Xylooligosaccharide as well as preparation method and application thereof

Abstract

According to the xylooligosaccharide and the preparation method and application thereof, the solution containing the xylooligosaccharide and the residues are obtained after the Yuan River asparagus bamboo shoot shells are subjected to electron beam irradiation, hydro-thermal treatment and solid-liquid separation, so that the yield of the xylooligosaccharide of the Yuan River asparagus bamboo shoot shells is increased, technical reference is provided for efficient utilization of Yuan River asparagus processing byproducts, and the Yuan River asparagus bamboo shoot shells are suitable for industrial production. The sustainable development of the Yuan River asparagus processing industry is promoted.

Description

Technical Field

[0001] The present invention relates to the field of biochemistry, and particularly to xylo-oligosaccharide, a preparation method thereof and uses thereof. Background Art

[0002] Yuanjiang asparagus is the tender bud of Miscanthus lutarioriparius, an amphibious herbaceous plant of the genus Miscanthus in the Poaceae family. It is rich in nutrients such as flavonoids, amino acids, and minerals, has a fresh, crispy and tender taste, and has significant nutritional value and medicinal effects. However, due to the strong seasonality of Yuanjiang asparagus picking, it is difficult to store the freshly picked asparagus for a long time. Production enterprises usually adopt the whole asparagus pickling technology, and a large amount of waste asparagus shells will be generated after pickling. If these by-products are not reasonably utilized, it will cause waste of resources and environmental pollution.

[0003] The components of asparagus shells are similar to those of Yuanjiang asparagus, containing a large amount of cellulose, xylan and lignin, and are high-quality raw materials for preparing dietary fiber and xylo-oligosaccharide. Xylo-oligosaccharide is composed of 2-7 xylose molecules linked by β-1,4 glycosidic bonds and has a variety of physiological activities. Hydrothermal treatment is one of the common methods for preparing xylo-oligosaccharide, which does not require the addition of chemical reagents and is environmentally friendly. It has been reported that Yuanjiang asparagus is used as a raw material to prepare asparagus xylo-oligosaccharide by enzymatic hydrolysis, and the yield is 29.94%.

[0004] At present, there are few studies on the utilization of Yuanjiang asparagus shells. The existing technologies mainly focus on Yuanjiang asparagus itself. The treatment of asparagus shells is mostly simple discard or use as low-value fertilizers, and their potential value has not been fully utilized. And the yield of xylo-oligosaccharide still needs to be improved. For example, the highest yield of xylo-oligosaccharide from bamboo shoots is 20.86%, and there are similar problems with the yield of xylo-oligosaccharide in wheat bran. It is necessary to further optimize the process to improve the yield of xylo-oligosaccharide. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a xylo-oligosaccharide, a preparation method thereof and uses thereof, which are used to solve the problems of insufficient utilization of Yuanjiang asparagus shells and the yield of xylo-oligosaccharide to be improved in the prior art.

[0006] The first aspect of the present invention provides a xylo-oligosaccharide, a preparation method thereof and uses thereof, and the steps are as follows:

[0007] Perform electron beam irradiation and hydrothermal treatment on Yuanjiang asparagus shells, and after solid-liquid separation, obtain a solution containing xylo-oligosaccharide and residues.

[0008] Preferably, desalination treatment is performed on wet Yuanjiang asparagus shells. The salt content in the dry matter of Yuanjiang asparagus shells without desalination treatment is relatively high, which leads to a relatively lower content of other components, especially the xylan content, and will also increase the subsequent desalination process of xylo-oligosaccharide. Therefore, desalination treatment is carried out before hydrothermal treatment.

[0009] Preferably, the desalination treatment includes soaking the wet Yuanjiang asparagus husks and water in a certain mass ratio. The soaking time is 0.25 - 96 h, the soaking temperature is 18 - 40 °C, and the number of soaking times is 2 - 5 times.

