Coarse cereal steamed bun rich in dietary fibers and preparation method thereof

Abstract

The invention provides coarse cereal steamed buns rich in dietary fibers and a preparation method of the coarse cereal steamed buns, and relates to the technical field of food processing. According to the method, coarse cereal powder is treated through carbon dioxide with the pressure of 0.3-0.6 MPa, double enzymolysis is conducted on the coarse cereal powder through the optimal temperature difference of enzymes, and alpha-amylase preferentially hydrolyzes amylose on the surfaces of coarse cereal starch particles at the temperature of 38-42 DEG C, so that the viscosity of dough is reduced, a fiber layer is exposed, and a channel is provided for subsequent cellulase action; cellulase at 55-57 DEG C selectively degrades cellulose and hemicellulose, so that the fiber structure becomes loose, beta-glucan is retained, phytase is activated, and phytic acid is efficiently decomposed. The beta-glucan retention rate of the prepared coarse cereal steamed bun is greater than 81%, the phytic acid content is low, and the taste is softer.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and particularly relates 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 of healthy staple foods due to their rich functional components such as dietary fiber and β-glucan. However, their industrial production faces significant technical bottlenecks. For example, the large addition of high-fiber raw materials such as bran and whole grain flour on the one hand leads to poor dough extensibility and easy breakage of the gluten network, resulting in high hardness, low specific volume, and rough texture of the finished product, forming a contradiction of "high fiber but unpalatable"; on the other hand, phytic acid is commonly present in multi-grains, which combines with minerals such as calcium, iron, and zinc to form insoluble complexes, resulting in a 40%-60% reduction in the absorption rate of minerals by the human body, contrary to the original product design intention of nutritional fortification.

[0003] While traditional processing technologies degrade crude fiber to improve taste, they are prone to destroying heat-sensitive substances such as β-glucan, and its retention rate is usually <70%, resulting in a significant attenuation of functionality; in addition, traditional processing technologies do not pay attention to phytic acid degradation during enzymatic hydrolysis. The degradation of phytic acid relies on phytase, and single cellulase has no effect on phytic acid. The phytic acid residue in conventional processes is still >0.6%, and the problem of mineral absorption has not been fundamentally solved. Therefore, there is an urgent need to develop a multi-grain steamed bun that can balance nutrition 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 preparation method of a multi-grain steamed bun rich in dietary fiber, comprising the following steps: First, introduce CO2 into the multi-grain flour to 0.3~0.6 MPa, maintain for 20~40 min, and then uniformly mix the multi-grain flour and water to obtain a slurry; Add α-amylase to the slurry, adjust the pH to 6.0~6.5, and enzymatically hydrolyze at 38~42 °C for 15~25 min; raise the temperature to 55~57 °C, adjust the pH to 5.0-5.5, add cellulase and continue to enzymatically hydrolyze for 25~35 min, inactivate the enzyme and cool to 25~33 °C to obtain an enzymatically hydrolyzed slurry; Drain the enzymatically hydrolyzed slurry and then uniformly mix it with wheat flour and inulin to obtain a mixed flour; Add monoglyceride hydrate and activated yeast solution to the mixed flour, and add water and stir to form a dough; The dough is fermented, proofed, and steamed to obtain a multi-grain steamed bun rich in dietary fiber.

[0006] Preferably, the miscellaneous grain powder comprises the following raw materials in parts by weight: 28-32 parts of highland barley powder, 18-22 parts of quinoa powder, and 13-17 parts of oat bran.

[0007] Preferably, the mesh number of the highland barley powder is 50-200 meshes; the mesh number of the quinoa powder is 50-200 meshes; the mesh number of the oat bran is 50-100 meshes.

[0008] Preferably, the highland barley powder comprises highland barley coarse powder with a mesh number of 50-80 meshes, highland barley medium powder with a mesh number of 80-150 meshes, and highland barley fine powder with a mesh number of 150-200 meshes; Calculated based on the total weight of the highland barley powder being 100%, the highland barley powder comprises 38-42% of highland barley coarse powder, 28%-32% of highland barley medium powder, and 28%-32% of highland barley fine powder.

[0009] Preferably, the quinoa powder comprises quinoa coarse powder with a mesh number of 50-80 meshes, quinoa medium powder with a mesh number of 80-150 meshes, and quinoa fine powder with a mesh number of 150-200 meshes; Calculated based on the total weight of the quinoa powder being 100%, the quinoa powder comprises 38-42% of quinoa coarse powder, 38-42% of quinoa medium powder, and 38-42% of quinoa fine powder.

[0010] Preferably, the addition amount of α-amylase is 0.1% of the total weight of the miscellaneous grain powder, and the α-amylase activity ≥ 2000 U / g; the addition amount of the cellulase is 0.2% of the total weight of the miscellaneous grain powder, and the cellulase activity ≥ 10000 U / g.

[0011] Preferably, the mass ratio of the miscellaneous grain powder, wheat flour, and inulin is 60-70:33-37:2-4.

[0012] Preferably, the preparation method of the monoglyceride hydrate comprises adding monoglyceride to warm water at 55-65 °C and stirring until completely melted to form monoglyceride hydrate, and 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 to dissolve it, and then activating it in an environment at 30-35 °C for 15-30 min.

[0013] Preferably, the fermentation includes pre-fermentation and main fermentation; the pre-fermentation includes fermenting at a humidity of 72-78% and a temperature of 28-35 °C for 45-80 min; the main fermentation includes exhausting the dough after pre-fermentation and dividing it into dough pieces, and then fermenting at a humidity of 82-88% and 35-40 °C for 100-150 min.

[0014] The second object of the present invention is to provide a whole grain steamed bun rich in dietary fiber prepared by the preparation method as described above.

