Fermented low-GI purple potato noodles and preparation method thereof

Abstract

The invention provides fermented low-GI purple potato noodles and a preparation method thereof, compound bacteria of fermented lactobacillus mucus, lactobacillus casei and lactobacillus helveticus are added into mixed powder of purple potato powder and wheat flour, and the purple potato noodles are prepared through fermentation. The GI value of the prepared purple potato noodles is 47.32, the purple potato noodles have the advantages of low energy, low glycemic index, regulation of intestinal beneficial flora composition, high satiety and good taste, and the preparation method is low in cost, low in nutrition loss and suitable for people with special chronic diseases with sugar and fat control requirements to eat.

Description

Technical Field

[0001] The invention belongs to the field of noodle product and functional food development, and particularly relates to fermented low-GI purple potato noodles and a preparation method thereof. Background Art

[0002] In recent years, with the rapid increase in the number of people with abnormal glucose and lipid metabolism, abnormal glucose and lipid metabolism has become one of the main factors endangering modern human health. Such people are also prone to complications, such as diabetes, hyperlipidemia, coronary artery disease, hyperuricemia, etc. At present, there are three main intervention methods for abnormal glucose and lipid metabolism: drug intervention, dietary intervention, and lifestyle intervention. However, since patients with chronic diseases are highly dependent on drugs, they have to bear the side effects of drugs for a long time, which also creates an economic burden. Therefore, at this stage, researchers prefer to use a combination of dietary intervention and lifestyle intervention to control abnormal glucose and lipid metabolism. Dietary intervention is the main means of intervening in abnormal glucose and lipid metabolism. Fermented foods contain metabolites with physiological functions, which can improve the symptoms related to glucose and lipid metabolism in organisms. In recent years, as the number of patients with chronic diseases of glucose and lipid metabolism homeostasis disorder has become larger and larger, scholars in related fields have conducted more extensive and in-depth research on the intervention of lactic acid bacteria fermentation products in glucose and lipid metabolism. Lactic acid bacteria (LAB) and probiotics have been widely used as the main ingredients of dietary supplements and over-the-counter drugs. In the context of the concept of "big health" and its industrialization, it is of great significance to develop new intestinal probiotic staple food products with excellent performance. Fermenting foods with lactic acid bacteria can not only give staple foods such as noodles richer nutritional properties, but also improve the flavor of staple foods and enhance the preservation performance. Purple potato (Solanum tuberosum L.) is a perennial herbaceous plant of the Solanaceae family. It is mainly distributed in the southwestern mountainous areas, northwest China, Inner Mongolia and northeast China in China. Purple potato is named because its skin and flesh are purple. It is resistant to adversity and easy to reproduce. It is rich in vitamins, minerals, polyphenols and resistant starch. It is an important food crop and is called "underground apple". Compared with ordinary potatoes, purple potatoes have a lower glycemic index and higher anti-inflammatory, antioxidant, liver protection and blood sugar lowering abilities. The market prospects of its deep-processed products are very broad. Among purple potatoes, the main substances with blood sugar regulating functions are anthocyanins and resistant starch. Among them, purple potato anthocyanins can achieve the function of lowering blood sugar by regulating intestinal flora and inhibiting the activity of related enzymes. Purple potatoes can be used as ingredients or main raw materials in food. With the advancement of potato staple food, purple potatoes have been developed and applied in flour product processing, including purple potato biscuits, purple potato steamed bread and purple potato noodles. The present invention found that purple potato fermentation produces some products that are beneficial to sugar and lipid metabolism, including gentianose, usnic acid, acetylosing acid anhydride, nicotinamide, 13-HOTE and vitamin K, which further provides a new theoretical basis for the functional material basis of sugar and lipid metabolism activity in lactic acid bacteria fermented noodles. Compared with ordinary potatoes, purple potatoes have better sugar and lipid metabolism regulation potential, so the market prospect of purple potato deep-processing products is very broad. Lactic acid bacteria are probiotics. Studies have shown that lactic acid bacteria fermentation can improve the quality of starchy foods, reduce the GI value of starchy staple foods, improve the sugar and lipid metabolism in organisms, and improve the intestinal microecological environment. Therefore, research on the process technology of lactic acid bacteria fermented noodles is of great significance to people's pursuit of healthy diet. It is also a food processing method that improves nutrition and flavor. Summary of the invention

[0003] Technical problems to be solved: In view of the technical deficiencies of existing noodle products that easily increase blood sugar after meals, and in order to implement potato as the staple food and reduce the risk of abnormal glucose and lipid metabolism caused by directly eating potato whole flour noodles, the purpose of the present invention is to provide a fermented low GI purple potato noodles and a preparation method thereof. A composite bacteria of fermented mucus Lactobacillus, casei Lactobacillus and helveticus is added to a mixture of purple potato flour and wheat flour to ferment and prepare purple potato noodles. The process is simple, the raw materials are natural and harmless, the produced noodles have a good taste, the cooking loss rate is low, and it is a low GI food, and has the effects of lowering blood sugar and lipids and regulating the homeostasis of intestinal flora.

