Generally speaking, factors affecting granulation include raw material source, moisture in raw materials, starch, protein, fat, crude fiber content, bulk density, material structure and particle size.
1. Particle size: The powder is pulverized to be fine, which is beneficial to the progress of hydrothermal treatment. On the contrary, the coarse-grained powder has low water absorption capacity and poor quenching and tempering effect.
Second, the bulk density: the bulk density of the material has a direct impact on the output. When the same granules are produced and the material with a large capacity is granulated, the output is high and the power consumption is small. On the contrary, the output is low and the power consumption is large.
Third, the impact of chemical composition of materials
1) Starch: Different forms of starch have different effects on granulation. The raw starch microparticles have a rough surface and a large resistance to granulation. When the raw starch content is high, the granulation yield is low and the stamper wear is severe. Raw starch particles have poor binding ability to other components, and the final product is loose. The cooked starch, that is, the gelatinized starch, is quenched and hydrated and then exists in a gel form, and the gel is favorable for the material to pass through the die hole, so that the granulation yield is improved. At the same time, the gel can be dried and cooled to bond the other components around, so that the granular product has better quality. During the quality process, the starch granules are viscous after being steamed and partially damaged and gelatinized by the pressing and pressing rolls, so that the prepared granules are precise in structure and quality. In addition to the structure and properties of various starches, it is also related to the fineness of the powder. Therefore, when using corn and sorghum as the main raw materials, attention should be paid to crushing the particle size before granulation.
2) Protein: The protein is heated and deformed to enhance the adhesion.
3) Grease: The oil and fat inherent in the raw material does not cause the oil to be squeezed out due to the temperature and pressure during the granulation process, so the effect on the granulation is not great, and the added fat has obvious yield and quality to the granulation. influences. Adding 1% of the oil to the material will soften the granules, and will significantly increase the granulation yield, which will reduce the wear of the stamper and the press roll. However, the raw material has a high oil content before granulation, and the obtained particles are loose. The amount of fat added before granulation should be limited to 3%.
4) Molasses: usually added in an amount less than 10%, which can be used as a binder, which is beneficial to the hardness of the reinforced particles, and the effect depends on the ability of the material to absorb the molasses.
5) Cellulose: There is no cohesive force in itself, but if the fiber is too much, the resistance is too large, the yield is reduced, and the die wear is fast. The material with high crude fiber content is loose and porous inside, and should be controlled to moisture in the mold. If the moisture is too high and the temperature is high, the particles will expand rapidly after being released from the mold and are prone to cracking.
6) Heat-sensitive raw materials: When adding certain vitamins, seasonings and other materials that are subject to heat and damage, the granulation temperature should be appropriately reduced and added in excess to ensure the effective content of these ingredients in the finished product.
4. Binders Some starches, proteins or other components with binding effects contained in some feeds are difficult to prepare. Therefore, a binder is required to achieve the desired degree of solidification of the particles.
What are the physical and chemical changes in protein, carbohydrates, fats and vitamins during the granulation process:
Protein
Physical changes: The protein will show a tendency to reduce the water solubility of the protein. The water content of the different varieties of raw materials will be different under the granulation conditions due to the difference in protein content. The general trend is that the higher the protein content, the more the water solubility decreases. The second is the ambiguity. The greater the ambiguity, the smaller the water solubility of the protein.
Changes in chemical properties: The protein is gradually reduced, and the hydrolysis time of the protein in the digestive tract is reduced. The protein content is basically unchanged throughout the process, and the amino acid stability and titer are not significantly reduced.
Carbohydrates:
Physical changes: starch absorbs moisture and begins to dissolve, losing its original crystal structure. Different raw starches have different swelling temperatures, and under high temperature extrusion conditions, starch can reach the desired degree of starch gelatinization. Such a preparation process can simultaneously achieve the requirements of improving granulation and nutrition, and the structure has protective properties and Improve the function of feeding effects.
Chemical change: In addition to the expansion of the starch, the starch also undergoes hydrolysis, thereby providing more suitable conditions for the enzymatic digestion of the animal. The feed hygiene index after granulation is good, with almost no source bacteria.
Changes in fat: high temperature inactivates lipase, reduces hydrolysis of fat during storage, improves stability, and inactivates fatty acid-protected structure-cracked lipoxygenase, reducing acidification rate.
Vitamins: Friction is a major factor in the instability of vitamins, which destroys the crystal layer of vitamins, causing a large amount of vitamins to be oxidized. The pressure will seriously damage the gel layer of fat-soluble vitamins such as vitamin A.
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