Preparation method of flaxseed oligosaccharide

Abstract

The invention discloses a preparation method of flaxseed oligosaccharide, and belongs to the technical field of biological extraction. According to the method, HDES composed of L-menthol and octanoic acid is used as an organic phase, ammonium sulfate is combined to form a three-phase system, a microbubble-assisted interface separation technology is introduced, protein is selectively adsorbed through the high specific surface area of bubbles and the electrical effect of an interface, the protein is promoted to migrate to an intermediate phase, layering is accelerated, and efficient separation of polysaccharide and protein is achieved. Under the optimized gas dissolving and pressure releasing conditions, the system layering is rapid, the distribution selectivity is high, and the high-purity polysaccharide is obtained; further, through directional enzymolysis, polysaccharide is converted into oligosaccharide with a uniform structure and good activity. The process integrates extraction, purification and enzymolysis, has the characteristics of greenness, environmental protection, simplicity and convenience in operation and high yield, and provides a new technical approach for high-value utilization of the flaxseed cakes.

Description

Technical Field

[0001] This invention relates to the field of bio-extraction technology, specifically to a method for preparing flaxseed oligosaccharides. Background Technology

[0002] Flax (Linum usitatissimum L.) is an important oilseed crop, its seeds rich in alpha-linolenic acid, unsaturated fatty acids, and lignans, among other active ingredients. With the development of the flaxseed oil industry, a large amount of flaxseed cake is generated during pressing and refining. Currently, this cake is mainly used as animal feed or fertilizer, with low added value. However, flaxseed cake still contains abundant protein and polysaccharides, among other active substances. Polysaccharides possess various biological functions, including antioxidant, immunomodulatory, hypoglycemic, and gut microbiota-improving effects, and have significant potential for development into functional foods and pharmaceutical preparations. However, its resource utilization is currently insufficient and far from matching the scale of the flaxseed oil industry.

[0003] Although flaxseed cake removes most of the oil during pressing, it remains rich in protein, phenolic substances, and residual lipids. These impurities easily form complexes with polysaccharides, increasing the difficulty of separation and purification. Traditional hot water extraction-ethanol precipitation processes require steps such as activated carbon decolorization, Sevag method, or enzymatic deproteinization, which are cumbersome, time-consuming, and have limited protein and phenol removal efficiency, resulting in low product purity. Furthermore, decolorization with some organic solvents or strong oxidizing agents can damage the polysaccharide structure, leading to decreased activity. Therefore, current technologies struggle to simultaneously achieve extraction efficiency, purity, and preservation of bioactivity.

[0004] Triple-phase extraction (TPP) is used for the separation of natural products because it can simultaneously extract and remove impurities. However, traditional TPP often uses organic solvents such as tert-butanol, which pose toxicity and environmental problems, and results in slow separation and high protein residue in high-protein plant systems. In recent years, hydrophobic deep eutectic solvents (HDES) have been introduced into TPP as a green alternative solvent, but efficient separation in high-protein-polysaccharide systems remains difficult to achieve.

[0005] HDES combines low toxicity, biodegradability, and excellent selectivity, which can improve phase separation efficiency and reduce environmental burden. However, the flaxseed meal system is characterized by high oil, high protein, and high viscosity, which leads to easy emulsification, slow phase separation, and difficulty in separating protein and polysaccharide complexes. This has become a key issue limiting the efficient application of TPP in this system. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a novel method for preparing flaxseed oligosaccharides using a microbubble-enhanced hydrophobic deep eutectic solvent (HDES) three-phase extraction coupled with an enzymatic process. This method utilizes HDES and ammonium sulfate to construct a three-phase system, introducing microbubble-assisted interfacial separation technology during the extraction process to significantly enhance the traditional three-phase extraction process. Microbubbles are generated by the release of nitrogen or inert gases through dissolved gas. Leveraging their high specific surface area and interfacial charge effect, they selectively adsorb proteins and promote their migration to the mesophase, thereby enhancing interfacial mass transfer, accelerating layering, and significantly reducing protein residue. The resulting high-purity polysaccharides can be converted into oligosaccharides with uniform polymerization and excellent activity through targeted enzymatic hydrolysis. This method achieves the organic coupling of bubble enhancement, green separation, and enzymatic conversion, providing an efficient technical pathway for the high-value utilization of flaxseed meal.

