A method of directed enzymatic fermentation of a composite cereal flour

Abstract

The application discloses a kind of composite grain powder directional enzymolysis fermentation method, belongs to grain deep processing and bio-fermentation technical field.The application provides a kind of composite grain powder directional enzymolysis fermentation method, including with oat flour, brown rice powder, buckwheat powder, millet powder, corn powder and highland barley powder as main raw material, by stage addition high-temperature resistant alpha-amylase, cellulase, saccharifying enzyme, xylanase and neutral protease are carried out enzymolysis, and using lactic acid bacteria and yeast fermentation, starch, protein and non-starch polysaccharide in composite grain powder are transformed, release nutritional components, reduce the content of phytic acid and other anti-nutritional factors, improve product flavor and infusion property, the obtained directional enzymolysis fermentation composite grain powder has multiple nutritional components and the like characteristics, can be applied to solid beverage, meal replacement food, baked food and other grain deep processing products.

Description

Technical Field

[0001] This invention relates to the field of grain deep processing and bio-fermentation technology, and in particular to a method for targeted enzymatic hydrolysis fermentation of compound grain powder. Background Technology

[0002] With the development of the health food industry, compound grain powder, due to its combination of the nutritional characteristics of various grains, is widely used in solid beverages, meal replacement foods, instant foods, and baked goods. Grains such as oats, brown rice, buckwheat, millet, corn, and highland barley are rich in dietary fiber, protein, vitamins, and minerals. After scientific formulation, they can form compound grain products with a more balanced nutritional composition.

[0003] However, traditional processing of compound grain powder still has some shortcomings. On the one hand, some nutrients such as protein and polyphenols in grains are embedded in the cell wall, limiting their utilization. On the other hand, anti-nutritional factors such as phytic acid can affect the absorption and utilization of minerals and some nutrients. In addition, unprocessed compound grain powder usually has problems such as a strong raw grain taste, rough texture, and insufficient stability when mixed, which to some extent affects product quality and application range.

[0004] Currently, although there are related technologies for improving grain quality using enzymatic hydrolysis or microbial fermentation, such as using α-amylase to reduce slurry viscosity, using cellulase and xylanase to degrade cell wall components, using proteases to promote protein hydrolysis, and using lactic acid bacteria or yeast to improve product flavor, these methods mostly use single enzymatic hydrolysis or single fermentation processes, which are insufficient for the synergistic conversion of starch, protein and non-starch polysaccharides. It is also difficult to balance the action conditions of different enzyme preparations. Simultaneous fermentation of lactic acid bacteria and yeast can also easily lead to substrate competition, affecting fermentation stability and final flavor quality.

[0005] Therefore, there is a need for a compound grain powder processing method that is stable, has a clear enzymatic hydrolysis direction, is easy to control during fermentation, and is suitable for industrial production. Summary of the Invention

[0006] The purpose of this invention is to provide a targeted enzymatic fermentation method for compound grain powder, addressing the problems of insufficient nutrient release, difficulty in controlling the degree of protein hydrolysis, high content of anti-nutritional factors, and the need for improvement in product flavor and reconstitution properties during existing compound grain powder processing. This invention achieves controllable conversion of starch, protein, and non-starch polysaccharides in compound grain powder through staged targeted hydrolysis using heat-resistant α-amylase, cellulase, saccharifying enzyme, xylanase, and neutral protease, combined with staged synergistic fermentation by lactic acid bacteria and yeast. This facilitates the release of nutrient components, reduces anti-nutritional factors such as phytic acid, and improves product flavor and processing performance.

[0007] The technical solution is: a method for targeted enzymatic hydrolysis and fermentation of compound grain powder, comprising the following steps: S1. Preparation of compound grain powder: 20-40 parts by weight of oat flour, 15-30 parts by weight of brown rice flour, 10-25 parts by weight of buckwheat flour, 10-20 parts by weight of millet flour, 5-15 parts by weight of corn flour and 5-15 parts by weight of highland barley flour are passed through a 60-100 mesh sieve and then mixed evenly to obtain compound grain powder; preferably, the sum of the weight parts of each grain powder is 100 parts by weight.

