Method for preparing low-grafted glucosyl stevioside at high temperature and high pressure

Abstract

The invention discloses a method for preparing low-grafted glucosyl stevioside at high temperature and high pressure, which comprises the following steps: taking stevioside as a receptor, beta-cyclodextrin as a donor and CGT enzyme as a catalyst for reaction to obtain reaction liquid containing glucosyl stevioside; putting the reaction liquid containing the glucosyl stevioside into a high-pressure reaction kettle, and adding a catalyst to carry out high-temperature and high-pressure cracking reaction; after the high-temperature and high-pressure cracking reaction is finished, cooling a cracking solution to room temperature, filtering, concentrating for multiple times by adopting a polymeric membrane, and collecting a trapped fluid; and carrying out spray drying on the trapped fluid to obtain the low-grafting glucosyl stevioside. According to the method, firstly, glucosyl stevioside is prepared by adopting an enzyme modification method, then splitting decomposition is performed under certain conditions, and then a specific purification process is performed, so that the prepared product is high in stability, the proportion of low-grafted glucosyl stevioside in the product is high, and the product tastes good.

Description

Technical Field

[0001] This invention relates to the field of glucosylstevioside preparation technology, specifically to a method for preparing low-grafted glucosylstevioside under high temperature and high pressure. Background Technology

[0002] Glucosylsteviosides typically refer to steviol glycoside derivatives produced through enzymatic modification. The core process involves introducing one or more glucose molecules onto specific sugar groups in the steviol glycoside nucleus, resulting in a mixture of glucosylsteviosides with varying numbers of grafts. Furthermore, this reaction process is difficult to control, leading to variations in the product's taste and texture.

[0003] Currently, there is a growing market demand for low-grafted glucosyl steviol glycosides, which offer a smoother taste and less aftertaste. The main industrial production method for these products currently involves enzymatic hydrolysis using saccharifying enzymes. However, this method is susceptible to instability due to factors such as enzyme activity, temperature, and pH, and the low proportion of low-grafted glucosyl steviol glycosides results in a poor taste. Furthermore, existing production processes for low-grafted glucosyl steviol glycosides typically employ enzymatic catalysis and resin purification, which are cumbersome, use large amounts of organic solvents, and consume significant energy. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure, which addresses the shortcomings of the existing technology. The method first uses an enzymatic modification method to obtain glucosyl steviol glycosides, then cleaves them under certain conditions, and then purifies them through a specific process. The resulting product has high stability, a high proportion of low-grafted glucosyl steviol glycosides, and a good taste.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure includes the following steps:

[0007] (1) Using steviol glycosides as acceptors, β-cyclodextrin as donors, and CGT enzyme as catalysts, a reaction solution containing glucosyl steviol glycosides was obtained.

[0008] (2) The reaction solution containing glucosylstevioside was placed in a high-pressure reactor and a catalyst was added to carry out a high-temperature and high-pressure pyrolysis reaction;

[0009] (3) After the high temperature and high pressure pyrolysis reaction is completed, the pyrolysis liquid is cooled to room temperature, filtered, and the filtrate is concentrated multiple times using a polymer membrane and the retentate is collected.

[0010] (4) The retentate collected in step (3) is spray-dried to obtain low-grafted glucosyl steviol glycoside.

[0011] Preferably, in step (1), the steviol glycoside is RA97, the mass ratio of RA97 to β-cyclodextrin is 1:(0.9-1.3), and the amount of CGT enzyme added is 1.8-2.3 wt% of the mass of steviol glycoside.

[0012] Preferably, in step (1), the reaction temperature is 70-72℃, the pH of the reaction system is 5-5.5, the reaction time is 24h, and the solid content of the reaction system is 30-40wt%.

[0013] Preferably, in step (2), the temperature of the high-temperature and high-pressure pyrolysis reaction is 109-112℃, the pressure is 0.09-0.12MPa, and the time is 18-20h.

[0014] Preferably, in step (2), the catalyst is a sulfonic acid-modified Sn-Na bimetallic MOF catalyst, and the amount of catalyst added is 5-10 wt% of the solid mass in the reaction solution.

[0015] Preferably, the preparation method of the sulfonic acid-modified Sn-Na bimetallic MOF catalyst includes the following steps:

[0016] I. Using zirconium tetrachloride and 2-aminoterephthalic acid as raw materials and DMF as solvent, a hydrothermal reaction was carried out to obtain metal-organic framework materials.