[0004] Technical solution: A method for preparing fermented low-GI purple potato noodles, comprising the following steps: S1. Powder mixing: Mix purple potato flake powder and wheat flour of equal quality to obtain a mixed powder; S2. Compound bacteria mixing: while adding water to the mixed powder, add saline solution containing compound bacteria; S3. Preparation of fermented dough: The mixed flour, compound bacteria and water were stirred for 15-20min to form a dough, and fermented at 42°C and 70-80% RH for 5-7h to obtain a fermented dough; S4. Fermentation dough preparation: adding purple potato flour, wheat flour and water to the fermentation dough, and stirring again to form a new dough; S5. Sheeting and cutting: the new dough is squeezed into sheets, cut into noodles, and dried to obtain fermented low GI purple potato noodles. Further, in step S2, the composite bacteria are fermented mucus lactobacillus, casei lactobacillus and helveticus, and the composite ratio is 1:(1-2):(1-2). Furthermore, in step S2, the physiological saline containing the composite bacteria is added to 3-5 mL of the physiological saline for every 0.01-0.02 g of the composite bacteria; the mass volume ratio of the mixed powder to the total amount of water and the physiological saline containing the composite bacteria is 5:(4-6). Further, in step S4, the mass ratio of purple potato flour to wheat flour is 3:(7-9), and the total water content is 30-35%. Further, in step S4, the mass ratio of the total amount of purple potato flour to wheat flour and fermented dough is 5:(8-11). Further, in step S5, the thickness of the sheet is 0.8, 2 or 3 mm. Furthermore, in step S5, the drying temperature is 15-35° C., and the drying humidity is 70-90% RH. Beneficial effects: 1. The present invention uses purple potato whole flour rich in anthocyanins to produce noodles. The purple potato flour is added in an amount of 30%, which can achieve the function of lowering blood sugar by regulating intestinal flora and inhibiting the activity of related enzymes, and provides a new method for the development of potato staple food products based on fermentation technology; 2. The present invention combines the composite bacteria fermentation technology, and adds the composite bacteria of fermented Lactobacillus mucilaginosus, Lactobacillus casei and Lactobacillus helveticus to the mixed powder for fermentation to prepare purple potato noodles. By secreting proteases such as amylase and lipase, the resistant starch content is increased, and the postprandial glycemic index of the product is reduced. Based on the characteristics of the purple potato substrate, some beneficial sugar and lipid metabolism products are produced through fermentation, including gentioyl, usnic acid, acetylosingrin anhydride, nicotinamide, 13-HOTE and vitamin K, etc., which effectively reduces the high sugar and high fat risks caused by eating traditional pasta. Animal experiments and human GI tests show that the fermented noodles provided by the present invention are low GI foods, which are in line with the modern healthy dietary concept of nutritious and healthy light meals. 3. The low GI purple potato fermented noodles produced by the present invention improve the texture and nutritional quality of the noodles through the effects of fermentation metabolic enzymes, organic acids and other metabolites. The product has good color, chewy and elastic taste, is not easy to break, is not easy to muddy the soup, and has small cooking loss; 4. The production raw materials used in the present invention are only lactic acid bacteria, purple potato whole flour and wheat flour, all of which are pure natural and do not contain food additives, thus achieving clean label food production; and the production method has simple steps, is easy to operate, and is easy to promote industrialization. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a diagram of the preparation of purple potato fermented dough in Example 1, wherein A is the preparation stage; B is the fermentation process; and C is the end of fermentation; Figure 2 This is a diagram of the purple potato fermented dough of Example 1; Figure 3 This is a diagram of purple potato fermented noodles from Example 1; Figure 4 This is a picture of cooked purple potato fermented noodles in Example 1; Figure 5 The graphs of pH value and enzyme activity at different time points of purple potato dough fermentation in Example 1 are shown in Figure 1. a, b, c, d, and e represent significant differences (P < 0.05) between different samples, where A is pH value; B is α-amylase activity; and C is lipase activity. Figure 6 This is a laser confocal image of the purple potato dough fermentation process in Example 1, wherein A is 0h; B is 2h; C is 4h; D is 6h; E is 7h; Figure 7 It is a non-targeted metabolomics analysis diagram of Comparative Example 2 and Example 1, wherein A is the top 20 substances up-regulated and down-regulated after dough fermentation; B is a heat map of metabolites before and after dough fermentation; C is a cluster heat map of differential metabolites in dough pathways before and after fermentation; Figure 8 The effect of dietary intervention on the body weight and food intake of mice, where A is body weight; B is food intake; Fig. 9 The figure is the effect of dietary intervention on the blood glucose parameters of mice, where A is the fasting blood glucose of mice; B is the glucose tolerance curve of mice; C is the area under the glucose tolerance curve; D is the fasting insulin level; Fig.10 Stacked bar chart of relative abundance of species at phylum level for different ASV-based groupings. 