Low-GI steamed bun and preparation method thereof

Abstract

The invention provides low-GI steamed buns and a preparation method thereof. Saccharomyces cerevisiae, lactobacillus brevis, lactobacillus plantarum and lactobacillus pentosus which are separated and screened from traditional yeast are used for performing multi-strain fermentation on dough, a composite modifier composed of polydextrose, isoamylase and tannic acid is added after fermentation, and steaming is performed after fermentation to obtain the low-GI steamed buns. The prepared steamed bun has low GI value and excellent sensory quality, the bottleneck problem that low GI, texture characteristics and sensory quality are difficult to consider in the traditional process is solved, the unification of low GI health function and excellent eating quality is realized, the process is simple, the trend of cleaning labels is met, and industrial production is easy.

Description

Technical Field

[0001] This invention belongs to the field of food bio-fermentation technology, specifically relating to a low-GI steamed bun and its preparation method. Background Technology

[0002] Steamed buns, made primarily from wheat flour through fermentation and steaming processes, are a traditional fermented staple food. They are characterized by mature production techniques and a wide consumer base, holding an important place in the daily diet of Chinese residents. However, due to starch gelatinization during steaming, they are easily and rapidly digested and absorbed by the body, resulting in a high post-meal blood sugar response and a generally high glycemic index (GI). Long-term consumption is not conducive to the health needs of individuals requiring blood sugar control. Therefore, reducing the GI value of steamed buns while maintaining their edible quality has become an important technological direction in the current research and development of healthy staple foods.

[0003] To lower the glycemic index (GI), the mainstream technological approach currently focuses on ingredient blending, which involves adding whole grain flours such as buckwheat and sweet buckwheat, dietary fiber, high amylose, or functional extracts from plant sources to reduce the digestibility of starch or regulate sugar metabolism. However, in practical processing applications, the introduction of a large number of non-wheat components often interferes with the formation and stability of the gluten network, leading to a decline in dough fermentation performance, reduced specific volume of steamed buns, harder texture, stickier mouthfeel, and problems such as enhanced whole grain flavor or even increased bitterness. It is difficult to balance the low GI characteristics with the soft texture and flavor harmony that traditional steamed buns should have, which seriously restricts the industrial promotion and market acceptance of low GI steamed bun products.

[0004] Fermentation regulation is considered a more promising solution. Fermentation not only improves the flavor and texture of steamed buns, but its metabolic products (such as organic acids) can also induce starch retrogradation, forming resistant starch (RS), thereby reducing the GI value. However, in current industrial production, single commercial yeasts are commonly used as leavening agents. Their advantages lie in their strong gas production capacity, stable fermentation process, and ease of operation, but their metabolic pathway is relatively simple, mainly producing CO2 through the rapid consumption of sugars. Their ability to regulate the starch structure, flavor compound formation, and synergistic effects of functional components in the dough system is limited, making it difficult to compensate for the shortcomings in taste and flavor of low-GI formulations. In contrast, traditional leavening agents (such as sourdough starter, yeast extract, etc.) are usually composed of multiple yeasts and lactic acid bacteria. Multi-strain fermentation can produce organic acids, alcohols, and various flavor precursors, which helps improve the fermentation characteristics of dough and the flavor quality of the finished product. However, the microbial composition of traditional leavening agents is greatly affected by the source of raw materials, geographical environment, and production process. The proportion and activity of the strains are difficult to control, resulting in poor batch stability and failing to meet the requirements of modern food industry for standardization, repeatability, and safety controllability of leavening agents. Even if fermentation with specific microorganisms (such as lactic acid bacteria) produces organic acids to promote starch retrogradation, the total amount of resistant starch formed is limited and the structure is loose, making it easily destroyed during subsequent steaming or reheating, resulting in an insignificant and unstable GI reduction effect.

[0005] Existing technologies often focus on isolated strain screening or single additives. Therefore, there is an urgent need in this field for an innovative technical solution that can overcome the limitations of existing single methods and achieve a fundamental and stable reduction in the GI value of steamed buns without affecting their textural properties and sensory quality. Summary of the Invention

[0006] Technical problems to be solved: In view of the above-mentioned technical problems, the purpose of this invention is to provide a low-GI steamed bun and its preparation method. By fermenting with multiple strains of bacteria and adding compound improvers, the invention solves the problems of low resistant starch production efficiency, dry and hard texture, insufficient elasticity, easy to crumble and stick to teeth, and poor flavor of low-GI steamed buns prepared by traditional methods. Finally, a high-quality low-GI steamed bun with high resistant starch content, low GI value, moderate softness, refreshing and non-sticky texture, no crumbling, and mellow flavor is obtained.

[0007] Technical solution: A method for preparing low-GI steamed buns, comprising the following steps:

[0008] S1. Take the compound raw material powder, add water, and then add fresh wet cells of brewer's yeast, lactobacillus brevis, lactobacillus plantarum and lactobacillus pentosaccharide. After mixing evenly, place the dough in a constant temperature incubator to ferment and obtain the leavening agent.

