A method for rapid growth control of lactic acid bacteria for fermentation of cereal products

Abstract

The application discloses a kind of for rice flour product fermentation lactic acid bacteria fast growth regulation method, belong to food fermentation technical field. With low polymer as core material, with crosslinking denatured starch as wall material, starch-based microspheres are added to rice flour slurry, inoculated with screened extracellular amylase lactic acid bacteria and added calcium ion. The extracellular amylase secreted by the bacterial body releases the core material carbon source by directional enzymolysis of the wall material of microsphere, and the release rate automatically accelerates with the growth of bacterial amount, and the same enzyme system synchronously hydrolyzes the surface layer starch of rice flour particles, and the double sources complement each other to supply sugar. The core material is depleted at the same time as the fermentation endpoint when the microsphere load is set, and the temperature is regulated in stages to preserve the starch core and gelatinize the texture in the heating process. The application triggers the release of carbon source by the output of bacterial metabolism, and the sugar supply automatically follows the growth, shortens the fermentation period and improves the texture of the final product under the conditions of low exogenous sugar, zero exogenous enzyme and no need for feed equipment.

Description

Technical Field

[0001] This invention belongs to the field of food fermentation technology, specifically relating to a method for rapidly regulating the growth of lactic acid bacteria in rice and flour products. Background Technology

[0002] Fermentation of rice and flour products is a core process in the production of traditional foods such as steamed buns and fermented rice cakes. The starch in rice and flour raw materials exists in granular form with a dense crystalline structure, making it difficult for lactic acid bacteria to utilize directly. This results in a long lag phase after inoculation, insufficient carbon source supply during the logarithmic growth phase, and an excessively long fermentation cycle.

[0003] Existing technologies primarily address the carbon source supply issue using three methods. The first is adding exogenous sugars, such as glucose, sucrose, or maltose, to directly provide fermentable carbon sources for lactic acid bacteria. This method is costly, and a large amount of free sugar alters the rheological properties of the dough, resulting in a sticky texture and textural collapse in the finished product. Furthermore, excessive reducing sugars in the early stages can create osmotic pressure stress on the bacteria. The second method is adding exogenous amylases to hydrolyze starch into reducing sugars before or during fermentation. This method increases the number of processing steps and production costs, and the amount, reaction time, and temperature of the exogenous enzymes are difficult to precisely match with the lactic acid bacteria growth curve, often resulting in excessive reducing sugars in the early stages inhibiting bacterial growth and carbon source depletion leading to fermentation stagnation in the later stages. The third method is fed-batch feeding, adding carbon sources in stages during fermentation. This method relies on feeding equipment and manual timing; the viscosity of rice and flour slurries leads to uneven dispersion of the added carbon source, and open operation introduces the risk of contamination by other microorganisms.

[0004] The common drawback of these three methods is that the timing of carbon source supply must rely on external means and human judgment, and none of them utilize the metabolic information of the fermentation system itself. There is a temporal misalignment between the concentrated carbon source demand of the cells during the logarithmic growth phase and the actual supply, and the carbon source supply rhythm cannot be automatically adjusted to follow the cell growth state.

[0005] Furthermore, the known applications of microencapsulation technology in the food industry have long been limited to isolation and delay. For example, encapsulating organic acids to prevent premature reaction with leavening agents, and encapsulating lactic acid bacteria to prevent inactivation during storage or premature proliferation in dough that could compete with yeast for carbon. In these applications, microcapsules are used as isolation tools, with the purpose of encapsulation being to prevent or delay the interaction between the contents and the system. The use of microcapsules as a supply interface for microorganisms to autonomously acquire carbon sources, and the use of enzymes secreted by the microorganisms themselves as the key to unlocking the cell wall material, has not been seen in the fermentation of rice and flour products.

[0006] In view of this, the present invention provides a method for regulating the rapid growth of lactic acid bacteria in rice and flour products. The fermentation sugar supply program is encoded in the material parameters, and the extracellular amylase of the bacteria is used as the trigger key for carbon source release. This allows the carbon source supply rhythm to automatically follow the growth needs of the bacteria, achieving rapid proliferation of lactic acid bacteria under conditions of low exogenous sugar, zero exogenous enzyme, and no need for feeding equipment, while preserving the core structure of rice and flour starch to take into account the texture of the final product.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A method for rapidly regulating the growth of lactic acid bacteria in rice and flour products includes the following steps.

