Preparation method of vitamin C with low solvent residue

Abstract

The invention relates to the technical field of industrial preparation of vitamin C, and discloses a preparation method of vitamin C with low solvent residue. The preparation method comprises the following steps: (1) hydrolyzing corn starch with hydrochloric acid; (2) aspergillus niger fermentation; (3) acidizing citric acid; (4) cation exchange resin purification; (5) vacuum concentration and gradient crystallization; (6) performing segmented vacuum drying; (7) grading particles; (8) carrying out microfiltration-ultrafiltration membrane separation; (9) ultraviolet sterilization; and (10) nitrogen-filled packaging. By optimizing hydrolysis conditions (hydrochloric acid concentration is 0.8-1.0%, 50 + / -2 DEG C), fermentation control (AS3.758 bacterial strain, 30 + / -0.5 DEG C), resin purification (sulfonic acid type resin, 6.5-7.2% ammonium sulfate elution) and a segmented drying process, the product solvent residue is lower than 2ppm, the purity is greater than or equal to 99.9%, and the stability is remarkably improved. The method is environment-friendly in process, high in yield and suitable for production of medicine and food-grade vitamin C.

Description

Technical Field

[0001] The invention relates to the technical field of industrial preparation of vitamin C, and in particular to a method for preparing vitamin C with low solvent residue. Background Art

[0002] Vitamin C (ascorbic acid) is an important water-soluble vitamin widely used in medicine, food, cosmetics, and other fields. Traditional methods for preparing vitamin C primarily include chemical synthesis and fermentation, with fermentation becoming the mainstream process due to its environmental friendliness and low cost. However, vitamin C products produced using existing fermentation methods often suffer from issues such as high solvent residues, insufficient purity, and poor stability, hindering their application in high-end applications.

[0003] Currently, conventional processes often use organic solvents (such as methanol and ethanol) for extraction and crystallization during post-fermentation purification, making it difficult to control residual solvents in the final product. Furthermore, some processes lack effective protective measures during sterilization and packaging, making vitamin C susceptible to oxidative degradation and reducing product quality. Therefore, developing a method for preparing vitamin C with low solvent residues, high purity, and excellent stability is of great industrial value. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a preparation method of low-solvent residual vitamin C, which solves the shortcomings of some processes that lack effective protection measures in the sterilization and packaging links, making vitamin C easily oxidized and degraded, thereby reducing product quality.

[0005] In order to achieve the above object, the present invention discloses a method for preparing low-solvent residual vitamin C, comprising the following steps: Step (1) corn starch and a hydrochloric acid solution with a mass concentration of 0.5-1.2% are mixed in a mass ratio of 1:5-8, and hydrolysis reaction is carried out at 45-55° C. for 1.5-2.5 hours. After the reaction is completed, anhydrous ethanol is added to terminate the reaction, and the hydrolyzate is obtained by centrifugation; Step (2) adding the hydrolyzate and Aspergillus niger to a fermentation tank at a volume ratio of 1:0.03-0.05, controlling the temperature at 28-32°C, introducing sterile air to maintain a dissolved oxygen content of 20-30%, and adjusting the pH to 6.8-7.2 after fermentation for 48-72 hours; Step (3) adding citric acid to the fermentation broth to adjust the pH to 2.0-2.5, heating to 70-80°C and keeping warm for 0.5-1h, and centrifuging to remove mycelium to obtain a crude vitamin C solution; Step (4) passing the crude product solution through a cation exchange resin column, washing with deionized water, 0.1 mol / L NaOH solution, and 0.05 mol / L HCl solution in sequence, and then gradient eluting with 5-8% ammonium sulfate solution; Step (5) collecting the eluate and concentrating it under reduced pressure at 40-45°C to a solid content of 50-60%, adding seed crystals and cooling it to 4-6°C at a rate of 0.5-1°C / min, crystallizing for 8-12 hours, and then centrifuging to separate the crystals; Step (6) placing the crystals in a vacuum drying oven, controlling the vacuum degree to -0.08~-0.1MPa, heating to 50°C in stages and drying for 3-4h, then cooling to 35°C and drying for 6-8h; The dried product in step (7) is classified through a 200-300 mesh vibrating sieve to collect particles with a particle size of 80-150 μm; Step (8) dispersing the particles in ultrapure water to form a 10-15% suspension, and sequentially passing through a 0.45 μm microfiltration membrane and a 1000 Da ultrafiltration membrane; Step (9) the filtrate is sterilized by ultraviolet irradiation with an irradiation intensity of 30-50 mW / cm² and an irradiation time of 15-30 s; Step (10) The sterilized solution is packaged into aluminum foil composite film packaging bags in a sterile environment, and the bags are sealed with nitrogen and stored away from light.

[0006] Preferably, in step (1), the concentration of the hydrochloric acid solution is 0.8-1.0%, the mass ratio of corn starch to the hydrochloric acid solution is 1:6-7, the hydrolysis temperature is 50±2°C, and the reaction time is 2-2.2h.

[0007] Preferably, the Aspergillus niger species in step (2) is strain AS3.758, the fermentation temperature is controlled at 30±0.5°C, the dissolved oxygen content is 25-28%, and the fermentation period is 60-65h.