[0009] S2. Take a new compound raw material powder, add a leavening agent and water, knead the dough, let it rise, repeatedly roll out the dough to release the air, and spread the dough into a flatbread shape. Set aside. Based on the dry basis of the compound raw material powder, dissolve polydextrose, tannic acid and isoamylase in a small amount of room temperature water, and evenly pour it onto the surface of the risen flatbread. Knead the dough repeatedly until the surface is smooth and delicate, cover with plastic wrap, let it relax at room temperature, and then divide it into small dough balls of equal weight. Let them rise a second time, place the risen dough in a steamer and steam with cold water. After steaming, remove the dough and let it cool naturally at room temperature to obtain low-GI steamed buns.

[0010] Preferably, the components of the composite raw material powder in step S1 include wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract.

[0011] Furthermore, the mass ratio of wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract is 77~81:20~24:29~33:14~18:13~17:1.

[0012] Preferably, the brewing yeast in step S1 is HautWYH101801 Saccharomyces cerevisiae, deposited at Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67133 and deposit date of October 20, 2025.

[0013] The preferred Lactobacillus brevis is HautWYHI01802, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67134 and deposit date of October 20, 2025.

[0014] The preferred Lactobacillus plantarum is HautWYH101803, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No: 67135 and deposit date of October 20, 2025.

[0015] The preferred Lactobacillus pentosus is HautWYH101804, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No: 67136 and deposit date of October 20, 2025.

[0016] Preferably, the volume ratio of fresh and wet cells of Saccharomyces cerevisiae, Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus pentosus in step S1 is 1:0.1~0.3:0.1~0.3:0.1~0.3.

[0017] Preferably, the viable count of the brewer's yeast in step S1 is 1.0~2.5×10⁻⁶. 8 CFU / mL.

[0018] Preferably, the viable count of *Lactobacillus brevis* in step S1 is 1.0~2.5 × 10⁻⁶. 8 CFU / mL.

[0019] Preferably, the viable count of *Lactobacillus plantarum* in step S1 is 1.0~2.5 × 10⁻⁶. 8 CFU / mL.

[0020] Preferably, the viable count of *Lactobacillus pentosus* in step S1 is 1.0~2.5 × 10⁻⁶. 8 CFU / mL.

[0021] Preferably, the fermentation time in step S1 is 6-8 hours.

[0022] Preferably, in step S2, the amount of fermentation agent added to the compound raw material powder is 10-15%.

[0023] Preferably, in step S2, the amount of polydextrose added to the composite raw material powder is 0.5-3%, the amount of tannic acid added to the composite raw material powder is 0.002-0.01%, and the amount of isoamylase added to the composite raw material powder is 3-10 U / g.

[0024] The low-GI steamed bun prepared by the above method.

[0025] Beneficial effects:

[0026] 1. This invention utilizes polydextrose, isoamylase, and tannic acid to prepare a composite modifier, establishing a three-stage reaction system after co-fermentation. The fermented dough provides a suitable weakly acidic environment. Under this environment, polydextrose acts as a specific carbon source for the fermenting bacteria, metabolizing to produce organic acids, primarily acetic acid. This not only regulates the pH of the reaction system but also, acetic acid is more efficient than other organic acids in promoting starch retrogradation and the formation of resistant starch. Within this pH range, isoamylase is activated, hydrolyzing the α-1,6-glycosidic bonds of starch, converting the branched structure into linear starch fragments, and increasing the concentration of linear starch precursors suitable for retrogradation and crystallization. During high-temperature steaming, the starch gelatinizes, destroying the crystalline structure within the starch granules and releasing the linear starch from the crystals. The high temperature and the trace amounts of reducing sugars released from the gelatinized starch oxidize the pyrogallol structure of tannic acid to quinone. The quinone covalently cross-links with nucleophilic groups present in the dough (such as the reducing ends or hydroxyl groups of linear starch chains, amino or thiol groups of modified gluten proteins, fermentation-produced peptides, and amino acids), forming a network structure. As the steamed buns cool, the linear starch chains rearrange themselves in the cross-linked network. Due to restricted movement, the starch chains are forced to arrange themselves in a highly ordered and oriented manner (retrogradation), forming resistant starch (RS3) to reduce the GI value of the steamed buns.

[0027] 2. This invention improves the resistant starch content and structural stability. The debranching action of isoamylase solves the fundamental problem of insufficient starch retrogradation substrate at the molecular level, providing sufficient linear starch substrate for the formation of resistant starch. During cooling, these linear chains rearrange and crystallize within the rigid confinement space formed by the tannic acid covalent network. The spatial confinement effect forces the linear chains to arrange themselves in a highly ordered and uniformly oriented manner, thereby forming small-sized, highly crystalline, and uniformly distributed resistant starch crystals. This covalent network not only acts as a template to guide crystallization but also physically anchors and encapsulates these crystals, making them difficult to destroy during subsequent reheating or mechanical shearing, thus endowing resistant starch with excellent thermal and enzymatic stability.

