Extruder history introduction
First, the development history of extrusion technology Since the United States Ward applied for the first patent on puffing in 1856, many developed countries have extensively studied the equipment and processes related to extrusion, and the extrusion technology in the industry Applications in the world are becoming more and more popular.
Extrusion technology applied to the feed industry began in the United States in the 1950s. It is mainly used to process pet food, pre-treat animal feed to improve digestibility and palatability, and produce urea feed for ruminant protein supplements. In the 1980s, extrusion technology has become the fastest growing feed processing technology in foreign countries. It has the unparalleled advantages of traditional processing methods in the processing of special animal feed, aquatic feed, early weaned piglets and feed resource development.
The application of puffing technology in China was first used in the feed processing enterprises owned by Zhengda Group. After nearly ten years of publicity and promotion, the superiority of puffed materials has been accepted by the majority of aquaculture enterprises, and the production technology of puffing machines has gradually matured. According to the analysis of the development stage of the industry (introduction period, development period, peak period, decline period), the production of puffing machines and the application of puffing machines in China are currently in the development stage, and it is expected that the peak period will be reached in 3-5 years.
Second, the extruder (a), the basic composition of the extruder The extruder is mainly composed of power transmission device, feeding device, pre-conditioner, extrusion parts and discharge cutting device. The extruded part is the core part and consists of a screw, an outer cylinder and a die. Generally, the extruder is divided into a single screw extruder and a twin screw extruder according to the number of screws in the outer cylinder. Due to the large investment in twin-screw extruders, they are used less than some special feeds. At present, the most widely used in the feed industry is the single-screw extruder, which has the advantages of low investment and simple operation. According to whether steam is added to the material during the expansion process, the extruder can be further divided into a dry extruder and a wet extruder. The dry puffing machine relies on mechanical friction and extrusion to pressurize and heat the material. This method is suitable for the processing of raw materials with more water and oil, such as the expansion of full-fat soybeans. For other materials with less water and grease, steam or water should be added during the extrusion process, usually using a wet extruder. The extruder 膛 is generally assembled to facilitate replacement and maintenance of the required components. The casing section has a straight groove type and a spiral groove type. The straight groove type has shearing and stirring action, and is generally located in the middle section of the extruder; the spiral groove type helps to advance the material, usually located at the inlet port, and the segment near the template is also designed as a spiral groove to make the template pressure and out. Keep the material evenly. From the feeding end to the discharge end of the single screw, the root of the screw is gradually thickened, and the screw of the fixed pitch is gradually lightened, so that the material capacity in the machine is gradually reduced. At the same time, some shear locks with different diameters are installed in the middle of the screw to slow down the material flow and strengthen the ripening. The twin-screw extruder's twin-screws are parallel to each other and come in four forms: non-intermeshing co-rotation, non-engagement relative rotation, meshing co-rotation, and meshing relative rotation. The non-intermeshing twin-screw extruder can be used as two separate parallel screws, each having different fullness and discharge. Twin-screw extruders have the advantage of quality control and processing flexibility to process viscous, oily or very wet materials and materials that can slip in a single screw extruder.
(2) Function of each component of the extruder 1. The feeder is generally connected to the buffer tank to store a certain amount of material. The material in the bin is continuously and uniformly entered into the modulator under the push of the feeder.
The extruder generally adopts a screw feeder, and the feed section often adopts a variable diameter or variable pitch spiral to ensure uniform discharge of the buffer outlet. The diameter and pitch of the helix should be compatible with the productivity of the extruder to avoid fluctuations in the feed.
Generally, the speed of the feeder should be higher than 100RPM, and the fluctuation of the supply caused by the low speed should be minimized. The speed of the feeder should be adjustable, and the speed switch should be set at the operation site of the extruder. The operator can adjust the feed amount at any time according to the current and working conditions of the extruder.
2, the conditioner is a mechanical device that thoroughly mixes additives such as steam and liquid with raw materials. The tempering device can improve the puffing property of the material, increase the output, reduce the energy consumption, and improve the life of the spiral, gas plug and puffing chamber of the extruder. Through quenching and tempering, the material is softened and more malleable, avoiding a large amount of mechanical energy being converted into heat energy during the expansion process, and at the same time slowing the wear of the spiral, gas plug and puffing cavity.