[0007] This invention provides a method for preparing flaxseed oligosaccharides, comprising the following steps: (1) After pulverizing flaxseed cake, it is mixed with hydrophobic deep eutectic solvent and ammonium sulfate solution, and microbubbles are used for three-phase extraction to separate and purify flaxseed cake polysaccharide; the microbubbles are generated by nitrogen or inert gas through dissolved gas release, and adsorb protein molecules through high specific surface area and interfacial charge effect during the extraction process, so that the protein migrates to the intermediate phase, thereby achieving interfacial separation with hydrophilic polysaccharide. (2) The flaxseed cake polysaccharide obtained in (1) was prepared into an aqueous solution of flaxseed cake polysaccharide, and then subjected to directional enzymatic hydrolysis. The hydrolysate was then separated and purified to obtain flaxseed oligosaccharide.

[0008] In one embodiment of the present invention, the microbubbles in step (1) are generated by the release of nitrogen or inert gas through dissolved gas. During the extraction process, they adsorb protein molecules through high specific surface area and interfacial charge effect, causing the proteins to migrate to the meso phase, thereby achieving interfacial separation with hydrophilic polysaccharides.

[0009] In one embodiment of the present invention, the microbubbles in step (1) are generated by nitrogen gas, the dissolved gas pressure is 2-5 bar, and the release pressure difference is 1-3 bar; the microbubbles are introduced in the following order: first, dissolved gas is released in the brine system to generate bubbles, and then HDES is added for mixing and extraction and stratification.

[0010] In one embodiment of the present invention, in step (1), the pH of the mixture in the microbubble-assisted three-phase extraction system is 3.0-5.0.

[0011] In one embodiment of the present invention, the flow rate of the nitrogen microbubbles in step (1) is 0.2-0.5 L / min.

[0012] In one embodiment of the present invention, the ventilation time of the nitrogen microbubbles in step (1) is 5-15 min.

[0013] In one embodiment of the present invention, in the three-phase extraction process described in step (1), the amount of flaxseed cake powder added is 2-10% (g / mL) of ammonium sulfate solution, the mass fraction of ammonium sulfate solution is 10-30%, the volume ratio of ammonium sulfate solution to hydrophobic deep eutectic solvent is 1:0.5-1:2, the reaction temperature is 50-70℃, and the extraction time is 120min.

[0014] In one embodiment of the present invention, the separation and purification in step (1) involves mixing the aqueous phase after three-phase extraction with 4 times the volume of anhydrous ethanol, letting it stand at 4°C for 12 hours, and then centrifuging (4000 rpm, 15 min) to obtain flaxseed meal polysaccharide.

[0015] In one embodiment of the present invention, the concentration of the flaxseed cake polysaccharide aqueous solution in step (2) is 2-20 mg / mL; preferably 10 mg / mL.

[0016] In one embodiment of the present invention, in the enzymatic hydrolysis reaction described in step (2), the directional enzyme includes one or more of Shearzyme 500L enzyme, Pentopan Mono BG CN enzyme, and Pectinex UF enzyme; more preferably, Pectinex UF enzyme.

[0017] In one embodiment of the present invention, in the enzymatic hydrolysis reaction described in step (2), the pH is 4.0-6.0, the enzymatic hydrolysis temperature is 40-60℃, the amount of enzyme added is 0.001-0.01% (v / v) of the flaxseed cake polysaccharide aqueous solution, and the enzymatic hydrolysis time is 6-24h.

[0018] In one embodiment of the present invention, in the enzymatic hydrolysis reaction described in step (2), the amount of Shearzyme 500L enzyme added is 0.001%-0.006%, the amount of Pentopan Mono BG CN enzyme added is 0.004%-0.01%, and the amount of Pectinex UF enzyme added is 0.002%-0.01%; the directional enzyme hydrolysis time is 10h.

[0019] This invention provides flaxseed oligosaccharides prepared by the method described above.