[0010] More preferably, the soaking time is 12 - 72 h, the soaking temperature is 18 - 28 °C, and the number of soaking times is 1 - 3 times. The soaking time is also 12 - 24 h, 24 - 36 h, 36 - 48 h, 48 - 60 h, 60 - 72 h. Such as 12 h, 24 h, 36 h, 48 h, 60 h, 72 h. The soaking temperature is also 18 - 20 °C, 20 - 22 °C, 22 - 24 °C, 24 - 26 °C, 26 - 28 °C. Such as 18 °C, 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C.

[0011] Adding ultrasonic treatment can shorten the soaking time. The ultrasonic soaking time is 15 - 30 min, 30 - 40 min, 40 - 50 min, 50 - 60 min, such as 15 min, 20 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min. The ultrasonic soaking temperature is 25 - 30 °C, 30 - 35 °C, 35 - 40 °C, such as 25 °C, 30 °C, 32 °C, 35 °C, 38 °C, 40 °C.

[0012] Preferably, the mass ratio of the wet Yuanjiang asparagus husks to water is 1 g:(3 - 6) mL.

[0013] More preferably, the mass ratio of the wet Yuanjiang asparagus husks to water is 1 g:(3 - 4) mL, 1 g:(4 - 5) mL, 1 g:(5 - 6) mL, 1 g:(3 - 5) mL, 1 g:(4 - 6) mL. Such as 1 g:3 mL, 1 g:4 mL, 1 g:4.5 mL, 1 g:5 mL, 1 g:5.5 mL, 1 g:6 mL.

[0014] In a preferred embodiment, the soaking time is 48 - 72 h, the soaking temperature is 18 - 25 °C, and the number of soaking times is 2 - 3 times; after adding ultrasonic treatment, the soaking time can be shortened. The ultrasonic soaking temperature is 25 - 35 °C, and the ultrasonic soaking time is 25 - 35 min.

[0015] More preferably, the number of soaking times is 2 - 3 times, 2 - 4 times, 3 - 4 times, 2 - 5 times, 4 - 5 times. Such as 2 times, 3 times, 4 times, 5 times.

[0016] The number of soaking times will affect the desalination effect. Too few times will lead to a decrease in the desalination rate, affecting the subsequent yield of xylooligosaccharides. Too many times will affect the desalination treatment efficiency and increase costs. As shown in Table 1, there is no significant difference between dextran and xylan after 2 and 3 times of desalination treatment, but the salt content decreases from 5.12% to 1.48%. The lower the salt content, the more able to reduce the subsequent desalination cost of xylooligosaccharides.

[0017] In a preferred embodiment, the desalination rate of simple soaking desalination is higher than that of short-time ultrasonic desalination. As shown in Table 1, the effect of soaking desalination is better than that of ultrasonic soaking desalination. This is because the soaking desalination time is longer, allowing the salt in the shell of Yuanjiang asparagus to be fully released into the water. However, since the desalination treatment time should not be too long, on the one hand, it will lead to a decrease in treatment efficiency, increase water consumption and treatment costs; on the other hand, due to the rich nutrients in the shell, soaking treatment for too long will cause the shell to rot and deteriorate.

[0018] Preferably, the desalted shell is subjected to one or more of drying, pulverizing, or electron beam irradiation.

[0019] More preferably, in actual production, water is directly added to the desalted shell for homogenization treatment.

[0020] Preferably, the shell is pulverized and then sieved, and the sieve mesh is 20 - 60 mesh. Such as 20 - 30 mesh, 30 - 40 mesh, 40 - 50 mesh, 50 - 60 mesh.

[0021] The salt content of the shell after the above-mentioned desalination treatment, drying, and pulverization is determined with reference to GB 5009.42-2016 "National Food Safety Standard Determination of Salt Index".

