Method for preparing xylooligosaccharide based on ferrous ion synergistic hydrogen peroxide pretreatment coupling puffing and enzymolysis

Abstract

The invention discloses a method for preparing xylooligosaccharide based on ferrous ion synergistic hydrogen peroxide pretreatment coupling puffing and enzymolysis, and belongs to the technical field of wood fiber resource high-value utilization. The method comprises the following steps: crushing and drying a raw material rich in xylan to obtain a powder raw material; the raw material powder and water are mixed and stirred, ferrous sulfate and hydrogen peroxide are added, the pH is adjusted, a pretreatment reaction is conducted, and pretreated slurry is obtained; the pretreated slurry is dried and then sent into a bulking machine to be subjected to bulking treatment, and a bulked material is obtained; adding a buffer solution into the puffed material, and then adding a compound enzyme preparation to carry out an enzymatic hydrolysis reaction to obtain an enzymatic hydrolysate; and performing centrifugation, membrane filtration, concentration and drying on the enzymatic hydrolysate to obtain a xylooligosaccharide product. According to the method, a large amount of. OH is generated through Fenton reaction by virtue of a Fe < 2 + >-hydrogen peroxide synergistic system, lignin is directionally degraded, and the fracture effect of a lignin-carbohydrate complex is improved by 40% compared with that of single puffing pretreatment by virtue of physical damage of puffing treatment to a fiber structure.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization technology of lignocellulose resources, specifically involving a method for preparing xylooligosaccharides based on ferrous ion-coordinated hydrogen peroxide pretreatment coupled with puffing and enzymatic hydrolysis. Background Technology

[0002] Xylooligosaccharides, as a functional prebiotic, are widely used in feed, food and other fields. The core production bottleneck lies in how to efficiently break down the three-dimensional dense structure of cellulose-hemicellulose-lignin in lignocellulose raw materials such as corn cobs, so as to achieve the directional release and conversion of xylan.

[0003] In existing technologies, pretreatment methods for lignocellulose mainly include acid methods, alkali methods, and single hydrogen peroxide oxidation methods. Although acid pretreatment (such as the dilute acid pretreatment technology disclosed in CN1556110A) can degrade lignin to a certain extent, it easily leads to excessive hydrolysis of xylan into monosaccharides, resulting in low yield of xylooligosaccharides and generating a large amount of acidic waste liquid, which puts great pressure on environmental protection. The single hydrogen peroxide oxidation method relies on hydroxyl radicals (·OH) to degrade lignin, but the reaction efficiency is low, and high concentrations of hydrogen peroxide are required to achieve the desired effect, which increases production costs.

[0004] Ferrous ions (Fe) 2+ The Fenton reaction mechanism can promote the decomposition of hydrogen peroxide to generate a large amount of ·OH, thereby enhancing the degradation effect of lignin. Related research has been initially applied in the pretreatment of wood fibers, but its use alone still has problems such as insufficient fiber structure porosity and limited enzyme molecule accessibility during enzymatic hydrolysis. Expansion treatment, as a physical strengthening technology, can destroy the internal hydrogen bond network of fibers through instantaneous pressure changes, but when used alone, it cannot effectively remove the encapsulation effect of lignin on xylan. The synergistic effect of the two and the matching of process parameters have not yet been reported in patent publications.

[0005] Furthermore, patent CN1556110A has achieved the industrialization of xylooligosaccharide preparation from corn cobs, but this technology does not involve the coupling of the ferrous ion-hydrogen peroxide synergistic system with the puffing treatment, and there is still room for improvement in lignin degradation rate and enzymatic hydrolysis efficiency. Therefore, developing a coupled process that combines efficient lignin degradation, directional protection of xylan, and enhanced enzymatic hydrolysis effect is of great significance for promoting the upgrading of the xylooligosaccharide industry. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method for preparing xylooligosaccharides by coupling ferrous ion-assisted hydrogen peroxide pretreatment of corn cobs with puffing and enzymatic hydrolysis. This method utilizes Fe... 2+ - The hydrogen peroxide synergistic system generates a large amount of ·OH through the Fenton reaction, which directionally degrades lignin. Combined with the physical destruction of the fiber structure by the expansion treatment, it achieves efficient conversion of xylan and directional preparation of xylooligosaccharides in lignocellulosic raw materials such as corn cobs.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing xylooligosaccharides based on ferrous ion-synergistic hydrogen peroxide pretreatment coupled with puffing and enzymatic hydrolysis includes the following steps:

[0009] 1) The raw material rich in xylan is crushed and dried to obtain raw material powder;

[0010] 2) Mix the raw material powder with hydrogen peroxide, add ferrous sulfate, adjust the pH, and carry out the pretreatment reaction to obtain the pretreated slurry;

[0011] 3) After drying the pretreated slurry obtained in step 2), send it to an extruder for extrusion to obtain extruded material;

[0012] 4) Add water to the puffed material obtained in step 3), then add the compound enzyme preparation to carry out the enzymatic hydrolysis reaction to obtain the enzymatic hydrolysate;

[0013] 5) Centrifuge, filter through a membrane, concentrate, and dry the enzymatic hydrolysate to obtain xylooligosaccharide product.

[0014] Furthermore, in step 1), the raw material rich in xylan is selected from one of birch wood, corn cob, sugarcane bagasse, and sorghum stalk.

[0015] Furthermore, in step 1), the raw material rich in xylan is pulverized to a mesh size of 80-120.

[0016] Furthermore, in step 2), the mass ratio of raw material powder to hydrogen peroxide is 1:5 to 1:12, and the mass concentration of hydrogen peroxide is 0.5-3.0%.

[0017] Furthermore, in step 2), Fe is added. 2+ The concentration is 0.01~0.03 mol / L.

[0018] Further, in step 2), the pH is adjusted to 2.0-4.0; the acid used to adjust the pH is an organic acid, including acetic acid and gluconic acid.

[0019] Furthermore, in step 2), the pretreatment temperature is 50~90℃, the time is 40~60min, and the stirring speed is 100-200r / min.

[0020] Further, in step 3), the pretreated slurry is dried to a moisture content of 10-20%; the expansion temperature is 130℃, the pressure is 0.3-0.5MPa, and the time is 1-6min.

[0021] Further, in step 4), the compound enzyme preparation is: the enzyme activity ratio of xylanase to acetylxylan esterase is 4~5:1, and the total enzyme activity is 100-250U / g substrate.

[0022] Furthermore, in step 4), the temperature of the enzymatic hydrolysis reaction is 45~55℃, and the time is 12~24h.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) This invention utilizes Fe 2+ - The hydrogen peroxide synergistic system generates a large amount of ·OH through the Fenton reaction, which directionally degrades lignin. Combined with the physical destruction of fiber structure by the expansion treatment, the lignin-carbohydrate complex (LCC) breaking effect is 40% higher than that of single expansion pretreatment.

[0025] (2) The weakly acidic medium temperature reaction conditions (pH 3.0-4.0, 50-90℃) and instantaneous puffing process of the present invention avoid excessive hydrolysis of xylan, the xylan retention rate reaches 90%, and the yield of xylooligosaccharide exceeds 60% (based on corn cob powder).

[0026] (3) The hydrogen peroxide used in this invention can be partially recovered through subsequent treatment, Fe 2+ It can be recycled through ion exchange, reducing pollutant emissions by 60% compared to traditional acid pretreatment; at the same time, it eliminates the complicated acid and alkali recovery steps, reducing production costs by 25%.

[0027] (4) The xylooligosaccharide product prepared by the present invention has a xylooligosaccharide content of ≥35% and a xylobiose-xylotetraose ratio of ≥80%, which meets the feed additive standards. Attached Figure Description

[0028] Figure 1 This is a test image of the xylooligosaccharide product in Example 1 of this application. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0030] In the following examples, the xylooligosaccharide detection was performed according to the method of the national standard GB / T 35545-2017 Xylooligosaccharides, and the xylooligosaccharide yield was calculated using the following formula:

[0031]

[0032] Example 1

[0033] A method for preparing xylooligosaccharides from corn cobs through ferrous ion-assisted hydrogen peroxide pretreatment coupled with puffing and enzymatic hydrolysis includes the following steps:

[0034] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0035] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 4.92g of ferrous sulfate (Fe 2+ The concentration was 0.03 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0036] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 44.1% through the two-step treatment.

[0037] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0038] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 36 g of xylooligosaccharide product was obtained (product testing results are as follows). Figure 1 As shown in the figure, xylooligosaccharides account for 58.6%, xylobiose-xylotetraose accounts for 85% of the total xylooligosaccharide content, and the yield of xylooligosaccharides is 62%.