[0020] Compared with the prior art, the beneficial effects of the present invention include: (1) Significantly improved yield: Microbubbles are generated by the release of nitrogen or inert gas through dissolved gas, possessing a high specific surface area and an electro-hydraulic interface. In the salting-out environment of the HDES three-phase system, microbubbles can selectively enrich protein molecules through electrostatic adsorption and hydrophobic induction, and promote their migration to the intermediate phase, achieving spatial separation and selective allocation of proteins and polysaccharides. During the rising process, the bubbles continuously update the interface and enhance mass transfer efficiency, significantly improving the interphase migration and stratification rate of the system. This synergistic mechanism effectively reduces interfacial hindrance and protein retention, improving the system's separation efficiency and polysaccharide recovery rate. After coupling with the directional enzymatic hydrolysis process, the oligosaccharide yield can reach 82.3%, significantly higher than the 58.6% of the traditional "hot water extraction-ethanol precipitation-enzymatic hydrolysis" process, achieving a significant improvement in resource utilization.

[0021] (2) Integrated extraction and purification: Traditional processes require cumbersome steps such as ethanol precipitation, activated carbon decolorization, and Sevag protein removal. However, in this method, microbubbles, salting out, and HDES work together, combining interfacial adsorption and interphase migration functions, so that deproteinization, defatting, depigmentation and extraction are carried out simultaneously, resulting in polysaccharides with light color, high purity and good solution clarity.

[0022] (3) Improved enzymatic hydrolysis efficiency: After microbubble-assisted decontamination, the protein and phenol residues in the polysaccharide sample are extremely low, which avoids the inhibition of enzyme activity, making the directional degradation efficiency of cellulase, pectinase, etc. higher, the reaction is milder, and the molecular weight distribution of oligosaccharides is more concentrated and uniform.

[0023] (4) Green and environmentally friendly and high-value utilization: The microbubble process does not require the addition of chemical flocculants, and HDES is a low-toxicity solvent system, making the process safe and environmentally friendly. The overall process realizes the coupling of interface enhancement, green solvent separation and high-purity substrate enzymatic hydrolysis and conversion, providing a feasible new path for the efficient utilization of flaxseed meal resources and the preparation of functional oligosaccharides. Detailed Implementation

[0024] The flaxseed meal used in this invention was purchased from Ningxia Junxingfang Food Technology Co., Ltd.

[0025] Example 1 (1) HDES was prepared by mixing L-menthol, the hydrogen bond acceptor, and octanoic acid, the hydrogen bond donor, at a molar ratio of 1:1 and stirring magnetically at 80°C. Flaxseed cake was mixed with 20 wt% ammonium sulfate solution at a mass fraction of 5%, and the volume ratio of ammonium sulfate solution to HDES was 1:1. The pH of the mixture was adjusted to 4.0 using hydrochloric acid solution, and microbubble-assisted three-phase extraction was performed at 60°C.

[0026] Microbubbles were directly released into the mixture from nitrogen gas via a dissolved gas release system: nitrogen gas was dissolved in a portion of the brine phase at a dissolved gas pressure of 3 bar in the dissolved gas tank, and then injected into the mixture through a release valve at a release pressure of 2 bar (pressure differential release) to form microbubbles; the aeration flow rate was 0.3 L / min, and the aeration time was 10 min. Under the condition of simultaneous aeration and stirring, interface enhancement and accelerated stratification were achieved, with a total extraction time of 120 min. After extraction, the lower aqueous phase was collected, mixed with 4 volumes of anhydrous ethanol, allowed to stand at 4°C for 12 h, centrifuged (4000 rpm, 15 min), and the precipitate was redissolved, dialyzed, and freeze-dried to obtain flaxseed meal polysaccharide.

[0027] (2) The flaxseed cake polysaccharide obtained in (1) was prepared into an aqueous solution of flaxseed cake polysaccharide with a concentration of 10 mg / mL. The pH of the flaxseed cake polysaccharide solution was adjusted to 5.0 with hydrochloric acid solution. Pectinex UF enzyme (from Novozymes) was added at 50℃. The amount of Pectinex UF enzyme added was 0.004%. The enzyme was hydrolyzed for 10 h. After enzyme inactivation, the flaxseed cake oligosaccharide was obtained by separation through a 2000 Da membrane.

[0028] Example 2 The only difference between Example 2 and Example 1 is that the dissolved gas pressure in step (1) is 2 bar and the release pressure difference is 3 bar.

