Dietary fiber as well as preparation method and application thereof

Abstract

The invention provides dietary fiber as well as a preparation method and application thereof, and belongs to the technical field of food. The preparation method of the dietary fiber provided by the invention does not adopt a chlorine-containing reagent and / or ozone, and comprises the following steps: mixing lignocellulose biomass with a laccase reagent, and carrying out enzyme treatment to obtain enzyme treated fiber; mixing the enzyme treated fiber with a bleaching reagent, and performing bleaching treatment under ultrasonic and microwave conditions to obtain bleached fiber; the bleaching reagent is an aqueous solution containing hydrogen peroxide and an acid reagent; mixing the bleached fibers with an alkaline solution, and carrying out alkali treatment under ultrasonic and microwave conditions to obtain an alkali treatment feed liquid; and mixing the alkali treatment feed liquid with a hydrogen peroxide aqueous solution, and carrying out oxidation treatment to obtain the dietary fiber. The dietary fiber prepared by the method has high whiteness, lignin and pigment chromophores are remarkably removed, functional characteristics are improved, and the preparation process is environment-friendly.

Description

Technical Field

[0001] The present invention relates to the field of food technology, and in particular to dietary fiber and a preparation method and application thereof. Background Art

[0002] Brewer's spent grains (BSG) are a valuable source of dietary fiber, containing arabinoxylan and β-glucan, which have significant functional advantages for food and nutraceutical applications. However, BSG fiber is usually brown in color due to the presence of lignin and other color-causing compounds, which limits its application in food and nutraceuticals.

[0003] Traditional fiber bleaching methods usually require the use of chlorine-containing reagents or ozone, but these methods often fail to achieve the desired whiteness of dietary fiber and are prone to destroying the structural integrity of the fiber. At the same time, chlorine-containing reagents and ozone produce toxic byproducts that harm the environment and require complex waste management procedures, limiting their application in the preparation of dietary fiber. Hydrogen peroxide (H2O2) is an environmentally friendly bleaching agent that decomposes into water and oxygen and is environmentally friendly, but if only hydrogen peroxide is used as a bleaching agent, it is difficult to achieve the desired whiteness of dietary fiber. Summary of the invention

[0004] The purpose of the present invention is to provide a dietary fiber and a preparation method and application thereof. The dietary fiber prepared by the method of the present invention has high whiteness and good structural integrity, and the preparation process is environmentally friendly.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing dietary fiber, which does not use chlorine-containing reagents and / or ozone, and comprises the following steps:

[0007] mixing lignocellulosic biomass with a laccase reagent and performing enzyme treatment to obtain enzyme-treated fibers;

[0008] The enzyme-treated fiber is mixed with a bleaching agent, and bleached under ultrasonic and microwave conditions to obtain bleached fiber; the bleaching agent is an aqueous solution containing hydrogen peroxide and an acid agent;

[0009] The bleached fiber is mixed with an alkaline solution, and subjected to an alkali treatment under ultrasonic and microwave conditions to obtain an alkali-treated feed solution;

[0010] The alkali-treated feed liquid is mixed with a hydrogen peroxide aqueous solution and subjected to oxidation treatment to obtain the dietary fiber.

[0011] Preferably, the lignocellulosic biomass comprises one or more of brewer's grains, bagasse, rice husks and straw.

[0012] Preferably, the laccase reagent comprises laccase and a buffer, the activity of the laccase is 180-250 U / g, the pH value of the buffer is 4.5-5.5; and the concentration of the laccase in the laccase reagent is 13.5-16.5 U / g.

[0013] Preferably, the mass ratio of the lignocellulosic biomass to the laccase reagent is 13-14:1; the temperature of the enzyme treatment is 35-50° C., and the time is 6-14 hours.

[0014] Preferably, the concentration of hydrogen peroxide in the bleaching agent is 2-3wt%, the concentration of the acid agent in the bleaching agent is 2-5wt%, and the acid agent is acetic acid; the dosage ratio of the enzyme-treated fiber to the bleaching agent is 40g:280-320mL; the conditions of the bleaching treatment include: ultrasonic frequency of 60-80kHz, microwave power of 500-700W, temperature of 40-70°C, and time of 8-20min.

