Method for preparing high-activity xylooligosaccharide from bamboo wood under catalysis of conjugated acid and base

Abstract

The method comprises the following steps: S1, adding a formic acid-sodium formate solution into raw material powder, carrying out high-temperature oil bath, cooling to room temperature, carrying out suction filtration to obtain a supernatant A containing xylooligosaccharide, repeatedly cleaning and carrying out suction filtration until the extracted liquid is neutral, and drying at low temperature to obtain the xylooligosaccharide powder; pre-treated lignin raw materials are obtained; s2, putting the supernate into a dialysis bag, and magnetically stirring to obtain primary dialysis liquid B; s3, putting the preliminary dialysis liquid B into a dialysis bag, and magnetically stirring to obtain dialysis liquid C; s4, concentrating the dialysis liquid C to obtain concentrated liquid D; and S5, pre-freezing the concentrated liquid D, and freeze-drying the sample to obtain xylooligosaccharide powder E. According to the method, formic acid-sodium formate is used as a catalytic medium, different acid concentrations and molar ratios are adopted, high-temperature oil bath and dialysis freeze-drying are utilized for two-step extraction, and the yield of xylooligosaccharide after catalysis is obviously increased.

Description

Technical Field

[0001] The invention belongs to the technical field of substrates containing cellulose materials, and in particular relates to a method for preparing highly active xylooligosaccharides from bamboo materials by catalyzing conjugate acid and base (formic acid-sodium formate). Background Art

[0002] Bamboo, a widely distributed, rapidly growing, and renewable biomass resource in my country with an annual production of tens of millions of tons, is an ideal raw material for producing high-value-added xylo-oligosaccharides (XOS). Its high hemicellulose content (approximately 20%-30%) and rich xylan components make it an ideal raw material for producing high-value-added XOS. However, bamboo's dense cell wall structure, due to the chemical cross-linking of lignin-carbohydrate complexes (LCCs), and the high degree of acetylation and complex branching of hemicellulose itself, form a natural anti-degradation barrier. This results in traditional acid / alkali pretreatment processes facing bottlenecks such as harsh reaction conditions (high temperature and high pressure), the formation of a large number of inhibitory byproduct compounds, and low selectivity for the target product. Lignin, a rigid aromatic polymer, forms a three-dimensional network barrier with polysaccharides through ether and ester bonds, hindering the effective contact of chemical or biological catalysts with hemicellulose. Traditional processes are also inefficient in removing lignin, further limiting the dissolution rate of hemicellulose and the yield of XOS. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing oligoxylose from bamboo using formic acid-sodium formate synergistic catalysis. The method uses formic acid and sodium formate as catalytic reagents and fully utilizes the synergistic effect of formic acid and sodium formate to directly extract oligoxylose from bamboo, thereby solving the cumbersome problem that traditional oligoxylose extraction requires destroying the lignin barrier before extraction.

[0004] To achieve the above object, the present invention is implemented through the following scheme:

[0005] A method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis comprises the following steps:

[0006] S1: Weigh 4 parts of lignocellulose raw material powder and put them into a reactor, then add formic acid-sodium formate solution with a solid-liquid ratio of 1:10. After mixing evenly, place in a high-temperature oil bath at 150-170°C for 30-120 minutes. After the reaction is completed, cool to room temperature and filter the turbid liquid to obtain supernatant A containing oligoxylose. Repeat the washing and filtration until the extracted liquid is neutral, and dry at low temperature to obtain the pretreated lignin raw material.

[0007] S2: extract supernatant A and place it into a dialysis bag, place the dialysis bag into a beaker, add deionized water, and stir magnetically to obtain preliminary dialysis liquid B;

[0008] S3: Transfer the preliminary dialysis liquid B to a dialysis bag, place the dialysis bag in a beaker, add deionized water, and after magnetic stirring, replace the deionized water every 24 hours. Collect all the liquid to obtain dialysis liquid C;

[0009] S4: concentrating the dialyzed liquid C to obtain concentrated liquid D;

[0010] S5: The sample of concentrated liquid D is placed in a -80°C freezer for pre-freezing. After the pre-freezing is completed, the sample is dried at low temperature to obtain oligoxylose powder E.