There are a wide variety of conditioners, such as single-axis paddle conditioners, steam jacket conditioners, and dual-axis differential differential paddle conditioners. At present, there are three types of conditioners on the market. The general extruder uses a single-shaft paddle conditioner or a steam jacket conditioner, and the aquatic extruder uses a dual-axis differential differential paddle conditioner.
The conditioner mainly consists of an outer chamber and a paddle rotor. In order to maintain an appropriate amount of material in the conditioner, so as to provide sufficient time for the steam to be thoroughly mixed with the material and then absorbed by the material, the angle of the blade should be adjustable. Generally, the rotation speed of the single-axis blade-type conditioner should not be lower than 150r/min, the minimum is not less than 100r/min.
The two-axis differential differential paddle conditioner can adjust the blade angle alone to change the tempering time in several tens of seconds to 240 seconds, so it is not necessary to change the rotation speed of the blade shaft in general work. The adjustment of the angle of the blade can be started from the blade at the upper end of the length of the conditioner at the inlet of the tempering device. If the quenching and tempering time is required, the angle between the large diameter and low velocity positive pulp blade and the blade axis can be increased. Although the double-axis different-diameter blade-type conditioner has improved the sticking-staying phenomenon, some materials retain the wall retention phenomenon. In this case, the clip of the small-diameter high-speed counter-pulp blade and the stirring shaft can be appropriately reduced. The angle, in order to increase the reverse turbulence of the anti-slurry blades against the powder, reducing the amount of residue.
3, extrusion parts extrusion parts are the main working parts of the extruder, including: expansion chambers, screws, gas plugs and tamping blocks and other mechanical components. In the single-screw extrusion chamber, the material is substantially tightly wrapped around the screw, in the form of a spiral continuous strip. When the screw rotates, the material moves forward along the spiral like a nut, but when the friction between the material and the screw is greater than the material When the friction with the barrel, the material will co-rotate with the screw, which can not achieve the forward extrusion and conveying of the material. This trend becomes more pronounced as the moisture and oil content of the material is higher. In order to avoid these problems, most of the single-screw extruders now use segmented, single and double helix, combination of pressure ring and kneading ring and inner wall slotting barrel to adapt to changes in materials in the cavity. Happening.
(1), puffing chamber:
In order to facilitate the replacement and maintenance of the required components, the expansion chamber is generally assembled. The puffing chamber is cylindrical, and there is only a small gap between the screw and the screw in order to increase the frictional shear force with the material. The inner wall of the expansion chamber has a straight groove type and a spiral groove type. The straight groove type has shearing and stirring action, and is generally located in the middle section of the extruder; the spiral groove type helps to advance the material, usually located at the inlet port, and the segment near the template is also designed as a spiral groove to make the template pressure and out. Keep the material evenly. The puffing chamber can also be made into a jacket type for easy access to steam or cooling water. For ease of operation, pressure sensors and thermometers are typically installed on the puff chamber.
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(2), screw:
The screw is one of the most important accessories of the extruder. The quality of the screw is the main indicator to measure the quality of the extruder. At present, the screw materials on the market mainly include: 40 chrome molybdenum aluminum, high chromium cast iron, stainless steel and alloy steel carburizing, nitriding, and tungsten carbide treatment. Different materials, different wear resistance, the price gap is very large.
The parameters indicating the screw structure are: diameter, pitch, root diameter, helix angle and blade section structure.
The screw is divided into a single head screw and a multi-head screw.
(3), steam plug:
The steam plug has no transmission capacity and blocks the flow of the material. When the material is transferred from one spiral to the other, the steam plug can reverse the inside and outside of the material, accompanied by flow and mixing.
The steam plug can produce different cutting zones with high and low shearing, has strong shearing and smashing effect, has strong friction on the passing material, and has a remarkable heating effect.
Products of varying degrees of expansion are typically obtained by varying the number and diameter of plugs used.
(4) The discharge device of the discharge device of the discharge device is the final checkpoint of the product through the extruder, which has a great influence on the shape, texture, density and appearance characteristics of the product and the production capacity of the extruder.
The discharge of the extruder generally has three forms: single hole discharge, annular gap discharge and die hole discharge.
