Starch slowly-digestible wheat flour and preparation method of fine dried noodles

Abstract

The invention discloses a preparation method of starch-slowly-digestible wheat flour and fine dried noodles, and relates to the field of grain processing and production. The invention relates to a preparation method of starch slowly-digested wheat flour. The preparation method comprises the following steps: S1, preparing large-particle wheat flour from oversize products of primary cleaning and secondary cleaning of a flour cleaning system; s2, putting the large-particle wheat powder into a smooth roll flour mill, and lightly pressing to obtain wheat particle powder with the particle size of 91-224 microns or mixed powder of 10-30% of large-particle powder with the particle size of 224 microns and 90-70% of small-particle powder with the particle size of 68 microns. According to the invention, large-particle wheat flour prepared from oversize products of primary cleaning and secondary cleaning of a flour cleaning system is used as a raw material, and is rich in complete endosperm cell clusters and dietary fibers; the particle size range of systematic flour in the wheat flour milling process is controlled, and the prepared starch slowly-digestible wheat flour and fine dried noodles are low in damaged starch content, so that the digestion rate of the starch and the wheat fine dried noodles in a human body is slowed down, and the rising range of a glycemic index is slowed down.

Description

Technical Field

[0001] The present invention belongs to the field of grain processing and production, and particularly relates to a method for preparing slowly digestible wheat flour and noodles. Background Art

[0002] Wheat flour is the basic raw material for making various staple flour foods such as noodles, steamed buns, and bread, playing a crucial role in the human diet structure. Since consumers tend to choose white, delicate refined wheat flour, it has given rise to the phenomenon that the wheat flour processing industry unilaterally pursues "precision, fineness, and whiteness". Although this over - processing trend of wheat flour caters to the market, it also brings a series of potential health hazards. During the refining process of wheat flour, repeated grinding and sieving often lead to the formation of a large amount of damaged starch, and damaged starch is easily hydrolyzed into monosaccharides by amylase in the oral cavity and gastrointestinal tract, thus increasing the digestion rate of refined wheat flour - based food products. At the same time, the significant lack of dietary fiber content in over - processed wheat flour will also significantly reduce its potential benefits to intestinal health and have a negative impact on metabolic health. Therefore, long - term intake of staple flour foods mainly made of refined wheat flour with a relatively fast starch digestion rate and low dietary fiber content will increase the risk of various chronic diseases such as obesity and type II diabetes.

[0003] In response to this problem, experts at home and abroad have conducted a large number of studies aimed at delaying the digestion rate of starch in wheat flour. The existing main methods include: breeding wheat varieties with high amylose content, hydrolyzing amylopectin with amylase and then adding it back, or adding methods such as extrusion, freezing, wet - pressing heat treatment, and resistant starch from other sources to delay the hydrolysis rate of refined wheat flour - based food products into glucose. For example, the patent with the publication number CN114698778B discloses a low - glycemic - index instant cereal noodle, adding resistant starch to slow down the digestion rate; adding wheat bran, aleurone layer, cereal crude fiber, etc. to delay the digestion rate of refined wheat flour - based food products; breeding wheat varieties with a high content of high - molecular - weight glutenin subunits, adding a certain proportion of wheat gluten, free - sulfhydryl oxidant, protease preparation, and flour additives such as salt, alkaline salts (Na2CO3, NaHCO3), and organic acids to strengthen the aggregation behavior of gluten proteins when forming dough from refined wheat flour, so that the gluten network structure is more continuous and compact, and the starch embedding is more firm, thereby hindering the bio - accessibility of amylase to starch and ultimately delaying the hydrolysis rate of refined wheat flour - based food products into glucose. Although these methods and technical means have a certain effect on delaying the starch digestion rate of refined wheat flour, the effect is limited, the cost is high, the cycle is long, and there are certain limitations in the mechanized production of flour - based food products.

[0004] The components of wheat grains, mainly including proteins, starches, dietary fibers, etc., have obvious differences in content, structure, and physicochemical properties from the inside to the outside. Therefore, during the wheat flour milling process, there are significant differences in the particle size, starch and protein properties, and processing quality of the flour in different system flours. The particle size, amylose content, starch swelling power, gel strength, hardness, and chewiness of the flour from the front road middlings system are significantly higher than those of the back road flour, but its amylose / branched amylose ratio is lower than that of the back road flour; there are also obvious differences in the ratio of amylose and branched amylose, the content of damaged starch, and the starch-lipid, starch-protein, and starch-protein-lipid complexes in different system flours. These differences will significantly affect the aggregation and multi-scale structure of starch granules, and thus affect the bioaccessibility of amylase and starch. Some studies have also shown that with the decrease in particle size, the attenuation value and water absorption rate of wheat flour increase significantly, the peak viscosity and retrogradation value show a decreasing trend, and the relative crystallinity and in vitro hydrolysis rate of starch first increase and then decrease.

[0005] Therefore, it becomes an ideal and feasible way to control the digestion rate of starch and wheat noodles in the human body by controlling the particle size range of the system flour during the wheat flour milling process. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method of slowly digestible wheat flour. Using the large-particle wheat flour rich in intact endosperm cell clusters and dietary fibers made from the oversize materials of the 1st and 2nd plansifters of the plansifter system as raw materials, it is made after being lightly pressed by a smooth roll. The slowly digestible wheat flour obtained by processing has a low content of damaged starch, a relatively complete crystal structure and α-helix structure of starch, a high short / long-range order within the molecule, and a significantly reduced digestibility; another object is to provide a preparation method of slowly digestible wheat noodles, which reduces the formation of damaged starch by controlling the particle size range of the system flour during the wheat flour milling process and slows down the digestion rate of refined wheat flour noodles in the human body.