[0039] Example 2

[0040] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0041] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 1.64g of ferrous sulfate (Fe 2+The concentration was 0.01 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0042] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 42.2% through the two-step treatment.

[0043] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0044] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 34.8 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 51.8%, xylobiose-xylotetraose accounted for 82% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 53.1%.

[0045] Example 3

[0046] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0047] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 4.92g of ferrous sulfate (Fe 2+ The concentration was 0.01 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.0, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0048] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 44.2% through the two-step treatment.

[0049] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0050] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 36.2 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 51.7%, xylobiose-xylotetraose accounted for 81.7% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 55.1%.

[0051] Example 4

[0052] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0053] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 3% hydrogen peroxide, stir and disperse, then add 1.64g of ferrous sulfate (Fe 2+ The concentration was 0.01 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 90℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0054] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 48.9% through two-step treatment.

[0055] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0056] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 33.5 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 48.9%, xylobiose-xylotetraose accounted for 77.1% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 48.2%.

[0057] Example 5

[0058] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0059] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 1.64g of ferrous sulfate (Fe 2+ The concentration was 0.01 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0060] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 1 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 40.5% through two-step treatment.

[0061] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0062] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 31.2 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 44.8%, xylobiose-xylotetraose accounted for 83.1% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 41.2%.

[0063] Example 6

[0064] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0065] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 1.64g of ferrous sulfate (Fe 2+ The concentration was 0.01 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0066] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 6 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 48.3% through the two-step treatment.

[0067] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0068] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 37.1 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 34.1%, xylobiose-xylotetraose accounted for 82% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 37.2%.

[0069] Example 7

[0070] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0071] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 4.92g of ferrous sulfate (Fe 2+ The concentration was 0.03 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0072] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 44.1% through the two-step treatment.

[0073] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 80 U / g, acetyl xylan esterase 20 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0074] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 35.4 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 47.5%, xylobiose-xylotetraose accounted for 83.5% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 49.5%.

[0075] Example 8

[0076] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0077] (2) Take 100g of corn cob powder (raw material xylan content is 34%), add 1000mL of 1% hydrogen peroxide, stir and disperse, then add 4.92g of ferrous sulfate (Fe 2+ The concentration was 0.03 mol / L. Then, glacial acetic acid was added to adjust the pH to 3.5, the temperature was raised to 85℃, and the mixture was stirred at 180 r / min for 40 min. After the reaction was completed, the pretreated slurry was obtained.

[0078] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 44.1% through the two-step treatment.

[0079] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 200 U / g, acetyl xylan esterase 40 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0080] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 36.1 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 47.5%, xylobiose-xylotetraose accounted for 83.5% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 49.5%.

[0081] Comparative Example 1

[0082] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0083] (2) Take 100g of corn cob powder (the raw material xylan content is 24%), add 1000mL of hydrogen peroxide with a mass fraction of 1%, then add glacial acetic acid to adjust the pH to 3.5, heat to 85℃, stir at 180r / min for 40min, and after the reaction is completed, the pretreated slurry is obtained.

[0084] (3) The pretreated slurry was vacuum dried at 60°C to a moisture content of 18%, and fed into a twin-screw extruder. The extrusion temperature was controlled at 130°C, the barrel pressure at 0.4 MPa, and the screw speed at 120 r / min. After holding the pressure for 3 min, the pressure was released instantly to obtain the extruded material. The lignin degradation rate was 33% through the two-step treatment.

[0085] (4) Take all the puffed material, add 800 mL of deionized water, adjust the pH to 6.0 with calcium hydroxide, add the compound enzyme preparation (acid-resistant xylanase 120 U / g, acetyl xylan esterase 30 U / g), and enzymatically hydrolyze in an enzymatic hydrolysis tank (enzymatic hydrolysis temperature 50℃, stirring speed 150 r / min) for 18 h.

[0086] (5) The enzymatic hydrolysate was centrifuged at 3500 r / min for 12 min. The supernatant was filtered through a 2000 Da ceramic membrane. The permeate was concentrated at 60℃ and -0.08 MPa to a solid content of 15%. After spray drying, 34.2 g of xylooligosaccharide product was obtained, of which xylooligosaccharide accounted for 48.6%, xylobiose-xylotetraose accounted for 78% of the total xylooligosaccharide content, and the xylooligosaccharide yield was 49%.