[0028] 3. This invention, while imparting a low-GI function to steamed buns, significantly improves their textural quality and enhances their sensory qualities. During steaming, the active quinones formed by the oxidation of tannic acid covalently cross-link with gluten proteins and peptides. This reaction strengthens the gluten network, enhancing its strength and elasticity, and forming a denser and more resilient protein-polyphenol complex gel structure. This structure more effectively encapsulates and retains the gases produced during fermentation, resulting in a more uniform and delicate pore structure and increased specific volume in the steamed buns. Simultaneously, the debranching effect of isoamylase on amylopectin reduces the content of short-chain dextrins, which are the main factor contributing to the sticky texture of the product. This reduction improves the refreshing taste. Furthermore, the acetic acid and other flavor compounds produced by the fermentation bacteria using polydextrose as a carbon source, along with the flavor compounds generated by tannic acid itself during the thermal reaction, contribute to a mellow, acceptable slightly acidic and rich flavor background. This effectively harmonizes the undesirable flavors from raw materials (such as buckwheat flour and mulberry leaf extract), enabling the product to maintain its core low-GI function while achieving superior overall sensory quality compared to traditional functional flour products.

[0029] 4. This invention combines multi-strain basic fermentation with subsequent chemical cross-linking, without altering the existing main equipment and process framework for steamed bun production. By adding a compound improver with clearly defined components after fermentation, the formation of the internal structure of the steamed bun can be directionally guided. While effectively reducing the GI value of the steamed bun, it enhances the gas retention and network strength of the dough, improves the processing tolerance and final texture of dough containing whole grains and dietary fiber, thereby enhancing its health benefits while maintaining the traditional sensory quality of steamed buns. The entire system is based on bio-enzymes and natural plant ingredients, with mild reaction conditions, aligning with the consumer trend towards clean labels. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0031] The traditional starter culture 1 involved in the embodiments and comparative examples of this invention was purchased from Rizhao, Shandong Province, and its main raw materials are koji, wheat flour, corn flour, and purified water; the traditional starter culture 2 was purchased from Tai'an, Shandong Province, and its main raw materials are corn flour, wheat flour, and purified water; the mulberry leaf extract was purchased from Hill Pharmaceutical Co., Ltd.; the brewer's yeast HautWYH101801 was deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67133; the lactobacillus brevis HautWYHI01802 was deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67134; the lactobacillus plantarum HautWYH101803 was deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67135; the lactobacillus pentosaccharide HautWYH101804 was deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67136; and the isoamylase was purchased from Shanghai Tiankuo Biotechnology Co., Ltd., with an enzyme activity of 1000 U / g.

[0032] Example 1

[0033] This embodiment describes the screening, isolation, and identification of Saccharomyces cerevisiae HautWYH101801. The specific method includes the following steps:

[0034] S1. Take 10 g of traditional fermentation agent 1 and magnetically stir it in 90 mL of sterile physiological saline for 30 min, according to 10 -3 ~10 -6 Serial dilutions were performed, and 100 μL of each dilution was spread on WL nutrient agar medium and incubated at 30°C for 48 h. Based on the colony morphology (2 mm in diameter, opaque, milky white, spherical protrusion, neat edges, and no luster), single colonies were randomly selected and streaked again for isolation. After 2-3 days of incubation, single yeast cells were obtained.

[0035] S2. Identification: Yeast DNA was extracted according to the operating procedures of the DNA extraction kit. Using the extracted yeast DNA as a template, the ITS sequence was amplified using primers ITS4 and ITS5. Primer ITS4: 5'-TCCTCCGCTGACTAATATGC-3'; Primer ITS5: 5'-GGAAGTAAAAGTCGTAACAAGG-3'. The amplification system was: 12.5 µL of 2×Power Tap PCR Master Mix, 1 µL of ITS4, 1 µL of ITS5, 9.5 µL of double-distilled water, and 1 µL of template DNA. The PCR amplification conditions were: 94℃ pre-denaturation for 5 min followed by 30 cycles: 94℃ denaturation for 30 s, 52℃ annealing for 45 s, and 72℃ extension for 45 s. The PCR product was then extended at 72℃ for 5 minutes. The PCR product was sent to Sangon Biotech (Shanghai) Co., Ltd. for sequencing. The sequencing results were compared with the sequences in the Blast database of NCB1GenBank to obtain the sequence information of strains with high homology. The yeast strain HautWYH101801 was identified.

[0036] S3. Activate and culture the identified yeast strain HautWYH101801, add glycerol and bacterial solution in a 1:1 ratio to cryovials, and store at -80℃.

[0037] Example 2

[0038] This embodiment describes the screening, isolation, and identification of Lactobacillus brevis HautWYHI01802. The specific method includes the following steps:

[0039] S1. Take 10 g of traditional fermentation agent 1 and magnetically stir it in 90 mL of sterile physiological saline for 30 min, according to 10 -3 ~10 -6 Serial dilutions were performed, and 100 μL of each dilution was spread on MRS solid medium and incubated at 36°C for 48 h. Based on the colony morphology (white, regular edges, moist surface, and the presence of a dissolution zone on MRS medium containing calcium carbonate), single colonies were randomly selected and re-streaked for isolation. After incubation for 2-3 days, single lactic acid bacteria colonies were obtained.