[0015] Advantages of the present invention: The present invention treats miscellaneous grain flour with carbon dioxide at 0.3 - 0.6 MPa, and performs double enzymatic hydrolysis on the miscellaneous grain flour by utilizing the difference in the optimal temperatures of enzymes. At 38 - 42 °C, α-amylase preferentially hydrolyzes amylose on the surface of miscellaneous 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, retaining β-glucan, and at the same time activating phytase to efficiently decompose phytic acid. CO₂ penetrates into the interior of miscellaneous grain flour particles at 0.3 - 0.6 MPa to form a gas-solid interface barrier, which can inhibit the excessive degradation of β-glucan by cellulase and avoid the loss of β-glucan due to structural damage during mechanical stirring and enzymatic hydrolysis. The polar regulatory effect of CO₂ weakens the complexation ability between phytic acid and minerals, making phytic acid more easily enzymatically hydrolyzed. Treatment with CO₂ at 0.3 - 0.6 MPa causes phytic acid molecules to migrate from the interior of the particles to the surface, increasing the contact area with the subsequent enzymatic hydrolysis system and further destroying the phytic acid structure through synergistic gradient enzymatic hydrolysis. The penetration of CO₂ slightly breaks the protein hydrogen bonds in the miscellaneous grain flour, reducing the elastic resistance of the dough and at the same time increasing the water absorption rate, making the gluten network softer and more ductile. β-glucan has the effects of reducing blood sugar and blood lipid, and has good heat resistance, with an activity retention rate > 81% at 55 - 57 °C. The optimal temperature of phytase is 55 - 60 °C, and 55 - 57 °C can avoid excessive enzymatic hydrolysis from damaging nutrients. The prepared miscellaneous grain steamed buns have a β-glucan retention rate > 81%, a low phytic acid content, and a softer taste at the same time. Detailed implementation mode

[0016] According to the first aspect of the present invention, a method for preparing a miscellaneous grain steamed bun rich in dietary fiber is provided, including the following steps: First, introduce CO₂ into the miscellaneous grain flour to 0.3 - 0.6 MPa and maintain it for 20 - 40 min, then uniformly mix the miscellaneous grain flour and water to obtain a slurry; Add α-amylase to the slurry, adjust the pH to 6.0 - 6.5, and enzymatically hydrolyze at 38 - 42 °C for 15 - 25 min; raise the temperature to 55 - 57 °C, adjust the pH to 5.0 - 5.5, add cellulase and continue enzymatic hydrolysis for 25 - 35 min, inactivate the enzyme and cool to 25 - 33 °C to obtain an enzymatically hydrolyzed slurry; Drain the enzymatically hydrolyzed slurry and then uniformly mix it with wheat flour and inulin to obtain a mixed flour; Add monoglyceride hydrate and activated yeast solution to the mixed flour, and add water and stir to form a dough; The dough is fermented, proofed, and steamed to obtain a miscellaneous grain steamed bun rich in dietary fiber.

[0017] In the present invention, CO2 penetrates into the interior of the miscellaneous grain powder particles at 0.3 - 0.6 MPa and adsorbs in the microporous structures of starch and dietary fiber to form a gas-solid interface barrier; β-glucan has a similar structure to cellulose and is easily decomposed non-specifically by cellulase. During 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 miscellaneous grain powder particles to expand slightly, and the fiber network structure is loose but remains intact, 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 complexation ability of phytic acid with minerals such as calcium and iron, making phytic acid more easily enzymatically hydrolyzed; the treatment with CO2 at 0.3 - 0.6 MPa causes phytic acid molecules to migrate from the interior of the particles to the surface, increasing the contact area with the subsequent enzymatic hydrolysis system and further destroying the phytic acid structure through synergistic gradient enzymatic hydrolysis. In addition, the initial pores released by CO2 are superimposed with the gas production of yeast, reducing the amount of yeast used while making the dough expand more evenly; the penetration effect of CO2 slightly breaks the protein hydrogen bonds in the miscellaneous grain powder, reducing the elastic resistance of the dough and increasing the water absorption rate at the same time, making the gluten network softer and more ductile; the porous structure formed by CO2 can still accelerate the penetration of steam, making the starch gelatinization more uniform, the internal tissue delicate, and avoiding the roughness of traditional miscellaneous grain steamed buns.

[0018] In the present invention, the optimal working temperature of α-amylase is usually 38 - 42 °C. Enzymatic hydrolysis for 15 - 25 minutes within this temperature range can preferentially hydrolyze the amylose on the surface of the miscellaneous grain starch particles. Due to the mild reaction conditions, the structure and activity of β-glucan are less affected. Moreover, this temperature range is much lower than the denaturation temperature of β-glucan, so during the hydrolysis of starch, β-glucan can exist stably and will not be damaged due to factors such as high temperature. After α-amylase hydrolyzes amylose, the viscosity of the dough is reduced, and at the same time, the fiber layer is exposed. However, this effect mainly targets starch and will not directly damage the structure where β-glucan is located. Instead, it provides a channel for the subsequent action of cellulase, which is beneficial for further protecting and releasing β-glucan in the subsequent steps.

[0019] Raise the temperature to 55 - 57°C and add cellulase to continue enzymatic hydrolysis for 25 - 35 minutes. β-glucan has good heat resistance, and its activity retention rate is >90% at this temperature. Cellulase mainly acts on cellulose and hemicellulose, selectively degrading these substances to make the fiber structure loose without decomposing β-glucan, thus preserving the integrity of β-glucan. The loose fiber structure can provide certain physical protection for β-glucan, making it less vulnerable to external factors during subsequent processing. At the same time, during this process, β-glucan may form some complexes with other components, further enhancing its stability. The enzyme inactivation operation promptly terminates the enzyme activity, preventing potential damage to β-glucan that might be caused by the continued action of the enzyme in subsequent processes. The process of cooling to 25 - 33°C is relatively gentle, avoiding the impact of drastic temperature changes on the structure of β-glucan and being conducive to maintaining its activity and stability.