[0007] To achieve the above object, the present invention provides the following technical solutions: A preparation method of slowly digestible wheat flour, comprising the following steps: S1: Using the large-particle wheat flour made from the oversize materials of the 1st and 2nd plansifters of the plansifter system; S2: Placing the large-particle wheat flour in a smooth roll flour mill and lightly pressing it to obtain slowly digestible wheat flour.

[0008] Generally, the feed material of the first cleaning flour system is endosperm particles with more cortex and relatively larger particle size (commonly known as wheat dregs) obtained after grading and sieving the ground materials from the first break roller mill and the second break roller mill. The feed material of the second cleaning flour system is endosperm particles with reduced cortex and smaller particle size (commonly known as wheat middlings) obtained after grading and sieving the ground materials from the first break roller mill and the second break roller mill. Compared with the material obtained after grading and purification by the first cleaning flour system, the sifted material obtained after grading and purification by the second cleaning flour system has less cortex content and higher pure endosperm content.

[0009] Among them, the particle size of the prepared wheat flour is granular flour with a particle size of 91 - 224 μm, or a mixed flour of 10% - 30% large particle flour with a particle size of 224 μm and 90% - 70% small particle flour with a particle size of 68 μm.

[0010] In the S2, the light pressure treatment is carried out by rolling with a smooth roller. The roller gap is adjusted to 0.08 - 0.10 mm, the number of roller presses is 1 - 3 times, and the roller pressure per unit area is 90 - 100 MPa.

[0011] The ratio of the wheat flour with a particle size of 224 μm to the wheat flour with a particle size of 68 μm is: 1:9 - 3:7.

[0012] The present invention also provides another technical solution: A preparation method of slow-digesting starch noodles, comprising the following steps: S1: Add a certain amount of water to wheat flour and knead it with a plate paddle vacuum dough mixer to make dough flakes. The wheat flour is the slow-digesting starch wheat flour prepared by the above-mentioned preparation method of slow-digesting starch wheat flour; S2: Use a sheeter to roll the dough flakes into a smooth noodle sheet and place it in a constant temperature and humidity box for proofing; S3: After proofing, cut the noodles into fresh wet noodles, and obtain dried noodles after drying treatment.

[0013] In the S1, the water addition amount of the wheat flour is 36 - 38%, and the water temperature is 35 ± 2°C. When the wheat flour is large particle flour with a particle size of 224 μm, it needs to be left standing until the water is completely absorbed before kneading.

[0014] In the S2, the vacuum degree of the plate paddle vacuum dough mixer is -0.05 Mpa, and the kneading time is 50 rpm, 200 g of flour / 3 min; 120 rpm, 200 g of flour / 7 min.

[0015] In the S3, the roller gap of the sheeter is adjusted to 5.0 mm for rolling once, 4.0 mm for rolling once, 3.0 mm for rolling twice, and 2.0 and 1.0 mm for rolling twice each.

[0016] In step S3, the proofing temperature is 35 - 40°C, the relative humidity is 75 - 80%, and the proofing time is 15 - 30 min for 200 g of flour.

[0017] In step S3, the nip of the cutter is 1.0 mm, and the length of the fresh wet noodle is 20 cm.

[0018] In the drying process of step S3, the temperature is 20 - 45°C, the humidity is 55% - 85%, and the moisture content of the noodle is 14.5%.

[0019] Preferably, under the conditions of a temperature of 20 - 30°C and a humidity of 75% - 85%, ventilation is carried out until the moisture content of the fresh wet noodle drops to 27% - 28%; then the temperature is raised to 40°C, and the relative humidity is controlled at 75% - 85% until the moisture content of the noodle drops to 25%; the temperature is continuously raised to 45°C, and the humidity is reduced to 55% - 60% until the moisture content of the noodle drops to 16% - 17%; the temperature is reduced at a rate of 1°C per 2 - 3 minutes until the moisture content of the noodle drops to 14.5%.

[0020] Damaged starch refers to the structural damage of starch granules caused by mechanical force during wheat grinding. Compared with intact starch granules, damaged starch has a larger surface area and is more accessible to enzymes. Therefore, damaged starch is easily hydrolyzed by amylase in the oral cavity and gastrointestinal tract into monosaccharides, thereby increasing the digestion rate of refined wheat flour products. The amylose and amylopectin in wheat flour also affect the digestion rate of starch. Amylose is composed of long-chain glucose units linked by α-1,4-glycosidic bonds. Due to its linear structure, it limits the rapid degradation by enzymes, so its digestion rate is usually low in the gastrointestinal tract. Amylopectin, on the other hand, is easily degraded by digestive enzymes due to its branched structure and has a higher digestion rate, resulting in a faster increase in blood sugar. The present invention controls the particle size of wheat flour so that the wheat flour has a complete prismatic endosperm cell mass, the starch granules are wrapped in endosperm cells, the amylose content is high, the damaged starch content is low, and it is not easy to combine with amylase, so the starch digestion rate is low.