[0011] In a further embodiment, in step S1, the formic acid-sodium formate acid treatment temperature is set to 170° C., and the treatment time is set to 60 min.

[0012] In a further embodiment, in step S1, the low-temperature drying temperature is 40-50°C, and the moisture content of the pretreated lignin raw material after drying is less than 10%.

[0013] In a further scheme, in step S1, the wood cellulose raw material powder is bamboo powder, and the bamboo is beaten into shavings, dried, and then crushed into fine particles using a grinder. The particles are then passed through an 80-mesh sieve and dried at a low temperature of 40-50°C until the moisture content is less than 10%, thereby obtaining the wood cellulose raw material powder.

[0014] In a further embodiment, in step S1, the acid concentration of the formic acid-sodium formate solution is 0.4-0.8 M, and the molar ratio of the formic acid-sodium formate solution is 1:10-10:1.

[0015] In a further embodiment, in step S1, the acid concentration of the formic acid-sodium formate solution is 0.6 M, and the molar ratio of the formic acid-sodium formate solution is 10:1.

[0016] In a further scheme, in step S2, 20 mL of supernatant A is extracted, the dialysis bag is 200 KDa, the dialysis bag is placed in a beaker, and 500 mL of deionized water is added, and the magnetic stirring time is 72 h.

[0017] In a further solution, in step S3, the dialysis bag is 1000KDa, the dialysis bag is placed in a beaker, and 500mL of deionized water is added, and the magnetic stirring time is 72h.

[0018] In a further embodiment, in step S4, the concentration temperature is set to 50°C, and the liquid volume of the concentrated liquid D is concentrated to 10 mL.

[0019] In a further scheme, in step S5, the vacuum degree of vacuum drying is set to 0.5 Pa, the temperature is set to -55°C, and the duration is 24 hours. After drying, the moisture content of the oligoxylose powder E is less than 5%; the pre-freezing time is maintained for 2-4 hours to ensure that the pre-freezing is completed when the sample is completely crystallized and the ice crystals are evenly distributed.

[0020] The beneficial effects of the present invention are:

[0021] The present invention uses formic acid and sodium formate as catalytic reagents, adopts different catalytic temperatures, and utilizes a high-temperature oil bath for catalysis, and the output of oligoxylose is significantly increased after catalysis. Using formic acid and sodium formate as catalytic reagents, the synergistic effect of formic acid and sodium formate is fully utilized to directly extract oligoxylose from bamboo, solving the cumbersome problem that traditional oligoxylose extraction requires destroying the lignin barrier before hemicellulose extraction. The present invention, through the above method, can use a high-temperature oil bath to synergistically catalyze bamboo with formic acid and sodium formate without removing lignin, with controllable heating temperature, simple and safe operation, high yield of oligoxylose, and high antioxidant activity of the extracted oligoxylose. The cost is low, the process is economical and environmentally friendly, and the catalytic effect is better than that of a single solvent.

[0022] The present invention proposes a formic acid-sodium formate synergistic catalytic system, which uses the weak acidity of formic acid to gently dissociate the lignin-carbohydrate bond, while utilizing the buffering effect of sodium formate to stabilize the pH value of the system, inhibit excessive hydrolysis of cellulose, and significantly improve the conversion selectivity of xylan to oligoxylose. This process can achieve efficient degradation under normal pressure conditions; its synergistic effect effectively breaks down the lignin barrier and retains the integrity of the hemicellulose skeleton, thereby increasing the yield of oligoxylose by more than 30% compared to the traditional acid method. At the same time, it has a wide adaptability to raw materials of different bamboo ages and bamboo species, overcoming the stringent requirements of traditional methods for raw material uniformity. By optimizing the catalytic system and process parameters, this technology provides a green and economical solution for the high-value utilization of bamboo resources, which is in line with the sustainable development needs of biomass refining. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of the method for the synergistic catalysis of lignocellulosic raw materials by formic acid and sodium formate provided by the present invention;