[0017] 2. The above-mentioned metal-organic framework material was modified with chlorosulfonic acid to obtain a sulfonic acid-modified metal-organic framework material.

[0018] 3. Add stannous chloride pentahydrate and sodium acetate to anhydrous ethanol, then add the above-mentioned sulfonic acid group-modified metal-organic framework material, react at 65-70℃ for 10-12 h, then filter, wash the precipitate, dry it and disperse it in deionized water, add polyethylene glycol, ultrasonically disperse, and finally vacuum dry to obtain the catalyst.

[0019] Preferably, in step one, the molar ratio of zirconium tetrachloride to 2-aminoterephthalic acid is (2-3):(2-3).

[0020] Preferably, in step one, the hydrothermal reaction temperature is 118-125℃ and the time is 18-24h.

[0021] Preferably, in step two, the specific process of modifying the above metal-organic framework material with chlorosulfonic acid is as follows: the above metal-organic framework material is added to anhydrous dichloromethane, then chlorosulfonic acid is added under an ice bath at 0°C, and the reaction is refluxed under a nitrogen atmosphere for 5-6 hours. After the reaction is completed, the reaction solution is filtered, the precipitate is washed until neutral and then dried to obtain the final product.

[0022] Preferably, the ratio of metal-organic framework material to chlorosulfonic acid is 1g:(0.3-0.8)ml, and the reflux reaction temperature is 40-45℃.

[0023] Preferably, in step three, the ratio of tin chloride pentahydrate, sodium acetate, and sulfonic acid-modified metal-organic framework material is (1-2) g: (0.7-0.8) mmol: (1.2-1.3) mmol.

[0024] Preferably, in step three, the polyethylene glycol is polyethylene glycol 4000-6000, and the amount of polyethylene glycol added is 10-20 wt% of the mass of the precipitate after drying; the ultrasonic dispersion power is 300-500W, and the time is 20-30 min.

[0025] Preferably, in step (3), the molecular weight cutoff of the polymer membrane is 300-500 Da, and the pressure during concentration is 2-3 MPa.

[0026] Preferably, in step (3), the specific process of multiple concentrations is as follows: first, the pyrolysis liquid is concentrated to a solid content of 40-46 wt%, then the retentate is diluted with water to a solid content of 30-35 wt%, and then concentrated a second time to a solid content of 40-46 wt%.

[0027] Preferably, in step (4), the spray drying conditions are: inlet air temperature of 179-182℃, outlet air temperature of 82-86℃, and air flow rate of 12-16 m³ / h. 3 / h.

[0028] The glycosylation degree of the low-grafted glucosyl steviol glycosides of the present invention is <4 glucosyl groups (mainly including 1-substituent, 2-substituent, and 3-substituent).

[0029] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] This invention provides a method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure. First, using steviol glycosides as the acceptor and β-cyclodextrin as the donor, glucosyl steviol glycosides are prepared under enzymatic catalysis. Then, through subsequent cleavage and purification, a product with good stability and a high content of low-grafted glucosyl steviol glycosides is obtained. This invention achieves high content of low-grafted glucosyl steviol glycosides through a single enzymatic catalysis and high-temperature and high-pressure cleavage, with minimal enzyme addition. Furthermore, the only solvent used in the process is water, making it more environmentally friendly and cost-effective.

[0031] In the process of enzyme-catalyzed preparation of glucosylstevioside, this invention uses CGT enzyme catalysis to ensure that the glucose group is efficiently and specifically transferred from β-cyclodextrin to steviol glycoside to form the initial glucosylstevioside. By effectively optimizing the catalytic reaction conditions, the efficiency of the grafting reaction and the product yield are greatly improved.

[0032] This invention involves the cleavage and transformation of the reacted glucosylstevioside, selectively cleaving away excessively long glucose chains or redundant glucose groups from the initial product, thereby converting the highly grafted initial product into the target product, low-grafted glucosylstevioside. During the cleavage process, a certain amount of catalyst is added. The sulfonic acid group in this catalyst provides a strong Brønsted acid site, which can effectively catalyze the hydrolysis and cleavage of the glycosidic bond; Sn 4+ It is a strong Lewis acid that can adsorb and polarize the lone pair electrons of the oxygen atom on the target glycosidic bond in the glucosylstevioside molecule, weakening the CO bond strength of the glycosidic bond and making it easier to break; Na + The introduction of [a specific ingredient] can partially neutralize or balance the charge environment near the sulfonic acid group, making the reaction process milder and more selective. By optimizing the cleavage process conditions and selecting the type of catalyst, side reactions and damage to the steviol glycoside nucleus can be reduced.

