Pregelatinized starch is α-starch with hydrogen bonds broken after physical denaturation, which is divided into tapioca pregelatinized starch, corn pregelatinized starch and potato pregelatinized starch, and so on. Based on the original starch’s green and easy degradation and other properties, it also has the advantages of cold water stability and solubility, good water retention, and good viscoelasticity. Factors affecting the solubility of pregelatinized starch in cold water are mainly the granule size of pregelatinized starch, the content of straight-chain starch, and molecular structure.
There are differences in the properties of pregelatinized starch products when the source of raw materials is different. Plants grown in regions with cold climates and large diurnal temperature differences produce coarse starch granules and high relative molecular weights, which improve the viscoelasticity of pregelatinized starches. The relative molecular mass of starch granules can also be increased by applying phosphorus fertilizer to the crop.
An increase in the purity of the original starch significantly improves the viscoelasticity of pregelatinized starches. When the purity of raw starch is the same, the more straight-chain amylopectin is contained, the higher the viscoelasticity of the product is. The viscoelasticity of pregelatinized starch products made from raw starch with a short storage period is high.
Starch water content determines the degree of pasting – the higher the water content the more pasty the starch.
Resistant starch content affects aging, such as paste starch storage at 4 ℃, 25 ℃, and 18 ℃, respectively, 4 ℃ aging fastest because the storage process of resistant starch content is higher.
Pregelatinized starch has smaller grains and poorer crystal structure compared to the original starch. The higher the moisture content in the original starch paste, the lower the peak temperature of solubilization and heat absorption. The granular structure of grain-like starches protects the unsaturated fatty acids, which the pre gelatinization process destroys, making them susceptible to rancidity in storage. The flavor is affected when applied to food. Countermeasures can be the addition of 0.2-2.0% alkali metal orthophosphates, tartrates or citrates, or the addition of disodium hydrometaphosphate, ethylenediamine tetraacetic acid, 0.005-5.0% tetrasodium metaphosphate, or mixtures thereof, as appropriate.
The solubility of pregelatinized starch is related to the integrity of the vacuoles of proteins and lipids on the surface of starch granules. The hydrated form formed by the continued swelling of starch granules after pre gelatinization in water is called a vacuole. Among the proteins and lipids on the surface of the granules are a determining factor for the stable presence of vacuoles, but are not critical for the formation of vacuoles.
A few starch polymers do not exist to recover after the formation of the vacuolar granules. The starch polymers are able to migrate before being captured by cross-linking. Because the formation of the vacuolar polysaccharide chains is due to cross-linking of the swollen granules, it most likely involves double helix formation. The free movement of the polymeric chains dry heat to cause swelling. The vacuolar granules show a very important role in industrial chemical modification of starch function.
Starch dextrinization occurs under certain conditions of temperature, plasticizer and shear. The hydrogen bonds between starch molecules are gradually broken, the granules crack and melt, and the crystal conformation disappears. Then, the hydroxyl groups on the chain of starch molecules interact more easily with starch/polyvinyl alcohol (PVA). It also enhances the affinity of the starch interface, resulting in a more homogeneous distribution and higher compatibility between starch molecules and PVA.
SEM analysis: the hydroxypropyl crosslinked starch after pre gelatinization was cracked into fragments, and no longer possessed the original truncated round, round, and polygonal morphology.XRD analysis: hydroxypropyl crosslinked starch (HP) diffraction peaks appeared at 23 °, 18 °, 17 ° and 15 °, which belonged to the “A” type of diffraction peaks; the crystallization area of pregelatinized starch granules was damaged, and there was no “A” type of characteristic diffraction peaks, and the x-ray diffraction pattern showed the typical “bread peak” of pasted starch. The crystalline zone of the pre-pasteurized starch granules was damaged, and there were no more “A” type diffraction peaks, and the x-ray diffraction pattern showed the typical “bread peak” of pasteurized starch.
The characteristic peak of organically modified montmorillonite OMMT is 2θ = 2.97°. The characteristic peaks of the composite films incorporating pregelatinized starch migrated to 2 θ = 1.91° to 2.04°. It indicates that the pregelatinized starch facilitates the formation of composite structures with nano-inserts. The amorphous structure formed due to the cleavage of the pregelatinized starch particles resulted in an increase in light transmittance after film formation.
The properties of pregelatinized starches from the same production method are different, for example, the viscosity, water absorption, solubility, and viscoelasticity of the paste of the product obtained by the roller method are better than those of the product obtained by the extrusion method. The reason is that the shear force of the extruder used in the extrusion method can cause serious degradation of starch macromolecules. The factors affecting the viscosity of the products under different production conditions during the preparation of pregelatinized starch were, in descending order, the pasting time of the starch paste, pH value, temperature, and mass fraction.
The optimum conditions for production were time for paste T=3h, PH=8, 95°C, and 5% mass fraction. Mixture moisture and extrusion temperature had a significant effect on the properties of pregelatinized starch. The pregelatinized dough had high absorption in water and oil phases at an extrusion temperature of 90°C and 16% moisture.
