A method for crystallizing fructose and crystalline fructose prepared thereby

Abstract

The present invention discloses a crystallization method of fructose and the crystalline fructose prepared thereby, belonging to the technical field of crystallization. The crystallization method of fructose and the crystalline fructose prepared thereby disclosed in the present invention comprise the following steps: taking the isomerized fructose syrup, adding glucose oxidase, catalase and calcium carbonate under stirring and aeration until the pH is stable, and obtaining the feed liquid A by plate and frame filtration; filtering the feed liquid A through a microbial flocculant, and removing impurities through a ceramic membrane, an ultrafiltration membrane and an electrodialysis system at a certain temperature and pressure to obtain the feed liquid B; evaporating and concentrating the feed liquid B, adding a nucleating agent and a sugar molecule chelating agent under stirring, and performing stepwise cooling crystallization to obtain the feed liquid C; centrifuging the feed liquid C and drying it by vacuum microwave to obtain the crystalline fructose. The method of the present invention has high extraction yield and purity, large processing capacity and high degree of continuity, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of crystallization, and more specifically, to a method for crystallizing fructose. Background Art

[0002] Fructose is a high-value-added sweetener with advantages such as good taste, high sweetness, low glycemic index, and low susceptibility to dental caries, and is widely used in industries such as frozen foods, baked goods, functional beverages, and pharmaceuticals.

[0003] Chinese Patent CN101077140A discloses a process for continuously producing crystalline fructose using a vertical crystallizer. First, the syrup is evaporated and concentrated to a dry matter content of 88% - 90%, the pH is adjusted to 3.7 - 4.3, then it is cooled to 58 - 60 °C, and 10% - 15% of seed crystals are added, and gradient cooling is achieved through multi-stage coiled pipes. This method shortens the crystallization cycle, but the particle size of the product cannot be controlled during the continuous production process. Chinese Patent CN101268817A introduces a method for continuously producing crystalline fructose and a special crystallization tank. The crystallization tank is equipped with five sections of heat-insulating water jackets from top to bottom, and the temperatures of each section of heat-insulating water jackets gradually decrease, thereby controlling the cooling rate of different sections and realizing the segmented temperature control operation that can only be achieved in an intermittent process, but its yield is slightly lower.

[0004] Due to the high viscosity of the fructose aqueous solution, the method of cooling is usually used for crystallization. However, these methods either prepare crystalline fructose by adding alcohol solvents or obtain semi-crystalline fructose by methods such as spraying and drying. These products are difficult to meet the requirements of the Food Chemical Codex. Although some literatures introduce the process for producing crystalline fructose in an aqueous solution, the particle size and distribution of the products are often difficult to control during these production processes. The product shape is irregular, the aggregation is serious, the sensory quality is poor, and the competitive advantage is not obvious, which greatly restricts the marketization process of crystalline fructose.

[0005] Therefore, providing a method for crystallizing fructose is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for crystallizing fructose. By using this method, the fructose yield and purity are high, and the fructose quality is good.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for crystallizing fructose, the specific steps are as follows:

[0009] (1) Take the isomerized fructose syrup, add glucose oxidase, catalase, and calcium carbonate under stirring and aeration until the pH is stable, and obtain the feed liquid A by plate and frame filtration.

[0010] The soluble solid content of the isomerized fructose syrup is 40-50% (wt%), and the fructose purity is 40-55%; the stirring speed is 150-300 r / min, and the ventilation volume is 1000-1600 m 3 / h; the enzyme activity of glucose oxidase is 20000 U / mL, and the addition amount is 1.0-2.0‰ (wt%) of the glucose content in the isomerized fructose syrup; the enzyme activity of catalase is 600000 U / mL, and the addition amount is 1.0-2.0‰ (wt%) of the glucose content in the isomerized fructose syrup; the addition amount of calcium carbonate is 20-25% (wt%) of the glucose content in the isomerized fructose syrup; the pH is 5.3-5.8, and the temperature is 35-40 °C; the plate and frame filtration pressure is 0.2-0.8 MPa, and the pore diameter is 10-50 µm.

[0011] (2) After filtering the liquid A with a microbial flocculant, impurities are removed through a ceramic membrane, an ultrafiltration membrane, and an electrodialysis system at a certain temperature and pressure to obtain liquid B.

[0012] The dosage of the microbial flocculant is 0.02‰-0.05‰ (wt%) of the dosage of liquid A.

[0013] The pore diameter of the ceramic membrane is 20-100 nm, the inlet pressure is 0.2-1 MPa, and the temperature is 10-45 °C.

[0014] The pore diameter of the ultrafiltration membrane is 2000-4000 Da, the inlet pressure is 0.2-0.6 MPa, and the temperature is 10-45 °C.

[0015] The voltage of the electrodialysis system is 30-35 V, the flow rate is 10-20 L / h, and the desalting time is 0.5-2 h.