[0010] Preparation of S1 Rice and Flour Slurry and Supply of Starting Carbon Source

[0011] Rice and flour raw materials are mixed with water at a mass ratio of 1:1.5 to 1:2.0 and processed through a colloid mill to produce a uniform slurry with a particle size D50 of 50 to 150 micrometers. The natural pH of the slurry is between 6.0 and 6.5. The rice and flour raw materials are at least one of wheat flour, rice flour, glutinous rice flour, or mixed grain flour. Food-grade oligomaltose with a degree of polymerization of DP3 to DP7 is added to the slurry as a starting carbon source at an amount of 0.3% to 0.8% of the dry weight of the rice and flour raw materials.

[0012] The technical function of the initial carbon source is to provide an immediately available carbon source for lactic acid bacteria in the early stage of inoculation, enabling the bacteria to quickly pass through the lag phase. The amount of initial carbon source added is limited to below the threshold that affects the rheological properties of dough, and it only provides sugar during the lag phase. The main carbon source is provided by the starch-based microspheres of S2, thereby avoiding the dough rheological deterioration and osmotic pressure stress caused by adding a large amount of exogenous sugar at once in existing technologies.

[0013] Preparation and Program Setting of S2 Enzymatic Hydrolysis Triggered Starch-Based Microspheres

[0014] The starch-based microspheres are prepared using oligomaltose or maltodextrin as the core material with a degree of polymerization of DP3 to DP7, and food-grade cross-linked esterified starch as the wall material, preferably acetylated adipic acid distarch, but acetylated phosphate distarch can also be used. The preparation process of starch-based microspheres is as follows: starch milk is prepared to a mass fraction of 10% to 20%, heated to 85 to 95 degrees Celsius for gelatinization, and the core material is added at a mass ratio of 1:3 to 1:9 to disperse it evenly. After emulsification and granulation, it is cross-linked and cured with a food-grade cross-linking agent. The amount of cross-linking agent is 0.1% to 1.0% of the mass of the wall material, the cross-linking temperature is 40 to 50 degrees Celsius, and the cross-linking time is 1 to 3 hours. After washing, drying at 40 to 60 degrees Celsius, and sieving, starch-based microspheres with a particle size of 50 to 200 micrometers are obtained.

[0015] The enzymatic resistance level of starch-based microspheres is determined by the degree of crosslinking and substitution of the wall material. Higher crosslinking results in a slower rate of amylase hydrolysis of the wall material and a later release of the core material. Since the crosslinked esterified starch raw material itself has a low basic crosslinking degree, the final enzymatic resistance level of the wall material is adjusted by the crosslinking and curing process after granulation, controlled by the amount of food-grade crosslinking agent and the crosslinking reaction time. This invention sets the enzymatic resistance level of the wall material to be such that the release curve of the oligosaccharides in the core material is phase-shifted from the hydrolysis curve of the starch on the surface of the rice and flour granules. In the early stage of logarithmic growth, the hydrolysis rate of the surface starch is still low, and the carbon source is mainly released from the microspheres.

[0016] As the microsphere release rate decreases with the consumption of wall material, the hydrolysis rate of starch on the surface of rice and flour particles increases due to the accumulation of bacterial and enzyme levels. The two sources work together to form a stable sugar supply platform in the system, which matches the sugar demand intensity during the logarithmic growth phase.

[0017] The loading of starch-based microspheres is set according to the principle of total carbon source conservation, ensuring that the depletion point of the core material coincides with the arrival of the target pH of fermentation. The loading, calculated as core material, is 1.0% to 3.0% of the dry weight of the rice and flour raw materials. The specific method for setting the loading is as follows: pre-fermentation is performed on rice and flour slurry without added starch-based microspheres. The total amount of oligosaccharides consumed to reach the target pH is measured, and the core material loading is calculated based on this total amount. The technical function of the loading setting is to encode the fermentation endpoint into the material: when the core material is depleted, the sugar supply from the microspheres terminates, and the cell proliferation naturally slows down due to the decrease in carbon source supply intensity; the fermentation endpoint does not require manual determination.