[0040] S2. Identification: Lactic acid bacteria DNA was extracted according to the DNA extraction kit procedure. Using the extracted DNA as a template, the ITS sequence was amplified using primers P0 and P6. Primer P0: 5'-GAGAGTTTGATCCTGGCTCAG-3'; Primer P6: 5'-CTACGGCTACCTTGTTAC-3'. The amplification system consisted of: 12.5 µL of 2×Power Tap PCR Master Mix, 1 µL of ITS4, 1 µL of ITS5, 9.5 µL of double-distilled water, and 1 µL of template DNA. The PCR amplification conditions were: 94℃ pre-denaturation for 5 min followed by 30 cycles: 94℃ denaturation for 60 s, 52℃ annealing for 60 s, 72℃ extension for 90 s, and a final extension at 72℃ for 5 min. The PCR products were sent to Sangon Biotech (Shanghai) Co., Ltd. for sequencing. The sequencing results were compared with those obtained from NCBI. The sequence was compared with the Blast sequence in the GenBank database to obtain the sequence information of the strain with high homology, and Lactobacillus brevis HautWYHI01802 was identified.

[0041] S3. Activate and culture the identified Lactobacillus brevis HautWYHI01802, add glycerol and bacterial solution in a 1:1 ratio to cryovials, and store at -80℃.

[0042] Example 3

[0043] This example describes the screening, isolation, and identification of Lactobacillus plantarum HautWYH101803. The specific method includes the following steps:

[0044] S1. Take 10 g of traditional fermentation agent 1 and magnetically stir it in 90 mL of sterile physiological saline for 30 min, according to 10 -3 ~10 -6 Serial dilutions were performed, and 100 μL of each dilution was spread on MRS solid medium and incubated at 36°C for 48 h. Based on the colony morphology (white, regular edges, moist surface, and the presence of a dissolution zone on MRS medium containing calcium carbonate), single colonies were randomly selected and re-streaked for isolation. After incubation for 2-3 days, single lactic acid bacteria colonies were obtained.

[0045] S2. Identification: Lactic acid bacteria DNA was extracted according to the operating procedures of the DNA extraction kit. Using the extracted lactic acid bacteria DNA as a template, the ITS sequence was amplified using primers P0 and P6. Primer P0: 5'-GAGAGTTTGATCCTGGCTCAG-3'; Primer P6: 5'-CTACGGCTACCTTGTTAC-3'. The amplification system was: 12.5 µL of 2×Power Tap PCR Master Mix, 1 µL of ITS4, 1 µL of ITS5, 9.5 µL of double-distilled water, and 1 µL of template DNA. The PCR amplification conditions were: 94℃ pre-denaturation for 5 min followed by 30 cycles: 94℃ denaturation for 60 s, 52℃ annealing for 60 s, 72℃ extension for 90 s, and a final extension at 72℃ for 5 min. The PCR products were sent to Sangon Biotech (Shanghai) Co., Ltd. for sequencing. The sequencing results were compared with those obtained from NCBI. The sequence was compared with the Blast sequence in the GenBank database to obtain the sequence information of the strain with high homology, and Lactobacillus plantarum HautWYH101803 was identified.

[0046] S3. Activate and culture the identified Lactobacillus plantarum HautWYH101803, add glycerol and bacterial solution in a 1:1 ratio to cryovials, and store at -80℃.

[0047] Example 4

[0048] This example describes the screening, isolation, and identification of Lactobacillus pentosus HautWYH101804. The specific method includes the following steps:

[0049] S1. Take 10 g of traditional fermentation agent 2 and magnetically stir it in 90 mL of sterile physiological saline for 30 min, according to 10 -3 ~10 -6 Serial dilutions were performed, and 100 μL of each dilution was spread on MRS solid medium and incubated at 36°C for 48 h. Based on the colony morphology (white, regular edges, moist surface, and the presence of a dissolution zone on MRS medium containing calcium carbonate), single colonies were randomly selected and re-streaked for isolation. After incubation for 2-3 days, single lactic acid bacteria colonies were obtained.

[0050] S2. Identification: Lactic acid bacteria DNA was extracted according to the operating procedures of the DNA extraction kit. Using the extracted lactic acid bacteria DNA as a template, the ITS sequence was amplified using primers P0 and P6. Primer P0: 5'-GAGAGTTTGATCCTGGCTCAG-3'; Primer P6: 5'-CTACGGCTACCTTGTTAC-3'. The amplification system was: 12.5 µL of 2×Power Tap PCR Master Mix, 1 µL of ITS4, 1 µL of ITS5, 9.5 µL of double-distilled water, and 1 µL of template DNA. The PCR amplification conditions were: 94℃ pre-denaturation for 5 min followed by 30 cycles: 94℃ denaturation for 60 s, 52℃ annealing for 60 s, 72℃ extension for 90 s, and a final extension at 72℃ for 5 min. The PCR products were sent to Sangon Biotech (Shanghai) Co., Ltd. for sequencing. The sequencing results were compared with those obtained from NCBI. The sequence was compared with the Blast sequence in the GenBank database to obtain the sequence information of the strain with high homology, and Lactobacillus pentosaccharide HautWYH101804 was identified.