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 A method for preparing fermented low-GI purple potato noodles comprises the following steps: S1. Powder mixing: Mix purple potato flake powder and wheat flour of equal quality to obtain a mixed powder; S2. Mixing of composite bacteria: fermented Lactobacillus mucus, Lactobacillus casei and Lactobacillus helveticus were added to saline in a ratio of 1:1:1, and saline containing composite bacteria was added while adding water to the mixed powder. The ratio of the mixed powder to the amount of water (including saline for lysing bacteria) was 5:4; S3. Fermented dough preparation: Mix the flour, compound bacteria and water with a dough mixer for 15 min to form a dough, and ferment at 42 ° C, 80% RH for 7 h to obtain a fermented dough; S4. Preparation of fermented dough: adding purple potato flour and wheat flour in a mass ratio of 3:7 to the fermented dough, the mass ratio of the total flour to the fermented dough was 5:9, adding water so that the total moisture content reached 30%, and stirring again to form a new dough; S5. Sheeting and strip cutting: Put the new dough into an automatic noodle press, extrude it into sheets with a thickness of 2 mm, and then cut it into noodles. Dry it at 20° C. and 70% RH to obtain fermented low GI purple potato noodles. Comparative Example 1 Comparative Example 1 is commercially available common wheat noodles. Comparative Example 2 The difference between this comparative example and Example 1 is that no composite bacteria fermentation is added, specifically as follows: The purple potato whole flour and wheat flour are directly mixed in a ratio of 3:7, 32% water is added, the dough is kneaded, pressed into sheets and cut into strips, and unfermented purple potato noodles are obtained. Performance Test: 1. Changes in pH and enzyme activity during purple potato dough fermentation For the purple potato dough prepared in Example 1, during the fermentation period of 0-7h, the pH value of the purple potato dough fermented with the composite bacterial starter changed as follows: Figure 5 As shown. With the extension of fermentation time, the pH value of fermented dough tends to decrease ( Figure 5 A), and showed a significant difference (P < 0.05). Specifically, the initial pH value of the fermented dough before fermentation was about 5.5, which slowly decreased from 0 to 4 hours, decreased sharply from 4 to 6 hours, and stabilized at about 3.9 from 6 to 7 hours. This is because the fermented Lactobacillus mucilaginosus & Lactobacillus casei & Lactobacillus helveticus (abbreviated as LLL196) produced a series of organic acids such as lactic acid during the fermentation process. As the fermentation time increases, these acidic substances gradually accumulate; on the other hand, when too much acidic substances accumulate in the environment, the lactic acid bacteria themselves will use organic acids as a carbon source, thus producing a dynamic balance, causing the pH value of the dough to eventually remain at a stable level. Changes in α-amylase activity in fermented dough Figure 5 As shown in B. As can be seen from the figure, the initial activity of α-amylase is 24.48U / g. During the first and middle period of 0-4h, the activity of α-amylase decreases slowly and drops to 22.43U / g in the 4th hour. During this period, the activity of anthocyanins in purple potatoes increases with the decrease of environmental pH value, which slightly inhibits α-amylase. After 4h, the activity of amylase increases and then tends to be stable with no significant difference, and reaches a higher value than the initial enzyme activity, which is 25.75U / g. α-amylase can decompose starch in the dough into short-chain glucose, thereby affecting the cross-linking state of starch and protein in the dough, and also increases the viscosity of the dough and improves the flavor of the dough. During dough fermentation, there are also changes in lipase activity, such as Figure 5 C. In general, the lipase activity of purple potato dough fermented by the compound lactic acid bacteria increased with the extension of fermentation time. During the fermentation period of 0-6h, the lipase activity increased from the initial 0.12U / g to 0.15U / g, and showed significant differences at each time point (P < 0.05). The enzyme activity tended to be stable at 6-7h, which was also the end of the fermentation, and the growth state of the compound lactic acid bacteria decreased. The above analysis shows that the metabolic enzymes produced during the fermentation process of the composite lactic acid bacteria starter help to improve the toughness and structure of the purple potato fermented dough, and make the dough produce unique fermentation texture and flavor characteristics. 