Low-browning carrot dietary fiber as well as extraction method and application thereof

Abstract

The invention provides a low-browning carrot dietary fiber and an extraction method and application thereof.According to the method, accurate layered dissociation of carrot cell walls is achieved through the synergistic effect of low-temperature high-pressure pulse and targeted enzymolysis, and fiber skeletons are physically separated from browning substrates; meanwhile, natural bamboo fiber hollow nanotubes are adopted to load mulberry anthocyanin and hesperidin to form a composite color fixative, and enzymatic browning and non-enzymatic browning are inhibited respectively through a sequential controlled release mechanism. The whole process of the method is low in temperature and free of chemical addition, the problem of color deterioration in the extraction process is further solved, and high-value utilization of by-products is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of agricultural product processing, and particularly relates to a low-browning carrot dietary fiber as well as an extraction method and application thereof. BACKGROUND

[0002] Dietary fiber is known as the "seventh nutrient" and has important physiological functions in regulating intestinal health, preventing cardiovascular diseases, etc. The market demand is increasingly booming. Developing new sources of dietary fiber and green and efficient extraction processes is of great significance to meet the needs of the health food industry.

[0003] Carrots, also known as "longevity vegetable", "dirt ginseng" and "golden bamboo shoots", belong to the Umbelliferae family and contain many nutrients beneficial to the human body, such as proteins, sugars, vitamins, iron, calcium, potassium, etc. They are a kind of vegetable commonly kept in residents' homes. Research shows that carrots and their products can enhance human immunity, resist aging and decay, lower blood pressure, prevent cancer, etc., and have important medicinal value and health functions, high nutritional value, unique flavor and bright color, and thus occupy a very important position in healthy food and food processing and production.

[0004] Existing carrot dietary fiber extraction technologies still have technical problems. For example, physical methods such as mechanical crushing can damage cell structure, causing phenolic substances and enzymes to mix violently and causing severe enzymatic browning; high-temperature treatment such as blanching can inactivate enzymes, but can easily lead to loss of water-soluble fiber and damage to cell structure; and adding chemical color protectants can only temporarily inhibit browning and cannot fundamentally remove browning substrates, and there is a risk of chemical residues, which is difficult to meet the clean label consumption trend.

[0005] In summary, the existing technologies generally have problems such as large loss of functional ingredients and low resource utilization. Therefore, there is an urgent need in the art for a new green extraction method for carrot dietary fiber that can block browning from the source and has high efficiency and safety. SUMMARY

[0006] The technical problem to be solved is that, in view of the above technical problems, the purpose of the present application is to provide an extraction method for low-browning carrot dietary fiber. The method realizes precise layering and dissociation of carrot cell walls through low-temperature high-pressure pulse and targeted enzyme hydrolysis, and physically separates the fiber skeleton and browning substrates. At the same time, a composite color protectant composed of mulberry anthocyanins and hesperidin loaded in natural bamboo fiber hollow nanotubes is used to inhibit enzymatic and non-enzymatic browning through a time sequence controlled release mechanism. The method is low-temperature throughout and does not add chemicals, further solving the problem of color deterioration during extraction, and realizing high-value utilization of by-products.

[0007] Technical scheme: An extraction method for low-browning carrot dietary fiber, comprising the following steps: S1. washing and cutting the carrot, and then performing low-temperature high-pressure pulse treatment to obtain pretreated carrot pieces; S2. adding 1-2 times the mass of water to the pretreated carrot pieces, and adding pectinase to perform enzymatic reaction to obtain enzymatically treated carrot pieces; S3. adding 2-3 times the mass of 4-10℃ cold water to the enzymatically treated carrot pieces, and then performing low-temperature centrifugation to collect the precipitate to obtain a fiber skeleton; S4. adding 4-5 times the mass of deionized water to the fiber skeleton, and adding a double-active-ingredient-loaded composite color protection agent, stirring for 45-50 min, filtering through a 0.2 µm microfiltration membrane, and freeze-drying to obtain low-browning carrot dietary fiber.

[0008] Further, the low-temperature high-pressure pulse treatment in step S1 is specifically performed as follows: in a working medium containing a glycerol aqueous solution, a pressure of 300-350 MPa is applied at 15-18℃, and the pulse frequency is 2-3 times / min, and the treatment time is 8-10 min.