[0018] Thus, the material parameters of the starch-based microspheres encode the fermentation sugar supply program: the degree of cross-linking of the wall material sets the release start point and phase relationship, the microsphere loading sets the self-limiting endpoint, and the sugar supply platform is synthesized by the relay of microsphere release and surface starch hydrolysis. The sugar supply sequence throughout the fermentation process is preset by the materials, and the process side only needs conventional temperature control, without the need for feeding equipment or timing judgment.

[0019] The starch-based microspheres, with a particle size of 50 to 200 micrometers, are on the same scale as the D50 particle size of the rice and flour slurry. The microspheres are uniformly dispersed between the rice and flour particles. The carbon source released after enzymatic hydrolysis of the wall material maintains a high local concentration near the surface of the rice and flour particles, which is beneficial for improving local sugar supply efficiency. The starch-based microspheres are structurally stable in the aqueous phase of the slurry, with only a small amount of core material seeping out from the surface; the main core material remains within the wall material and can only be released by enzymatic hydrolysis of amylase. Since the wall material and the main rice and flour material are both starch, the enzymatic hydrolysis residue is incorporated into the product, with no added foreign matter remaining.

[0020] S3 strain screening, inoculation, and enzyme production initiation

[0021] Fermentation strains were screened from conventional commercial food-grade strains, with *Lactobacillus plantarum* or *Lactobacillus paracasei* as candidate strains. The screening criteria included three indicators: first, the ability to secrete extracellular amylase; second, the optimal pH for extracellular amylase being in the acidic range of 4.0 to 5.5; and third, the expression of extracellular amylase not being repressed in the presence of oligosaccharides as the initial carbon source, and the strain being able to directly utilize oligosaccharides with a degree of polymerization (DP3 to DP7). The screening method was as follows: plate culture was performed using starch as the sole carbon source, and the starch hydrolysis zone was measured to confirm enzyme production capacity; a crude enzyme solution was prepared from the cell-free fermentation supernatant, and enzyme activity was measured under different pH conditions to determine the optimal pH and verify the extracellular secretion property of the amylase; the culture was conducted in a medium containing oligosaccharides as the initial carbon source, and the enzyme activity of the cell-free supernatant was measured to exclude strains whose enzyme production was repressed by the carbon source. The strains used were commercial food-grade strains, and no strain preservation was required.

[0022] The technical function of the three screening indicators is as follows: First, the extracellular amylase secretion capacity ensures that the bacteria possess the key to unlock starch-based microspheres. Second, the optimal pH of the enzyme is in the acidic range, ensuring that as fermentation produces acid and the system pH decreases, the enzyme activity remains stable throughout the fermentation process, allowing surface starch hydrolysis to continue in the late logarithmic growth phase and ensuring the phase complementarity relationship set by S2 is maintained. Third, the indicator ensures that the expression of the key enzyme is not inhibited by the initial carbon source and the released carbon source, and that the initial carbon source is utilized immediately. Maltose-based carbon sources have an inducing effect on the expression of amylase in some starch-degrading lactic acid bacteria. The third indicator fixes this inducing characteristic to the selected strain, so that the carbon source released from the core material simultaneously acts as an inducing signal for key enzyme expression, and the enzyme production capacity increases synchronously when the core material release is enhanced. If a strain with an optimal enzyme pH in the neutral range is selected, acidification in the later stages of fermentation will cause enzyme activity to decrease, and the surface starch hydrolysis will not be able to support the fallback phase of microsphere release, resulting in the breakage of the sugar supply platform.