[0015] Preferably, the alkaline solution includes NaOH solution or Na2CO3 solution, the concentration of the NaOH solution is 0.5-1wt%, and the concentration of the Na2CO3 solution is 1.5-2wt%; the dosage ratio of the bleached fiber to the alkaline solution is 1-2g:7.5-10mL; the conditions of the alkali treatment include: ultrasonic frequency of 60-90kHz, microwave power of 500-700W, temperature of 70-80°C, and time of 20-30min.

[0016] Preferably, the concentration of the aqueous hydrogen peroxide solution is 2-4wt%, and the usage ratio of the bleached fiber to the aqueous hydrogen peroxide solution is 40g:280-320mL; the oxidation treatment comprises sequentially performing a first-stage oxidation treatment and a second-stage oxidation treatment; the first-stage oxidation treatment is performed under ultrasonic and microwave conditions, and the conditions of the first-stage oxidation treatment include: an ultrasonic frequency of 60-90kHz, a microwave power of 500-700W, a temperature of 40-70°C, and a time of 10-20min; the conditions of the second-stage oxidation treatment include: a temperature of 20-30°C and a time of 1.5-2.5h.

[0017] The present invention provides dietary fiber prepared by the preparation method described in the above technical scheme.

[0018] Preferably, the CIE whiteness index of the dietary fiber is 77-86%.

[0019] The present invention provides application of the dietary fiber described in the above technical solution in food or nutritional products.

[0020] Beneficial effects: The present invention provides an environmentally friendly bleaching method for insoluble dietary fiber (IDF) in lignocellulosic biomass. Specifically, the present invention uses laccase to perform enzyme treatment on lignocellulosic biomass (such as brewer's grains, etc.), which can oxidize and degrade lignin to make it easier to remove. The present invention uses an aqueous solution containing hydrogen peroxide and an acid reagent as a bleaching agent. By performing bleaching treatment under ultrasonic and microwave conditions, lignin can be further degraded, which is beneficial to improving the bleaching effect and ensuring the integrity of the fiber structure. Specifically, ultrasonic waves can produce local agitation and cavitation phenomena, forming a high-energy microenvironment, promoting the penetration of bleaching agents into the fiber matrix, accelerating chemical reactions, and promoting the decomposition of lignin and other coloring compounds; microwaves can provide rapid and uniform heating, which is beneficial to accelerating the chemical reaction between the bleaching agent and lignin and other coloring compounds, thereby shortening the overall processing time and reducing energy consumption. The present invention performs alkali treatment under ultrasonic and microwave conditions, and then performs oxidation treatment, which is beneficial to further improve the bleaching effect on the basis of ensuring the integrity of the fiber structure. The method provided by the present invention does not use chlorine-containing reagents and / or ozone, is environmentally friendly, and the dietary fiber finally prepared is suitable for use in food or nutritional products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flowchart of preparing dietary fiber in an embodiment of the present invention;

[0022] Figure 2 The physical pictures of the products prepared in Examples 1 to 3 and Comparative Examples 1 to 3;

[0023] Figure 3 The Fourier transform infrared spectra of the products prepared in Examples 1 to 3 and Comparative Example 1;

[0024] Figure 4 X-ray diffraction spectra of the products prepared in Examples 1 to 3 and Comparative Example 1;

[0025] Figure 5 The TGA curves of the products prepared in Examples 1 to 3 and Comparative Example 1;

[0026] Figure 6 The DSC curves of the products prepared in Examples 1 to 3 and Comparative Example 1;

[0027] Figure 7 These are SEM images of the products prepared in Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing dietary fiber, which does not use chlorine-containing reagents and / or ozone, and comprises the following steps:

[0029] mixing lignocellulosic biomass with a laccase reagent and performing enzyme treatment to obtain enzyme-treated fibers;

[0030] The enzyme-treated fiber is mixed with a bleaching agent, and bleached under ultrasonic and microwave conditions to obtain bleached fiber; the bleaching agent is an aqueous solution containing hydrogen peroxide and an acid agent;

[0031] The bleached fiber is mixed with an alkaline solution, and subjected to an alkali treatment under ultrasonic and microwave conditions to obtain an alkali-treated feed solution;

[0032] The alkali-treated feed liquid is mixed with a hydrogen peroxide aqueous solution and subjected to oxidation treatment to obtain the dietary fiber.