2. Changes in texture properties of purple potato dough during fermentation Table 1 Texture changes of purple potato dough during fermentation Note: a, b, c, d, e with different letters indicate significant differences between different groups in the same row (P < 0.05). For the purple potato dough prepared in Example 1, samples were taken at 0, 2, 4, 6, and 7 hours of fermentation for texture test analysis, and the results are shown in Table 1. As can be seen from the table, with the progress of the fermentation process, the elasticity, hardness, chewiness, cohesion and resilience of the purple potato dough all showed a significant downward trend, among which the elasticity decreased from 0.59 to 0.45; the hardness decreased from 186.91 gf to 80.78 gf; the chewiness decreased from 61.97 gf to 21.25 gf; the cohesion decreased from 0.60 gf / s to 0.46 gf / s; and the resilience decreased from 0.10 to 0.07. This shows that during the fermentation process, the dough's gluten strength gradually decreases, the texture gradually becomes soft, and the cross-linking of starch and protein changes. The reasons for the changes are related to the destruction of starch structure by amylase, which causes changes in the ratio of amylose and amylopectin, the emulsification reaction caused by lipase, which causes changes in the dough network structure, the accumulation of acidic substances leading to a decrease in dough pH, ​​changes in the secondary structure of gluten protein, and the protective effect of anthocyanins on starch. 3. Laser Confocal Microscopy Image Analysis of Purple Potato Dough The laser confocal image of the purple potato fermented dough prepared in Example 1 is shown in Figure 6 , Figure 6 (A)-(E) represent doughs with fermentation times of 0, 2, 4, 6, and 7 h, respectively. The protein component is preferentially labeled with 5-isothiocyanate FITC and characterized by red, while starch is preferentially stained with rhodamine B and characterized by green. The yellow color shown in the CLSM image usually represents a composite matrix formed by starch and protein. As can be seen from the figure, in the early and middle stages of fermentation, the starch clusters in the fermented dough are linear or flaky in some areas, with strong continuity and extensibility, while the color of the cross-linked area between starch and gluten protein gradually changes from yellow to orange and then continues to approach red. This means that at this stage, anthocyanins inhibit the activity of amylase to a certain extent, making the destructive effect of amylase on starch structure less severe. After the fermentation time reaches 6 h, it is observed that the continuity of green fluorescence is interrupted, and the color of the area where starch and protein are cross-linked becomes increasingly red, indicating that the starch cluster structure is destroyed and the site with affinity to the fluorescent agent is also damaged. As the fermentation proceeds, the acidity of the matrix increases, and the amylase active site is further exposed, making it easier for amylase to invade the starch molecule and destroy its structure. At this stage, not only the exposed part of the starch is broken down and its structure is destroyed, but also the part that is cross-linked with the protein and anthocyanin is destroyed, so the cross-linked area shows more red fluorescence of the protein. 4. Metabolite analysis of purple potato dough before and after fermentation Non-targeted metabolomics analysis was performed on the unfermented dough (Comparative Example 2) and the purple potato dough fermented for 7 h (Example 1), and a total of 2794 compounds were detected, mainly including: 973 amino acids and their derivatives, 338 organic acids, 93 sugars, 98 phenolic acids, 13 anthocyanins, 64 flavonoids and their derivatives, 24 lignans, 22 coumarins, 10 vitamins, and 9 isoflavones. Depend on Figure 7 B shows that there are great differences in metabolites before and after fermentation. The fermentation of compound lactic acid bacteria improves the nutritional properties of the dough. Amino acids and their derivatives show great changes before and after fermentation, followed by organic acids. The contents of other secondary compounds including sugars, lipids and vitamins have generally changed after fermentation. For sugars and acids, the content of α-maltose is significantly reduced after fermentation, while the content of gentiosaccharide, usnic acid and acetylosporin anhydride is significantly increased after fermentation. Gentiosaccharide is a low-calorie, low-sweetness substance. The purple potato present in the sample can improve the microecological environment of the colon; the increase in usnic acid content has the effects of improving oral ulcers, preventing tooth decay and preventing dental plaque in physiological functions; and acetylosporin anhydride can be used to prevent and treat atherosclerosis in the case of low high-density lipoprotein. exist Figure 7 B shows that the content of some functional vitamins and amino acids also increased through fermentation, including niacinamide, 13-HOTE and vitamin K, etc. Niacinamide is a common ingredient in skin care products and is very popular. 