[0021] Previous studies found that after the whole wheat flour from the 1st break system enters the purifying system, the median particle size (D50) of the oversize materials retained on the sieves of the 1st purifying (1P) and 2nd purifying (2P) systems is about 224 μm. It has intact prismatic endosperm cell clusters, starch granules are wrapped inside the endosperm cells, and only a small amount of type A starch is exposed; the damaged starch content is only 0.71%, much lower than that of the commercially available refined wheat flour of the same batch (17.45%); the total dietary fiber content is as high as 4.11%, about 3.5 times that of the commercially available refined wheat flour of the same batch; under the same conditions, the glucose content generated by digesting 100 g of the oversize materials from the 1P and 2P sieves for 2 hours is about 21.60 g, and the glucose content generated by digesting the cooked noodles for 2 hours is about 29.42 g, which are 36% of the refined wheat flour (Fc, 68 μm, 59.70 g) and the refined wheat flour noodles (81.33 g), respectively.

[0022] Compared with the refined wheat flour added with bran, the slow-digesting wheat flour of the present invention is white in color, and the noodles made from it have a smooth, chewy and elastic texture; compared with the refined wheat flour, this kind of wheat flour has a low damaged starch content, the crystal structure and α-helix structure of the starch are relatively complete, and the short / long-range order within the molecule is relatively high, thus significantly reducing its digestibility and significantly slowing down the increase in blood glucose index 2 hours after eating the cooked noodles.

[0023] Therefore, the present invention has the following beneficial effects: (1) Using the oversize materials from the 1st and 2nd purifying sieves of the purifying system to make wheat coarse particle flour with a particle size of 224 μm as the raw material, which is rich in intact endosperm cell clusters and dietary fiber, the slow-digesting wheat flour made has a low damaged starch content, the crystal structure and α-helix structure of the starch are relatively complete, and the short / long-range order within the molecule is relatively high, thus significantly reducing its digestibility. (2) By controlling the particle size range of the systematic flour in the wheat flour milling process to regulate the digestion rate of starch and wheat noodles in the human body and slow down the increase in blood glucose index. Description of the Drawings

[0024] Figure 1 It is the apparent morphological structure of the starch granules in the wheat flour system of Example 1.

[0025] Figure 2 It is the apparent morphological structure of the starch granules in the wheat flour system of Example 2.

[0026] Figure 3 It is the apparent morphological structure of the starch granules in the wheat flour system of Example 3.

[0027] Figure 4 It is the apparent morphological structure of the starch granules in the wheat flour system of Example 4.

[0028] Figure 5 It is the apparent morphological structure of the starch granules in the wheat flour system of Example 5.

[0029] Figure 6 It is the apparent morphological structure of starch granules in the wheat flour system in Example 6. Detailed implementation manners

[0030] Example 1 A slowly digestible starch wheat granule flour (F1) with a particle size of 224 μm; A preparation method of the above-mentioned wheat flour, comprising the following steps: Take the large wheat granule flour on the sieve of the purifying system in the wheat flour milling process, place it in a smooth roll flour mill, and perform light pressing treatment. The particle size is measured to be 224 μm by dry method using a laser particle size analyzer.

[0031] A slowly digestible starch noodles, comprising the following steps: S1: Accurately weigh 200 g of the above-mentioned wheat granule flour, add an appropriate amount of distilled water, let it stand until the water is completely absorbed, and then use a plate paddle vacuum dough mixer. The vacuum degree is -0.05 Mpa, the mixing time is 50 rpm, 200 g of flour / 3 min; let it stand for 5 min; 120 rpm, 200 g of flour / 10 min to obtain dough flakes with a moisture content of 37%. S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) for proofing for 15 - 30 min; S3: Adjust the roll gap of the rolling machine to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodles is 20 cm. Hang the raw noodles on the rod and place them on the intelligent noodle drying test platform, ventilate under the conditions of a temperature of 20 - 30 °C and a humidity of 75% - 85% until the noodle moisture content drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% for ventilation until the noodle moisture content drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% for ventilation until the noodle moisture content drops to 16% - 17%; cool down at a cooling rate of 1 °C per 2 - 3 minutes until the noodle moisture content drops to 14.5%.

[0032] Example 2 A slowly digestible starch wheat granule flour (F2) with a particle size of 115 μm; A preparation method of the above-mentioned wheat flour, comprising the following steps: Place the slowly digestible starch wheat granule flour (F1) with a particle size of 224 μm in a smooth roll flour mill, adjust the roll gap to 0.16 mm and the unit area pressure to 90 MPa, and roll once to obtain wheat flour with a particle size of 115 μm.

[0033] A slowly digestible starch noodles, comprising the following steps: S1: Accurately weigh 200 g of the above-mentioned wheat granule flour, add an appropriate amount of distilled water, and use a plate blade vacuum dough mixer with a vacuum degree of -0.05 Mpa. The kneading time is 50 rpm, 200 g of flour per 3 min; 120 rpm, 200 g of flour per 7 min to obtain dough flakes with a moisture content of 37%; S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) and proof for 15 - 30 min; S3: Adjust the roll gap of the rolling machine to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodles is 20 cm. Hang the raw noodles on a rod and place them on an intelligent noodle drying test platform. Ventilate under the conditions of a temperature of 20 - 30 °C and a humidity of 75% - 85% until the moisture content of the noodles drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% and ventilate until the moisture content of the noodles drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% and ventilate until the moisture content of the noodles drops to 16% - 17%; cool down at a cooling rate of 1 °C every 2 - 3 minutes until the moisture content of the noodles drops to 14.5%.

[0034] Example 3 A slowly digestible wheat granule flour (F3) with a particle size of 91 μm; A method for preparing the above-mentioned wheat flour, comprising the following steps: Place the slowly digestible wheat granule flour (F1) with a particle size of 224 μm in a smooth roll flour mill, adjust the roll gap to 0.12 mm and the unit area pressure to 100 MPa, and roll three times to obtain wheat flour with a particle size of 91 μm.