[0008] S2. Slurry preparation, gelatinization, and high-temperature liquefaction: The composite grain powder and water are mixed at a mass ratio of 1:2.5 to 1:5 to form a slurry. The mixture is heated to 85–95°C and kept at this temperature for 10–30 minutes for gelatinization. Subsequently, at 85–95°C, a heat-resistant α-amylase is added for liquefaction treatment for 10–40 minutes. The amount of heat-resistant α-amylase added is 30–120 U / g. After liquefaction, the slurry is cooled to 50–60°C, the pH is adjusted to 5.5–6.5, and cellulase is added for enzymatic hydrolysis for 20–90 minutes. The amount of cellulase added is 20–100 U / g.

[0009] S3. Second Stage Complex Enzymatic Hydrolysis: After the first stage of enzymatic hydrolysis, the slurry is adjusted to 45–52℃ and pH 4.5–5.5. A combination of saccharifying enzyme, xylanase, and neutral protease is added for 1–3 hours of complex enzymatic hydrolysis. The dosage of saccharifying enzyme is 50–200 U / g, xylanase is 20–100 U / g, and neutral protease is 100–500 U / g. After hydrolysis, the hydrolysate is heated to 85–95℃ and maintained for 5–15 minutes to inactivate the enzymes.

[0010] S4. Fermentation substrate adjustment: Cool the enzyme hydrolysate after enzyme inactivation to 35-40°C, adjust the solid content to 20%-35%, and adjust the pH to 5.5-6.2 to obtain the fermentation substrate. Preferably, one or more of fructooligosaccharides, xylooligosaccharides, or inulin, accounting for 0.2%-1.0% of the dry weight of the compound grain powder, can be added as a prebiotic.

[0011] S5. First-stage directed fermentation of lactic acid bacteria: Lactic acid bacteria are inoculated into the fermentation substrate. The lactic acid bacteria are selected from one or more of Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus fermentum. The total inoculation amount is 1×10⁻⁶. 6 ~1×10 8 CFU / g. Ferment at 35–39℃ for 6–16 h until the pH of the system drops to 4.0–4.8.

[0012] S6. Second-stage yeast-directed fermentation: Yeast is inoculated into the lactic acid bacteria fermentation product. The yeast is selected from Saccharomyces cerevisiae or Kluyveromyces martensii, and the inoculation amount is 1×10⁻⁶. 5 ~1×107 CFU / g. Continue fermentation at 28–34℃ for 4–12 hours.

[0013] S7. Fermentation Termination and Post-processing: After yeast fermentation is complete, terminate the fermentation and heat the fermented material to 75–90°C and maintain this temperature for 5–20 minutes. Then, dry the material using one of the following methods: vacuum low-temperature drying, spray drying, or freeze drying. After drying, pulverize the powder and pass it through a 60–120 mesh sieve to obtain the directional enzymatic hydrolysis fermented composite grain powder. Preferably, the vacuum low-temperature drying temperature is 45–65°C; the spray drying inlet air temperature is 140–180°C, and the outlet air temperature is 65–85°C.

[0014] The present invention has the following advantages: 1. The present invention adopts a staged directional hydrolysis method that combines high-temperature liquefaction of high-temperature resistant α-amylase, cell wall degradation of cellulase, and complex enzymatic hydrolysis of saccharifying enzyme, xylanase and neutral protease. The temperature, pH, enzyme addition amount and reaction time are controlled according to the suitable action conditions of different enzyme preparations, which is conducive to the staged conversion of starch, cell wall polysaccharides and proteins, and avoids the problem of insufficient enzyme activity or difficulty in controlling the processing direction caused by adding all enzyme preparations at once.

[0015] 2. This invention utilizes heat-resistant α-amylase to moderately liquefy gelatinized starch, reducing the viscosity of the grain slurry; utilizes cellulase and xylanase to moderately degrade grain cell wall components, promoting the release of encapsulated nutrients; utilizes neutral protease to moderately hydrolyze grain proteins, increasing small-molecule nitrogenous substances; and utilizes saccharifying enzymes to form sugars usable by microorganisms, thereby providing suitable substrates for subsequent lactic acid bacteria and yeast fermentation. Attached Figure Description Figure 1 This is a schematic diagram of the process flow of the directional enzymatic hydrolysis fermentation method for compound grain powder of the present invention.

