Slowly digestible tartary buckwheat and highland barley steamed bun and preparation method thereof

Abstract

The invention belongs to the technical field of steamed bun processing, and provides slowly digestible tartary buckwheat and highland barley steamed bun and a preparation method thereof. The slowly digestible tartary buckwheat and highland barley steamed bun provided by the invention is mainly prepared from wheat flour, vital gluten, amylose and other main raw materials through dough kneading, rolling, shaping, fermentation and steaming. The tartary buckwheat flour and the highland barley flour are precisely proportioned, the vital gluten and the whole egg liquid are added, and a quick-freezing fresh-keeping technology is combined, so that the GI of the steamed buns is successfully reduced, the health value, the formability, the texture and the taste are improved, and the shelf life is prolonged to 12 months.

Description

Technical Field

[0001] The invention belongs to the technical field of steamed bread processing, and particularly relates to a slow-digestible tartary buckwheat and highland barley steamed bread and a preparation method thereof. Background Art

[0002] At present, most traditional steamed bread uses wheat flour as raw material, and the starch content in wheat flour is as high as 75%. After digestion, starch will be converted into sugars and other ingredients. Therefore, the glycemic index (GI) of steamed bread is relatively high. In order to reduce the GI value of steamed bread, the strategy of using raw materials such as buckwheat and highland barley has received increasing research attention.

[0003] Both buckwheat and highland barley are rich in bioactive compounds, such as phenols, flavonoids and dietary fiber. Among these compounds, phenols and flavonoids have lipid-lowering and anti-inflammatory benefits, while dietary fiber is beneficial to human health and can play a role in slow release of carbohydrates.

[0004] However, there is a problem when using bitter buckwheat and highland barley as raw materials for steamed bread: they do not contain gluten protein. If too much bitter buckwheat and highland barley are added, the network structure of the gluten inside the steamed bread will be reduced, affecting the formation of pores and possibly increasing the bitterness of the steamed bread; if the amount added is too low, it will not meet the requirements of slow-digesting food. This poses a great challenge to the rapid and efficient production of steamed bread.

[0005] In addition, as a food with high water content, long-term preservation is crucial. As the storage time increases, the quality of steamed bread will gradually decline, accompanied by sensory deterioration in taste, smell, etc. Therefore, the length of preservation time becomes one of the key factors affecting the taste of steamed bread in the later stage. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a slow-digestion buckwheat and highland barley steamed bread and a preparation method thereof. By improving the processing raw materials and preparation process of the buckwheat and highland barley steamed bread, the GI value of the steamed bread can be effectively reduced, the stability of the protein in the steamed bread can be improved, and a good taste can be maintained during long-term storage. The preparation process is not only simple to operate and low in cost, but also easy to achieve large-scale production.

[0007] A slow-digestible buckwheat and highland barley steamed bread consists of the following components in parts by mass: 20-40 parts of wheat flour, 15-25 parts of gluten powder, 15-25 parts of amylose, 1-3 parts of defatted flaxseed powder, 5-10 parts of buckwheat powder, 5-10 parts of black highland barley powder, 3-5 parts of bran fiber powder, 1-3 parts of soy protein powder, 1-2 parts of improver, 0.8-1.5 parts of yeast, 3-5 parts of whole egg liquid, and the balance is water.

[0008] The method for preparing the above-mentioned slowly digestible buckwheat and highland barley steamed bread mainly comprises the following steps:

[0009] (1) Mixing: 20-40 parts of raw materials wheat flour, 15-25 parts of gluten powder, 15-25 parts of amylose, 1-3 parts of defatted flaxseed powder, 5-10 parts of tartary buckwheat powder, 5-10 parts of black barley powder, 3-5 parts of bran fiber powder, 1-3 parts of soy protein powder, and 1-2 parts of improver are added in order from small to large, and each raw material is stirred for 30-60 seconds when added, and dilution and mixing are performed step by step to obtain a mixed powder;

[0010] (2) Kneading the dough: Mix the yeast, water and egg liquid and add to the mixed flour, stir for 3 to 10 minutes, and knead into a dough;

[0011] (3) rolling, shaping, and fermenting the dough in (2);

[0012] (4) Steaming and quick-freezing the dough fermented in (3) to obtain slow-digestible buckwheat and highland barley steamed bread.

[0013] Preferably, the improver is selected from at least one of bitter melon powder and polydextrose powder.