[0009] Further, the amount of pectinase added in step S2 is 0.03-0.05% of the mass of the pretreated carrot pieces, and the enzyme activity is 6000-10000 U / g; the temperature of the enzymatic reaction is 32-34℃, the pH is 4.8-5.0, and the reaction time is 30-35 min.

[0010] Further, the low-temperature centrifugation in step S3 is performed at 1500-2000 r / min for 10-12 min at 4℃.

[0011] Further, the double-active-ingredient-loaded composite color protection agent in step S4 is prepared according to the following steps: Step 1. Food-grade bamboo fibers are taken, crushed, and placed in a 0.5 mol / L NaOH solution, and then subjected to alkaline treatment at 80-85℃ for 2-3 h, and then the pH is adjusted to neutral with 0.1 mol / L HCl, and then washed with deionized water to obtain purified bamboo fibers; Step 2. The purified bamboo fibers are dispersed in water, and then subjected to ultrasonic treatment at 200-300 W for 20-30 min to obtain bamboo fiber hollow nanotubes; Step 3. The bamboo fiber hollow nanotubes are dispersed in water, and then subjected to ultrasonic treatment at 150-200 W for 15-20 min to obtain a bamboo fiber hollow nanotube suspension with a concentration of 0.8-1.0%; Step 4. 0.08-0.1% mulberry anthocyanins and 0.05-0.07% hesperidin are added to the bamboo fiber hollow nanotube suspension, and then stirred at 25-28℃ and 500-600 r / min for 40-50 min to obtain a double-active-ingredient-loaded composite color protection agent.

[0012] Further, the amount of the double active ingredient loaded composite color protection agent added in step S4 is 0.25-0.3% of the mass of the fiber framework.

[0013] The low-browning carrot dietary fiber extracted by the extraction method.

[0014] The low-browning carrot dietary fiber in the functional food, the health care product.

[0015] Beneficial effects: In the process of extracting the carrot dietary fiber, the present application first realizes the accurate hierarchical dissociation of the carrot cell wall through the synergistic effect of low-temperature high-pressure pulse and targeted enzymolysis pretreatment, so as to physically separate the fiber framework and the browning substrate. Specifically, (1) low-temperature high-pressure pulse cell wall relaxation: the low-temperature high-pressure pulse can act on the middle layer (pectin layer) of the carrot cell wall, so that the hydrogen bonds between pectin molecules are broken, the middle layer of the cell wall is relaxed, but the outer layer (cellulose layer) and the inner layer (cell membrane) are not damaged, so as to avoid the leakage of phenolic substances in the cells; the low temperature further protects the cell wall enzyme from being activated, so as to avoid overall softening; (2) targeted enzymolysis of middle layer pectin: because the middle layer of the cell wall has been relaxed, the pectinase can quickly target and degrade the soluble pectin in the middle layer, so that the outer layer (cellulose-hemicellulose framework) and the inner layer (cell membrane) of the cell wall are separated, at this time the fiber framework remains intact, and the cell membrane encapsulates the phenolic substances, forming a separation state of “fiber framework-cell membrane”; (3) low-temperature centrifugal separation of fiber framework: the low-temperature environment can inhibit the activity of phenol oxidase throughout the process, so as to avoid the triggering of enzymatic browning; the centrifugal force can make the fiber framework with a larger density settle down, and the cell membrane (with a smaller density) encapsulating the phenolic substances is suspended in the upper layer solution, so as to realize the efficient separation of “fiber framework-cell membrane”; the solution containing the cell membrane in the upper layer can be recycled for the extraction of carotene, and the fiber framework in the lower layer enters the subsequent extraction link, so as to cut off the contact between the browning substrate and the fiber from the source; After obtaining the pretreated fiber framework, the present application adds a double active ingredient loaded composite color protection agent, takes the bamboo fiber hollow nanotube as the carrier, the mulberry anthocyanin is fixedly embedded in the tube through hydrogen bond, and the hesperidin is adsorbed on the outer wall of the tube through electrostatic action, so as to form a double active ingredient loaded composite color protection agent of “in-tube-out-tube”; in the early stage of extraction, the water in the material solution makes the hesperidin on the outer wall of the tube quickly dissolve and release, combines with the phenol oxidase on the surface of the fiber, and inhibits the enzymatic browning; with the progress of the extraction, the mulberry anthocyanin in the tube is gradually released through the slow swelling of the nanotube, so as to scavenge the free radicals in the system and block the Maillard reaction (non-enzymatic browning); in addition, the bamboo fiber nanotube itself can also form an interwoven structure of “fiber-nanotube” with the fiber framework, so as to reduce the shrinkage and browning of the fiber in the drying process; after the extraction is completed, the fiber and the nanotube are separated through microfiltration membrane filtration (the nanotube can be recycled and reused), so as to avoid the influence of the carrier residue on the fiber quality. DETAILED DESCRIPTION

