The instruments needed during the experiment: Kjeldahl (Zhejiang Top Instrument Co., Ltd.); Ultraviolet spectrophotometer; Farinograph; Stretcher; laboratory grinding mill; Sulfuric acid, potassium sulfate, copper sulfate, boric acid , Sodium hydroxide, etc. are all analytically pure. Wheat starch extraction process: Wheat flour was sieved through 100 mesh, soaked in alkali water with a ratio of material to water of 1:12 plus pH = 11 for 15 minutes. Centrifugal separation was performed. The residue was filtered and dried to obtain wheat starch.
Experimental procedure: Determination of blue value: Accurately weigh 1mg of starch and prepare a solution, in which iodine 2mg, potassium iodate 20mg, constant volume to 100mL. The absorbance of this solution at a wavelength of 680 nm was measured. Determination of transparency: Weigh 1g of starch, adjust it into 1% of starch milk, measure 50mL of it into a 100mL beaker, place in a boiling water bath and stir with heat for 15min, cool to 25°C, and measure the transmittance at 620nm wavelength. That is transparency. Freeze-thaw stability measurement: Weigh the quantitative starch into a mass fraction of 6% of the starch paste, heat and stir in a boiling water bath for 15 minutes, and cool to room temperature. Weigh a certain amount of starch paste into a centrifuge tube, place it in a refrigerator at -20 to -18°C overnight, and take it out and thawed at room temperature. Centrifuge at 3000 r/min for 15 min and discard the supernatant. Weigh the quality of the sediment and calculate the rate of precipitation. If water does not precipitate, continue freezing until water is deposited.
Physicochemical properties of wheat flour extracted starch: The amount of free starch is an important indicator to measure the quality of starch. Amylose has a higher degree of coloration, while amylopectin absorbs less than 1/10 of the amylose at the same concentration. Therefore, in the samples containing the same free starch, the blue value of the higher amylose content was correspondingly higher. The experimental data shows that the starch content in starch in common wheat flour is higher than that in mechanical milling wheat flour, but the difference is not significant. After starch gelatinization, the degree of molecular rearrangement and mutual association is an important factor affecting the transparency of the starch paste. The amylose starch first escapes from the starch granules during the gelatinization process, and molecular rearrangements and mutual associations easily occur. From the test results, it can be known that starch contained in ordinary wheat flour has low transparency, which may be due to the high content of amylose in the starch. After gelatinization, it is prone to ageing, resulting in gelation or retrogradation, making the transparency lower. Poor transparency will cause aging and affect processing characteristics. Freeze-thaw stability was calculated by freezing and thawing, and the water shrinkage rate of the starch paste was calculated to examine the phenomenon of the occurrence of syneresis. The mechanical starch crushing wheat flour has a high rate of starch precipitation, poor freeze-thaw stability, and is less suitable for making frozen food than the starch contained in ordinary wheat.
Milling in the laboratory enabled the utilization of wheat to reach almost 100%, which changed the proportion of the main components in wheat flour and improved the yield. The starch content in common wheat flour is higher than that contained in mechanically ground wheat flour. The freeze-thaw stability of starch is better than that of the latter, but the transparency is worse than the latter. Due to the lack of gliadin and glutenin in wheat flour, gluten quality cannot be formed and the dough rheological properties are greatly different from wheat dough. However, the better homogeneity of the mechanical comminution of the wheat flour makes the formation process of the dough more stable; the drawing of the tensile curve shows that the dough has small elasticity and high fluidity.
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