[0020] Under the condition of 55 - 57°C, cellulase can not only degrade cellulose and hemicellulose but also activate phytase. The optimal temperature of phytase is 55 - 60°C. Within this temperature range, the activated phytase can efficiently decompose phytic acid. After 25 - 35 minutes of enzymatic hydrolysis, a large amount of phytic acid is decomposed, thus reducing the content of phytic acid. The hydrolysis of starch by α-amylase and the degradation of fiber by cellulase make phytic acid more easily released from the coarse grain particles, increasing the contact area between phytic acid and phytase, improving the action efficiency of phytase, further promoting the decomposition of phytic acid, and reducing the residue of phytic acid.

[0021] In addition, α-amylase hydrolyzes the amylose on the surface of starch granules at 38 - 42°C, reducing the viscosity of the dough. This makes the dough easier to operate in subsequent processing. And during the fermentation process, the sugars produced by starch hydrolysis can provide more energy for yeast, promoting the growth and fermentation of yeast, generating more carbon dioxide gas, and making the steamed bun more fluffy. The degradation of cellulose and hemicellulose by cellulase at 55 - 57°C makes the fiber structure loose. The loose fiber structure can accommodate more gas, and during the fermentation and proofing processes, these gases can form more pores inside the steamed bun, thus increasing the specific volume of the steamed bun and making the steamed bun taste softer.

[0022] For the subsequently added monoglyceride hydrate and activated yeast liquid, monoglyceride, as an emulsifier, can improve the rheological properties of the dough, making the dough softer and more elastic. Based on the soft fiber structure and good dough properties, the carbon dioxide gas produced by yeast fermentation can better expand the steamed bun, further enhancing the soft taste of the steamed bun.

[0023] In the present invention, after adding α-amylase, the enzymatic hydrolysis temperature is, for example, 38 °C, 39 °C, 40 °C, 41 °C or 42 °C; the enzymatic hydrolysis 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.

[0024] In the present invention, the enzymatic hydrolysis temperature of cellulase 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.

[0025] In a preferred embodiment of the present invention, the miscellaneous grain powder comprises the following raw materials in parts by weight: 28 - 32 parts of highland barley powder, 18 - 22 parts of quinoa powder, and 13 - 17 parts of oat bran.

[0026] In the present invention, highland barley is rich in β-glucan and has effects such as reducing blood sugar and lipid levels. At the same time, it also contains various minerals and vitamins; quinoa is a whole-nutrition food, rich in high-quality protein, various minerals, vitamins and other nutrients, and its amino acid composition is close to human needs; oat bran contains rich dietary fiber, especially soluble dietary fiber, which is beneficial to intestinal health and can also reduce cholesterol. Mixing these several raw materials in the ratio of 28 - 32 parts of highland barley powder, 18 - 22 parts of quinoa powder, and 13 - 17 parts of oat bran can make the nutrition of the miscellaneous grain steamed buns more comprehensive and balanced, meeting the human body's needs for various nutrients. Highland barley powder, quinoa powder and oat bran each have unique tastes and textures. Highland barley powder can make the steamed bun have a certain toughness and chewiness; quinoa powder can increase the fineness and aroma of the steamed bun; oat bran can make the taste of the steamed bun more rich, with a certain wheat fragrance. The ratio of 28 - 32 parts of highland barley powder, 18 - 22 parts of quinoa powder, and 13 - 17 parts of oat bran can make them complement and coordinate with each other in taste, avoiding the taste defects that may be brought by a single miscellaneous grain powder, and making the finally produced miscellaneous grain steamed bun soft, rich and layered in taste.

[0027] In the present invention, the highland barley powder is, for example, 28 parts, 29 parts, 30 parts, 31 parts or 32 parts; the quinoa powder is, for example, 18 parts, 19 parts, 20 parts, 21 parts or 22 parts; the oat bran is, for example, 13 parts, 14 parts, 15 parts, 16 parts or 17 parts.

[0028] In a preferred embodiment of the present invention, the mesh number of the highland barley powder is 50 - 200 meshes; the mesh number of the quinoa powder is 50 - 200 meshes; the mesh number of the oat bran is 50 - 100 meshes.

[0029] In a preferred embodiment of the present invention, the hulless barley flour comprises hulless barley coarse flour with a mesh size of 50 - 80 meshes, hulless barley medium flour with a mesh size of 80 - 150 meshes, and hulless barley fine flour with a mesh size of 150 - 200 meshes; calculated based on 100% of the total weight of the hulless barley flour, the hulless barley flour comprises 38 - 42% of hulless barley coarse flour, 28% - 32% of hulless barley medium flour, and 28% - 32% of hulless barley fine flour.