[0016] The application will be further described in connection with the following examples, which are intended to be illustrative only and not limiting of the application. Example 1

[0017] The preparation steps of the dual-active-ingredient-loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush it, and place it in a 0.5 mol / L NaOH solution. Alkaline treatment is carried out at 80°C for 3 hours. Then, 0.1 mol / L HCl is used to adjust the pH to neutral. Deionized water is used for washing, and purified bamboo fiber is obtained. Step 2. Disperse the purified bamboo fiber in water, and perform ultrasonic treatment at 200W for 30 minutes to obtain bamboo fiber hollow nanotubes. Step 3. Disperse the bamboo fiber hollow nanotubes in water, and perform ultrasonic treatment at 150W for 20 minutes to obtain a bamboo fiber hollow nanotube suspension with a concentration of 0.8%. Step 4. Add 0.08% mulberry anthocyanins and 0.05% hesperidin to the bamboo fiber hollow nanotube suspension. Stir at 25°C and 500r / min for 45 minutes to obtain the dual-active-ingredient-loaded composite color protection agent.

[0018] Example 2 The preparation steps of the dual-active-ingredient-loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush it, and place it in a 0.5 mol / L NaOH solution. Alkaline treatment is carried out at 80°C for 3 hours. Then, 0.1 mol / L HCl is used to adjust the pH to neutral. Deionized water is used for washing, and purified bamboo fiber is obtained. Step 2. Disperse the purified bamboo fiber in water, and perform ultrasonic treatment at 200W for 30 minutes to obtain bamboo fiber hollow nanotubes. Step 3. Disperse the bamboo fiber hollow nanotubes in water, and perform ultrasonic treatment at 150W for 20 minutes to obtain a bamboo fiber hollow nanotube suspension with a concentration of 0.9%. Step 4. Add 0.08% mulberry anthocyanins and 0.05% hesperidin to the bamboo fiber hollow nanotube suspension. Stir at 25°C and 500r / min for 45 minutes to obtain the dual-active-ingredient-loaded composite color protection agent.

[0019] Example 3 The preparation steps of the dual-active-ingredient-loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush it, and place it in a 0.5 mol / L NaOH solution. Alkaline treatment is carried out at 85°C for 3 hours. Then, 0.1 mol / L HCl is used to adjust the pH to neutral. Deionized water is used for washing, and purified bamboo fiber is obtained. Step 2. Disperse the purified bamboo fibers in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotubes; Step 3. Disperse the bamboo fiber hollow nanotubes in water, 150W ultrasonic for 20min, to obtain a bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.08% mulberry anthocyanin and 0.05% hesperidin to the bamboo fiber hollow nanotube suspension, stir at 25℃, 500r / min for 45min, to obtain a double active ingredient loaded composite color protection agent.

[0020] Example 4 The preparation steps of the double active ingredient loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fibers, crush them, and place them in a 0.5mol / L NaOH solution. Alkaline treatment at 85℃ for 3h, then adjust the pH to neutral with 0.1mol / L HCl, and wash with deionized water to obtain purified bamboo fibers; Step 2. Disperse the purified bamboo fibers in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotubes; Step 3. Disperse the bamboo fiber hollow nanotubes in water, 150W ultrasonic for 20min, to obtain a bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.09% mulberry anthocyanin and 0.05% hesperidin to the bamboo fiber hollow nanotube suspension, stir at 25℃, 500r / min for 45min, to obtain a double active ingredient loaded composite color protection agent.