[0033] This invention effectively selects the type of polymer membrane and concentration conditions during the purification of the pyrolysis product, efficiently removing impurities such as monosaccharides, disaccharides, small molecule organic acids, and inorganic salts generated during pyrolysis, while effectively retaining the target molecule with a large molecular weight, low-grafted glucosyl steviol glycoside; through multiple concentrations, the purity of the final product is significantly improved. Detailed Implementation

[0034] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0036] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0037] The preparation method of the sulfonic acid-modified Sn-Na bimetallic MOF catalyst in the following examples and comparative examples includes the following steps:

[0038] 1. Add 2.5 mmol zirconium tetrachloride and 2.5 mmol 2-aminoterephthalic acid to 50 ml DMF, stir and mix to obtain a reaction solution, place it in a hydrothermal reactor, and react at 120 °C for 24 h. After the reaction is completed, cool to room temperature, filter the reaction solution, wash the precipitate with DMF and then vacuum dry at 80 °C for 12 h to obtain a metal-organic framework material.

[0039] 2. Mix 1g of the above metal-organic framework material with 30ml of anhydrous dichloromethane, and add 0.5ml of chlorosulfonic acid dropwise under an ice bath at 0℃. After the addition is completed, heat to 42℃ under a nitrogen atmosphere and react for 6h. After the reaction is completed, cool to room temperature, filter, wash the precipitate with water until neutral, and then dry at 60℃ for 8h to obtain the sulfonic acid group modified metal-organic framework material.

[0040] 3. Dissolve 0.8 mmol SnCl4·5H2O and 1.2 mmol sodium acetate in 40 ml anhydrous ethanol, then add 1 g of the sulfonic acid group-modified metal-organic framework material from step 2, and react at 70 °C for 12 h. After the reaction is complete, filter the reaction solution, wash the precipitate with anhydrous ethanol and dry it to obtain the supported catalyst.

[0041] 4. Add 1g of the supported catalyst from step 3 to 20ml of deionized water, then add 0.1g of polyethylene glycol 6000, sonicate at 300W for 30min, then filter the dispersion, and after drying the precipitate, obtain the sulfonic acid-modified Sn-Na bimetallic MOF catalyst.

[0042] The following examples and comparative examples contain some raw material performance parameters or sources:

[0043] CGT enzyme: purchased from Novozymes (China) Biotechnology Co., Ltd.

[0044] Example 1

[0045] A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure includes the following steps:

[0046] (1) Add 100g RA97 to 200ml deionized water, heat to 70℃, add CGT enzyme (the amount added is 2% of the mass of RA97), stir evenly to obtain solution 1;

[0047] (2) Add 100g of β-cyclodextrin to 250ml of deionized water, heat to 70℃, stir and mix to obtain solution 2; add solution 2 dropwise to solution 1, adjust the pH of the system to 5, react at 70℃ for 24h to obtain a reaction solution containing glucosylstevioside;

[0048] (3) Transfer the reaction solution containing glucosyl steviol glycosides from step (2) to a high-pressure reactor, add a sulfonic acid-modified Sn-Na bimetallic MOF catalyst (the amount added is 5 wt% of the heavy solid mass of the reaction solution containing glucosyl steviol glycosides), and pyrolyze it at 110℃ and 0.1MPa for 20 h to obtain the pyrolyte.

[0049] (4) After cooling the lysis solution from step (3) to room temperature, filter it. The filtrate is concentrated with a polymer membrane (polyamide membrane) with a molecular weight cutoff of 300 Da at a pressure of 2 MPa until the solid content of the retentate is 45 wt%. Then, deionized water is added to the retentate to dilute it to a solid content of 35 wt%. The retentate is concentrated a second time at a pressure of 2 MPa until the solid content of the retentate is 45 wt%. The retentate after the second concentration is collected.

[0050] (5) The retentate after secondary concentration is subjected to an inlet air temperature of 180℃, an outlet air temperature of 85℃, and a gas flow rate of 15m³. 3 Spray drying under conditions of / h yields low-grafted glucosyl steviol glycosides.