13-HOTE plays an important role in human immunity, such as anti-inflammation, anti-oxidation and anti-platelet aggregation; vitamin K has the functions of preventing osteoporosis, improving cardiovascular diseases and diabetes; the peptide functional compound Ile-Pro-Ile can inhibit HIV-1 or HIV-2 from entering T lymphocytes and monocytes, as well as the blood pressure-lowering peptide Ile-Ser-Asp-Arg-Ile discovered recently. After fermentation, the substances whose contents in the metabolic pathway increase steadily include 2'-deoxyadenosine, adenosine tetraphosphate, guanine and 2'-deoxyadenosine-5'-diphosphate sodium salt. Among them, 2'-deoxyadenosine is not only an important raw material for genetic medicine and genetic engineering research, but also has good physiological activity itself. It can inhibit insulin release induced by sugar, and has the effect of reducing specific phosphodiesterase inhibitors or adenylate cyclase activators to promote insulin secretion; the substances whose contents decrease steadily include adenosine-5'-monophosphate, 2'-deoxyinosine, guanosine 5'-monophosphate and adenosine-3'-5'-cyclic monophosphate hydrate. Table 2 Metabolite Index serial number English name Chinese name CAS Number MW0114515 Gentianose Gentian Sugar 2595-44-3 QM0015536 Acetylmogroside Anhydride Acetyl mogroside anhydride 344327-48-6 MEDL02050 Niacinamide Niacinamide 98-92-0 MW0010023 Usnicacid Usnic acid 125-46-2 MEDN1366 3,5-Dihydroxybenzoic acid Alpha-Razooctane Carboxylic Acid 99-10-5 MW0009415 Phenylacetic acid Phenylacetic acid 103-82-2 MEDTP01202 2-Hydroxymyristicacid 2-Hydroxymyristic acid 2507-55-3 MEDP0208 Succinic acid Succinic acid 110-15-6 MEDN0284 Leucinicacid 2-Hydroxy-4-methylvaleric acid 498-36-2 MW0007582 Menadione Vitamin K3 58-27-5 MEDP0574 Oleamide Oleic acid amide (9-octadecene amide) 301-02-0 MEDN0555 Hydroxyphenyllacticacid 2-Hydroxy-3-(4-hydroxyphenyl)propionic acid 306-23-0 MEDN0806 Aceglutamide N-Acetyl-L-Glutamine 2490-97-3 MW0062080 Pisumsaponin I Pea saponin I 333334-36-4 MW0157910 Thr-Ser-Lys Threonine-Serine-Lysine 71730-64-8 MEDN1615 Ile-Pro-Ile L-Isoleucine-L-Proline-L-Isoleucine 90614-48-5 MEDN0375 13-HOTE 13S-Hydroxy-9Z,11E,15Z-octadecatrienoic acid 67597-26-6 MW0106100 Canavaninosuccinate Phaseolus succinate 56073-32-6 MEDTP01202 2-Hydroxymyristicacid 2-Hydroxymyristic acid 2507-55-3 MEDL02772 D-Erythrose4-phosphate D-erythrose-4-phosphate 585-18-2 5. Analysis of basic nutritional components of purple potato noodles Table 3 Basic nutritional content of potato noodles prepared in Example 1 and Comparative Examples 1-2 As shown in Table 3, compared with the common wheat noodles on the market (Comparative Example 1), the energy, fat, carbohydrate and sodium contents of the fermented noodles prepared in Example 1 are all low, which is in line with the current concept of healthy food; the low sodium content reflects the low salt content in the noodles; the protein content of the fermented noodles is between that of the common wheat noodles and the unfermented noodles (Comparative Example 2), which is caused by the different production raw materials and the depolymerization reaction of the biomacromolecules involved in the fermentation process; after fermentation, the dietary fiber content of the noodles has increased, but is slightly lower than that of the common wheat noodles. Lactic acid bacteria use starch for their own reproduction and metabolism. In this study, the insoluble dietary fiber in the dough mainly comes from wheat flour, and the soluble dietary fiber mainly comes from purple potato whole flour and lactic acid bacteria fermentation. The measured nutrient content was analyzed by ratio with the corresponding substance content recommended for daily intake by the human body. From the nutrient reference values ​​of fat, carbohydrates and sodium, it can be reflected that the fermented noodles themselves have low energy and meet the current people's demand for controlling salt, sugar and fat staple foods. 6.Texture characteristics of purple potato noodles Table 4 Texture characteristics of potato noodles prepared in Example 1 and Comparative Examples 1-2 Hardness(gf) elasticity Cohesiveness Chewing (gf) Responsiveness Example 1 36.01±1.15 0.66±0.01 0.80±0.01 15.87±2.49 1.19±0.03 Comparative Example 1 14.00±0.00 0.43±0.06 0.47±0.03 2.64±0.21 0.59±0.02 Comparative Example 2 16.00±1.15 0.60±0.11 0.71±0.01 8.22±0.32 1.04±0.05 The texture test results are shown in Table 4. The noodles prepared in Example 1 show obvious advantages over the control example in terms of hardness, elasticity, cohesion, chewiness and resilience. Among them, the various indicators of purple potato fermented noodles are at a relatively high value, followed by unfermented noodles, and the values ​​of various indicators of ordinary wheat noodles are all low. In terms of hardness, the hardness of the fermented noodles reached 36.01gf, which is much higher than the fermented noodles prepared in the control example. High temperature will promote the cross-linking reaction of gluten protein and starch in the dough, forming a more compact and firm network structure, thereby changing the physical properties of the dough. In addition, the pH value of the dough after fermentation is changed, which can affect the structure and state of the protein, increase the cohesion of glutenin, and change the activity of phenolic substances such as anthocyanins in purple potatoes, which is conducive to the phenolic substances to wrap starch, slow down the gelatinization of starch to a certain extent, improve the anti-digestion effect, and reduce the increase in blood sugar after meals. The chewiness of the fermented noodles reached 15.87 gf, which also exceeded the fermented noodles prepared in the other comparative examples. This allows the fermented noodles to present a chewy and refreshing excellent taste without adding any noodle improvers. 