AU2020104425A4

AU2020104425A4 - Method for producing xylooligosaccharides under catalysis of xylonic acid

Info

Publication number: AU2020104425A4
Application number: AU2020104425A
Authority: AU
Inventors: Yong Xu; Xin Zhou
Original assignee: Nanjing Forestry University
Current assignee: Nanjing Forestry University
Priority date: 2019-10-28
Filing date: 2020-06-02
Publication date: 2021-06-24
Anticipated expiration: 2028-06-02
Also published as: CN110616238B; CN110616238A; WO2021082440A1; AU2020323957A1

Abstract

The disclosure discloses a method for producing xylooligosaccharides under the catalysis of xylonic acid. Wherein, a method for producing xylooligosaccharides from xylonic acid, which comprises mixing xylan raw material with xylonic acid to make them react by heating with stirring, to get xylooligosaccharides; on the basis of mass fraction, the xylan raw material is 1 part, and the xylonic acid is 5~12 parts; and a method for producing xylooligosaccharides through fermentative catalysis, which comprises mixing xylose with bacterium to get a mixed liquor; adjusting the pH of the mixed liquor and stirring at low temperature for biological oxidation; adding xylan raw material and heating with stirring, to get xylooligosaccharides. The disclosure utilizes the reaction of oxidizing xylose to xylonic acid with microbial whole-cell organisms, and the resulting xylonic acid is used as the catalyst. Compared with acetic acid and other inorganic acids, the resulting glycan does not over-degrade easily, the yield is high and there are few byproduct xylose furfural.