[0022] Preferably, the dose of the electron beam irradiation is 150 - 600 kGy. Such as 150 - 200 kGy, 200 - 250 kGy, 250 - 300 kGy, 350 - 400 kGy, 400 - 500 kGy, 500 - 600 kGy.

[0023] If the dose of electron beam irradiation is too low, the degree of damage to the lignocellulose structure of the shell is insufficient, which will increase the difficulty of subsequent hydrothermal treatment and affect the yield of xylooligosaccharides; if the irradiation dose is too high, it will greatly increase the irradiation cost, and the increased degree of damage will directly decompose the raw material xylan component into harmful substances such as monosaccharides or furfural, causing a sharp drop in the yield of xylooligosaccharides.

[0024] More preferably, the dose of the electron beam irradiation is 200 kGy, 250 kGy, 300 kGy, 350 kGy, 400 kGy, 450 kGy, 500 kGy, 550 kGy, 600 kGy.

[0025] In a preferred embodiment, the dose of electron beam irradiation is 200 - 600 kGy.

[0026] The steps of the hydrothermal treatment include subjecting bamboo shoot husks and acetic acid solution to a hydrothermal reaction according to a certain solid-liquid ratio. The temperature of the hydrothermal treatment is 140 - 180 °C and the time is 30 - 50 min. The concentration of the acetic acid solution is less than 0.25 wt%.

[0027] In a preferred embodiment, the hydrothermal treatment is accompanied by stirring, and the stirring speed is 200 - 500 rpm.

[0028] Preferably, the solvent of the acetic acid solution is water.

[0029] Low-concentration acetic acid can promote the conversion of xylan in bamboo shoot husks of Yuanjiang asparagus into xylo-oligosaccharides. However, with the increase of acetic acid concentration, the converted xylo-oligosaccharides will be further degraded into xylose and other small-molecule compounds, resulting in a decrease in the conversion efficiency.

[0030] Preferably, the concentration of the acetic acid solution is 0 - 0.2 wt%. Such as 0 - 0.1 wt%, 0.1 - 0.15 wt%, 0.15 - 0.2 wt%.

[0031] More preferably, the concentration of the acetic acid solution is 0 wt%, 0.1 wt%, 0.15 wt%, 0.18 wt%, 0.2 wt%.

[0032] In a preferred embodiment, the concentration of the acetic acid solution is 0.1 - 0.2 wt%.

[0033] Preferably, the solid-liquid ratio is the mass-volume ratio of bamboo shoot husks to the reaction solution of 1 g:(5 - 15) mL.

[0034] More preferably, the solid-liquid ratio is the mass-volume ratio of bamboo shoot husks to the reaction solution of 1 g:(5 - 8) mL, 1 g:(8 - 10) mL, 1 g:(10 - 12) mL, 1 g:(12 - 15) mL. Such as 1 g:5 mL, 1 g:6 mL, 1 g:7 mL, 1 g:8 mL, 1 g:9 mL, 1 g:10 mL, 1 g:11 mL, 1 g:12 mL, 1 g:13 mL, 1 g:14 mL, 1 g:15 mL.

[0035] The temperature of hydrothermal treatment has a significant impact on the yield of xylooligosaccharides. If the hydrothermal treatment temperature is too high, the xylooligosaccharides produced by the hydrolysis of xylan will be further degraded to form small molecular by-products such as xylose, formic acid, and acetic acid, resulting in the loss of xylooligosaccharides. If the hydrothermal treatment temperature is too low, the hydrolysis rate of xylan in bamboo shoots is small, leading to a low yield of xylooligosaccharides. If the time of hydrothermal treatment is too short, the yield of xylooligosaccharides will decrease. If the treatment time is too long, not only the production efficiency will be reduced, but also the excessive hydrolysis of xylan will be promoted, thus reducing the yield of xylooligosaccharides.

[0036] Preferably, the temperature of the hydrothermal treatment is 140 - 150 °C, 150 - 160 °C, 160 - 170 °C, 170 - 180 °C.

