Preparation method of high-activity green banana powder with biological de-browning and structure modification

Abstract

The application discloses a preparation method of high-activity green banana powder with biological astringency removal and structure modification, and belongs to the technical field of starch modification. The application adopts a compound fermentation strain system of plant lactobacillus plantarum Lp90 and animal bifidobacterium lactis BLa80, carries out solid-state fermentation under micro-oxygen conditions, and directionally degrades astringency substances on the surface layer of starch particles; gradient low-temperature drying technology and low-temperature ultrafine grinding are combined to realize the regulation effect of modifying only the surface structure of starch and reserving the complete internal crystal structure. The method does not add any chemical reagent in the whole process, the prepared green banana powder has a tannin degradation rate of no less than 83%, a cold water solubility of no less than 12%, a cold water dispersion turbidity retention rate of no less than 89% and a RS2 resistant starch retention rate of no less than 93%, effectively solves the problem that the astringency removal effect, cold water dispersion performance and resistant starch retention rate are difficult to be considered in the traditional preparation process, the process has low energy consumption, can realize large-scale continuous production, the finished product has no bitter and astringent flavor, and can be widely applied to the field of food.

Description

Technical Field

[0001] This invention relates to a method for preparing highly active green banana powder through biological deastringency and structural modification, belonging to the field of starch modification technology. Background Technology

[0002] Green banana powder is rich in RS2 resistant starch. Even samples without enzymatic extraction can achieve an RS purity of around 60%, making it one of the fruit and vegetable sources with the highest natural RS particle content. Green banana powder has functions such as low glycemic index, regulating intestinal flora, and improving metabolism, making it a popular functional non-grain raw material in recent years.

[0003] However, directly processing green banana raw materials into highly active functional powders faces three major technical bottlenecks, making it difficult to improve overall quality: First, the large amount of condensed tannins and gallic polyphenols in green bananas causes a strong astringent taste. Existing conventional water washing, blanching, and single fermentation de-astringency processes struggle to achieve a balance between de-astringency and resistant starch retention. Incomplete de-astringency can lead to poor palatability, while excessively strong processing (such as extrusion puffing) can easily cause degradation and structural damage to the resistant starch. Second, the high crystallinity and dense, smooth surface of natural green banana starch particles result in poor wettability in cold water and a tendency for the powder to agglomerate. Existing technologies often employ physical methods such as ultrafine grinding for refining. For example, CN102987282A discloses a method for preparing ultrafine natural banana resistant starch, which uses vacuum freeze-drying combined with ultrafine grinding to prepare resistant starch. The product particle size can reach 20–30 μm, exhibiting good looseness and flowability. However, this physical refining process can only reduce particle size and is difficult to improve surface hydrophilicity without damaging the core crystal structure. Third, existing patents and literature mainly focus on optimizing single steps in the processing of green banana starch / whole banana powder—such as adjusting extraction process parameters, improving drying methods, optimizing color protection processes, or adjusting ordinary pulverizing parameters. Bai Yongliang et al. compared the effects of three modification methods—compound enzyme method, lactic acid fermentation method, and extrusion puffing method—on the characteristics of green banana starch. Among them, fermentation modification of the prepared banana starch using lactic acid bacteria showed that fermentation treatment could, to some extent, increase the mass fraction of resistant starch and reduce sedimentation. Furthermore, CN102793120A discloses a method for preparing whole banana powder, which has the technical effects of delicate taste, no astringency, non-hygroscopicity, and good dispersibility. However, its use of citric acid color protection combined with hot air blanching and deastringency removal process involves high heat treatment intensity during deastringency removal and does not target the retention of resistant starch structure, still resulting in the problem of resistant starch degradation and loss.