[0023] The inoculation amount of lactic acid bacteria seed culture is 1% to 5% of the slurry volume. After inoculation, food-grade soluble calcium salts are added to the slurry, at least one of calcium chloride, calcium lactate, or calcium gluconate, to achieve a Ca²⁺ concentration of 50 to 200 mg / L. The amylase is a calcium metalloenzyme; calcium ions participate in maintaining the spatial conformation of the enzyme protein, thus stabilizing the activity of extracellular amylase. The addition of calcium ions and the S2 enzymatic trigger design form a positive synergy: the enzyme stabilized by calcium ions is both a sugar-supplying enzyme for hydrolyzing the starch on the surface of rice and flour particles and a key enzyme for unlocking the microsphere wall material.

[0024] After inoculation, the fermentation system temperature is controlled at the upper limit of the strain's optimal growth temperature, i.e., 35 to 37 degrees Celsius, and maintained for 2 to 3 hours. During this stage, the initial carbon source provides sugar immediately, the cells proliferate rapidly to overcome the lag phase, and the secretion of extracellular amylase is initiated.

[0025] S4 enzyme-triggered release and phase-complementary glucose supply regulation

[0026] Once the bacteria enter the logarithmic growth phase, extracellular amylase accumulates continuously, leading to the targeted enzymatic hydrolysis of the starch-based microsphere wall material and the continuous release of oligosaccharides from the core material. Since enzyme levels are positively correlated with cell mass, the more cells there are, the faster the enzymatic hydrolysis of the wall material and the release of carbon sources occur. The carbon source release rate automatically follows the growth needs of the bacteria, forming a self-feedback sugar supply cycle where cell mass, enzyme levels, carbon release, and growth are sequentially promoted. This cycle uses the bacteria's own metabolic output as the trigger signal for carbon source release, eliminating the need for external feeding equipment or manual timing judgment.

[0027] The same extracellular amylase system simultaneously hydrolyzes the surface starch of rice and flour particles, releasing a complementary carbon source that complements the carbon source from the surface starch hydrolysis. During the early logarithmic growth phase, sugar supply is primarily provided by microsphere release, while during the subsequent drop-off phase, sugar supply is relayed by surface starch hydrolysis. The superposition of these two sources forms a stable sugar supply platform, with the sugar supply intensity matching the sugar demand intensity during the logarithmic growth phase.

[0028] The stability of the sugar supply platform is ensured by the slope relationship between the two release curves. The enzymatic hydrolysis rate of the microsphere wall material shows a bell-shaped curve that first rises and then falls with the consumption of the wall material, while the hydrolysis rate of the surface starch shows a climbing curve that continuously rises with the accumulation of cell mass and enzyme amount. The two curves intersect in the mid-logarithmic growth phase, with one source declining and the other source continuing. The fluctuation of reducing sugar concentration in the system is compressed within a narrow range. The cells do not experience carbon source surges or carbon source shortages during the logarithmic growth phase, and rapid acid production stress and proliferation stagnation are both inhibited.

[0029] During this stage, the fermentation temperature is reduced by 2 to 4 degrees Celsius, i.e., controlled at 32 to 34 degrees Celsius, and maintained for 4 to 6 hours. The purpose of cooling is to suppress cell division and acid production rates, preventing premature acid stress; extracellular amylases maintain catalytic activity within the fermentation temperature range, allowing the sugar supply process of microsphere release and surface starch hydrolysis to continue. The sugar supply process is monitored during this period by the rate of pH decrease or the concentration of reducing sugars.

[0030] S5 endpoint self-limitation and low-temperature flavor settling period regulation

[0031] When the core material of the starch-based microspheres is depleted to the preset loading capacity, the system pH reaches the target range of 4.8 to 5.2. Sugar supply from the microspheres ceases, cell proliferation slows, and the residual sugar from surface starch hydrolysis supports the accumulation of flavor compounds. At this point, the temperature is lowered to 28 to 32 degrees Celsius and maintained for 1 to 3 hours. The cells accumulate lactic acid, acetic acid, and ester flavor compounds. The low-temperature environment inhibits excessive acid production by lactic acid bacteria, preventing over-acidification in the final product. Fermentation ends when the pH naturally drops to 4.0 to 4.5. The wall material is a starch homolog, and enzymatic hydrolysis residue is incorporated into the product, with no added foreign matter remaining.

