Multi-grain steamed bread rich in dietary fiber and preparation method thereof

Abstract

The present invention provides a multi-grain steamed bun rich in dietary fiber and a preparation method thereof, relating to the field of food processing technology. Multi-grain flour is treated by 0.3~0.6MPa of carbon dioxide, and the multi-grain flour is subjected to double enzymatic hydrolysis using the optimal temperature difference of the enzyme. At 38~42°C, α-amylase preferentially hydrolyzes the surface amylose of multi-grain starch granules, reduces dough viscosity, exposes the fiber layer, and provides a channel for subsequent cellulase action; at 55~57°C, cellulase selectively degrades cellulose and hemicellulose, making the fiber structure loose, retaining β-glucan, and activating phytase at the same time, efficiently decomposing phytic acid. The prepared multi-grain steamed bun has a β-glucan retention rate of >81%, a low phytic acid content, and a softer taste.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and in particular to a multi-grain steamed bun rich in dietary fiber and a preparation method thereof. Background Art

[0002] Traditional multi-grain steamed buns have become an important development direction for healthy staple foods because they are rich in functional ingredients such as dietary fiber and β-glucan. However, their industrial production faces significant technical bottlenecks. For example, the large amount of high-fiber raw materials such as bran and whole grain flour lead to poor dough extensibility and easy breakage of the gluten network. The finished product has high hardness, low specific volume and rough taste, forming a "high fiber but unpalatable" contradiction; on the other hand, phytic acid is commonly found in multi-grain foods. It combines with minerals such as calcium, iron, and zinc to form insoluble complexes, resulting in a 40%-60% reduction in the body's absorption rate of minerals, which goes against the original intention of nutritionally fortified products.

[0003] While traditional processing techniques degrade crude fiber to improve taste, they also tend to destroy heat-sensitive substances like β-glucan, resulting in a retention rate typically below 70%, significantly diminishing their functionality. Furthermore, traditional processing techniques fail to address phytic acid degradation during enzymatic hydrolysis, as phytic acid degradation relies on phytase, while single cellulase has no effect on phytic acid. Consequently, phytic acid residues in conventional processes remain above 0.6%, leaving the mineral absorption issue unresolved. Therefore, there is an urgent need to develop a multi-grain steamed bread that balances nutritional value and palatability. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention aims to provide a multi-grain steamed bun rich in dietary fiber and a preparation method thereof.

[0005] One of the purposes of the present invention is to provide a method for preparing multi-grain steamed bread rich in dietary fiber, comprising the following steps:

[0006] First, introduce CO2 into the grain powder to 0.3-0.6 MPa and maintain it for 20-40 minutes, then evenly mix the grain powder and water to obtain a slurry;

[0007] Add α-amylase to the slurry, adjust the pH to 6.0-6.5, and perform enzymatic hydrolysis at 38-42° C. for 15-25 minutes; raise the temperature to 55-57° C., adjust the pH to 5.0-5.5, add cellulase, and continue enzymatic hydrolysis for 25-35 minutes; inactivate the enzyme and cool to 25-33° C. to obtain an enzymatic hydrolyzed slurry;

[0008] Draining the enzymatic hydrolyzed slurry and then mixing it evenly with wheat flour and inulin to obtain mixed powder;

[0009] Add monoglyceride hydrate and activated yeast solution to the mixed flour, add water and stir into dough;

[0010] The dough is fermented, proofed and steamed to obtain multi-grain steamed buns rich in dietary fiber.

[0011] Preferably, the miscellaneous grain flour comprises the following raw materials in parts by weight: 28-32 parts of highland barley flour, 18-22 parts of quinoa flour and 13-17 parts of oat bran.

[0012] Preferably, the mesh number of highland barley flour is 50-200 mesh; the mesh number of quinoa flour is 50-200 mesh; and the mesh number of oat bran is 50-100 mesh.

[0013] Preferably, the highland barley flour comprises 50-80 mesh highland barley coarse powder, 80-150 mesh highland barley medium powder and 150-200 mesh highland barley fine powder;

[0014] Based on 100% of the total weight of the highland barley flour, the highland barley flour includes 38% to 42% of coarse highland barley powder, 28% to 32% of medium highland barley powder and 28% to 32% of fine highland barley powder.

[0015] Preferably, the quinoa flour comprises quinoa coarse powder of 50-80 mesh, quinoa medium powder of 80-150 mesh, and quinoa fine powder of 150-200 mesh;

[0016] Based on 100% of the total weight of the quinoa flour, the quinoa flour includes 38-42% of coarse quinoa flour, 38-42% of medium quinoa flour and 38-42% of fine quinoa flour.

[0017] Preferably, the added amount of α-amylase is 0.1% of the total weight of the miscellaneous grain flour, and the α-amylase activity is ≥2000 U / g; the added amount of cellulase is 0.2% of the total weight of the miscellaneous grain flour, and the cellulase activity is ≥10000 U / g.

[0018] Preferably, the mass ratio of the miscellaneous grain flour, the wheat flour and the inulin is 60-70:33-37:2-4.

[0019] Preferably, the method for preparing monoglyceride hydrate comprises adding monoglyceride to warm water at 55-65°C and stirring until the monoglyceride is completely melted to form monoglyceride hydrate, wherein the mass ratio of monoglyceride to water is 1:16-17; the method for preparing the activated yeast solution comprises adding yeast to warm water at 33-38°C and dissolving it, and then activating it in an environment at 30-35°C for 15-30 minutes.

[0020] Preferably, fermentation includes pre-fermentation and main fermentation; the pre-fermentation includes fermentation at a humidity of 72-78% and a temperature of 28-35°C for 45-80 minutes; the main fermentation includes deflating the pre-fermented dough and dividing it into small pieces, and then fermenting at a humidity of 82-88% and 35-40°C for 100-150 minutes.

[0021] The second object of the present invention is to provide a multi-grain steamed bun rich in dietary fiber prepared by the preparation method as described above.