[0004] Therefore, existing patents and literature mostly focus on optimizing single drying processes, improving conventional color-protecting processes, and adjusting ordinary pulverizing parameters. There are few integrated technical systems that combine targeted metabolic modification of the microbial surface layer, controllable reconstruction of starch granule structure, and gradient low-temperature crystal form locking. This makes it difficult to simultaneously achieve comprehensive quality improvements such as low astringency, high cold water dispersibility, high RS retention rate, and high storage stability. Therefore, the industry urgently needs a high-level modification technology solution with innovative mechanisms, unique processes, and industrializability. Summary of the Invention

[0005] To address the challenges of existing technologies in simultaneously achieving effective deastringency removal, cold water dispersibility, and retention of resistant starch, as well as insufficient targeted modification and limited improvement in powder structure and properties, this invention provides a method for preparing highly active green banana powder based on bio-directed deastringency removal and controllable starch structure modification. A specific composite probiotic system is used to precisely degrade surface astringent substances, and low-temperature physical modification is employed to reconstruct the starch structure by destroying only the surface layer without damaging the internal structure. Combined with gradient low-temperature crystal form locking technology, a high-end green banana powder with low astringency, high cold water dispersibility, high RS2 retention rate, and high storage stability is obtained, providing a new technological path for the high-quality industrial production of functional green banana powder.

[0006] To achieve the above objectives, this invention provides a method for preparing highly active, low-astringency green banana powder based on bio-directed deastringency and controllable structural modification, comprising the following steps: (1) Wash, peel, slice and soak green bananas to obtain green banana slices; (2) Treat the green bananas to inactivate enzymes; (3) Inoculate the enzyme-inactivated green banana slices with mixed bacterial agent and ferment in solid state for 18-24 h to directionally degrade the tannins and fruit gums on the surface of starch granules to obtain fermentation products; (4) The fermentation product is subjected to gradient drying to obtain the dried product; (5) The dried product is subjected to low-temperature ultrafine pulverization at 8-12℃ to obtain green banana powder; The mixed microbial agent includes *Lactobacillus plantarum* (… Lactiplantibacillus plantarum ) and Bifidobacterium animalis subsp. lactis ( Bifidobacterium animalis subsp. lactis The viable bacteria ratio was (2.5–3.5):1; The gradient drying includes: First stage of drying: temperature 38-42℃, wind speed 0.8-1.0 m / s, drying to a moisture content of 20%-25%; The second stage of drying: the temperature is 43-47℃, the wind speed is 1.0-1.2 m / s, and the moisture content is dried to 10%-15%. The third stage of drying: the temperature is 47-51℃, the wind speed is 1.1-1.3 m / s, and the moisture content is dried to 6%-8%.

[0007] In one embodiment of the present invention, in step (1), the thickness of the slices of the green banana is 1.5 to 3.0 mm; after slicing, the slices are soaked in ice water for 1 to 5 minutes and then drained.

[0008] In one embodiment of the present invention, in step (1), the pulp starch of the green banana is ≥28%.

[0009] In one embodiment of the present invention, in step (2), the enzyme inactivation is performed by sequentially treating at 80-85°C for 30-40 seconds and then at 85-90°C for 20-30 seconds.

[0010] In one embodiment of the present invention, in step (3), the total viable count of the mixed bacterial agent is 1 × 10⁻⁶. 9 ~5×10 9 CFU / mL; preferably 2×10 9 CFU / mL.

[0011] In one embodiment of the present invention, in step (3), the inoculation amount is 2% to 5% (v / w); preferably 3% (v / w).

[0012] In one embodiment of the present invention, the *Lactobacillus plantarum* in the mixed microbial agent is *Lactobacillus plantarum* (… Lactiplantibacillus plantarum Lp90, the Bifidobacterium animalis subsp. lactis is Bifidobacterium animalis subsp. lactis ( Bifidobacterium animalis subsp. lactis )BLa80.

[0013] In one embodiment of the present invention, in step (3), the solid-state fermentation temperature is 28-32°C, the humidity is 75%-85%, and the oxygen content is 5%-10%.

[0014] In one embodiment of the present invention, in step (4), the first stage of drying is performed at a temperature of 38–42°C, a wind speed of 0.8–1.0 m / s, and a drying time of 3–5 h. The second stage of drying: the temperature is 43-47℃, the wind speed is 1.0-1.2 m / s, and the drying time is 5-7 h; The third stage of drying: the temperature is 47-51℃, the wind speed is 1.1-1.3 m / s, and the drying time is 1.5-2.5 h.

[0015] In one embodiment of the present invention, in step (5), the pulverizing speed is 2200-2400 r / min; after pulverization, the material is passed through a 120-160 mesh sieve.