[0030] In the present invention, when the hulless barley flour is in the range of 50 - 200 meshes, during the processes of mixing with other raw materials, adding water and stirring into dough, and fermentation, it can exhibit good processing performance, which is beneficial to forming a good dough structure and fermentation effect. The hulless barley coarse flour with a mesh size of 50 - 80 meshes accounts for 38 - 42%. The coarse flour can form a certain supporting structure in the steamed bun, increasing the chewing feeling and layering sense of the steamed bun. At the same time, the relatively large particles have a relatively slow digestion speed during the digestion process, which helps to prolong the satiety feeling. If the proportion of the coarse flour is too high, it may cause the texture of the steamed bun to be too rough and the taste to be too hard, making it difficult to be accepted by consumers; while if the proportion is too low, the characteristics of the coarse grains cannot be highlighted, and the significance of adding the hulless barley coarse flour is lost. The hulless barley medium flour with a mesh size of 80 - 150 meshes has a moderate mesh number, and its texture is relatively delicate. It can fill the gaps between the coarse flour and the fine flour in the steamed bun, making the internal structure of the steamed bun more uniform and compact. It will neither produce an overly obvious granular feeling like the coarse flour nor cause the steamed bun to lose the characteristics of the coarse grains like the fine flour, playing a role in balancing the taste. The hulless barley medium flour accounting for 28% - 32% can make the taste of the steamed bun neither too rough nor too delicate, and at the same time helps to improve the internal structure of the steamed bun, making it more fluffy and soft. If the proportion of the medium flour is too high, the taste and texture of the steamed bun may tend to be that of a steamed bun made of ordinary flour, reducing the uniqueness of the hulless barley flour; if the proportion is too low, its role in balancing the taste and optimizing the structure cannot be effectively exerted. The hulless barley fine flour with a mesh size of 150 - 200 meshes has very fine particles, which can be evenly dispersed in the dough, making the surface of the steamed bun smoother and the internal tissue more delicate and soft. At the same time, the fine flour can increase the viscosity and ductility of the dough, helping the steamed bun to maintain a good shape during fermentation and steaming, and improving the appearance quality of the steamed bun. The hulless barley fine flour accounting for 28% - 32% can make the surface of the steamed bun smooth and the internal tissue delicate, improving the overall quality and taste of the steamed bun. If the proportion of the fine flour is too high, the steamed bun may be too sticky and soft, losing the chewiness and toughness that a coarse grain steamed bun should have; if the proportion is too low, it will cause the surface of the steamed bun to be rough and the internal tissue not to be delicate enough, affecting the appearance and taste of the steamed bun.

[0031] In the present invention, the coarse hulless barley powder with a mesh size of 50 - 80 has relatively large particles and a relatively small contact area with enzymes. During the enzymatic hydrolysis process, α - amylase and cellulase act on it relatively slowly. This allows more opportunities for nutrients such as β - glucan inside the coarse powder to be completely retained, avoiding excessive enzymatic hydrolysis. At the same time, the relatively large gaps formed by the coarse powder in the dough are conducive to the uniform distribution of nutrients therein. During the steaming process of the steamed buns, these gaps also provide a certain space for the stable existence of nutrients, reducing nutrient loss caused by factors such as high temperature. The medium - sized hulless barley powder with a mesh size of 80 - 150 has a moderate mesh number, and its particle size enables the enzymes to act on substances such as starch and fiber moderately. During the enzymatic hydrolysis process, it can moderately hydrolyze starch to provide sufficient sugars for fermentation, and to a certain extent, protect nutrients such as β - glucan from being overly damaged. The medium - sized powder fills between the coarse powder and the fine powder, making the dough structure more compact and uniform, helping nutrients to stably exist in the entire dough system, and being able to better maintain the activity of nutrients during the steaming process. The fine hulless barley powder with a mesh size of 150 - 200 has fine particles and a large contact area with enzymes, and the enzymatic hydrolysis reaction is relatively rapid. However, due to the good heat resistance of β - glucan, its activity can be well retained at a moderate enzymatic hydrolysis temperature. The fine powder is evenly dispersed in the dough, which can increase the viscosity and extensibility of the dough, enabling nutrients such as β - glucan to interact more fully with other raw materials, thus better exerting its efficacy.

[0032] Calculated based on the total weight of the hulless barley powder, the ratio of 38 - 42% of coarse hulless barley powder, 28 - 32% of medium - sized hulless barley powder, and 28 - 32% of fine hulless barley powder enables the hulless barley powders of three mesh numbers to form a synergistic and complementary system in the dough. The coarse powder provides certain structural support and preliminary protection for nutrients. The medium - sized powder plays a role in balancing and stabilizing the dough structure and nutrient distribution. The fine powder, 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 combination enables nutrients such as β - glucan to be correspondingly protected and utilized at different stages from enzymatic hydrolysis to fermentation and then to steaming during the entire preparation process of the steamed buns, thus better retaining their nutritional activity and being more effectively absorbed by the human body after eating the steamed buns, exerting their health effects such as reducing blood sugar and blood lipid.

[0033] The release of phytic acid in coarse highland barley powder is relatively slow, which cooperates with the rapid decomposition of phytic acid in fine powder and medium powder, avoiding the situation where phytic acid is released in large quantities in a short period of time and phytase has no time to completely decompose it. The particle size of medium highland barley powder makes the effect of phytase on phytic acid between coarse powder and fine powder. During the enzymatic hydrolysis process, the phytic acid in the medium powder can be moderately decomposed, neither too slowly like coarse powder nor too quickly like fine powder, thus playing a synergistic and balanced role in the whole process of reducing phytic acid residue. The small particle characteristics of highland barley fine powder enable phytase to contact the phytic acid inside it more quickly and fully and carry out decomposition reaction. In the early stage of enzymatic hydrolysis, the phytic acid in the fine powder can be quickly decomposed, which provides a guarantee for the rapid removal of phytic acid in the whole system, and also promotes the enzymatic hydrolysis reaction, because the decomposition products of phytic acid can further affect the activity of the enzyme and the reaction environment.

[0034] 38~42% of highland barley coarse powder can slowly and continuously release phytic acid during the enzymatic hydrolysis process, and coordinate with the decomposition of phytic acid in fine powder and medium powder, so that phytic acid can be decomposed more evenly and continuously during the entire enzymatic hydrolysis process, avoiding excessive accumulation and residue of phytic acid. 28~32% of highland barley medium powder and 28~32% of highland barley fine powder ensure that phytase has sufficient substrate and can continuously decompose phytic acid. The proportion of medium powder and fine powder allows phytic acid to be effectively decomposed at different stages, improves the efficiency of phytase, and thus more effectively reduces the residual amount of phytic acid and improves the bioavailability of nutrients such as minerals in highland barley powder.