[0016] (3) After evaporating and concentrating the liquid B until the fructose content reaches 85-90%, seed crystals, a nucleating agent, and a sugar molecule chelating agent are added under stirring, and cooling crystallization is carried out in stages to obtain liquid C.

[0017] The temperature for adding the seed crystals is 55-60 °C, the addition amount of the seed crystals is 2-5% (wt%) of fructose, and the mesh number of the seed crystals is 80-100 mesh.

[0018] The nucleating agent is citric acid, sorbitol, mannitol, or gelatin; the addition amount of the nucleating agent is 0.1-0.8% (wt%) of fructose.

[0019] The sugar molecule chelating agent is trisodium citrate, calcium dihydrogen phosphate, glycine, lactic acid, or sucrose fatty acid ester; the addition amount of the sugar molecule chelating agent is 0.02-0.5% (wt%) of fructose.

[0020] The stirring speed is 100-200 rpm.

[0021] The cooling rate for the staged cooling crystallization is 0.2 - 0.3 °C / h from 60 - 50 °C, 0.3 - 0.5 °C / h from 50 - 40 °C, 0.5 - 0.7 °C / h from 40 - 30 °C, 0.7 - 1.0 °C / h from 30 °C to the discharge temperature, and the discharge temperature is 25 - 28 °C.

[0022] (4) Centrifuge the liquid C and vacuum microwave dry it to obtain crystalline fructose.

[0023] Furthermore, the isomerized fructose syrup in step (1) is prepared by enzyme-catalyzed reaction with corn starch milk as the raw material: Take 17.5 °Bé corn starch milk, adjust the pH to 5.6, add 0.02‰ of thermotolerant α-amylase with an enzyme activity of 40000 U / mL, and perform a liquefaction reaction at 110 °C until the DE value (the percentage of reducing sugars in the saccharified liquid calculated as glucose and accounting for the dry matter) is 8 to obtain maltodextrin; adjust the temperature to 58 °C, pH to 4.2, add 1% of glucoamylase with an enzyme activity of 50000 U / mL and stir for 8 h, adjust the temperature to 80 °C, and inactivate the enzyme for 30 min to obtain glucose solution; adjust the temperature to 50 °C, pH to 8.0, add 35 mg of MgSO4·7H2O, 0.5% of glucose isomerase with an enzyme activity of 500 U / mL, and react for 6 h to obtain the isomerized fructose syrup.

[0024] Furthermore, the preparation method of the microbial flocculant in step (2) is as follows: Aspergillus niger mycelium is added with chitosan with a mass 0.8 - 1.5 times that of the Aspergillus niger mycelium, 2 - 4 times the mass of glutaraldehyde or epichlorohydrin at pH 4 - 6 and 25 - 35 °C, and stirred and reacted at 150 - 200 rpm for 2 - 3 h, and then 2 - 4 times the mass of sodium tripolyphosphate is added for curing for 0.5 - 1 h.

[0025] Furthermore, the seed crystal in step (3) is a fructose crystal with a purity > 99.5%.

[0026] Furthermore, the centrifugation speed in step (4) is 3000 - 4000 r / min and the time is 3 - 5 min; for the vacuum microwave drying, the vacuum degree is -40 ~ -90 kPa and the microwave power is 800 - 2000 W.

[0027] Furthermore, the crystalline fructose prepared by the crystallization method of a kind of fructose.

[0028] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method for crystallizing fructose. By adding a microbial flocculant, the adhesion and accumulation of pollutants on the membrane can be inhibited, thereby prolonging the service life of the membrane. By adding a nucleating agent, the crystallization of fructose can be made more regular and the crystallization process can be accelerated. Using a sugar molecule chelating agent can reduce the hygroscopicity of fructose, avoid caking, and improve the quality of fructose. Crystallizing fructose by the method of the present invention has high yield and purity, large processing capacity, and high degree of continuity, and is suitable for large-scale industrial production. Detailed Embodiments

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The isomerized fructose syrup is prepared by enzymatic catalytic reaction using corn starch milk as a raw material: Take 17.5°Bé corn starch milk, adjust the pH to 5.6, add 0.02‰ thermostable α-amylase, and carry out a liquefaction reaction at 110°C until the DE value reaches 8 to obtain maltodextrin; adjust the temperature to 58°C, pH to 4.2, add 1% glucoamylase and stir for 8 hours, adjust the temperature to 80°C, and inactivate the enzyme for 30 minutes to obtain a glucose solution; adjust the temperature to 50°C, pH to 8.0, add 35 mg of MgSO4·7H2O and 0.5% glucose isomerase, and react for 6 hours to obtain the isomerized fructose syrup.

[0031] All the reagents used above are commercially available. Among them, the enzyme activity of the thermostable α-amylase is 40000 U / mL, the enzyme activity of the glucoamylase is 50000 U / mL, the enzyme activity of the glucose isomerase is 500 U / mL, the enzyme activity of the glucose oxidase is 20000 U / mL, and the enzyme activity of the catalase is 600000 U / mL.