[0016] In one embodiment of the present invention, the green banana powder from step (5) is sterilized.

[0017] In one embodiment of the present invention, the sterilization is ultraviolet hot air sterilization, the sterilization temperature is ≤40℃, and the sterilization time is 10-20 min; the packaging is vacuum light-proof packaging.

[0018] A second objective of this invention is to provide green banana powder prepared by the method described above.

[0019] In one embodiment of the present invention, the microstructure of the green banana powder is a porous hydrophilic surface and a highly crystalline RS2 starch core; the finished product has a tannin degradation rate of ≥83%, a cold water dispersion turbidity retention rate of ≥89%, an RS2 resistant starch retention rate of ≥93%, and no obvious bitter or astringent odor.

[0020] A third objective of this invention is to provide a food product comprising the green banana powder.

[0021] In one embodiment of the present invention, the food is a fermented food, baked food, dairy product, beverage, solid beverage, meal replacement powder, or energy bar.

[0022] A fourth objective of this invention is to provide the application of the preparation method or the green banana powder in the preparation of food, health food, pharmaceuticals, or feed additives.

[0023] Compared with the prior art, the present invention has the following advantages: (1) This invention constructs a composite strain system using *Lactobacillus plantarum* Lp90 and *Bifidobacterium animalis* subsp. *lactobacter* BLa80, and conducts microaerobic solid-state fermentation modification treatment. The deastringency effect is achieved through the surface-directed action of the strains. Compared with single-strain fermentation and direct processing without fermentation, this system can directionally degrade tannins and polyphenols on the surface of starch granules, significantly reducing the bitter flavor of green banana powder, while not invading the starch core and destroying the RS2 crystal structure. It can simultaneously achieve efficient deastringency removal and high-resistant starch retention.

[0024] (2) This invention couples the fermentation process with a three-stage gradient low-wind-speed heat pump low-temperature crystal-locking drying process, which slowly removes free water and bound water from the material through staged gradient treatment. Traditional constant-temperature hot air drying is prone to causing high-temperature gelatinization of starch, resulting in a large amount of degradation and loss of resistant starch; in contrast, this invention adopts a mild temperature control mode throughout the process, which can effectively avoid the collapse of starch crystals and can stably maintain the retention rate of RS2 resistant starch at more than 93%.

[0025] (3) In this invention, solid-state fermentation is first used to achieve the biological disruption and softening of the cell walls on the surface of green banana chips. Then, low-temperature controllable ultrafine grinding at 8-12℃ is used to modify the surface of starch granules, inducing them to form a porous hydrophilic structure. Conventional high-temperature and high-force pneumatic grinding will cause overall structural tearing of starch granules. This invention can achieve precise control by destroying only the surface structure of the granules while completely preserving the internal crystalline structure, significantly improving the turbidity of the powder in cold water dispersion. After stirring in cold water, no hard agglomeration occurs, solving the common industry problem of poor water solubility and easy sedimentation of natural resistant starch.

[0026] (4) The entire processing flow of this invention does not add any chemical additives such as color protectants or dispersants, and only relies on the synergistic effect of biological fermentation and physical modification to improve the quality of powder. Compared with the modification process that adds chemical modifiers, this technical route fully meets the current development requirements of food clean labeling, has no risk of chemical residues, and can be adapted to the application scenarios of various food products such as meal replacement products and infant supplementary diets.

[0027] (5) The present invention uses low temperature heat pump drying to replace the traditional vacuum freeze drying process. In view of the defects of high energy consumption and large scale production cost of vacuum freeze drying process, the present invention can significantly reduce production energy consumption and processing cost; and the raw materials used are commercially available strains with stable supply chain and stronger industrialization feasibility. Attached Figure Description

[0028] Figure 1 This is a comparison chart of the two main indicators under different strain ratios of the present invention; Figure 2 This is a comparison chart of the two main indicators under different fermentation times of the present invention; Figure 3 This is a comparison chart of the two main indicators of the present invention at different fermentation temperatures. Detailed Implementation

[0029] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0030] In the examples, solutions without a specific solvent are water; operations without a specific temperature refer to room temperature, which is 15-35°C; and percentages without a specific meaning refer to mass percentages.