[0016] Figure 2 A comparison chart showing the degree of protein hydrolysis in composite grain flour obtained through different processing techniques.

[0017] Figure 3 A comparison chart showing the phytic acid reduction rate of composite grain flour obtained through different processing techniques. Detailed Implementation

[0018] The following examples are for illustrative purposes only and do not constitute a limitation on the scope of protection of this invention. Equivalent substitutions or adjustments made by those skilled in the art based on the technical solutions of this invention should all fall within the scope of protection of this invention. Unless otherwise specified, the enzyme addition amounts described in these examples are calculated in units of enzyme activity (U / g) per gram of dry-based compound grain powder. The thermostable α-amylase, cellulase, saccharifying enzyme, xylanase, and neutral protease used are all food industry enzyme preparations. The *Lactobacillus plantarum*, *Lactobacillus casei*, *Lactobacillus fermentum*, *Saccharomyces cerevisiae*, and *Kluyveromyces martensii* strains used are all commonly used in food fermentation.

[0019] Example 1 like Figure 1 As shown, this embodiment provides a method for targeted enzymatic hydrolysis and fermentation of compound grain flour, including the following steps: S1: Preparation of Compound Grain Powder Weigh out 30 kg of oat flour, 25 kg of brown rice flour, 15 kg of buckwheat flour, 15 kg of millet flour, 8 kg of corn flour, and 7 kg of highland barley flour. Pass each grain flour through an 80-mesh sieve to remove lumps and larger particles, then mix them thoroughly to obtain 100 kg of compound grain flour. This blend of grain ingredients retains the dietary fiber of oats, brown rice, and highland barley while also taking into account the nutritional and flavor characteristics of buckwheat, millet, and corn.

[0020] S2: Slurry preparation, gelatinization, and first-stage enzymatic hydrolysis Add 350 kg of water to 100 kg of compound grain powder while stirring to fully disperse the powder and form a uniform slurry. Heat the slurry to 90℃ and maintain this temperature for 20 minutes to allow the grain starch to fully absorb water, swell, and gelatinize. After gelatinization, add 80 U / g of heat-resistant α-amylase at 90℃ and liquefy for 20 minutes. Maintain slow stirring during liquefaction to reduce slurry viscosity and prevent localized sedimentation. After liquefaction, cool the slurry to 55℃, adjust the pH to 6.0 using food-grade sodium carbonate solution, and then add 60 U / g of cellulase. Enzymatically hydrolyze the slurry at 55℃ for 40 minutes. This stage of treatment improves the slurry's fluidity and partially disrupts the grain cell wall structure, creating conditions for subsequent compound enzymatic hydrolysis.

[0021] S3: Second-stage directional enzymatic hydrolysis The slurry after the first stage of enzymatic hydrolysis was cooled to 48℃ and the pH was adjusted to 5.0. 120 U / g of saccharifying enzyme, 60 U / g of xylanase, and 300 U / g of neutral protease were added to the slurry, and enzymatic hydrolysis was carried out at 48℃ for 120 min with low-speed stirring. The saccharifying enzyme continued to act on the liquefied starch hydrolysates, forming sugars that can be utilized by microorganisms; xylanase moderately degraded non-starch polysaccharides such as xylan in the grains; and the neutral protease converted some grain proteins into small peptides and amino acids. After enzymatic hydrolysis, the slurry was heated to 90℃ and maintained for 10 min to inactivate the enzymes and terminate the enzymatic hydrolysis reaction.