[0051] S3. Activate and culture the identified Lactobacillus pentosus HautWYH101804, add glycerol and bacterial solution in a 1:1 ratio to cryovials, and store at -80℃.

[0052] Example 5

[0053] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0054] S1. The *Saccharomyces cerevisiae* HautWYH101801 obtained in Example 1 was streaked on WL nutrient agar medium and cultured at 28°C for 48 h. Single colonies on the plate were picked and placed in YPD liquid medium and shaken at 30°C for 24 h. After centrifugation at 4°C and 5000 r / min for 10 min, the supernatant was discarded and the precipitate was collected to obtain fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801.

[0055] S2. The *Lactobacillus brevis* HautWYHI01802 obtained from Example 2, *Lactobacillus plantarum* HautWYH101803 obtained from Example 3, and *Lactobacillus pentosaccharide* HautWYH101804 obtained from Example 4 were streaked on MRS solid medium and cultured at 36°C for 48 h. Single colonies from the plates were picked and placed in MRS liquid medium and shaken at 36°C for 24 h. After centrifugation at 4°C and 5000 r / min for 10 min, the supernatant was discarded and the precipitate was collected to obtain fresh wet cells of *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804, respectively.

[0056] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 79:23:32:16:16:16 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.1:0.3:0.3. The viable count of each of the four strains was 1.0 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0057] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 10% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the dough to release the air, and then spread the dough into a flatbread shape.

[0058] S5. Based on the dry weight of wheat flour as described in S4, take 1.5% of the total mass of wheat flour polydextrose, 0.005% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 3 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and proof them a second time for 25 minutes. Place the proofed dough balls in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0059] Example 6

[0060] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0061] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0062] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0063] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 79:23:32:16:16:16 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.1:0.3:0.3. The viable count of each of the four strains was 1.5 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0064] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 12% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the air and spread the dough into a flatbread shape.

[0065] S5. Based on the dry weight of wheat flour as described in S4, take 1.2% of the total mass of wheat flour polydextrose, 0.005% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 5 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and let them rise a second time for 25 minutes. Place the dough balls that have risen a second time in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0066] Example 7

[0067] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0068] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0069] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0070] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 80:24:30:16:16:16 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.2:0.1:0.3. The viable count of each of the four strains was 1.5 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0071] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 15% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the air and spread the dough into a flatbread shape.

[0072] S5. Based on the dry basis of wheat flour as described in S4, take 1.5% of the total mass of wheat flour polydextrose, 0.003% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 3 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and let them rise a second time for 25 minutes. Place the dough balls that have risen a second time in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0073] Example 8

[0074] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0075] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0076] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0077] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 80:24:30:16:16:16 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.2:0.1:0.3. The viable count of each of the four strains was 2.0 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0078] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 10% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the dough to release the air, and then spread the dough into a flatbread shape.

[0079] S5. Based on the dry basis of wheat flour as described in S4, take 1.0% of the total mass of wheat flour polydextrose, 0.008% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 6 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and let them rise a second time for 25 minutes. Place the dough balls that have risen a second time in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0080] Example 9

[0081] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0082] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0083] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0084] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 79:23:32:16:16:16 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.3:0.3:0.2. The viable count of each of the four strains was 1.0 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0085] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 10% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the dough to release the air, and then spread the dough into a flatbread shape.

[0086] S5. Based on the dry basis of wheat flour as described in S4, take 2.0% of the total mass of wheat flour polydextrose, 0.005% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 3 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and proof them a second time for 25 minutes. Place the proofed dough balls in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0087] Example 10

[0088] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0089] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0090] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0091] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 78:23:32:14:15:1 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.3:0.3:0.2. The viable count of each of the four strains was 2.0 × 10⁻⁶. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% and cultured for 6 h to obtain the starter culture;

[0092] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 15% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the air and spread the dough into a flatbread shape.

[0093] S5. Based on the dry basis of wheat flour as described in S4, take 2.0% of the total mass of wheat flour polydextrose, 0.008% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 8 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it rest at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and proof them a second time for 25 minutes. Place the proofed dough balls in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0094] Example 11

[0095] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0096] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0097] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0098] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 78:24:31:16:17:1 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.2:0.2:0.2, with a viable count of 1.0 × 10⁻⁶ for each of the four strains. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% for 6 h to obtain the starter culture;

[0099] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 10% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the dough to release the air, and then spread the dough into a flatbread shape.