Description

METHOD FOR PRODUCING XYLOOLIGOSACCHARIDES UNDER CATALYSIS OF XYLONIC ACID

This application claims priority to Chinese Patent Application No. 201911032990.6, entitled "METHOD FOR PRODUCING XYLOOLIGOSACCHARIDES UNDER CATALYSIS OF XYLONIC ACID", filed to China National Intellectual Property Administration on Oct. 28, 2019, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The disclosure relates to the technical field of food engineering and chemical engineering, and specially relates to a method for producing xylooligosaccharides under the catalysis of xylonic acid. BACKGROUND Xylooligosaccharides, also known as Xylo-oligosaccharides, mainly derive from the hydrolysis of xylan in wood fiber, which, serving as functional foods or feed additives, cannot be absorbed by the digestive system, but can selectively proliferate bifidobacteria in the gut, meanwhile activate activities of various immune cells. Therefore, under the traction and drive of the rapid development of human health and micro-ecology, food safety and green animal farming, ecological agriculture and other industries, the xylooligosaccharide products derived from !0 wood fibers have a promising future as "super prebiotics". At present, the production of xylooligosaccharides mainly employs endo-xylanase preparations to catalyze the hydrolysis of xylan extracted with bases. However, this method is dependent on expensive bio-enzymes, and involves a high cost and a long cycle, and the alkaline extraction and treatment processes are complicated and difficult. !5 In addition, xylooligosaccharides can be prepared by a common process of strong acid hydrolysis, but the yield of xylooligosaccharides is low, with a lot of byproducts and a poor quality of products. SUMMARY The purpose of this section is to outline some aspects of the embodiments of the disclosure and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section as well as in the abstract of the specification and the title of the disclosure in this application to avoid ambiguity in the purpose of this section as well as the abstract of the specification and the title of the disclosure, while the simplifications or omissions are not intended to limit the scope of the disclosure. In view of the above technical defects, the disclosure is proposed. Therefore, as one aspect of the disclosure, the disclosure overcomes the deficiencies in the prior art and provides a method for producing xylooligosaccharides under the catalysis of xylonic acid. To overcome the above technical issues, the disclosure provides a technical scheme as below: A method for producing xylooligosaccharides from xylonic acid, which comprises mixing xylan raw material with xylonic acid to make them react by heating with stirring; on the basis of mass fraction, the xylan raw material is 1 part, and the xylonic acid is 5~12 parts. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: the xylan raw material is xylan and/or a wood fiber raw material containing xylan. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: for the reaction by heating with stirring, the stirring rate is 30~100 rpm, the temperature is 130~170°C, and the time is 0.25~2.0 h. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: after the reaction by heating with stirring, it further comprises adjusting the pH value after cooling, adding bacterium !5 and stirring at low temperature for biological oxidation, to get fermentation liquor; adding xylan raw material into the fermentation liquor, and heating with stirring. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: after the biological oxidation, it further comprises placing the fermentation liquor in a salt compartment of a bipolar membrane electrodialysis device, adding deionized water into an acid compartment and a base compartment respectively, activating an electrodialysis reaction through an external DC power supply, taking xylonic acid solution from the acid compartment and adding the xylan raw material into it; the electrodialysis reaction is continued until the electrical conductivity of the salt compartment is stable. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: the bacterium is xylose-oxidized bacterium, which is 0.01~0.1 parts. As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: the adjustment of pH after cooling is to adjust to weak acid after cooling down to room temperature, and for the stirring at low temperature, the temperature is 25~35°C, and the stirring rate is 100~200 rpm As a preferable scheme of the method for producing xylooligosaccharides from xylonic acid of the disclosure, wherein: the xylan raw material mixed with xylonic acid is not the same as the xylan raw material added into the fermentation liquor.As another aspect of the disclosure, the disclosure overcomes the deficiencies in the prior art and provides a method for producing xylooligosaccharides through fermentative catalysis, which comprises mixing xylose with bacterium to get a mixed liquor; adjusting the pH of the mixed liquor and stirring at low temperature; adding xylan raw material and heating with stirring, to get xylooligosaccharides. As a preferable scheme of the method for producing xylooligosaccharides through fermentative catalysis of the disclosure, wherein: after the biological !5 oxidation, it further comprises placing the mixed liquor in a salt compartment of a bipolar membrane electrodialysis device, adding deionized water into an acid compartment and a base compartment respectively, activating an electrodialysis reaction through an external DC power supply, taking xylonic acid solution from the acid compartment and adding the xylan raw material into it; the electrodialysis reaction is continued until the electrical conductivity of the salt compartment is stable. As a preferable scheme of the method for producing xylooligosaccharides through fermentative catalysis of the disclosure, wherein: the bacterium is xylose-oxidized bacterium; the xylan raw material is xylan and/or a wood fiber raw material containing xylan; on the basis of mass fraction, the xylose is 1 part, the bacterium is 0.01~0.1 parts, and the xylan raw material is 1~5 parts. As a preferable scheme of the method for producing xylooligosaccharides through fermentative catalysis of the disclosure, wherein: the adjustment of the pH of the mixed liquor is to adjust the pH of the mixed liquor to weak acid; and for the stirring at low temperature, the temperature is 25~35°C, and the stirring rate is 100~200 rpm; for the reaction by heating with stirring, the stirring rate is 30~100 rpm, the temperature is 130~170°C, and the time is 0.25~2.0 h. The disclosure has the following beneficial effects: The disclosure employs xylonic acid as the catalyst, allowing a high yield and few byproduct xylose and furfural; technologies such as biological oxidation and electrodialysis coupling are selected to be used in the disclosure to convert xylose into xylonic acid, wherein xylonic acid can be recovered as a self-supplying catalyst and the xylooligosaccharide products are purer. BRIEF DESCRIPTION OF THE DRAWINGS O In order to more clearly illustrate the technical schemes of the embodiments of the disclosure, the appended drawings required for the description of the embodiments will be briefly introduced below. It is obvious that the appended drawings described below are only some embodiments of the disclosure. For ordinary technicians in this field, other drawings can be obtained according to !5 these drawings without creative labor. Wherein: Fig. 1 shows a high performance anion-exchange chromatogram of embodiment 1; Fig. 2 shows the production process flow diagram of embodiment 6; Fig. 3 shows the schematic diagram of electrodialysis reaction of embodiment 6.

