Preparation method of low-bitterness tartary buckwheat noodles

Abstract

The invention provides a preparation method of low-bitterness tartarian buckwheat noodles. The tartarian buckwheat noodles comprise the following components: mixed powder of tartarian buckwheat core powder and tartarian buckwheat bran powder, high-amylose corn starch and glycyrrhetinic acid. The content of dietary fibers, free phenols, combined phenols and total phenols in the noodles and the antioxidant activity are remarkably improved by adding the tartary buckwheat bran powder, and the retention rate of rutin is further improved by reasonably setting the screw configuration of an extruder, increasing the initial temperature of a feeding area and adding glycyrrhetinic acid; the amylose can include quercetin, the bitter taste in the tartary buckwheat noodles is reduced to a greater extent, meanwhile, the effect of reducing the glycemic index of the tartary buckwheat noodles can be achieved, the eating and nutritional quality of the noodles is improved, and large-scale production of the tartary buckwheat noodles is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and particularly relates to a method for preparing low-bitterness tartary buckwheat noodles. Background Art

[0002] Buckwheat is an important medicinal and edible plant in my country. It is nutritionally comprehensive and rich in polyphenols, flavonoids and other bioactive ingredients. It has attracted increasing attention for its antioxidant, cholesterol-lowering and diabetes prevention effects. In recent years, as people pay more and more attention to nutrition and health issues, traditional wheat noodles can no longer meet people's needs. Buckwheat products, especially its noodle products, have received more and more attention worldwide. However, due to the lack of gluten protein in buckwheat and the relatively high fiber content, it is difficult to form an effective network structure to support the noodle structure, which makes it difficult to shape and poor quality when using traditional wheat noodle processing methods; therefore, buckwheat noodles are usually mixed with wheat flour to prepare buckwheat noodles. In addition, traditional noodle processing requires pre-adding water and kneading to form dough. However, there is a highly specific and active rutin-degrading enzyme in buckwheat, which can quickly convert rutin into bitter quercetin when it comes into contact with water, resulting in bitter taste of buckwheat products, which are not popular with consumers and hinder the development of buckwheat noodles. In order to solve the problem of bitterness of buckwheat products, existing research mainly focuses on pre-treatment of buckwheat grains or buckwheat flour with hydrothermal treatment or superheated steam to inactivate rutin degrading enzymes, so as to reduce bitterness or remove bitterness. However, hydrothermal treatment or superheated steam pretreatment may cause water-soluble substances in buckwheat to be dissolved, and heat-sensitive substances to be oxidized and destroyed, resulting in serious nutritional loss of buckwheat. In addition, it also leads to problems such as complex processing technology and high processing costs. Therefore, it is necessary to find more suitable and efficient methods to produce and improve the quality and "bitterness" of buckwheat noodles. Summary of the invention

[0003] Technical problem to be solved: The purpose of the present invention is to provide a method for preparing low-bitter bitter buckwheat noodles, the components of which are bitter buckwheat mixed flour, high-amylose corn starch and glycyrrhetinic acid. The addition of bitter buckwheat bran powder significantly increases the dietary fiber, free phenols, bound phenols, total phenol content and antioxidant activity in the noodles. The retention rate of rutin is further improved by the reasonable setting of the extruder screw configuration, the increase of the initial temperature of the feeding zone and the addition of glycyrrhetinic acid; amylose can include quercetin to form an inclusion complex, thereby reducing the bitterness in bitter buckwheat noodles to a greater extent, and at the same time, it can also reduce the glycemic index of the noodles, improve the edible and nutritional quality of the noodles, and is conducive to the large-scale production of bitter buckwheat noodles.