[0022] Beneficial effects of the present invention:

[0023] The present invention treats the grain flour with 0.3-0.6MPa of carbon dioxide and performs a double enzymatic hydrolysis on the grain flour by utilizing the optimal temperature difference of the enzymes. At 38-42°C, α-amylase preferentially hydrolyzes the surface amylose of the grain starch granules, reducing the viscosity of the dough, exposing the fiber layer, and providing a channel for the subsequent action of cellulase; at 55-57°C, cellulase selectively degrades cellulose and hemicellulose, making the fiber structure loose and retaining β-glucan, while activating phytase and efficiently decomposing phytic acid. CO2 penetrates into the grain flour particles at 0.3-0.6MPa, forming a gas-solid interface barrier, which can inhibit the excessive degradation of β-glucan by cellulase and prevent the loss of β-glucan due to structural damage during mechanical stirring and enzymatic hydrolysis. The polarity regulation effect of CO2 weakens the complexing ability of phytic acid with minerals, making phytic acid more susceptible to enzymatic hydrolysis. Treatment with CO2 at 0.3-0.6 MPa causes phytic acid molecules to migrate from the interior of the pellets to the surface, increasing the contact area with the subsequent enzymatic hydrolysis system and further disrupting the phytic acid structure through synergistic gradient enzymatic hydrolysis. The osmotic effect of CO2 slightly disrupts the protein hydrogen bonds in the grain flour, reducing the elastic resistance of the dough while increasing water absorption, making the gluten network softer and more extensible. β-glucan has the effect of lowering blood sugar and lipids and exhibits excellent heat resistance, with an activity retention rate of >81% at 55-57°C. The optimal temperature for phytase is 55-60°C, and 55-57°C prevents excessive enzymatic hydrolysis from damaging nutrients. The resulting multi-grain steamed buns exhibit a β-glucan retention rate of >81%, a low phytic acid content, and a softer texture. DETAILED DESCRIPTION

[0024] According to a first aspect of the present invention, a method for preparing multi-grain steamed bread rich in dietary fiber is provided, comprising the following steps:

[0025] First, introduce CO2 into the grain powder to 0.3-0.6 MPa and maintain it for 20-40 minutes, then evenly mix the grain powder and water to obtain a slurry;

[0026] Add α-amylase to the slurry, adjust the pH to 6.0-6.5, and perform enzymatic hydrolysis at 38-42° C. for 15-25 minutes; raise the temperature to 55-57° C., adjust the pH to 5.0-5.5, add cellulase, and continue enzymatic hydrolysis for 25-35 minutes; inactivate the enzyme and cool to 25-33° C. to obtain an enzymatic hydrolyzed slurry;

[0027] Draining the enzymatic hydrolyzed slurry and then mixing it evenly with wheat flour and inulin to obtain mixed powder;

[0028] Add monoglyceride hydrate and activated yeast solution to the mixed flour, add water and stir into dough;

[0029] The dough is fermented, proofed and steamed to obtain multi-grain steamed buns rich in dietary fiber.

[0030] In the present invention, CO2 penetrates into the interior of the grain powder particles at 0.3~0.6MPa, adsorbs in the microporous structure of starch and dietary fiber, and forms a gas-solid interface barrier; β-glucan is similar to cellulose structure and is easily non-specifically decomposed by cellulase. In the subsequent enzymatic hydrolysis process, the low polarity environment of CO2 can inhibit the excessive degradation of β-glucan by cellulase, thereby selectively retaining more β-glucan; the swelling effect of CO2 causes the grain powder particles to swell slightly, and the fiber network structure is loose but maintains integrity, avoiding the loss of β-glucan due to structural damage during mechanical stirring and enzymatic hydrolysis. At the same time, the polarity regulation effect of CO2 weakens the complexing ability of phytic acid with minerals such as calcium and iron, making phytic acid more susceptible to enzymatic hydrolysis; CO2 treatment at 0.3~0.6MPa causes phytic acid molecules to migrate from the inside of the particles to the surface, increasing the contact area with the subsequent enzymatic hydrolysis system, and synergistic gradient enzymatic hydrolysis further destroys the phytic acid structure. In addition, the initial pores released by CO2 are superimposed on the gas production of yeast, which reduces the amount of yeast used while making the dough expand more evenly; the penetration of CO2 slightly interrupts the protein hydrogen bonds in the multi-grain flour, reducing the elastic resistance of the dough, while increasing the water absorption rate, making the gluten network softer and more extensible; the porous structure formed by CO2 can still accelerate steam penetration, making the starch gelatinization more uniform and the internal structure delicate, avoiding the roughness of traditional multi-grain steamed buns.

[0031] In the present invention, the optimum action temperature of α-amylase is generally between 38 and 42°C. Enzymatic hydrolysis within this temperature range for 15 to 25 minutes can preferentially hydrolyze the amylose on the surface of the grain starch granules. Due to the mild reaction conditions, the structure and activity of β-glucan are less affected. Moreover, this temperature range is far below the denaturation temperature of β-glucan, so during the starch hydrolysis process, β-glucan can exist stably and will not be destroyed by factors such as high temperature. After α-amylase hydrolyzes amylose, the viscosity of the dough is reduced and the fiber layer is exposed. However, this action is mainly directed at starch and will not cause direct damage to the structure where the β-glucan is located. Instead, it provides a channel for the subsequent action of cellulase, which is conducive to further protection and release of β-glucan in subsequent steps.

[0032] Raise the temperature to 55-57°C, then add cellulase and continue enzymatic hydrolysis for 25-35 minutes. β-glucan exhibits excellent heat resistance, with >90% activity retention at this temperature. Cellulase primarily targets cellulose and hemicellulose, selectively degrading these substances and loosening the fiber structure without degrading β-glucan, thereby preserving its integrity. This loose fiber structure provides physical protection for β-glucan, making it less susceptible to external factors during subsequent processing. Furthermore, during this process, β-glucan may form complexes with other components, further enhancing its stability. Enzyme inactivation promptly terminates enzyme activity, preventing potential damage to β-glucan from continued action in subsequent processing. Cooling to 25-33°C is a gentle process, avoiding the effects of drastic temperature fluctuations on the β-glucan structure and helping to maintain its activity and stability.