[0035] A slowly digestible starch noodle, comprising the following steps: S1: Accurately weigh 200 g of the above-mentioned wheat granule flour, add an appropriate amount of distilled water, and use a plate blade vacuum dough mixer with a vacuum degree of -0.05 Mpa. The kneading time is 50 rpm, 200 g of flour per 3 min; 120 rpm, 200 g of flour per 7 min to obtain dough flakes with a moisture content of 37%; S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) and proof for 15 - 30 min; S3: Adjust the roll gap of the tablet press to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodle is 20 cm. Hang the raw noodles on the rod and place them on the intelligent noodle drying test platform. Ventilate under the conditions of temperature 20 - 30 °C and humidity 75% - 85% until the moisture content of the noodles drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% and ventilate until the moisture content of the noodles drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% and ventilate until the moisture content of the noodles drops to 16% - 17%; cool down at a cooling rate of 1 °C per 2 - 3 minutes until the moisture content of the noodles drops to 14.5%.

[0036] Example 4 A starch slowly digested wheat blended flour (F5) with a particle size of 224 μm and a particle size of 68 μm mixed in a ratio of 1:9; A method for preparing the above wheat flour, comprising the following steps: Place the starch slowly digested wheat particle flour (F1) with a particle size of 224 μm in a smooth roll flour mill, adjust the roll gap to 0.04 mm and the unit area pressure to 80 MPa, and roll 5 times to obtain wheat flour (F4) with a particle size of 68 μm. Then mix the starch slowly digested wheat particle flour (F1) with a particle size of 224 μm and the wheat flour (F4) with a particle size of 68 μm evenly in a ratio of 1:9 to obtain a starch slowly digested wheat particle blended flour F5 with a particle size of 224 μm and a particle size of 68 μm.

[0037] A starch slowly digested noodle, comprising the following steps: S1: Accurately weigh 200 g of the above wheat particle flour, add an appropriate amount of distilled water, and use a plate blade vacuum dough mixer with a vacuum degree of -0.05 Mpa, kneading time 50 rpm, 200 g of flour / 3 min; 120 rpm, 200 g of flour / 7 min to obtain noodle flocs with a moisture content of 37%; S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) and let it proof for 15 - 30 min; S3: Adjust the roll gap of the tablet press to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodle is 20 cm. Hang the raw noodles on the rod and place them on the intelligent noodle drying test platform. Ventilate under the conditions of temperature 20 - 30 °C and humidity 75% - 85% until the moisture content of the noodles drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% and ventilate until the moisture content of the noodles drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% and ventilate until the moisture content of the noodles drops to 16% - 17%; cool down at a cooling rate of 1 °C per 2 - 3 minutes until the moisture content of the noodles drops to 14.5%.

[0038] Example 5 A starch slowly digested wheat blended flour (F6) with a particle size of 224 μm and a particle size of 68 μm mixed in a ratio of 2:8; A method for preparing the above wheat flour, comprising the following steps: Place the starch slowly digested wheat particle flour (F1) with a particle size of 224 μm in an optical roller flour mill, adjust the roll gap to 0.04 mm and the unit area pressure to 80 MPa, and roll 5 times to obtain wheat flour (F4) with a particle size of 68 μm. Then mix the starch slowly digested wheat particle flour (F1) with a particle size of 224 μm and the wheat flour (F4) with a particle size of 68 μm evenly in a ratio of 2:8 to obtain a starch slowly digested wheat particle blended flour F6 with a particle size of 224 μm and a particle size of 68 μm.

[0039] A starch slowly digested noodle, comprising the following steps: S1: Accurately weigh 200 g of the above wheat particle flour, add an appropriate amount of distilled water, and use a plate blade vacuum dough mixer with a vacuum degree of -0.05 Mpa, kneading speed 50 rpm, 200 g of flour / 3 min; 120 rpm, 200 g of flour / 7 min to obtain noodle flocs with a moisture content of 37%; S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) and proof for 15 - 30 min; S3: Adjust the roll gap of the tablet press to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodle is 20 cm. Hang the raw noodles on the rod and place them on the intelligent noodle drying test platform. Ventilate under the conditions of temperature 20 - 30 °C and humidity 75% - 85% until the moisture content of the noodles drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% and ventilate until the moisture content of the noodles drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% and ventilate until the moisture content of the noodles drops to 16% - 17%; cool down at a cooling rate of 1 °C every 2 - 3 minutes until the moisture content of the noodles drops to 14.5%.

[0040] Example 6 A starch slowly digested wheat blended flour (F7) with a particle size of 224 μm and a particle size of 68 μm mixed in a ratio of 3:7; A method for preparing the above wheat flour, comprising the following steps: Place the starch slowly digested wheat granular flour (F1) with a particle size of 224 μm in a smooth roll flour mill, adjust the roll gap to 0.04 mm and the unit area pressure to 80 MPa, and roll 5 times to obtain wheat flour (F4) with a particle size of 68 μm. Then mix the starch slowly digested wheat granular flour (F1) with a particle size of 224 μm and the wheat flour (F4) with a particle size of 68 μm evenly in a ratio of 3:7 to obtain a starch slowly digested wheat granular blended flour F7 with a particle size of 224 μm and a particle size of 68 μm.