[0004] Technical solution: A low-bitterness tartary buckwheat noodle, comprising the following components: by weight, 75-85 parts of tartary buckwheat mixed flour, 15-25 parts of high-amylose corn starch and 0.5-1.5 parts of glycyrrhetinic acid. Furthermore, the tartary buckwheat mixed flour is a mixture of tartary buckwheat bran flour and tartary buckwheat core flour, and the addition amount of tartary buckwheat bran flour is 6-30% of the tartary buckwheat mixed flour; the amylose content in the high-amylose corn starch is>50%. Furthermore, the preparation steps of the tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour, pass it through a 60-mesh sieve, and separate the buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix the tartary buckwheat bran powder and the tartary buckwheat core powder to obtain tartary buckwheat mixed powder. Furthermore, the preparation steps of glycyrrhizic acid are as follows: weigh licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, perform ultrasonic-assisted extraction, centrifuge, take the supernatant, and purify it with D101 macroporous resin to obtain glycyrrhizic acid. Furthermore, the solid-liquid ratio of the licorice coarse powder to 70% ethanol is 1:(10-15). Furthermore, the ultrasonic frequency of the ultrasonic-assisted extraction is 40-45 kHz, and the extraction time is 40-60 min. Furthermore, the centrifugal speed is 8000-10000 rpm, and the centrifugal time is 5-8 min. Furthermore, the method for preparing low-bitterness buckwheat noodles is characterized by comprising the following steps: Step 1: Mixing bitter buckwheat mixed flour, high amylose corn starch and glycyrrhetinic acid for 10 minutes to obtain a mixture; Step 2: Extruding the mixture into buckwheat noodles through a twin-screw extruder; Step 3: Dry the buckwheat noodles in a 40°C oven until the moisture content reaches 12%, thereby obtaining low-bitterness buckwheat noodles. Furthermore, the parameters of the twin-screw extruder in step 2 are: screw diameter of 20 mm, aspect ratio of 40:1, die diameter of 1 mm, screw speed of 120 r / min, and feed rate of 25 g / min. Further, a method for preparing low-bitterness buckwheat noodles, wherein the twin-screw extruder in step 2 is divided into a feeding zone, a mixing zone, a gelatinization zone, a melting zone and a die head zone, and the specific extrusion steps are: (1) The mixture is fed to a feeding zone through a feeder, and the temperature of the feeding zone is set to 80-100° C.; (2) using a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%, the temperature of the mixing zone is set at 100-140°C, and one kneading element is used to fully mix the mixture and water; (3) The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and achieve a gelatinization degree of 90%; (4) The melting zone temperature is set at 95°C; (5) The temperature of the die zone is set at 80°C to extrude buckwheat noodles. Beneficial effects: 1. By adding tartary buckwheat bran powder and blending tartary buckwheat core powder and tartary buckwheat bran powder, the contents of free phenol, bound phenol and total phenol in the prepared tartary buckwheat mixed powder are increased, and the contents of dietary fiber, free phenol, bound phenol, total phenol and antioxidant activity in the extruded noodles are improved; the glycemic index is significantly reduced, the health benefits of tartary buckwheat extruded noodles are improved, and the characteristics of low GI food are presented; 2. In the process of extruding bitter buckwheat noodles through a twin-screw extruder, the present invention increases the heat treatment temperature of bitter buckwheat mixed flour before it meets water by setting a suitable screw configuration and increasing the initial temperature of the feeding zone (80-100° C.), thereby inactivating rutin degrading enzymes, and reducing the shear force and residence time of the extrusion process by reducing the kneading elements, thereby reducing the heat and shear loss of rutin and increasing the retention of rutin; maintaining a relative balance between temperature and shear force is the key to ensuring the quality of noodles and retaining the nutritional components of noodles, including the cooking loss, total phenol content and antioxidant activity of noodles; 3. The addition of glycyrrhetinic acid in the present invention can inhibit the activity of rutin degrading enzymes, prevent the conversion of rutin to quercetin, and further increase the rutin retention rate, thereby reducing the bitterness of buckwheat noodles and improving the flavor of buckwheat noodles; 4. The addition of high-amylose corn starch in the present invention allows amylose to react easily with glycyrrhetinic acid and polyphenols in buckwheat, which can improve the network structure of noodles to a certain extent, avoiding the problems of difficult noodle forming and poor quality caused by the lack of gluten protein in buckwheat. At the same time, the formation of starch-polyphenol complex can significantly reduce the glycemic index of buckwheat noodles. In addition, amylose can include a small amount of quercetin produced during the preparation of noodles to form an inclusion compound, thereby reducing the bitterness of buckwheat noodles to a greater extent, achieving multiple effects. 5. This study used a one-step extrusion cooking technology to prepare buckwheat noodles, which avoided unnecessary pre-treatment processes, saved the cost of buckwheat noodle processing, improved the production efficiency of noodles, and was conducive to the large-scale production of buckwheat noodles. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The free phenol, bound phenol and total phenol content of the tartary buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 are shown in Figure 1, wherein A is free phenol; B is bound phenol; and C is total phenol; Figure 2 This is a graph showing the antioxidant activity of the tartary buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7, wherein A is DPPH and B is FRAP. DETAILED DESCRIPTION The present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Example 1 The preparation steps of tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour and pass it through a 60-mesh sieve to obtain buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix tartary buckwheat bran powder and tartary buckwheat core powder, wherein the bran powder accounts for 6%, to obtain tartary buckwheat mixed powder. Example 2 The preparation steps of tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour and pass it through a 60-mesh sieve to obtain buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix tartary buckwheat bran powder and tartary buckwheat core powder, wherein the bran powder accounts for 12%, to obtain tartary buckwheat mixed powder. Example 3 The preparation steps of tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour and pass it through a 60-mesh sieve to obtain buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix tartary