[0031] The test methods involved in the following embodiments: In this invention, all performance indicators of the green banana powder were tested using the following method, and all samples were tested at a constant temperature of 25 ℃: 1. Determination of soluble tannins and tannin degradation rate: The soluble tannin content of the samples was determined by the Folin-phenol colorimetric method, and a standard curve was established using gallic acid as the standard. Formula for calculating tannin degradation rate:

[0032] 2. Determination of RS2 resistant starch content: The AOAC2002.02 standard method was used for detection. The RS2 resistant starch retention rate was calculated by enzymatic hydrolysis, separation, hydrolysis, color development and quantification. Formula for calculating RS2 resistant starch retention rate:

[0033] 3. Determination of turbidity retention rate in cold water dispersion: Accurately weigh 2 g of green banana powder, add 100 mL of 25 ℃ deionized water, stir magnetically for 30 s, and let stand for 5 min; take the upper suspension and measure the turbidity value using a turbidimeter; Formula for calculating the retention rate of dispersed turbidity in cold water:

[0034] 4. Cold water solubility determination: Accurately weigh 2 g of powder, add 100 mL of 25 ℃ deionized water, stir magnetically for 60 min, centrifuge at 3000 r / min for 10 min, take the supernatant, dry and weigh it, and calculate the percentage of dissolved substances in the powder mass. Formula for calculating the solubility of cold water:

[0035] 5. Powder particle size observation: The median volume D50 of the powder was determined using a laser particle size analyzer; the sample after pulverization and passing through a 140-mesh sieve was directly diluted and tested on the instrument.

[0036] 6. Observation of agglomeration during room temperature storage: Seal the powder and place it in a room temperature environment of 25℃ for 30 days. Take it out and pass it through a 140-mesh standard sieve. Record the quality of agglomeration on the sieve. The less agglomeration, the better the stability of the powder.

[0037] The raw materials used in the following examples: Green bananas: Judgment is based on the appearance and color of the peel and the texture of the flesh. The peel is generally greenish-blue with clear ridges, and the flesh is firm. The starch content of the flesh is 30.2%, based on fresh weight, and was determined using the method for determination of starch in food (GB 5009.9-2023).

[0038] Lactobacillus plantarum Lp90 and Bifidobacterium animalis subsp. lactis BLa80: Commercially available food-grade probiotic powder from Microcon Probiotics (Suzhou) Co., Ltd.

[0039] Aspergillus niger: Commercially available food-grade Aspergillus niger spore powder meets the microbial safety standards for food processing.

[0040] Example 1: Highly active green banana powder modified by microaerobic solid-state fermentation using a compound strain This embodiment utilizes a compound bacterial strain to prepare green banana powder, as detailed below: 1. Raw material preparation: Wash and peel green bananas, cut into 2.2 mm thin slices, soak in ice water for 3 minutes, and then drain. 2. Segmented enzyme inactivation: Place the drained green banana slices from step 1 at 83 ℃ for 35 s, then raise the temperature to 87 ℃ for 25 s. 3. Preparation of fermentation broth: A bacterial suspension of *Lactobacillus plantarum* Lp90 and a bacterial suspension of *Bifidobacterium animalis* subsp. *lactamase* BLa80 were mixed at a viable cell ratio of 3:1 to obtain a total viable cell count of 2 × 10⁻⁶. 9 A mixed bacterial suspension with CFU / mL; 4. Inoculation and fermentation: Spread the enzyme-inactivated green banana slices from step 2 evenly on a sterile fermentation tray in a single layer, with the thickness controlled to be 1 layer. Then, spray the prepared mixed bacterial suspension evenly at an inoculation rate of 3% (v / w) by dry weight. After gently mixing and stirring evenly, place it in a constant temperature and humidity incubator at 30 ℃, 80% humidity, and 7% oxygen content for solid-state fermentation for 21 h. 5. Gradient drying: First stage drying: drying temperature 40 ℃, air velocity 0.9 m / s, drying time 4 h, drying to a moisture content of 22.6%; Second stage drying: drying temperature increased to 45 ℃, air velocity 1.1 m / s, drying time 6 h, drying to a moisture content of 11.4%; Third stage drying: drying temperature 49 ℃, air velocity 1.2 m / s, drying time 2 h, until the final moisture content is 7.1%. 6. Low-temperature pulverization: Place the dried banana slices from step 5 into a low-temperature ultrafine pulverizer and pulverize them at 10 ℃ and 2300 r / min. The pulverized material is then passed through a 140-mesh sieve to obtain sieved green banana powder. 7. Sterilization and Packaging: Place the green banana powder obtained in step 6 into a UV hot air sterilizer at ≤40 ℃ for 15 min, and then vacuum seal it in a light-proof environment.

