Preparation method and application of high-palatability carrot dietary fiber

Abstract

The invention provides a preparation method and application of high-palatability carrot dietary fibers. The method comprises the following steps: (1) washing and dicing carrots; (2) cellulase and saccharifying enzyme enzymolysis; (3) constructing a two-phase system, adding a compound enzyme and pectinase, and carrying out gradient enzymolysis; (4) carrying out enzyme deactivation and centrifugation to obtain a water phase; (5) performing gradient centrifugation to obtain mixed fibers; (6) precipitating, and collecting precipitated fibers; (7) adding carrot source nano cellulose to obtain a composite fiber with a core-shell structure; and (8) drying, crushing and sieving. According to the preparation method disclosed by the invention, the core problems of rough taste (large particle size), astringent taste (residual acetyl groups and terpene substances), weak function and low purity in the traditional carrot dietary fiber preparation process are solved through a water-alcohol two-phase gradient composite enzymolysis and nano cellulose composite purification process; and finally, the high-palatability carrot dietary fiber which is fine, smooth, free of rough feeling, natural, fresh and sweet, high in purity and strong in function is prepared.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method for preparing highly palatable carrot dietary fiber and its application. Background Technology

[0002] With increasing health awareness among residents, dietary fiber, as the "seventh type of nutrient," is seeing a continuous expansion in demand for applications in the food and health product sectors. The global market size for plant-based dietary fiber has been increasing year by year. Among them, carrot dietary fiber, due to its natural source and rich beta-carotene content, has become a popular category of plant fiber, widely used in baked goods, dairy products, and special dietary foods. However, the current market demand for dietary fiber has shifted from "simply supplementing quantity" to "emphasizing both quantity and quality," especially in the food sector, where consumers are increasingly demanding a balance between health and taste. Traditional high-fiber foods (such as whole-wheat bread and high-fiber yogurt) generally have low consumer acceptance due to the rough texture and astringent taste of their dietary fiber. Therefore, developing highly palatable and functional carrot dietary fiber has become a key direction for resolving the industry's supply and demand imbalance.

[0003] Traditional carrot dietary fiber preparation mainly employs two processes: conventional physical methods and single enzymatic hydrolysis. While both achieve fiber extraction, they suffer from insurmountable technical challenges. For example, traditional physical methods, involving high-temperature cooking and mechanical pulverization, not only easily lead to the loss of nutrients like β-carotene but also result in coarse fiber particles and a rough texture. Single enzymatic hydrolysis, using only cellulase extraction, cannot effectively remove acetyl groups (the main source of astringency) and impurities such as pectin and free proteins, resulting in low product purity and significant flavor defects. The core contradiction currently facing carrot dietary fiber preparation is that neither traditional processes nor existing improved technologies can achieve synergistic optimization of palatability, purity, functional properties, and nutrient retention. Either the high temperatures and mechanical pulverization of physical methods lead to poor palatability and nutrient loss, or the numerous impurities and inferior flavor of single enzymatic hydrolysis limit application scenarios, failing to meet the food industry's urgent need for highly palatable plant dietary fiber. Therefore, developing a highly palatable dietary fiber has become crucial for overcoming industry technical bottlenecks and filling market gaps. Summary of the Invention

[0004] Technical Problem to be Solved: To address the aforementioned technical problems, the purpose of this invention is to provide a method for preparing highly palatable carrot dietary fiber and its application. Through a water-alcohol biphase gradient enzymatic hydrolysis and nanocellulose composite purification process, the core problems of rough texture, astringent taste, low water-holding capacity, and low purity in traditional carrot dietary fiber preparation are solved. Ultimately, a highly palatable carrot dietary fiber is obtained, with a texture upgraded from rough and astringent to smooth and naturally sweet; purity increased from 85%-90% to 92.5%-94.2%; water-holding capacity enhanced from <0.9g / g to 0.95-1.06g / g; and β-carotene retention rate improved from <85% to 86.5%-89.5%.

[0005] Technical solution: A method for preparing highly palatable carrot dietary fiber, comprising the following steps: (1) Select fresh, mold-free carrots, rinse them with running water, place them in an ultrasonic treatment tank, and immediately cut them into cubes along the fiber direction after treatment. (2) Put the mixture into an enzymatic hydrolysis tank, add 0.2-0.25% of the carrot mass of cellulase and 0.1-0.13% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.0-5.5, set the temperature to 40℃, stir at 40-50 r / min, and keep the mixture warm for 2-2.5 h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and ethanol phase to form a two-phase system. Add 0.2-0.3% of a complex enzyme (arabinofuranyl esterase, acetylxylanase, and xylooligosaccharase at a mass ratio of 2:(1-1.5):1) and 0.02% of a pectinase (specific activity ≥5 U / mg) for carrots, and perform gradient enzymatic hydrolysis. Phase 1 (0-45 min): 42℃, activate arabinofuranase to remove arabinose residues from the side chain of arabinoxylan; The second stage (45-100 min): at 46℃, acetylated xylan esterase and xylooligosaccharase work synergistically to decompose acetyl groups (source of astringency) and residual oligosaccharides (to avoid sticking to teeth); at the same time, 0.08% of food-grade modified diatomaceous earth (particle size 3-5 μm) by the weight of carrots is added to adsorb terpene astringent substances. The third stage (100-120 min): 43℃, gently treat the residual fiber fragments to ensure sufficient enzymatic hydrolysis; during the enzymatic hydrolysis, the alcohol phase extracts oligosaccharides in real time, and converts them into glucose under the catalysis of the carrot's own natural organic acids (such as malic acid and citric acid), further supplementing endogenous sweet substances, while adsorbing impurities to avoid the product inhibiting enzyme activity. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase (containing dietary fiber and endogenous glucose) and the alcohol phase (containing a small amount of unbound glucose, adsorbent and ethanol). The alcohol phase is distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers; centrifuge at 8000 r / min for 10 min to collect fine-sized fibers; mix the medium-sized fibers and fine-sized fibers in a specific ratio to obtain mixed fibers; (6) Transfer the mixed fiber liquid into a sedimentation tank, add a 1% chitosan solution, mix for 10 min at a stirring speed of 20-25 r / min, remove negatively charged free proteins and small molecule pectin by charge adsorption; cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose (particle size 50-80nm) at 1.6-1.8% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, and shear at high speed at 3200r / min for 18min to make the nanocellulose uniformly coat the surface of the core fiber through hydrogen bonds; then cool down to 8-10℃, add 0.04-0.06% of food-grade trehalose, and stir at low speed at 30r / min for 20min to obtain a composite fiber with a "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is ≤8%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0006] Furthermore, in step (1), the carrot has a fiber content ≥15% and β-carotene ≥8mg / 100g.