Characteristics of the discharge die:
The discharge mold of the feed extruder uses a treated steel mold;
The working pressure of the feed extruder is generally 21 - 175kgf / cm;
The die hole should have proper control of the material to ensure that the puffing chamber of sufficient length is filled.
(5) There are three types of cutting devices commonly used in cutting device;
Synchronous cutter: a cutter mounted on the spindle of the extruder;
Asynchronous cutter: a cutter driven by a separate power;
Cut-off cutter: used for long or slow extrusion.
Generally, the gap between the cutter and the die is adjusted before the operation, and the position of the blade can be individually adjusted; in the case of high molding requirements, a spring blade is generally used, and the blade is kept in contact with the die face.
(6) Steam system steam is the source of moisture and heat during quenching and tempering. Therefore, the quality of the steam system directly affects the effect of quenching and tempering. The blade-type conditioner must be designed with reasonable steam lines during installation. The steam pressure reducing valve and the steam trap ensure that the pressure-stabilized dry saturated steam enters the conditioner; the steam should enter the conditioner from the tangential line and be sprayed in the axial direction to make it more strongly mixed with the powder; the steam direction cannot be perpendicular The tempering shaft is not only unable to achieve a good mixing effect, but instead causes the steam to "cavigate" the modulator shaft and cut the conditioner shaft. When quenching and tempering, select the appropriate steam pressure and addition amount according to the change of raw materials, formula and climate. When the humidity is high and the moisture content of the raw material is high, the steam pressure should be appropriately increased to reduce the steam addition amount; when the drying season and the moisture content of the raw material are low, Reduce steam pressure and increase steam addition; higher room temperature in summer can reduce steam pressure, because low pressure steam releases heat and moisture more quickly; low temperature in winter can increase steam pressure, enhance quenching and tempering temperature, and reduce condensate in steam pipeline. Helps the ripening of the powder.
The steam pressure is not less than 5 - 7kgf / cm; the general steam supply is 10% of the dry material handling capacity.
(7), the electronic control device due to the different characteristics of the puffed raw materials, the output of the extruder is very different, the speed of the feeder and the cutter should be adjustable.
The control cabinet should be installed on site so that the operator can adjust it at any time.
(3) Working parameters of the extruder 1. Feeding amount Under normal circumstances, the feeding amount should be so small that the extruder is in the “under-feeding†state, that is, the spiral blade gap of the feeding section is not completely filled with materials. As the spiral root diameter of the transition section increases and the size of the expansion chamber decreases, the spiral blade gap is completely filled as the material enters the homogeneous section.
2. The spiral speed of the spiral speed directly affects the fullness of the expansion chamber, the residence time of the material in different areas of the expansion chamber, the thermal conductivity, the mechanical energy input of the extruder, and the force applied to the material.
Usually the screw speed is in the range of 100 - 700 rpm.
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3, than mechanical energy The so-called specific mechanical energy refers to the electrical energy consumed per unit of output. It is proportional to the mechanical energy and the screw speed and the spindle torque, and inversely proportional to the feed amount. The material required for puffing different materials is much different than the mechanical energy.
4. When the expansion chamber temperature extruder is working, most of the temperature needs to be controlled. During operation, due to conduction convection, the heat energy gradually diffuses from the material filling area of ​​the expansion chamber to the non-filling area.
The specific heat exchange method depends not only on the physical properties of the material (such as specific heat, phase transition temperature, humidity, specific gravity, particle size) and rheological properties, but also on the structural configuration and motor power of the extruder.
Directly puffed grain raw materials, with changes in sugar and fat content, the moisture in the cavity is usually between 12 and 18%, and the temperature of the material can reach 180 degrees.
In order to prevent excessive browning of the material by scorching the inner surface of the expansion chamber or to limit the degree of protein denaturation, cold water may also be added to the expansion chamber compartment.
Increasing the moisture or oil content, or reducing the degree of shear by lowering the screw speed or changing the spiral configuration can reduce the temperature of the material.
The stability of the extruder temperature directly affects the continuity of the discharge and the quality of the product.
Factors affecting the temperature of the extruder:
The internal cavity of the puffing chamber;
Wear level of wearing parts;
raw material;
Control parameter setting;
Thermal energy input changes;
Ambient temperature fluctuations.