[0100] S5. Based on the dry weight of wheat flour as described in S4, take 2.5% of the total mass of polydextrose, 0.006% of the total mass of tannic acid, and isoamylase (addition amount of 6 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it rest at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and proof them a second time for 25 minutes. Place the proofed dough balls in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0101] Example 12

[0102] This embodiment describes the preparation of low-GI steamed buns, and the specific method includes the following steps:

[0103] S1. The method for preparing fresh wet cells of Saccharomyces cerevisiae HautWYH101801 is the same as in Example 5 S1;

[0104] S2. The preparation method of fresh wet cells of Lactobacillus brevis HautWYHI01802, Lactobacillus plantarum HautWYH101803 and Lactobacillus pentosaccharide HautWYH101804 is the same as in Example 5 S2;

[0105] S3. Wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract were mixed in a mass ratio of 78:23:32:14:15:1 to prepare a compound raw material powder. 45% water was added to every 200 g of the compound raw material powder, and then fresh wet cells of *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804 were added in a volume ratio of 1:0.2:0.2:0.2, with a viable count of 1.5 × 10⁻⁶ for each of the four strains. 8 CFU / mL; after mixing evenly, the dough was placed in a constant temperature incubator at 35℃ and 85% for 6 h to obtain the starter culture;

[0106] S4. Add the leavening agent to the new compound raw material powder at a mass ratio of 12% (the proportion of each component is the same as in S3), then add 45% water and flour, place it in a proofing box at a temperature of 35℃ and a humidity of 85%, and proof for 40 minutes. After proofing, repeatedly roll out the air and spread the dough into a flatbread shape.

[0107] S5. Based on the dry basis of wheat flour as described in S4, take 2.5% of the total mass of wheat flour polydextrose, 0.002% of the total mass of wheat flour tannic acid, and isoamylase (addition amount of 4 U / g wheat flour), dissolve them in a small amount of room temperature water, and evenly pour them onto the surface of the proofed dough. Knead the dough repeatedly until the surface is smooth and delicate, cover it with plastic wrap, let it relax at room temperature for 10 minutes, then divide it into small dough balls of 100 g each and let them rise a second time for 25 minutes. Place the dough balls that have risen a second time in a steamer and steam them in cold water for 20 minutes. After steaming, remove them and let them cool naturally at room temperature for 1 hour to obtain low-GI steamed buns.

[0108] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 5 is that only Saccharomyces cerevisiae HautWYH101801 was added to the microbial agent in this comparative example, while the other steps are the same as in Example 5.

[0111] Comparative Example 2

[0112] The difference between this comparative example and Example 5 is that only Lactobacillus brevis HautWYHI01802 was added to the bacterial agent in this comparative example, while the other steps are the same as in Example 5.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 5 is that only Lactobacillus plantarum HautWYH101803 was added to the bacterial agent in this comparative example, while the other steps are the same as in Example 5.

[0115] Comparative Example 4

[0116] The difference between this comparative example and Example 5 is that only Lactobacillus pentosolicus HautWYH101804 was added to the bacterial agent in this comparative example, while the other steps are the same as in Example 5.

[0117] Comparative Example 5

[0118] The difference between this comparative example and Example 5 is that the microbial agent used in this comparative example is Angel Yeast, with a viable count of 1.0 × 10⁻⁶ cells. 8 CFU / mL, the remaining steps are the same as in Example 5.

[0119] Comparative Example 6

[0120] The difference between this comparative example and Example 5 is that polydextrose, isoamylase, and tannic acid are not added in this comparative example, while the other steps are the same as in Example 5.

[0121] Comparative Example 7

[0122] The difference between this comparative example and Example 5 is that only polydextrose is added in this comparative example, and isoamylase and tannic acid are not added. The remaining steps are the same as in Example 5.

[0123] Comparative Example 8

[0124] The difference between this comparative example and Example 5 is that only isoamylase is added in this comparative example, and polydextrose and tannic acid are not added. The remaining steps are the same as in Example 5.

[0125] Comparative Example 9

[0126] The difference between this comparative example and Example 5 is that only tannic acid is added in this comparative example, and isoamylase and polydextrose are not added. The remaining steps are the same as in Example 5.

[0127] Table 1. Resistant starch (RS3) content and glycemic index (eGI) of steamed buns

[0128]

[0129] As shown in Table 1, compared with the comparative examples, the steamed buns prepared in Examples 5-12 of this invention have the characteristics of high resistant starch (RS3) content and low eGI. According to Chinese health industry standards, a GI ≤ 55 is considered a low-GI food; 55 ≤ GI ≤ 70 is considered a medium-GI food; and GI > 70 is considered a high-GI food. The eGI of the steamed buns prepared in Examples 5-12 of this invention is between 35.68 and 41.64, classifying them as low-GI foods. The eGI of the steamed buns prepared in Comparative Examples 1-9 is between 56.18 and 65.30, classifying them as medium-GI foods.