[0051] Example 2

[0052] A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure includes the following steps:

[0053] (1) Add 100g RA97 to 200ml deionized water, heat to 71℃, add CGT enzyme (the amount added is 1.9% of the mass of RA97), stir evenly to obtain solution 1;

[0054] (2) Add 100g of β-cyclodextrin to 250ml of deionized water, heat to 71℃, stir and mix to obtain solution 2; add solution 2 dropwise to solution 1, maintain the pH of the system at 5.1 using sodium acetate buffer, react at 71℃ for 24h to obtain a reaction solution containing glucosylstevioside.

[0055] (3) Transfer the reaction solution containing glucosyl steviol glycosides from step (2) to a high-pressure reactor, add a sulfonic acid-modified Sn-Na bimetallic MOF catalyst (the amount added is 6 wt% of the solid mass in the reaction solution containing glucosyl steviol glycosides), and pyrolyze it for 20 h at 110 °C and 0.1 MPa to obtain the pyrolyte.

[0056] (4) After cooling the lysis solution from step (3) to room temperature, filter it. The filtrate is concentrated with a polymer membrane (polyamide membrane) with a molecular weight cutoff of 400 Da at a pressure of 2.5 MPa until the solid content of the retentate is 45 wt%. Then, deionized water is added to the retentate to dilute it to a solid content of 35 wt%. The retentate is concentrated a second time at a pressure of 2.5 MPa until the solid content of the retentate is 45 wt%. The retentate after the second concentration is collected.

[0057] (5) The retentate after secondary concentration is subjected to an inlet air temperature of 180℃, an outlet air temperature of 85℃, and a gas flow rate of 14m³. 3 Spray drying under conditions of / h yields low-grafted glucosyl steviol glycosides.

[0058] Example 3

[0059] A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure includes the following steps:

[0060] (1) Add 100g RA97 to 200ml deionized water, heat to 72℃, add CGT enzyme (the amount added is 2.0% of the mass of RA97), stir evenly to obtain solution 1;

[0061] (2) Add 100g of β-cyclodextrin to 250ml of deionized water, heat to 72℃, stir and mix to obtain solution 2; add solution 2 dropwise to solution 1, maintain the pH of the system at 5.2 using sodium acetate buffer, react at 72℃ for 24h to obtain a reaction solution containing glucosylstevioside;

[0062] (3) Transfer the reaction solution containing glucosyl steviol glycosides from step (2) to a high-pressure reactor, add a sulfonic acid-modified Sn-Na bimetallic MOF catalyst (the amount added is 7wt% of the solid mass in the reaction solution containing glucosyl steviol glycosides), and pyrolyze it for 20h at 110℃ and 0.1MPa to obtain the pyrolyte.

[0063] (4) After cooling the lysis solution from step (3) to room temperature, filter it. The filtrate is concentrated with a polymer membrane (polyamide membrane) with a molecular weight cutoff of 400 Da at a pressure of 3 MPa until the solid content of the retentate is 43 wt%. Then, deionized water is added to the retentate to dilute it to a solid content of 35 wt%. The retentate is concentrated a second time at a pressure of 3 MPa until the solid content of the retentate is 43 wt%. The retentate after the second concentration is collected.

[0064] (5) The retentate after secondary concentration is subjected to an inlet air temperature of 181℃, an outlet air temperature of 83℃, and a gas flow rate of 15m³. 3 Spray drying under conditions of / h yields low-grafted glucosyl steviol glycosides.

[0065] Example 4

[0066] A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure includes the following steps:

[0067] (1) Add 100g RA97 to 200ml deionized water, heat to 72℃, add CGT enzyme (the amount added is 2.1% of the mass of RA97), stir evenly to obtain solution 1;

[0068] (2) Add 100g of β-cyclodextrin to 250ml of deionized water, heat to 72℃, stir and mix to obtain solution 2; add solution 2 dropwise to solution 1, maintain the pH of the system at 5.5 using sodium acetate buffer, react at 72℃ for 24h to obtain a reaction solution containing glucosylstevioside;

[0069] (3) Transfer the reaction solution containing glucosyl steviol glycosides from step (2) to a high-pressure reactor, add sulfonic acid-modified Sn-Na bimetallic MOF catalyst (the amount added is 8wt% of the solid mass in the reaction solution containing glucosyl steviol glycosides), and pyrolyze for 20h at 110℃ and 0.1MPa to obtain the pyrolyte.