[0032] Example 1

[0033] A method for crystallizing fructose, the specific steps are as follows:

[0034] (1) Take the isomerized fructose syrup with a soluble solid content of 40% and a fructose purity of 40%. Under aeration at 150 r / min and 1600 m 3 / h, add 1‰ glucose oxidase, 1.5‰ catalase and 20% calcium carbonate based on the glucose content (measured by high performance liquid chromatography) in the isomerized fructose syrup respectively until the pH is stabilized at 5.3. Filter through a 50 µm plate and frame at 35°C and 0.2 MPa to obtain the feed liquid A.

[0035] (2) After filtering the liquid material A through a microbial flocculant at a concentration of 0.02‰, the cell protein is removed by filtering through a 20-nm ceramic membrane at 10°C and 0.2 MPa. Then, the polysaccharides and pigments are removed by filtering through a 2000-Da ultrafiltration membrane at 10°C and 0.2 MPa, and the salts are removed by electrodialysis at a flow rate of 10 L / h for 2 h at 30 V, obtaining the liquid material B.

[0036] The microbial flocculant is prepared by adding 1-fold mass of chitosan, 3-fold mass of glutaraldehyde to Aspergillus niger mycelia at pH 4 and 25°C, stirring and reacting at 200 rpm for 3 h, and then adding 2.5-fold mass of sodium tripolyphosphate for solidification for 0.5 h.

[0037] (3)After evaporating and concentrating the liquid material B to a content of 85%, 2% of 80-100 mesh seeds (fructose crystals with a purity > 99.5%), 0.1% citric acid and 0.05% trisodium citrate are added under stirring at 55°C and 100 rpm. Crystallization is carried out in stages with a cooling rate of 0.2-0.3°C / h from 55-50°C, 0.3-0.5°C / h from 50-40°C, 0.5-0.7°C / h from 40-30°C, and 0.7-1.0°C / h from 30-25°C, obtaining the liquid material C.

[0038] (4)After centrifuging the liquid material C at 3000 r / min for 5 min, vacuum microwave drying is carried out at -40 kPa and 2000 W to obtain crystalline fructose.

[0039] Among them, the purity of the liquid material B is 96.97%, the yield of the obtained crystalline fructose is 46.7%, and the purity is 99.6%; the crystal size is 17.52% for 20-30 mesh, 81.52% for 30-60 mesh, and 0.96% for 60-80 mesh; the crystallization period is 85 h, and the moisture absorption rate is 13.28%.

[0040] Calculation method of crystallization yield: Yield (%) = (M 结晶 x C 结晶 ) / (M 原料 x C 原料 )x 100%.

[0041] Among them, M 原料 : Total mass of the liquid material B (kg or g); C 原料 : Mass fraction of fructose in the liquid material B; M 结晶 : Total mass of the dried fructose crystals after crystallization (kg or g); C 结晶 : Purity of fructose in the crystallization product.

[0042] The method for measuring the soluble solid content is: measured by an Abbe refractometer.

[0043] The method for measuring the purity is: measured by high performance liquid chromatography.

[0044] Method for measuring moisture absorption rate: Measured by placing the fructose sample in a desiccator using a saturated potassium nitrate solution to maintain a relative humidity of approximately 92.5% for 48 hours.

[0045] Example 2

[0046] A crystallization method for fructose, the specific steps are as follows:

[0047] (1) Take a fructose syrup after isomerization with a soluble solid content of 45% and a fructose purity of 55%. Under aeration at 200 r / min and 1300 m 3 / h, respectively add glucose oxidase at 2‰ of the glucose content (measured by high-performance liquid chromatography) in the isomerized fructose syrup, 2‰ of catalase, and 25% of calcium carbonate until the pH stabilizes at 5.8. Filter through a 20-μm plate and frame at 40°C and 0.5 MPa to obtain feed liquid A.

[0048] (2) After filtering the feed liquid A through a 0.05‰ microbial flocculant, filter out the microbial protein through a 100-nm ceramic membrane at 45°C and 0.5 MPa, then remove polysaccharides and pigments through a 4000-Da ultrafiltration membrane at 45°C and 0.6 MPa, and finally remove salts by electrodialysis at a flow rate of 20 L / h under 35 V for 0.5 h to obtain feed liquid B.

[0049] The microbial flocculant is prepared by adding 0.8 times the mass of chitosan, 2 times the mass of epichlorohydrin to Aspergillus niger mycelium at pH 5.2 and 33°C, stirring and reacting at 150 rpm for 2 h, and then adding 2 times sodium tripolyphosphate to solidify for 1 h.