DESCRIPTION OF THE EMBODIMENTS In order to make the above purposes, features and advantages of the disclosure clearer and understandable, the specific implementation mode of the disclosure will be described in detail below in combination with specific embodiments. The following description sets forth many specific details in order to fully understand the present disclosure, but the disclosure can also be practiced by employing other ways different from those described herein. Technical personnel in this field may make similar extensions without deviating the meaning of the disclosure, and therefore the disclosure is not limited to specific embodiments disclosed below. Then, "an embodiment" or "embodiments" referred herein means specific features, structures or properties included in at least one implementation mode of the disclosure. The description of "in one embodiment" occurring at different locations of the specification is not intended to refer to the same one embodiment, nor an embodiment which is exclusive with other embodiments independently or selectively. Embodiment 1 50 g xylan extracted from corncob by an alkaline method was mixed with 500 mL of 5% (mass fraction) xylonic acid solution in a 1-L mechanically agitated stainless steel high-pressure reactor. After loading, the sealed stainless steel reactor started stirring (50 rpm), and heated to 150°C for 75 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and !5 filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The chromatogram was as shown in Fig. 1, in which xylonic acid (XA) and xylose, xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could be detected simultaneously. Wherein, the main components were xylose to xylooctaose, the yields of which were 27.6%, 19.2%, 13.1%, 8.8%, 5.9%, 2.5%, 1.6% and 1.3% respectively, totally 80%, wherein xylooligosaccharides is 52.4% totally; additionally, the yield of furfural was 0.05%. In addition, specific operations of elution at a binary gradient with 100 mmol/L of sodium hydroxide (NaOH) and 500 mmol/L of sodium acetate (NaAc) as the mobile phase are shown in the table below: Time (min) 100 mmol/L of NaOH() 500 mmol/L of NaAc(%) 0 100 0 9 100 0 26 92 8 26 50 50 40 50 50 40 100 0 50 100 0 Embodiment 2 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g xylan extracted from corncob by an alkaline method and 500 mL of 10% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 160°C for 45 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting !0 solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic !5 conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. Its chromatogram showed that xylonic acid (XA) and xylose (Xylose), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could be detected simultaneously. The main components were xylose to xylooctaose, the yields of which were 30.5%,17.2%,13.2%, 9 .1%, 6.8%, 3.9%,2.6% and 1.7% respectively, totally 86.2%, wherein xylooligosaccharides were 55.7% totally; additionally, the yield of furfural was 0.07%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 2 g/L of Gluconobacter oxydans for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 24 h, and 98% of xylose was converted to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt !5 compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 96.8%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. Embodiment 3 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g corncob and 500 mL of 5% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 170°C for 15 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. Its chromatogram showed that xylonic acid (XA) and xylose (Xylose), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could be detected simultaneously. The main components were xylose to xylooctaose, the yields of which were 16.2%, 15.8%, 10.2%, 9.3%, 6.1%, 4.8%, 2.5% and 1.8% respectively, totally 66.7%, wherein xylooligosaccharides were 50% totally; additionally, the yield of furfural was 0.03%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 8 g/L of Gluconobacteroxydans (American Type Culture Collection, ATCC 621H) for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 12 h, and 99% of xylose was converted !5 to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 96.3%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. Embodiment 4 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g bagasse dry powder and 500 mL of 10% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 150°C for 60 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. Wherein, xylonic acid (XA) and xylose (Xylose), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could !5 be detected simultaneously. The main components were xylose to xylooctaose, the yields of which were 35.2%, 16.5%, 12.1%, 8.2%, 6.3%, 4.4%, 3.6%, 1.9% and 1.6% respectively, totally 89.8%, wherein xylooligosaccharides were 54.6% totally; additionally, the yield of furfural was 0.08%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 2 g/L of Gluconobacterfrateurii(American Type Culture Colection, ATCC IFO 3264) for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 12 h, and 94% of xylose was converted to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 97.1%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. Embodiment 5 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g corncob dry powder and 500 mL of 5% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 150°C for 70 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was !5 analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. Its chromatogram showed that xylonic acid (XA) and xylose (Xylose), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could be detected simultaneously. Wherein, the main components were xylose to xylooctaose, the yields of which were 19.1%, 17.6%, 11.2%, 8.4%, 6.8%, 5.1%, 2.5%, and 1.3% respectively, totally 72%, wherein xylooligosaccharides were 52.9% totally; additionally, the yield of furfural was 0.06%. Embodiment 6 The production process flow diagram was as shown in Fig. 2, into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g xylan extracted from corncob by an alkaline method and 500 mL of 10% (mass fraction) xylonic acid solution, sealed and then started stirring (60 rpm), and heated to 150°C for45 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were !5 xylose to xylooctaose, the yields of which were 25.6%, 15.8%, 12.2%, 10.1%, 5.5%, 4.2%, 2.8% and 1. 