[0037] More preferably, the temperature of the hydrothermal treatment is 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C.

[0038] In a specific embodiment, the temperature of the hydrothermal treatment is 160 - 180 °C.

[0039] Preferably, the time of the hydrothermal treatment is 30 - 40 min, 40 - 50 min.

[0040] More preferably, the time of the hydrothermal treatment is 30 min, 35 min, 40 min, 45 min, 50 min.

[0041] More preferably, the stirring speed is 200 - 250 rpm, 250 - 300 rpm, 300 - 350 rpm, 350 - 400 rpm, 400 - 450 rpm, 450 - 500 rpm. Such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm.

[0042] Preferably, the solid-liquid separation includes centrifugation or filtration.

[0043] For the liquid obtained by centrifugation or filtration of the above method, the determination of crude protein content is carried out with reference to GB 5009.5 - 2016 "National Food Safety Standard Determination of Protein in Foods", the determination of crude fat content is carried out with reference to GB 5009.6 - 2016 "National Food Safety Standard Determination of Fat in Foods", and the determination of lignocellulose component content is carried out with reference to NY / T 3494 - 2019 "Determination of Cellulose, Hemicellulose and Lignin in Agricultural Biomass Raw Materials".

[0044] Preferably, the determination of glucose and xylose contents is carried out for the liquid obtained by centrifugation or filtration of the above method.

[0045] In a more preferred embodiment, the dose of the electron beam irradiation is 200 - 600 kGy, the concentration of the acetic acid solution is 0.1 - 0.2 wt%, the temperature of the hydrothermal treatment is 160 - 180 °C, and the time of the hydrothermal treatment is 30 - 50 min.

[0046] In a preferred embodiment, the yield of xylo-oligosaccharides is not less than 55%.

[0047] In the second aspect of the present invention, it is required to protect the solution containing xylo-oligosaccharides obtained by the above method.

[0048] Preferably, the solution containing xylo-oligosaccharides is separated by a membrane separation technique to obtain xylo-oligosaccharides with a molecular weight lower than 1000 Da, and the purified xylo-oligosaccharides are obtained through dehydration treatment.

[0049] Preferably, the proportion of xylobiose - xylotetraose in the total xylo-oligosaccharides in the solution containing xylo-oligosaccharides is not less than 50%.

[0050] In a preferred embodiment, the proportion of xylobiose - xylotetraose in the total xylo-oligosaccharides in the solution containing xylo-oligosaccharides is not less than 60%.

[0051] In the third aspect of the present invention, it is also required to protect the use of the solution containing xylo-oligosaccharides as described above in the preparation of foods or feed additives for promoting intestinal health.

[0052] As described above, the method of the present invention has the following beneficial effects:

[0053] The present invention provides a method for increasing the yield of xylo-oligosaccharides from the husks of Yuanjiang asparagus. This method can achieve the efficient utilization of the processing by-products of Yuanjiang asparagus and provide technical support for the sustainable development of the Yuanjiang asparagus processing industry. Specific Embodiments

[0054] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0055] Before further describing the specific embodiments of the present invention, it should be understood that the protection scope of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present invention are for the purpose of describing specific embodiments and not for limiting the protection scope of the present invention; in the specification and claims of the present invention, unless otherwise clearly indicated in the text, the singular forms "a", "an" and "the" include the plural forms.

[0056] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of the present invention, any methods, equipment, and materials of the prior art similar to or equivalent to those described in the embodiments of the present invention can also be used to implement the present invention.

[0057] The inventors of the present application used the by-product bamboo shoot shells of Yuanjiang asparagus processing as raw materials, prepared xylooligosaccharides by the hydrothermal method, explored the effects of desalting treatment, irradiation treatment, and different acetic acid concentrations on the hydrothermal preparation of xylooligosaccharides from Yuanjiang asparagus bamboo shoot shells, and finally optimized the preparation process of xylooligosaccharides from bamboo shoot shells through an orthogonal experiment of four factors and three levels, providing a technical reference for the efficient utilization of the by-products of Yuanjiang asparagus processing.