7. Purple potato noodles cooking characteristics Table 5 Cooking characteristics of potato noodles prepared in Example 1 and Comparative Examples 1-2 Cooking loss (g / g) Swelling index (g / g) Optimal cooking time (min) Example 1 0.13±0.01 2.04±0.02 5.05±0.01 Comparative Example 1 0.15±0.01 1.81±0.04 4.89±0.06 Comparative Example 2 0.19±0.01 1.27±0.06 6.06±0.01 The cooking characteristics are shown in Table 5. The cooking loss of the noodles prepared in Example 1 is 0.13 (g / g). In the unfermented noodles of Comparative Example 2, since purple potato flour replaces 30% of ordinary wheat flour, the gluten protein is not able to bind the starch in the dough enough. At the same time, the potato starch particles are large and easy to break the gluten network. During the cooking process, the starch absorbs water and swells, so it is easier to be freed. Fermentation can reduce the volume of macromolecular starch particles. Some small particles fill the pores of the gluten network. The other small particles are easier to interact with proteins and anthocyanins in purple potatoes through hydrogen bonds and charge interactions due to the increased surface area to volume ratio. In addition, the expansion index of fermented noodles reached 2.04 (g / g), which was higher than that of noodles prepared in each comparative example. This indicated that the compound lactic acid bacteria fermented noodles had a strong sense of fullness, which was beneficial for people who controlled their diet. From the perspective of the optimal cooking time, the cooking time of noodles was shortened after fermentation, and the optimal cooking time was 5.05 min, which was longer than that of ordinary wheat noodles. On the one hand, this result reflected the inhibitory effect of anthocyanins in purple potato flour on the gelatinization of starch granules under high-temperature water bath conditions. On the other hand, it indicated that water molecules were more likely to penetrate into the dough network after fermentation, thereby accelerating the gelatinization process of starch. 8. In vitro digestibility of purple potato noodles The starch hydrolysis curve area indicates the proportion of starch hydrolyzed into free glucose during the simulated in vitro digestion of food. The starch hydrolysis rate HRS (%), starch hydrolysis index HI and estimated glycemic index eGI calculated according to formulas (1)-(3) are shown in Table 6. Estimated glycemic index eGI = 0.862 × HI + 8.198 (3) Table 6 In vitro digestibility of potato noodles prepared in Example 1 and Comparative Examples 1-2 Starch hydrolysis curve area (AUC) Starch hydrolysis index (%) eGI value Example 1 8151.2±357.5 50.6±4.7 51.8±2.5 Comparative Example 1 10691.4±412.7 66.4±5.2 65.4±3.3 Comparative Example 2 9508.1±407.3 59.0±4.8 59.1±2.2 As can be seen from Table 6, the starch hydrolysis curve area (AUC), starch hydrolysis index (%) and eGI value of the fermented purple potato noodles in Example 1 are lower than those of the wheat noodles in Comparative Example 1 and the unfermented purple potato noodles in Comparative Example 2, indicating that the addition and fermentation of purple potatoes are beneficial to preventing the release of free glucose in the noodles; at the same time, it can be found that the estimated glycemic index (eGI value) of Example 1 is 51.8, which is less than the threshold value of 55 for low GI foods, and is lower than the eGI values ​​of the other comparative examples. It can be seen that the fermented noodles have the effect of inhibiting the increase in blood sugar to a certain extent, and have the potential to become low GI foods through further certification. It can be seen that the inhibitory effect of anthocyanins in purple potatoes on starch gelatinization also has a positive effect on delaying the rapid release of glucose in food into the blood and causing blood sugar increase. 9. Animal Experiment Verification Animal experiments were conducted on the noodles prepared in Example 1 and Comparative Example 2, and the specific experimental methods are as follows: The experimental animal research plan was approved by the Experimental Animal Ethics and Use Committee (IACUC) of Shanghai Jiaotong University, and the research plan number is A2023164-001. Mouse feed: normal feed (number: D12450J); high-fat feed (D12492, 60% high-fat feed); unfermented purple potato noodles (Comparative Example 2) and fermented purple potato noodles (Example 1) were added to the high-fat and high-sugar feed at 40%, and the nutrients of the corresponding customized feed were adjusted to keep their energy consistent. SPF-grade 6-week-old C57BL / 6 male mice were purchased from Shanghai Slake and raised in an SPF-grade animal room. The feeding conditions were an indoor temperature of 22±2°C, a humidity of 40%, 12h of light, and 12h of darkness, alternately maintained, and the mice were free to eat and drink water. After one week of adaptive feeding, the mice were randomly divided into 4 groups: (1) normal group CK, n = 6; (2) model group MK, n = 6; (3) unfermented noodle group UNF, n = 6; (4) fermented noodle group FNF, n = 6. The mice were fed with free diet for 13 weeks. 