[0033] At 55-57°C, cellulase not only degrades cellulose and hemicellulose but also activates phytase. The optimum temperature for phytase is 55-60°C. Within this temperature range, activated phytase can efficiently decompose phytic acid. After 25-35 minutes of enzymatic hydrolysis, phytic acid is significantly decomposed, thereby reducing the phytic acid content. The hydrolysis of starch by α-amylase and the degradation of fiber by cellulase facilitate the release of phytic acid from the grain particles, increasing the contact area between phytic acid and phytase, improving the efficiency of phytase, further promoting the decomposition of phytic acid, and reducing phytic acid residues.

[0034] Additionally, α-amylase hydrolyzes amylose on the surface of starch granules at 38-42°C, reducing the viscosity of the dough. This makes the dough easier to handle during subsequent processing. During fermentation, the sugars produced by starch hydrolysis provide more energy for the yeast, promoting yeast growth and fermentation, and producing more carbon dioxide, making the steamed buns fluffier. Cellulase degrades cellulose and hemicellulose at 55-57°C, loosening the fiber structure. This loose fiber structure can accommodate more gas. During fermentation and proofing, these gases create more pores within the steamed buns, increasing their specific volume and making them softer.

[0035] The subsequent addition of monoglyceride hydrate and activated yeast extract, monoglyceride as an emulsifier, improves the rheological properties of the dough, making it softer and more elastic. The carbon dioxide produced by yeast fermentation, based on the soft fiber structure and good dough properties, further enhances the steamed buns' soft texture.

[0036] In the present invention, after adding α-amylase, the enzymolysis temperature is, for example, 38°C, 39°C, 40°C, 41°C or 42°C; the enzymolysis time is, for example, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min or 25 min.

[0037] In the present invention, the cellulase hydrolysis temperature is, for example, 55°C, 56°C or 57°C; the enzymatic hydrolysis time is 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min or 35 min.

[0038] In a preferred embodiment of the present invention, the coarse grain flour comprises the following raw materials in parts by weight: 28-32 parts of highland barley flour, 18-22 parts of quinoa flour and 13-17 parts of oat bran.

[0039] In the present invention, highland barley is rich in β-glucans, which have benefits such as lowering blood sugar and lipids, and also contains various minerals and vitamins. Quinoa is a complete nutritional food, rich in high-quality protein, various minerals, vitamins, and other nutrients, and its amino acid composition is close to human needs. Oat bran is rich in dietary fiber, especially soluble dietary fiber, which is beneficial to intestinal health and can also lower cholesterol. Combining these ingredients in a ratio of 28-32 parts highland barley flour, 18-22 parts quinoa flour, and 13-17 parts oat bran can make the multi-grain steamed buns more nutritionally comprehensive and balanced, meeting the human body's needs for multiple nutrients. Highland barley flour, quinoa flour, and oat bran each have a unique taste and texture. Highland barley flour can give the steamed buns a certain toughness and chewiness; quinoa flour can increase the smoothness and aroma of the steamed buns; and oat bran can enrich the steamed buns with a certain wheat flavor. The combination of 28-32 parts of highland barley flour, 18-22 parts of quinoa flour and 13-17 parts of oat bran can complement and coordinate each other in taste, avoiding the taste defects that may be caused by a single grain flour, and making the final grain steamed buns soft, rich and layered.

[0040] In the present invention, the amount of highland barley flour is, for example, 28 parts, 29 parts, 30 parts, 31 parts or 32 parts; the amount of quinoa flour is, for example, 18 parts, 19 parts, 20 parts, 21 parts or 22 parts; and the amount of oat bran is, for example, 13 parts, 14 parts, 15 parts, 16 parts or 17 parts.

[0041] In a preferred embodiment of the present invention, the mesh size of the highland barley flour is 50-200 meshes; the mesh size of the quinoa flour is 50-200 meshes; and the mesh size of the oat bran is 50-100 meshes.

[0042] In a preferred embodiment of the present invention, the highland barley flour comprises 50-80 mesh highland barley coarse powder, 80-150 mesh highland barley medium powder and 150-200 mesh highland barley fine powder; based on 100% of the total weight of the highland barley flour, the highland barley flour comprises 38-42% of the highland barley coarse powder, 28%-32% of the highland barley medium powder and 28%-32% of the highland barley fine powder.

[0043] In the present invention, highland barley flour in the 50-200 mesh range exhibits excellent processing properties during mixing with other ingredients, adding water to form dough, and fermentation, promoting a good dough structure and fermentation effect. Highland barley flour with a mesh size of 50-80 mesh accounts for 38-42%. This flour provides a supporting structure in the steamed buns, enhancing the chewiness and texture of the buns. Furthermore, larger particles digest more slowly during digestion, helping to prolong satiety. If the proportion of highland barley flour is too high, the steamed buns may be too rough and have a hard texture, making them unacceptable to consumers. However, if the proportion is too low, the characteristic coarse grain will not be highlighted, defeating the purpose of adding highland barley flour. Highland barley with a mesh size of 80-150 mesh has a moderate mesh size and a relatively fine texture. It can fill the gaps between coarse and fine flours in the steamed buns, making the internal structure more uniform and compact. This flour neither creates an overly grainy texture like coarse flour nor detracts from the coarse grain's characteristics like fine flour, achieving a balanced taste. A 28-32% proportion of medium highland barley flour ensures that the steamed buns are neither too rough nor too fine, while also improving their internal structure and making them fluffier and softer. If the proportion of medium highland barley flour is too high, the taste and texture of the buns may resemble those made with regular flour, diminishing the uniqueness of highland barley flour. A too low proportion will prevent it from effectively balancing the taste and optimizing the structure. Fine highland barley flour, with a particle size of 150-200 mesh, is very fine and disperses evenly throughout the dough, resulting in a smoother surface and a finer, softer internal structure. Furthermore, fine highland barley flour increases the stickiness and extensibility of the dough, helping the buns maintain their shape during fermentation and steaming, enhancing their appearance. A 28-32% proportion of fine highland barley flour results in a smoother surface and a finer internal structure, improving the overall quality and taste of the buns. If the proportion of fine flour is too high, the steamed buns may be too sticky and soft, losing the chewiness and toughness that coarse grain steamed buns should have; if the proportion is too low, the surface of the steamed buns will be rough and the internal structure will not be delicate enough, affecting the appearance and taste of the steamed buns.