[0058] All kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods. In the embodiments of the present application, the bamboo shoot shells are selected from Yuanjiang asparagus bamboo shoot shells and provided by Yuanjiang Lu Xiaomei Co., Ltd.; the water content of the pickled wet Yuanjiang asparagus bamboo shoot shells is 83.80% and the salt content is 4.92%. The electron beam irradiation treatment is carried out in Chizhou Jiuwei New Materials Co., Ltd.

[0059] In order to further illustrate the technical solutions, technical effects, and technical problems of the present application. The following specific embodiments and comparative examples of the present application provide a method for preparing xylooligosaccharides. Before that, the effects of desalting treatment on the component content in the dry matter of Yuanjiang asparagus bamboo shoot shells and the preparation of xylooligosaccharides are explored first.

[0060] The present application uses ultrasonic or soaking desalting treatment on Yuanjiang asparagus bamboo shoot shells and measures their component content. The specific steps are as follows:

[0061] (1) Perform ultrasonic or soaking desalting on Yuanjiang asparagus bamboo shoot shells: Place 100 g of wet Yuanjiang asparagus bamboo shoot shells in 450 mL of water, at a temperature of 30 °C, with an ultrasonic frequency of 40 kHz and an ultrasonic power of 200 W. Treat for 30 min, then take out and drain, which is the sample of ultrasonic desalting once; repeat the above operation 2 times and 3 times to perform 2 times and 3 times of ultrasonic desalting. The steps of soaking desalting treatment are the same as those of ultrasonic desalting, except that the treatment temperature is 20 °C and the soaking time is 24 h, then take out and drain, and repeat the above operation 2 times and 3 times to perform 2 times and 3 times of soaking desalting.

[0062] (2) Dry and crush the bamboo shoot shells treated by the above different desalting treatments in an oven at 60 °C, collect the powder passing through a 40-mesh sieve, and put it into a self-sealing bag for standby.

[0063] (3) Measure the contents of table salt, crude protein, crude fat, lignin, glucan and xylan components in the above-mentioned spare bamboo shoot shell powders respectively according to relevant national food safety standards. Among them, high performance liquid chromatography (HPLC) is used to measure the contents of glucose and xylose required in the process of detecting glucan and xylan: the chromatographic column is Aminex HPX-87H (7.8 mm × 300 mm), the column temperature is 55 °C, and the mobile phase is 0.005 mol·L -1 sulfuric acid, and the flow rate is 0.6 mL·min -1 , a differential refractive index detector (temperature 45 °C), and the injection volume is 10 μL. The results are shown in Table 1.

[0064] Table 1 Effects of desalting treatment on the component contents in the dry matter of Yuanjiang asparagus bamboo shoot shells (%)

[0065] CK represents the untreated desalting; CS-1, CS-2, and CS-3 represent ultrasonic desalting once, twice, and three times respectively; JP-1, JP-2, and JP-3 represent soaking desalting once, twice, and three times respectively.

[0066] Table 1 shows that with the increase of the desalting times, the table salt content gradually decreases, and the soaking desalting effect is better than the ultrasonic desalting. After soaking three times, the table salt content decreases to 1.48%. The change trends of the glucan, xylan, and lignin contents are opposite to that of the table salt. With the increase of the desalting rate, the corresponding glucan, xylan, and lignin contents in the dry matter increase. There is no significant difference between the glucan and xylan after soaking desalting twice and three times, but the table salt content decreases from 5.12% to 1.48%. The lower the table salt content, the lower the subsequent desalting cost of xylo-oligosaccharide.