7 % respectively, totally 7 7 .9 %, wherein xylooligosaccharides were 52.3% totally; additionally, the yield of furfural was 0.04%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 5 g/L of Gluconobacter oxydans for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 12 h, and 98% of xylose was converted to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device. The schematic diagram of electrodialysis reaction was as shown in Fig. 3, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, and the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 97.9%, its mass concentration was about 11%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. The 11% xylonic acid solution recovered from the acid compartment was diluted to 10%, from which 500 mL was taken and mixed with 50 g xylan extracted from corncob by an alkaline method in a1-L mechanically agitated stainless steel high-pressure reaction tank, sealed and then started stirring (60 rpm), and heated to 155°C for 45 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides), wherein the main !5 components were xylose to xylooctaose, the yields of which were 29.0%, 16.1%, 13.1%, 9.6%, 6.1%, 3.4%, 1. 9 % and 0. 9 % respectively, totally 80.1%, wherein xylooligosaccharides were 51.1% totally; additionally, the yield of furfural was 0.04%. Embodiment 7 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g corncob dry powder and 500 mL of 10% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 170°C for 50 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were xylose to xylooctaose, the yields of which were 72.6%, 8.2%, 6.1%, 3.2%, 0. 9 %, 0.1%, 0.1% and 0.02% respectively, totally 91.2%, wherein xylooligosaccharides were 18.6% totally; additionally, the yield of furfural was 0.8%. Due to xylonic acid hydrolyzes xylan more thoroughly under high strength (high acid, high temperature) conditions, the content of xylose will be higher. Embodiment 8 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g corncob dry powder and 500 mL of 10% (mass fraction) tartaric acid solution, sealed and then started stirring (50 rpm), and heated to 150°C for 45 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum !5 washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were xylose to xylooctaose, the yields of which were 65. 2 %, 9 .2 %, 7.1%, 4 .2 %, 3.0%, 1.6%, 0.5% and 0.1% respectively, totally 90.9%, wherein xylooligosaccharides were 25.7% totally; additionally, the yield of furfural was 0.4%. Embodiment 9 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g poplar powder and 500 mL of 10% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 150°C for 45 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were xylose to xylooctaose, the yields of which were 11. 6 %, 8 . 8 %, 8 .2 %, 7 .3 %, 5.0%, 3 .9 %, 2.1% and 1.5% respectively, totally 4 8 .4 %, wherein xylooligosaccharides !5 were 36.8% totally; additionally, the yield of furfural was 0.04%. Embodiment 10 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g xylan extracted from corncob by an alkaline method and 500 mL of 5% (mass fraction) xylonic acid solution, sealed and then started stirring (50 rpm), and heated to 170°C for 15 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid waste from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. Its chromatogram showed that xylonic acid (XA) and xylose (Xylose), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), xylohexaose (X6), xyloheptaose (X7), xylooctaose (X8) could be detected simultaneously. Wherein the main components were xylose to xylooctaose, the yields of which were 10.1%, 9.8%, 9.2%, 8.1%, 6.9%, 4.8%, 3.7%, and 3.3% respectively, totally 55.9%, wherein xylooligosaccharides were 45.8% totally; additionally, the yield of furfural was 0.02%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 4 g/L of Gluconobacter oxydans for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 6 h, and 98% of xylose was converted to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions !5 were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 96.5%, its mass concentration was about 5.5%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. The 5.5% xylonic acid solution recovered from the acid compartment was mixed with the solid waste from the reaction of xylan extracted from corncob by an alkaline method in a 1-L mechanically agitated stainless steel high-pressure reaction tank, sealed and then started stirring (60 rpm), and heated to 170°C for 15 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides), wherein the main components were xylose to xylooctaose, the yields of which (calculated with respect to the initial raw material of 50 g xylan) were 8.2%, 7.2%, 6.3%, 4.1%, 3.2%, 2.4%, 0.9% and 0.7% respectively, totally 33%, wherein xylooligosaccharides were 24.8% totally; additionally, the yield of furfural was 0.04%. Embodiment 11 Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g xylan extracted from corncob by an alkaline method and 500 mL of 5% (mass fraction) xylonic acid solution, sealed and then started stirring (60 rpm), and heated to 170°C for 30 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to !5 separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were xylose to xylooctaose, the yields of which were 21.6%, 18.7%, 14.9%, 13.8%, 9.6%, 5.7%, 2.9% and 1.5% respectively, totally 88.7%, wherein xylooligosaccharides were 67.1% totally; additionally, the yield of furfural was 0.05%. The xylan hydrolysate was neutralized to pH 5.5 with sodium hydroxide, and then fed into a 2-L bioreactor together with 5 g/L of Gluconobacteroxydans for biological oxidation, the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 0.5 vvm, the reaction time was 12 h, and 98% of xylose was converted to xylonic acid. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid and xylooligosaccharides; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 500 mL deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 97.9%, its mass concentration was about 11%, and the recovery rate of xylooligosaccharides in the salt compartment was 100%. The 5.5% xylonic acid solution recovered from the acid compartment was diluted to 5%, from which 500 mL was taken and mixed with 50 g bagasse dry powder in a 1-L mechanically agitated stainless steel high-pressure reaction tank, sealed and then started stirring (60 rpm), and heated to 170°C for 30 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides), wherein the main components were xylose to xylooctaose, the yields of which were 22.0%, 19.2%, 15.3%, 11.2%, 8.0%, 4.9%, 1.8% and 0.5% respectively, totally 82.9%, wherein xylooligosaccharides were 60.9% totally; additionally, the yield of furfural was 0.04%. Embodiment 12 Into a 3-L bioreactor were added 1.5 L of 100 g/L xylose solution and 9 g Gluconobacteroxydans for the biological oxidation of xylose, wherein the reaction conditions for the biological oxidation were: the temperature was 30°C, the stirring speed was 150 rpm, the air inflow was 1.0 vvm, the reaction time was 24 h, the pH is controlled with sodium hydroxide during the process of fermentation, and 98% of xylose was converted to xylonic acid at the end of the reaction. Upon completion of the reaction, the bacterium was separated from the fermentation liquor through centrifugation on a centrifuge, wherein the centrifugal conditions were: 5000 rpm, 5 min. The main components of the fermentation liquor were xylonic acid; The fermentation liquor was placed in a salt compartment of a bipolar membrane electrodialysis device, 1.5 L deionized water was respectively added into an acid compartment and a base compartment, and an electrodialysis reaction was activated through an external DC power supply. The separation and reaction processes were detected with reference to the electrical conductivity of the salt compartment; after reaction for 1 h, the electrical conductivity of the salt compartment became stable, the reaction was terminated. At this point, the recovery rate of xylonic acid in the acid compartment was 97.0%, its mass concentration was about 10%. Into a 1-L mechanically agitated stainless steel high-pressure reaction tank were added 50 g corncob dry powder and 500 mL of 10% xylonic acid solution as prepared above, sealed and then started stirring (60 rpm), and heated to 155°C for 60 min. Upon completion of the reaction, the reaction tank was cooled down to room temperature, and then the resulting solid-liquid mixture was fed into a vacuum washer to be extruded and filtered to separate non-hydrolyzed solid from xylan hydrolysate (the hydrolysate mainly included a mixed liquor of xylose, xylonic acid and xylooligosaccharides). The obtained xylan hydrolysate sample was analyzed for its sugar components by high performance anion-exchange chromatography, wherein the chromatographic conditions were: Thermo Fisher Scientific ICS 5000 Ion Chromatography, equipped with a CarboPacTM PA200 (3 mm x 250 mm) chromatographic column, and a PAD integrated amperometric detector, column temperature 30°C, sample volume 10 pL; and eluted at a binary gradient with 100 mmol/L of sodium hydroxide and 500 mmol/L of sodium acetate as the mobile phase, the flow rate was 0.3 mL/min. The main components were xylose to xylooctaose, the yields of which were 35.2%, 16.5%, 11.7%, 9.1%, 5.9%, 4.6%, 3.7% and 1.4% respectively, totally 88.1%, wherein xylooligosaccharides were 52.9% totally; additionally, the yield of furfural was 0.08%. The disclosure utilizes the reaction of oxidizing xylose to xylonic acid with microbial whole-cell organisms, and the resulting xylonic acid is used as the catalyst. Compared with acetic acid and other inorganic acids, the resulting glycan does not over-degrade easily, the yield is high and there are few byproduct xylose and furfural. This process has technical universality and can be used for various wood fiber raw materials (xylan extracted with alkaline, straw, corncob, bagasse, etc.). The amount of xylonic acid, the time and the temperature should be controlled strictly in the disclosure. Too low acid concentration leads to long treatment time and high energy consumption; Too high temperature and too long time make the products prone to over-degradation and make the yield of the products to decrease; appropriate conditions and proportions are required. Technologies such as biological oxidation and electrodialysis coupling are selected to be used in the disclosure to convert xylose into xylonic acid, wherein xylonic !5 acid can be recovered as a self-supplying catalyst and the xylooligosaccharide products are more pure. It should be noted that the above embodiments are only used to illustrate the technical schemes of the disclosure and not intended to be restrictive. Although the disclosure has been set forth in detail with reference to preferable embodiments, ordinary technical personnel in this field should understand that modifications or equivalent substitutions can be made to the technical schemes of the disclosure without deviating from the spirit and scope of the technical schemes of the disclosure, which shall be all covered within the scope of the claims of the disclosure.