[0033] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art or are prepared by methods well known to those skilled in the art.

[0034] The present invention mixes lignocellulosic biomass with a laccase reagent, performs enzyme treatment, and obtains enzyme-treated fiber. As one embodiment of the present invention, the lignocellulosic biomass may include one or more of brewer's grains (BSG), bagasse, rice husks, and straws, and the straws may be corn straws and / or wheat straws; in the embodiment of the present invention, brewer's grains are specifically used as an example for explanation. As one embodiment of the present invention, the lignocellulosic biomass is preferably dried, ground, and sieved in sequence before the enzyme treatment; the drying temperature may be 75 to 85°C, specifically 80°C, and the time may be 10 to 15h, specifically 12h; the lignocellulosic biomass with a particle size of 50 to 100 μm obtained after the sieving is subjected to subsequent enzyme treatment. The present invention has no special limitation on the grinding and sieving, and it is sufficient to ensure that the lignocellulosic biomass with a particle size that meets the requirements is obtained.

[0035] As an embodiment of the present invention, the laccase reagent may include laccase and buffer; the activity of the laccase may be 180-250U / g, specifically 180U / g, 190U / g, 200U / g, 210U / g, 220U / g, 230U / g, 240U / g or 250U / g; the buffer may be a sodium acetate buffer, and the pH value of the buffer may be 4.5-5.5, specifically 4.5, 4.8, 5, 5.2 or 5.5; for example, based on BSG, the concentration of laccase in the laccase reagent may be 13.5-16.5U / g BSG, specifically 14U / g BSG, 14.5U / g BSG, 15U / gBSG, 15.5U / g BSG or 16U / gBSG. The present invention uses laccase to enzymatically treat lignocellulosic biomass, which can effectively oxidize and decompose lignin and other non-cellulose impurities. In the embodiments of the present invention, the pH value of the buffer solution is limited to the above range, which is beneficial for making the laccase have better activity and reducing the impact on the environment.

[0036] As an embodiment of the present invention, the mass ratio of the lignocellulosic biomass to the laccase reagent can be 13 to 14: 1, specifically 13.33: 1. As an embodiment of the present invention, the temperature of the enzyme treatment can be 35 to 50°C, specifically 35°C, 37°C, 40°C, 42°C, 45°C, 47°C or 50°C; the time can be 6 to 14h, specifically 6h, 8h, 10h, 12h or 14h. In the embodiment of the present invention, enzyme treatment under the above conditions can improve the accessibility of the fiber, fully oxidize and degrade lignin, and make it easier to remove.

[0037] As an embodiment of the present invention, the enzyme treatment further includes solid-liquid separation, and the solid-liquid separation can be carried out by filtration. The solid material obtained after the solid-liquid separation is the enzyme-treated fiber.

[0038] After obtaining the enzyme-treated fiber, the present invention mixes the enzyme-treated fiber with a bleaching agent, and performs a bleaching treatment under ultrasonic and microwave conditions to obtain a bleached fiber. In the present invention, the bleaching agent is an aqueous solution containing hydrogen peroxide and an acid agent. The present invention uses an aqueous solution containing hydrogen peroxide and an acid agent as a bleaching agent, and performs a bleaching treatment under ultrasonic and microwave conditions. Based on the synergistic effect of cavitation and dielectric heating generated by ultrasonic and microwave radiation, the chemical penetration effect can be improved, the chemical reaction can be accelerated, and the processing time can be reduced, which is beneficial to further promote the decomposition of lignin and thus improve the bleaching effect.