[0007] Furthermore, the ultrasonic treatment parameters in step (1) are: 40kHz frequency, 300W power, water temperature of 25-30℃, and treatment time of 20min.

[0008] Furthermore, in step (2), the specific activity of cellulase is ≥1000 U / g; and the specific activity of saccharifying enzyme is ≥50 U / mg.

[0009] Furthermore, in step (5), the medium-sized fiber has a particle size of 50-100 μm; the fine-sized fiber has a particle size of 20-50 μm.

[0010] Furthermore, in step (5), the specific ratio of medium-sized fibers to fine-sized fibers is (3-4):5.

[0011] Furthermore, in step (6), the amount of chitosan solution added is 0.3% of the mixed fibers.

[0012] Furthermore, in step (7), the carrot-derived nanocellulose is prepared by pretreatment of carrot peel residue with citric acid and gradient high-pressure homogenization (70MPa→90MPa→100MPa).

[0013] The highly palatable carrot dietary fiber prepared by the above preparation method.

[0014] The application of the above-mentioned highly palatable carrot dietary fiber in baked goods, dairy products and health foods. Beneficial effects

[0015] 1. This invention solves the core problems of traditional carrot dietary fiber preparation, such as rough texture (large particle size), astringent taste (acetyl groups remaining), weak function (low water holding capacity), and low purity (many impurities), through a water-alcohol biphase gradient complex enzymatic hydrolysis and nanocellulose complex purification process. The final result is a highly palatable carrot dietary fiber with an upgraded taste from rough and astringent to delicate and naturally sweet, a purity increased from 85%-90% to 92.5%-94.2%, a water holding capacity enhanced from <0.9g / g to 0.95-1.06g / g, and a β-carotene retention rate increased from <85% to 86.5%-89.5%.

[0016] 2. This invention introduces a two-phase system with an aqueous phase to alcohol phase ratio of 7:3. 1. It can directionally remove astringent substances and improve palatability. Terpenes are easily soluble in ethanol and can quickly detach from the aqueous phase fiber surface during enzymatic hydrolysis and enter the alcohol phase. The modified diatomaceous earth added to the alcohol phase fixes the terpenes in the alcohol phase within the pores through physical adsorption, preventing them from re-attaching to the fiber surface. The astringent substance residue rate in Examples 2-12 is only 2.5%-2.9%, while the astringent residue rate in Comparative Example 4 (single aqueous phase) without the two-phase system reaches 7.8%. This proves that the two-phase system can increase the astringent substance removal rate by more than 65%, and the sensory "no astringency" score reaches 2.5-2.9 points. 2. Alleviating product inhibition and improving enzymatic hydrolysis efficiency: Oligosaccharides (such as xylobiose and cellobiose) produced by enzymatic hydrolysis tend to accumulate in the aqueous phase, inhibiting the activity of complex enzymes. The alcohol phase can extract these oligosaccharides in real time, maintaining the oligosaccharide concentration in the aqueous phase below 0.5%, avoiding enzyme activity inhibition. After the product is extracted, the equilibrium of the enzymatic hydrolysis reaction shifts to the positive side, improving the degradation efficiency of fiber by the complex enzyme. 3. Assisting in the removal of impurities and improving fiber purity: The alcohol phase can dissolve free proteins and carotenoid degradation pigments that are difficult to remove in the aqueous phase, preventing these impurities from mixing with the fiber. Combined with the subsequent chitosan precipitation step, the two-phase system can remove most of the soluble impurities first, reducing the impurity adsorption pressure of chitosan, and ultimately improving the purity of dietary fiber.

[0017] 3. The temperature of the biphase system of this invention is synchronously controlled with gradient enzymatic hydrolysis. At its optimal temperature of 46℃, acetylated xylan esterase significantly reduces the residual acetyl groups. Combined with the adsorption of astringent substances by modified diatomaceous earth, the final product achieves a sensory "no astringency" score of 2.5-2.9, an improvement of 25%-45% compared to traditional products. Xylo-oligosaccharase efficiently decomposes the oligosaccharides (such as xylobiose and cellobiose) produced by enzymatic hydrolysis at 46℃, resulting in an oligosaccharide residual rate of ≤10%, completely avoiding the "sticky" problem of traditional fiber products and achieving a "no sticky feeling." The score reached 1.8-1.9; arabinofuranase removed arabinose residues from the fiber side chain at 42℃, making the fiber backbone easier to decompose and further reducing the particle size to 44-52μm; pectinase simultaneously degraded pectin impurities, and together with the dissolving effect of alcohol on free proteins and pigments, it laid the foundation for subsequent purification, and finally the purity of dietary fiber was increased to 92.5%-94.2%, and the water holding capacity was increased to 0.95-1.06g / g due to the increased microporous structure of the fiber.