[0044] In the present invention, the 50-80 mesh highland barley flour has larger particles, resulting in a relatively small contact area with enzymes. During the enzymatic hydrolysis process, α-amylase and cellulase act relatively slowly on it. This allows for greater opportunities for nutrients such as β-glucan to be preserved intact within the flour, preventing excessive enzymatic hydrolysis. Furthermore, the larger gaps created by the flour within the dough facilitate even distribution of nutrients. During the steaming process, these gaps provide space for nutrients to stabilize, reducing nutrient loss due to factors such as high temperatures. The 80-150 mesh highland barley flour has a moderate mesh size, allowing enzymes to more effectively target starch and fiber. During the enzymatic hydrolysis process, it not only allows for moderate starch hydrolysis, providing sufficient sugars for fermentation, but also protects nutrients such as β-glucan from being excessively degraded. The medium flour, which fills the gap between the coarse and fine flours, creates a more compact and uniform dough structure, helps stabilize nutrients throughout the dough, and better maintains their activity during the steaming process. Fine barley flour with a mesh size of 150-200 mesh has small particles, providing a large contact area with enzymes and enabling a rapid enzymatic hydrolysis reaction. However, due to its excellent heat resistance, β-glucan retains its activity at moderate enzymatic hydrolysis temperatures. Fine flour evenly disperses in dough, increasing its viscosity and extensibility, allowing nutrients like β-glucan to interact more fully with other ingredients, thereby enhancing their effectiveness.

[0045] Based on the total weight of highland barley flour, the ratio of 38-42% coarse highland barley flour, 28-32% medium highland barley flour, and 28-32% fine highland barley flour allows the three mesh sizes of highland barley flour to form a synergistic and complementary system in the dough. The coarse flour provides certain structural support and initial protection of nutrients, the medium flour balances and stabilizes the dough structure and nutrient distribution, and the fine flour, through its good dispersibility and full interaction with other raw materials, further promotes the stability and efficacy of nutrients such as β-glucan. This ratio ensures that throughout the preparation process of steamed buns, from enzymatic hydrolysis to fermentation to steaming, nutrients such as β-glucan can be protected and utilized accordingly at different stages, thereby better retaining their nutritional activity and being more effectively absorbed by the human body after consumption, exerting their health benefits such as lowering blood sugar and lipids.

[0046] The relatively slow release of phytic acid from coarse highland barley flour, combined with the rapid decomposition of phytic acid in fine and medium highland barley flour, prevents a large amount of phytic acid from being released in a short period of time, preventing phytase from fully decomposing it. The particle size of medium highland barley flour ensures that the phytic acid activity of phytase is intermediate between that of coarse and fine highland barley flour. During the enzymatic hydrolysis process, the phytic acid in the medium highland barley flour is moderately decomposed, neither as slowly as coarse highland barley flour nor as rapidly as fine highland barley flour. This creates a synergistic and balanced effect in the overall reduction of phytic acid residues. The small particle size of fine highland barley flour allows phytase to more quickly and fully contact the phytic acid within it and decompose it. During the initial enzymatic hydrolysis phase, the phytic acid in the fine highland barley flour is rapidly decomposed, ensuring rapid removal of phytic acid from the entire system. This also promotes the enzymatic hydrolysis reaction, as the phytic acid decomposition products can further affect enzyme activity and the reaction environment.

[0047] 38-42% coarse highland barley flour slowly and continuously releases phytic acid during the enzymatic hydrolysis process, coordinating with the decomposition of phytic acid in the fine and medium highland barley flours. This ensures a relatively uniform and continuous decomposition of phytic acid throughout the enzymatic hydrolysis process, preventing excessive accumulation and residual phytic acid. 28-32% medium highland barley flour and 28-32% fine highland barley flour ensure sufficient substrate for phytase to continuously decompose phytic acid. This balanced ratio of medium to fine highland barley flour ensures effective phytic acid decomposition at different stages, improving the efficiency of phytase, thereby more effectively reducing phytic acid residues and increasing the bioavailability of nutrients such as minerals in highland barley flour.

[0048] In a preferred embodiment of the present invention, the quinoa flour comprises quinoa coarse powder of 50-80 mesh, quinoa medium powder of 80-150 mesh and quinoa fine powder of 150-200 mesh; based on 100% of the total weight of the quinoa flour, the quinoa flour comprises 38-42% of the coarse quinoa powder, 38-42% of the medium quinoa powder and 38-42% of the fine quinoa powder.