[0021] Example 5 The preparation steps of the double active ingredient loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fibers, crush them, and place them in a 0.5mol / L NaOH solution. Alkaline treatment at 85℃ for 3h, then adjust the pH to neutral with 0.1mol / L HCl, and wash with deionized water to obtain purified bamboo fibers; Step 2. Disperse the purified bamboo fibers in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotubes; Step 3. Disperse the bamboo fiber hollow nanotubes in water, 150W ultrasonic for 20min, to obtain a bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.1% mulberry anthocyanin and 0.05% hesperidin to the bamboo fiber hollow nanotube suspension, stir at 25℃, 500r / min for 45min, to obtain a double active ingredient loaded composite color protection agent.

[0022] Example 6 The preparation steps of the double active ingredient loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush, and place in 0.5 mol / L NaOH solution, alkali treatment at 85℃ for 3h, then adjust pH to neutral with 0.1 mol / L HCl, deionized water washing, to obtain purified bamboo fiber; Step 2. Disperse the purified bamboo fiber in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotube; Step 3. Disperse the bamboo fiber hollow nanotube in water, 150W ultrasonic for 20min, to obtain bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.1% mulberry anthocyanin and 0.07% hesperidin to the bamboo fiber hollow nanotube suspension, stir at 25℃, 500r / min for 45min, to obtain the dual active ingredient loaded composite color protection agent.

[0023] Comparative Example 1 The difference between this comparative example and Example 6 is that mulberry anthocyanin is not added, as follows: The preparation steps of the dual active ingredient loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush, and place in 0.5 mol / L NaOH solution, alkali treatment at 85℃ for 3h, then adjust pH to neutral with 0.1 mol / L HCl, deionized water washing, to obtain purified bamboo fiber; Step 2. Disperse the purified bamboo fiber in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotube; Step 3. Disperse the bamboo fiber hollow nanotube in water, 150W ultrasonic for 20min, to obtain bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.07% hesperidin to the bamboo fiber hollow nanotube suspension, stir at 25℃, 500r / min for 45min, to obtain the dual active ingredient loaded composite color protection agent.

[0024] Comparative Example 2 The difference between this comparative example and Example 6 is that hesperidin is not added, as follows: The preparation steps of the dual active ingredient loaded composite color protection agent are as follows: Step 1. Take food-grade bamboo fiber, crush, and place in 0.5 mol / L NaOH solution, alkali treatment at 85℃ for 3h, then adjust pH to neutral with 0.1 mol / L HCl, deionized water washing, to obtain purified bamboo fiber; Step 2. Disperse the purified bamboo fiber in water, 200W ultrasonic for 30min, to obtain bamboo fiber hollow nanotube; Step 3. Disperse the bamboo fiber hollow nanotubes in water, 150W ultrasonic for 20 min, to obtain a bamboo fiber hollow nanotube suspension with a concentration of 1.0%; Step 4. Add 0.1% mulberry anthocyanin to the bamboo fiber hollow nanotube suspension, stir at 25°C and 500 r / min for 45 min, to obtain a dual active ingredient loaded composite color protection agent.

[0025] Comparative Example 3 The difference between this comparative example and Example 6 is that the bamboo fiber hollow nanotubes are replaced by chitosan nanoparticles, as follows: The preparation steps of the dual active ingredient loaded composite color protection agent are as follows: Step 1. Dissolve chitosan in a 1% acetic acid solution, stir at 40°C and 400 r / min for 2 h, to obtain a chitosan solution with a concentration of 1%; Step 2. Under magnetic stirring at a speed of 600 r / min, use a constant flow pump to slowly add 20 mL of a 0.5 mg / mL sodium tripolyphosphate solution to the chitosan solution at a rate of 1 mL / min, and continue to react for 30 min, to obtain a chitosan nanoparticle suspension with a concentration of 2%; Step 3. Take the above chitosan nanoparticle suspension, dilute with deionized water to a final concentration of 1%, 150W ultrasonic for 10 min, and disperse uniformly; then add 0.1% mulberry anthocyanin and 0.07% hesperidin, stir at 25°C and 500 r / min for 45 min, to obtain a dual active ingredient loaded composite color protection agent.