[0039] As an embodiment of the present invention, the concentration of hydrogen peroxide in the bleaching agent can be 2-3wt%, specifically 2wt%, 2.5wt% or 3wt%; the concentration of the acid agent in the bleaching agent can be 2-5wt%, specifically 2wt%, 3wt%, 4wt% or 5wt%; the acid agent can be acetic acid. In the embodiment of the present invention, peracetic acid is produced based on the synergistic oxidation of hydrogen peroxide and acetic acid, which can more effectively degrade the remaining lignin and other color-causing compounds, thereby achieving a significant bleaching effect.

[0040] As an embodiment of the present invention, the dosage ratio of the enzyme-treated fiber to the bleaching agent can be 40g:280-320mL, specifically 40g:300mL. As an embodiment of the present invention, the conditions of the bleaching treatment include: the ultrasonic frequency can be 60-80kHz, specifically 60kHz, 65kHz, 70kHz, 75kHz or 80kHz; the microwave power can be 500-700W, specifically 500W, 550W, 600W, 650W or 700W; the temperature can be 40-70℃, specifically 40℃, 50℃, 60℃ or 70℃; the time can be 8-20min, specifically 8min, 10min, 15min or 20min. In the embodiment of the present invention, the bleaching treatment is carried out under the above conditions. The cavitation phenomenon generated by ultrasound can maximize the permeability of the bleaching agent, and microwaves are used to maintain a stable temperature and improve chemical reactivity, thereby ensuring a good bleaching effect while avoiding damage to the integrity of the fiber structure, and is conducive to reducing the amount of reagents used and energy consumption, thereby improving the eco-friendliness of the preparation process.

[0041] As an embodiment of the present invention, the bleaching treatment further includes: performing solid-liquid separation on the system obtained after the bleaching treatment, washing and drying the obtained solid product to obtain the bleached fiber; the solid-liquid separation method can be filtration; the reagent used for washing can be water, specifically distilled water; the drying can be air-drying.

[0042] After obtaining the bleached fiber, the present invention mixes the bleached fiber with an alkaline solution and performs an alkali treatment under ultrasonic and microwave conditions to obtain an alkali-treated feed solution. The present invention performs an alkali treatment under ultrasonic and microwave conditions, which can further improve the bleaching effect, achieving a whiteness level of more than 80% of the final dietary fiber, while maintaining the fiber structure integrity, functional properties (such as water retention, texture and viscosity), fermentability and nutritional quality.

[0043] As an embodiment of the present invention, the alkaline solution may include a NaOH solution or a Na2CO3 solution; the concentration of the NaOH solution may be 0.5-1wt%, specifically 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%; the concentration of the Na2CO3 solution may be 1.5-2wt%, specifically 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2wt%. As an embodiment of the present invention, the amount ratio of the bleached fiber to the alkaline solution may be 1-2g:7.5-10mL, specifically 1g:7.5mL. As an embodiment of the present invention, the conditions of the alkali treatment include: the ultrasonic frequency can be 60-90kHz, specifically 60kHz, 65kHz, 70kHz, 75kHz, 80kHz, 85kHz or 90kHz; the microwave power can be 500-700W, specifically 500W, 55W, 600W, 650W or 700W; the temperature can be 70-80℃, specifically 70℃, 72℃, 75℃, 77℃ or 80℃; the time can be 20-30min, specifically 20min, 25min or 30min. In the embodiment of the present invention, the alkali treatment is carried out under the above conditions, and the cavitation phenomenon generated by the ultrasonic wave can maximize the permeability of the alkaline solution, and the microwave is used to maintain a stable temperature and improve the chemical reactivity, which can effectively remove lignin and other coloring compounds to ensure a good bleaching effect, and can avoid damage to the integrity of the fiber structure, and is conducive to reducing the dosage of the agent and energy consumption, and improving the eco-friendliness of the preparation process.