[0032] The essence of load coding is to move the endpoint determination forward to the material preparation stage. The load is set according to the conservation of total carbon source. The total amount of carbon source required to reach the target pH is the total amount of core material. Excessive load will result in an acidic endpoint, while insufficient load will result in insufficient fermentation. The fermentation endpoint is set once by the material and no longer depends on the operator's experience.

[0033] S6 Fermentation Termination and Texture Formation

[0034] The termination method is selected based on the product type. Steamed products are steamed at 100°C for 10 to 20 minutes, inactivating lactic acid bacteria and fixing flavor. The core starch of the rice and flour granules gelatinizes at the high steaming temperature, forming a gel network. Baked products directly enter a baking process at 160 to 200°C, where the core starch gelatinizes and expands, forming a honeycomb texture together with the surface hydrolysate. In this invention, the rice and flour starch undergoes no gelatinization pretreatment throughout the process; the core crystalline structure of the granules remains intact during fermentation, gelatinizing only during the final product heating process. Therefore, fermentation efficiency and the final product texture are no longer mutually constrained.

[0035] Compared with the prior art, the present invention has the following beneficial effects.

[0036] This invention uses the metabolic output of the microbial cells themselves as the trigger signal for carbon source release, overcoming the technical bias that carbon source regulation must rely on external means. The larger the cell volume, the more enzymes are produced, the faster the enzymatic hydrolysis of the microsphere wall material, and the faster the carbon source is released. The sugar supply rhythm automatically follows the growth needs, eliminating the need for feeding equipment and manual timing judgment.

[0037] This invention encodes the fermentation sugar supply program into the material parameters. The degree of cross-linking of the wall material sets the release start point and phase relationship, the microsphere loading sets the self-limiting endpoint, and the sugar supply platform is synthesized by the relay of microsphere release and surface starch hydrolysis. The sugar supply sequence throughout the fermentation process is preset by the material, and only conventional temperature control is required at the process end.

[0038] This invention achieves functional coupling of a single enzyme serving two purposes. The same extracellular amylase system is both the key to unlocking the microsphere wall material and the sugar supply tool for hydrolyzing the starch on the surface of rice and flour particles. Calcium ion stabilization and enzymatic triggering form a positive synergy, and the combination of various technical features produces an overall effect superior to independent operation.

[0039] The microcapsules of this invention have the opposite application to those in the prior art. The prior art uses microcapsules as a barrier to prevent or delay the interaction between the contents and the system. In this invention, they are used as a supply interface for the microorganisms to autonomously obtain carbon sources. The wall material and the main ingredient (rice or flour) are both starch, which is enzymatically hydrolyzed and incorporated into the product, resulting in clean ingredients.

[0040] This invention adopts a commercial food-grade strain screening route, which eliminates the need for strain preservation, shortens the fermentation cycle, and results in a final product with intact texture, making it suitable for large-scale application in the rice and flour product fermentation industry. Attached Figure Description

[0041] Figure 1 This is a flowchart of the method for rapid growth regulation of lactic acid bacteria in rice and flour products according to the present invention.

[0042] Figure 2 This is a flowchart of the method for preparing starch-based microspheres according to the present invention. Detailed Implementation

[0043] To make the technical solution of the present invention clearer, the present invention will be further described below in conjunction with embodiments and comparative examples.

[0044] Example 1: Fermented Steamed Buns

[0045] Take 1 kg of medium-gluten flour, add 1.6 L of water, and process it into a slurry with a particle size D50 of 80 μm through a colloid mill. Add 5 g of oligomaltose with a degree of polymerization of DP4 to DP6 as the starting carbon source. Starch-based microsphere preparation: Heat and gelatinize the starch slurry of acetylated adipic acid distarch, add oligomaltose and disperse evenly, emulsify and granulate, then crosslink and solidify with a food-grade crosslinking agent. After washing, drying, and sieving, obtain starch-based microspheres with a particle size of 100 to 150 μm. The core material loading is calculated as 2.0% of the dry weight of the flour. The degree of crosslinking of the wall material is set according to the phase difference between the release curve and the surface starch hydrolysis curve. The loading is set according to the coincidence of the core material depletion point and the endpoint pH point. Inoculate 50 mL of *Lactobacillus plantarum* seed culture that has passed three screening indicators, and add food-grade calcium chloride to make the Ca²⁺ concentration in the slurry 100 mg / L. The fermentation process is as follows: maintain 36 degrees Celsius for 2.5 hours, 33 degrees Celsius for 5 hours, and 31 degrees Celsius for 2 hours, with the final pH at 4.3 to 4.5. After shaping, the dough is steamed at 100 degrees Celsius for 15 minutes. No additional ingredients are needed during the entire fermentation process, shortening the total fermentation cycle by 20% to 30% compared to traditional fermentation methods. The finished product has a uniform honeycomb structure, no collapse, a soft texture, and a natural fermented aroma.