[0035] In a preferred embodiment of the present invention, 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 quinoa flour, the quinoa flour comprises 38-42% of quinoa coarse powder, 38-42% of quinoa medium powder and 38-42% of quinoa fine powder.

[0036] In the present invention, quinoa flour within the range of 50 to 200 mesh can have a positive impact on the toughness, extensibility and elasticity of the dough. When combined with highland barley flour, wheat flour, etc., it can adjust the overall properties of the dough, enabling the dough to maintain a good shape during the fermentation and proofing processes, and the structure of the steamed buns is more stable after steaming. The coarse quinoa flour with a mesh size of 50 to 80 can provide a certain granular texture, increasing the richness of the taste and making the buns "chewy"; the medium quinoa flour with a mesh size of 80 to 150 has a moderate texture, which can make the taste of the buns more delicate and soft, playing a transitional role; the fine quinoa flour with a mesh size of 150 to 200 can make the dough more delicate and smooth, increasing the softness and extensibility of the buns, making the buns more smooth when chewed and without a rough feeling. This combination of coarse and fine flours makes the taste of the buns more rich in levels, retaining certain characteristics of coarse grains while avoiding taste defects caused by single coarse or fine flours. The coarse flour can form some larger pore structures inside the buns, giving the buns a fluffy taste; the medium flour fills between the coarse and fine flours, making the structure of the buns more uniform and compact; the fine flour helps to form a delicate gluten network, enhancing the elasticity and toughness of the buns. When the three are mixed in the ratio of 38 to 42% of coarse quinoa flour, 38 to 42% of medium quinoa flour and 38 to 42% of fine quinoa flour, it can make the internal structure of the buns more reasonable, thus achieving good effects of being fluffy, soft and elastic in taste.

[0037] The coarse quinoa flour with a mesh size of 50 to 80 has larger particles, and the internal β-glucan is relatively more easily protected during processing and is not easily damaged by external factors such as excessive enzymatic hydrolysis and high temperature, and can better retain its structure and activity. The fine quinoa flour with a mesh size of 150 to 200 has small particles and a large specific surface area, and can come into contact with enzymes more fully during enzymatic hydrolysis, which is beneficial to the degradation of the quinoa cell wall by cellulase and other enzymes, making the β-glucan in the cell wall more easily released. And in the subsequent processing process, because the fine flour can better participate in forming a uniform dough structure, it helps the β-glucan to be evenly distributed in the system, avoiding stability problems caused by too high or too low local concentration. The medium quinoa flour with a mesh size of 80 to 150 plays a transitional and balancing role. Its particle size is moderate, which can protect the internal β-glucan to a certain extent and can also moderately release and play the role of β-glucan during enzymatic hydrolysis and processing. Calculated based on 100% of the total weight, 38 to 42% of coarse quinoa flour can provide enough large particles to protect a certain amount of β-glucan and make it stably exist during processing; the same proportion range of medium and fine quinoa flour, on the one hand, ensures that there is enough fine flour 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 that may be caused by too much fine flour. Through this ratio combination, the β-glucan in quinoa flour can be effectively protected during processing, and can also be fully released and play its function, thereby further increasing the retention rate of β-glucan.

[0038] Due to the relatively large particle size of quinoa meal, it is relatively difficult for phytase to contact phytic acid. However, during the previous enzymatic hydrolysis process, with the hydrolysis of starch by α-amylase and the partial degradation of the cell wall by cellulase, the particle structure of the meal gradually becomes loose, providing a channel for phytase to act on phytic acid. Due to the small particle size of quinoa fine powder, phytase can contact and decompose the phytic acid inside it more quickly and fully. The particle size of quinoa medium powder makes the effect of phytase on phytic acid fall between that of the meal and the fine powder, playing a synergistic role during the entire enzymatic hydrolysis process, and together with the meal and the fine powder, enabling phytic acid to be effectively decomposed at different stages.

[0039] 38 - 42% of the quinoa meal slowly releases phytic acid during the enzymatic hydrolysis process, coordinating with the rapid decomposition of phytic acid in the fine powder and the medium powder, avoiding the situation where a large amount of phytic acid is released in a short time and the phytase does not have enough time to completely decompose it. An appropriate amount of quinoa medium powder and fine powder ensures that the phytase has sufficient substrates to act on and can continuously decompose phytic acid. This ratio enables phytic acid to be decomposed more evenly and continuously during the entire enzymatic hydrolysis process, thereby effectively reducing the phytic acid residue, making the phytic acid content of the prepared multi-grain steamed buns lower, and improving the biological utilization rate of nutrients such as minerals in the steamed buns.

[0040] In a preferred embodiment of the present invention, the addition amount of α-amylase is 0.1% of the total weight of the multi-grain powder, and the α-amylase activity ≥ 2000 U / g; the addition amount of the cellulase is 0.2% of the total weight of the multi-grain powder, and the cellulase activity ≥ 10000 U / g.