[0130] This invention isolated and screened four fermentation bacteria from traditional yeasts: *Saccharomyces cerevisiae* HautWYH101801, *Lactobacillus brevis* HautWYHI01802, *Lactobacillus plantarum* HautWYH101803, and *Lactobacillus pentosaccharide* HautWYH101804. These four bacteria were used for multi-strain fermentation of dough, establishing a weakly acidic environment. In this environment, polydextrose was utilized by lactic acid bacteria, metabolizing it to produce organic acids, primarily acetic acid. These organic acids not only regulated the pH of the reaction system and activated isoamylase, but also promoted starch retrogradation to form resistant starch (RS3). Isoamylase hydrolyzed the α-1,6-glycosidic bonds of starch, converting the branched structure into linear starch fragments, providing sufficient substrate for subsequent retrogradation. During high-temperature steaming, starch gelatinizes, disrupting the internal crystalline structure of starch granules and releasing linear starch. The reducing sugars produced during gelatinization oxidize the pyrogallol structure of tannins to quinones. These quinones then covalently cross-link with the reducing ends of linear starch chains, the amino groups of gluten proteins, and fermentation-produced peptides and amino acids, forming a network structure. During cooling, the linear starch chains undergo highly ordered rearrangement and crystallization within the confined space of this network, forming resistant starch with strong thermal stability and high resistance to enzymatic hydrolysis. This effectively delays starch digestion and absorption, reducing the eGI value of the steamed bun. In contrast, Comparative Examples 1-5, which only added a single strain of bacteria for fermentation, suffered from insufficient acetic acid production due to the single bacterial population. This prevented precise pH control of the dough to the optimal range for isoamylase, reducing the enzymatic hydrolysis efficiency of isoamylase and weakening the retrogradation-promoting effect of acetic acid. Consequently, the content of resistant starch (RS3) decreased, and the eGI value increased. Comparative Example 6, without the addition of polydextrose, isoamylase, and tannic acid, relied solely on multi-strain fermentation. While it produced acid, the lack of polydextrose resulted in limited production of organic acids such as acetic acid. The absence of isoamylase led to a severe deficiency of linear starch substrate, and the lack of tannic acid prevented the formation of a covalent network, affecting the formation of resistant starch (RS3), thus increasing the eGI value. Comparative Example 7, with the addition of polydextrose only, allowed the fermenting bacteria to produce acid, but the starch could not be debranched to form linear starch. The lack of linear starch substrate and the inability to form a covalent cross-linked network resulted in this problem. Comparative Example 8, with the addition of isoamylase only, resulted in insufficient production of organic acids such as acetic acid due to a lack of carbon source, reducing the efficiency of isoamylase hydrolysis. Although a small amount of linear starch was produced, the lack of a tannic acid cross-linked network for encapsulation and anchoring led to loose and unstable starch crystals formed during cooling, which were easily destroyed during digestion. Comparative Example 9, with the addition of tannic acid only, formed a cross-linked network, but the starch was not extensively debranched, making it difficult for long-chain starch to effectively rearrange and crystallize, resulting in limited resistant starch (RS3) production.

[0131] Table 2. Texture properties of steamed buns

[0132]

[0133] As shown in Table 2, Comparative Examples 1-5, which only added a single strain of bacteria for fermentation, resulted in limited resistant starch production and an unbalanced gluten network structure. Comparative Example 6, which completely lacked functional components, produced steamed buns with high hardness and chewiness, poor elasticity and resilience, and significant crumb shedding during consumption.

[0134] Comparative Example 7, with the addition of polydextrose alone, reduced the hardness to 3796.55±113.56 g, but the lack of a cross-linking network resulted in limited improvement in elasticity, leading to a mushy and sticky texture. Comparative Example 8, with the addition of isoamylase alone, produced linear starch, reducing the hardness to 3368.07±127.57 g, but due to the lack of tannic acid anchoring, the resulting starch crystal structure was loose and easily destroyed, exhibiting a low cohesiveness of only 0.75±0.02, making it prone to crumbling during consumption. Comparative Example 9, with the addition of tannic acid alone, enhanced cross-linking, elasticity, and resilience, but lacked the water-retaining properties of polysaccharides and enzymatic modification, resulting in a still relatively high hardness. Compared to Comparative Examples 7-9, Examples 5-12 produced a significant synergistic effect: the fermenting bacteria utilized the acetic acid produced by polydextrose metabolism to regulate the pH of the dough; isoamylase hydrolyzed starch at the optimal pH to produce linear starch, providing numerous cross-linking anchors for tannic acid and constructing a stable starch-polyphenol network; simultaneously, the water-retaining properties of polydextrose softened the texture of this network. Therefore, the steamed buns prepared in Examples 5-12 have a hardness of 2046.33±95.76~2534.91±122.12 g, an elasticity of 0.82±0.03~0.95±0.04, a cohesiveness of 0.75±0.02~0.88±0.02, a chewiness of 1658.24±36.85~1825.27±45.25, and a resilience of 0.54±0.05~0.66±0.02, exhibiting excellent qualities of being moderately soft, refreshing, non-sticky, and quick to rebound when pressed.

[0135] Table 3 Sensory evaluation criteria for low-GI steamed buns

[0136] Ten evaluators (5 males and 5 females, aged 20-34) with sensory evaluation experience were selected to form a sensory evaluation team. Sensory evaluation of low-GI steamed bun samples was conducted based on the specific volume and sensory properties of the steamed buns. The evaluation criteria are shown in Table 3.