[0049] In the present invention, quinoa flour in the range of 50 to 200 meshes can have a positive impact on the toughness, ductility and elasticity of the dough. When paired with highland barley flour, wheat flour, etc., the overall properties of the dough can be adjusted, so that the dough can maintain a good shape during fermentation and proofing, and the structure of the steamed buns is more stable after steaming. Quinoa coarse flour with a mesh size of 50 to 80 can provide a certain granularity, increase the richness of the taste, and make the steamed buns taste "chewy"; quinoa medium flour with a mesh size of 80 to 150 has a moderate texture, which can make the taste of the steamed buns more delicate and soft, and play a transitional role; quinoa fine flour with a mesh size of 150 to 200 can make the dough more delicate and smooth, increase the softness and ductility of the steamed buns, and make the steamed buns more palatable when chewed without a rough feeling. This combination of coarse and fine flours makes the steamed buns have a richer taste layer, retaining a certain coarse grain characteristic while avoiding the taste defects caused by a single coarse flour or fine flour. The coarse quinoa flour creates larger pores within the steamed buns, giving them a fluffy texture. The medium quinoa flour fills the gap between the coarse and fine flours, making the buns' structure more uniform and compact. The fine flour helps form a delicate gluten network, enhancing their elasticity and toughness. A mixture of 38-42% coarse quinoa flour, 38-42% medium quinoa flour, and 38-42% fine quinoa flour creates a more balanced internal structure, resulting in a fluffy, soft, and springy texture.

[0050] Quinoa flour with a mesh size of 50-80 is larger, and its β-glucan is relatively well protected during processing, making it less susceptible to damage from external factors such as excessive enzymatic hydrolysis and high temperatures, thereby better preserving its structure and activity. Quinoa flour with a mesh size of 150-200, due to its smaller particles and larger specific surface area, is more accessible to enzymes during enzymatic hydrolysis, facilitating the degradation of quinoa cell walls by cellulase and other enzymes, thereby facilitating the release of β-glucan from the cell walls. Furthermore, during subsequent processing, the fine powder is better able to form a uniform dough structure, contributing to the even distribution of β-glucan throughout the system and avoiding stability issues caused by localized concentrations of excessively high or low concentrations. Quinoa flour with a mesh size of 80-150 plays a transitional and balancing role. Its moderate particle size protects the β-glucan within to a certain extent, while also allowing for its proper release and activity during enzymatic hydrolysis and processing. Based on 100% total weight, 38-42% coarse quinoa flour can provide enough large particles to protect a certain amount of β-glucan, allowing it to exist stably during processing; the same proportion range of medium and fine quinoa flour, on the one hand, ensures that there is enough fine powder to fully release β-glucan, and on the other hand, the presence of medium flour avoids the problem of excessive exposure and instability of β-glucan caused by excessive fine powder. Through this ratio, the β-glucan in quinoa flour can be effectively protected during the processing, and can be fully released and exert its function, thereby further improving the retention rate of β-glucan.

[0051] Due to the large size of quinoa coarse meal, phytase and phytic acid are relatively difficult to contact. However, during the initial enzymatic hydrolysis process, as α-amylase hydrolyzes starch and cellulase partially degrades the cell walls, the coarse meal particle structure gradually becomes loose, providing a pathway for phytase to act on phytic acid. The smaller particles of quinoa fine flour allow phytase to more quickly and fully contact the phytic acid within it and initiate the decomposition reaction. The particle size of quinoa medium flour makes phytase's effect on phytic acid intermediate between coarse and fine flours. It acts synergistically throughout the enzymatic hydrolysis process, effectively breaking down phytic acid at different stages, along with coarse and fine flours.

[0052] The 38-42% coarse quinoa meal slowly releases phytic acid during the enzymatic hydrolysis process. This, combined with the rapid decomposition of phytic acid in the fine and medium quinoa meal, prevents a large amount of phytic acid from being released too quickly, preventing phytase from fully decomposing it. The appropriate amount of medium and fine quinoa meal ensures sufficient substrate for phytase to continuously decompose phytic acid. This ratio ensures a relatively uniform and continuous breakdown of phytic acid throughout the enzymatic hydrolysis process, effectively reducing residual phytic acid and resulting in a lower phytic acid content in the prepared multi-grain steamed bread, thereby increasing the bioavailability of nutrients such as minerals.

[0053] In a preferred embodiment of the present invention, the addition amount of α-amylase is 0.1% of the total weight of the coarse grain flour, and the α-amylase activity is ≥2000U / g; the addition amount of the cellulase is 0.2% of the total weight of the coarse grain flour, and the cellulase activity is ≥10000U / g.

[0054] In the present invention, adding 0.1% α-amylase ensures sufficient enzyme molecules are in full contact with the starch substrate, achieving an appropriate degree of starch hydrolysis within the 15-25 minute enzymatic hydrolysis period. This reduces dough viscosity, facilitates subsequent processing, and provides sufficient sugars for yeast fermentation. Excessive α-amylase addition can lead to over-hydrolysis of starch, making the dough too watery and soft, preventing the formation of a good gluten network, and affecting the shape and texture of the steamed buns. Furthermore, over-hydrolysis can cause the steamed buns to collapse after steaming and exhibit an uneven surface. A 0.1% addition, however, ensures effective starch hydrolysis while avoiding these adverse effects, helping to maintain the quality and texture of the steamed buns. Adding 0.2% cellulase can moderately loosen and degrade the fiber structure after 25-35 minutes of enzymatic hydrolysis at a temperature of 55-57°C. This helps to disrupt the structure of the plant cell wall, facilitating the release of phytic acid, while also better exposing and retaining β-glucan, and improving the taste and texture of the steamed buns. An appropriate amount of cellulase can break down fibers into smaller fragments, increasing their solubility and creating a finer pore structure within the steamed buns, thereby improving their softness. However, adding too much cellulase may overly damage the fiber structure, resulting in a decrease in the dough's gas retention capacity. This prevents sufficient air from being retained during fermentation and steaming, causing the buns to shrink and become hard. Furthermore, excessive enzymatic degradation may affect the nutritional value and taste of the steamed buns. Therefore, a 0.2% addition is an appropriate choice to ensure fiber degradation while avoiding adverse effects on product quality.

[0055] In a preferred embodiment of the present invention, the mass ratio of the miscellaneous grain flour, the wheat flour and the inulin is 60-70:33-37:2-4.