[0022] S4: Fermentation substrate regulation The enzyme-inactivated hydrolysate was cooled to 37°C, and its solid content was measured to be approximately 22%. The pH was adjusted to 5.8 using food-grade sodium carbonate solution, and then 0.5% (by dry weight of the compound grain powder) of fructooligosaccharides was added and stirred thoroughly to obtain the fermentation substrate. Fructooligosaccharides, as an optional prebiotic, can provide some nutritional support for the initial stage of lactic acid bacteria fermentation; without the addition of fructooligosaccharides, the fermentable sugars formed by enzymatic hydrolysis can also meet the needs of subsequent fermentation.

[0023] S5: Lactic acid bacteria fermentation Lactobacillus plantarum and Lactobacillus casei were inoculated into the fermentation substrate at a viable count ratio of 2:1, with a total inoculum size of 1×10⁻⁶. 7 CFU / g, based on wet-based fermentation substrate. After inoculation, the mixture was thoroughly stirred to ensure uniform dispersion of the bacteria, and fermentation was carried out at 37°C for 10 hours. The pH of the system was monitored periodically during lactic acid bacteria fermentation, and this stage of fermentation was terminated when the pH dropped to 4.5. This stage primarily involves the formation of lactic acid and related metabolites, while simultaneously lowering the pH of the fermentation system.

[0024] S6: Yeast fermentation After lactic acid bacteria fermentation is complete, inoculate the fermented product with brewer's yeast at a rate of 1×10⁻⁶. 6 CFU / g, based on wet-based fermentation substrate. The fermentation temperature was adjusted to 30℃, and fermentation continued for 6 hours. The yeast utilized the remaining sugars and some nitrogenous substances after lactic acid bacteria fermentation to metabolize, forming volatile components such as alcohols and esters, resulting in a more harmonious fermented aroma of the compound grain flour. At the end of fermentation, the pH of the system was measured to be 4.1. A staged inoculation method for lactic acid bacteria and yeast reduced substrate competition between the two strains in the early stages of fermentation.

[0025] S7: Fermentation Termination and Post-treatment The fermented material was heated to 80℃ and held for 10 minutes to terminate the metabolic activity of lactic acid bacteria and yeast. It was then dried using a vacuum low-temperature drying method at 55℃ and a vacuum gauge pressure of -0.08 MPa until the product moisture content was below 8%. The dried material was pulverized and passed through a 100-mesh sieve to obtain a directional enzymatic fermentation compound grain powder. The resulting product has a relatively uniform powder composition and a reduced raw grain flavor, making it suitable as a raw material for solid beverages, meal replacement powders, instant foods, or baked goods.

[0026] This invention employs a technical route combining staged, targeted enzymatic hydrolysis with staged co-fermentation of lactic acid bacteria and yeast, achieving the phased transformation of the main nutrients in compound grain flour. In the first stage, a thermostable α-amylase is used to liquefy the starch at its gelatinization temperature, causing moderate degradation of the gelatinized starch, reducing the viscosity of the slurry, improving the system's fluidity, and providing favorable mass transfer conditions for subsequent enzymatic hydrolysis. Subsequently, cellulase is added at a lower temperature to moderately degrade cellulose and some structural polysaccharides in the grain cell walls, further releasing proteins, polyphenols, and other nutrients embedded within the cell walls. The second stage uses a combination of saccharifying enzymes, xylanase, and neutral protease for enzymatic hydrolysis. Specifically, the saccharifying enzyme further degrades the liquefied starch into fermentable sugars, providing a carbon source for microbial fermentation; xylanase degrades non-starch polysaccharides such as xylan, increasing the degree of cell wall disruption; and the neutral protease hydrolyzes some grain proteins into small peptides and free amino acids, improving protein utilization and providing a nitrogen source for microbial metabolism. During the lactic acid bacteria fermentation stage, lactic acid bacteria preferentially utilize the fermentable sugars formed by enzymatic hydrolysis to produce lactic acid and other metabolites, gradually lowering the pH of the system and creating a suitable fermentation environment. Simultaneously, the lactic acid bacteria metabolic process helps reduce the content of anti-nutritional factors such as phytic acid and promotes the release of some bound active ingredients. During the yeast fermentation stage, yeast further utilizes the remaining sugars and some amino acids for metabolism, generating alcohols, esters, and other volatile flavor compounds, enriching the product's aroma, reducing the raw grain taste and bitterness present in traditional compound grain flours, and improving the overall sensory quality of the product.