[0024] Figure 2 This is an infrared spectrum of bamboo under different catalytic conditions provided by the present invention;

[0025] Figure 3 This is a graph showing the yield of xylooligosaccharides from bamboo under different catalytic conditions provided by the present invention;

[0026] Figure 4 This is a graph showing the antioxidant activity of oligosaccharides from bamboo under different catalytic conditions provided by the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Example 1

[0029] A method for preparing xylooligosaccharides from lignocellulose raw materials by synergistic catalysis of formic acid and sodium formate comprises the following steps:

[0030] S1: Weigh 4 g of raw material powder and put it into the reactor, then add formic acid-sodium formate solution, the acid concentration is 0.4 M, the molar ratio of formic acid-sodium formate solution is 1:10 (calculated based on formate concentration), the solid-liquid ratio is set to 1:10, mix well, tighten the reaction bottle cap, put it into a high-temperature oil bath, the temperature of the high-temperature oil bath is set to 170 ° C, and the high-temperature working time is 60 min. After the reaction is completed, take out the reaction bottle and cool it to room temperature. Pour the turbid liquid in the reaction bottle into a suction funnel, filter and obtain supernatant A containing oligoxylose, use distilled water to filter and wash, repeatedly wash and filter until the extracted liquid is neutral, and dry it in a low-temperature oven to obtain the pretreated lignin raw material;

[0031] S2: 20 mL of supernatant A was drawn and placed into a 200 KDa dialysis bag, which was then placed into a beaker. 500 mL of deionized water was then added and magnetically stirred for 72 h to obtain preliminary dialyzed liquid B.

[0032] S3: Transfer the preliminary dialysis fluid B to a 1000 kDa dialysis bag, place the dialysis bag in a beaker, add 500 mL of deionized water, and stir magnetically for 72 hours. Replace the deionized water every 24 hours, and collect all the liquid to obtain dialysis fluid C.

[0033] S4: Add the dialyzed liquid C to a rotary evaporator for concentration, set the temperature to 50°C, and concentrate the liquid volume to 10 mL to obtain concentrated liquid D;

[0034] S5: Transfer the concentrated liquid D to a Petri dish and prefreeze the sample in a -80°C freezer for 2-4 hours to ensure complete crystallization and uniform distribution of ice crystals. After prefreezing, transfer the sample to a vacuum freeze dryer and dry at low temperature to obtain dry xylo-oligosaccharide powder E.

[0035] Example 2

[0036] A method for preparing xylooligosaccharides from lignocellulose raw materials by synergistic catalysis of formic acid and sodium formate comprises the following steps:

[0037] S1: Weigh 4 g of raw material powder and put it into the reactor, then add formic acid-sodium formate solution, the acid concentration is 0.4 M, the molar ratio of formic acid-sodium formate solution is 1:5 (calculated based on formate concentration), the material-liquid ratio is set to 1:10, mix well, tighten the reaction bottle cap, put it into a high-temperature oil bath, the temperature of the high-temperature oil bath is set to 170 ° C, and the high-temperature working time is 60 min. After the reaction is completed, take out the reaction bottle and cool it to room temperature. Pour the turbid liquid in the reaction bottle into a suction funnel, filter and obtain supernatant A containing oligoxylose, use distilled water to filter and wash, repeatedly wash and filter until the extracted liquid is neutral, and dry it in a low-temperature oven to obtain the pretreated lignin raw material;

[0038] S2: 20 mL of supernatant A was drawn and placed into a 200 KDa dialysis bag, which was then placed into a beaker. 500 mL of deionized water was then added and magnetically stirred for 72 h to obtain preliminary dialyzed liquid B.