[0014] Preferably, the whole egg liquid in (2) is used after being subjected to the following treatment:

[0015] Stir the fresh egg liquid at 4000-6000 r / min for 3-5 minutes.

[0016] Preferably, the mass ratio of mixed flour: yeast: water: whole egg liquid in (2) is (90-100): (0.8-1.5): (40-50): (3-5).

[0017] Preferably, the rolling conditions in (3) are to adjust the gap between the two rollers of the noodle press to 2.5 mm and perform 10-15 times of rolling.

[0018] Preferably, the proofing conditions in (3) are fermentation at 35-40° C. and 82-88% humidity for 32-38 minutes.

[0019] Preferably, the steaming condition in (4) is steaming at 95-100° C. for 25-35 min.

[0020] Preferably, the quick freezing condition in (4) is quick freezing at -30 to -40°C for 30 to 60 minutes, and the center temperature of the steamed buns after quick freezing is -18 to -20°C.

[0021] Compared with the prior art, the present invention has the following advantages and effects:

[0022] (1) The present invention effectively improves the formability of buckwheat and highland barley steamed bread by adding gluten and whole egg liquid to the steamed bread raw materials. The gluten enhances the gluten property of the dough, and the whole egg liquid increases the cohesiveness of the steamed bread, making the dough easier to handle. At the same time, the step-by-step dilution and stirring method ensures the uniform mixing of the raw materials. Experimental results show that this improved method significantly improves the binding property of the raw material components in the steamed bread and optimizes the texture and taste of the steamed bread.

[0023] (2) The present invention successfully reduces the glycemic index (GI) of steamed bread to as low as 49.46 by accurately mixing buckwheat flour and highland barley flour, which is suitable for people with diabetes and other conditions who need to control blood sugar;

[0024] (3) The preparation method of the present invention is combined with quick-freezing preservation technology to effectively extend the shelf life of buckwheat and highland barley steamed bread. The steamed bread can be stored for 12 months at -18°C in a vacuum bag, maintaining its fresh taste and nutritional value, solving the problem of short shelf life of traditional steamed bread and facilitating storage and long-distance transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The protein secondary structure diagrams of different steamed breads in Examples 1 to 6;

[0026] Figure 2 The starch digestion characteristic curves of different steamed breads in Examples 1 to 6;

[0027] Figure 3 It is the content of protein secondary structure in Comparative Examples 1 to 4. DETAILED DESCRIPTION

[0028] Example 1

[0029] A method for preparing slowly digestible buckwheat and highland barley steamed bread comprises the following steps:

[0030] (1) Preparation of steamed bread ingredients, by weight: 30 parts of wheat flour, 22 parts of gluten powder, 15 parts of amylose, 2 parts of defatted flaxseed powder, 10 parts of buckwheat powder, 10 parts of black barley powder, 3 parts of bran fiber powder, 2 parts of soy protein powder, 1 part of bitter melon powder, and 1 part of polydextrose powder;

[0031] (2) Mixing: adding bitter melon powder, polydextrose powder, soy protein powder, defatted flaxseed powder, bran fiber powder, black barley powder, buckwheat powder, amylose, gluten powder and wheat flour in order from small to large portions, stirring uniformly for 45 seconds each time a raw material is added, and diluting and mixing step by step to obtain a mixed powder;

[0032] (3) Mixing the dough: First, stir 4 portions of fresh egg liquid with an electric stirrer at a speed of 5000 r / min for 4 min to make it emulsified to obtain whole egg liquid;

[0033] Then, 1 part of yeast, 45 parts of water and the whole egg liquid obtained in (3) were mixed, and then added to 95 parts of the mixed flour and stirred for 7 minutes to obtain a uniform and smooth unproofed dough;

[0034] (4) Fermentation: The gap between the two rollers of the dough sheeter is adjusted to 2.5 mm, and the dough in (3) is rolled 12 times, then kneaded into a steamed bun shape, and sent to a fermentation box for fermentation at 37° C. and 85% humidity for 35 min;

[0035] (5) Steaming and quick freezing: The fermented dough in (4) is steamed at 100°C for 30 min, and then quick-frozen at -35°C for 45 min to obtain slowly digestible buckwheat and highland barley steamed bread. The central temperature of the steamed bread after quick freezing is -19°C. After vacuum packaging, the steamed bread is frozen at -18°C and stored for 12 months.