[0027] Example 2 This embodiment provides a targeted enzymatic hydrolysis fermented compound grain powder without added prebiotics. Its process steps are basically the same as those in Example 1, except that fructooligosaccharides are not added during the fermentation substrate conditioning stage.

[0028] S1 to S3: The ratio of compound grain powder, slurry preparation, gelatinization, first-stage enzymatic hydrolysis and second-stage enzymatic hydrolysis are the same as in Example 1.

[0029] S4: Fermentation substrate adjustment. Cool the enzyme hydrolysate after enzyme inactivation to 37°C, adjust the pH to 5.8, and use it directly as the fermentation substrate without adding fructooligosaccharides.

[0030] S5 to S7: The inoculation methods for lactic acid bacteria, yeast, fermentation parameters, and post-treatment conditions are the same as in Example 1.

[0031] The resulting product can complete the staged fermentation of lactic acid bacteria and yeast normally, indicating that the sugars formed in the enzymatic hydrolysate can meet the needs of bacterial growth and fermentation.

[0032] Example 3 This embodiment provides a targeted enzymatic hydrolysis fermented compound grain powder using a single Lactobacillus plantarum fermentation method. The overall steps are the same as in Example 1, with the following specific adjustments: S1 to S4: The preparation of compound grain powder, two-stage enzymatic hydrolysis and fermentation substrate adjustment are the same as in Example 1.

[0033] S5: Lactic acid bacteria fermentation. During the lactic acid bacteria fermentation stage, only *Lactobacillus plantarum* is inoculated, with an initial inoculum size of 1×10⁻⁶. 7 The concentration of CFU / g was increased, and fermentation was carried out at 37°C for 10 hours. Fermentation was terminated once the pH of the system reached the target range.

[0034] S6 to S7: The yeast fermentation and post-processing steps are the same as in Example 1.

[0035] The fermentation process of the obtained product was stable, indicating that *Lactobacillus plantarum* can be used alone in the lactic acid bacteria fermentation stage of this invention.

[0036] Example 4 This embodiment provides a directional enzymatic fermentation of compound grain powder using a single Lactobacillus casei, and its overall steps are consistent with those of Embodiment 1.

[0037] S1 to S4: The preparation of compound grain powder, two-stage enzymatic hydrolysis and fermentation substrate adjustment are the same as in Example 1.

[0038] S5: Lactic acid bacteria fermentation. During the lactic acid bacteria fermentation stage, only *Lactobacillus casei* is inoculated, with a total inoculum of 1×10⁻⁶. 7 CFU / g, fermented at 37℃ for 10h.

[0039] S6 to S7: After the lactic acid bacteria fermentation is completed, yeast fermentation, inactivation, drying, pulverization and sieving are carried out in accordance with Example 1.

[0040] The resulting product has the characteristic sour and yeasty aroma of fermented grains.

[0041] Example 5 This embodiment provides a directional enzymatic fermentation compound grain powder using three types of lactic acid bacteria for fermentation, and its overall steps are the same as those in Example 1.

[0042] S1 to S4: The steps for preparing the compound grain powder, enzymatic hydrolysis, and adjusting the fermentation substrate are the same as in Example 1.

[0043] S5: Lactic acid bacteria fermentation, using Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus fermentum in a live count ratio of 1:1:1, with a total inoculum of 1×10⁻⁶. 7 CFU / g. Fermented at 37°C for 10 hours after inoculation.

[0044] S6 to S7: Yeast fermentation and post-treatment conditions are the same as in Example 1.

[0045] When three types of lactic acid bacteria are combined, the resulting product has a richer fermented aroma. The appropriate combination of bacteria can be selected according to the flavor requirements of the product.

[0046] Example 6 In this embodiment, the brewing yeast in Example 1 is replaced with Max Kluyveromyces.

[0047] In practice, after the lactic acid bacteria fermentation is completed, *Kluyveromyces martensii* is inoculated at a rate of 1 × 10⁻⁶. 6 The CFU / g was fermented at 30°C for 6 hours, while all other process conditions remained unchanged.