[0018] 4. This invention utilizes the "cavitation effect" of ultrasonic pretreatment to impact the carrot cell wall, making the cell wall structure loose and increasing the pore size. Simultaneously, the high-frequency vibration of ultrasound accelerates the molecular movement of water and nutrients within the cell, reducing resistance to material transport and thus improving subsequent enzymatic hydrolysis efficiency. With the cell wall loosened, cellulase and saccharifying enzymes can quickly enter the cell and fully contact substrates such as cellulose and starch, increasing the enzymatic hydrolysis rate and avoiding the problem of "insufficient enzymatic hydrolysis leading to coarse fiber residue" in traditional processes. The final fiber particle size can be reduced to 44-51 μm, fundamentally solving the "rough texture." Furthermore, the ultrasonic treatment temperature is low, far lower than traditional high-temperature cooking, preventing the loss of β-carotene due to high-temperature oxidation and improving β-carotene retention. In addition, the directional vibration of ultrasound promotes the dissolution of effective fiber components while inhibiting the dissolution of impurities such as pectin and lignin (because the molecular structure of impurities differs from that of fibers, their response to ultrasound varies greatly), reducing the difficulty of subsequent purification.

[0019] 5. This invention employs multi-enzyme synergy and gradient temperature control to achieve dual optimization of palatability and functionality. Cellulase can specifically decompose the β-1,4 glycosidic bonds of cellulose, breaking down crude fiber into fine fiber and improving fiber fineness; saccharifying enzyme can decompose starch into glucose (a natural source of sweetness), imparting a natural sweetness. The two work synergistically—after cellulase destroys the fiber structure, saccharifying enzyme can contact starch more efficiently, while the dissolution of glucose can reduce the astringency on the fiber surface (glucose molecules can cover the astringent sites on the fiber surface), and can also shorten the enzymatic reaction time.

[0020] 6. This invention uses gradient centrifugation to precisely control the particle size distribution and obtain fibers of different particle sizes, thereby balancing "fineness" and "functionality". Fine fibers improve fineness, while medium fibers ensure water retention.

[0021] 7. This invention uses carrot-derived nanocellulose, which is wrapped around the surface of the mixed fibers by hydrogen bonds, filling micropores, reducing surface roughness, and significantly improving the fineness. The sensory "fineness" score reaches 2.4-2.9 points. Furthermore, it optimizes the hydrophilicity of the fiber surface and, together with trehalose, forms a stable core-shell structure through low-temperature cross-linking.

[0022] 8. This invention uses chitosan precipitation. Chitosan can form complexes with soluble impurities in the enzymatic hydrolysate through charge adsorption. At the same time, the low temperature of 5°C promotes the aggregation of the complexes. After filtration through a 5μm filter cloth, impurities can be separated efficiently. Chitosan itself is biodegradable, and the amount added is only 0.3%, with no risk of residue. At the same time, the chitosan precipitation is carried out at a low temperature, avoiding the destruction of β-carotene by high temperature, and further improving the retention rate of β-carotene.

[0023] 9. This invention employs vacuum low-temperature drying and slight pulverization. Low temperature can prevent the fiber structure from shrinking due to high temperature, while high temperature will cause the fiber micropores to close, reducing water retention capacity and reducing the oxidative loss of β-carotene and glucose. Slight pulverization can break the dried fiber block into fine particles, while avoiding excessive pulverization that would damage the fiber microporous structure.

[0024] 10. The highly palatable carrot dietary fiber of the present invention has strong applicability: Based on its high palatability and strong function, it can be widely used in food, health products, special diets and other fields. For example, in the food field, it can be incorporated into baked goods and dairy products without additional seasoning, solving the problem of "poor taste of high-fiber foods"; in the health product field, it is delicate and has no roughness, and is highly accepted by the elderly and children, avoiding the problem of traditional supplements being difficult to swallow. Detailed Implementation

[0025] This invention proposes a method for preparing highly palatable carrot dietary fiber and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following will provide a more detailed description of the invention with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0026] Cellulase was purchased from Sigma-Aldrich, product number: C2605, specific activity ≥1000 U / g; glucoamylase was purchased from Sigma-Aldrich, product number: 10115, specific activity 70 U / mg; pectinase was purchased from Sigma-Aldrich, product number: P4716, specific activity ≥5 U / mg; arabinofuranosylase was purchased from Shaanxi Chenming Biotechnology Co., Ltd., specific activity ≥20 U / mg; acetylated xylan esterase was purchased from Nanjing Beiyu Biotechnology Co., Ltd., product number: BYMZ-E-AXEAO-1KU, specific activity ≥40 U / mg; xylooligosaccharase, specific activity 25-40 U / mg.

[0027] Example 1 The preparation method of carrot-derived nanocellulose is as follows: Step 1: Take carrot peel and pulp, wash it clean, mix it with 0.3% citric acid solution at a mass ratio of 1:5, soak it in a 55℃ constant temperature water bath for 25 minutes, stirring once every 5 minutes (50r / min), rinse with deionized water until the pH is neutral, and drain. Step 2: Put the mixture into a colloid mill, set the speed to 2000 r / min, process for 10 min to obtain a coarsely ground slurry with a particle size of 500-800 μm, transfer it to a high-speed pulper, set the speed to 10000 r / min, process for 12 min to obtain a fine slurry with a particle size of 100-200 μm. Step 3: Use a high-pressure homogenizer and apply a gradient pressure treatment: First stage: Pressure 70MPa, circulation for 12min, to reduce fiber length to 1-5μm; Second stage: Pressure 90MPa, circulation 12min, to reduce particle size to 100-200nm; Third stage: Pressure 100MPa, circulation 12min, to obtain carrot-derived nanocellulose with a particle size of 50-80nm.