[0067] Subsequently, the present application conducts hydrothermal treatment on the above 7 groups of samples, and the hydrothermal treatment process parameters are exactly the same. The specific method is as follows:

[0068] Weigh 5 g of the above-mentioned desalted bamboo shoot shell raw materials, add 45 mL of water, and place them in a 100 mL stainless steel hydrothermal reactor. Stir at a hydrothermal temperature of 180 °C for 30 min, and the stirring speed is 300 rpm. After the reaction is completed, cool it in cold water, take out the hydrothermal reaction solution, centrifuge it at 8000 rpm for 5 min, collect the supernatant, dilute it 10 times, and directly measure the xylose content in it by HPLC. Calculate the xylose yield through formula (A); hydrolyze the supernatant with 4% dilute sulfuric acid at 121 °C for 60 min, then measure the xylose content in the hydrolyzate, and calculate the xylo-oligosaccharide yield through formula (B).

[0069] (A) Xylose yield (%) = C1 × 100 / (M × P);

[0070] (B) Yield of xylooligosaccharide (%) = (C2 - C1) × 100 / (M × P).

[0071] Wherein, C1 is the content of xylose in the hydrothermal solution (g); C2 is the content of xylose after the hydrothermal solution is hydrolyzed with sulfuric acid (g); M is the absolute dry mass of the sample (g); P is the percentage content of xylan in the sample (%).

[0072] Table 2 Different desalination treatments and yields (%)

[0073] Treatment method Xylose yield Xylo-oligosaccharide yield CK 8.59±0.30 38.89±1.89 CS-1 6.92±0.32 50.31±1.02 CS-2 5.18±0.24 52.79±0.63 CS-3 5.11±0.29 55.36±0.98 JP-1 7.08±0.69 45.21±1.91 JP-2 6.13±0.31 50.63±1.45 JP-3 5.21±0.24 55.18±0.36

[0074] As shown in Table 2, the xylose yield is the highest in the CK group. With the increase of the desalination times, the xylose yield shows a gradually decreasing trend, and the xylose yield in the CS-3 group is the lowest; the yield of xylooligosaccharide gradually increases with the increase of the desalination times, with the lowest yield in the CK group, and the yields of xylooligosaccharide in the CS-3 group and the JP-3 group both exceed 55%.

[0075] Examples 1-3, Comparative Example 1

[0076] Examples 1-3 and Comparative Example 1 are about the influence of different irradiation treatments on the yield of xylooligosaccharide. Using the sample treatment of the above CK group as Comparative Example 1 of this application, the difference between Examples 1-3 and Comparative Example 1 lies in the irradiation dose. The specific grouping and results are shown in Table 3, and the specific steps are as follows:

[0077] 1) Using the shell of Yuanjiang asparagus after soaking and desalination three times as the raw material, irradiate it with a 3 MeV electron beam, and the irradiation doses are 200 kGy, 400 kGy, and 600 kGy respectively;

[0078] 2) Then carry out catalytic hydrothermal treatment, and the hydrothermal conditions are: react at 180 °C for 30 min, and the rotation speed is 300 rpm.

[0079] Table 3 Different irradiation treatments and yields (%)

[0080] As can be seen from Table 3, the irradiation treatment improves the yield of xylooligosaccharide in the shell of Yuanjiang asparagus. At an irradiation dose of 200 kGy, the yield of xylooligosaccharide reaches 57.98%; when the irradiation dose increases to 400 kGy, the yield further increases to 62.60%; but when the irradiation dose increases to 600 kGy, the yield slightly decreases to 61.34%.

[0081] Example 4, Comparative Examples 2-4

[0082] Example 4 and Comparative Examples 2-4 of this application are about the influence of acetic acid solutions with different concentrations on the yield of xylooligosaccharide. The difference from Example 1 lies in the acetic acid concentration, and the others are the same. The specific grouping and results are shown in Table 4 below.