buckwheat bran powder and tartary buckwheat core powder, wherein the bran powder accounts for 18%, to obtain tartary buckwheat mixed powder. Example 4 The preparation steps of tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour and pass it through a 60-mesh sieve to obtain buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix tartary buckwheat bran powder and tartary buckwheat core powder, wherein the bran powder accounts for 24%, to obtain tartary buckwheat mixed powder. Example 5 The preparation steps of tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour and pass it through a 60-mesh sieve to obtain buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix tartary buckwheat bran powder and tartary buckwheat core powder, wherein the bran powder accounts for 30%, to obtain tartary buckwheat mixed powder. Comparative Example 1 The difference between this comparative example and Example 1 is that tartary buckwheat bran powder is not prepared, specifically: S1. Grind the tartary buckwheat into powder and pass it through a 60-mesh sieve to obtain tartary buckwheat core powder, which is tartary buckwheat flour. Table 1 Free phenol, bound phenol and total phenol contents of tartary buckwheat mixed flour prepared in Examples 1-5 and tartary buckwheat flour prepared in Comparative Example 1 The contents of free phenol, bound phenol and total phenol in the mixed buckwheat flour with different bran powder addition amounts are shown in Table 1. Compared with the buckwheat flour in Comparative Example 1, the contents of free phenol, bound phenol and total phenol all increase with the increase of the bran powder ratio. Therefore, it can be seen that the addition of buckwheat bran powder can increase the polyphenol content of buckwheat flour. In summary, the tartary buckwheat mixed flour prepared in Example 5 was selected for the subsequent preparation of tartary buckwheat noodles. Example 6 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:10, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, perform ultrasonic assisted extraction at 40kHz for 60min, centrifuge at 8000rpm for 8min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 84.5 parts of tartary buckwheat mixed flour, 15 parts of high-amylose corn starch and 0.5 parts of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 100°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Example 7 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:10, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, perform ultrasonic assisted extraction at 40kHz for 60min, centrifuge at 8000rpm for 8min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 84.5 parts of tartary buckwheat mixed flour, 15 parts of high-amylose corn starch and 0.5 parts of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Example 8 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:11, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, perform ultrasonic assisted extraction at 42kHz for 55min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 82.5 parts of tartary buckwheat mixed flour, 17 parts of high-amylose corn starch and 0.5 parts of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Example 9 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:11, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 42kHz for 50 minutes, centrifuge at 9000rpm for 6 minutes, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 82 parts of bitter buckwheat mixed flour, 17 parts of high-amylose corn starch and 1 part of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture was sent to a feeding area through a feeder, and the temperature of the feeding area was set to 100° C.; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Example 10 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:12, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 44kHz for 50min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 79 parts of bitter buckwheat mixed flour, 20 parts of high-amylose corn starch and 1 part of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture was sent to a feeding area through a feeder, and the temperature of the feeding area was set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Embodiment 11 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:14, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 45kHz for 40min, centrifuge at 10000rpm for 5min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: Mix 76.5 parts of bitter buckwheat mixed flour, 22 parts of high amylose corn starch and 1.5 parts of glycyrrhetinic acid for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 100°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Example 12 A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:15, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 45kHz for 40min, centrifuge at 10000rpm for 5min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 74.5 parts of bitter buckwheat mixed flour, 25 parts of high amylose corn starch and 1.5 parts of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 100°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 140°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 2 The difference between this comparative example and Example 10 is that the tartary buckwheat flour prepared in Comparative Example 1 is as follows: A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:12, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 44kHz for 50min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: Mix 79 parts of tartary buckwheat flour prepared in Comparative Example 1, 20 parts of high-amylose corn starch and 1 part of glycyrrhetinic acid for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 3 The difference between this comparative example and Example 10 is that high-amylose corn starch is not added, and the details are as follows: A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:12, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 44kHz for 50min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: Mix 79 parts of tartary buckwheat mixed powder and 1 part of glycyrrhetinic acid for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 4 The difference between this comparative example and Example 10 is that glycyrrhetinic acid is not added, and the details are as follows: A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:12, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 44kHz for 50min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: Mix 79 parts of bitter buckwheat mixed flour and 20 parts of high amylose corn starch for 10 minutes to obtain a mixture; Step 3: The mixture is sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 5 The difference between this comparative example and Example 10 is that no straight-chain corn starch and glycyrrhetinic acid are added, and the details are as follows: A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: 79 portions of bitter buckwheat mixed flour are sent to the feeding area through a feeder, and the temperature of the