1) Effects of dietary intervention on body weight and food intake of mice Effects of dietary intervention on body weight in mice Figure 8 As shown in A, from 1 to 7 weeks, the body weight of the CK group increased steadily, while the body weight of the UNF and FNF groups increased rapidly, which was significantly higher than that of the CK and MK groups; from 7 to 12 weeks, the CK group continued to maintain a steady growth, the body weight of the MK group began to increase rapidly, and the weight growth rate of the UNF and FNF groups was relatively slow; by the 12th week, the body weights of the four groups of mice showed significant differences (P<0.05), among which the average body weight of the CK group was 27.4g; the average body weight of the MK group was 39.6g, which was 1.45 times that of the CK group; the UNF group reached 34.3g, which was 1.25 times that of the CK group, with a large increase in weight; the average body weight of the FNF group was 30.2g, which was a normal weight. Effects of dietary intervention on food intake in mice Figure 8 As shown in B, Figure 8 A. It was found that the food intake and body weight of mice were positively correlated. During the 1st to 7th week of feeding, the food intake of the MK group was lower than that of the UNF and FNF groups. This was because the greasy lard components in the MK group feed caused the mice to have a poor appetite, while the UNF and FNF groups improved the feed flavor. After the 7th week, the food intake of the MK group increased significantly and led the CK group, UNF group and FNF group, indicating that the mice adapted to the feed, while the CK group, UNF group and FNF group showed linear growth, with the CK group having the lowest growth rate, the FNF group slightly higher, and the UNF group higher. The results of dietary intervention on body weight showed that both UNF and FNF feeds helped control the weight gain of mice, but the intervention effect of FNF was more prominent. 2) Effects of dietary intervention on blood glucose parameters in mice The fasting blood glucose levels of the four groups of mice were shown in Fig. 9 A. As can be seen from the figure, the fasting blood glucose value of the CK group was significantly the lowest, at 5.4mmol / L; the fasting blood glucose value of the MK group reached 7.4mmol / L, which was significantly higher than that of the CK group, UNF group and FNF group (P<0.05), indicating that the MK group had developed a certain insulin resistance; the fasting blood glucose value of the UNF group was second only to that of the MK group and higher than that of the FNF group. Fig. 9 B describes the glucose tolerance of the four groups of mice. Overall, the blood glucose levels of the four groups of mice reached the highest value at 30 minutes, and then began to decline. At 120 minutes, it was noticed that the blood glucose level of the CK group had dropped to around 7, while the blood glucose level of the MK group was as high as 10.7 mmol / L, which was significantly higher than that of the CK group, UNF group and FNF group (P < 0.05), indicating that the blood glucose regulation function of the MK group was impaired. The blood glucose level of the UNF group was 9.1 mmol / L, which also fell into the category of impaired glucose tolerance. The blood glucose level of the FNF group was close to that of the CK group. Fig. 9 C reflects the area under the glucose tolerance level curve. The four groups from high to low are MK group, UNF group, FNF group and CK group. It can be seen that the glucose regulation of mice in the MK group and the UNF group is impaired, and the purple potato noodles fermented with the composite bacteria have a better intervention effect and can maintain the blood sugar of mice in a stable normal range. Fig. 9 D reflects the fasting insulin level. Compared with the CK group, the fasting insulin level of the MK group increased significantly, indicating that a high-fat diet can lead to insulin resistance, which is believed to be caused by damage to the insulin signaling system. Compared with MK, the fasting insulin levels of the UNF group and the FNF group were significantly reduced, and the effect of the FNF group was better, indicating that the purple potato noodles fermented by the compound bacteria have a good intervention effect, which helps to control blood sugar levels and reduce insulin resistance. 3) Effects of dietary intervention on serum glucose and lipid metabolism parameters in mice The mouse serum was subjected to physiological and biochemical analysis, and the specific results are shown in Table 7. As can be seen from the table, compared with the CK group, the LDLC value, CHO value, TG value, ALT value, ALP value, AST value, UA value and CHE value of the MK group were significantly higher, and the HDLC value was significantly lower (P < 0.05), indicating that the blood lipid level, liver function index, and glucose and lipid metabolism index of the MK group were abnormal. It is reported that when low-density lipoprotein (LDLC) is too high, there is a risk of causing atherosclerosis, which is regarded as one of the main lipid factors of cardiovascular risk. The increase in CHE value may be caused by excessive accumulation of fat in liver cells. It can be seen that the glucose and lipid metabolism of mice in the MK group has been impaired to a certain extent and has affected liver function. After the UNF dietary intervention, the LDLC value, CHO value, TG value, ALT value, ALP value, AST value, and CHE value of mice were significantly higher, and the HDLC value decreased significantly (P < 0.05), but the UA value still failed to form a significant difference with the MK group (P < 0.05), which shows that purple potato noodles can alleviate abnormal blood lipid levels to a certain extent and have a certain effect on the protection of liver function. Among