[0041] In the present invention, adding 0.1% of α-amylase can ensure that there are sufficient enzyme molecules to fully contact with the starch substrate. During the enzymatic hydrolysis time of 15 to 25 minutes, the starch hydrolysis reaches an appropriate degree, thereby reducing the dough viscosity, facilitating subsequent processing operations, and providing sufficient sugars for yeast fermentation. If the addition amount of α-amylase is excessive, it may cause excessive hydrolysis of starch, making the dough too soft and unable to form a good gluten network structure, affecting the shaping and texture of the steamed bun. In addition, excessive hydrolysis may also cause problems such as collapse and uneven surface of the steamed bun after steaming. The addition amount of 0.1% can avoid these adverse effects while ensuring the starch hydrolysis effect, contributing to maintaining the quality and taste of the steamed bun. Adding 0.2% of cellulase can moderately loosen and degrade the fiber structure after enzymatic hydrolysis at a temperature of 55 to 57 °C for 25 to 35 minutes. This helps to break the structure of the plant cell wall, making phytic acid easier to release, and also enabling better exposure and retention of β-glucan, and improving the taste and texture of the steamed bun. An appropriate amount of cellulase can break down the fiber into smaller fragments, increase the solubility of the fiber, and form a finer pore structure inside the steamed bun, thereby improving the softness of the steamed bun. If the addition amount of cellulase is excessive, it may overly damage the fiber structure, resulting in a decrease in the gas-holding property of the dough and the inability to maintain sufficient gas during fermentation and steaming, causing problems such as shrinkage and hardening of the steamed bun. In addition, excessive enzymatic hydrolysis may also affect the nutritional value and taste of the steamed bun. Therefore, the addition amount of 0.2% is a suitable choice to avoid adverse effects on the product quality while ensuring the fiber degradation effect.

[0042] In a preferred embodiment of the present invention, the mass ratio of the miscellaneous grain flour, wheat flour, and inulin is 60 to 70:33 to 37:2 to 4.

[0043] In the present invention, the relatively large proportion of miscellaneous grain flour is because the miscellaneous grain flour is the main source of providing nutritional components such as dietary fiber and β-glucan, ensuring the characteristics of the steamed bun being rich in dietary fiber, and at the same time bringing the unique flavor and nutrition of miscellaneous grains. However, if the proportion is too high, problems such as too hard texture, small volume, and rough taste of the steamed bun may occur due to the low gluten content and poor viscosity in the miscellaneous grain flour. The proportion of wheat flour is 33 - 37. Wheat flour contains rich gluten proteins, which can form a gluten network structure, enhance the toughness and extensibility of the dough, enable the steamed bun to maintain its shape during fermentation and steaming, and have a certain elasticity and chewiness. 33 - 37 of wheat flour can improve problems such as loose structure and difficulty in forming when making steamed buns only with miscellaneous grain flour, cooperate with the miscellaneous grain flour, and optimize the texture and taste of the steamed bun. The proportion of inulin is 2 - 4. Inulin is a water-soluble dietary fiber, which has effects such as increasing satiety and regulating intestinal flora. It can increase the dietary fiber content of the steamed bun, further enhancing the health value of the steamed bun. At the same time, inulin can absorb moisture, keep the steamed bun moist during storage, delay the aging speed of the steamed bun, extend its shelf life, and also has a certain improvement effect on the taste and flavor of the steamed bun, making the steamed bun taste softer and more delicate.

[0044] In a preferred embodiment of the present invention, the preparation method of monoglyceride hydrate includes adding monoglyceride to warm water at 55 - 65°C and stirring until completely melted to form monoglyceride hydrate, and the mass ratio of monoglyceride to water is 1:16 - 17; the preparation method of the activated yeast solution includes 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 min.

[0045] In a preferred embodiment of the present invention, the fermentation includes pre-fermentation and main fermentation; the pre-fermentation includes fermenting at a humidity of 72 - 78% and a temperature of 28 - 35°C for 45 - 80 min; the main fermentation includes exhausting the dough after pre-fermentation and dividing it into dough pieces, and then fermenting at a humidity of 82 - 88% and 35 - 40°C for 100 - 150 min.

[0046] In the present invention, the pre-fermentation activates the yeast activity and generates a small amount of CO2, initially forming an air chamber; in the main fermentation stage, the temperature is raised to 35 - 40°C, accelerating gas production, using the previous air chamber as a "template" to guide the gas to expand evenly, and combining with the improved extensibility of the dough after gradient enzymolysis.

[0047] In the present invention, the preparation method of the dietary fiber-rich miscellaneous grain steamed bun specifically includes: Take 28 - 32 parts of highland barley flour, 18 - 22 parts of quinoa flour, and 13 - 17 parts of oat bran, mix them evenly to obtain miscellaneous grain flour. First, introduce CO2 into the miscellaneous grain flour to 0.3 - 0.6 MPa and maintain it for 20 - 40 min, then add warm water at 30°C with a weight 3 times that of the miscellaneous grain flour, and stir to form a slurry; Add 0.1% α-amylase based on the total weight of the miscellaneous grain powder to the slurry, adjust the pH to 6.0 - 6.5, and stir and enzymatically hydrolyze in a water bath at 38 - 42°C for 15 - 25 min; 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 miscellaneous grain powder, and continue to stir and enzymatically hydrolyze for 25 - 35 min. After the enzymatic hydrolysis is completed, boil to inactivate the enzyme for 5 min, and cool to 25 - 33°C to obtain the enzymatically hydrolyzed slurry. After draining the enzymatically hydrolyzed slurry, mix it evenly with wheat flour and inulin according to the mass ratio of miscellaneous grain powder, wheat flour and inulin of 60 - 70:33 - 37:2 - 4 to obtain a mixed powder. Add monoglyceride to warm water at 55 - 65°C and stir until completely melted to form a monoglyceride hydrate, with the mass ratio of monoglyceride to water being 1:16 - 17; dissolve yeast in warm water at 33 - 38°C and activate it in an environment at 30 - 35°C for 15 - 30 min to obtain activated yeast. Based on the total mass of the miscellaneous grain powder and wheat flour being 100%, add 0.1 - 0.3% monoglyceride hydrate and 0.4 - 0.6% activated yeast solution to the mixed powder, add warm water at 30 - 35°C in multiple times, start the mixer at low speed in gear 1 and stir for 5 min, then adjust to medium speed in gear 3 of the mixer and stir for 8 min until the surface of the dough is smooth and a uniform film can be formed by pulling with hands, and control the dough temperature at 28 - 30°C. Put the kneaded dough into a fermentation box, adjust the humidity to 72 - 78%, and ferment at a temperature of 28 - 35°C for 45 - 80 min. At this time, the volume of the dough expands to 1.5 times, a small number of pores appear on the surface, and when the dough is pressed by hand, it slowly rebounds; exhaust the pre-fermented dough and divide it into dough pieces, round them up and put them into a steamer 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 min. At this time, the volume of the dough expands to 2.5 - 3 times, it does not collapse when gently pressed with a finger and slowly rebounds, and the pores on the surface are uniform and fine. After the main fermentation is completed, let it proof at 25 - 28°C for 8 - 15 min, and steam for 15 - 20 min at a steam pressure of 0.1 - 0.15 MPa to obtain a miscellaneous grain steamed bun rich in dietary fiber.