[0048] The resulting product has aroma characteristics that are distinct from those of brewer's yeast fermentation products, indicating that different food yeasts can be applied to the second stage fermentation process of this invention.

[0049] Comparative Example To verify the combined effect of the compound enzyme staged hydrolysis and lactic acid bacteria-yeast staged fermentation of the present invention, the following control group was set up.

[0050] Control group 1: Compound grain powder that has not undergone enzymatic hydrolysis and fermentation, but has only undergone slurry preparation and drying.

[0051] Control group 2: Only heat-resistant α-amylase was used for liquefaction treatment, without subsequent complex enzymatic hydrolysis and microbial fermentation.

[0052] Control group 3: The complete compound enzymatic hydrolysis process was used, but no microbial fermentation treatment was performed.

[0053] Control group 4: Only lactic acid bacteria and yeast fermentation treatment was performed, without enzymatic pretreatment.

[0054] The experimental group adopted the complete process of Example 1.

[0055] The degree of protein hydrolysis, phytic acid content, total phenol content, reconstitution performance, and sensory quality of each group of samples were tested separately.

[0056] The results showed that, compared with the untreated group and the single-treated group, the compound grain powder prepared by the method of the present invention exhibited better overall effects in terms of nutrient release, reduction of anti-nutritional factors and improvement of sensory quality, indicating that there is a synergistic effect between the staged enzymatic hydrolysis of compound enzymes and the staged fermentation of lactic acid bacteria and yeast.

[0057] Implementation effect analysis The product obtained in Example 1 and the control group products were subjected to tests for protein hydrolysis degree, phytic acid content, total phenol content, reconstitution performance, and sensory quality. The results showed that the process of combining staged directional enzymatic hydrolysis with lactic acid bacteria-yeast staged fermentation in this invention resulted in moderate protein hydrolysis, increased content of small peptides and free amino acids, and a significant decrease in the content of anti-nutritional factors such as phytic acid. Some bound nutrients in the grains were further released. Simultaneously, after staged fermentation with lactic acid bacteria and yeast, the raw grain flavor of the product was significantly reduced, the fermented aroma was more harmonious, and the reconstitution dispersibility was improved. The overall sensory quality was superior to that of the untreated compound grain powder and samples treated with single enzymatic hydrolysis or single fermentation processes.

[0058] Further comparison of different embodiments reveals that, within the scope of the process described in this invention, high-quality targeted enzymatic fermentation compound grain powder can be obtained by adjusting the amount of different enzyme preparations added, the combination of lactic acid bacteria, and the drying method. Specifically, when using a combination of *Lactobacillus plantarum* and *Lactobacillus casei* for fermentation, the product exhibits better fermentation stability and overall flavor; when using a combination of three lactic acid bacteria for fermentation, the product's aroma is further enriched; when using *Kluyveromyces martensii* instead of *Saccharomyces cerevisiae*, the product displays different fermentation aroma characteristics; spray drying helps improve production efficiency; and freeze drying helps maintain the product's color and some heat-sensitive components. This demonstrates that the process of this invention has good adaptability and controllability, and appropriate process parameters can be selected according to different product development needs.

[0059] In summary, this invention, through the rational matching of the action conditions of different enzyme preparations and the staged inoculation method of lactic acid bacteria and yeast, enables each treatment stage to fully exert its own role, reduces the mutual influence between different enzymes and different strains, and achieves comprehensive improvement in the quality of compound grain flour.

[0060] The technical principles of the embodiments of the present invention have been described above with reference to specific examples. These descriptions are merely for explaining the principles of the embodiments of the present invention and should not be construed as limiting the scope of protection of the embodiments of the present invention in any way. Based on the explanation herein, those skilled in the art can conceive of other specific embodiments of the present invention without creative effort, and these embodiments will all fall within the scope of protection of the embodiments of the present invention.