[0029] Example 3 The only difference between Example 3 and Example 1 is that the dissolved gas pressure in step (1) is 5 bar and the release pressure difference is 1 bar.

[0030] Example 4 The only difference between Example 4 and Example 1 is that the pH of the mixture in step (1) is 3.0.

[0031] Example 5 The only difference between Example 5 and Example 1 is that the pH of the mixture in step (1) is 5.0.

[0032] Example 6 The only difference between Example 6 and Example 1 is that the flow rate of nitrogen microbubbles in step (1) is 0.2 L / min and the ventilation time is 15 min.

[0033] Example 7 The only difference between Example 7 and Example 1 is that the flow rate of nitrogen microbubbles in step (1) is 0.5 L / min and the ventilation time is 5 min.

[0034] Example 8 The difference between Example 8 and Example 1 is that in step (1), during the three-phase extraction process, the amount of flaxseed cake powder added is 2% (g / mL) of ammonium sulfate solution, the mass fraction of ammonium sulfate solution is 30%, the volume ratio of ammonium sulfate solution to hydrophobic deep eutectic solvent is 1:0.5, the reaction temperature is 50℃, and the extraction time is 120min.

[0035] Example 9 The difference between Example 9 and Example 1 is that in step (1), during the three-phase extraction process, the amount of flaxseed cake powder added is 10% (g / mL) of ammonium sulfate solution, the mass fraction of ammonium sulfate solution is 10%, the volume ratio of ammonium sulfate solution to hydrophobic deep eutectic solvent is 1:2, the reaction temperature is 70℃, and the extraction time is 120min.

[0036] Example 10 The only difference between Example 10 and Example 1 is that the directional enzyme in step (2) is Pentopan Mono BGCN enzyme (from Novozymes).

[0037] Example 11 The only difference between Example 11 and Example 1 is that in step (2), the pH is 4.0, the enzymatic hydrolysis temperature is 60℃, the amount of enzyme added is 0.002% (v / v), and the enzymatic hydrolysis time is 6h.

[0038] Example 12 The only difference between Example 12 and Example 1 is that in step (2), the pH is 6.0, the enzymatic hydrolysis temperature is 40°C, the amount of enzyme added is 0.01% (v / v), and the enzymatic hydrolysis time is 24h.

[0039] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the dissolved gas pressure in step (1) is 1 bar and the release pressure difference is 5 bar.

[0040] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the dissolved gas pressure in step (1) is 6 bar and the release pressure difference is 0.5 bar.

[0041] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the pH of the mixture in step (1) is 2.0.

[0042] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the pH of the mixture in step (1) is 7.0.

[0043] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the nitrogen microbubble flow rate in step (1) is 0.1 L / min and the ventilation time is 3 min.

[0044] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the nitrogen microbubble flow rate in step (1) is 0.7 L / min and the ventilation time is 20 min.

[0045] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that in step (1), during the three-phase extraction process, the amount of flaxseed cake powder added is 1% (g / mL) of ammonium sulfate solution, the mass fraction of ammonium sulfate solution is 5%, the volume ratio of ammonium sulfate solution to hydrophobic deep eutectic solvent is 1:0.3, the reaction temperature is 40℃, and the extraction time is 120min.

[0046] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that in step (1), during the three-phase extraction process, the amount of flaxseed cake powder added is 15% (g / mL) of ammonium sulfate solution, the mass fraction of ammonium sulfate solution is 40%, the volume ratio of ammonium sulfate solution to hydrophobic deep eutectic solvent is 1:2.5, the reaction temperature is 80℃, and the extraction time is 120min.

[0047] Comparative Example 9 The only difference between Comparative Example 9 and Example 1 is that the directional enzyme mentioned in step (2) is Shearzyme 500L enzyme (from Novozymes).

[0048] Comparative Example 10 The only difference between Comparative Example 10 and Example 1 is that in step (2), the pH is 3.5, the enzymatic hydrolysis temperature is 30°C, the amount of enzyme added is 0.01% (v / v), and the enzymatic hydrolysis time is 2h.

[0049] Comparative Example 11 The only difference between Comparative Example 11 and Example 1 is that in step (2), the pH is 7.0, the enzymatic hydrolysis temperature is 70°C, the amount of enzyme added is 0.001% (v / v), and the enzymatic hydrolysis time is 24h.

