic feed is: fresh water fish feed should pass 20 mesh sieve, 40 mesh on sieve should not exceed 30%; shrimp feed should pass 40 mesh sieve, 60 mesh on sieve should not exceed 20%. Too much feed and too much raw material will increase feed coefficient. In addition, conditioning process is very important to the quality of feed. Steam pressure and the time of material passing through the conditioner determine the degree of material curing. The processing parameters of different raw materials are different. If the water content is insufficient and the temperature is insufficient, the digestibility will be affected by inadequate gelatinization of raw materials, and excessive maturation will destroy the nutrients in feed, of which lysine is the most important one. Thus, the utilization ratio of feed decreased and feed coefficient increased. For aquatic feed, the optimum moisture content of conditioning is about 12%, and the material temperature is 70℃. This can not only improve the production efficiency of the fish feed extruder, but also produce high-quality fish feed products.

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