[0044] After the alkali treatment, the present invention does not need to perform post-treatment, and directly mixes the obtained alkali-treated liquid with an aqueous hydrogen peroxide solution for oxidation treatment to obtain the dietary fiber. As one embodiment of the present invention, the concentration of the aqueous hydrogen peroxide solution can be 2 to 4wt%, specifically 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%; the dosage ratio of the bleached fiber to the aqueous hydrogen peroxide solution can be 40g:280 to 320mL, specifically 40g:300mL. As one embodiment of the present invention, the oxidation treatment includes sequentially performing a first-stage oxidation treatment and a second-stage oxidation treatment. As an embodiment of the present invention, the first stage oxidation treatment is carried out under ultrasonic and microwave conditions, and the conditions of the first stage oxidation treatment include: the ultrasonic frequency can be 60-90kHz, specifically 60kHz, 65kHz, 70kHz, 75kHz, 80kHz, 85kHz or 90kHz; the microwave power can be 500-700W, specifically 500W, 55W, 600W, 650W or 700W; the temperature can be 40-70℃, specifically 40℃, 50℃, 60℃ or 70℃; the time can be 10-20min, specifically 10min, 15min or 20min. As an embodiment of the present invention, the conditions of the second stage oxidation treatment include: the temperature can be 20-30℃, specifically room temperature (25℃); the time can be 1.5-2.5h, specifically 1.5h, 2h or 2.5h; the second stage oxidation treatment of the present invention can be carried out under static conditions, that is, without stirring, ultrasonic and microwave conditions. In the embodiment of the present invention, oxidation treatment is carried out under the above conditions, which can fully remove residual lignin and other coloring compounds, ensure complete bleaching of dietary fiber, and maintain the structural integrity, functional properties (such as water retention, texture and viscosity), fermentability and nutritional quality of dietary fiber, which is suitable for food-grade applications. Specifically, during the first stage oxidation treatment, the generation of hydroxyl radicals (·OH) is promoted by ultrasonic cavitation, and the temperature is kept at 40 to 70°C by controlling the microwave power for a duration of 10 to 20 minutes. Ultrasonic induced cavitation plays a key role in the bleaching process. It produces local bubbles and ruptures, thereby generating strong shear forces and turbulence. These extreme local conditions decompose hydrogen peroxide to form highly active hydroxyl radicals (·OH). These hydroxyl radicals attack the lignin structure and promote the decomposition of the polymer.

[0045] H2O2→·OH+HO - .

[0046] In addition, the uniform dielectric heating provided by the microwave system accelerates the decomposition of hydrogen peroxide, thereby increasing the overall reaction rate. The process also ensures the maintenance of the integrity of the fiber structure while promoting efficient bleaching. The second stage oxidation treatment is then continued at 20-30°C for 1.5-2.5h without stirring, ultrasound, and microwave conditions. This extended incubation period ensures that lignin and other chromophores in the biomass are completely oxidized and decomposed, which helps to effectively remove color and further enhance the decolorization process.

[0047] As an embodiment of the present invention, after the oxidation treatment, the process further comprises: performing solid-liquid separation on the system obtained after the oxidation treatment, washing the obtained solid product and then freeze-drying it to obtain the dietary fiber; the solid-liquid separation method can be filtration; the reagent used for washing can be water, specifically distilled water; the present invention has no special limitation on the conditions of the freeze-drying, and the conditions familiar to those skilled in the art can be used.

[0048] The present invention first uses laccase delignification, and then uses ultrasonic microwave assisted hydrogen peroxide and acid reagent (such as acetic acid) for bleaching treatment, so that the bleaching agent can penetrate deeper into the fiber, ensuring excellent bleaching effect, and then uses ultrasonic microwave assisted alkali treatment to strengthen bleaching, and then uses hydrogen peroxide for final whitening, the whole process can ensure that lignin is effectively decomposed and removed and the fiber is fully bleached, while maintaining the structural integrity, functional characteristics (such as water retention, texture and viscosity), fermentability and nutritional quality of the fiber to a great extent. And the present invention uses an aqueous solution containing hydrogen peroxide and an acid reagent (such as acetic acid) as a bleaching agent, which can ensure that the byproducts produced are environmentally friendly and biodegradable, such as hydrogen peroxide decomposition into water and oxygen, avoiding the use of toxic bleaching agents, thereby minimizing potential environmental and health risks, and simplifying the waste treatment process. In addition, the present invention adopts a gentle step-by-step bleaching process, with less energy consumption and reagent consumption, high production efficiency, and is suitable for large-scale production.