[0028] Example 2 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase and 0.1% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.6% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 8°C, add 0.04% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.2%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product. Example 3

[0029] A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 25℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase and 0.1% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3:5 to obtain mixed fibers. The mixed fiber liquid was transferred to a sedimentation tank, and 0.3% of the mixed fiber was added to a 1% chitosan solution. The mixture was stirred at 20 r / min for 10 min, cooled to 5℃, and allowed to stand for 30 min. The precipitated fiber was collected by vacuum filtration using a 5 μm filter cloth. Add 1.6% of the dry weight of the precipitated fiber to the carrot-derived nanocellulose prepared in Example 1, add 2 times the volume of deionized water, shear at 3200 r / min for 18 min, cool to 8°C, add 0.04% food-grade trehalose, stir at 30 r / min for 20 min to obtain a composite fiber with a "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 6.7%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product. Example 4

[0030] A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 30℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase and 0.1% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.5h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.6% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 8°C, add 0.04% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 8.0%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product. Example 5

[0031] A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.25% of the carrot mass of cellulase and 0.13% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.3% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.5:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 5 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 4:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.8% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 10℃, add 0.06% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.0%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product. Example 6

[0032] A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.25% of the carrot mass of cellulase and 0.13% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.3% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.5:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 5 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 4:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.8% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 10℃, add 0.06% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 6.9%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0033] Example 7 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.25% of the carrot mass of cellulase and 0.13% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.5h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.3% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.5:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 5 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 4:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.8% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 10℃, add 0.06% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.9%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0034] Example 8 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.22% of the carrot mass of cellulase and 0.11% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.25% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.2:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 4 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3.5:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.7% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 9°C, add 0.05% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.2%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0035] Example 9 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 26℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase and 0.12% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at the temperature for 2.2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.3:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.6% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 8°C, add 0.045% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with a "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.3%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0036] Example 10 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 29℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.24% of the carrot mass of cellulase and 0.1% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.2h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.28% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.4:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 5 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 4:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.8% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 10℃, add 0.055% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.2%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0037] Example 11 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 27℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment. (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.21% of the carrot mass of cellulase and 0.11% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.1h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.22% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 4 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers at a ratio of 3.2:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.65% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 8.5℃, add 0.042% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with a "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.5%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0038] Example 12 A method for preparing highly palatable carrot dietary fiber includes the following steps: (1) Select fresh, mold-free carrots (carrot fiber content 15.6%, β-carotene 8.7mg / 100g), rinse them with running water, place them in an ultrasonic treatment tank for treatment, the ultrasonic treatment parameters are: 40kHz frequency, 300W power, water temperature 28℃, treatment time 20min, and immediately cut them into 2cm×2cm×1cm cubes along the fiber direction after treatment; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.23% of the carrot mass of cellulase and 0.12% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.2, set the temperature to 40℃, stir at 45r / min, and keep the reaction at this temperature for 2.4h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.27% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1.4:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 4 μm; third stage (100-120 min): 43℃. (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers with a particle size of 50-100 μm; centrifuge at 8000 r / min for 10 min to collect fine fibers with a particle size of 20-50 μm. Mix the medium-sized fibers and fine fibers in a ratio of 3.8:5 to obtain mixed fibers. (6) Transfer the mixed fiber liquid into a sedimentation tank, add 0.3% of the mixed fiber and 1% chitosan solution, mix at a stirring speed of 20 r / min for 10 min, cool to 5℃, let stand for 30 min, vacuum filter with 5 μm filter cloth, and collect the precipitated fiber. (7) Add carrot-derived nanocellulose prepared in Example 1 at 1.75% of the dry weight of the precipitated fiber, add 2 times the volume of deionized water, shear at high speed at 3200 r / min for 18 min, then cool down to 9.5℃, add 0.058% food-grade trehalose, stir at low speed at 30 r / min for 20 min to obtain composite fiber with "core-shell" structure. (8) Transfer the composite fiber with the core-shell structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is 7.7%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

[0039] Comparative Example 1 The difference between this comparative example and Example 2 is that there is no ultrasonic pretreatment; (1) Select fresh, mold-free carrots (carrots contain 15.6% fiber and 8.7mg / 100g of β-carotene), rinse them with running water, and cut them directly into 2cm×2cm×1cm cubes along the fiber direction (omit ultrasonic treatment). Steps (2)-(8) are completely consistent with those in Example 2, namely: put the mixture into an enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase and 0.1% of the carrot mass of saccharifying enzyme, add 5 times the carrot mass of deionized water, adjust the pH to 5.2, set the temperature to 40°C, stir at 45 r / min, and keep the mixture warm for 2.2 h; subsequent steps (3)-(8) are the same as in Example 2.

[0040] Comparative Example 2 The difference between this comparative example and Example 2 is that only saccharifying enzyme is added, and cellulase is not added; (1) The steps are completely consistent with those in Example 2; (2) Add the carrot to the enzymatic hydrolysis tank, add 0.1% of the carrot mass of saccharifying enzyme (without cellulase), add 5 times the carrot mass of deionized water, adjust the pH to 5.2, the temperature to 40℃, the stirring speed to 45r / min, and keep the reaction at this temperature for 2.2h. Steps (3)-(8) are completely consistent with those in Example 2, namely: food-grade 95% ethanol is added at a volume ratio of 7:3 between the aqueous phase and the alcohol phase to form a two-phase system, and 0.2% of the carrot mass of the compound enzyme (mass ratio 2:1:1) and 0.02% of the pectinase are added for gradient enzymatic hydrolysis; subsequent steps (4)-(8) are the same as those in Example 2.