[0026] Determination of mulberry anthocyanin encapsulation rate and hesperidin loading rate: Standard curve drawing: Prepare standard solutions of mulberry anthocyanin and hesperidin, respectively, and determine the absorbance at the maximum absorption wavelength to draw a standard curve; Free ingredient separation: Centrifuge the freshly prepared composite color protection agent suspension at high speed to separate the supernatant (containing unloaded free active ingredients); Mulberry anthocyanin encapsulation rate (%) = (total amount of feed - free amount in supernatant) / total amount of feed x 100% Hesperidin loading rate (%) = (total amount of feed - free amount in supernatant) / carrier mass x 100% Table 1. Mulberry anthocyanin encapsulation rate and hesperidin loading rate of the dual active ingredient loaded composite color protection agent

[0027] As can be seen from Table 1, for the bamboo fiber nanotube, at a low dosage, mulberry anthocyanins have a high and stable encapsulation rate because they are embedded in the tube by hydrogen bonds, and hesperidin has a relatively low loading rate because it is adsorbed on the outer wall; as the dosage increases, both will decrease in encapsulation / loading rate due to the saturation of carrier sites; Example 6 shows that when the dosages of the two components are both high, they will compete for limited adsorption sites, which may result in a lower loading rate than the single component with a high dosage, but the total loading amount is the highest.

[0028] Therefore, the double active ingredient loaded composite color protection agent prepared in Example 6 is selected for subsequent extraction of carrot dietary fiber.

[0029] Example 7 A method for extracting low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into pieces, and perform low-temperature high-pressure pulse treatment in a working medium containing a glycerol aqueous solution, at 15°C, apply a pressure of 300 MPa, at a pulse frequency of 3 times / min, and treat for 10 min to obtain pretreated carrot pieces; S2. Add 2 times the mass of water to the pretreated carrot pieces, and add pectinase (0.03% of the mass of the pretreated carrot pieces, with an enzyme activity of 8000 U / g), and perform enzymatic reaction at 34°C, pH 5.0, for 30 min to obtain enzymatically treated carrot pieces; S3. Add 2 times the mass of 4°C cold water to the enzymatically treated carrot pieces, and centrifuge at 1500 r / min for 12 min at 4°C to collect the precipitate to obtain a fiber skeleton; S4. Add 4 times the mass of deionized water to the fiber skeleton, and add the double active ingredient loaded composite color protection agent prepared in Example 6 (0.25% of the mass of the fiber skeleton), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain low-browning carrot dietary fiber.

[0030] Example 8 A method for extracting low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into pieces, and perform low-temperature high-pressure pulse treatment in a working medium containing a glycerol aqueous solution, at 15°C, apply a pressure of 300 MPa, at a pulse frequency of 3 times / min, and treat for 10 min to obtain pretreated carrot pieces; S2. Add 2 times the mass of water to the pretreated carrot pieces, and add pectinase (0.04% of the mass of the pretreated carrot pieces, with an enzyme activity of 8000 U / g), and perform enzymatic reaction at 34°C, pH 5.0, for 30 min to obtain enzymatically treated carrot pieces; S3. Add 2 times the mass of 4°C cold water to the enzymolysis carrot block, centrifuge at 1500 r / min for 12 min at 4°C, collect the precipitate, and obtain the fiber skeleton; S4. Add 4 times the mass of deionized water to the fiber skeleton, and add the double-active-ingredient loaded composite color protection agent prepared in Example 6 (0.26% of the mass of the fiber skeleton), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain the low-browning carrot dietary fiber.

[0031] Example 9 A method for extracting a low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into blocks, perform low-temperature high-pressure pulse treatment, apply a pressure of 350 MPa in a working medium containing a glycerol aqueous solution, at 15°C, at a pulse frequency of 3 times / min, for 10 min, to obtain pretreated carrot blocks; S2. Add 2 times the mass of water to the pretreated carrot block, and add pectinase (0.05% of the mass of the pretreated carrot block, with an enzyme activity of 8000 U / g), perform enzymolysis at 34°C and pH 5.0 for 30 min, to obtain an enzymolysis carrot block; S3. Add 2 times the mass of 4°C cold water to the enzymolysis carrot block, centrifuge at 1500 r / min for 12 min at 4°C, collect the precipitate, and obtain the fiber skeleton; S4. Add 4 times the mass of deionized water to the fiber skeleton, and add the double-active-ingredient loaded composite color protection agent prepared in Example 6 (0.28% of the mass of the fiber skeleton), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain the low-browning carrot dietary fiber.