[0050] (3) After evaporating and concentrating the feed liquid B to a content of 90%, add 5% of 80-100 mesh crystal seeds (fructose crystals with a purity > 99.5%), 0.3% of sorbitol, and 0.02% of calcium dihydrogen phosphate under stirring at 60°C and 200 rpm. Carry out stepwise cooling crystallization at a cooling rate of 60 - 50°C at 0.2 - 0.3°C / h, 50 - 40°C at 0.3 - 0.5°C / h, 40 - 30°C at 0.5 - 0.7°C / h, and 30 - 28°C at 0.7 - 1.0°C / h to obtain feed liquid C.

[0051] (4) After centrifuging the feed liquid C at 4000 r / min for 3 min, vacuum microwave dry it at -40 kPa and 2000 W to obtain crystalline fructose.

[0052] Among them, the purity of the feed liquid B is 97.23%, the yield of the obtained crystalline fructose is 50.2%, and the purity is 99.5%; the crystal size is 14.34% for 20 - 30 mesh, 85.05% for 30 - 60 mesh, and 0.61% for 60 - 80 mesh; the crystallization cycle is 90 h, and the moisture absorption rate is 13.47%.

[0053] Example 3

[0054] A method for crystallizing fructose, the specific steps are as follows:

[0055] (1) Take a fructose syrup after isomerization with a soluble solid content of 50% and a fructose purity of 43%. Under aeration at 250 r / min and 1000 m / h, add glucose oxidase with a glucose content (measured by high performance liquid chromatography) of 1.5‰, catalase of 1.8‰, and calcium carbonate of 23% to the isomerized fructose syrup respectively until the pH is stabilized at 5.8. Filter through a 10-μm plate and frame at 38°C and 0.8 MPa to obtain feed liquid A. 3 / h aeration, add glucose oxidase with a glucose content (measured by high performance liquid chromatography) of 1.5‰, catalase of 1.8‰, and calcium carbonate of 23% to the isomerized fructose syrup respectively until the pH is stabilized at 5.8. Filter through a 10-μm plate and frame at 38°C and 0.8 MPa to obtain feed liquid A.

[0056] (2) After filtering feed liquid A through a microbial flocculant of 0.03‰, filter out the bacterial protein through a 50-nm ceramic membrane at 37°C and 1 MPa, then remove polysaccharides and pigments through a 3000-Da ultrafiltration membrane at 37°C and 0.5 MPa, and finally remove salts by electrodialysis at a flow rate of 15 L / h at 32 V for 1.5 h to obtain feed liquid B.

[0057] The microbial flocculant is prepared by adding 1.5 times the mass of chitosan and 4 times the mass of epichlorohydrin to Aspergillus niger mycelia at pH 6 and 35°C, stirring and reacting at 180 rpm for 2.5 h, and then adding 4 times the mass of sodium tripolyphosphate for curing for 0.3 h.

[0058] (3) After evaporating and concentrating feed liquid B to a content of 87%, add 3% of 80-100 mesh seed crystals (fructose crystals with a purity > 99.5%), 0.8% citric acid, and 0.3% glycine under stirring at 56°C and 150 rpm. Carry out stepwise cooling crystallization at a cooling rate of 0.2-0.3°C / h from 56-50°C, 0.3-0.5°C / h from 50-40°C, 0.5-0.7°C / h from 40-30°C, and 0.7-1.0°C / h from 30-25°C to obtain feed liquid C.

[0059] (4) After centrifuging feed liquid C at 3500 r / min for 4 min, vacuum microwave dry it at -40 kPa and 2000 W to obtain crystalline fructose.

[0060] Among them, the purity of feed liquid B is 97.06%, the yield of the obtained crystalline fructose is 47.36%, and the purity is 99.5%; the crystal size is 16.31% for 20-30 mesh, 81.85% for 30-60 mesh, and 1.84% for 60-80 mesh; the crystallization period is 88 h, and the moisture absorption rate is 14.03%.

[0061] Example 4

[0062] A method for crystallizing fructose, the specific steps are as follows:

[0063] (1) Take the isomerized fructose syrup with 45% soluble solids and 42% fructose purity. Under aeration at 300 r / min and 1600 m / h, add glucose oxidase with a glucose content of 1.8‰ (measured by high performance liquid chromatography), catalase with a content of 2.0‰, and 25% calcium carbonate to the isomerized fructose syrup respectively until the pH stabilizes at 5.6. Filter through a 30 µm plate and frame filter at 35 °C and 0.5 MPa to obtain feed liquid A. 3 / h aeration, add glucose oxidase with a glucose content of 1.8‰ (measured by high performance liquid chromatography), catalase with a content of 2.0‰, and 25% calcium carbonate to the isomerized fructose syrup respectively until the pH stabilizes at 5.6. Filter through a 30 µm plate and frame filter at 35 °C and 0.5 MPa to obtain feed liquid A.

[0064] (2) After filtering feed liquid A through 0.03‰ microbial flocculant, remove the bacterial protein by filtering through a 20 nm ceramic membrane at 10 °C and 0.2 MPa, then remove polysaccharides and pigments by filtering through a 2000 Da ultrafiltration membrane at 10 °C and 0.2 MPa, and finally remove salts by electrodialysis at a flow rate of 16 L / h for 1.2 h at 33 V to obtain feed liquid B.