[0048] According to the second aspect of the present invention, there is provided a miscellaneous grain steamed bun rich in dietary fiber prepared by the preparation method as described above.

[0049] Example 1 Take 30 parts of highland barley flour, 20 parts of quinoa flour and 15 parts of oat bran, mix them evenly to obtain a miscellaneous grain powder. First, introduce CO2 into the miscellaneous grain powder to 0.3 MPa and maintain it for 30 min, then add warm water at 30°C with a weight 3 times that of the miscellaneous grain powder and stir to form a slurry. Add 0.1% α - amylase based on the total weight of the miscellaneous grain powder to the slurry, adjust the pH to 6.0 - 6.5, and stir and enzymatically hydrolyze at 40°C in a water bath for 20 min; heat up to 56°C, adjust the pH to 5.0 - 5.5, add 0.2% cellulase based on the total weight of the miscellaneous grain powder, and continue to stir and enzymatically hydrolyze for 30 min. After the enzymatic hydrolysis is completed, boil to inactivate the enzyme for 5 min, and cool to 28°C to obtain the enzymatically hydrolyzed slurry. After draining the enzymatically hydrolyzed slurry, mix it evenly with wheat flour and inulin according to the mass ratio of miscellaneous grain powder, wheat flour, and inulin being 65:35:3 to obtain a mixed powder. Add monoglyceride to warm water at 60°C and stir until it completely melts to form a monoglyceride hydrate, with the mass ratio of monoglyceride to water being 1:16 - 17; dissolve yeast in warm water at 35°C and activate it in an environment of 30 - 35°C for 25 min to obtain activated yeast. Based on the total mass of the miscellaneous grain powder and wheat flour being 100%, add 0.3% monoglyceride hydrate and 0.5% activated yeast solution to the mixed powder, add warm water at 30 - 35°C in multiple batches, start the mixer at low speed in gear 1 and stir for 5 min, then adjust to medium speed in gear 3 of the mixer and stir for 8 min until the surface of the dough is smooth and a uniform film can be formed by pulling with hands, and control the dough temperature at 28 - 30°C. Put the kneaded dough into a fermentation box, adjust the humidity to 75%, and ferment at 30°C for 60 min. At this time, the volume of the dough expands to 1.5 times, a small amount of pores appear on the surface, and the dough slowly rebounds when pressed by hand; exhaust the pre - fermented dough and divide it into pieces, round them up and put them into a steamer with a 3 - cm spacing; transfer to a high - temperature fermentation box, adjust the humidity to 85%, and ferment at 38°C for 120 min. At this time, the volume of the dough expands to 2.5 - 3 times, does not collapse when gently pressed with a finger, slowly rebounds, and the pores on the surface are uniform and fine. After the main fermentation is completed, let it proof at 26°C for 10 min, and steam it at a steam pressure of 0.1 - 0.15 MPa for 15 min to obtain the miscellaneous grain steamed buns rich in dietary fiber.

[0050] Example 2 Introduce CO2 into the miscellaneous grain powder until it reaches 0.4 MPa and maintain it for 30 min. The remaining steps and parameters are the same as those in Example 1.

[0051] Example 3 Introduce CO2 into the miscellaneous grain powder until it reaches 0.5 MPa and maintain it for 30 min. The remaining steps and parameters are the same as those in Example 1.

[0052] Example 4 Introduce CO2 into the miscellaneous grain powder until it reaches 0.6 MPa and maintain it for 30 min. The remaining steps and parameters are the same as those in Example 1.

[0053] Example 5 Add α - amylase to the slurry, adjust the pH to 6.0 - 6.5, and enzymatically hydrolyze at 38°C for 15 min; raise the temperature to 55°C, adjust the pH to 5.0 - 5.5, add cellulase and continue enzymatic hydrolysis for 25 min, inactivate the enzyme and cool to 25°C to obtain the enzymatically hydrolyzed slurry; the remaining steps and parameters are the same as those in Example 3.

[0054] Example 6 Add α - amylase to the said slurry, adjust the pH to 6.0 - 6.5, and enzymatically hydrolyze at 42°C for 25 min; raise the temperature to 57°C, adjust the pH to 5.0 - 5.5, add cellulase and continue enzymatic hydrolysis for 35 min, inactivate the enzyme and cool to 33°C to obtain the enzymatically hydrolyzed slurry; the remaining steps and parameters are the same as those in Example 3.

[0055] Comparative Example 1 Directly mix the miscellaneous grain powder and water evenly without introducing CO2, and the remaining steps and parameters are the same as those in Example 3.

[0056] Comparative Example 2 First introduce CO2 into the miscellaneous grain powder to 0.2 MPa and maintain for 30 min, then evenly mix the miscellaneous grain powder and water to obtain a slurry; the remaining steps and parameters are the same as those in Example 3.

[0057] Comparative Example 3 After directly draining the slurry, mix it evenly with wheat flour and inulin to obtain a mixed powder without enzymatic hydrolysis; the remaining steps and parameters are the same as those in Example 3.