[0087] Comparative Example 2

[0088] (1) Remove impurities such as stones and soil from the corn cob, crush it to 100 mesh, and dry it at 80℃ for 3 hours to obtain corn cob powder with a moisture content of 7%.

[0089] (2) Take 100g of corn cob powder (raw material xylan content is 34%), and use the dilute acid pretreatment process of CN1556110A (Example 1), that is, after the corn cob is crushed, soak it in 0.5% (W / W) sulfuric acid at 50℃ for 12 hours, then filter out the liquid, cook the solid phase at 150℃ for 1 hour, then add water at a ratio of 1:10 (W / W) to make a slurry, adjust the pH of the resulting mixed phase to 6.5, add xylanase, the amount of xylanase is 20 IU / g corn cob, and hydrolyze at 50℃ for 24 hours. After the reaction, filter out the residue of corn cob with silk cloth to obtain the filtrate, which is the enzymatic hydrolysate. The lignin degradation rate of dilute acid pretreatment is 34.1%, the yield of xylooligosaccharides is 40.4%, and the yield of monosaccharides reaches 21.1%.

[0090] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing xylooligosaccharides based on ferrous ion-synergistic hydrogen peroxide pretreatment coupled with puffing and enzymatic hydrolysis, characterized in that: The method comprises the following steps: 1) crushing and drying the xylan-rich raw material to obtain a raw material powder; 2) mixing and stirring the raw material powder with hydrogen peroxide, adding ferrous sulfate, adjusting the pH, and performing a pretreatment reaction to obtain a pretreated slurry; 3) drying the pretreated slurry obtained in step 2) and feeding it into an extruder for puffing treatment to obtain a puffed material; 4) adding water to the puffed material obtained in step 3), and then adding a composite enzyme preparation for enzymatic hydrolysis to obtain an enzymatic hydrolysis liquid; 5) centrifuging, membrane filtering, concentrating, and drying the enzymatic hydrolysis liquid to obtain an xylooligosaccharide product.

2. The method according to claim 1, wherein the method is characterized by: In step 1), the xylan-rich raw material is selected from one of birch, corn cob, sugarcane residue, and sorghum stalk.

3. The method according to claim 1, wherein the method is characterized by: In step 1), the xylan-rich raw material is crushed to a mesh size of 80-120 mesh.

4. The method according to claim 1, wherein the method is characterized by: In step 2), the mass ratio of the raw material powder to hydrogen peroxide is 1:5-1:12, and the mass concentration of the hydrogen peroxide is 0.5-3.0%.

5. The method according to claim 1, wherein the method is characterized by: In step 2), Fe 2+ at a concentration of 0.01 to 0.03 mol / L. 6.The method of claim 1, wherein the pretreatment is performed by using ferrous ions in combination with hydrogen peroxide. In step 2), the pH is adjusted to 2.0-4.0, and the acid used for adjusting the pH is an organic acid, including acetic acid and gluconic acid. 7.The method according to claim 1, wherein the method is characterized by the following steps: 7-1) pretreating the lignocellulosic material with ferrous ions and hydrogen peroxide; 7-2) expanding the pretreated lignocellulosic material; 7-3) enzymatically hydrolyzing the expanded lignocellulosic material to produce xylo-oligosaccharides. In step 2), the pretreatment temperature is 50-90℃, the time is 40-60 min, and the stirring speed is 100-200 r / min.

8. The method for preparing xylooligosaccharides based on ferrous ion-coordinated hydrogen peroxide pretreatment coupled with puffing and enzymatic hydrolysis according to claim 1, characterized in that: In step 3), the pretreated slurry is dried to a moisture content of 10-20%, the puffing temperature is 130℃, the pressure is 0.3-0.5 MPa, and the time is 1-6 min. 9.The method according to claim 1, wherein the method is characterized by the following steps: 9-1) pretreating the lignocellulosic material with ferrous ions and hydrogen peroxide; 9-2) expanding the pretreated lignocellulosic material; 9-3) enzymatically hydrolyzing the expanded lignocellulosic material to produce xylo-oligosaccharides. In step 4), the composite enzyme preparation has a xylanase to acetyl xylan esterase enzyme activity ratio of 4-5:1, and a total enzyme activity of 100-250 U / g substrate.

10. The method according to claim 1, wherein the method is characterized by: In step 4), the enzymatic hydrolysis temperature is 45-55℃, and the time is 12-24 h.

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