Claims

1. A method for targeted enzymatic hydrolysis fermentation of compound grain flour, characterized in that, Includes the following steps: S1. Preparation of compound grain powder: Mix 20-40 parts by weight of oat flour, 15-30 parts by weight of brown rice flour, 10-25 parts by weight of buckwheat flour, 10-20 parts by weight of millet flour, 5-15 parts by weight of corn flour and 5-15 parts by weight of highland barley flour evenly to obtain compound grain powder. S2. Slurry preparation, gelatinization, and first-stage enzymatic hydrolysis: The compound grain powder and water are mixed at a mass ratio of 1:2.5 to 1:5 to form a slurry. The mixture is heated to 85-95℃ and kept at this temperature for 10-30 minutes for gelatinization. Then, heat-resistant α-amylase is added for liquefaction for 10-40 minutes. The mixture is cooled to 50-60℃, the pH is adjusted to 5.5-6.5, and cellulase is added for enzymatic hydrolysis for 20-90 minutes. S3, Second stage of enzymatic hydrolysis: Cool the slurry after the first stage of enzymatic hydrolysis to 45-52℃ and adjust the pH to 4.5-5.5; add saccharifying enzyme, xylanase and neutral protease to continue enzymatic hydrolysis for 1-3 hours; after enzymatic hydrolysis, heat at 85-95℃ for 5-15 minutes to inactivate the enzymes. S4. Fermentation substrate adjustment: Cool the enzyme hydrolysate after enzyme inactivation to 35-40℃, adjust the solid content to 20%-35%, and adjust the pH to 5.5-6.2; S5. Lactic acid bacteria fermentation: Inoculate with lactic acid bacteria and ferment at 35-39℃ for 6-16 hours to reduce the pH of the system to 4.0-4.

8. S6. Yeast fermentation: Inoculate with yeast and continue fermentation at 28-34℃ for 4-12 hours; S7. Post-processing: Fermentation is terminated when the pH of the fermentation system reaches 3.8 to 4.

5. After drying, crushing and sieving, the directional enzymatic fermentation compound grain powder is obtained.

2. The method for targeted enzymatic hydrolysis and fermentation of compound grain powder according to claim 1, characterized in that, In step S2, the amount of heat-resistant α-amylase added is 30-120 U / g, and the amount of cellulase added is 20-100 U / g, both calculated based on the enzyme activity per gram of dry-based compound grain powder.

3. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, In step S3, the amount of saccharifying enzyme added is 50-200 U / g, the amount of xylanase added is 20-100 U / g, and the amount of neutral protease added is 100-500 U / g, all based on the enzyme activity per gram of dry-based compound grain powder.

4. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, In step S4, a food-grade acid-base regulator is used to adjust the pH. The acid-base regulator is one or more of citric acid, lactic acid, sodium carbonate, sodium bicarbonate, or sodium hydroxide.

5. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, In step S4, 0.2% to 1.0% of the dry weight of the compound cereal powder is further added as a prebiotic, consisting of one or more of the following: fructooligosaccharides, xylooligosaccharides, or inulin.

6. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, The lactic acid bacteria are one or more of Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus fermentum, with a total inoculum size of 1×10⁻⁶. 6 ~1×10 8 CFU / g.

7. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, The yeast is either *Saccharomyces cerevisiae* or *Kluyveromyces martensii*, and the inoculum size is 1×10⁻⁶. 5 ~1×10 7 CFU / g.

8. The method for targeted enzymatic hydrolysis and fermentation of compound grain flour according to claim 1, characterized in that, The drying method described in step S7 is one of vacuum low-temperature drying, spray drying, or freeze drying.

9. The method for directional enzymatic hydrolysis and fermentation of compound grain powder according to claim 8, characterized in that, The vacuum low-temperature drying temperature is 45-65℃; the spray drying inlet air temperature is 140-180℃, and the outlet air temperature is 65-85℃; the freeze drying includes pre-freezing and vacuum sublimation drying stages.

10. The application of the directional enzymatic fermentation compound grain powder prepared by the directional enzymatic fermentation method according to any one of claims 1 to 9 in solid beverages, meal replacement foods, instant foods, baked foods or other deep-processed grain foods.

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