[0041] The results showed that the banana powder prepared in this embodiment did not clump significantly and had no bitter taste after 30 days of storage.

[0042] Comparative Example 1: Preparation of green banana powder from untreated green bananas Untreated green bananas were used as the blank group. Green bananas of the same batch and maturity as those in Example 1 were selected and subjected to only washing, peeling, slicing, ice water soaking, and draining. They were then directly dried with conventional room temperature hot air and pulverized at room temperature, and passed through a 140-mesh sieve to obtain unmodified blank green banana powder.

[0043] Example 2: Highly active green banana powder modified by microaerobic solid-state fermentation using a composite strain This embodiment is based on Example 1, except that the ratio of live bacteria to the two strains in step 3 of the fermentation stage is adjusted to 1:1, 2.5:1, 3:1, 3.5:1, and 5:1, while the remaining steps are the same as in Example 1. See Table 1 for details. Figure 1 As shown: Table 1. Effect of live bacteria ratio on green banana powder

[0044] The above results indicate that when the ratio of viable bacteria of *Lactobacillus plantarum* Lp90 to *Bifidobacterium lactis* BLa80 is 3:1, the tannin degradation effect is optimal, and the retention rate of RS2 resistant starch and cold water dispersibility are also at their highest levels. Further increasing the proportion of *Bifidobacterium lactis* BLa80 will actually reduce the tannin degradation rate, RS2 resistant starch, and cold water solubility.

[0045] Example 3: Highly active green banana powder modified by microaerobic solid-state fermentation using a compound strain This embodiment is based on Example 1, except that the fermentation time in step 4 is adjusted to 15 h, 20 h, 21 h, 22 h, and 30 h, while the remaining steps are the same as in Example 1. See Table 2 for details. Figure 2 As shown: Table 2 Effect of fermentation time on green banana powder

[0046] The above results indicate that within the fermentation time range of 20-22 hours, the overall levels of tannin degradation, cold water dissolution and dispersion, and RS2 resistant starch retention remained relatively high. When the fermentation time was shortened to 15 hours, the fermentation reaction was insufficient, the enzyme production of the strain was inadequate, the tannin degradation rate was only 63.7%, and the cold water solubility and cold water dispersion turbidity retention rates were significantly reduced, resulting in a severe astringent residue in the finished product. When the fermentation time was extended to 30 hours, over-fermentation occurred, and the continuous metabolic activity of the microorganisms began to erode the surface structure of the starch granules, causing a significant loss of RS2 resistant starch, with the RS2 retention rate decreasing to 86.1%. Simultaneously, the cold water dispersion performance deteriorated significantly.

[0047] Example 4: Highly active green banana powder modified by microaerobic solid-state fermentation using a composite strain This embodiment is based on Example 1, except that the low-temperature pulverization temperature in step 6 is adjusted to 5℃, 10℃, and 15℃, while the remaining steps are the same as in Example 1. See Table 3 for details. Figure 3 As shown: Table 3. Effect of low-temperature grinding temperature on green banana powder

[0048] The above results indicate that at a temperature of 5 ℃, the friction of the powder particles is insufficient, fewer hydrophilic pores are formed on the surface, and the cold water dispersion ability is weak; at 15 ℃, the heat generation during pulverization is significant, the starch core is degraded by heat, and the RS2 resistant starch decreases significantly; 10 ℃ is the optimal temperature for balancing the hydrophilic modification of the surface and protecting the resistant starch, so this temperature is considered the better value.