[0039] S3: Transfer the preliminary dialysis fluid B to a 1000 kDa dialysis bag, place the dialysis bag in a beaker, add 500 mL of deionized water, and stir magnetically for 72 hours. Replace the deionized water every 24 hours, and collect all the liquid to obtain dialysis fluid C.

[0040] S4: Add the dialyzed liquid C to a rotary evaporator for concentration, set the temperature to 50°C, and concentrate the liquid volume to 10 mL to obtain concentrated liquid D;

[0041] S5: Transfer the concentrated liquid D to a Petri dish and prefreeze the sample in a -80°C freezer for 2-4 hours to ensure complete crystallization and uniform distribution of ice crystals. After prefreezing, transfer the sample to a vacuum freeze dryer and dry at low temperature to obtain dry xylo-oligosaccharide powder E.

[0042] Example 3

[0043] A method for preparing xylooligosaccharides from lignocellulose raw materials by synergistic catalysis of formic acid and sodium formate comprises the following steps:

[0044] S1: Weigh 4 g of raw material powder and put it into the reactor, then add formic acid-sodium formate solution, the acid concentration is 0.4 M, the molar ratio of formic acid-sodium formate solution is 1:1 (calculated based on formate concentration), the material-liquid ratio is set to 1:10, mix well, tighten the reaction bottle cap, put it into a high-temperature oil bath, the temperature of the high-temperature oil bath is set to 170°C, and the high-temperature working time is 60 minutes. After the reaction is completed, take out the reaction bottle and cool it to room temperature. Pour the turbid liquid in the reaction bottle into a suction funnel, filter and obtain supernatant A containing oligoxylose, use distilled water to filter and wash, repeatedly wash and filter until the extracted liquid is neutral, and dry it in a low-temperature oven to obtain the pretreated lignin raw material;

[0045] S2: 20 mL of supernatant A was drawn and placed into a 200 KDa dialysis bag, which was then placed into a beaker. 500 mL of deionized water was then added and magnetically stirred for 72 h to obtain preliminary dialyzed liquid B.

[0046] S3: Transfer the preliminary dialysis fluid B to a 1000 kDa dialysis bag, place the dialysis bag in a beaker, add 500 mL of deionized water, and stir magnetically for 72 hours. Replace the deionized water every 24 hours, and collect all the liquid to obtain dialysis fluid C.

[0047] S4: Add the dialyzed liquid C to a rotary evaporator for concentration, set the temperature to 50°C, and concentrate the liquid volume to 10 mL to obtain concentrated liquid D;

[0048] S5: Transfer the concentrated liquid D to a Petri dish and prefreeze the sample in a -80°C freezer for 2-4 hours to ensure complete crystallization and uniform distribution of ice crystals. After prefreezing, transfer the sample to a vacuum freeze dryer and dry at low temperature to obtain dry xylo-oligosaccharide powder E.

[0049] Example 4

[0050] A method for preparing xylooligosaccharides from lignocellulose raw materials by synergistic catalysis of formic acid and sodium formate comprises the following steps:

[0051] S1: Weigh 4 g of raw material powder and put it into the reactor, then add formic acid-sodium formate solution, the acid concentration is 0.4 M, the molar ratio of formic acid-sodium formate solution is 5:1 (calculated based on formate concentration), the material-liquid ratio is set to 1:10, mix well, tighten the reaction bottle cap, put it into a high-temperature oil bath, the temperature of the high-temperature oil bath is set to 170°C, and the high-temperature working time is 60 minutes. After the reaction is completed, take out the reaction bottle and cool it to room temperature. Pour the turbid liquid in the reaction bottle into a suction funnel, filter and obtain supernatant A containing oligoxylose, use distilled water to filter and wash, repeatedly wash and filter until the extracted liquid is neutral, and dry it in a low-temperature oven to obtain the pretreated lignin raw material;

[0052] S2: 20 mL of supernatant A was drawn and placed into a 200 KDa dialysis bag, which was then placed into a beaker. 500 mL of deionized water was then added and magnetically stirred for 72 h to obtain preliminary dialyzed liquid B.