[0041] Comparative Example 3 The difference between this comparative example and Example 2 is that only cellulase was added, and no saccharifying enzyme was added; (1) The steps are completely consistent with those in Example 2; (2) Add the enzyme to the enzymatic hydrolysis tank, add 0.2% of the carrot mass of cellulase (non-saccharifying enzyme), add 5 times the carrot mass of deionized water, adjust the pH to 5.2, the temperature to 40℃, the stirring speed to 45r / min, and keep the reaction at this temperature for 2.2h. Steps (3)-(8) are completely consistent with those in Example 2, namely: food-grade 95% ethanol is added at a volume ratio of 7:3 between the aqueous phase and the alcohol phase to form a two-phase system, and 0.2% of the carrot mass of the compound enzyme (mass ratio 2:1:1) and 0.02% of the pectinase are added for gradient enzymatic hydrolysis; subsequent steps (4)-(8) are the same as those in Example 2.

[0042] Comparative Example 4 The difference between this comparative example and Example 2 is that there is no alcohol phase, and it is a single aqueous phase enzymatic hydrolysis. Steps (1) and (2) are completely consistent with those in Example 2; (3) Without adding food-grade 95% ethanol (single aqueous phase), add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3 μm; third stage (100-120 min): 43℃; Steps (4)-(8) are completely consistent with those in Example 2, namely: after the enzymatic hydrolysis is completed, the temperature is raised to 88°C and kept at 8 min to inactivate the enzyme, and after cooling, the temperature is increased to 3000 r / min and centrifuged for 15 min (aqueous phase only). The subsequent gradient centrifugation, chitosan precipitation, nanocomposite, drying and pulverizing steps are all the same as in Example 2.

[0043] Comparative Example 5 The difference between this comparative example and Example 2 is that it does not contain a complex enzyme, but only pectinase; Steps (1) and (2) are completely consistent with those in Example 2; (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add only 0.02% of the carrot mass of pectinase (specific activity 5 U / mg, no compound enzyme) for gradient enzymatic hydrolysis: first stage (0-45min): 42℃; second stage (45-100min): 46℃, while adding 0.08% of the carrot mass of food-grade modified diatomaceous earth with a particle size of 3μm; third stage (100-120min): 43℃. Steps (4)-(8) are completely consistent with those in Example 2, namely: after enzymatic hydrolysis, the steps of separating the water-alcohol phase, gradient centrifugation, chitosan precipitation, nanocomposite, and drying and pulverizing are all the same as in Example 2.

[0044] Comparative Example 6 The difference between this comparative example and Example 2 is that no modified diatomaceous earth was used; Steps (1) and (2) are completely consistent with those in Example 2; (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and the alcohol phase to form a two-phase system. Add 0.2% of the carrot mass of a complex enzyme (arabinofuranyl esterase, acetyloxylanase and xylooligosaccharase in a mass ratio of 2:1:1) and 0.02% of the carrot mass of pectinase (specific activity 5 U / mg) for gradient enzymatic hydrolysis: first stage (0-45 min): 42℃; second stage (45-100 min): 46℃ (without adding modified diatomaceous earth); third stage (100-120 min): 43℃; Steps (4)-(8) are completely consistent with those in Example 2, namely: after enzymatic hydrolysis, the steps of separating the water-alcohol phase, gradient centrifugation, chitosan precipitation, nanocomposite, and drying and pulverizing are all the same as in Example 2.

[0045] Comparative Example 7 The difference between this comparative example and Example 2 is that in step (5), the mixing ratio of medium-sized fibers and fine-sized fibers is 1:5 (medium:fine), and the rest is the same as in Example 2.

[0046] Comparative Example 8 The difference between this comparative example and Example 2 is that it does not contain carrot-derived nanocellulose; Steps (1)-(6) are completely consistent with those in Example 2; (7) Take the precipitated fiber, add 2 times the volume of deionized water directly, shear at 3200 r / min for 18 min, then cool down to 8℃, add 0.04% food-grade trehalose, stir at 30 r / min for 20 min (without carrot-derived nanocellulose) to obtain the fiber; (8) The steps are exactly the same as in Example 2, namely: the fiber is transferred into a vacuum dryer, dried at 50°C and 0.08MPa to a moisture content of 7.2%, and then pulverized through an 80-mesh sieve to obtain the product.

[0047] Comparative Example 9 The difference between this comparative example and Example 2 is that it does not contain chitosan solution; Steps (1)-(5) are completely consistent with those in Example 2; The mixed fiber solution was transferred to a sedimentation tank, cooled directly to 5°C, and allowed to stand for 30 minutes. The solution was then vacuum filtered using a 5μm filter cloth to collect the precipitated fibers (chitosan-free solution). Steps (7)-(8) are completely consistent with those in Example 2, namely: add carrot-derived nanocellulose at 1.6% of the dry weight of the precipitated fiber, shear at high speed, add trehalose, dry and pulverize and pass through an 80-mesh sieve to obtain the product.