[0036] Example 2

[0037] A method for preparing slowly digestible buckwheat and highland barley steamed bread comprises the following steps:

[0038] (1) Preparation of steamed bread raw materials, by weight: 29 parts of wheat flour, 23 parts of gluten powder, 16 parts of amylose, 2 parts of defatted flaxseed powder, 10 parts of buckwheat powder, 10 parts of black barley powder, 4 parts of bran fiber powder, 2 parts of soy protein powder, 1 part of bitter melon powder, and 1 part of polydextrose powder;

[0039] (2) Mixing: adding bitter melon powder, polydextrose powder, soy protein powder, defatted flaxseed powder, bran fiber powder, black barley powder, buckwheat powder, amylose, gluten powder and wheat flour in order from small to large portions, stirring evenly for 30 seconds each time a raw material is added, and diluting and mixing step by step to obtain a mixed powder;

[0040] (3) Mixing the dough: First, stir 4 portions of fresh egg liquid with an electric stirrer at a speed of 4000 r / min for 3 min to make it emulsified to obtain whole egg liquid;

[0041] Then, 0.8 parts of yeast, 40 parts of water and the whole egg liquid obtained in (3) were mixed, and then added to 90 parts of the mixed flour and stirred for 3 minutes to obtain a uniform and smooth unproofed dough;

[0042] (4) Fermentation: The gap between the two rollers of the dough sheeter is adjusted to 2.5 mm, and the dough in (3) is rolled 10 times, then kneaded into a steamed bun shape, and sent to a fermentation box for fermentation at 35° C. and 82% humidity for 32 min;

[0043] (5) Steaming and quick freezing: The fermented dough in (4) is steamed at 95°C for 25 min, and then quick-frozen at -30°C for 30 min to obtain slowly digestible buckwheat and highland barley steamed bread. The central temperature of the steamed bread after quick freezing is -18°C. After vacuum packaging, the steamed bread is frozen at -18°C and stored for 12 months.

[0044] Example 3

[0045] A method for preparing slowly digestible buckwheat and highland barley steamed bread comprises the following steps:

[0046] (1) Preparation of steamed bread raw materials, by weight: 28 parts of wheat flour, 25 parts of gluten powder, 19.5 parts of amylose, 2 parts of defatted flaxseed powder, 8 parts of buckwheat powder, 8 parts of black barley powder, 4 parts of bran fiber powder, 2 parts of soy protein powder, 1 part of bitter melon powder, and 1 part of polydextrose powder;

[0047] (2) Mixing: adding bitter melon powder, polydextrose powder, soy protein powder, defatted flaxseed powder, bran fiber powder, black barley powder, buckwheat powder, amylose, gluten powder and wheat flour in order from small to large portions, stirring uniformly for 60 seconds each time a raw material is added, and diluting and mixing step by step to obtain a mixed powder;

[0048] (3) Mixing the dough: First, stir 5 portions of fresh egg liquid with an electric stirrer at a speed of 6000 r / min for 5 min to make it emulsified to obtain whole egg liquid;

[0049] Then, 1.5 parts of yeast, 50 parts of water and the whole egg liquid obtained in (3) were mixed, and then added to 100 parts of the mixed flour and stirred for 3 minutes to obtain a uniform and smooth unproofed dough;

[0050] (4) Fermentation: The gap between the two rollers of the dough sheeter is adjusted to 2.5 mm, and the dough in (3) is rolled 15 times, then kneaded into a steamed bun shape, and sent to a fermentation box for fermentation at 40° C. and 88% humidity for 38 min;

[0051] (5) Steaming and quick freezing: The fermented dough in (4) is steamed at 100°C for 35 min, and then quick-frozen at -40°C for 60 min to obtain slowly digestible buckwheat and highland barley steamed bread. The central temperature of the steamed bread after quick freezing is -20°C. After vacuum packaging, the steamed bread is frozen at -18°C and stored for 12 months.

[0052] Example 4

[0053] On the basis of Example 1, the formula of the raw material components was adjusted, and the remaining operations and the preparation process of the steamed bread were the same as those in Example 1.