[0083] Table 4 Concentrations (wt%) of different acetic acid solutions and yields (%)

[0084] Concentration of acetic acid solution Xylose yield Xylo-oligosaccharide yield Example 1 0 13.93±0.95 57.98±0.71 Example 4 0.10 14.02±0.95 60.54±0.76 Comparative example 2 0.25 16.33±0.72 47.71±1.65 Comparative example 3 0.50 18.78±1.38 44.25±1.80 Comparative example 4 0.75 22.02±0.67 41.27±1.40

[0085] As can be seen from Table 4, with the increase in acetic acid concentration, the xylose yield gradually increases to 22.02%, while the xylo-oligosaccharide yield first increases and then decreases. When the acetic acid concentration is 0.1 wt%, the xylo-oligosaccharide yield reaches the highest, which is 60.54%. When the acetic acid concentration increases to 0.75%, the xylo-oligosaccharide yield decreases to 41.27%.

[0086] Examples 5 - 6, Comparative Examples 5 - 9

[0087] The differences between Examples 5 - 6 and Comparative Examples 5 - 9 of this application and Example 2 lie in the hydrothermal temperature or hydrothermal time, and the others are the same. The specific example grouping is shown in Table 5, and the results are also shown in Table 5.

[0088] As can be seen from Table 5, under the condition of the same hydrothermal treatment time, the xylo-oligosaccharide yield first increases and then decreases with the increase in temperature. When the temperature rises from 120 °C to 180 °C, the yield significantly increases from 23.05% to 62.60%. However, when the temperature continues to rise to 200 °C, the yield drops sharply to 0.75%. Under the condition of a fixed temperature, when the treatment time is extended from 20 min to 40 min, the yield increases from 43.21% to 60.59%. However, when it is further extended to 60 min, the yield instead drops to 41.75%.

[0089] Table 5 Different hydrothermal temperatures, hydrothermal times and yields (%)

[0090]

[0091]

[0092] Examples 7 - 8, Comparative Examples 10 - 15

[0093] The differences between Examples 7 - 8 and Comparative Examples 10 - 15 of this application and Example 1 lie in the change of one or more of the acetic acid concentration (A), hydrothermal temperature (B), hydrothermal time (C) and irradiation dose (D), and the others are the same. The specific example grouping is shown in Table 7, and the results are also shown in Table 7.

[0094] Table 6 Using the above four indicators as factors and the xylo-oligosaccharide yield as the evaluation index, a four-factor three-level orthogonal experiment was carried out to further improve the xylo-oligosaccharide yield.

[0095] Table 6 Orthogonal experiment factor level table

[0096]

[0097] The results are shown in Table 7. The order of influence of each factor on the yield of xylo-oligosaccharides is hydrothermal temperature (B) > irradiation dose (D) > acetic acid concentration (A) > hydrothermal time (C). The optimal conditions are A3B1C2D2, that is, the concentration of acetic acid solution is 0.2 wt%, the hydrothermal temperature is 160 °C, the hydrothermal time is 30 min, and the irradiation dose is 200 kGy.

[0098] Table 7 L9(4 3 ) Orthogonal test table

[0099]

[0100]

[0101] Example 9, Comparative Example 16

[0102] The differences between Example 9 and Comparative Example 16 of this application and Example 8 lie in the hydrothermal time or irradiation dose, and the others are the same.

[0103] Since the obtained optimal group A3B1C2D2 is not in the nine orthogonal tests, the optimal conditions are verified. As can be seen from Table 8, the yield of xylo-oligosaccharides in Example 9 is 65.88%, which is higher than that of Example 8, the best result in the orthogonal test. In Comparative Example 16, without irradiation treatment, the yield of xylo-oligosaccharides is 41.32%. The irradiation treatment can increase the yield of xylo-oligosaccharides.