[0050] Comparative Example 12 The only difference between Comparative Example 12 and Example 1 is that the three-phase extraction in step (1) was replaced by the traditional water extraction and alcohol precipitation. Flaxseed cake was mixed with deionized water at a ratio of 1:20, the pH was adjusted to 4.0 using hydrochloric acid solution, and extracted at 60°C for 120 min. The aqueous phase was mixed with 4 volumes of anhydrous ethanol and allowed to stand at 4°C for 12 h. Then it was centrifuged (4000 rpm / min, 15 min) to obtain flaxseed cake polysaccharide.

[0051] Comparative Example 13 The only difference between Comparative Example 13 and Example 1 is that step (2) in Example 1 is omitted.

[0052] Comparative Example 14 The only difference between Comparative Example 14 and Example 1 is that the microbubble operation in the three-phase extraction process in step (1) of Example 1 is omitted.

[0053] The weight of flaxseed meal in Examples 1-12 and Comparative Examples 1-14 is recorded as m0, the weight of flaxseed meal polysaccharide is recorded as m1, and the weight of the prepared flaxseed meal oligosaccharide is recorded as m2. The units of m0, m1, and m2 are all g, and the calculation formula is as follows:

[0054] The total sugar content after the reaction was determined by the phenol-sulfuric acid method, and the uronic acid content was determined by the pyrazole-sulfuric acid method. Each sample was measured in triplicate. The results are shown in Table 1.

[0055] Table 1. Polysaccharide extraction rate, polysaccharide content, protein content, oligosaccharide extraction rate, and oligosaccharide content of each example and comparative example.

[0056] Analysis of the experimental results from Examples 1-12 and Comparative Examples 1-14 shows that introducing microbubble-assisted three-phase extraction technology under suitable salt concentration, phase volume ratio, pH value, and temperature can significantly improve the system's phase separation rate and protein migration efficiency. In the experiments, when the dissolved gas pressure was 3 bar and the release pressure was 2 bar, nitrogen microbubbles formed a high specific surface area charged interface in the mixed system. Through electrostatic adsorption and hydrophobic induction, they selectively captured protein molecules and promoted their migration to the intermediate phase, achieving spatial separation of polysaccharides and proteins. During the microbubble rise, the system interface was continuously disturbed, accelerating interphase material transfer and renewal, effectively eliminating the interfacial hindrance phenomenon commonly found in salting-out systems, and significantly shortening the phase separation time. The results indicate that the polysaccharide extraction rate and purity were significantly higher in the microbubble-assisted three-phase extraction system compared to the un-aerated system.

[0057] In Examples 2-12, changes in microbubble generation parameters (including dissolved gas pressure, release pressure, mixed solution pH, aeration flow rate, and aeration time) or system operating conditions (such as salt concentration, phase volume ratio, and temperature) all resulted in a significant decrease in polysaccharide extraction efficiency and oligosaccharide yield, indicating that these factors have a significant impact on product recovery and purity. Although acceptable products could still be obtained under some conditions, the overall performance was not as good as in Example 1, demonstrating that the optimal combination of conditions has a significant advantage.

[0058] The experimental results of Comparative Examples 1-14 were significantly lower than those of the Example Group. Specifically, changing the microbubble generation parameters (including dissolved gas pressure, release pressure, mixed solution pH, aeration flow rate, and aeration time) or system operating conditions (such as salt concentration, phase volume ratio, and temperature), as well as changing the enzyme type or deviating from the optimal enzymatic hydrolysis conditions, all led to a significant decrease in the extraction efficiency of polysaccharides and oligosaccharides. Under some conditions, effective oligosaccharide products could not even be obtained. Comparative Example 12 used the traditional water extraction and alcohol precipitation method to replace three-phase extraction. Even under the same enzymatic hydrolysis conditions, the polysaccharide extraction rate decreased significantly, and the oligosaccharide yield also decreased significantly. This indicates that relying solely on water extraction and alcohol precipitation cannot fully extract polysaccharides, resulting in limited enzymatic hydrolysis efficiency and unsatisfactory product purity and yield. Comparative Example 13 omitted the directional enzymatic hydrolysis step while retaining the three-phase extraction condition. The amount of oligosaccharide product obtained was extremely low, or no effective oligosaccharides were obtained. This indicates that even if the polysaccharide extraction rate is high, without directional enzymatic hydrolysis, polysaccharides cannot be converted into oligosaccharides. Comparative Example 14, maintaining the same HDES system and salt concentration, omitted the microbubble introduction step and relied solely on conventional salting out and the three-phase system for separation. Experimental results showed that protein migration was restricted in this system, and the purity and extraction efficiency of polysaccharides were significantly reduced. This demonstrates that microbubbles play a crucial role in the selective adsorption and migration of proteins in the three-phase system, and their interfacial enhancement effect cannot be replaced by traditional salting out or mechanical stirring. It is a necessary condition for achieving rapid phase separation and high-purity extraction.