[0032] Example 10 A method for extracting a low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into blocks, perform low-temperature high-pressure pulse treatment, apply a pressure of 350 MPa in a working medium containing a glycerol aqueous solution, at 15°C, at a pulse frequency of 3 times / min, for 10 min, to obtain pretreated carrot blocks; S2. Add 2 times the mass of water to the pretreated carrot block, and add pectinase (0.05% of the mass of the pretreated carrot block, with an enzyme activity of 8000 U / g), perform enzymolysis at 34°C and pH 5.0 for 30 min, to obtain an enzymolysis carrot block; S3. Add 2 times the mass of 4°C cold water to the enzymolysis carrot block, centrifuge at 1500 r / min for 12 min at 4°C, collect the precipitate, and obtain the fiber skeleton; S4. Add 4 times mass of deionized water to the fiber framework, and add the double active ingredient loaded composite color protection agent prepared in Example 6 (0.3% of the mass of the fiber framework), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain the low-browning carrot dietary fiber.

[0033] Comparative Example 4 The difference between this comparative example and Example 10 is that low-temperature high-pressure pulse treatment is not used, and the specific process is as follows: A method for extracting a low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into pieces, add 2 times mass of water, and add pectinase (0.05% of the mass of the carrot pieces, with an enzyme activity of 8000 U / g), carry out enzymatic reaction at 34°C and pH 5.0 for 30 min to obtain the enzymatically treated carrot pieces; S2. Add 2 times mass of 4°C cold water to the enzymatically treated carrot pieces, centrifuge at 1500 r / min for 12 min at 4°C to collect the precipitate to obtain the fiber framework; S3. Add 4 times mass of deionized water to the fiber framework, and add the double active ingredient loaded composite color protection agent prepared in Example 6 (0.3% of the mass of the fiber framework), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain the low-browning carrot dietary fiber.

[0034] Comparative Example 5 The difference between this comparative example and Example 10 is that pectinase is not used for enzymatic treatment, and the specific process is as follows: A method for extracting a low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrot into pieces, and carry out low-temperature high-pressure pulse treatment, apply a pressure of 350 MPa in a working medium containing a glycerol aqueous solution, at a pulse frequency of 3 times / min, at 15°C for 10 min to obtain the pretreated carrot pieces; S2. Add 4 times mass of deionized water to the pretreated carrot pieces, and add the double active ingredient loaded composite color protection agent prepared in Example 6 (0.3% of the mass of the pretreated carrot pieces), stir for 50 min, filter through a 0.2 µm microfiltration membrane, and freeze-dry to obtain the low-browning carrot dietary fiber.

[0035] Comparative Example 6 The difference between this comparative example and Example 10 is that the double active ingredient loaded composite color protection agent is not added, and the specific process is as follows: A method for extracting a low-browning carrot dietary fiber, comprising the following steps: S1. Wash and cut the carrots, and then perform low-temperature high-pressure pulse treatment. In a working medium containing a glycerol aqueous solution, the carrots are treated at 15℃, 350 MPa, 3 times / min, and 10 min to obtain pretreated carrot pieces; S2. Add 2 times the mass of water to the pretreated carrot pieces, and add pectinase (0.05% of the mass of the pretreated carrot pieces, with an enzyme activity of 8000 U / g). Perform enzymatic hydrolysis at 34℃, pH 5.0, for 30 min to obtain enzymatically hydrolyzed carrot pieces; S3. Add 2 times the mass of 4℃ cold water to the enzymatically hydrolyzed carrot pieces, and then centrifuge at 1500 r / min for 12 min at 4℃ to collect the precipitate to obtain a fiber skeleton; S4. Add 4 times the mass of deionized water to the fiber skeleton, and then stir for 50 min. Filter through a 0.2 µm microfiltration membrane, and then freeze-dry to obtain low-browning carrot dietary fiber.

[0036] Comparative Example 7 This comparative example differs from Example 10 in that a dual- active-ingredient loaded composite color protection agent prepared in Comparative Example 1 is used.

[0037] Comparative Example 8 This comparative example differs from Example 10 in that a dual- active-ingredient loaded composite color protection agent prepared in Comparative Example 2 is used.

[0038] Comparative Example 9 This comparative example differs from Example 10 in that a dual- active-ingredient loaded composite color protection agent prepared in Comparative Example 3 is used.