[0049] The present invention provides dietary fiber prepared by the preparation method described in the above technical solution. As an embodiment of the present invention, the dietary fiber is bright white fiber, and the CIE whiteness index of the dietary fiber can be 77-86%, specifically 77.60%, 82.42% or 85.30%.

[0050] The present invention provides the application of the dietary fiber described in the above technical solution in food or nutritional products. The present invention has no special limitation on the specific application of the dietary fiber, and any method familiar to those skilled in the art can be used.

[0051] Figure 1The flowchart of preparing dietary fiber in the embodiment of the present invention is described below in conjunction with the embodiment of the present invention to clearly and completely describe the technical scheme in the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, rather than all the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in the art without making creative work are within the scope of protection of the present invention.

[0052] The brewer's grains (BSG) used in the following experiments were provided by China Resources Snow Beer (Henan) Co., Ltd., with a moisture content of 8.7 wt %; laccase was from solarbio life sciences.

[0053] Example 1

[0054] (1) drying BSG at 80° C. for 12 h, grinding and sieving the obtained dried BSG to obtain BSG fibers with a particle size of 50 to 100 μm; mixing laccase (200 U / g) with sodium acetate buffer (pH=4.5) to obtain a laccase reagent with a laccase concentration of 14.5 U / g; mixing the BSG fibers and the laccase reagent at a mass ratio of 13.33:1, subjecting the obtained mixture to enzyme treatment at 40° C. under stirring conditions for 12 h, and then filtering to collect the filter cake as the enzyme-treated BSG fibers;

[0055] (2) mixing an aqueous hydrogen peroxide solution with acetic acid to obtain a bleaching agent, wherein the concentration of hydrogen peroxide in the bleaching agent is 2 wt % and the concentration of acetic acid is 3 wt %; mixing the enzyme-treated BSG fiber with the bleaching agent at a solid-liquid ratio of 40 g:300 mL, performing a bleaching treatment for 10 min at a temperature of 70° C., an ultrasonic frequency of 70 kHz, and a microwave power of 600 W, and then filtering, collecting the filter cake, washing it with distilled water, and then air-drying it to obtain a bleached BSG fiber;

[0056] (3) The bleached BSG fiber is mixed with a NaOH solution with a concentration of 0.8wt% in a ratio of 40g:300mL, and alkali-treated for 25min at a temperature of 70°C, an ultrasonic frequency of 70kHz and a microwave power of 600W. Then, a 3wt% aqueous hydrogen peroxide solution is added to the obtained alkali-treated solution, and the bleached BSG fiber and the hydrogen peroxide solution are kept at a temperature of 70°C, an ultrasonic frequency of 70kHz and a microwave power of 600W for 15min. Then, the ultrasonic wave and the microwave are removed, and the mixture is kept at room temperature (25°C) and static conditions for 2h. After filtering, the filter cake is collected and washed with distilled water to a pH value of 7, and then freeze-dried to obtain dietary fiber.

[0057] Example 2

[0058] The method of Example 1 is used for operation, except that in step (1), the activity of laccase is 250 U / g, the concentration of laccase reagent is 15.5 U / g, the enzyme treatment temperature is adjusted to 45°C, and the enzyme treatment time is shortened to 10 h; in step (2), the ultrasonic frequency is adjusted to 80 kHz, the microwave power is adjusted to 700 W, and the bleaching time is extended to 15 min; in step (3), the concentration of NaOH solution is adjusted to 1.0 wt% during alkali treatment, the alkali treatment time is extended to 30 min, the concentration of hydrogen peroxide solution is adjusted to 4 wt%, and the holding time under static conditions is shortened to 1.5 h.