[0053] S3: Transfer the preliminary dialysis fluid B to a 1000 kDa dialysis bag, place the dialysis bag in a beaker, add 500 mL of deionized water, and stir magnetically for 72 hours. Replace the deionized water every 24 hours, and collect all the liquid to obtain dialysis fluid C.

[0054] S4: Add the dialyzed liquid C to a rotary evaporator for concentration, set the temperature to 50°C, and concentrate the liquid volume to 10 mL to obtain concentrated liquid D;

[0055] S5: Transfer the concentrated liquid D to a Petri dish and prefreeze the sample in a -80°C freezer for 2-4 hours to ensure complete crystallization and uniform distribution of ice crystals. After prefreezing, transfer the sample to a vacuum freeze dryer and dry at low temperature to obtain dry xylo-oligosaccharide powder E.

[0056] Example 5

[0057] A method for preparing xylooligosaccharides from lignocellulose raw materials by synergistic catalysis of formic acid and sodium formate comprises the following steps:

[0058] S1: Weigh 4 g of raw material powder and put it into the reactor, then add formic acid-sodium formate solution, the acid concentration is 0.4 M, the molar ratio of formic acid-sodium formate solution is 10:1 (calculated based on formate concentration), the solid-liquid ratio is set to 1:10, mix well, tighten the reaction bottle cap, put it into a high-temperature oil bath, the temperature of the high-temperature oil bath is set to 170°C, and the high-temperature working time is 60 minutes. After the reaction is completed, take out the reaction bottle and cool it to room temperature. Pour the turbid liquid in the reaction bottle into a suction funnel, filter and obtain supernatant A containing oligoxylose, use distilled water to filter and wash, repeatedly wash and filter until the extracted liquid is neutral, and dry it in a low-temperature oven to obtain the pretreated lignin raw material;

[0059] S2: 20 mL of supernatant A was drawn and placed into a 200 KDa dialysis bag, which was then placed into a beaker. 500 mL of deionized water was then added and magnetically stirred for 72 h to obtain preliminary dialyzed liquid B.

[0060] S3: Transfer the preliminary dialysis fluid B to a 1000 kDa dialysis bag, place the dialysis bag in a beaker, add 500 mL of deionized water, and stir magnetically for 72 hours. Replace the deionized water every 24 hours, and collect all the liquid to obtain dialysis fluid C.

[0061] S4: Add the dialyzed liquid C to a rotary evaporator for concentration, set the temperature to 50°C, and concentrate the liquid volume to 10 mL to obtain concentrated liquid D;

[0062] S5: Transfer the concentrated liquid D to a Petri dish and prefreeze the sample in a -80°C freezer for 2-4 hours to ensure complete crystallization and uniform distribution of ice crystals. After prefreezing, transfer the sample to a vacuum freeze dryer and dry at low temperature to obtain dry xylo-oligosaccharide powder E.

[0063] Comparative test

[0064] Example 5 of the present invention was taken as experimental group 1, that is, the acid concentration of the formic acid-sodium formate solution was 0.4 M, the molar ratio was 10:1, the reaction temperature was 170° C., and the reaction time was 60 min to obtain pretreated lignocellulose raw material I and oligoxylose powder I.

[0065] Experimental group 2: lignocellulosic raw material II without any treatment.

[0066] Experimental Group 3: The method for preparing xylo-oligosaccharides was followed as in Example 1, except that the catalytic agent was replaced with distilled water. Pretreated lignocellulose raw material III and xylo-oligosaccharide powder II were obtained.