[0049] Comparative Example 2 Referring to Example 1, the difference is that the compound bacteria fermentation process (steps 3 and 4) is omitted, while the remaining steps are the same as in Example 1. The green banana slices after segmented enzyme inactivation are directly subjected to gradient drying, pulverization, and sterilization.

[0050] Comparative Example 3 Referring to Example 1, the difference is that only a single Lactobacillus plantarum Lp90 was used for fermentation (2 × 10⁻⁶ live bacteria). 9 (CFU / mL), without the addition of Bifidobacterium lactis subsp. BLa80, and the other parameters are the same as in Example 1.

[0051] Comparative Example 4 Referring to Example 1, the difference is that only a single type of Bifidobacterium animalis subsp. lactis BLa80 was used for fermentation (2 × 10⁻⁶ live bacteria). 9 (CFU / mL), without the addition of Lactobacillus plantarum Lp90, and the other parameters are the same as in Example 1.

[0052] Comparative Example 5 Referring to Example 1, the difference lies in adjusting the three-stage gradient heat pump drying in step 5, replacing the gradient drying with 55 ℃ constant temperature hot air drying, and the remaining steps are the same as in Example 1.

[0053] Comparative Example 6 Referring to Example 1, the difference lies in adjusting the pulverizing temperature in step 6, turning off the water cooling system of the pulverizing chamber, pulverizing the dried green banana slices at 2300 r / min at a normal temperature of 25 ℃, and passing them through a 140-mesh sieve. The remaining steps are the same as in Example 1.

[0054] Comparative Example 7 Referring to Example 1, the difference lies in adjusting the low-temperature pulverization in step 6, replacing it with directly crushing the dried banana chips using a regular pulverizer (not ultrafine pulverization), and sieving them through a 140-mesh standard sieve. The remaining steps are the same as in Example 1.

[0055] Comparative Example 8 Refer to Example 1, except that the compound strain is replaced with Aspergillus niger.

[0056] Comparative Example 9 Referring to Example 1, the difference is that after washing and peeling the green bananas in step 1, they are directly mashed into banana puree and then placed in an ice bath for 3 minutes. The rest is the same as in Example 1.

[0057] Table 4. Results of performance testing of banana powder for each comparative example.

[0058] Regarding the deastringency removal effect, the soluble tannin content of untreated green banana powder (Comparative Example 1) was 6.73%, and the tannin degradation rate was calculated based on this. The blank control group, without any treatment, had a tannin degradation rate of 0%. Comparative Example 2, without fermentation, showed only a 12.7% tannin degradation, with a large amount of astringent substances remaining. The degradation effect of single-strain fermentation (Comparative Examples 3 and 4) was far lower than that of the dual-strain combination example, proving that Lp90 and BLa80 have a synergistic effect in degrading tannins, and that compound fermentation is the core process for achieving deep deastringency removal.

[0059] Regarding the cold water solubility and dispersion effect, the cold water solubility of the treated green banana powder (Comparative Example 1) was 6.5%, and the cold water dispersion turbidity retention rate was 11.4%. The cold water solubility of Comparative Example 2 was only 6.8%. The cold water solubility of Comparative Example 6, which was pulverized at room temperature, was only 7.1%. Example 1 achieved the best result of 12.5%, with the highest simultaneous turbidity retention rate, proving that the dual modification of fermentation surface perforation combined with low-temperature ultrafine modification is the key to improving cold water solubility and preventing agglomeration. The cold water solubility of Comparative Example 6, which was pulverized at room temperature, was significantly reduced because the hydrophilic structure of the green banana surface was damaged due to the excessively high pulverization temperature.

[0060] Regarding the retention of resistant starch, only 76.4% of RS2 resistant starch was retained in Comparative Example 5, which was dried by hot air, and only 84.7% in Comparative Example 6. In all examples using gradient drying, the RS2 resistant starch content was higher than 91%. The three-stage gradient low-temperature drying can effectively protect the starch core crystalline structure and avoid high-temperature degradation.