Claims

Claims WHAT IS CLAIMED IS:

1. A method for producing xylooligosaccharides from xylonic acid, wherein, it comprises, Mixing xylan raw material with xylonic acid to make them react by heating with stirring, to get xylooligosaccharides; On the basis of mass fraction, the xylan raw material is 1 part, and the xylonic acid is 5~12 parts.

2. The method for producing xylooligosaccharides from xylonic acid according to claim 1, wherein, the xylan raw material is xylan and/or a wood fiber raw material containing xylan.

3. The method for producing xylooligosaccharides from xylonic acid according to claim 1, Wherein, for the reaction by heating with stirring, the stirring rate is 30~100 rpm, the temperature is 130~170°C, and the time is 0.25~2.0 h.

4. The method for producing xylooligosaccharides from xylonic acid according to any one of claims 1~3, wherein, after the reaction by heating with stirring, it further comprises adjusting the pH value after cooling, adding bacterium and stirring at low temperature for biological oxidation, to get fermentation liquor; Adding xylan raw material into the fermentation liquor, and heating with stirring.

5. The method for producing xylooligosaccharides from xylonic acid according to claim 4, wherein, after the biological oxidation, it further comprises placing the fermentation liquor in a salt compartment of a bipolar membrane electrodialysis device, adding deionized water into an acid compartment and a base compartment respectively, activating an electrodialysis reaction through an external DC power supply, taking xylonic acid solution from the acid compartment and adding the xylan raw material into it; The electrodialysis reaction is continued until the electrical conductivity of the salt compartment is stable.

6. The method for producing xylooligosaccharides from xylonic acid according to claim 4 or 5, Wherein, the bacterium is xylose-oxidized bacterium, which is 0.01~0.1 parts.

7. The method for producing xylooligosaccharides from xylonic acid according to claim 4 or 5, Wherein, the adjustment of pH after cooling is to adjust to weak acid after cooling down to room temperature, and for the stirring at low temperature, the temperature is 25~35°C, and the stirring rate is 100~200 rpm.

8. The method for producing xylooligosaccharides from xylonic acid according to claim 4 or 5, wherein, the xylan raw material mixed with xylonic acid is not the same as the xylan raw material added into the fermentation liquor.

9. A method for producing xylooligosaccharides through fermentative catalysis, wherein, it comprises, Mixing xylose with bacterium to get a mixed liquor; adjusting the pH of the mixed liquor and stirring at low temperature for biological oxidation; adding xylan raw material and heating with stirring, to get xylooligosaccharides.

10. The method for producing xylooligosaccharides through fermentative catalysis according to claim 9, Wherein, after the biological oxidation, it further comprises placing the mixed liquor in a salt compartment of a bipolar membrane electrodialysis device, adding deionized water into an acid compartment and a base compartment respectively, activating an electrodialysis reaction through an external DC power supply, taking xylonic acid solution from the acid compartment and adding the xylan raw material into it; The electrodialysis reaction is continued until the electrical conductivity of the salt compartment is stable.

11. The method for producing xylooligosaccharides through fermentative catalysis according to claim 9 or 10, Wherein, the bacterium is xylose-oxidized bacterium; the xylan raw material is xylan and/or a wood fiber raw material containing xylan; On the basis of mass fraction, the xylose is 1 part, the bacterium is 0.01~0.1 parts, and the xylan raw material is 1~5 parts.

12. The method for producing xylooligosaccharides through fermentative catalysis according to any one of claims 9~11, Wherein, the adjustment of the pH of the mixed liquor is to adjust the pH of the mixed liquor to weak acid; and for the stirring at low temperature, the temperature is 25~35°C, and the stirring rate is 100~200 rpm; For the heating with stirring, the stirring rate is 30~100 rpm, the temperature is 130~170°C, and the time is 0.25~2.0 h.