5, the pressure of the expansion chamber pressure expansion chamber is related to the material characteristics. Generally, the higher the viscosity, the larger the expansion chamber pressure; the higher the expansion chamber temperature, the larger the expansion chamber pressure; the larger the general expansion chamber pressure, the greater the power consumption; The greater the chamber pressure, the more severe the wear.
6. The greater the pressure of the compression molding die, the worse the molding condition; the larger the opening area of ​​the die, the smaller the die pressure; the pressure inside the die hole of the extruder is generally about 25 - 40 bar; the pressure of the die is larger, The stronger the puffing, the more severe the flashing, the greater the moisture loss; the greater the die pressure, the greater the power consumption; the greater the die pressure, the more severe the die loss.
Third, the changes in feed nutrients during the extrusion process.
(I) Changes in Carbohydrates During Extrusion Carbohydrates are the main constituents of feeds, usually accounting for 60% to 70% of feed, and are therefore the main factors affecting the properties of extruded feed. Carbohydrates can be divided into starch, fiber, hydrocolloid and sugar according to their molecular weight, structure and physical and chemical properties. Their changes and roles in extrusion process are different.
1. Starch extrusion can promote the cleavage of 1-4 glycosidic bonds in starch molecules to produce low molecular weight products such as glucose, maltose, maltotriose and maltodextrin, resulting in a decrease in starch content after extrusion. However, the main effect of extrusion on starch is to promote the intermolecular hydrogen bond cleavage and gelatinization. The effective gelatinization of starch makes the extrusion treatment not only improve the nutrition of the feed, but also facilitate the granulation of the feed, thereby improving the quality of feed processing.
The degree of gelatinization of starch during extrusion is affected by factors such as extrusion temperature, material moisture, shear force, screw structure, residence time in the extruder, and die shape. The general rule is that high moisture and low temperature extrusion make the starch partially gelatinized. Low moisture and high temperature extrusion are beneficial to increase the gelatinization degree of starch, and partially crack the starch into dextrin.
Generally, cereal starch begins to swell at 50 - 60 °C, and legume starch begins to swell at 55 - 75 °C. The denaturation temperature of the raw material varies depending on the moisture, and the gelatinization temperature of the pure wheat starch containing 20% ​​of water is 120 °C.
Starch has the distinction between amylose and amylopectin, which exhibit different properties during extrusion. In terms of the degree of expansion, the general trend is that the amylose content in the starch is increased, and the degree of expansion is lowered. It has been reported that 50% amylose and 50% amylopectin can be extruded to obtain the best puffing effect. In addition, starch with different sources has different extrusion effects. The grain starch in wheat, corn and rice has a good puffing effect. The tuber starch not only has good puffing performance but also has very good bonding ability.
By the expansion process, not only the starch granules and the intermediate surface area between the semi-crystals and the crystal regions can be significantly enlarged, but also the structure of the starch can be greatly collapsed. The starch granules are greatly destroyed and merged to form a gentle area like plastic. It is because of this change that although the activity of amylase in the small intestine of suckling pigs is extremely low, the digestibility of starch can also be improved.
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2. Fibrous fibers include cellulose, hemicellulose, and lignin, which typically act as fillers in feed. Due to the different materials and process conditions for the fiber raw materials used for extrusion and extrusion, the literature on the change in the number of fibers during extrusion has been widely reported. Fornal et al.'s study on the extrusion of buckwheat and barley, Wang et al.'s studies on wheat and wheat bran showed that the amount of fiber after extrusion decreased, while Bjorck (1984) and Ostergard (1989) squeezed whole wheat flour and whole barley flour respectively. The results of the pressure study are exactly the opposite of the above; as for the study by Silijestron (1986) and Schweizer (1986), the total fiber content of whole wheat flour does not change during extrusion. However, the results of fiber mass change during extrusion process are consistent. Both indicate that the amount of soluble dietary fiber is relatively increased after extrusion, and the general increase is about 3%. Table 1 shows that Wang et al. Study results of fiber changes after whole wheat and wheat bran extrusion. Since soluble dietary fiber has a special physiological effect on human health (Gordon, R. Huber, 1991; Cummings, JH, 1978), it is undoubtedly a good method to develop dietary fiber by extrusion.