[0054] The components of each raw material in this embodiment are as follows:

[0055] 40 parts of wheat flour, 15 parts of gluten powder, 23 parts of amylose, 2 parts of defatted flaxseed powder, 5 parts of tartary buckwheat powder, 5 parts of black barley powder, 4 parts of bran fiber powder, 2 parts of soy protein powder, 1 part of bitter melon powder, and 1 part of polydextrose powder;

[0056] The weight proportions of the mixed flour, yeast, water and whole egg liquid in the preparation step (3) are 90 parts, 1.0 parts, 45 parts and 3 parts respectively.

[0057] Example 5

[0058] On the basis of Example 1, the formula of the raw material components was adjusted, and the remaining operations and the preparation process of the steamed bread were the same as those in Example 1.

[0059] The components of each raw material in this embodiment are as follows:

[0060] 37 parts of wheat flour, 17 parts of gluten powder, 23 parts of amylose, 2 parts of defatted flaxseed powder, 6 parts of buckwheat powder, 6 parts of black barley powder, 3 parts of bran fiber powder, 2 parts of soy protein powder, 1 part of bitter melon powder, and 1 part of polydextrose powder;

[0061] The weight proportions of the mixed flour, yeast, water and whole egg liquid in the preparation step (3) are 95 parts, 1.0 parts, 40 parts and 5 parts respectively.

[0062] Example 6

[0063] On the basis of Example 1, the formula of the raw material components was adjusted, and the remaining operations and the preparation process of the steamed bread were the same as those in Example 1.

[0064] The components of each raw material in this embodiment are as follows:

[0065] 35 parts of wheat flour, 19 parts of gluten powder, 25 parts of amylose, 2 parts of defatted flaxseed meal, 6 parts of buckwheat flour, 6 parts of black barley flour, 3 parts of bran fiber powder, 2 parts of soy protein powder;

[0066] In the preparation step (3), the weight proportions of the mixed flour, yeast, water and whole egg liquid are 100 parts, 0.8 parts, 40 parts and 4 parts respectively.

[0067] Example 7

[0068] 10 tasters were selected to conduct sensory evaluation on the steamed buns prepared in Examples 1 to 6. All evaluators participating in the sensory evaluation should meet the requirements of GB / T 10220, receive special training on the knowledge related to the sensory evaluation of steamed buns, and have the same inspection capabilities. Referring to GB / T 35991-2018, sensory evaluation was performed based on the color, appearance, elasticity, internal structure, taste and flavor of the steamed buns after re-steaming. The scoring criteria and scores are shown in the following table:

[0069] Table 1 Sensory scoring standard for buckwheat and highland barley steamed bread

[0070]

[0071] Table 2 Sensory evaluation results of different examples

[0072] project Color Appearance elasticity Internal structure Taste Flavor Total score Example 1 8 9 17 16 18 17 85 Example 2 8 8 16 15 18 17 83 Example 3 8 9 18 17 19 17 88 Example 4 7 7 13 14 15 15 71 Example 5 6 7 13 13 14 14 67 Example 6 6 6 12 13 14 13 64

[0073] As can be seen from the table, the total scores of Examples 1 to 3 are greater than the total scores of Examples 4 to 6, among which the total score of Example 3 is the highest, 88 points. Example 3 performs well in all the scores, especially in terms of elasticity and taste. Therefore, the effect of Example 3 is the best.

[0074] Table 3 Nutrients and GI values ​​of different examples

[0075] project Protein / g Fat / g Dietary fiber / g Carbohydrate / g GI Example 1 30.89 2.99 19.96 42.78 54.16 Example 2 29.48 2.97 20.97 43.23 52.37 Example 3 30.73 2.82 24.12 41.97 49.46 Example 4 24.24 2.59 23.27 43.17 52.21 Example 5 25.22 2.25 22.40 42.61 50.84 Example 6 26.60 2.27 24.19 41.42 55.73

[0076] The protein, fat, dietary fiber, carbohydrates and GI value of buckwheat and highland barley steamed bread were determined with reference to GB 5009.5-2016, GB 5009.6-2016, GB 5009.88-2023, GB 5009.7-2016 and in vitro digestion simulation.

[0077] First, it is necessary to determine the standard for low GI. Generally speaking, a GI value below 55 is considered to be low GI. Therefore, data points with a GI value below 55 are screened out from the data. Examples 1 to 5 all meet the low GI standard. According to the scoring criteria, Example 3 is considered to be the best among low GI foods. This result is based on a comprehensive consideration of the following two factors: GI value: Example 3 has the lowest GI value of 49.46, which is beneficial for blood sugar control. Nutritional composition: Example 3 performs well in terms of protein, fat, dietary fiber and carbohydrate content.