[0070] (4) After cooling the lysis solution from step (3) to room temperature, filter it. The filtrate is concentrated with a polymer membrane (polyamide membrane) with a molecular weight cutoff of 500 Da at a pressure of 3 MPa until the solid content of the retentate is 45 wt%. Then, deionized water is added to the retentate to dilute it to a solid content of 35 wt%. The retentate is concentrated a second time at a pressure of 3 MPa until the solid content of the retentate is 40-46 wt%. The retentate after the second concentration is collected.

[0071] (5) The retentate after secondary concentration is subjected to an inlet air temperature of 180℃, an outlet air temperature of 86℃, and a gas flow rate of 15m³. 3 Spray drying under conditions of / h yields low-grafted glucosyl steviol glycosides.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 4 is that step (3) is not included, while the other operations are the same as in Example 4.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 4 is that in step (3), no sulfonic acid-modified Sn-Na bimetallic MOF catalyst is added, and the other operations are the same as in Example 4.

[0076] Comparative Example 3

[0077] The difference between this comparative example and Example 4 is that in step (3), the amount of sulfonic acid modified Sn-Na bimetallic MOF catalyst added is 12wt% of the solid mass in the reaction solution containing glucosylstevioside, and the other operations are the same as in Example 4.

[0078] Comparative Example 4

[0079] The difference between this comparative example and Example 4 is that step (4) is not included, while the other operations are the same as in Example 4.

[0080] Comparative Example 5

[0081] The difference between this comparative example and Example 4 is that in step (4), the molecular weight cutoff of the polymer membrane is 200 Da, and the other operations are the same as in Example 4.

[0082] Comparative Example 6

[0083] The difference between this comparative example and Example 4 is that in step (4), the molecular weight cutoff of the polymer membrane is 600 Da, and the other operations are the same as in Example 4.

[0084] The performance parameters of the products obtained in the above embodiments and comparative examples are shown in Table 1.

[0085] The low-grafted glucosylstevioside in this invention is a 1-3 substituted glucosylstevioside.

[0086] Effective yield of low-grafted glucosyl steviol glycosides (%) = [(Percentage of low-grafted glucosyl steviol glycosides in the product × yield) / Total weight of raw materials 200g] × 100%.

[0087] Table 1

[0088]

[0089]

[0090] As can be seen from the test results in Table 1, this invention prepares glucosylstevioside through enzyme catalysis, followed by high-temperature pyrolysis and conversion, and finally purification, thus obtaining high-content, low-grafted glucosylstevioside.

[0091] If a key step is missing in the comparison process or the conditions in the key step are not properly controlled, the resulting product will have a low content of low-grafted glucosyl steviol glycosides and a reduced effective yield.

[0092] In Comparative Example 1, excluding the pyrolysis step, the core function of pyrolysis is to break the over-grafted sugar chains. The unpyrolyzed reaction solution contains a large amount of highly grafted products with large molecular weights and poor solubility. When directly separated by membrane, the high molecular weight products are retained, but the low-grafted products of the target molecule, due to their low proportion, are encapsulated or co-precipitated by high molecular weight impurities, resulting in a significant decrease in the purity and yield of the target product. In Comparative Example 2, no catalyst is added during pyrolysis, which relies on the self-dissociation of water at high temperature. The insufficient hydrogen ion concentration leads to a slow pyrolysis rate, and some highly grafted products remain, reducing the content of low-grafted products in the target product and the effective yield. In Comparative Example 3, the excessive amount of catalyst during pyrolysis leads to over-pyrolysis. The strong acidity of the sulfonic acid groups in the catalyst further breaks the glycosidic bonds of the low-grafted products of the target molecule, generating monoglycosides with excessively small molecular weights. These small molecules are removed in the permeate during membrane separation, resulting in the loss of the target product.

[0093] In Comparative Example 4, the lack of a membrane separation step allows impurities in the lysis buffer to encapsulate certain target molecules, thus affecting the proportion of the target product in the final product. In Comparative Example 5, the membrane's molecular weight cutoff is too low, resulting in some impurities being retained in the target product, thereby reducing the effective yield and proportion of the low-grafted product. In Comparative Example 6, the membrane's molecular weight cutoff is too high, leading to the loss of some target product, thus reducing the effective yield of the low-grafted product.