[0056] In the present invention, the proportion of coarse grain flour is relatively high because it is the primary source of nutrients such as dietary fiber and β-glucan, ensuring the steamed buns are rich in dietary fiber while also providing the unique flavor and nutrition of coarse grains. However, if the proportion is too high, the low gluten content and poor viscosity of the coarse grain flour may lead to problems such as hard texture, small size, and rough taste in the steamed buns. Wheat flour accounts for 33-37%. Wheat flour is rich in gluten protein, which can form a gluten network structure, enhance the toughness and ductility of the dough, and enable the steamed buns to maintain their shape during fermentation and steaming, while also having a certain elasticity and chewiness. 33-37% wheat flour can improve the loose structure and difficulty in forming steamed buns made with coarse grain flour alone. It works in conjunction with the coarse grain flour to optimize the texture and taste of the steamed buns. Inulin accounts for 2-4%. Inulin is a water-soluble dietary fiber that has the effects of increasing satiety and regulating intestinal flora. It can increase the dietary fiber content of steamed buns, further enhancing their health benefits. At the same time, inulin can absorb moisture, allowing steamed buns to retain moisture during storage, slowing down the aging of steamed buns and extending their shelf life. It also has a certain improvement effect on the taste and flavor of steamed buns, making them softer and more delicate.

[0057] In a preferred embodiment of the present invention, the method for preparing monoglyceride hydrate comprises adding monoglyceride to warm water at 55-65°C and stirring until completely melted to form monoglyceride hydrate, wherein the mass ratio of monoglyceride to water is 1:16-17. The method for preparing the activated yeast solution comprises adding yeast to warm water at 33-38°C, dissolving it, and then activating it in an environment at 30-35°C for 15-30 minutes.

[0058] In a preferred embodiment of the present invention, fermentation includes pre-fermentation and main fermentation; the pre-fermentation includes fermentation at a humidity of 72-78% and a temperature of 28-35°C for 45-80 minutes; the main fermentation includes degassing the pre-fermented dough and dividing it into small pieces, and then fermenting at a humidity of 82-88% and 35-40°C for 100-150 minutes.

[0059] In the present invention, pre-fermentation activates yeast activity and produces trace amounts of CO2, initially forming a gas chamber; the temperature in the main fermentation stage is raised to 35-40°C to accelerate gas production, and the early gas chamber is used as a "template" to guide the uniform expansion of the gas, combined with the improvement of the dough extensibility after gradient enzymatic hydrolysis.

[0060] In the present invention, the preparation method of the multi-grain steamed bread rich in dietary fiber specifically comprises:

[0061] Take 28-32 parts of highland barley flour, 18-22 parts of quinoa flour and 13-17 parts of oat bran and mix them evenly to obtain a grain flour. First, introduce CO2 into the grain flour to 0.3-0.6 MPa and maintain it for 20-40 minutes. Then, add 30°C warm water 3 times the weight of the grain flour and stir to form a slurry.

[0062] Add 0.1% α-amylase based on the total weight of the grain flour to the slurry, adjust the pH to 6.0-6.5, and stir and enzymolyze in a water bath at 38-42°C for 15-25 minutes; raise the temperature to 55-57°C, adjust the pH to 5.0-5.5, add 0.2% cellulase based on the total weight of the grain flour, and continue stirring and enzymolyzing for 25-35 minutes; after the enzymolysis is completed, boil and inactivate the enzyme for 5 minutes, and cool to 25-33°C to obtain an enzymolysis slurry;

[0063] Drain the enzymatic hydrolyzed slurry and mix it evenly with wheat flour and inulin in a mass ratio of 60-70:33-37:2-4 to obtain a mixed powder;

[0064] Monoglyceride is added to warm water at 55-65°C and stirred until completely dissolved to form monoglyceride hydrate, with the mass ratio of monoglyceride to water being 1:16-17; yeast is added to warm water at 33-38°C and dissolved, and activated in an environment at 30-35°C for 15-30 minutes to obtain activated yeast;

[0065] Based on the total mass of the multi-grain flour and the wheat flour as 100%, 0.1-0.3% of monoglyceride hydrate and 0.4-0.6% of activated yeast solution are added to the mixed flour, and 30-35°C warm water is added in several portions. The mixture is stirred at low speed at gear 1 for 5 minutes, and then adjusted to medium speed at gear 3 for 8 minutes until the dough surface is smooth and can be formed into a uniform film by hand. The dough temperature is controlled at 28-30°C.

[0066] Place the kneaded dough in a fermentation box, adjust the humidity to 72-78%, and ferment at 28-35°C for 45-80 minutes. At this time, the dough has expanded to 1.5 times its volume, a small amount of pores appear on the surface, and it slowly rebounds when pressed by hand. Degas the pre-fermented dough and divide it into small pieces. Roll them into balls and place them in steaming trays with a spacing of 3 cm. Transfer to a high-temperature fermentation box, adjust the humidity to 82-88%, and ferment at 35-40°C for 100-150 minutes. At this time, the dough has expanded to 2.5-3 times its volume, does not collapse when pressed lightly with a finger, slowly rebounds, and has uniform and fine pores on the surface.

[0067] After the main fermentation is completed, the steamed buns are placed at 25-28°C for 8-15 minutes for proofing, and steamed at a steam pressure of 0.1-0.15 MPa for 15-20 minutes to obtain the multi-grain steamed buns rich in dietary fiber.

[0068] According to the second aspect of the present invention, there is provided a multi-grain steamed bun rich in dietary fiber prepared by the preparation method described above.

[0069] Example 1

[0070] Take 30 parts of highland barley flour, 20 parts of quinoa flour and 15 parts of oat bran and mix them evenly to obtain coarse grain powder. First, introduce CO2 into the coarse grain powder to 0.3MPa and maintain it for 30 minutes. Then, add 30°C warm water 3 times the weight of the coarse grain powder and stir to form a slurry.

