Introduction,Influencing factors,Pasteurization temperature,Necessary stages,1) Reversible water absorption stage,2) Irreversible water absorption stage,3) Granule disintegration stage, Introduction Starch is insoluble in water at room temperature, but when the water temperature reaches 53℃ or above, the physical properties of starch undergoes a significant change. The property of starch to dissolve and split to form a uniform paste solution at high temperature is called the gelatinization of starch. Raw starch is heated in water until the micellar structure collapses completely, and the starch molecules form single molecules and become a solution state surrounded by water. As the starch molecules are chained or even branched, pulling each other, resulting in the formation of a viscous paste solution, a phenomenon known as gelatinization. Starch paste temperature must reach a certain degree, different starch paste temperature is not the same, the same kind of starch, particle size is not the same, paste temperature is not the same, large particles of the first paste, small particles of the paste. Enzymatic pasting can also be used. For example: double enzyme method of hydrolyzing starch to make starch syrup. Is to α - - - amylase to make starch in the α - 1, 4 glycosidic bond hydrolysis to generate small molecules of dextrin and other oligosaccharides, and then glycolytic enzyme will dextrin, oligosaccharides in the α - - 1, 6 glycosidic bond and α-1, 4 glycosidic bond to cut off, and finally generate glucose. Take 100 grams of starch in a 400 ml beaker, add 200 ml of water, stir well, formulated into starch slurry, adjust pH = 6.2-6.3 with 5% Na2CO3, add 2 ml of 5% CaCL2 solution, heated on a water bath at 90-95 ℃, and constantly stirring, starch slurry from the beginning of the paste until the complete formation of paste. Add liquefied α---amylase 60 mg, stirring constantly to liquefy, and keep the temperature at 70--80 ℃. The beaker was then moved to an electric furnace and heated to 95°C to boiling and inactivated for 10 minutes. Filtration, filtrate cooled to 55 ℃, add glycolytic enzyme 200 mg, adjust pH = 4.5, in 60-65 ℃ constant temperature water bath paste 3-4 hours, that is, the starch syrup, if you want thick syrup, can be further concentrated. Influencing factors Factors affecting starch pasting are: A starch type and particle size; B water content in food; C additives: high concentration of sugar reduces starch pasting, lipids can form a complex with starch to reduce the degree of pasting and increase the pasting temperature, salt sometimes raises the pasting temperature, and sometimes lowers the pasting temperature; D Acidity: in the range of pH 4-7, the effect of acidity on pasting is not obvious, and when pH is greater than 10.0, the effect is not obvious. D Acidity: the effect of acidity on pasting is not obvious in the range of pH 4-7, but when the pH is greater than 10.0, lowering the acidity will accelerate the paste. The temperature at which the birefringence phenomenon begins to disappear is called the starting paste temperature, and the temperature at which the birefringence phenomenon completely disappears is called the complete paste temperature. The pasting temperature of various starches is different, in which the higher the content of straight-chain starch, the higher the pasting temperature; even for the same kind of starch, because of the different particle sizes, its pasting temperature is also different. Generally speaking, the pasting temperature of small granule starch is higher than that of large granule starch. Necessary Stage The starch in food or the starch in thickening or glazing is heated and absorbs water during cooking, resulting in the pasting of starch. To complete the whole pasting process, starch must go through three stages: reversible water absorption stage, irreversible water absorption stage and granule disintegration stage. (1) Reversible water-absorbing stage Starch is at room temperature, even if it is immersed in cold water, it will not undergo any property change. The starch present in cold water becomes turbid liquid after stirring, and the starch granules will sink again slowly if the stirring is stopped. In the process of cold water immersion, although the starch granules are slightly expanded due to the absorption of a small amount of water, it does not affect the crystalline part of the granules, so the basic properties of starch do not change. In this stage of the starch granule, the water molecules entering the granule can be discharged with the re-drying of the starch and the water molecules inhaled, and the drying is still completely restored to the original state, so this stage is called the reversible water-absorbing stage of starch. (2) Irreversible water-absorbing stage When starch and water are under the condition of heat and warming, water molecules start to enter the crystallization area of starch granules gradually, and then the phenomenon of irreversible water-absorbing appears. This is because some chemical bonds within the starch molecules become very unstable when the external temperature rises, thus favoring the breaking of these bonds. With the breakage of these bonds, the crystalline regions within the starch granules change from the original tightly arranged state to a loose state, which makes the water absorption of starch increase rapidly. The volume of starch granules also expands dramatically, and its volume can be expanded to 50 to 100 times of the original volume. If the starch in this stage is dried again, the water will not be completely discharged and restored to the original structure, so it is called irreversible water absorption stage. (3) Granule disintegration stage After the second stage of irreversible water absorption, starch granule will soon enter the third stage - granule disintegration stage. Because, at this time, the ambient temperature where starch is located continues to increase, so the starch granules still continue to absorb water and expand. When its volume swells to a certain limit, the granule will appear rupture phenomenon, the starch molecules within the granule to the direction of stretching and diffusion, dissolved out of the granule body, the starch molecules will be extended to link each other, entanglement, the formation of a mesh-shaped water-containing colloid. This is the starch paste after the completion of the pasting of the performance of the paste.