[0078] Furthermore, peakfit was used to analyze the secondary structure of proteins in steamed bread, and the data are shown in Table 4.

[0079] Table 4 Content of protein secondary structure in different examples

[0080]

[0081]

[0082] It was observed that in buckwheat and highland barley steamed bread, the secondary structure of the protein mainly includes β-fold, random curl, α-helix and β-turn, and the relative contents of these structures are different. In particular, α-helix and β-fold, as relatively stable ordered structures, play an important role in the overall stability of steamed bread. The disordered β-turn and random curl constitute the unstable part. Among these structures, the proportion of β-turn protein and β-fold protein is relatively high, accounting for about 75% to 85% of the total protein, and is a key part of the gluten network.

[0083] from Figure 1 It can be observed that the content of β-fold and α-helix in Example 3 is the highest, reaching 56.11% and 18.13% respectively (Table 4), which indicates that the stability of protein in steamed bread is good. This improvement in stability may be caused by several factors, among which the change in the raw material ratio, especially the increase in gluten content, may be one of the key factors. Gluten is rich in protein, mainly including glutenin and gliadin, which play an important role in the formation of gluten network.

[0084] Among them, Example 3 performed best in buckwheat and highland barley steamed bread, with the lowest GI value. After screening, the coarse grain steamed bread prepared under the formula of Example 3 above had the best comprehensive performance in terms of sensory and nutritional quality.

[0085] In summary, the present invention successfully develops slow-digesting, low-GI buckwheat and highland barley steamed bread suitable for people with diabetes and other conditions who need to control blood sugar by accurately proportioning buckwheat flour and highland barley flour, and significantly improves the formability and texture of the steamed bread by adding gluten powder and whole egg liquid and combining the step-by-step dilution and stirring method. In addition, combined with the quick-freezing preservation technology, the shelf life of the steamed bread is effectively extended, which is convenient for storage and long-distance transportation, solving the problem of short shelf life of traditional steamed bread.

[0086] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent changes and modifications made within the scope of the present invention should still fall within the scope of the present invention.

[0087] Comparative Example 1

[0088] On the basis of Example 3, only 12 portions of tartary buckwheat flour were added to prepare tartary buckwheat steamed bread.

[0089] Comparative Example 2

[0090] On the basis of Example 3, only 12 portions of highland barley flour were added to prepare highland barley steamed bread.

[0091] Comparative Example 3

[0092] On the basis of Example 3, only 3 parts of tartary buckwheat flour and 9 parts of black barley flour were added to prepare steamed bread.

[0093] Comparative Example 4

[0094] On the basis of Example 3, only 9 parts of tartary buckwheat flour and 3 parts of black highland barley flour were added to prepare steamed bread.

[0095] By simulating the in vitro digestion process of starch in the mouth, stomach and small intestine, the starch hydrolysis rate within 0 to 180 minutes can be determined, and the starch hydrolysis curve can be drawn accordingly. By calculating the area under the curve, the digestion speed and degree of starch in steamed bread can be quantified, and finally the approximate glycemic index (eGI) of steamed bread can be obtained using a specific formula to evaluate its impact on blood sugar levels.

[0096] (1) Calculation of starch hydrolysis index (HI)

[0097]

[0098] (2) Calculation of eGI

[0099] eGI=39.71+(0.549×HI)

[0100] Table 5 Starch hydrolysis rate of different steamed bread

[0101] Time / min Comparative Example 3 / % Comparative Example 1 / % Comparative Example 2 / % Example 3 / % 0 7.59±0.32 7.36±0.13 4.94±0.47 2.01±0.44 20 23.01±0.42 8.80±1.40 6.56±1.45 3.94±0.67 30 31.07±2.76 13.61±1.13 9.35±0.35 4.89±1.60 60 35.61±0.90 22.07±1.57 17.11±0.82 10.89±1.39 90 45.01±0.31 28.41±1.65 21.84±1.78 11.52±1.11 120 51.51±0.25 35.38±0.90 28.45±2.35 16.61±1.23 150 58.99±0.47 38.45±1.32 31.01±1.98 18.84±1.68 180 60.50±0.31 40.11±1.66 32.54±3.04 20.32±1.57

[0102] from Figure 2 It can be seen from Table 5 that the trends of all curves are roughly the same. Overall, the hydrolysis rate of Example 3 at 180 min is comparable to the starch hydrolysis rates of Comparative Example 3, Comparative Example 1 and Comparative Example 2 at 20 min, 60 min and 90 min, respectively, and the order of starch hydrolysis rate is Example 3 < Comparative Example 2 < Comparative Example 1 < Comparative Example 3.