[0041] A method for making starch slowly digested noodles, comprising the following steps: S1: Accurately weigh 200 g of the above wheat granular flour, add an appropriate amount of distilled water, and use a plate blade vacuum dough mixer with a vacuum degree of -0.05 Mpa, mixing speed 50 rpm, 200 g of flour / 3 min; 120 rpm, 200 g of flour / 7 min to obtain noodle flocs with a moisture content of 37%; S2: Place it in a constant temperature and humidity box (humidity 75 - 85%, 35 - 40 °C) and proof for 15 - 30 min; S3: Adjust the roll gap of the tablet press to 5.0 mm and roll once, 4.0 mm and roll once, 3.0 mm and roll twice, and then roll twice at 2.0 and 1.0 mm respectively. The cutting knife rolling distance is 1.0 mm, and the length of the raw noodles is 20 cm. Hang the raw noodles on the rod and place them on the intelligent noodle drying test platform. Ventilate under the conditions of a temperature of 20 - 30 °C and a humidity of 75% - 85% until the moisture content of the noodles drops to 27% - 28%; raise the temperature to 40 °C and the relative humidity drops to 70% - 80% and ventilate until the moisture content of the noodles drops to 25%; continue to raise the temperature to 45 °C and reduce the humidity to 55% - 60% and ventilate until the moisture content of the noodles drops to 16% - 17%; cool down at a cooling rate of 1 °C per 2 - 3 minutes until the moisture content of the noodles drops to 14.5%.

[0042] Characterize the apparent morphological structure of the starch granules in the wheat flour system prepared in the above examples, then measure the contents of total starch, amylose, amylopectin, damaged starch, and dietary fiber, and finally measure the starch digestion levels of wheat flour and cooked noodles, namely the amount of glucose generated by in vitro digestion for 2 hours.

[0043] I. Characterization of the Morphological Structure of Starch Granules in the Wheat Flour System Use a high - power scanning electron microscope to characterize the apparent morphological structure of starch granules in wheat particle flour samples with different particle sizes. Use tape to pick up the dry sample and spread it evenly, and blow off the excess particles on the surface. Conduct sputtering treatment in a vacuum environment, and then observe the apparent morphology of the starch in wheat particle flour under the magnification conditions of 200 times and 1000 times respectively. The results are as Figure 1-6 shown.

[0044] Observed by a high - power scanning electron microscope, in Example 1, the wheat flour has a complete prismatic endosperm cell mass, and the starch granules are wrapped in the endosperm cells, with only a small amount of type A starch exposed; in Example 2, a small amount of prismatic endosperm cell masses are damaged, the amount of precipitated starch granules increases, scattered near the endosperm cells, showing free state, AB starch - bound state, and starch - protein - bound state; in Example 3, some prismatic endosperm cell masses are damaged, releasing relatively more starch granules, scattered near the endosperm cells, showing free state, AB starch - bound state, and starch - protein - bound state; in Examples 4 - 6, the prismatic endosperm cell masses are completely damaged, and the starch granules are completely precipitated, scattered near the endosperm cells.

[0045] II. Total Starch Content Test The total starch content was determined using a direct / branched chain starch kit. The test steps were as follows: The determination of total starch was selected from the starch content detection kit of Solarbio. The reagents included: Reagent 1 (1 bottle of 35 mL liquid), Reagent 2 (1 bottle of 35 mL liquid), Reagent 3 (2 bottles of powder), and standard (1 vial of powder: glucose standard solution). Standard: Before use, add 1 mL of distilled water to dissolve it, prepare a 10 mg / mL glucose standard solution, and store it at 2 - 8 °C for two weeks. Preparation of working solution: Before use, add 1 bottle of Reagent 3 to 6.75 mL of distilled water, then slowly add 38.25 mL of concentrated sulfuric acid, stir continuously, and dissolve it completely for use. Operating steps: Sample treatment: Weigh about 0.03 g of the sample and grind it in a mortar. Add 0.6 mL of Reagent 1, transfer it to an EP tube after thorough homogenization, extract it in a water bath at 80 °C for 30 min, centrifuge at 3000 g at room temperature for 5 min, discard the supernatant, and keep the precipitate. Add 0.3 mL of double-distilled water to the precipitate, put it in a boiling water bath for gelatinization for 15 min (seal tightly to prevent water loss), cool it, add 0.6 mL of Reagent 2, put it in a boiling water bath for extraction for 15 min, shake it 3 - 5 times, cool it, centrifuge at 8000 g at room temperature for 15 min, and take the supernatant for testing. If it is still turbid after centrifugation, centrifuge again and take the supernatant. Determination steps: Preheat the spectrophotometer for more than 30 min, adjust the wavelength to 620 nm, and zero with distilled water. Adjust the water bath to 95 °C. Preparation of standard: Dilute the 10 mg / mL glucose standard solution to obtain 0.2, 0.1, 0.05, 0.04, 0.03, 0.02, 0.01 mg / mL standard solutions for standby. Standard determination: Take 0.2 mL of the standard solution (using distilled water as the blank) and 1 mL of the working solution into an EP tube, place it in a water bath at 95 °C for 10 min (seal tightly to prevent water loss), cool it naturally to room temperature, measure the absorbance values A standard and A blank at a wavelength of 620 nm, calculate ΔA = A standard - A blank. The standard curve only needs to be made 1 - 2 times. Take 0.2 mL of the sample and 1 mL of the working solution into an EP tube, place it in a water bath at 95 °C for 10 min (seal tightly to prevent water loss), cool it naturally to room temperature, measure the absorbance value A determination at a wavelength of 620 nm, ΔA' = A determination - A blank. The blank tube only needs to be made 1 - 2 times. Calculation of starch content, drawing of standard curve: Based on the concentration of the standard tube (x, mg / mL) and the absorbance ΔA standard (y, ΔA standard), establish a standard curve. According to the standard curve, substitute ΔA' into the equation to obtain x (mg / mL). Calculation of starch content: Starch content (mg / g mass) = x × V extraction ÷ W ÷ 1.11 × F = 0.811x ÷ W × F. V extraction: Volume after extraction, 0.9 mL; W: Sample mass, g; F: Sample dilution factor; 1.11: A constant for converting the glucose content measured by this method to starch content, that is, 111 μg of glucose colored with anthrone reagent is equivalent to the color shown by 100 μg of starch colored with anthrone reagent. The results are shown in Table 1.