[0061] Comparative Example 8 used *Aspergillus niger* instead of the compound probiotic of this invention. *Aspergillus niger* possesses a strong tannin-degrading ability, but it also secretes multiple complex hydrolytic enzymes. Besides decomposing tannins, *Aspergillus niger* excessively degrades the surface structure of starch granules, eroding the RS2 resistant starch core, resulting in a retention rate of only 75.3%. Simultaneously, the powder's cold water solubility and dispersion performance significantly decreased. This invention aims to achieve moderate modification of the starch granule surface, degrading only surface astringent substances while preserving the starch core crystals as much as possible. Excessive enzymatic hydrolysis damages the granule structure, severely impairing the core functional indicators of the powder.

[0062] In Comparative Example 9, banana slices were replaced with banana puree. After the material was pulped and compacted, the porosity of the material layer disappeared, making it impossible to maintain the microaerobic solid-state fermentation environment. Simultaneously, a large number of fruit pulp cells were broken down, resulting in the dissolution of large amounts of intracellular sugars and polyphenols, leading to a loss of metabolic control in the fermentation system. The final sample showed a tannin degradation rate of only 44.6%, severe loss of RS2 resistant starch, and a significant deterioration in cold water solubility and dispersion performance. This further confirms the necessity of using a slicing process and maintaining material porosity in the pretreatment stage for the entire microaerobic solid-state fermentation process.

[0063] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a highly active, low-astringency green banana powder, characterized in that, Includes the following steps: (1) Wash, peel, slice and soak green bananas to obtain green banana slices; (2) Treat the green bananas to inactivate enzymes; (3) Inoculate the enzyme-inactivated green banana slices with mixed bacterial agent and ferment in solid state for 18-24 h to directionally degrade the tannins and fruit gums on the surface of starch granules to obtain fermentation products; (4) The fermentation product is subjected to gradient drying to obtain the dried product; (5) The dried product is subjected to low-temperature ultrafine pulverization at 8-12℃ to obtain green banana powder; The mixed microbial agent includes *Lactobacillus plantarum* (… Lactiplantibacillus plantarum ) and Bifidobacterium animalis subsp. lactis ( Bifidobacterium animalis subsp. lactis The viable bacteria ratio was (2.5–3.5):1; The gradient drying includes: First stage of drying: temperature 38-42℃, wind speed 0.8-1.0 m / s, drying to a moisture content of 20%-25%; The second stage of drying: the temperature is 43-47℃, the wind speed is 1.0-1.2 m / s, and the moisture content is dried to 10%-15%. The third stage of drying: the temperature is 47-51℃, the wind speed is 1.1-1.3 m / s, and the moisture content is dried to 6%-8%.

2. The preparation method according to claim 1, characterized in that, In step (1), the pulp starch of green bananas is ≥28%, and the slice thickness is 1.5-3.0 mm; after slicing, soak in ice water for 1-5 minutes and then drain.

3. The preparation method according to claim 1, characterized in that, In step (2), the enzyme inactivation is achieved by sequentially treating the enzyme at 80-85℃ for 30-40 seconds and then at 85-90℃ for 20-30 seconds.

4. The preparation method according to claim 1, characterized in that, In step (3), the total viable count of the mixed microbial agent is 1×10⁻⁶. 9 ~5×10 9 CFU / mL, the inoculation amount is 2% to 5% (v / w).

5. The preparation method according to claim 1, characterized in that, In step (3), the solid-state fermentation temperature is 28-32°C, the humidity is 75%-85%, and the oxygen content is 5%-10%.

6. The preparation method according to claim 1, characterized in that, In step (5), the pulverizing speed is 2200-2400 r / min; after pulverization, the material is passed through a 120-160 mesh sieve.

7. The preparation method according to claim 1, characterized in that, The green banana powder from step (5) is sterilized.

8. A highly active, low-astringency green banana powder, characterized in that, The green banana powder is prepared by any one of the preparation methods described in claims 1 to 7; the powder surface is porous and hydrophilic, and the core is highly crystalline RS2 starch; the cold water dispersion turbidity retention rate is ≥89%, the tannin degradation rate is ≥83%, the RS2 resistant starch retention rate is ≥93%, and there is no bitter or astringent odor.

9. A food product, characterized in that, The food product includes the green banana powder as described in claim 8.

10. The preparation method according to any one of claims 1 to 7 or the green banana powder according to claim 8 in the preparation of food, health food, pharmaceutical or feed additive.

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