[0137] Table 4 Sensory Evaluation Scores

[0138] As shown in Table 4, the preparation methods of Examples 5-12 of this invention achieve the regulation of steamed bun quality in the post-fermentation stage, and this mechanism is directly reflected in various dimensions of sensory evaluation. First, in terms of internal structure and elasticity, this invention utilizes the weakly acidic environment of the fermented dough to activate isoamylase. The linear starch fragments generated by the hydrolysis of starch α-1,6-glycosidic bonds not only provide sufficient substrates for the formation of resistant starch, but more importantly, reduce the content of short-chain dextrins that cause a sticky texture. At the same time, tannic acid is oxidized to quinone during high-temperature steaming, and covalently cross-links with the amino or thiol groups of gluten protein to form a dense and resilient protein-polyphenol complex network. This network, while encapsulating gas, endows the dough with excellent gas retention and resilience, thereby giving the steamed bun a uniform and delicate pore structure and excellent elasticity. Secondly, regarding specific volume and appearance, polydextrose, as the carbon source for fermentation bacteria, metabolizes in a weakly acidic environment to produce organic acids, primarily acetic acid. This not only optimizes the pH of the reaction system to match enzyme activity but also synergistically strengthens the gluten network, allowing the dough to maintain good proofing tolerance and ultimately achieve a firm and full appearance. Thirdly, regarding toughness and stickiness, the debranching action of isoamylase removes short-chain dextrins from amylopectin at the molecular level, which easily cause stickiness. Meanwhile, the covalent network formed by tannins anchors and encapsulates the rearranged linear starch crystals, preventing crystal damage during cooling or reheating and avoiding the crumbly defect caused by loose starch crystallization. This results in a soft, chewy, and non-sticky steamed bun. Finally, in terms of flavor, the fermentation bacteria utilize acetic acid and other flavor substances produced by polydextrose metabolism, as well as flavor substances generated by tannins during the thermal reaction, to jointly construct a mellow and rich flavor background, effectively harmonizing any undesirable flavors from buckwheat flour, mulberry leaf extract, and other whole grain components.

[0139] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing low-GI steamed buns, characterized in that, Includes the following steps: S1. Take the compound raw material powder, add water, and then add fresh wet cells of brewer's yeast, lactobacillus brevis, lactobacillus plantarum and lactobacillus pentosaccharide. After mixing evenly, place the dough in a constant temperature incubator to ferment and obtain the leavening agent. S2. Take a new compound raw material powder, add a leavening agent and water, knead the dough, let it rise, repeatedly roll out the dough to release the air, and spread the dough into a flatbread shape. Set aside. Based on the dry basis of the compound raw material powder, dissolve polydextrose, tannic acid and isoamylase in a small amount of room temperature water, and evenly pour it onto the surface of the risen flatbread. Knead the dough repeatedly until the surface is smooth and delicate, cover with plastic wrap, let it relax at room temperature, and then divide it into small dough balls of equal weight. Let them rise a second time, place the risen dough in a steamer and steam with cold water. After steaming, remove the dough and let it cool naturally at room temperature to obtain low-GI steamed buns.

2. The method for preparing a low-GI steamed bun according to claim 1, characterized in that, The components of the composite raw material powder in step S1 include wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract; the mass ratio of wheat flour, tartary buckwheat flour, sweet buckwheat flour, gluten, high amylose, and mulberry leaf extract is 77~81:20~24:29~33:14~18:13~17:

1.

3. The method for preparing a low-GI steamed bun according to claim 1, characterized in that: The *Saccharomyces cerevisiae* strain mentioned in step S1 is HautWYH101801, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67133; *Lactobacillus brevis* is HautWYHI01802, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67134; *Lactobacillus plantarum* is HautWYH101803, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67135; and *Lactobacillus pentosaccharide* is HautWYH101804, deposited at the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC No:67136.

4. The method for preparing a low-GI steamed bun according to claim 1, characterized in that: In step S1, the volume ratio of fresh and wet cells of *Saccharomyces cerevisiae*, *Lactobacillus brevis*, *Lactobacillus plantarum*, and *Lactobacillus pentosus* is 1:0.1~0.3:0.1~0.3:0.1~0.3; the viable count of *Saccharomyces cerevisiae* is 1.0~2.5×10⁻⁶. 8 CFU / mL, viable count of Lactobacillus brevis is 1.0~2.5×10⁻⁶. 8 CFU / mL, viable count of Lactobacillus plantarum is 1.0~2.5×10⁻⁶. 8 The viable count of Lactobacillus pentosus was 1.0~2.5×10 CFU / mL. 8 CFU / mL.

5. The method for preparing a low-GI steamed bun according to claim 1, characterized in that: The fermentation time in step S1 is 6-8 hours.

6. The method for preparing a low-GI steamed bun according to claim 1, characterized in that: In step S2, the amount of fermentation agent added to the compound raw material powder is 10-15%.

7. The method for preparing a low-GI steamed bun according to claim 1, characterized in that: In step S2, the amount of polydextrose added to the composite raw material powder is 0.5-3%, the amount of tannic acid added to the composite raw material powder is 0.002-0.01%, and the amount of isoamylase added to the composite raw material powder is 3-10 U / g.

8. The low-GI steamed bun prepared by the preparation method according to any one of claims 1 to 7.

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