[0046] Table 1 Test results of total starch content. Wheat flour sample Total starch / % Example 1 (F1) 69.9±0.00 Example 2 (F2) 69.64±0.58 Example 3 (F3) 69.23±0.58 D50 = 68μm (F4) 68.33±0.57 Example 4 (F5) 65.91±2.95 Example 5 (F6) 66.19±2.04 Example 6 (F7) 68.27±2.68 Refined wheat flour 69.86±2.07

[0047] As can be seen from Table 1, the total starch contents of Examples 1-6 and wheat with a particle size D50 = 68 μm (F4) are all higher than 65%, and are basically close to the total starch content of commercially available refined wheat flour.

[0048] III. Test of damaged starch content The test method for damaged starch content refers to "GB / T 31577-2015 Grain and oil inspection - Determination of damaged starch in wheat flour - Ammeter method"; accurately weigh 1.000 ± 0.100 g of the above wheat flour sample with a special sample spoon for the instrument. Place the glass reaction cup in the correct position of the instrument and lower the measuring rod. Input the accurate sample mass (accurate to 0.001 g), protein content (dry basis) and moisture value, insert the sample into the sample feeding port of the instrument, and perform the test according to the requirements of the instrument instruction manual. After the test, record the obtained iodine absorption rate (AI%), UCD and UCDc values. The measurement results are retained to one decimal place, and three parallel tests are performed on the same group of samples. The results are shown in Table 2.

[0049] Table 2 Test results of damaged starch content. Wheat flour sample Damaged starch / % Example 1 (F1) 0.71±0.07 Example 2 (F2) 1.41±0.21 Example 3 (F3) 7.77±0.52 D50 = 68μm (F4) 13.19±0.75 Example 4 (F5) 11.24±0.01 Example 5 (F6) 10.17±0.04 Example 6 (F7) 8.80±0.06 Refined wheat flour 17.45±0.15

[0050] As can be seen from Table 2, the damaged starch content of the wheat flour in Example 1 is only 0.71%, which is much lower than the damaged starch content (17.45%) of the commercially available refined wheat flour in the same batch; the damaged starch content of the wheat flour in Example 2 increases to 1.41%, which is 2 times the damaged starch content of the wheat flour in Example 1. The damaged starch content of the wheat flour in Example 3 continues to increase to 7.77%, but the damaged starch contents of the wheat flours in Examples 1-3 are still much lower than the damaged starch content (17.45%) of the commercially available refined wheat flour in the same batch. The damaged starch contents of the mixed wheat flours in Examples 4-6 are lower than those of D50 = 68 μm (F4). Although they are higher than the damaged starch contents of Examples 1-3, they are much lower than the damaged starch content (17.45%) of the commercially available refined wheat flour in the same batch.

[0051] IV. Determination of amylose and amylopectin content The method for determining amylose and amylopectin content is carried out using an amylose / amylopectin kit; amylopectin, also known as glutinous starch, is generally composed of thousands of glucose residues. The ratio and content of amylose and amylopectin in starch have a direct impact on the processing, physical and chemical properties, gelatinization temperature, etc. of starch products. Amylopectin forms a red-violet complex with iodine. Ethanol is used to separate soluble sugars and starch in the sample, and then iodine is reacted with it to obtain the amylopectin content. The specific determination process is as follows: I. Sample treatment: 1. Weigh 0.005 g of the dried sample and add 1 mL of Reagent I, and homogenize thoroughly. 2. Extract in a water bath at 80 °C for 30 min, centrifuge at 3000 g and 25 °C for 5 min, discard the supernatant, and keep the precipitate. 3. Add 1 mL of Reagent II (ether) to the precipitate in step 2 and shake for 5 min; centrifuge at 3000 g and 25 °C for 5 min, discard the supernatant, and keep the precipitate. 4. Add 5 mL of Reagent IV to the precipitate in step 3 and dissolve it completely, heat in a water bath at 90 °C for 10 min, cool, centrifuge at 3000 g and 25 °C for 5 min, and take the supernatant for testing. II. Determination steps: 1. Preheat the spectrophotometer / microplate reader for more than 30 min, adjust the dual wavelengths to 530 nm and 755 nm, and zero the spectrophotometer with distilled water. 2. Dilution of the standard solution: Dilute the 10 mg / mL standard solution with Reagent IV to 1, 0.8, 0.6, 0.4, 0.2, 0.1, 0.05 mg / mL standard solutions for testing. III. Calculation of amylopectin content: 1. Establishment of the standard curve Taking the concentration of the amylopectin standard solution as the x-axis (x, mg / mL) and the corresponding ΔA standard of the standard solution as the y-axis (y, ΔA standard), establish the standard curve to obtain the standard equation y = kx + b, and substitute ΔA determination into the equation to obtain x (mg / mL). 2. Amylopectin content (mg / g mass) = x × V total sample ÷ W = 5x ÷ W V total sample: Volume of Reagent IV added, 5 mL; W: Sample mass, g. Amylose content = Total starch content - Amylopectin content. The results are shown in Table 3.