feeding area is set to 80°C; Step 2: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 120°C, and there is one kneading element to fully mix the mixture and water; Step 3: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 4: The melting zone temperature is set at 95°C; Step 5: The temperature of the die head zone is set at 80°C to extrude buckwheat noodles; Step 6: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 6 The difference between this comparative example and Example 10 is that the temperature of the mixing zone is 80° C. and there are 3 kneading elements, as follows: A method for preparing low-bitterness tartary buckwheat noodles comprises the following steps: Step 1: Take licorice coarse powder, crush it through a 50-mesh sieve, add 70% ethanol, the solid-liquid ratio is 1:12, add sulfuric acid solution to adjust the pH to 4, add 0.5% cellulase and stir well, extract with ultrasound at 44kHz for 50min, centrifuge at 9000rpm for 6min, take the supernatant, purify with D101 macroporous resin, and obtain glycyrrhetinic acid; Step 2: 79 parts of bitter buckwheat mixed flour, 20 parts of high-amylose corn starch and 1 part of glycyrrhetinic acid were mixed for 10 minutes to obtain a mixture; Step 3: The mixture was sent to a feeding area through a feeder, and the temperature of the feeding area was set to 80°C; Step 4: Use a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%. The temperature of the mixing zone is set at 80°C, and there are 3 kneading elements to fully mix the mixture and water; Step 5: The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and the gelatinization degree reaches 90%; Step 6: The melting zone temperature is set at 95°C; Step 7: The temperature of the die area is set at 80°C to extrude buckwheat noodles; Step 8: Place the buckwheat noodles in a 40° C. oven and dry for 2 hours, and then air-dry them at room temperature for 24 hours until the moisture content is reduced to 12%, thereby obtaining low-bitterness buckwheat noodles. Comparative Example 7 The difference between this comparative example and Example 10 is that the noodles are prepared by using a traditional process, which is as follows: Step 1: Add the bitter buckwheat powder into the blender, mix evenly, add water to mix, and stir until mature; Step 2: The mixture is rolled by a rolling machine to make the ingredients in the mixture uniform and ductile, and the rolled material is made into noodle shape by a forming machine; Step 3: Dry the noodles naturally until they are completely dry; Step 4: Cut the dried noodles into noodles of required length using a cutting machine to obtain bitter buckwheat noodles. Performance Test: (1) Rutin and quercetin content Rutin and quercetin were determined according to the method described by Kalinova et al. (2018). Table 2 Rutin and quercetin contents of buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 As can be seen from Table 2, the rutin retention rate in the tartary buckwheat noodles prepared in Examples 6-12 reaches 91.05-98.93%, which shows that the addition of glycyrrhetinic acid in the present invention can inhibit the activity of rutin degrading enzymes, and the extrusion temperature is set at 80-100°C and the reduction of kneading elements can also increase the retention of rutin; the rutin retention rate of the tartary buckwheat noodles prepared in Comparative Example 2 using the tartary buckwheat flour of Comparative Example 1 and Comparative Example 3 without adding straight-chain corn starch is decreased; the rutin retention rates of the tartary buckwheat noodles prepared in Comparative Example 4 without adding glycyrrhetinic acid, Comparative Example 5 without adding straight-chain corn starch and glycyrrhetinic acid, Comparative Example 6 with a mixing zone temperature of 80°C and 3 kneading elements are 75.27%, 68.94% and 45.98% respectively; Comparative Example 7 uses a traditional process to prepare tartary buckwheat noodles, and the rutin degrading enzyme present in the tartary buckwheat causes the tartary buckwheat flour to quickly convert all rutin into quercetin after contacting water, and the rutin retention rate is 0. In addition, the quercetin content in the noodles after extrusion is low, so the bitterness of buckwheat noodles is correspondingly weakened. At the same time, the quercetin content in the noodles after extrusion is significantly lower than the rutin content before extrusion. The reason may be the degradation of rutin during thermal processing and the conversion of rutin into quercetin and / or rutinose and / or other compounds by rutin-degrading enzymes. (2) Free phenol, bound phenol, and total phenol content 1) Free phenol extraction 1 g of frozen buckwheat noodle powder was mixed with 10 mL of 70% methanol, ultrasonicated for 30 min, and then centrifuged at 4°C, 12000 r / min, 15 min. The supernatant was taken and the operation was repeated twice. The supernatants were combined and stored at -20°C for testing. 2) Combined with phenol extraction The combined phenols were extracted according to the method described by Jambrec et al. (2015). The residue was mixed with 15 mL of n-hexane and centrifuged (4 °C, 5000 r / min, 10 min) to remove the supernatant. The residue was alkaline hydrolyzed. 50 mL of methanol and 10 mL of 50% potassium hydroxide (in water) were reacted under nitrogen for 20 min. The hydrolyzate was filtered with filter paper and neutralized with 6N hydrochloric acid. The final extract was extracted three times with 50 mL of ether / ethyl acetate (1:1, v / v). The organic fractions were collected and evaporated to dryness in a rotary evaporator at 40 °C. All dried samples were stored at -20 °C before analysis. 3) Determination of total phenol content The total phenol content was determined by the Folin-Ciocalteu method. 250 μL of the extract was mixed with 2.75 mL of distilled water and 250 μL of Folin-Ciocalteu phenol reagent and reacted in the dark for 5 minutes; then 2.75 mL of 7.5% sodium carbonate solution was added, mixed and reacted in a 50°C water bath in the dark for 15 minutes, then further reacted in the dark for 90 minutes, and the absorbance was tested at 750 nm. The results were expressed as gallic acid equivalents (mg / 100 g). Depend on Figure 1 It can be seen that the buckwheat noodles prepared in Comparative Example 2 using the buckwheat core flour of Comparative Example 1 and the buckwheat noodles prepared in Comparative Example 6 by lowering the mixing zone temperature to 80°C and increasing the number of kneading elements to 3, have significantly lower free phenol, bound phenol and total phenol contents than the buckwheat noodles prepared in the embodiment of the present invention. (3) Dietary fiber The total dietary fiber (TDF), soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) in buckwheat noodles were tested using the Megazyme dietary fiber kit and the enzymatic gravimetric method (AOCC 991.43). Table 3 Dietary fiber content of buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 