[0046] Example 2 Fermented Rice Cake

[0047] Take 1 kg of japonica rice, add 1.8 liters of water, and process it into a slurry with a particle size D50 of 70 micrometers through a colloid mill. Add 6 g of oligomaltose with a degree of polymerization of DP3 to DP5 as the starting carbon source. Starch-based microspheres are prepared using acetylated distarch as the wall material, following the same process as in Example 1. The microsphere particle size is 80 to 130 micrometers, and the core material loading is 2.5% of the dry weight of the japonica rice. Inoculate 40 ml of Lactobacillus paracasei seed culture that has passed three screening criteria, and add food-grade calcium lactate to make the Ca²⁺ concentration in the slurry 150 mg / L. The fermentation program is as follows: maintain at 37°C for 2 hours, maintain at 34°C for 4.5 hours, maintain at 30°C for 1.5 hours, and the final pH of fermentation is 4.2 to 4.5. The slurry is molded and then steamed. The fermentation process has a stable sugar supply during the logarithmic phase, with no excessive acid production in the later stage. The finished rice cake has a delicate texture and good elasticity, with the surface and core layers having the same texture, and no layering or collapse.

[0048] Comparative Example 1: Single Sugar Addition Process

[0049] Take 1 kg of the same all-purpose flour as in Example 1 and mix it with 1.6 liters of water to make a slurry. Add 25 g of glucose at once. The amount of glucose is equivalent to the total amount of the starting carbon source and microsphere core material in Example 1. Inoculate 50 ml of the same Lactobacillus plantarum seed culture, without adding starch-based microspheres and calcium salts, and ferment at a constant temperature of 36 degrees Celsius throughout the process. In the early stage of fermentation, the reducing sugar is supplied in a concentrated manner, the acid production rate is fast, the pH of the system drops rapidly, acid stress arrives early, and the bacteria die prematurely. At the end of fermentation, the pH drops to 3.8 to 4.0, which is lower than the target range. The finished product has an abrupt sour taste, unbalanced flavor, sticky dough, low specific volume, and collapsed internal structure. Moreover, the fermentation endpoint cannot be self-limiting and the termination point needs to be manually determined.

[0050] Comparative Example 2: Exogenous Enzyme Process

[0051] The same amount of flour and water as in Example 1 was used to make a slurry, and exogenous α-amylase preparation was added and inoculated with the same strain for constant temperature fermentation. In the early stage of fermentation, the rate of starch hydrolysis and sugar production exceeded the rate of sugar consumption by the cells, and the accumulation of reducing sugar inhibited cell proliferation; in the middle and late stages of fermentation, starch was excessively hydrolyzed, the finished product was sticky and had reduced gas holding capacity, and the exogenous enzyme preparation increased the cost of raw materials and the burden on the ingredient list.