[0065] The microbial flocculant is prepared by adding 1-fold mass of chitosan, 2.5-fold mass of epichlorohydrin to Aspergillus niger mycelium at pH 5.5 and 35 °C, stirring and reacting at 200 rpm for 2 h, and then adding 3-fold mass of sodium tripolyphosphate for curing for 0.5 h.

[0066] (3) After evaporating and concentrating feed liquid B to a content of 89%, add 4% of 80 - 100 mesh seed crystals (fructose crystals with a purity > 99.5%), 0.2% gelatin, and 0.5% lactic acid under stirring at 58 °C and 200 rpm. Carry out stepwise cooling crystallization at a cooling rate of 58 - 50 °C at 0.2 - 0.3 °C / h, 50 - 40 °C at 0.3 - 0.5 °C / h, 40 - 30 °C at 0.5 - 0.7 °C / h, and 30 - 25 °C at 0.7 - 1.0 °C / h to obtain feed liquid C.

[0067] (4) After centrifuging feed liquid C at 3300 r / min for 4 min, vacuum microwave dry it at - 40 kPa and 2000 W to obtain crystalline fructose.

[0068] Among them, the purity of feed liquid B is 96.91%, the yield of the obtained crystalline fructose is 48.23%, and the purity is 99.5%; the crystal size is 10.79% for 20 - 30 mesh, 88.78% for 30 - 60 mesh, and 0.43% for 60 - 80 mesh; the crystallization cycle is 89 h, and the moisture absorption rate is 13.12%.

[0069] Example 5

[0070] A method for crystallizing fructose, the specific steps are as follows:

[0071] (1) Take the isomerized fructose syrup with 48% soluble solids content and 45% fructose purity. Under aeration at 200 r / min and 1600 m / h 3Under / h ventilation, add glucose oxidase at 1.5‰ of the glucose content (measured by high performance liquid chromatography) in the isomerized fructose syrup, catalase at 1.5‰, and 25% calcium carbonate respectively until the pH stabilizes at 5.4. Filter through a 50 µm plate and frame at 38°C and 0.3 MPa to obtain feed liquid A.

[0072] (2) After filtering feed liquid A through 0.05% microbial flocculant, filter out the microbial protein through a 100 nm ceramic membrane at 25°C and 0.5 MPa, then remove polysaccharides and pigments through a 2500 Da ultrafiltration membrane at 25°C and 0.5 MPa, and finally remove salts by electrodialysis at a flow rate of 20 L / h for 1 h at 35 V to obtain feed liquid B.

[0073] The microbial flocculant is prepared by adding chitosan with a mass of 1 time, epichlorohydrin with a mass of 2.5 times to Aspergillus niger mycelium at pH 4 and 35°C, stirring and reacting at 160 rpm for 2.5 h, and then adding trisodium polyphosphate with a mass of 3 times for curing for 0.5 h.

[0074] (3) After evaporating and concentrating feed liquid B to a content of 89%, add 4% of 80 - 100 mesh seeds (fructose crystals with a purity > 99.5%), 0.5% mannitol and 0.1% sucrose fatty acid ester under stirring at 57.5°C and 100 rpm. Carry out cooling crystallization in stages at a cooling rate of 0.2 - 0.3°C / h from 57.5 - 50°C, 0.3 - 0.5°C / h from 50 - 40°C, 0.5 - 0.7°C / h from 40 - 30°C, and 0.7 - 1.0°C / h from 30 - 25°C to obtain feed liquid C.

[0075] (4) After centrifuging feed liquid C at 4000 r / min for 3 min, vacuum microwave dry it at -40 kPa and 2000 W to obtain crystalline fructose.

[0076] Among them, the purity of feed liquid B is 97.24%, the yield of fructose crystallization is 48.98%, and the purity is 99.6%; the crystal size is 12.79% for 20 - 30 mesh, 86.28% for 30 - 60 mesh, and 0.93% for 60 - 80 mesh; the crystallization period is 90 h, and the moisture absorption rate is 13.74%.

[0077] Comparative Example 1

[0078] A crystallization method for fructose, the specific steps are as follows:

[0079] (1) Take fructose syrup with a soluble solid content of 40% and a fructose purity of 40% after isomerization, 150 r / min 1600 m 3Under / h ventilation, 1‰ of glucose oxidase, 1.5‰ of catalase and 20% of calcium carbonate were respectively added to the glucose content (measured by high performance liquid chromatography) in the isomerized fructose syrup until the pH was stabilized at 5.3. The resulting liquid A was obtained by plate and frame filtration through a 50 µm filter at 35°C and 0.2 MPa.

[0080] (2)The liquid A was filtered through a 20 nm ceramic membrane at 10°C and 0.2 MPa to remove the microbial protein, and then through a 2000 Da ultrafiltration membrane at 10°C and 0.2 MPa to remove polysaccharides and pigments. Finally, salts were removed by electrodialysis at a flow rate of 10 L / h at 30 V for 2 h to obtain liquid B.