[0059] Example 3

[0060] The method of Example 1 is used for operation, except that in step (1), the activity of laccase is 180 U / g, the concentration of laccase reagent is 16 U / g, the enzyme treatment temperature is adjusted to 35°C, and the enzyme treatment time is extended to 14 h; in step (2), the ultrasonic frequency is adjusted to 60 kHz during bleaching treatment, the microwave power is reduced to 500 W, and the bleaching treatment time is shortened to 8 min; in step (3), the concentration of NaOH solution is adjusted to 0.6 wt% during alkali treatment, the alkali treatment time is shortened to 20 min, the concentration of hydrogen peroxide solution is adjusted to 2.5 wt%, and the holding time under static conditions is extended to 2.5 h.

[0061] Comparative Example 1

[0062] The sample in this comparative example is specifically the enzyme-treated BSG fiber prepared in step (1) of Example 1.

[0063] Comparative Example 2

[0064] The sample in this comparative example is specifically the bleached BSG fiber prepared in step (2) of Example 1.

[0065] Comparative Example 3

[0066] The chlorine-bleached fiber is prepared, comprising the following steps: 40 g of BSG is mixed with 200 mL of sodium chlorite (NaClO2) solution (with a concentration of 0.05 g / mL), the pH value of the obtained mixed system is adjusted to 4 with hydrochloric acid (with a concentration of 100 mM), and bleaching is performed for 7 hours under stirring at a temperature of 80°C; after the bleaching treatment is completed, the filter cake is collected after filtering and washed with distilled water until the pH value is 7, and then freeze-dried to obtain the chlorine-bleached fiber.

[0067] Test Example 1

[0068] The products prepared in each embodiment and comparative example were characterized and tested for performance, and compared with untreated BSG, as follows:

[0069] Figure 2The figures are actual pictures of the products prepared in Examples 1 to 3 and Comparative Examples 1 to 3. The results show that the dietary fiber prepared by the method of the present invention has a higher whiteness.

[0070] Figure 3 The Fourier transform infrared spectra (FTIR) of the products prepared in Example 1 and Comparative Examples 1 to 3 are shown in Figure 1. The difference in transmittance reflects the effectiveness of bleaching. The results show that at 1315 cm -1 and 1020cm -1 The isopent value is reduced, indicating that the removal effect of lignin in Example 1 is improved.

[0071] Figure 4 The X-ray diffraction (XRD) spectra of the products prepared in Example 1 and Comparative Examples 1 to 3 show that the strength of the amorphous region of the dietary fiber prepared in Example 1 is reduced and the crystalline peak is enhanced, indicating that the method of the present invention has a good delignification effect and is beneficial to improving the crystallinity of cellulose.

[0072] Figure 5 The TGA curves of the products prepared in Example 1 and Comparative Examples 1 to 3 show that the TGA curve of the dietary fiber prepared in Example 1 shows less weight loss, indicating that lignin is removed and more heat-stable cellulose is left.

[0073] Figure 6 The DSC curves of the products prepared in Example 1 and Comparative Examples 1 to 3 show that the exothermic peak at 200 to 400°C on the DSC curve indicates lignin decomposition. Example 1 shows a decrease in strength, indicating that lignin is effectively removed. The residual weight (above 600°C) represents the ash content, and Example 1 shows a slightly lower residue, which is due to effective delignification and impurity removal.

[0074] Figure 7 The SEM images of the products prepared in Example 1 and Comparative Examples 1 to 3 show that the surface of Example 1 is smoother, and the cracks and porosity are more obvious due to the removal of lignin. The internal structure of the dietary fiber in Example 1 is better exposed, which improves water absorption and other functional properties.

[0075] Table 1 shows the performance test results of the products prepared in Examples 1 to 3 and Comparative Examples 1 to 3. It can be seen from Table 1 that the dietary fiber prepared by the method of the present invention has high whiteness and excellent comprehensive performance.