[0052] As can be seen from the comparison of the examples and comparative examples, the present invention enables the carbon source supply rhythm to automatically follow the cell growth by using enzyme-triggered release and phase-complementary sugar supply of starch-based microspheres. This overcomes the defect of misaligned sugar supply and demand timing in exogenous sugar and exogenous enzyme processes, shortens the fermentation cycle, and results in a final product with complete texture.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. The scope of protection of the present invention is determined by the claims, and any equivalent modifications based on the technical essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for rapidly regulating the growth of lactic acid bacteria in rice and flour products fermentation, characterized in that, Includes the following steps: S1 mixes rice and flour raw materials with water to make a slurry, and adds oligosaccharides as the starting carbon source to obtain rice and flour slurry; S2 adds starch-based microspheres with oligosaccharides as the core material and cross-linked modified starch as the wall material to rice and flour slurry. The enzymatic hydrolysis resistance level of the wall material of the starch-based microspheres is set so that the release curve of the core material is phase-shifted from the hydrolysis curve of the starch on the surface of the rice and flour particles. S3 is inoculated with seed culture of lactic acid bacteria that has been screened to have the ability to secrete extracellular amylase, and food-grade soluble calcium salts are added. S4 controls the fermentation temperature for cultivation. During the growth of the cells, the extracellular amylase secreted by the cells directionally hydrolyzes the wall material of the starch-based microspheres, causing the oligosaccharides in the core material to be released gradually. The release rate increases with the increase of cell mass. The same extracellular amylase system simultaneously hydrolyzes the surface starch of rice and flour particles, releasing carbon sources that complement the surface starch hydrolysis carbon source for sugar supply. When the core material of S5 starch-based microspheres is depleted according to the preset loading, the sugar supply of the microspheres stops, the cell proliferation slows down and flavor substances accumulate, and fermentation ends when the target pH is reached. S6 terminates fermentation and undergoes heating processing, during which the core starch of rice and flour granules gelatinizes to form texture.

2. The method according to claim 1, characterized in that, The wall material described in S2 is acetylated adipic acid distarch or acetylated phosphate distarch. The starch-based microspheres are obtained by gelatinizing and embedding the core material and then cross-linking and curing them with a food-grade cross-linking agent. The particle size of the starch-based microspheres is 50 to 200 micrometers.

3. The method according to claim 1, characterized in that, The phase-staggered setting method described in S2 is as follows: in the early stage of logarithmic growth, sugar is mainly supplied by the release of starch-based microspheres, and in the fall-off stage of the release of starch-based microspheres, sugar is supplied by the hydrolysis of starch on the surface of rice and flour particles. The two sources superimpose to form a stable sugar supply platform.

4. The method according to claim 1, characterized in that, The loading of starch-based microspheres described in S2 is set according to the total carbon source conservation, so that the time when the core material is depleted coincides with the time when the target pH of fermentation is reached. The loading is 1.0% to 3.0% of the dry basis mass of rice and flour raw materials, based on the core material.

5. The method according to claim 1, characterized in that, The particle size D50 of the rice and flour slurry in S1 is 50 to 150 micrometers. The particle size of the starch-based microspheres is the same as that of the rice and flour particles, and the starch-based microspheres are uniformly dispersed in the gaps between the rice and flour particles.

6. The method according to claim 1, characterized in that, The screening criteria described in S3 are: having the ability to secrete extracellular amylase in the presence of the initial carbon source oligosaccharide, and the optimal pH of the extracellular amylase being in the range of 4.0 to 5.5; the lactic acid bacteria being at least one commercially available food-grade strain of Lactobacillus plantarum or Lactobacillus paracasei.

7. The method according to claim 1, characterized in that, The amount of food-grade soluble calcium salt added in S3 is such that the Ca²⁺ concentration in the slurry reaches 50 to 200 mg / L, and the calcium salt is at least one of calcium chloride, calcium lactate or calcium gluconate.

8. The method according to claim 1, characterized in that, The fermentation temperature in S4 is controlled in stages: at the initial stage of inoculation, the temperature is controlled at the upper limit of the optimal growth temperature of the strain, which is 35 to 37 degrees Celsius, and maintained for 2 to 3 hours; then the temperature is lowered by 2 to 4 degrees Celsius and maintained for 4 to 6 hours.

9. The method according to claim 1, characterized in that, In S5, when the pH of the system drops to 4.8 to 5.2, the temperature is reduced to 28 to 32 degrees Celsius and maintained for 1 to 3 hours to fix the flavor. Fermentation ends when the pH drops to 4.0 to 4.

5. The degree of polymerization of the starting carbon source oligosaccharide mentioned in S1 is DP3 to DP7, and the amount added is 0.3% to 0.8% of the dry basis mass of the rice and flour raw materials.

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