The fiber raw materials in the feed industry are mainly derived from corn, cakes and bran. In the extrusion process, the regularity is generally that the degree of expansion decreases with the increase of fiber addition, but the difference of the purity of fiber or fiber from different sources has a significant difference on the degree of expansion. Among them, the expansion ability of pea and soybean fiber is good. Their addition to the starch-based feed of 30% has no significant effect on the degree of puffing of the final product, while oat bran and rice bran, due to their high protein and fat, have a poor puffing ability. 3. Hydrocolloid colloid is mainly used in the production of aquatic feed. It usually has hydrocolloids such as gum arabic, pectin, agar, carrageenan and sodium alginate. After extrusion, the gelling ability will generally decrease. The hydrophilic properties during extrusion will also affect the conventional extrusion conditions, reduce the water evaporation rate and freezing rate of the extruded product, and improve the texture properties of the product. For a specific product, factors such as viscosity, gelation, emulsifying, hydration rate, dispersibility, mouthfeel, operating conditions, particle size and source of raw materials of the colloid are carefully considered when selecting a hydrophilic colloid.
4, sugar sugar is hydrophilic, in the extrusion process will regulate the water activity of the material, thereby affecting starch gelatinization. The high temperature and high shear of the extrusion cause the sugar to decompose to produce a carbonyl compound, which causes a Maillard reaction with the protein, free amino acid or peptide in the material, which affects the color of the extruded feed. In addition, the addition of a certain amount of sugar during the extrusion process can effectively reduce the viscosity of the material, thereby increasing the expansion effect of the material at the exit of the die, which is helpful for controlling the ups and downs of the aquatic feed. Therefore, in addition to providing energy, the sugar in the extruded feed is mainly used as a flavoring agent, a sweetener, a texture regulator, a water activity and a product color regulator. The commonly used sugar is sucrose. , dextrin, fructose, corn syrup, molasses, xylose and sugar alcohol.
(II) Changes in protein during extrusion The protein is subjected to high temperature, high pressure and strong mechanical shearing force in the extruder chamber, resulting in final denaturation of the protein. This degeneration makes it easier for proteases to enter the interior of the protein, thereby increasing digestibility.
The effect of extrusion on protein is mainly reflected in:
Denaturation: When a protein is heated or subjected to other physical or chemical effects, its unique structure will change, and its properties will also change, such as decreased solubility, increased sensitivity to enzymatic hydrolysis, loss of physiological activity, etc. The phenomenon is called denaturation. Denaturation is not the decomposition of proteins, but only the second and third levels of protein. Moderate destruction of the structure of the protein can improve the digestibility of the protein.
Thermally induced denaturation: The egg white solidifies upon heating, and the lean meat shrinks and hardens during cooking, which are caused by the thermal denaturation of the protein. The sensitivity of the protein to heat hydrolysis is increased after heat denaturation, so we do not eat raw meat and eat cooked meat, and the digestibility is high.
Thermal sterilization also utilizes the denaturation of proteins. Some protein elements inhibit his digestion and absorption. For example, urease in soy is an unwelcome enzyme that is easily inactivated in puffing. The lipase in rice bran is also harmful, which can accelerate the spoilage of rice bran. Lipase can be denatured by puffing.
In the case of very low starch content, puffing reduces the protein dispersion index (PDI) of the protein in water. However, due to the presence of starch in the material, the gelatinized starch encapsulates other nutrients in the starch matrix. Therefore, the protein is physically bound to the gelatinized starch and protected by the starch matrix. A simple aqueous solution cannot dissolve the protein, but the digestive enzymes in the intestine can easily dissolve the starch matrix and release the protein. So far, no studies have shown that puffing can damage proteins or reduce the utilization of amino acids.
Effect of expansion on the stability and availability of certain amino acids
It can be seen from the above table that there is no change in amino acids and applicable amino acids at 120 °C and 130 °C.