[0052] Table 3 Test results of amylose and amylopectin content. Wheat flour sample Amylose / % Amylopectin / % Example 1 (F1) 26.32±0.56 42.58±0.56 Example 2 (F2) 26.70±1.40 42.94±1.98 Example 3 (F3) 26.44±0.46 42.80±0.11 D50 = 68μm (F4) 26.70±1.40 41.63±1.96 Example 4 (F5) 27.99±0.4 37.92±2.05 Example 5 (F6) 28.87±0.73 37.32±1.80 Example 6 (F7) 28.73±1.48 39.48±2.07 Refined wheat flour 24.51±0.68 45.35±1.68

[0053] As can be seen from Table 3, the amylose content in the wheat flour of Examples 1-6 is higher than that in the commercially available refined wheat flour of the same batch, and the amylopectin content is lower than that in the commercially available refined wheat flour of the same batch, indicating that the digestion rate of the wheat flour of Examples 1-6 is lower than that of the commercially available refined wheat flour.

[0054] V. Determination of dietary fiber content Determination of dietary fiber content: Weigh 19.52 g of 2-(N-morpholino)ethanesulfonic acid and 12.2 g of tris(hydroxymethyl)aminomethane, and dissolve them in 1.7 L of distilled water. Adjust the pH with 6 mol / L sodium hydroxide solution according to the room temperature. Adjust the pH to 8.3 at 20 °C, 8.2 at 21 °C, 8.1 at 28 °C, and correct the pH by interpolation for other room temperatures between 20 °C and 28 °C. Dilute with water to 2 L to obtain MES-TRIS buffer solution (0.05 mol / L). Dry the wheat flour sample to a moisture content of <10%, weigh 1.0 g of the sample and transfer it to a 100 ml beaker, add 40 ml of MES-TRIS buffer solution, and stir magnetically until the sample is completely dispersed. At the same time, prepare blank sample solution and sample solution for synchronous operation; add 50 μL of thermostable α-amylase solution (CAS 9000-85-5, 10000 U / mL) to the sample solution and blank sample solution respectively, stir slowly, cover with aluminum foil, and place in a constant temperature shaking water bath at 95-100 °C for continuous shaking. Start timing when the temperature rises to 95 °C, and extend the reaction time to 2 h; take out the beaker and cool it to 60 °C at room temperature, then transfer it to a 60 °C water bath, add 100 μL of protease solution (CAS 9014-01-1, 300 U / mL), cover with aluminum foil, start timing, and continue shaking for 1 h; open the aluminum foil, add 5 mL of ethanol solution (3 moL / L) while stirring, control the temperature of the sample solution to be maintained at 60 °C ± 1 °C, and at the same time adjust the pH of the sample solution to 1.5 ± 0.2 with sodium hydroxide (1 moL / L) or hydrochloric acid solution (1 moL / L); add 100 μL of amyloglucosidase solution (CAS 9032-08-0, 2500 U / mL) while stirring, cover with aluminum foil, and continue to shake continuously in a water bath at 60 °C ± 1 °C for 1 h; add ethanol (95%) preheated to 60 °C ± 1 °C to the sample enzyme solution according to the volume ratio of ethanol to sample solution of 4:1, take out the beaker, cover with aluminum foil, and precipitate at room temperature for 3 h; use a vacuum filtration device to filter the sample ethanol precipitation solution, wash the obtained precipitate with 78% ethanol twice, 95% ethanol twice, and acetone twice, filter to remove the washing solution, dry to constant weight at 105 °C, weigh, and calculate the mass of the sample residue; use the Kjeldahl method, with 6.25 as the conversion factor, to determine and calculate the protein content in the residue; use the high-temperature (525 °C) ignition method to determine the ash content of the residue, and subtract the protein and ash content from the total residue content to obtain the dietary fiber content. The results are shown in Table 4. Wheat flour sample Dietary fiber content / % Example 1 (F1) 4.11±0.06 Example 2 (F2) 4.12±0.01 Example 3 (F3) 4.10±0.03 D50 = 68μm (F4) 4.15±0.01 Example 4 (F5) 4.09±0.01 Example 5 (F6) 4.15±0.01 Example 6 (F7) 4.07±0.01 Refined wheat flour 1.17±0.09

[0055] As can be seen from Table 4, the dietary fiber content in the wheat flour of Examples 1-6 is much higher than that of the commercially available refined wheat flour of the same batch, about 3.5 times that of the refined wheat flour, indicating that by controlling the particle size of the wheat flour, the dietary fiber content of the wheat flour can be effectively protected, the loss of dietary fiber can be reduced, and thus the digestion process of the wheat flour in the intestine can be slowed down.

[0056] VI. Determination of Glucose Production Amount after 2-Hour in Vitro Digestion of Starch Determination of glucose production amount after 2-hour in vitro digestion of starch; determination of the rate of starch digestion and hydrolysis into glucose in two stages of the gastrointestinal tract. First, take a sample containing 100 mg of starch on a dry basis, add 5 mL of deionized water to a 50 mL centrifuge tube, shake and mix uniformly, and heat at 90 °C for 10 min for gelatinization. After cooling, equilibrate the gelatinized sample in a 37 °C water bath for 20 min, add 2 mL of hydrochloric acid (0.02 mol / L) pepsin (1 mg / mL) mixed solution, and incubate in a 37 °C water bath for 30 min. Adjust the pH to 6.0 with sodium hydroxide (0.02 mol / L) to end the digestion simulation in the gastric stage. Subsequently, add 2.0 mL of acetate buffer (pH = 7), shake and mix well, then add 2 mL of a mixed enzyme solution of pancreatin (2 mg / mL) and amyloglucosidase (35 U / mL) for intestinal digestion. At different time points, take 100 μL of the sample solution and disperse it in 500 μL of absolute ethanol to terminate the enzymatic reaction. Centrifuge at 5000 r / min for 10 min, keep the supernatant and discard the precipitate. Use the dinitrosalicylic acid method to determine the glucose content released in the supernatant according to the glucose standard curve (y = 0.531x + 0.004, R 2 = 0.9996): The glucose release amount is fitted with a first-order kinetic equation: C t = C ∞ (1 - e -kt ). In the formula: C t is the starch hydrolysis percentage (%) at time t; C∞ is the equilibrium value (%) of glucose released by starch hydrolysis at ∞ time; k is the starch hydrolysis equilibrium constant, and t is the selected hydrolysis time. The results are shown in Table 5.