[0081] (3)After the liquid B was evaporated and concentrated to a content of 85%, 2% of 80 - 100 mesh seeds (fructose crystals with a purity > 99.5%), 0.1% of citric acid and 0.05% of trisodium citrate were added under stirring at 55°C and 100 rpm. Crystallization was carried out in stages with a cooling rate of 0.2 - 0.3°C / h from 55 - 50°C, 0.3 - 0.5°C / h from 50 - 40°C, 0.5 - 0.7°C / h from 40 - 30°C, and 0.7 - 1.0°C / h from 30 - 25°C to obtain liquid C.

[0082] (4)After the liquid C was centrifuged at 3000 r / min for 5 min, vacuum microwave drying was carried out at -40 kPa and 2000 W to obtain crystalline fructose.

[0083] Among them, the purity of liquid B was 94.37%, the yield of the obtained crystalline fructose was 45.13%, and the purity was 98.93%; the crystal size was 15.8% for 20 - 30 mesh, 78.31% for 30 - 60 mesh, and 5.89% for 60 - 80 mesh; the crystallization period was 85 h, and the moisture absorption rate was 14.49%.

[0084] From the results, it can be seen that the purity of fructose in liquid B was significantly lower than that with the addition of the microbial flocculant, indicating that the addition of the microbial flocculant can inhibit the adhesion and accumulation of pollutants on the membrane, thereby prolonging the service life of the membrane.

[0085] Comparative Example 2

[0086] A method for crystallizing fructose, the specific steps are as follows:

[0087] (1)Take the isomerized fructose syrup with a soluble solid content of 45% and a fructose purity of 55%, and ventilate at 200 r / min and 1300 m 3 Under / h ventilation, 2‰ of glucose oxidase, 2‰ of catalase and 25% of calcium carbonate were respectively added to the glucose content (measured by high performance liquid chromatography) in the isomerized fructose syrup until the pH was stabilized at 5.8. The resulting liquid A was obtained by plate and frame filtration through a 20 µm filter at 40°C and 0.5 MPa.

[0088] (2) The feed liquid A is filtered through 0.05‰ microbial flocculant, and then the cell protein is removed by filtration through a 100 nm ceramic membrane at 45°C and 0.5 MPa. Then, polysaccharides and pigments are removed by passing through a 4000 Da ultrafiltration membrane at 45°C and 0.6 MPa. Finally, salts are removed by electrodialysis at a flow rate of 20 L / h and 35 V for 0.5 h to obtain the feed liquid B.

[0089] The microbial flocculant is prepared by adding 0.8 times the mass of chitosan and 2 times the mass of epichlorohydrin to Aspergillus niger mycelia at pH 5.2 and 33°C, stirring and reacting at 150 rpm for 2 h, and then adding 2 times sodium tripolyphosphate for curing for 1 h.

[0090] (3)After the feed liquid B is evaporated and concentrated to a content of 90%, 5% of 80 - 100 mesh seed crystals (fructose crystals with a purity > 99.5%) and 0.02% calcium dihydrogen phosphate are added under stirring at 60°C and 200 rpm. Crystallization is carried out in stages with a cooling rate of 0.2 - 0.3°C / h from 60 - 50°C, 0.3 - 0.5°C / h from 50 - 40°C, 0.5 - 0.7°C / h from 40 - 30°C, and 0.7 - 1.0°C / h from 30 - 28°C to obtain the feed liquid C.

[0091] (4)After the feed liquid C is centrifuged at 4000 r / min for 3 min, vacuum microwave drying is carried out at -40 kPa and 2000 W to obtain crystalline fructose.

[0092] Among them, the purity of the feed liquid B is 97.19%, the yield of the obtained crystalline fructose is 48.98%, and the purity is 99.2%; the crystal size is 15.87% for 20 - 30 mesh, 76.52% for 30 - 60 mesh, and 7.61% for 60 - 80 mesh; the crystallization period is 90 h, and the moisture absorption rate is 14.85%.

[0093] It can be seen from the results that without adding a nucleating agent, the proportion of 30 - 60 mesh crystalline fructose is slightly lower, the uniformity is slightly worse, and the crystallization period is relatively slightly longer. It shows that adding a nucleating agent can make the fructose crystallization more regular and accelerate the crystallization process.

[0094] Comparative Example 3

[0095] A method for crystallizing fructose, the specific steps are as follows:

[0096] (1)Take a fructose syrup with a soluble solid content of 50% and a fructose purity of 43% after isomerization. Under aeration at 250 r / min and 1000 m 3 / h, glucose oxidase with a content of 1.5‰ of the glucose content (measured by high performance liquid chromatography) in the isomerized fructose syrup, catalase with a content of 1.8‰, and 23% calcium carbonate are respectively added until the pH is stabilized at 5.8. The feed liquid A is obtained by plate and frame filtration through a 10 µm filter at 38°C and 0.8 MPa.