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Effect of swelling on synthetic amino acids
Remarks: Processing conditions: temperature 140 °C, pressure 50 bar, moisture content 18%
However, in terms of protein quality, different extrusion conditions have different effects, which mainly depend on the loss of effective lysine during extrusion. The general trend is that the lower the moisture content when the raw material moisture is lower than 15% and the extrusion temperature is higher than 180 °C, the higher the temperature, the greater the loss of lysine and the lower the biological potency of the protein. (Maclean, WC, 1983; Noguchi, A., 1982; Bjorck, I. 1983). Appropriate changes in extrusion process conditions, such as reducing the content of reducing sugars such as glucose and lactose in feed, and increasing the moisture content of raw materials (Tossavainen, OS, 1986) can effectively reduce the occurrence of Maillard reaction. K. Dahlin (1993) and other eight grains treated with corn, wheat, rye and sorghum under different conditions showed that the raw material moisture was 15%, the extrusion temperature was 150 ° C, and the rotation speed was 100 rpm. The biological potency of product proteins is significantly improved compared to untreated raw materials (Dahlin, K., 1993).
(C), the change of fat during the extrusion process will cause partial hydrolysis of triglyceride, resulting in monoglycerides and free fatty acids, so from the simple treatment point of view, the extrusion process will reduce the stability of the oil, but the whole As far as the product is concerned, the increase of free fatty acid content in the extruded product is significantly lower than that in the unsqueezed sample, which is mainly attributed to the inactivation of factors such as lipohydrolase and lipoxygenase in the feed to promote fat hydrolysis. .
The fat and its hydrolyzate can form a complex with the gelatinized starch during extrusion, so that the fat cannot be extracted by petroleum ether. The formation of such a complex makes it difficult for the fat to exude from the product to give the product a good appearance. This complex dissociates in the acidic digestive tract and therefore does not affect the digestibility of fat.
Fat has a greater effect on the texture, shape and palatability of the feed, but in general, the presence of fat not only affects the quality of the final extruded product (mainly the degree of expansion), but may even affect the smooth progress of the entire extrusion process. For example, for the extrusion of defatted soybean powder, the fat content should not exceed 1%; in the production of bulk material in the feed industry, when the amount of grease added to the single-screw extruder is between 0% and 12%, there is no effect on the extrusion effect. When the addition amount is in the range of 12% to 17%, the weight of the product increases by 16g / L for each 1% increase, and the effect is even worse when the addition amount continues to increase. When the amount exceeds 22%, the product loses the general extrusion. Pressure characteristics. Therefore, the extrusion should be based on raw materials with low oil content.
(4) Changes in vitamins, minerals and flavor substances during extrusion The vitamins can be retained during processing, depending largely on the processing conditions. During the extrusion process, heat-sensitive vitamins such as VB1, folic acid, VC, VA, etc. are the most vulnerable, while other vitamins such as niacin, VH, and VB12 are relatively stable. From the point of view of ease of production, the addition of vitamins prior to extrusion is superior to that after extrusion, but must be added in excess to overcome the effects of partial vitamin loss on animal nutrition during extrusion. It has been reported that the addition of vitamins prior to extrusion not only destroys the vitamins during the extrusion process, but also reduces the loss of vitamins during storage. Therefore, the vitamins of the extruded material may be more economical to add after extrusion.
Minerals are generally not destroyed during extrusion, but the formation of new polymers with solidification properties may reduce the bioavailability of certain minerals. For example, phytic acid may be complexed with Zn, Mn, etc. Animal digested compounds.
Due to the high temperature during extrusion, high moisture will decompose the flavor material, and the volatile flavor material will be mostly lost as it evaporates along with the water vapor at the die port. Therefore, the addition of flavor during processing is added after extrusion.
Fourth, the comprehensive impact analysis of puffing 1, puffing processing changes the physical structure and chemical properties of the ingredients in the feed ingredients, especially the starch and protein components.
2. Gelatinized starch has strong water absorption and bonding function. Due to its high water absorption, we can add more liquid components (grease, molasses, etc.) to the product. At the same time, because it has much stronger bonding function than ordinary starch, the amount of starch added during the expansion process can be greatly increased. Reduction. This provides more room for the selection of other O raw materials. Manufacturers can choose more cheap raw materials to replace those expensive materials, which can reduce costs without affecting product quality.
3, because the starch matrix and protein are combined, it is not easy to lose when feeding, only when the animal's digestive enzymes break down the starch, the protein is released, which increases the protein titer.
4. The expansion process denatures the protein, inactivates many anti-nutritional factors, changes the tertiary structure of the protein, and shortens the hydrolysis time of the protein in the intestine.
5. Puffing treatment releases the encapsulated oil in the raw material molecules, and increases the thermal energy value of the fat.