As can be seen from Table 3, compared with the comparative example, the soluble dietary fiber content in the noodles of the embodiment is increased, and the insoluble dietary fiber content is decreased. These results are mainly due to the influence of high temperature, high pressure and high shear force during the extrusion process, which leads to the splitting of chemical bonds in the fiber and the change of molecular polarity; high-temperature extrusion cooking may more effectively destroy the glycosidic bonds between fiber molecules and convert the large molecule IDF into small molecule SDF; in addition, heat treatment may cause additional breakage of glycosidic bonds and convert insoluble polysaccharides into smaller components. This degradation leads to an increase in low molecular weight molecules, which may be too small to be detected as dietary fiber, and therefore leads to a decrease in TDF content after extrusion. (4) Antioxidant activity 1) DPPH free radical scavenging ability 1 mL of phenol extract was mixed with 4.5 mL of DPPH methanol solution (0.1 M), shaken thoroughly and reacted for 30 min in the dark, and the absorbance was measured at a wavelength of 517 nm. The results were expressed as equivalent micromoles of Trolox (μmol / 100 g). 2) Ferrous reducing ability (FRAP) FRAP was measured by referring to the method described by Benzie et al. (1999). 1 mL of phenol extract was mixed with 4.5 mL of FRAP working solution, shaken thoroughly and reacted in the dark for 30 min, and the absorbance was measured at a wavelength of 593 nm. The results were expressed as equivalent micromoles of Trolox (μmol / 100 g). Depend on Figure 2 It can be seen that the antioxidant activity (DPPH, FRAP) of the buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 is relatively high, which may be due to the high total phenol content after extrusion; the high phenol content and antioxidant activity have health benefits for people. In addition, the Maillard reaction occurred during the extrusion process, which may also lead to the generation of substances with antioxidant activity. The antioxidant activity of the buckwheat noodles prepared in Comparative Example 2 using the buckwheat core powder of Comparative Example 1 and the buckwheat noodles prepared in Comparative Example 6 by setting the mixing zone temperature to 80°C and increasing the number of kneading elements to 3 was significantly reduced. (5) Cooking loss Take 3g of buckwheat noodles and put them into 150g of boiling water. Cook until the hard core disappears. Then adjust the volume of the noodle soup to a 500mL volumetric flask. Take 50mL of the noodle soup and pour it into a constant weight aluminum box (M2). Dry it at 105℃ for 12h (M1). Each sample is measured three times in parallel. Calculate the cooking loss according to the following formula: Wherein, M1 is the dry weight (g) of the aluminum box after pouring the noodle soup; M2 is the dry weight (g) of the aluminum box; W is the moisture content of the buckwheat noodles; M0 is the weight of the buckwheat noodles. Table 4 Cooking loss of buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 Cooking loss (%) Cooking loss (%) Example 6 8.69±0.03 Comparative Example 2 7.17±0.12 Example 7 8.16±0.16 Comparative Example 3 9.54±0.17 Example 8 7.68±0.11 Comparative Example 4 9.33±0.08 Example 9 7.33±0.07 Comparative Example 5 9.74±0.12 Example 10 6.91±0.04 Comparative Example 6 8.12±0.05 Embodiment 11 8.01±0.19 Comparative Example 7 18.55±0.14 Example 12 8.93±0.15 It can be seen from Table 4 that with the increase of extrusion temperature, the cooking loss of noodles decreases. In Comparative Example 2, the bitter buckwheat noodles prepared by the bitter buckwheat core powder of Comparative Example 1 have a slightly increased cooking loss; in Comparative Example 3 and Comparative Example 5, no straight-chain corn starch is added, the structure of the noodles is loose, and the cooking loss is significantly increased; the cooking loss of the bitter buckwheat noodles prepared by not adding glycyrrhetinic acid in Comparative Example 4 is not greatly affected; in Comparative Example 6, the mixing zone temperature is set to 80°C, and the number of kneading elements is 3; Comparative Example 7 uses traditional technology to prepare noodles, and it can be seen that the cooking loss rate has increased. (6) In vitro digestibility of starch According to the research of Goh et al. (2015) and Woolnough et al. (2010), the in vitro digestibility of starch in extruded buckwheat noodles was tested. It was divided into three stages: oral, gastric, and pancreatic. Take 2.5g of cooked noodles and mix them with 30mL of distilled water, then place them in a shaking water bath at 37℃ (130r / min). Oral digestion: add 0.1mL of 10% α-amylase solution, and add 0.8mL of 1M HCl aqueous solution after 1min. Gastric digestion: add 1mL of 10% pepsin solution, and add 2mL1mol / LNaHCO3 solution, 5mL 0.1M maleate buffer, and 0.1mL glucoamylase after 30min. Pancreatic digestion: add 1mL of 5% trypsin. At 0, 20, 60, 120, 180 and 240 min in the digestion stage, 1 mL of the reaction solution and 4 mL of anhydrous ethanol were respectively mixed in a centrifuge tube, centrifuged at 3000 r / min for 10 min, and 0.1 mL of the supernatant was taken to measure the glucose concentration using a D-glucose (GOPOD method) kit. A nonlinear model is used to describe the starch hydrolysis kinetics, and the first-order equation is: C=C∞(1-e -kt ) Where C(%) is the glucose concentration at t(min), C∞(%) is the equilibrium concentration, k is the kinetic constant, and t is the time. The hydrolysis index (HI) is calculated as the area under the starch hydrolysis curve. Taking white bread as a reference, the predicted glycemic index (pGI) is estimated using the following equation: pGI=39.71+0.549HI Table 5 Predicted glycemic index of buckwheat noodles prepared in Examples 6-12 and Comparative Examples 2-7 pG pG Example 6 45.29±0.11 Comparative Example 2 59.74±0.39 Example 7 44.04±0.20 Comparative Example 3 55.33±0.52 Example 8 43.26±0.16 Comparative Example 4 49.37±0.32 Example 9 42.26±0.18 Comparative Example 5 59.23±0.47 Example 10 41.06±0.38 Comparative Example 6 54.32±0.51 Embodiment 11 39.75±0.14 Comparative Example 7 64.22±0.37 Example 12 38.16±0.19 As can be seen from Table 5, the pGI values ​​of the buckwheat noodles prepared in Examples 6-12 are all within the low GI range. This may be because the higher resistant starch content in buckwheat flour is an ideal raw material for preparing low GI foods, and buckwheat bran is rich in polyphenols, which may interact with starch to form a complex and reduce the digestibility and glycemic index of starch. The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A low-bitterness buckwheat noodle, characterized in that: The invention comprises the following components: by weight, 75-85 parts of bitter buckwheat mixed flour, 15-25 parts of high-amylose corn starch and 0.5-1.5 parts of glycyrrhetinic acid.