[0097] (2) Filter the feed liquid A through 0.03‰ microbial flocculant, then remove the cell protein by filtering through a 50 nm ceramic membrane at 37°C and 1 MPa, then remove polysaccharides and pigments by passing through a 3000 Da ultrafiltration membrane at 37°C and 0.5 MPa, and finally remove salts by electrodialysis at a flow rate of 15 L / h under 32 V for 1.5 h to obtain feed liquid B.

[0098] The microbial flocculant is prepared by adding 1.5 times the mass of chitosan and 4 times the mass of epichlorohydrin to Aspergillus niger mycelia at pH 6 and 35°C, stirring and reacting at 180 rpm for 2.5 h, and then adding 4 times sodium tripolyphosphate for curing for 0.3 h.

[0099] (3) After evaporating and concentrating the feed liquid B to a content of 87%, add 3% of 80 - 100 mesh seeds (fructose crystals with a purity > 99.5%), 0.8% citric acid under stirring at 56°C and 150 rpm, and carry out stepwise cooling crystallization at a cooling rate of 0.2 - 0.3°C / h from 56 - 50°C, 0.3 - 0.5°C / h from 50 - 40°C, 0.5 - 0.7°C / h from 40 - 30°C, and 0.7 - 1.0°C / h from 30 - 25°C to obtain feed liquid C.

[0100] (4) Centrifuge the feed liquid C at 3500 r / min for 4 min, and then vacuum microwave dry it at -40 kPa and 2000 W to obtain crystalline fructose.

[0101] Among them, the purity of feed liquid B is 97.14%, the yield of fructose crystallization is 47.36%, and the purity is 99.5%; the crystal size is 14.61% for 20 - 30 mesh, 81.93% for 30 - 60 mesh, and 3.46% for 60 - 80 mesh; the crystallization period is 88 h, and the moisture absorption rate is 21.06%.

[0102] It can be seen from the results that without adding a sugar molecule chelating agent, the hygroscopicity of crystalline fructose increases significantly, indicating that using a sugar molecule chelating agent can reduce the hygroscopicity of fructose, reduce the caking phenomenon during later storage, and improve the quality of fructose.

[0103] Comparative Example 4

[0104] A method for crystallizing fructose, the specific steps are as follows:

[0105] (1) Take a fructose syrup with a soluble solid content of 45% and a fructose purity of 42% after isomerization, and stir at 300 r / min and 1600 m 3Under / h ventilation, glucose oxidase with a glucose content of 1.8‰ (measured by high performance liquid chromatography), catalase with a content of 2.0‰, and 25% calcium carbonate were respectively added to the isomerized fructose syrup until the pH was stabilized at 5.6. The feed liquid A was obtained by plate and frame filtration through a 30 µm filter at 35 °C and 0.5 MPa.

[0106] (2) The feed liquid A was filtered through a 20 nm ceramic membrane at 10 °C and 0.2 MPa to remove the microbial protein, then passed through a 2000 Da ultrafiltration membrane at 10 °C and 0.2 MPa to remove polysaccharides and pigments, and finally desalted by electrodialysis at a flow rate of 16 L / h under 33 V for 1.2 h to obtain the feed liquid B.

[0107] (3) After the feed liquid B was evaporated and concentrated to a content of 89%, 4% of 80 - 100 mesh seeds (fructose crystals with a purity > 99.5%) were added under stirring at 58 °C and 200 rpm. Crystallization was carried out in stages with a cooling rate of 0.2 - 0.3 °C / h from 58 - 50 °C, 0.3 - 0.5 °C / h from 50 - 40 °C, 0.5 - 0.7 °C / h from 40 - 30 °C, and 0.7 - 1.0 °C / h from 30 - 25 °C to obtain the feed liquid C.

[0108] (4) After the feed liquid C was centrifuged at 3300 r / min for 4 min, it was vacuum microwave dried at -40 kPa and 2000 W to obtain crystalline fructose.

[0109] Among them, the purity of the feed liquid B was 97.20%, the yield of the obtained fructose crystals was 44.04%, and the purity was 98.41%; the crystal size was 8.54% for 20 - 30 mesh, 70.12% for 30 - 60 mesh, and 21.34% for 60 - 80 mesh; the crystallization cycle was 89 h, and the moisture absorption rate was 28.23%.

[0110] It can be seen from the results that without crystallizing according to the process of the present invention, the crystallization yield and purity are slightly lower, the crystals are smaller and have a wide distribution range, and the hygroscopicity is strong.