[0094] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure, characterized in that, Includes the following steps: (1) Using steviol glycosides as acceptors, β-cyclodextrin as donors, and CGT enzyme as catalysts, a reaction solution containing glucosyl steviol glycosides was obtained. (2) The reaction solution containing glucosylstevioside was placed in a high-pressure reactor and a catalyst was added to carry out a high-temperature and high-pressure pyrolysis reaction; (3) After the high temperature and high pressure pyrolysis reaction is completed, the pyrolysis liquid is cooled to room temperature, filtered, and the filtrate is concentrated multiple times using a polymer membrane and the retentate is collected. (4) The retentate collected in step (3) is spray-dried to obtain low-grafted glucosyl steviol glycoside.

2. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 1, characterized in that, In step (1), the steviol glycoside is RA97, the mass ratio of RA97 to β-cyclodextrin is 1:(0.9-1.3), and the amount of CGT enzyme added is 1.8-2.3 wt% of the mass of steviol glycoside.

3. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 1, characterized in that, In step (1), the reaction temperature is 70-72℃, the pH of the reaction system is 5-5.5, the reaction time is 24h, and the solid content of the reaction system is 30-40wt%.

4. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 1, characterized in that, In step (2), the temperature of the high-temperature and high-pressure pyrolysis reaction is 109-112℃, the pressure is 0.09-0.12MPa, and the time is 18-20h; the catalyst is a sulfonic acid-modified Sn-Na bimetallic MOF catalyst, and the amount of catalyst added is 5-10wt% of the solid mass in the reaction solution.

5. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 4, characterized in that, The preparation method of the sulfonic acid-modified Sn-Na bimetallic MOF catalyst includes the following steps: I. Using zirconium tetrachloride and 2-aminoterephthalic acid as raw materials and DMF as solvent, a hydrothermal reaction was carried out to obtain metal-organic framework materials.

2. The above-mentioned metal-organic framework material was modified with chlorosulfonic acid to obtain a sulfonic acid-modified metal-organic framework material.

3. Add stannous chloride pentahydrate and sodium acetate to anhydrous ethanol, then add the above-mentioned sulfonic acid group-modified metal-organic framework material, react at 65-70℃ for 10-12 h, then filter, wash the precipitate, dry it and disperse it in deionized water, add polyethylene glycol, ultrasonically disperse, and finally vacuum dry to obtain the catalyst.

6. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 5, characterized in that, In step one, the molar ratio of zirconium tetrachloride to 2-aminoterephthalic acid is (2-3):(2-3); the hydrothermal reaction temperature is 118-125℃ and the time is 18-24h.

7. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 5, characterized in that, In step two, the specific process of modifying the above metal-organic framework material with chlorosulfonic acid is as follows: the above metal-organic framework material is added to anhydrous dichloromethane, and then chlorosulfonic acid is added under an ice bath at 0°C. The ratio of metal-organic framework material to chlorosulfonic acid is 1g:(0.3-0.8)ml. The reaction is carried out under nitrogen atmosphere and refluxed at 40-45°C for 5-6 hours. After the reaction is completed, the reaction solution is filtered, the precipitate is washed until neutral and then dried to obtain the final product.

8. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 5, characterized in that, In step three, the ratio of stannous chloride pentahydrate, sodium acetate, and sulfonic acid-modified metal-organic framework material is (1-2) g : (0.7-0.8) mmol : (1.2-1.3) mmol; The polyethylene glycol is polyethylene glycol 4000-6000, and the amount of polyethylene glycol added is 10-20 wt% of the precipitate mass after drying; the ultrasonic dispersion power is 300-500W, and the time is 20-30min.

9. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 1, characterized in that, In step (3), the molecular weight cutoff of the polymer membrane is 300-500 Da, and the pressure during concentration is 2-3 MPa; The specific process of multiple concentrations is as follows: First, the pyrolysis liquid is concentrated to a solid content of 40-46 wt%. Then, the retentate is diluted with water to a solid content of 30-35 wt%, and a second concentration is performed to bring the solid content of the retentate to 40-46 wt%.

10. The method for preparing low-grafted glucosyl steviol glycosides under high temperature and high pressure according to claim 1, characterized in that, In step (4), the spray drying conditions are: inlet air temperature of 179-182℃, outlet air temperature of 82-86℃, and air flow rate of 12-16 m³ / h. 3 / h.

Images