[0071] Add 0.1% α-amylase based on the total weight of the grain flour to the slurry, adjust the pH to 6.0-6.5, and stir and enzymolyze in a 40°C water bath for 20 minutes; raise the temperature to 56°C, adjust the pH to 5.0-5.5, add 0.2% cellulase based on the total weight of the grain flour, and continue stirring and enzymolyzing for 30 minutes; after the enzymolysis is completed, boil and inactivate the enzyme for 5 minutes, and cool to 28°C to obtain an enzymolysis slurry;

[0072] Drain the enzymatic hydrolyzed slurry and mix it evenly with wheat flour and inulin in a mass ratio of 65:35:3 to obtain a mixed powder;

[0073] Monoglyceride was added to 60°C warm water and stirred until completely dissolved to form monoglyceride hydrate, with the mass ratio of monoglyceride to water being 1:16-17; yeast was added to 35°C warm water and dissolved, and activated in a 30-35°C environment for 25 minutes to obtain activated yeast;

[0074] Based on the total mass of the grain flour and wheat flour as 100%, 0.3% of monoglyceride hydrate and 0.5% of activated yeast solution were added to the mixed flour, and warm water at 30-35°C was added in several portions. The mixture was stirred at low speed at gear 1 for 5 minutes, and then adjusted to medium speed at gear 3 for 8 minutes until the dough surface was smooth and a uniform film could be formed by hand pulling. The dough temperature was controlled at 28-30°C.

[0075] Place the kneaded dough in a fermentation box, adjust the humidity to 75%, and ferment at 30°C for 60 minutes. At this time, the dough volume has expanded to 1.5 times, a small amount of pores appear on the surface, and the dough slowly rebounds when pressed by hand. Degas the pre-fermented dough and divide it into small pieces. After rolling them into balls, place them in a steamer with a spacing of 3 cm. Transfer to a high-temperature fermentation box, adjust the humidity to 85%, and ferment at 38°C for 120 minutes. At this time, the dough volume has expanded to 2.5-3 times, does not collapse when pressed lightly with a finger, slowly rebounds, and the pores on the surface are uniform and fine.

[0076] After the main fermentation is completed, the steamed buns are placed at 26°C for 10 minutes for proofing and steamed at a steam pressure of 0.1-0.15 MPa for 15 minutes to obtain the multi-grain steamed buns rich in dietary fiber.

[0077] Example 2

[0078] CO2 was introduced into the grain flour to a pressure of 0.4 MPa and maintained for 30 min. The remaining steps and parameters were the same as those in Example 1.

[0079] Example 3

[0080] CO2 was introduced into the grain flour to a pressure of 0.5 MPa and maintained for 30 min. The remaining steps and parameters were the same as those in Example 1.

[0081] Example 4

[0082] CO2 was introduced into the grain flour to a pressure of 0.6 MPa and maintained for 30 min. The remaining steps and parameters were the same as those in Example 1.

[0083] Example 5

[0084] α-amylase was added to the slurry, the pH was adjusted to 6.0-6.5, and enzymatic hydrolysis was carried out at 38°C for 15 min; the temperature was raised to 55°C, the pH was adjusted to 5.0-5.5, cellulase was added and enzymatic hydrolysis was continued for 25 min, the enzyme was inactivated and the mixture was cooled to 25°C to obtain an enzymatic hydrolyzed slurry; the remaining steps and parameters were the same as those in Example 3.

[0085] Example 6

[0086] α-amylase was added to the slurry, the pH was adjusted to 6.0-6.5, and enzymatic hydrolysis was carried out at 42° C. for 25 min. The temperature was raised to 57° C., the pH was adjusted to 5.0-5.5, cellulase was added, and enzymatic hydrolysis was continued for 35 min. The enzyme was inactivated and the mixture was cooled to 33° C. to obtain an enzymatic hydrolyzed slurry. The remaining steps and parameters were the same as those in Example 3.

[0087] Comparative Example 1

[0088] The mixed grain powder and water were directly mixed evenly without introducing CO2. The remaining steps and parameters were the same as those in Example 3.

[0089] Comparative Example 2

[0090] First, CO2 was introduced into the grain flour to 0.2 MPa and maintained for 30 minutes, and then the grain flour and water were evenly mixed to obtain a slurry; the remaining steps and parameters were the same as those in Example 3.

[0091] Comparative Example 3

[0092] The slurry was directly drained and then mixed evenly with wheat flour and inulin to obtain mixed flour without enzymatic hydrolysis; the remaining steps and parameters were the same as those in Example 3.

[0093] The multi-grain steamed bread prepared in the above examples and comparative examples was tested for β-glucan retention rate, phytic acid degradation rate, specific volume, hardness and sensory score. The test results are shown in Table 1.

[0094] β-glucan retention rate: determined by the phenol-sulfuric acid method, with the β-glucan content in the original grain flour as the benchmark, β-glucan retention rate (%) = β-glucan content in steamed bread (mg / g dry weight) / β-glucan content in the original grain flour (mg / g dry weight) × 100%;

[0095] Phytic acid degradation rate: Determine the phytic acid content by HPLC according to GB 5009.153-2016 "National Food Safety Standard - Determination of Phytic Acid in Foods". Phytic acid degradation rate = (original phytic acid content - finished product phytic acid content) / original phytic acid content × 100%;

[0096] Specific volume: rapeseed displacement method, unit: mL / g;

[0097] Hardness: Texture analyzer TPA mode (probe P / 50, test speed 1mm / s, compression 50%);

[0098] Sensory evaluation: 10-person professional panel (10-point scale, scoring items: softness, elasticity, roughness, flavor).