[0059] In summary, microbubble-assisted three-phase extraction and targeted enzymatic hydrolysis are both indispensable in this process: three-phase extraction ensures efficient separation of polysaccharides, while microbubble-assisted interface separation technology significantly promotes protein migration and phase separation by enhancing the adsorption and dynamic renewal process at the gas-liquid interface, accelerating system stratification and improving extraction efficiency; targeted enzymatic hydrolysis ensures that polysaccharides are converted into high-purity oligosaccharides. Only through the synergistic effect of the two can high-yield and high-purity flaxseed meal oligosaccharides be obtained.

[0060] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing flaxseed oligosaccharides, characterized in that, Includes the following steps: (1) After pulverizing flaxseed cake, it is mixed with hydrophobic deep eutectic solvent and ammonium sulfate solution to obtain a mixed solution. Microbubbles are used for three-phase extraction to separate and purify flaxseed cake polysaccharide. The microbubbles are generated by nitrogen or inert gas through dissolved gas release. During the extraction process, they adsorb protein molecules through high specific surface area and interfacial charge effect, causing the protein to migrate to the intermediate phase, thereby achieving interfacial separation with hydrophilic polysaccharide. (2) The flaxseed cake polysaccharide obtained in step (1) is prepared into an aqueous solution of flaxseed cake polysaccharide and subjected to directional enzymatic hydrolysis. The hydrolysate is separated and purified to obtain flaxseed oligosaccharide. The enzymes used for directional enzymatic hydrolysis are one or more of Pentopan Mono BG CN enzyme and Pectinex UF enzyme.

2. The preparation method according to claim 1, characterized in that, In step (1), the microbubbles are generated by nitrogen gas, the dissolved gas pressure is 2-5 bar, and the release pressure difference is 1-3 bar. The microbubbles are introduced in the following order: first, dissolved gas is released in the brine system to generate bubbles, and then the mixture is added for extraction and stratification.

3. The preparation method according to claim 1, characterized in that, In step (1), the pH of the mixed solution in the microbubble-assisted three-phase extraction system is 3.0-5.

0.

4. The preparation method according to claim 1, characterized in that, In step (1), the flow rate of nitrogen microbubbles is 0.2-0.5 L / min.

5. The preparation method according to claim 1, characterized in that, In step (1), the nitrogen microbubbles are ventilated for 5-15 minutes.

6. The preparation method according to claim 1, characterized in that, In step (1), during the three-phase extraction process, the amount of flaxseed cake powder added is 2-10% of the ammonium sulfate solution, g / mL; the mass fraction of the ammonium sulfate solution is 10-30%; the volume ratio of the ammonium sulfate solution to the hydrophobic deep eutectic solvent is 1:0.5-1:2; the reaction temperature is 50-70℃; and the extraction time is 120 min.

7. The preparation method according to claim 1, characterized in that, In step (2), the pH of the enzymatic hydrolysis reaction is 4.0-6.0, the enzymatic hydrolysis temperature is 40-60℃, and the enzymatic hydrolysis time is 6-24h.

8. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the flaxseed cake polysaccharide aqueous solution is 2-20 mg / mL.

9. The preparation method according to claim 1, characterized in that, In step (2), the amount of enzyme added in the enzymatic hydrolysis reaction is 0.001-0.01% of the volume of the flaxseed cake polysaccharide aqueous solution.

10. Flaxseed oligosaccharides prepared by any one of the methods described in claims 1-9.

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