Extrusion technology originated in Europe, and its application in the feed industry began in the United States in the 1950s. By the 1980s, it had become a rapidly developing new feed processing technology abroad. The characteristics of puffing technology are that it can enhance the palatability of the feed, sterilize and detoxify the feed, improve the liquid adding capacity of the feed, improve the particle quality and feed utilization rate. According to the number of screws in the extrusion part, the extruder can be divided into single-screw extruder and twin-screw extruder. According to whether steam or water is added to the material during the expansion process, it can be divided into dry expansion machine and wet expansion machine. Dry puffing machines rely on mechanical friction and extrusion to pressurize and heat materials. This method is mostly used for processing raw materials containing a lot of water and grease, such as the puffing of full-fat soybeans. Since many materials do not contain high moisture and oil like full-fat soybeans, external steam or water is often required during the puffing process, so wet puffing machines are often used.
Moderate heating can improve protein digestibility, but excessive heating can reduce protein digestibility. Because heating promotes the reaction between free amino acids and reducing sugars, lysine is easily lost in the reaction, followed by arginine and histidine. Therefore, when reducing sugars are present, overheating of the feed should be avoided and mastered. The appropriate degree of puffing is very important. Extrusion and puffing can cause the bonds between starch molecules in the feed to break and cause a gelation reaction to generate α-gelatinized starch. The higher the alpha degree of jade starch, the easier it is to be absorbed by enzymes in the animal body, and at the same time it can improve the bonding effect of feed, which is of great significance to the bonding of aquatic feed. The special friction and shearing in the extruder can rupture the oil cells, thereby increasing the digestibility of oil and increasing the heat energy value. Extrusion puffing inactivates the lipolytic enzymes and lipoxygenases in the raw materials, inhibits the degradation of oils, and improves the stability of the feed. In addition to its own chemical structure, the retention rate of vitamins during the puffing process also depends to a large extent on the processing conditions. The general rule of the influence of extrusion conditions on vitamins is that as the extrusion temperature increases, the residence time of the material in the extrusion cavity increases, the moisture content of the extruded material decreases, the die aperture or gap decreases, and the loss of vitamins increases.
Extruded barley and oat feeds can reduce protein solubility and increase ruminal protein levels, thereby increasing the flow of amino acids in the small intestine of animals and having a positive impact on the animal's production performance.
Using puffing technology, combined with other physical, chemical and biological technologies, to deeply develop and utilize various industrial and agricultural by-products will be an important and effective way to solve the shortage of feed resources in our country. Extrusion technology is used in the development of feed resources. Currently, it is mainly focused on conventional raw materials such as soybeans and their cakes, corn, etc. A large number of studies have proven that extruded and puffed corn can be used to replace part of the whey powder in suckling pig feed, and puffed full-fat soybeans can be used. It is completely feasible and economical to add some or even all fishmeal or soybean meal to oil. The use of puffing technology to process animal products such as intestinal feather meal, blood meal and fish meal can not only improve the digestibility of protein, but also eliminate various bacteria and contaminating viruses. In addition, cottonseed cake and rapeseed cake can also be detoxified to increase their proportion in animal food. (Document source: Zong Li, Agricultural Machinery, 2000, (6): 15-17. Anonymous editor)