them, the Patatin protein in purple potatoes has been shown to have lipid-lowering activity, and anthocyanins also play a certain role. Finally, under the intervention of FNF, the levels of HDLC value, LDLC value, CHO value, TG value, ALT value, ALP value, AST value, UA value, and CHE value all tended to normal. The intervention of compound lactic acid bacteria fermented noodles further improved the health of mice, reflecting the regulatory effect of fermented Lactobacillus mucilaginosus & Lactobacillus casei & Lactobacillus helveticus (abbreviated as LLL196) on the glucose and lipid metabolism-related indicators in mouse serum. Table 7 Physiological and biochemical parameters of mouse serum Note: a, b, c, d with different letters indicate significant differences between different groups in the same row (P < 0.05). CK, normal control group; MK, high sugar and high fat control group; UNF, unfermented purple potato noodle control group; FNF, fermented purple potato noodle experimental group. 4) Effects of dietary intervention on intestinal flora of mice The relative abundance of species at the phylum level in the fecal microbial samples of mice in different groups is shown in the bar graph. Fig.10 . Among them, Firmicutes, Actinobacteria, Bacteroidetes and Proteobacteria are more common in fecal microorganisms and are called "the four dominant bacterial phyla in the human intestine". It is noted that Proteobacteria was detected in the MK group, but not in the CK group, UNF group and FNF group. This is an important pathogenic microbial phylum. If Proteobacteria bacteria reach a certain number and exist for a long time, they will destroy the intestinal microecological environment and even cause intestinal inflammation. The ratio value of Firmicutes / Bacteroidetes (F / B) reflects whether the organism is obese. It can be observed from the figure that the F / B value of the MK group is the highest, followed by the CK group and the UNF group, and the FNF group has the lowest F / B value. This shows that compound lactic acid bacteria fermentation can intervene in the distribution of bacterial flora in mouse feces, alleviate the damage to the intestinal microecology caused by a high-sugar and high-fat diet, effectively maintain the F / B value at a relatively healthy level, and reduce the risk of obesity in mice. 10. Human trials The low GI fermented purple potato noodles were tested in human experiments using the industry standard WS / T 652-2019 "Method for Determination of the Glycemic Index of Foods" and in accordance with the ethical approval number (LL2023000096-FA). The GI value was less than 50, and the actual measured value was 47.32. In summary, the test results confirm that the present invention provides a low GI purple potato fermented noodle with a GI value of 47.32, good quality, and the ability to regulate postprandial blood glucose production levels and effectively regulate glucose and lipid metabolism. 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 method for preparing fermented low GI purple potato noodles, characterized in that: The following steps are involved: S1. Powder mixing: Mix purple potato flake powder and wheat flour of equal quality to obtain a mixed powder; S2. Compound bacteria mixing: while adding water to the mixed powder, add saline solution containing compound bacteria; S3. Preparation of fermented dough: The mixed flour, compound bacteria and water were stirred for 15-20min to form a dough, and fermented at 42°C and 70-80% RH for 5-7h to obtain a fermented dough; S4. Fermentation dough preparation: adding purple potato flour, wheat flour and water to the fermentation dough, and stirring again to form a new dough; S5. Sheeting and strip cutting: The new dough is squeezed into sheets, cut into noodles, and dried to obtain fermented low GI purple potato noodles.

2. The method for preparing fermented low GI purple potato noodles according to claim 1, characterized in that: In step S2, the composite bacteria are fermented Lactobacillus mucilaginosus, Lactobacillus casei and Lactobacillus helveticus, and the composite ratio is 1:(1-2):(1-2). The method for preparing fermented low-GI purple potato noodles according to claim 1 is characterized in that: the physiological saline containing the composite bacteria in step S2 is added to 3-5 mL of physiological saline for every 0.01-0.02 g of the composite bacteria; the mass volume ratio of the total amount of water of the mixed powder, water, and physiological saline containing the composite bacteria is 5:(4-6).

3. The method for preparing fermented low GI purple potato noodles according to claim 1, characterized in that: In step S4, the mass ratio of purple potato whole flour to wheat flour is 3:(7-9), and the total water content is 30-35%.

4. The method for preparing fermented low GI purple potato noodles according to claim 1, characterized in that: In step S4, the mass ratio of the total amount of purple potato flour and wheat flour to the fermented dough is 5:(8-11).

5. The method for preparing fermented low GI purple potato noodles according to claim 1, characterized in that: The thickness of the sheet in step S5 is 0.8, 2 or 3 mm.

6. The method for preparing fermented low GI purple potato noodles according to claim 1, characterized in that: In step S5, the drying temperature is 15-35° C., and the drying humidity is 70-90% RH.

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