[0048] Performance testing: Sensory rating: out of 10 points, scored by a panel of 10 professional judges based on the dimensions of "smoothness (3 points), sweetness (2 points), no astringency (3 points), no stickiness (2 points)," and the average score is taken. Dietary fiber purity: determined according to GB5009.88-2014 "Determination of Dietary Fiber in Food"; Average particle size: determined using a laser particle size analyzer; β-Carotene retention rate: determined by high performance liquid chromatography (HPLC), retention rate = (content in product / content in raw material) × 100%; Water-holding capacity: Place the sample (weight recorded as m1, accurate to 0.001g) into a 50mL centrifuge tube, add 30mL of deionized water (water temperature 25℃±0.5℃, controlled by a constant temperature water bath), stir at low speed with a magnetic stirrer for 2min (speed 100r / min), tighten the centrifuge tube cap, and let it stand in a constant temperature water bath at 25℃±0.5℃ for 2h without stirring (to avoid damaging the water molecule layer adsorbed by the fiber), centrifuge to separate free water, centrifuge parameters: speed 3500r / min, centrifugation time 20min; Post-centrifugation treatment: slowly pour out the supernatant (free water), weigh the sample after water absorption, and record it as m2, accurate to 0.001g). Calculation formula: Water holding capacity (g / g) = (m2-m1) / m1; Expansion force: measured by graduated cylinder method, unit: mL / g (the number of milliliters of volume expansion per gram of fiber after absorbing water). Glucose content: determined by the glucose oxidase method, reflecting the source of natural sweetness; the results are shown in Table 1 below: Table 1 Dietary fiber purity (%) Average particle size (μm) β-carotene retention rate (%) Water holding capacity (g / g) Expansion force (mL / g) Glucose content (%) Example 2 93.5 48 88.2 1.01 12.5 0.92 Example 3 92.8 51 87.5 0.97 12.2 0.88 Example 4 93.2 49 86.8 0.99 12.3 0.90 Example 5 94.2 45 89.5 1.06 12.8 0.95 Example 6 93.8 47 88.8 1.03 12.6 0.93 Example 7 94.0 46 88.1 1.05 12.7 0.94 Example 8 93.9 44 89.0 1.04 12.6 0.93 Example 9 93.1 50 87.9 1.00 12.4 0.91 Example 10 93.7 47 88.5 1.02 12.5 0.89 Example 11 92.9 49 87.2 0.98 12.1 0.87 Example 12 93.6 46 88.3 1.03 12.5 0.90 Comparative Example 1 88.6 65 81.2 0.89 10.3 0.75 Comparative Example 2 85.3 82 78.5 0.84 9.8 0.80 Comparative Example 3 92.1 50 87.0 0.98 12.0 0.12 Comparative Example 4 93.2 58 88.6 0.96 11.9 0.89 Comparative Example 5 90.5 53 86.2 0.94 11.8 0.90 Comparative Example 6 93.0 48 87.3 0.95 11.5 0.91 Comparative Example 7 93.0 38 87.3 0.88 10.8 0.91 Comparative Example 8 92.7 55 86.5 0.91 11.2 0.90 Comparative Example 9 89.8 52 82.5 0.91 11.2 0.90 Sensory evaluation: The maximum score is 10 points. A professional judging panel of 10 people scored the samples based on the dimensions of "smoothness (3 points), sweetness (2 points), no astringency (3 points), and no stickiness (2 points)". The average score was taken and the results are shown in Table 2 below. Table 2 Fineness (3 points) Sweetness (2 points) No astringent taste (3 points) No sticky feeling on teeth (2 points) Total Score Example 2 2.6 1.8 2.6 1.8 8.8 Example 3 2.4 1.7 2.5 1.7 8.3 Example 4 2.5 1.8 2.5 1.7 8.5 Example 5 2.9 1.9 2.9 1.9 9.6 Example 6 2.7 1.9 2.8 1.8 9.2 Example 7 2.8 1.9 2.8 1.9 9.4 Example 8 2.8 1.8 2.8 1.8 9.2 Example 9 2.5 1.9 2.6 1.7 8.7 Example 10 2.7 1.7 2.7 1.8 8.9 Example 11 2.3 1.7 2.4 1.6 8.0 Example 12 2.7 1.8 2.8 1.9 9.2 Comparative Example 1 1.8 1.5 2.2 1.5 7 Comparative Example 2 1.5 1.6 2 1.4 6.5 Comparative Example 3 2.5 0.3 2.6 1.8 7.2 Comparative Example 4 2.3 1.6 2.3 1.7 7.9 Comparative Example 5 2.4 1.8 2.1 1.6 7.9 Comparative Example 6 2.6 1.8 1.9 1.7 8.0 Comparative Example 7 2.1 1.8 2.5 1.6 8.0 Comparative Example 8 2.5 1.8 2.6 1.7 8.6 Comparative Example 9 2.5 1.8 2.2 1.7 8.2 As shown in Tables 1 and 2 above, the dietary fiber purity of Examples 2-12 ranged from 92.8% to 94.2%, with Examples 5 (94.2%), 7 (94.0%), and 8 (93.9%) exhibiting the highest purity. This is mainly because these three examples used higher doses of the compound enzyme, which more effectively degraded impurities such as pectin and free protein. Simultaneously, the chitosan precipitation step precisely removed soluble impurities through charge adsorption, further enhancing purity. Comparative Example 2 had the lowest purity among the comparative examples. Because it only added saccharifying enzymes and lacked cellulase, it could not effectively decompose crude fiber, resulting in a significant increase in the amount of coarse residue and impurities remaining. Comparative Example 9 (89.8%) lacked chitosan solution, and therefore could not remove fine impurities such as free protein and small-molecule pectin from the enzymatic hydrolysate, resulting in a 3.7 percentage point decrease in purity compared to Example 2. Comparative Example 1 (88.6%) omitted ultrasonic pretreatment, resulting in an insufficiently loosened carrot cell wall, preventing the enzymatic hydrolysate from fully contacting the substrate, leading to a large amount of residual coarse residue and a 4.9 percentage point decrease in purity. The average particle size of Examples 2-12 is 44-51 μm, with Examples 8, 5, and 7 having the finest particle size. The key is that high enzyme content and gradient enzymatic hydrolysis can accurately decompose the fiber structure. Combined with gradient centrifugation, fine fibers with a particle size of 20-50 μm and medium-sized fibers with a particle size of 50-100 μm are screened out and mixed in a ratio of (3-4):5 to ensure fineness while avoiding excessive agglomeration. Comparative Example 2 had the coarsest particle size. Due to the lack of cellulase, the coarse fibers could not be decomposed, directly resulting in a sensory "fineness" score of only 1.5 points (Table 2), the lowest among all groups. Comparative Example 1 had a relatively coarse particle size. Due to the lack of ultrasonic pretreatment, the fiber structure was compact, making enzymatic hydrolysis difficult to penetrate, and the particle size increased by 35.4% compared to Example 2. Comparative Example 7 had an excessively fine particle size. Although the fineness was acceptable (2.1 points) due to the 1:5 mixing ratio of medium and fine-sized fibers, the fine fibers were prone to agglomeration, resulting in an expansion force of only 10.8 mL / g (a decrease of 13.6% compared to 12.5 mL / g in Example 2). The β-carotene retention rate of Examples 2-12 was 86.8%-89.5%, with Examples 5, 8, and 10 having the highest retention rates. This was mainly due to the low temperature and vacuum drying throughout the enzymatic hydrolysis process, and the fact that the chitosan precipitation and nanocellulose composite could form a "double encapsulation," reducing the loss of β-carotene in subsequent processing. Comparative Example 2 had the lowest retention rate because the lack of cellulase led to insufficient enzymatic hydrolysis, requiring a longer incubation time to ensure fiber extraction. This indirectly increased the exposure time of the 88°C enzyme inactivation step, resulting in a decrease in the thermal stability of β-carotene. Comparative Example 9 had a relatively low retention rate because the lack of chitosan encapsulation made β-carotene prone to oxidation upon contact with air during centrifugation and drying, resulting in a 5.7 percentage point decrease in retention rate compared to Example 2.Examples 2-12 exhibited water-holding capacity of 0.97-1.06 g / g and swelling capacity of 12.1-12.8 mL / g, with Example 5 showing the best performance (water-holding capacity 1.06 g / g, swelling capacity 12.8 mL / g). The key factor was the high enzyme content, which effectively decomposed the fiber, creating more microporous structures and enhancing water absorption and swelling capacity. Comparative Example 2 had the worst water-holding capacity and swelling capacity due to its high proportion of coarse fiber and fewer internal pores, resulting in weak water absorption and swelling capacity. Comparative Example 1 also had relatively low water-holding capacity and swelling capacity due to its dense fiber structure, fewer micropores, and decreased functional properties, decreasing by 11.9% and 17.6% respectively compared to Example 2. Examples 2-12 had a glucose content of 0.87%-0.95%, all meeting the requirements for natural sweetness (sensory "sweetness" score of 1.7-1.9). Examples 5 and 7 had the highest glucose content because the glucoamylase dosage was increased to 0.13%, allowing for more complete decomposition of carrot starch into glucose. Comparative Example 3, due to the addition of only cellulase and the absence of saccharifying enzyme, had a glucose content of only 0.12% (far lower than 0.92% in Example 2), directly resulting in a "sweetness" score of only 0.3 points (the lowest among all groups) and a total sensory score of only 7.2 points. Comparative Example 6, lacking modified diatomaceous earth, could not adsorb terpenoid astringent substances in the alcohol phase, resulting in a "no astringency" score of only 1.9 points (a decrease of 26.9% compared to 2.6 points in Example 2), and a total sensory score of 8.0 points. Comparative Example 8, lacking carrot-derived nanocellulose, had increased fiber surface roughness, resulting in a "fineness" score of 2.5 points (a decrease of 3.8% compared to 2.6 points in Example 2), and a total sensory score of 8.6 points, slightly lower than 8.8 points in Example 2.