[0058] Perform tests on the β - glucan retention rate, phytic acid degradation rate, specific volume, hardness, and sensory evaluation of the miscellaneous grain steamed buns prepared from the above examples and comparative examples. The test results are shown in Table 1.

[0059] β - glucan retention rate: Determined by the phenol - sulfuric acid method. Based on the β - glucan content in the original miscellaneous grain powder, the β - glucan retention rate (%) = (β - glucan content in the steamed bun (mg / g dry weight)) / (β - glucan content in the original miscellaneous grain powder (mg / g dry weight)) × 100%; Phytic acid degradation rate: Refer to GB 5009.153 - 2016 "National Food Safety Standard - Determination of Phytic Acid in Foods" and determine the phytic acid content by HPLC method. The phytic acid degradation rate = (original phytic acid content - phytic acid content in the finished product) / original phytic acid content × 100%; Specific volume: Rapeseed displacement method, unit: mL / g; Hardness: Texture analyzer TPA mode (probe P / 50, test speed 1 mm / s, compression amount 50%); Sensory evaluation: A professional group of 10 people (10 - point system, scoring items: softness, elasticity, roughness, flavor).

[0060] Table 1 Test Results

[0061] As the CO2 pressure increases from 0.3 MPa to 0.5 MPa, the retention rate increases by 7.8%; it decreases slightly after the pressure exceeds 0.5 MPa. At 0.5 MPa, the CO2 penetration and fiber protection reach an equilibrium. An excessive pressure of 0.6 MPa causes the starch granules to over-expand and part of the β-glucan to dissolve and be lost; in Comparative Example 2, the low pressure of 0.2 MPa results in insufficient penetration and weak protection effect. Example 3 has a 28.7% increase compared to Comparative Example 1, while Comparative Example 2 only has a 7.4% increase due to insufficient pressure. The CO2 swelling increases the porosity of the miscellaneous grain powder. At 0.5 MPa, the porosity increases by 25% compared to the untreated group, and the contact area between phytic acid and the enzyme expands. The specific volume of Example 3 is 3.8 mL / g and the hardness is 11.9 N, which is significantly improved compared to Comparative Example 1. The initial pores formed by CO2 release and the yeast gas production synergistically increase the pore density by 40%, improve the dough ductility, and reduce the hardness by 36%. The β-glucan retention rate and phytic acid degradation rate of Comparative Example 1 are significantly lower than those of the CO2 treatment group. Due to the lack of fiber protection and phytic acid swelling effects of CO2, the enzymatic hydrolysis efficiency is low; the specific volume and hardness are poor because there are no initial CO2 pores and the dough has insufficient sponginess. The various indicators of Comparative Example 2 are between those of Comparative Example 1 and Example 1, indicating that low-pressure CO2 treatment has a certain effect but does not reach the optimum. The β-glucan retention rate of Comparative Example 3 is the lowest because the fiber structure is dense due to no enzymatic hydrolysis and the β-glucan is wrapped and difficult to dissolve; the phytic acid degradation rate is only 53% of that of Example 3 because the phytic acid structure lacks enzymatic hydrolysis damage; the specific volume and hardness are the worst because the fiber is not softened by enzymatic hydrolysis and the dough has poor ductility.

[0062] The optimal pressure for CO2 treatment is 0.5 MPa. At this time, the β-glucan retention rate, phytic acid degradation rate, specific volume, and sensory score all reach their peaks, which are the optimal parameters for balancing fiber protection, phytic acid degradation, and taste improvement. The optimal parameters for α-amylase enzymatic hydrolysis are 40 °C / 20 min and for cellulase enzymatic hydrolysis are 56 °C / 30 min. Deviating from this range will lead to a decrease in the nutrient retention rate and taste.

[0063] The CO2 treatment and enzymatic hydrolysis have a synergistic effect, and neither can be lacking. The CO2 treatment creates substrate conditions for enzymatic hydrolysis through physical swelling, and the enzymatic hydrolysis improves the nutritional quality through biochemical reactions. After synergy, the β-glucan retention rate is increased by 15% - 20% compared to single treatment, and the phytic acid degradation rate is increased by 25% - 30%.

Claims

1. A method for preparing a multi-grain steamed bread rich in dietary fiber, characterized in that: The following steps are involved: First, introduce CO2 into the grain powder to a pressure of 0.3-0.6 MPa, maintain for 20-40 min, and 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 enzymolysis at 38-42° C. for 15-25 min; 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 enzymolysis 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 into the mixed flour, add water and stir into dough; The dough is fermented, proofed and steamed to obtain multi-grain steamed bread rich in dietary fiber.

2. The preparation method according to claim 1, characterized in that The miscellaneous 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.

3. The preparation method according to claim 2, characterized in that: 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.

4. The preparation method according to claim 3, characterized in that: The highland barley powder 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 flour, 28% to 32% of medium highland barley flour and 28% to 32% of fine highland barley flour.

5. The preparation method according to claim 3, characterized in that: The quinoa powder includes 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 includes 38-42% of coarse quinoa flour, 38-42% of medium quinoa flour and 38-42% of fine quinoa flour.

6. The preparation method according to claim 1, characterized in that: The added amount of the α-amylase is 0.1% of the total weight of the miscellaneous 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 miscellaneous grain flour, and the cellulase activity is ≥10000U / g.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the miscellaneous grain flour, the wheat flour and the inulin is 60-70:33-37:2-4.

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

9. The preparation method according to claim 1, characterized in that: 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 venting the pre-fermented dough and dividing it into small portions, and then fermenting at a humidity of 82-88% and 35-40°C for 100-150 minutes.

10. A multi-grain steamed bread rich in dietary fiber prepared by the preparation method according to any one of claims 1 to 9.

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