2. The low-bitterness buckwheat noodles according to claim 1, characterized in that: The tartary buckwheat mixed flour is a mixture of tartary buckwheat bran flour and tartary buckwheat core flour, and the added amount of tartary buckwheat bran flour is 6-30% of the tartary buckwheat mixed flour; the amylose content in the high-amylose corn starch is greater than 50%.

3. The low-bitterness buckwheat noodles according to claim 1, characterized in that: The preparation steps of the tartary buckwheat mixed flour are as follows: S1. Grind the buckwheat flour, pass it through a 60-mesh sieve, and separate the buckwheat core flour and buckwheat bran; S2. The buckwheat bran was ultracentrifugally crushed and passed through a 60-mesh sieve to obtain buckwheat bran powder; S3. Mix the tartary buckwheat bran powder and the tartary buckwheat core powder to obtain tartary buckwheat mixed powder.

4. The low-bitterness buckwheat noodles according to claim 1, characterized in that: The preparation steps of glycyrrhetinic acid are as follows: weighing licorice coarse powder, crushing it through a 50-mesh sieve, adding 70% ethanol, adding sulfuric acid solution to adjust the pH to 4, adding 0.5% cellulase and stirring it fully, ultrasonic-assisted extraction, centrifugation, taking the supernatant, and purifying it with D101 macroporous resin to obtain glycyrrhetinic acid.