[0067] Experimental Group 4: Referring to the method for preparing xylo-oligosaccharides in Example 5, the concentration of the catalytic reagent formic acid-sodium formate solution was adjusted to 0.6 M to obtain pretreated lignocellulose raw material IV and xylo-oligosaccharide powder III.

[0068] Experimental Group 5: Referring to the method for preparing xylo-oligosaccharides in Example 5, the concentration of the catalytic reagent formic acid-sodium formate solution was adjusted to 0.8 M to obtain pretreated lignocellulose raw material V and xylo-oligosaccharide powder IV.

[0069] Analysis of the products obtained from the above five groups of experiments:

[0070] 1. The structure of the pretreated samples was characterized by Fourier transform infrared spectroscopy, and the changes in the cellulose, hemicellulose and lignin contents of the samples before and after pretreatment were analyzed.

[0071] The products obtained from the above five groups of experiments were subjected to FT-IR infrared spectrum image acquisition. The test instrument used was Nicolet iS10. The test conditions were: ATR method, scanning air background; resolution: 4cm -1 Scanning range: 400-4000cm -1 Scan times: 32 times. The three major components of bamboo, cellulose, hemicellulose and lignin, have changed in content after pretreatment, so they will show certain changes in infrared absorption spectra in different bands, such as Figure 2 shown.

[0072] This study uses infrared spectroscopy to identify functional groups in bamboo after pretreatment, using standard methods from the U.S. Department of Energy (NREL) to determine changes in the composition of cellulose, hemicellulose, and lignin. The functional groups in bamboo vary significantly under different treatment conditions. For ease of comparison, the functional groups corresponding to the main band values ​​in the infrared spectral overlay are summarized in Table 1.

[0073] Table 1 Characteristic peaks and corresponding functional groups

[0074]

[0075] Comprehensive changes in the spectrum of cellulose, hemicellulose, and lignin, 2978.3 cm -1 and 2896.2cm -1The absorption peaks at 1400.0 cm are attributed to the asymmetric and symmetric stretching vibrations of the CH bonds in cellulose and hemicellulose, respectively, indicating the presence of CH2 groups in the sample, which is a typical structural feature of cellulose and hemicellulose. -1 The absorption peak at 1238.0cm is derived from the CH2 bending vibration of the amorphous region of cellulose or the vibration of the aromatic ring skeleton of lignin, indicating that the sample contains both cellulose and lignin. The smaller absorption peak at this location indicates that the cellulose and lignin contents in the bamboo powder decreased after catalysis. -1 The CO stretching vibration peak at 1054.4 cm is related to the acetoxy group (-OAc) or ether bond of hemicellulose, indicating that the structural characteristics of hemicellulose are significant. -1 and 892.5cm -1 The strong absorption peaks at correspond to the β-1,4-glycosidic bond and sugar ring CO stretching vibration of cellulose, as well as the characteristic vibration of the β-configuration glycosidic bond, further confirming that cellulose is the main component of the sample and its β-glycosidic bond structure is clear.

[0076] Depend on Figure 2 It can be concluded that the functional group content of bamboo changed before and after catalysis, and the degree of change was different in different catalytic methods. As can be seen from the figure, hemicellulose decreased significantly after catalysis, indicating that the conjugate acid-base system can effectively degrade hemicellulose in bamboo into oligoxylose.

[0077] 2. The contents of cellulose, hemicellulose and lignin in the five experimental products were determined according to the standard method of the U.S. Department of Energy (NREL). The specific results are shown in Table 2 below:

[0078] Table 2 Chemical composition data of experimental products

[0079]

[0080] As can be seen from Table 2, the main chemical components of bamboo changed significantly before and after catalysis, and the contents of each component obtained by different catalytic methods were different. The similarity was that the hemicellulose content showed a significant decreasing trend after catalysis, and the relative contents of cellulose and lignin increased, indicating that the formic acid-sodium formate system can better retain cellulose while catalytically extracting hemicellulose.