[0039] Performance test: (1) Yield and purity of carrot dietary fiber Yield (%) = (M1-M0) × 100% In the formula, M1: mass (g) of low-browning carrot dietary fiber powder obtained by final freeze-drying; M0: mass (g) of fresh carrot pieces used at the beginning of step S1; Purity of dietary fiber: Accurately take about 1g of dried carrot dietary fiber sample (M1), place it in a beaker, add a hot stable alpha-amylase solution, react in a 95-100℃ water bath for 30min, hydrolyze starch, adjust the pH to the optimum condition of the protease, add a protease solution, react in a 60℃ water bath for 30min, hydrolyze protein, adjust the pH to the optimum condition of the cellulase, add a cellulase solution, react in a 60℃ water bath for 30min, add 4 times the volume of 95% ethanol preheated to 60℃, stand at room temperature for 1 hour, make the dietary fiber precipitate, filter with a known mass (M2) of sand core crucible, and sequentially wash the precipitate with 78% ethanol, 95% ethanol and acetone, dry the crucible together with the residue in an oven at 105℃ to a constant weight, weigh (M3), and at the same time, perform a blank experiment. The purity calculation formula is as follows: Purity (%) = [(M3-M2-M 空白 ) / M1] x 100% Table 2 Yield and purity of carrot dietary fiber

[0040] As can be seen from Table 2, the yield and purity of the carrot dietary fiber extracted by the "low-temperature high-pressure pulse-enzymatic hydrolysis synergistic pretreatment" and the "double active ingredient loaded composite color protection agent" proposed in the application are both high, and the absence or replacement of any link will lead to a decrease in the yield and purity of the final dietary fiber.

[0041] (2) Water holding capacity and swelling capacity Take 2.00g of the extracted dietary fiber and place it in a 100mL beaker, add 40mL of 20℃ distilled water, soak at room temperature for 1h, drain the water on a quantitative filter paper, quickly transfer to a watch glass and weigh. Calculate the water holding capacity according to the formula: Water holding capacity = (wet sample weight - dry sample weight) / dry sample weight Take 0.10g of the extracted dietary fiber in a 5mL measuring cylinder, read the volume, add 5mL of distilled water, soak for 24h, and read the volume. Calculate the swelling capacity according to the formula: Swelling capacity (mL / g) = (volume after soaking - dry product volume) / dry mass Table 3 Water holding capacity and swelling capacity of carrot dietary fiber

[0042] From Table 3, the present application first uses "low temperature high pressure pulse" to relax the cell wall gently, avoiding mechanical damage to the fiber skeleton; "targeted enzymatic hydrolysis" precisely removes the middle layer pectin, fully exposing the pore structure of the fiber skeleton; and the addition of "double active ingredient loaded composite color protection agent" interweaves the nanotube carrier with the fiber skeleton, further enhancing the stability of the network structure. The synergistic effect of the three maximizes the protection and optimization of the natural porous three-dimensional network structure of dietary fiber, thereby imparting excellent water binding and volume expansion capacity to the dietary fiber. In comparison, Comparative Examples 4 and 5, which lack the high pressure pulse or enzymatic hydrolysis steps, respectively, result in incomplete cell wall dissociation, with the fiber structure being wrapped or not fully released by impurities such as pectin, resulting in a dense structure with few pores, and thus significantly deteriorated functional properties; Comparative Example 6 lacks a color protection agent, although the fiber skeleton is intact, it lacks the structural reinforcement effect of nanotubes, and may be slightly brown, resulting in structural modification, so its performance is slightly lower than that of Example 10; Comparative Examples 7-9 use defective color protection agents, which have different degrees of decline in functional properties, especially Comparative Example 9, which replaces the carrier, because chitosan nanoparticles do not have the rigid tubular structure and interweaving ability of bamboo fiber nanotubes, the enhancement effect on the fiber structure is the weakest, further proving the important role of the specific carrier in the color protection agent in maintaining the high-level structure and functional integrity of the fiber.

[0043] (3) Browning index Accurately weigh 0.100 g of the freeze-dried carrot dietary fiber sample, transfer the sample to a 15 mL centrifuge tube, add 10.0 mL of 0.1 mol / L phosphate buffer at pH 6.8, vortex for 3 min, then centrifuge at 10,000 r / min at 4°C for 15 min, take the supernatant, filter, and obtain the test solution. Using a UV-visible spectrophotometer, with PBS buffer as the reference, measure the absorbance value of the test solution at a wavelength of 420 nm.