[0103] Table 6 eGI values ​​of steamed bread with different recipes

[0104] sample AUG HI(%) eGI Comparative Example 3 7234.97 72.35 79.43 Comparative Example 1 4533.63 45.45 64.66 Comparative Example 2 3632.05 36.32 59.65 Example 3 2049.18 20.49 50.96

[0105] The same is true from the eGI values ​​in Table 6. Only Example 3 reaches a low GI level, which is much lower than the comparative example. This phenomenon can be attributed to the synergistic effect of bitter buckwheat and highland barley. The addition of these two ingredients may change the structure of steamed bread or affect the digestive enzyme activity of starch, thereby reducing the digestion rate of steamed bread and resulting in a lower eGI value.

[0106] from Figure 3 It can be seen that the total contents of α-helix and β-sheet of Comparative Examples 1 to 4 are all lower than that of Example 3, indicating that the secondary structure of the protein in the comparative examples is poor, which may be caused by the different ratios of buckwheat flour and highland barley flour.

Claims

1. A slow-digestible buckwheat and highland barley steamed bread, characterized in that: The invention is composed of the following components in parts by mass: 20-40 parts of wheat flour, 15-25 parts of gluten powder, 15-25 parts of amylose, 1-3 parts of defatted flaxseed powder, 5-10 parts of tartary buckwheat powder, 5-10 parts of black barley powder, 3-5 parts of bran fiber powder, 1-3 parts of soy protein powder, 1-2 parts of improver, 0.8-1.5 parts of yeast, 3-5 parts of whole egg liquid, and the balance is water.

2. The method for preparing the slowly digestible buckwheat and highland barley steamed bread according to claim 1, characterized in that: The main steps include: (1) Mixing: 20-40 parts of wheat flour, 15-25 parts of gluten, 15-25 parts of amylose, 1-3 parts of defatted flaxseed meal, 5-10 parts of buckwheat meal, 5-10 parts of black barley meal, 3-5 parts of bran fiber powder, 1-3 parts of soy protein powder, and 1-2 parts of improver are added in order from small to large. Each raw material is stirred for 30-60 seconds after being added, and the mixture is diluted and mixed step by step to obtain a mixed powder. (2) Kneading the dough: Mix the yeast, water and whole egg liquid and add to the mixed flour. Stir for 3 to 10 minutes and knead into a dough. (3) Fermentation: rolling, shaping, and fermenting the dough in (2); (4) Steaming and quick freezing: Steaming and quick freezing the dough fermented in (3) to obtain slow-digestible buckwheat and highland barley steamed bread.

3. The slow-digestible buckwheat and highland barley steamed bread as claimed in claim 1, characterized in that: The improver is selected from at least one of bitter melon powder and polydextrose powder.

4. The preparation method as claimed in claim 2, characterized in that (2) The whole egg liquid is used after the following treatment: Stir the fresh egg liquid at 4000~6000 r / min for 3~5 min.

5. The preparation method as claimed in claim 2, characterized in that: (2) The mass ratio of mixed flour: yeast: water: whole egg liquid is (90~100): (0.8~1.5): (40~50): (3~5).

6. The preparation method as claimed in claim 2, characterized in that: (3) The conditions for medium rolling are to adjust the gap between the two rollers of the noodle press to 2.5 mm and perform 10-15 times of rolling.

7. The preparation method as claimed in claim 2, characterized in that: (3) The medium fermentation conditions are 35-40°C and 82-88% humidity for 32-38 min.

8. The preparation method as claimed in claim 2, characterized in that (4) The steaming conditions are 95-100°C for 25-35 min.

9. The preparation method as claimed in claim 2, characterized in that: (4) The medium-speed freezing condition is to freeze the steamed buns at -30 to -40°C for 30 to 60 minutes. After freezing, the center temperature of the steamed buns is between -18 and -20°C.

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