[0057] Table 5 Results of Glucose Production Amount Determination. Wheat flour sample Glucose content of wheat flour / g Glucose content of dried noodles / g Example 1 (F1) 21.60±0.32 29.42±0.31 Example 2 (F2) 21.67±1.74 21.67±0.22 Example 3 (F3) 21.52±0.21 21.52±0.24 D50 = 68μm (F4) 45.37±1.35 25.63±0.15 Example 4 (F5) 38.76±0.21 21.70±0.62 Example 5 (F6) 36.83±0.15 23.61±0.11 Example 6 (F7) 35.24±0.12 28.94±0.49 Commercially available refined 59.70±0.89 81.33±0.35

[0058] As shown in Table 5, the glucose production amounts after 2-hour in vitro digestion of starch in wheat flour and noodles in Examples 1 - 6 are much lower than those of starch in wheat flour and noodles sold on the market in the same batch. Among them, the glucose production amounts after 2-hour in vitro digestion of starch in wheat flour in Examples 1 - 3 are lower than those of starch in the wheat flour mixture in Examples 4 - 6.

[0059] Therefore, the present invention uses the large-grain wheat flour made from the overflows of the first and second purifying sieves in the purifying system as raw materials, which is rich in intact endosperm cell clusters and dietary fiber. By controlling the particle size range of the system flour in the wheat flour-making process, the prepared slow-digesting wheat flour and noodles have a low content of damaged starch, and the crystal structure and α-helix structure of the starch are relatively complete, with a relatively high short / long-range order within the molecule. As a result, the digestion rate of the starch and wheat noodles in the human body is reduced, and the increase in blood glucose index is slowed down.

Claims

1. A method for preparing slowly digestible starch wheat flour, characterized in that: The following steps are involved: S1: Wheat flour is made from the large-grain wheat flour from the 1st and 2nd sieves of the powder purification system; S2: placing the large-grain wheat flour in a smooth roller mill and lightly pressing it to obtain starch-slowly digestible wheat flour; The prepared slowly digestible starch wheat flour has a particle size of 91-224 μm, or a mixed powder of 10%-30% of large particle powder with a particle size of 224 μm and 90%-70% of small particle powder with a particle size of 68 μm.

2. The method for preparing slowly digestible starch wheat flour according to claim 1, characterized in that: The light pressing treatment in S2 adopts smooth roller rolling, the roller spacing is adjusted to 0.08-0.10 mm, the rolling times are 1-3 times, and the roller pressure per unit area is 90-100 MPa.

3. The method for preparing slowly digestible starch wheat flour according to claim 1, characterized in that: The ratio of the large-grain wheat flour with a particle size of 224 μm to the small-grain wheat flour with a particle size of 68 μm is 1:9 to 3:

7.

4. A method for preparing slowly digestible starch noodles, characterized in that: The following steps are involved: S1: adding a certain amount of water to wheat flour, and kneading the flour using a plate-type paddle vacuum dough mixer to make dough, wherein the wheat flour is the starch slowly digestible wheat flour prepared by the method for preparing starch slowly digestible wheat flour according to claim 1; S2: Use a sheeting machine to press the dough into a smooth dough strip, and place it in a constant temperature and humidity chamber for proofing; S3: After proofing, the noodles are cut into strips to make fresh wet noodles, and then dried to obtain noodles.

5. The method for preparing the slowly digestible starch noodles according to claim 4, characterized in that: The amount of water added to the wheat flour in S1 is 36-38%, and the water temperature is 35±2°C.

6. The method for preparing the slowly digestible starch noodles according to claim 4, characterized in that: The vacuum degree of the plate-type paddle vacuum dough mixer in S2 is -0.05Mpa, and the dough mixing time is 50rpm, 200g flour / 3min; 120rpm, 200g flour / 7min.

7. The method for preparing the slowly digestible starch noodles according to claim 4, characterized in that: The roller gap of the tablet press in S3 was adjusted to 5.0 mm for 1 time, 4.0 mm for 1 time, 3.0 mm for 2 times, and 2.0 and 1.0 mm for 2 times each.

8. The method for preparing slowly digestible starch noodles according to claim 4 or 7, characterized in that: In the S3, the proofing temperature is 35-40° C., the relative humidity is 75-80%, and the proofing time is 200 g flour / 15-30 min.

9. The method for preparing slowly digestible starch noodles according to claim 4, characterized in that: The cutting distance of the S3 cutter is 1.0 mm, and the length of the fresh wet noodles is 20 cm.

10. The method for preparing slowly digestible starch noodles according to claim 4, characterized in that: During the drying process in S3, the temperature is 20-45° C., the humidity is 55%-85%, and the moisture content of the noodles is 14.5%.

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