6. Puffing combines fat, starch and protein to form a composite product lipoprotein or lipopolysaccharide, which reduces the content of free fatty acids, deactivates lipase, inhibits the degradation of oil and fat, and reduces the rancidity of oil components during storage and transportation.
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7. Puffing treatment reduces the content of bacteria, mold and fungi in raw materials, improves the hygienic quality of feed and improves palatability. The extruded feed is subjected to a higher temperature than the granulation. After the pressure treatment, the pathogenic microorganisms in the feed are killed (E. coli, Salmonella, protozoa, residual pesticides, etc.), which can effectively prevent pig white diarrhea, jaundice and edema, and improve The survival rate of young cubs is beneficial to the health of livestock.
8. The expanded feed has the advantages of unique flavor and fluffy feeling, good palatability, high gelatinization degree and good attracting effect.
9. The pellet feed is determined by the working characteristics of the ring mold. It is difficult to produce high-fat feed, and the moisture content of the feed ingredients is strict. The expanded feed requires a wide range of oil and moisture content to produce high-energy feed, which fully meets the needs of livestock and poultry. .
V. Advantages and Disadvantages of Puffing Processing (I) Advantages of Puffing Processing: The material is fully matured in about 10 seconds. The puffing temperature varies depending on the raw materials, generally ranging from 120 °C to 175 °C. Curing can destroy growth inhibitors in a very short period of time, processing in an anaerobic state, helping to preserve protein, energy and vitamin content, but also reducing product browning due to oxidation; can improve product digestibility and Palatability.
Sterilization, degree of removal: After high temperature and high pressure treatment, the pathogenic microorganisms in the material are killed in a large amount (such as Escherichia coli, Salmonella, protozoa, residual pesticides, etc.), which can effectively prevent pig white diarrhea, jaundice and edema, and improve young The survival rate of cockroaches is good for the health of livestock and poultry.
Puffing molding: The raw material is suddenly reduced in pressure after continuous high pressure, which can cause gelatinization of starch cells, rupture of oil cells, and processing into the desired product status.
Product homogenization: The material has been pulverized or mixed before being expanded. The friction and shearing action of the screw and steam plug in the expansion chamber further mix and break the material to help homogenize the final product.
Dehydration: When the bulking material leaves the extruder, its internal moisture immediately evaporates (flashes) due to the high temperature and pressure in the chamber, which is very beneficial for storage.
Enhanced stability: The high temperature and high pressure in the expansion chamber can passivate the enzyme causing spoilage in the material, avoiding the rapid destruction of nutrients in the material in a short period of time, and enhancing the stability of the product storage process.
Good palatability: Puffed material has unique flavor and fluffy characteristics, good palatability, high degree of gelatinization and good attracting effect.
Wide range of raw materials: The pellet feed is determined by the working characteristics of the ring mold. It is difficult to produce high-fat feed, and the moisture content of the feed ingredients is strict. The expanded feed requires a wide range of oil and moisture content to produce high-energy feed. Livestock and poultry needs.
Significant benefits: Research by domestic and foreign breeding experts shows that compared with pelleted feed, the ratio of feed to meat can be reduced by 8 - 10%, which will reduce feeding costs, shorten fattening time and improve economic efficiency.
(B), the disadvantages of puffing processing:
High power consumption: Puffing processing belongs to frictional heat generation. In addition, the material structure of the material needs to be completely broken during processing, so the energy consumption is generally high.
Puffed corn: generally about 80kw.h/t;
Puffed soybean: generally about 40kw.h/t;
Expanded batch: generally about 30kw.h/t.
However, due to the sufficient quenching and tempering of the material during the puffing process, it has great advantages for the subsequent granulation process, and the granulator output can be increased by 30 - 60%.
High difficulty in operation: Puffing processing involves various working parameters such as temperature, pressure, humidity, load, etc. The operator not only understands various process parameters, but also needs to master the characteristics of various raw materials, and needs more comprehensive professional knowledge and work experience.
Preheating: Puffing processing is a kind of thermal processing, which requires a certain temperature. When the cold machine is started, the performance is not stable, so it is generally not suitable for shutdown.
Loss of heat-sensitive elements: Due to high temperatures and pressures, heat-sensitive elements are lost during processing.
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