5. The low-bitterness buckwheat noodles according to claim 4, characterized in that: The solid-liquid ratio of the licorice coarse powder to 70% ethanol is 1:(10-15).

6. The low-bitterness buckwheat noodles according to claim 4, characterized in that: The ultrasonic frequency of the ultrasonic-assisted extraction is 40-45 kHz, and the extraction time is 40-60 min.

7. The low-bitterness buckwheat noodles according to claim 4, characterized in that: The centrifugal speed is 8000-10000 rpm, and the centrifugal time is 5-8 min.

8. The method for preparing low-bitterness buckwheat noodles according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Mixing bitter buckwheat mixed flour, high amylose corn starch and glycyrrhetinic acid for 10 minutes to obtain a mixture; Step 2: Extruding the mixture into buckwheat noodles through a twin-screw extruder; Step 3: Dry the buckwheat noodles in a 40°C oven until the moisture content reaches 12%, thereby obtaining low-bitterness buckwheat noodles.

9. The method for preparing low-bitterness buckwheat noodles according to claim 8, characterized in that: The parameters of the twin-screw extruder in step 2 are: screw diameter of 20 mm, aspect ratio of 40:1, die diameter of 1 mm, screw speed of 120 r / min, and feed rate of 25 g / min.

10. The method for preparing low-bitterness buckwheat noodles according to claim 8, characterized in that: In step 2, the twin-screw extruder is divided into a feeding zone, a mixing zone, a gelatinization zone, a melting zone and a die zone, and the specific extrusion steps are: (1) delivering the above mixture to a feeding zone through a feeder, wherein the temperature of the feeding zone is set at 80-100° C.; (2) using a peristaltic pump to pump water into the extruder at a constant speed in the mixing zone to make the moisture content of the material in the barrel reach 40%, the temperature of the mixing zone is set at 100-140°C, and one kneading element is used to fully mix the mixture and water; (3) The temperature of the gelatinization zone is set at 110°C to fully gelatinize the starch and achieve a gelatinization degree of 90%; (4) The melting zone temperature is set at 95°C; (5) The temperature of the die zone is set at 80°C to extrude buckwheat noodles.

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