[0081] 3. The XOS content of the supernatant obtained in the above experiment was determined, and the oligoxylose content in the hydrolyzate was analyzed using an anion exchange chromatograph equipped with a pulsed amperometric detector and an anion exchange column. The anion exchange chromatograph was Dio-nex ICS-3000, and the chromatographic column was CarboPac TMPA20, mobile phase is 250mM sodium hydroxide and 50mM sodium hydroxide, the flow rate is controlled at 0.5mL / min. The yield of oligoxylose in the hydrolyzate is calculated according to formula 1:

[0082]

[0083] The analysis results are as follows Figure 3 As shown:

[0084] Depend on Figure 3 It can be seen that the formic acid-sodium formate conjugate acid-base solution of all three acid concentrations can achieve the purpose of catalyzing bamboo powder. Compared with the control group, the yield of oligoxylose in bamboo after catalysis was significantly increased. As the acid concentration increased from 0.4M to 0.6M, the yield of XOS (X2-X6) and total XOS showed a trend of first increasing and then decreasing. When the acid concentration was 0.6M, the highest oligoxylose yield (46.74%) and the lowest Xylose / XOS ratio (0.25) were obtained. The lower the Xylose / XOS ratio, the less xylose content in the supernatant, and the more oligoxylose content.

[0085] 4. The supernatant obtained from the above experiment was separated and purified and its antioxidant activity was determined. The xylooligosaccharides in the supernatant were separated by membrane dialysis. After dialysis, solid xylooligosaccharides were obtained by rotary evaporation concentration and freeze drying.

[0086] Prepare 0.1M DPPH solution, store it in a dark place in a 4℃ refrigerator for later use, use it within 24h, and use UV-2600 ultraviolet spectrophotometer to measure the absorbance of different working solutions at 517nm. Negative control group A0: 1mL anhydrous ethanol solution and 2mL DPPH free radical working solution, shake and mix, react in a dark environment for 30min, and measure the absorbance. Experimental group A1: 1mL gradient concentration oligosaccharide (XOS) sample solution and 2mL DPPH free radical working solution, shake and mix, react in a dark environment for 30min, and measure the absorbance. Blank control group A2: 1mL XOS test solution of different concentrations is mixed with 2mL anhydrous ethanol, shake and mix, react in a dark environment for 30min, and measure the absorbance. According to the public

[0087] Formula 2 calculates DPPH clearance rate:

[0088]

[0089] The analysis results are as follows Figure 4As shown in the results, with the increase of the concentration of xylo-oligosaccharide solution, the DPPH free radical scavenging rate gradually increased. At a concentration of 0.1 mg / mL, the DPPH scavenging rates of each experimental group reached 82.66% (0.4M group), 90.25% (0.6M group), and 73.16% (0.8M group), respectively. The IC50 values ​​of each experimental group calculated using the linear regression equation were 0.516 mg / mL (0.4M group), 0.444 mg / mL (0.6M group), and 0.602 mg / mL (0.8M group), respectively. The above results show that the experimentally prepared xylo-oligosaccharide has high antioxidant activity.

[0090] In summary, the present invention uses formic acid and sodium formate as the catalytic medium, employing different acid concentrations and molar ratios, to extract xylose oligosaccharides using a high-temperature oil bath. The main chemical components of bamboo powder before and after catalysis were studied, and changes in bamboo chemical composition before and after catalysis were examined by Fourier transform spectroscopy. The resulting supernatant was analyzed for xylose oligosaccharide yield and antioxidant activity. The composition and yield of xylose oligosaccharides after catalysis under different conditions were analyzed by anion exchange chromatography. Xylose oligosaccharide solids were obtained using a membrane dialysis separation-rotary evaporation concentration-freeze drying method, and DPPH scavenging rate was measured by ultraviolet spectrophotometry. The results showed that the yield of xylose oligosaccharides increased significantly after catalysis. The 0.6 M formic acid-sodium formate catalysis yielded the highest xylose oligosaccharide yield and the lowest Xylose / XOS ratio, followed by 0.8 M formic acid-sodium formate catalysis, and finally 0.4 M formic acid-sodium formate catalysis. The xylose oligosaccharides obtained by formic acid-sodium formate catalysis exhibited good DPPH scavenging ability, indicating that the xylose oligosaccharides prepared by the present invention have high antioxidant activity. The contents of cellulose, lignin and xylan in the bamboo material after catalysis were determined according to the standard method of the U.S. Department of Energy (NREL), which fully demonstrated that the output of the oligoxylose after catalysis of the present invention was significantly increased.