[0099] Table 1 Test results

[0100]

[0101] As the CO2 pressure increased from 0.3MPa to 0.5MPa, the retention rate increased by 7.8%; it decreased slightly after the pressure exceeded 0.5MPa. At 0.5MPa, CO2 penetration and fiber protection reached a balance. Excessive pressure of 0.6MPa caused excessive expansion of starch granules and partial dissolution and loss of β-glucan; the low pressure of 0.2MPa in Comparative Example 2 was insufficient for penetration and had a weak protection effect. Example 3 was improved by 28.7% compared with Comparative Example 1, while Comparative Example 2 only increased by 7.4% due to insufficient pressure. CO2 swelling increased the porosity of the grain flour. At 0.5MPa, the porosity increased by 25% compared with the untreated group, and the contact area between phytic acid and enzyme was expanded. The specific volume of Example 3 was 3.8mL / g and the hardness was 11.9N, which was significantly improved compared with Comparative Example 1. The initial pores formed by CO2 release synergized with yeast gas production, the pore density increased by 40%, the dough extensibility improved, and the hardness decreased by 36%. The β-glucan retention rate and phytic acid degradation rate of Comparative Example 1 were significantly lower than those of the CO2-treated group. Due to the lack of CO2 fiber protection and phytic acid swelling, the enzymatic hydrolysis efficiency was low. The specific volume and hardness were poor, and the dough lacked bulk due to the lack of CO2 initial pores. The indicators of Comparative Example 2 were between Comparative Example 1 and Example 1, indicating that low-pressure CO2 treatment had some effect but was not optimal. Comparative Example 3 had the lowest β-glucan retention rate. The lack of enzymatic hydrolysis resulted in a dense fiber structure, making the β-glucan difficult to dissolve. The phytic acid degradation rate was only 53% of that of Example 3, due to the lack of enzymatic hydrolysis that destroyed the phytic acid structure. The specific volume and hardness were the worst, and the dough had poor extensibility due to the lack of enzymatic hydrolysis to soften the fibers.

[0102] The optimal pressure for CO2 treatment is 0.5 MPa, at which β-glucan retention, phytic acid degradation, specific volume, and sensory scores all reach their peaks. This represents the optimal parameter for balancing fiber protection, phytic acid degradation, and taste improvement. Optimal enzymatic hydrolysis parameters are 40°C / 20 minutes for α-amylase and 56°C / 30 minutes for cellulose. Deviating from this range results in decreased nutrient retention and taste.

[0103] CO2 treatment and enzymatic hydrolysis work synergistically, and both are indispensable. CO2 treatment creates substrate conditions for enzymatic hydrolysis through physical swelling, and enzymatic hydrolysis improves nutritional quality through biochemical reactions. After synergy, the β-glucan retention rate is increased by 15%~20% compared with single treatment, and the phytic acid degradation rate is increased by 25%~30%.

Claims

1. A method for preparing multi-grain steamed bread rich in dietary fiber, characterized in that: The following steps are involved: First, introduce CO2 into the grain powder to 0.3-0.6 MPa and maintain it for 20-40 minutes, then evenly mix the grain powder and water to obtain a slurry; Add α-amylase to the slurry, adjust the pH to 6.0-6.5, and perform enzymatic hydrolysis at 38-42° C. for 15-25 minutes; Raise the temperature to 55-57°C, adjust the pH to 5.0-5.5, add cellulase and continue enzymolysis for 25-35 minutes, inactivate the enzyme and cool to 25-33°C to obtain enzymatic slurry; Drain the enzymatic hydrolyzed powder slurry and mix it evenly with wheat flour and inulin to obtain mixed powder; Add monoglyceride hydrate and activated yeast solution to the mixed flour, add water and stir into dough; The dough is fermented, proofed and steamed to obtain multi-grain steamed buns rich in dietary fiber; The coarse grain powder comprises the following raw materials in parts by weight: 28-32 parts of highland barley flour, 18-22 parts of quinoa flour and 13-17 parts of oat bran; The mass ratio of the coarse grain flour, the wheat flour and the inulin is 60-70:33-37:2-4.

2. The preparation method according to claim 1, wherein The mesh number of the highland barley flour is 50-200 meshes; the mesh number of the quinoa flour is 50-200 meshes; and the mesh number of the oat bran is 50-100 meshes.

3. The preparation method according to claim 2, wherein The highland barley flour comprises 50-80 mesh highland barley coarse powder, 80-150 mesh highland barley medium powder and 150-200 mesh highland barley fine powder; Based on 100% of the total weight of the highland barley flour, the highland barley flour includes 38% to 42% of coarse highland barley powder, 28% to 32% of medium highland barley powder and 28% to 32% of fine highland barley powder.

4. The preparation method according to claim 2, wherein The quinoa powder comprises quinoa coarse powder with mesh sizes of 50-80, quinoa medium powder with mesh sizes of 80-150 and quinoa fine powder with mesh sizes of 150-200.

5. The preparation method according to claim 1, wherein The added amount of the α-amylase is 0.1% of the total weight of the coarse grain flour, and the α-amylase activity is ≥2000U / g; the added amount of the cellulase is 0.2% of the total weight of the coarse grain flour, and the cellulase activity is ≥10000U / g.

6. The preparation method according to claim 1, wherein The preparation method of the monoglyceride hydrate comprises adding monoglyceride to warm water at 55-65°C and stirring until the monoglyceride is completely melted to form the monoglyceride hydrate, wherein the mass ratio of monoglyceride to water is 1:16-17. The preparation method of the activated yeast solution comprises adding yeast to warm water at 33-38°C, dissolving the yeast, and then activating the yeast in an environment at 30-35°C for 15-30 minutes.

7. The preparation method according to claim 1, wherein The fermentation includes pre-fermentation and main fermentation; the pre-fermentation includes fermentation at a humidity of 72-78% and a temperature of 28-35°C for 45-80 minutes; the main fermentation includes deflating the pre-fermented dough and dividing it into small pieces, and then fermenting at a humidity of 82-88% and 35-40°C for 100-150 minutes.

8. A multi-grain steamed bun rich in dietary fiber prepared by the preparation method according to any one of claims 1 to 7.

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