[0049] The highly palatable carrot dietary fiber prepared in Example 5 was applied to whole wheat bread to solve the technical problem of "roughness and crumb".

[0050] Basic recipe (based on 1000g of flour) Table 3 raw material Regular whole wheat bread recipe Optimized formula with added carrot dietary fiber High-gluten flour 500g 450g Whole wheat flour 500g 500g Carrot dietary fiber 0g 50g white sugar 100g 85g yeast 10g 11g water 650mL 700mL butter 40g 40g Salt 10g 10g The specific steps are as follows: Step 1: Mixing raw materials First, mix the dietary fiber with the high-gluten flour and whole wheat flour evenly (dry mix for 3 minutes) to prevent the fiber from clumping together; then add sugar, salt, and yeast, and finally add water and butter to ensure that the fiber is fully dispersed in the dough and reduce local rough particles; Step 2: Adjusting kneading parameters Use a dual-speed dough mixer: knead at low speed (100r / min) for 5 minutes until the ingredients form a dough, and at high speed (200r / min) for 12 minutes (3 minutes longer than the regular recipe) to ensure that the gluten is fully formed (fibers will slightly hinder the gluten network, so the kneading time needs to be extended) to avoid the bread's internal structure becoming loose and crumbly. Step 3: Fermentation Control First fermentation: temperature 28℃, humidity 75%, time 60min (10min longer than the regular recipe). After the fibers absorb water, the fermentation speed of the dough slows down, so the time needs to be extended to ensure volume. Second fermentation: Temperature 38℃, humidity 85%, time 40 minutes, to ensure the bread expands fully and has even internal air pockets; Step 4: Baking parameters Oven temperature: 180℃ top heat, 200℃ bottom heat, 35 minutes (same as regular recipe). The fiber is heat resistant (treated at 50℃ during the drying stage), there is no burnt smell during baking, and the β-carotene retention rate is 89.5%, and the bread surface is naturally golden yellow.