[0091] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0092] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis, characterized in that: The following steps are involved: S1: Weigh 4 parts of lignocellulose raw material powder and put them into a reactor, then add formic acid-sodium formate solution with a solid-liquid ratio of 1:

10. After mixing evenly, place in a high-temperature oil bath at 150-170°C for 30-120 minutes. After the reaction is completed, cool to room temperature and filter the turbid liquid to obtain supernatant A containing oligoxylose. Repeat the washing and filtration until the extracted liquid is neutral, and dry at low temperature to obtain the pretreated lignin raw material. S2: extract supernatant A and place it into a dialysis bag, place the dialysis bag into a beaker, add deionized water, and stir magnetically to obtain preliminary dialysis liquid B; S3: Transfer the preliminary dialysis liquid B to a dialysis bag, place the dialysis bag in a beaker, add deionized water, and after magnetic stirring, replace the deionized water every 24 hours. Collect all the liquid to obtain dialysis liquid C; S4: concentrating the dialyzed liquid C to obtain a concentrated liquid D; S5: The sample of concentrated liquid D is placed in a -80°C freezer for pre-freezing. After the pre-freezing is completed, the sample is dried at low temperature to obtain oligoxylose powder E.

2. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S1, the formic acid-sodium formate acid treatment temperature is set to 170° C., and the treatment time is set to 60 min.

3. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S1, the low-temperature drying temperature is 40-50° C., and the moisture content of the pretreated lignin raw material after drying is less than 10%.

4. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S1, the lignocellulose raw material powder is bamboo powder. The bamboo is beaten into shavings, dried, and crushed into fine particles using a grinder. The particles are then passed through an 80-mesh sieve and dried at 40-50° C. until the moisture content is less than 10%, thereby obtaining the lignocellulose raw material powder.

5. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S1, the acid concentration of the formic acid-sodium formate solution is 0.4-0.8 M, and the molar ratio of the formic acid-sodium formate solution is 1:10-10:

1.

6. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 5, characterized in that: In step S1, the acid concentration of the formic acid-sodium formate solution is 0.6 M, and the molar ratio of the formic acid-sodium formate solution is 10:

1.

7. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S2, 20 mL of supernatant A was extracted, the dialysis bag was 200 KDa, the dialysis bag was placed in a beaker, and 500 mL of deionized water was added, and the magnetic stirring time was 72 h.

8. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S3, the dialysis bag is 1000 KDa, and the dialysis bag is placed in a beaker, and 500 mL of deionized water is added, and the magnetic stirring time is 72 h.

9. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S4, the concentration temperature is set to 50°C, and the liquid volume of the concentrated liquid D is concentrated to 10 mL.

10. The method for preparing highly active xylooligosaccharides from bamboo using conjugated acid-base catalysis according to claim 1, characterized in that: In step S5, the vacuum degree of vacuum drying is set to 0.5 Pa, the temperature is set to -55°C, and the duration is 24 hours. After drying, the moisture content of the oligoxylose powder E is less than 5%. The pre-freezing time is maintained for 2-4 hours to ensure that the pre-freezing is completed when the sample is completely crystallized and the ice crystals are evenly distributed.

Images