[0076] Table 1 Performance test results of products prepared in Examples 1 to 3 and Comparative Examples 1 to 3

[0077] Test indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 CIE whiteness index (%) 82.42 85.30 77.60 13.39 15.24 55.56 Claessen lignin (%) 0.50 0.39 0.95 20.00 19.05 2.50 Acid soluble lignin (%) 1.18 1.05 1.23 4.07 3.66 3.58 Total wood (%) 1.68 1.45 3.75 24.07 22.71 6.08 Hemicellulose (%) 43.15 33.47 44.86 62.30 76.20 79.73 Cellulose(%) 56.65 66.33 54.94 37.50 23.60 20.07 Water holding capacity (WBC, g / g) 4.64 3.81 4.58 3.27 3.52 3.04 Swelling degree (SC, g / g) 3.00 2.65 3.80 1.15 2.12 1.92 Adhesion capacity (BC, g / mL) 0.54 0.51 0.54 0.79 0.72 0.51 Oil storage capacity (OHC, g / g) 3.16 2.40 3.57 1.68 2.24 4.08

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing dietary fiber without using chlorine-containing reagents and / or ozone, comprising the following steps: mixing lignocellulosic biomass with a laccase reagent and performing enzyme treatment to obtain enzyme-treated fibers; The enzyme-treated fiber is mixed with a bleaching agent, and bleached under ultrasonic and microwave conditions to obtain bleached fiber; the bleaching agent is an aqueous solution containing hydrogen peroxide and an acid agent; The bleached fiber is mixed with an alkaline solution, and subjected to an alkali treatment under ultrasonic and microwave conditions to obtain an alkali-treated feed solution; The alkali-treated feed liquid is mixed with a hydrogen peroxide aqueous solution and subjected to oxidation treatment to obtain the dietary fiber.

2. The preparation method according to claim 1, characterized in that: The lignocellulosic biomass includes one or more of brewer's grains, bagasse, rice husks and straw.

3. The preparation method according to claim 1, characterized in that: The laccase reagent comprises laccase and a buffer, the activity of the laccase is 180-250 U / g, the pH value of the buffer is 4.5-5.5; and the concentration of the laccase in the laccase reagent is 13.5-16.5 U / g.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The mass ratio of the lignocellulosic biomass to the laccase reagent is 13-14:1; the temperature of the enzyme treatment is 35-50°C, and the time is 6-14 hours.

5. The preparation method according to claim 1, characterized in that: The concentration of hydrogen peroxide in the bleaching agent is 2-3wt%, the concentration of the acid agent in the bleaching agent is 2-5wt%, and the acid agent is acetic acid; the dosage ratio of the enzyme-treated fiber to the bleaching agent is 40g:280-320mL; the conditions of the bleaching treatment include: an ultrasonic frequency of 60-80kHz, a microwave power of 500-700W, a temperature of 40-70°C, and a time of 8-20min.

6. The preparation method according to claim 1, characterized in that: The alkaline solution includes a NaOH solution or a Na2CO3 solution, the concentration of the NaOH solution is 0.5-1wt%, and the concentration of the Na2CO3 solution is 1.5-2wt%; the dosage ratio of the bleached fiber to the alkaline solution is 1-2g:7.5-10mL; the conditions for the alkali treatment include: an ultrasonic frequency of 60-90kHz, a microwave power of 500-700W, a temperature of 70-80°C, and a time of 20-30min.

7. The preparation method according to claim 1, characterized in that: The concentration of the aqueous hydrogen peroxide solution is 2-4wt%, and the dosage ratio of the bleached fiber to the aqueous hydrogen peroxide solution is 40g:280-320mL; the oxidation treatment comprises sequentially performing a first-stage oxidation treatment and a second-stage oxidation treatment; the first-stage oxidation treatment is performed under ultrasonic and microwave conditions, and the conditions of the first-stage oxidation treatment include: an ultrasonic frequency of 60-90kHz, a microwave power of 500-700W, a temperature of 40-70°C, and a time of 10-20min; the second-stage oxidation treatment does not use ultrasonic and microwave, and the conditions of the second-stage oxidation treatment include: a temperature of 20-30°C and a time of 1.5-2.5h.

8. The dietary fiber prepared by the preparation method according to any one of claims 1 to 7.

9. The dietary fiber according to claim 8, characterized in that The CIE whiteness index of the dietary fiber is 77-86%.

10. Use of the dietary fiber according to claim 8 or 9 in food or nutritional products.

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