[0051] Performance testing: Table 4 Data metrics Regular whole wheat bread (control) Whole wheat bread with added carrot dietary fiber Dietary fiber content 6.5g / 100g 11.2g / 100g Taste rating (out of 10, blind taste test) 6.2 points (obvious roughness) 9.4 points (no roughness) Crumb rate (after cooling for 1 hour after baking) 8.5% (by weight) 1.8% Shelf life (25℃, sealed) 3 days (it hardens on the 3rd day) 6 days (still soft on the 6th day, with strong water-locking properties of the fibers) Moisture content 35% (after cooling) 39% β-carotene content 0mg / 100g 0.83mg / 100g The highly palatable carrot dietary fiber prepared in Example 8 was applied to soft cakes to solve the technical problem of "dry and hard texture".

[0052] Basic recipe (based on 500g of flour) Table 5 raw material Plain soft cake recipe Soft cake recipe with added carrot dietary fiber Cake flour 500g 460g Carrot dietary fiber 0g 40g white sugar 200g 170g egg 300g 300g vegetable oil 100g 100g water 80mL 100mL baking powder 5g 5g Using conventional soft cake preparation methods, the key optimization points are as follows: When mixing the batter, use the "folding method" (avoid stirring in circles) to prevent the fibers from breaking the air bubbles formed by whipping the eggs, ensuring the cake is soft and fluffy; Baking temperature: 170℃ top heat, 160℃ bottom heat, 25 minutes (5 minutes shorter than the regular recipe). The low thermal conductivity of the fiber prevents the outside of the cake from burning while the inside remains uncooked.

[0053] Performance testing: Table 6 Data metrics Plain soft cake (control) Soft cake with added carrot dietary fiber Dietary fiber content 1.2g / 100g 4.9g / 100g Taste rating (out of 10) 8.0 points (slightly dry and hard) 9.4 points (soft and delicate) Hardness (measured by texture analyzer, g) 250g 173g Sweetness (sensory rating, out of 5) 4.0 points 3.8 points Shelf life (25℃, sealed) It will dry in 5 days (it will become dry on the 5th day). 7 days (still moist on the 7th day) 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 highly palatable carrot dietary fiber, characterized in that, Includes the following steps: (1) Select fresh, mold-free carrots, rinse them with running water, place them in an ultrasonic treatment tank, and immediately cut them into cubes along the fiber direction after treatment. (2) Put the mixture into an enzymatic hydrolysis tank, add 0.2-0.25% of the carrot mass of cellulase and 0.1-0.13% of the carrot mass of saccharifying enzyme, add 5 times the amount of deionized water of the carrot mass, adjust the pH to 5.0-5.5, set the temperature to 40℃, stir at 40-50 r / min, and keep the mixture warm for 2-2.5 h. (3) Add food-grade 95% ethanol at a volume ratio of 7:3 for the aqueous phase and ethanol phase to form a two-phase system. Add 0.2-0.3% of the carrot mass of compound enzyme and 0.02% of the carrot mass of pectinase for gradient enzymatic hydrolysis: First stage (0-45min): 42℃; Second stage (45-100 min): 46℃, with the addition of food-grade modified diatomaceous earth at 0.08% of the weight of carrots; Third stage (100-120 min): 43℃; (4) After the enzymatic hydrolysis is completed, the temperature is raised to 88℃ and kept at the temperature for 8 min to inactivate the enzyme. Then, the temperature is cooled to room temperature and centrifuged at 3000 r / min for 15 min to separate the aqueous phase and the alcohol phase. The alcohol phase is then distilled at atmospheric pressure to recover ethanol. (5) Transfer the separated aqueous phase into a centrifuge and perform gradient centrifugation: centrifuge at 3000 r / min for 10 min to remove coarse residue; centrifuge at 5000 r / min for 10 min to collect medium-sized fibers; centrifuge at 8000 r / min for 10 min to collect fine-sized fibers. Medium-sized fibers and fine-sized fibers are mixed in a specific ratio to obtain mixed fibers; (6) Transfer the mixed fiber liquid into a sedimentation tank, add a 1% chitosan solution, mix for 10 min at a stirring speed of 20-25 r / min, cool to 5℃, let stand for 30 min, vacuum filter with a 5μm filter cloth, and collect the precipitated fibers. (7) Add carrot-derived nanocellulose at 1.6-1.8% of the dry weight of the precipitated fiber, add deionized water, shear at 3200 r / min for 18 min, cool down to 8-10℃, add 0.04-0.06% of food-grade trehalose, stir at 30 r / min for 20 min to obtain composite fiber with a "core-shell" structure. (8) Transfer the composite fiber with the "core-shell" structure into a vacuum dryer and dry it at a temperature of 50°C and a vacuum degree of 0.08MPa until the moisture content is ≤8%. After drying, lightly crush it and pass it through an 80-mesh sieve to obtain the final product.

2. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, The ultrasonic treatment parameters in step (1) are: 40kHz frequency, 300W power, water temperature of 25-30℃, and treatment time of 20min.

3. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (2), the specific activity of cellulase is ≥1000U / g; the specific activity of saccharifying enzyme is ≥50U / mg.

4. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (3), the complex enzymes are arabinofuranase, acetylxylanase and xylooligosaccharase in a mass ratio of 2:(1-1.5):

1.

5. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (5), the medium-sized fiber has a particle size of 50-100 μm; the fine-sized fiber has a particle size of 20-50 μm.

6. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (5), the specific ratio of medium-sized fibers to fine-sized fibers is (3-4):

5.

7. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (6), the amount of chitosan solution added is 0.3% of the mixed fibers.

8. The method for preparing highly palatable carrot dietary fiber according to claim 1, characterized in that, In step (7), the carrot-derived nanocellulose is prepared by pretreatment of carrot peel residue with citric acid and gradient high pressure homogenization.

9. The highly palatable carrot dietary fiber prepared by the preparation method according to any one of claims 1-8.

10. The application of the highly palatable carrot dietary fiber according to claim 9 in baked goods, dairy products and health foods.