[0104] Table 8 Verification results of orthogonal test

[0105] Experimental group Xylose yield / % Xylo-oligosaccharide yield / % Example 9 <![CDATA[A3B1C2D2]]> 5.02±0.32 65.88±0.24 Example 8 <![CDATA[A3B1C3D2]]> 8.05±0.44 63.05±0.74 Comparative example 16 <![CDATA[A3B1C2D1]]> 3.36±0.28 41.32±2.65

[0106] Xylo-oligosaccharides with low degree of polymerization (X2-X4) are more easily utilized by beneficial intestinal microorganisms than high-degree-of-polymerization components, and the prebiotic activity increases significantly with the decrease of the degree of polymerization. To verify the influence of different treatment processes on the component distribution of xylo-oligosaccharides, HPLC was used to analyze the xylo-oligosaccharide solutions obtained in Example 9, Example 8 and Comparative Example 16, and the results are shown in Table 9.

[0107] As can be seen from Table 9, the total concentration of xylo-oligosaccharides in Comparative Example 16 is 7.44 g / L, and the proportion of X2-X4 is only 30.65%; after being treated by the optimized process of the present invention, the proportion of X2-X4 in Example 9 is significantly increased to 60.01%; the proportion of X2-X4 in Example 8 reaches 81.07%.

[0108] Table 9 Concentrations (g / L) and proportions (%) of xylose and xylo-oligosaccharides

[0109]

[0110] X2, X3, and X4 are xylobiose, xylotriose, and xylotetraose respectively.

[0111] In summary, the present application uses irradiation combined with acetic acid-catalyzed hydrothermal treatment of Yuanjiang asparagus husks to prepare xylooligosaccharides, which can improve the yield of xylooligosaccharides and the proportion of X2-X4, forming an efficient xylooligosaccharide conversion process, effectively increasing the content of bioactive components X2-X4 in the xylooligosaccharide solution, and thus enhancing its prebiotic function.

[0112] The above embodiments are intended to illustrate the embodiments disclosed in the present invention and should not be construed as limiting the present invention. In addition, various modifications listed herein and changes in the methods and compositions of the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in connection with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, all obvious modifications to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A xylo-oligosaccharide, its preparation method and use, characterized in that The bamboo shoot shells of Yuanjiang asparagus are subjected to electron beam irradiation and hydrothermal treatment, and after solid-liquid separation, a solution containing xylooligosaccharide and residues are obtained.

2. The method according to claim 1, wherein The method further includes soaking and / or ultrasonic desalting treatment of the wet bamboo shoot shells of Yuanjiang asparagus with water; and / or, the time of the desalting treatment is 0.25 - 96 h; and / or, the temperature of the desalting treatment is 18 - 40 °C; and / or, the number of times of the desalting treatment is 2 - 5 times.

3. The method according to claim 2, wherein The mass ratio of the wet bamboo shoot shells of Yuanjiang asparagus to water is 1 g : (3 - 6) mL.

4. The method according to claim 1, characterized in that, The dose of the electron beam irradiation is 150 - 600 kGy.

5. The method according to claim 1, characterized in that The steps of the hydrothermal treatment include carrying out hydrothermal reaction on the bamboo shoot shells and acetic acid solution according to a certain solid-liquid ratio, and the solid-liquid ratio is the mass-volume ratio of the bamboo shoot shells to the acetic acid solution as 1 g : (5 - 15) mL.

6. The method according to claim 5, wherein The temperature of the hydrothermal treatment is 140 - 180 °C.

7. The method according to claim 5, wherein The time of the hydrothermal treatment is 30 - 50 min.

8. The method according to claim 5, wherein The solvent of the acetic acid solution is water; and / or, the concentration of the acetic acid solution is lower than 0.25 wt%.

9. The solution containing xylooligosaccharide obtained by the method according to any one of claims 1 to 8, wherein the molecular weight of the xylooligosaccharide is lower than 1000 Da.

10. Use of the solution containing xylooligosaccharide according to claim 9 in the preparation of a food or feed additive for promoting intestinal health.

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