[0044] Table 4 Browning index of carrot dietary fiber

[0045] The greater the browning index, the higher the content of brown polymers dissolved in the buffer, i.e., the more severe the browning of the sample. As can be seen from Table 4, the browning index of the examples using the complete innovative process (low temperature high pressure pulse + targeted enzymatic hydrolysis + double active ingredient loaded composite color protection agent) is low, proving that this scheme can better inhibit the browning problem from the pretreatment to the extraction and drying process, while the absence of pretreatment or the absence or replacement of the color protection agent in the comparative examples will significantly increase the browning index, resulting in deterioration of the quality of the final extracted carrot dietary fiber.

[0046] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Any person skilled in the art, without departing from the spirit and technical solutions of the present application, can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, still belongs to the protection scope of the technical solutions of the present application.

Claims

1. A method for extracting low-browning dietary fiber from carrots, characterized by, It comprises the following steps: S1. After washing and cutting the carrots, low-temperature high-pressure pulse treatment is performed to obtain pretreated carrot pieces; S2. 1-2 times the mass of water is added to the pretreated carrot pieces, and pectinase is added for enzymatic reaction to obtain enzymatically treated carrot pieces; S3. 2-3 times the mass of 4-10℃ cold water is added to the enzymatically treated carrot pieces, and low-temperature centrifugation is performed to collect the precipitate to obtain a fiber skeleton; S4. 4-5 times the mass of deionized water is added to the fiber skeleton, and a double-active-ingredient-loaded composite color protection agent is added, and stirring extraction is performed for 45-50 min, and filtration and freeze-drying are performed to obtain low-browning carrot dietary fiber.

2. The method of claim 1, wherein the low-browning carrot dietary fiber is extracted by the method comprising the steps of: The low-temperature high-pressure pulse treatment in step S1 is specifically as follows: in a working medium containing a glycerol aqueous solution, a pressure of 300-350 MPa is applied at 15-18℃, and 2-3 times / min pulse frequency is used for 8-10 min. ​ 3. The process for the extraction of low browning dietary fiber from carrot as claimed in claim 1 wherein: The amount of pectinase added in step S2 is 0.03-0.05% of the mass of the pretreated carrot pieces, and the enzyme activity is 6000-10000 U / g; the temperature of the enzymatic reaction is 32-34℃, the pH is 4.8-5.0, and the reaction time is 30-35 min.

4. The method of claim 1, wherein the low-browning carrot dietary fiber is extracted by the method comprising the steps of: The low-temperature centrifugation in step S3 is performed at 4℃ at 1500-2000 r / min for 10-12 min. ​ 5. The method of claim 1, wherein the low-browning carrot dietary fiber is extracted by the method comprising the steps of: The preparation steps of the double-active-ingredient-loaded composite color protection agent in step S4 are as follows: ​ Step 1. Food-grade bamboo fibers are taken, crushed, and placed in a 0.5 mol / L NaOH solution, and alkali treatment is performed at 80-85℃ for 2-3 h, then the pH is adjusted to neutral with 0.1 mol / L HCl, and deionized water is used for washing to obtain purified bamboo fibers; Step 2. The purified bamboo fibers are dispersed in water, and ultrasonic treatment is performed at 200-300 W for 20-30 min to obtain bamboo fiber hollow nanotubes; Step 3. The bamboo fiber hollow nanotubes are dispersed in water, and ultrasonic treatment is performed at 150-200 W for 15-20 min to obtain a bamboo fiber hollow nanotube suspension with a concentration of 0.8-1.0%; Step 4. 0.08-0.1% mulberry anthocyanins and 0.05-0.07% hesperidin are added to the bamboo fiber hollow nanotube suspension, and stirring is performed at 25-28℃ and 500-600 r / min for 40-50 min to obtain a double-active-ingredient-loaded composite color protection agent.

6. The process for extraction of low browning dietary fiber from carrot as claimed in claim 1 wherein: The amount of the double-active-ingredient-loaded composite color protection agent added in step S4 is 0.25-0.3% of the mass of the fiber skeleton.

7. Low-browning carrot dietary fiber extracted by the extraction method according to any one of claims 1-6.

8. Application of the low-browning carrot dietary fiber according to claim 7 in functional food and health products.

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