[0111] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for crystallizing fructose, characterized in that, The specific steps are as follows: (1) Take the isomerized fructose syrup. Under stirring and aeration, add glucose oxidase, catalase and calcium carbonate until the pH is stable, and then perform plate and frame filtration to obtain the feed liquid A; The soluble solid content of the isomerized fructose syrup is 40 - 50% wt%, and the fructose purity is 40 - 55%; the stirring speed is 150 - 300 r / min, and the ventilation volume is 1000 - 1600 m 3 / h; the enzyme activity of glucose oxidase is 20000 U / mL, and the addition amount is 1.0 - 2.0‰ wt% of the glucose content in the isomerized fructose syrup; the enzyme activity of catalase is 600000 U / mL, and the addition amount is 1.0 - 2.0‰ wt% of the glucose content in the isomerized fructose syrup; the addition amount of calcium carbonate is 20 - 25% wt% of the glucose content in the isomerized fructose syrup; the pH is 5.3 - 5.8, and the temperature is 35 - 40°C; the plate and frame filtration pressure is 0.2 - 0.8 MPa, and the pore size is 10 - 50 µm; (2) After filtering the feed liquid A through a microbial flocculant, remove impurities through a ceramic membrane, an ultrafiltration membrane and an electrodialysis system at a certain temperature and pressure to obtain the feed liquid B; The preparation method of the microbial flocculant is as follows: Aspergillus niger mycelium is added with chitosan with a mass 0.8 - 1.5 times that of the Aspergillus niger mycelium, 2 - 4 times the mass of glutaraldehyde or epichlorohydrin at pH 4 - 6 and 25 - 35 °C, and stirred and reacted at 150 - 200 rpm for 2 - 3 h, and then 2 - 4 times sodium tripolyphosphate is added for curing for 0.5 - 1 h; The dosage of the microbial flocculant is 0.02‰ - 0.05‰ wt% of the dosage of the feed liquid A; The pore size of the ceramic membrane is 20 - 100 nm, the inlet pressure is 0.2 - 1 MPa, and the temperature is 10 - 45 °C; The pore size of the ultrafiltration membrane is 2000 - 4000 Da, the inlet pressure is 0.2 - 0.6 MPa, and the temperature is 10 - 45 °C; The voltage of the electrodialysis system is 30 - 35 V, the flow rate is 10 - 20 L / h, and the time is 0.5 - 2 h; (3) After evaporating and concentrating the feed liquid B until the fructose content is 85 - 90%, add crystal seeds, a nucleating agent and a sugar molecule chelating agent under stirring, and perform step - by - step cooling crystallization to obtain the feed liquid C; The temperature for adding the crystal seeds is 55 - 60 °C, the addition amount of the crystal seeds is 2 - 5% wt% of fructose, and the mesh number of the crystal seeds is 80 - 100 mesh; The nucleating agent is citric acid, sorbitol, mannitol or gelatin; the addition amount of the nucleating agent is 0.1 - 0.8% wt% of fructose; The sugar molecule chelating agent is trisodium citrate, calcium dihydrogen phosphate, glycine, lactic acid or sucrose fatty acid ester; the addition amount of the sugar molecule chelating agent is 0.02 - 0.5% wt% of fructose; The stirring speed is 100 - 200 rpm; The cooling rate for the step - by - step cooling crystallization is 0.2 - 0.3 °C / h from 60 - 50 °C, 0.3 - 0.5 °C / h from 50 - 40 °C, 0.5 - 0.7 °C / h from 40 - 30 °C, 0.7 - 1.0 °C / h from 30 °C to the discharge temperature, and the discharge temperature is 25 °C - 28 °C; (4) Centrifuge the feed liquid C and perform vacuum microwave drying to obtain crystalline fructose.

2. The crystallization method of fructose according to claim 1, characterized in that, The isomerized fructose syrup in step (1) is prepared by enzymatic catalytic reaction with corn starch milk as the raw material: Take 17.5 °Bé corn starch milk, adjust the pH to 5.6, add 0.02‰ of high - temperature resistant α - amylase with an enzyme activity of 40000 U / mL, and perform liquefaction reaction at 110 °C until the DE value reaches 8 to obtain maltodextrin; adjust the temperature to 58 °C and the pH to 4.2, add 1% of saccharifying enzyme with an enzyme activity of 50000 U / mL and stir for 8 h, adjust the temperature to 80 °C and inactivate the enzyme for 30 min to obtain glucose solution; adjust the temperature to 50 °C and the pH to 8.0, add 35 mg of MgSO4·7H2O, 0.5% of glucose isomerase with an enzyme activity of 500 U / mL, and react for 6 h to obtain the isomerized fructose syrup.

3. A crystallization method of fructose according to claim 1, characterized in that, The seed crystal described in step (3) is a fructose crystal with a purity > 99.5%.

4. A crystallization method of fructose according to claim 1, characterized in that, In step (4), the centrifugation speed is 3000 - 4000 r / min and the time is 3 - 5 min; for the vacuum microwave drying, the vacuum degree is -40 ~ -90 kPa and the microwave power is 800 - 2000 W.

5. Crystalline fructose prepared by a method for crystallizing fructose according to any one of claims 1 - 4.