1, starch gelatinization
About starch
For most animals, starch in the grain is the most abundant source of energy (70-80% comes from grain). Starch in nature exists in the form of water-soluble particles with unique chemical and physical properties. Starch is a polysaccharide polymerized from glucose and is divided into amylose and amylopectin. The former is a non-branched helical structure; the latter is formed by 24 to 30 glucose residues end-to-end with α-1,4-glycosidic linkages, and α-1,6-glycosidic linkages at the branch. Among them, amylopectin accounts for 70%-80%, and amylose accounts for 20%-30%.
â—‹ Amylose molecules have a wider range of hydrogen bonds due to their linearity. Therefore more energy is needed to break this bond and gelatinize the starch. This means working with saturated steam.
o Amylopectin molecules are non-linear and therefore have weaker binding hydrogen bonds and gel strength.
â—‹ Corn contains 72% starch.
Starch accumulates in the endosperm and deposits in the granular layer in the form of different amylopectin and amylose. The starch granules consist of alternating semi-crystalline and amorphous layers. Most starches will gelatinize when the water is heated above 80 °C. Svihus et al. (2005) describe gelatinization as an expansion drive process. The expansion occurs in the amorphous region. Since the crystallization region does not expand during the expansion process, the stress increases at the interface between the crystalline region and the amorphous region, which is between the crystalline region of amylopectin and the amorphous region of amylose. Meeting point. Therefore, the rapid irreversible cracking and gelatinization of the crystalline region at a certain point in the expansion process begins to occur. Expansion causes almost all of the amylose in the starch to dissolve. The viscosity increases during gelatinization, which is primarily a gel formed by swollen particles and dissolved amylose.
Note: A starch molecule consists of hundreds of glucose molecules, amylopectin contains multiple branches, and amylose is the one that does not contain branches.
Paste
Gelatinization is usually caused by combined moisture, heat, mechanical energy, and pressure.
The gelatinization temperature of starch is related to the type of starch. Amylose is a polymorphic starch that requires more calcination than amylopectin. Hoover defines ordered-disordered phase transitions of starch gelatinization, including water diffusion within the particles, hydration and swelling, absorption of heat, decreased crystallinity, and amylose leaching. The precipitated amylopectin rapidly forms a double helix in a hydrogen bond to form a semi-crystalline region. Since the gelatinized starch is cooled, the dispersed matrix forms a gel or a waxy form, and thus can be used as a binder or a binder.
The amount of heat required for gelatinization depends on the source of the starch. The heat required for wheat starch gelatinization (10.05 Joules/gram) is lower than corn (13.82 Joules/gram). This means that at least 10.05 joules and 13.82 joules of heat are required for each gram of wheat and corn starch gelatinization, respectively. Grains with high amylose content during gelatinization are more resistant to gelatinization than grains of normal or high amylopectin content.
Recent studies have shown that low levels of starch feed starch gelatinization are mainly due to limited water and application temperatures during conventional granulation. At present, the main starch gelatinization occurs when the feed passes through the granulation chamber, rather than during the quenching and tempering process, most likely due to the mechanical shearing force in the ring mold. We also know that gelatinization of these starch granules reduces the amount of water available for gelatinization of other particles during gelatinization.
The gelatinized starch water mixture is cooled to room temperature to crystallize, usually defined as starch aging. Aging is the recombination of molecules separated by starch gelatinization. This phenomenon can be seen as the opposite direction of gelatinization, which may reduce the digestibility of starch. Resistant starch reflects starch aging.
Broiler feed contains a high percentage of corn, which means a high proportion of starch. Under hydrothermal treatment, the starch is gelatinized and the feed particles are combined. It is well known that raw starch needs to be properly cooked to a suitable level of starch gelatinization so that the internal particles are effectively combined to achieve good particle formation and mechanical efficiency. Since no ready-made water can be absorbed during the granulation process, steam conditioning is the only way to obtain moisture and heat into the raw starch granules, only by the quality of the steam and sufficient steam powder action time. An excellently designed conditioner can provide all of these features. Steam conditioning is the core of the entire feed granulation.
Particle size
Control of particle size (diameter and length) is considered to be another possible method to improve particle quality at low tempering temperatures.
The pre-granular material with a diameter of 3 mm can increase the PDI and particle hardness by increasing the particle length (28% and 81%, respectively). The corresponding pellets with a diameter of 4.76 mm have a lower range of improvement (9.5% and 24%, respectively). A similar trend was observed in fattening diets, with PDI and hardness increased by 30% and 86%, respectively, for 3 mm diameter particles, and only 4% and 23% for particles with a diameter of 4.76 mm. WOOD (1987) reported the relationship between particle length and durability, and observed a change in particle length reduction with increasing durability. Interestingly, a 3 mm diameter 6 mm length diet has this highest PDI and particle hardness, whether it is a pre-feed or a fertilizer. Stevens (1987) reported a relatively high degree of gelatinization of the exterior compared to the entire particle. He showed that the heat generated by frictional heat and mechanical shear increases the degree of gelatinization of the particles near the surface of the annular die hole. Therefore, it is a very reasonable method to use a small aperture ring mold to enhance the friction to provide more heat transfer to the internal gelatinized particles.
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Property Unit Result
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Width(mm) Thickness(mm) Length(mm)
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