[0008] Preferably, the cation exchange resin in step (4) is a sulfonic acid resin, the resin column has a height-to-diameter ratio of 6:1-8:1, an elution flow rate of 1.5-2.0 BV / h, and the concentration of the ammonium sulfate solution is 6.5-7.2%.

[0009] Preferably, in step (5), the amount of seed crystals added is 0.03-0.05% of the mass of the concentrated solution, the cooling rate is 0.8-1.0°C / min, and the crystallization endpoint temperature is 5±0.5°C.

[0010] Preferably, the vacuum drying in step (6) is divided into three stages: the first stage is preheating at 20-30°C for 0.5h, the second stage is drying at 45-50°C for 2.5-3h, and the third stage is constant temperature drying at 35°C for 7-7.5h.

[0011] Preferably, in step (8), the operating pressure of the microfiltration membrane is 0.15-0.2 MPa, the transmembrane pressure difference of the ultrafiltration membrane is 0.25-0.3 MPa, and the feed liquid temperature is maintained at 10-15°C.

[0012] Preferably, in step (9), the ultraviolet wavelength is 254 nm, the irradiation intensity is 40±5 mW / cm², and the suspension transmission speed is 15-20 cm / s.

[0013] Preferably, the purity of the nitrogen filled in step (10) is ≥99.999%, the oxygen permeability of the packaging bag is ≤0.5 cm³ / (m²·24h·0.1MPa), and the humidity of the packaging environment is ≤15%RH.

[0014] Preferably, the amount of citric acid added in step (3) is 1.2-1.5% of the volume of the fermentation broth, the pH value at the acidification endpoint is 2.2-2.3, and the centrifuge speed is 8000-10000 r / min.

[0015] Beneficial effects: After the hydrolysis reaction is completed, anhydrous ethanol is added to terminate the reaction. In the subsequent separation, purification and drying processes, reduced pressure concentration, vacuum drying and other technologies are used to remove the solvent to the maximum extent, thereby preparing vitamin C with low solvent residue, which meets the strict requirements of high-end fields such as medicine and food for product quality and safety.

[0016] During the production process, cation exchange resin columns are used for separation and purification. By selecting the appropriate resin type, column height-to-diameter ratio, and elution conditions, impurities can be effectively removed. Microfiltration and ultrafiltration membranes are combined to further remove microparticles and macromolecular impurities. Ultraviolet sterilization ensures the microbiological safety of the product. These measures work together to significantly improve the purity and quality of the vitamin C product, enhancing its market competitiveness.

[0017] The hydrolysis reaction, fermentation process, and subsequent process parameters are precisely controlled, such as determining the appropriate hydrochloric acid concentration, starch-to-hydrochloric acid solution ratio, hydrolysis temperature, and time in the hydrolysis step, selecting a specific Aspergillus niger species in the fermentation step, and controlling the fermentation temperature, dissolved oxygen content, and cycle, etc., so that the reaction can be carried out more fully and efficiently, improving the utilization rate of raw materials, shortening the production cycle, thereby improving overall production efficiency, and reducing production costs. This preparation method reduces the amount of solvent used and the amount of residue by optimizing the process, and reduces the energy consumption and cost of subsequent solvent recovery processing; at the same time, a staged heating and drying method is adopted in the drying process, which rationally utilizes energy and avoids energy waste, conforms to the development trend of energy conservation and environmental protection, and has good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a process flow chart for the preparation of low-solvent residual vitamin C. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] Example 1: Step (1): 100 kg of corn starch was mixed with 600 kg of 0.8% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 50°C for a constant temperature hydrolysis reaction for 2 h. After the reaction was completed, 200 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 8000 r / min for 15 min. The supernatant was collected as the hydrolyzate.

[0021] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.04. The temperature was controlled at 30±0.5°C. Sterile air was introduced to maintain the dissolved oxygen content at 25%. After fermentation for 62 h, the pH was adjusted to 7.0 using 10% sodium hydroxide solution.

[0022] Step (3): 1.3% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.2, the temperature was raised to 75°C and kept warm for 45 minutes, and the mycelium was removed by centrifugation at 9000 rpm for 20 minutes to obtain a crude vitamin C solution.

[0023] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 7:1) at a flow rate of 1.8 BV / h, and rinsed with 3 BV of deionized water, 2 BV of 0.1 mol / L NaOH solution, and 2 BV of 0.05 mol / L HCl solution in sequence. Finally, a 6.8% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 15-20 mS / cm was collected.

[0024] Step (5): The eluate was concentrated under reduced pressure at 42°C to a solid content of 55%, 0.04% by mass of seed crystals was added, and the temperature was lowered to 5±0.5°C at a rate of 0.8°C / min. After crystallization for 10 hours, the crystals were separated by centrifugation.

[0025] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.09 MPa, and dry them in three stages: preheat at 25°C for 0.5 h in the first stage, dry at 48°C for 2.8 h in the second stage, and dry at a constant temperature of 35°C for 7.2 h in the third stage.

[0026] Step (7): The dried product was classified through a 250-mesh vibrating sieve to collect particles with a particle size of 90-140 μm.

[0027] Step (8): The particles were dispersed in ultrapure water to form a 12% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.18 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.28 MPa. The feed liquid temperature was controlled at 12 °C.

[0028] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 18 cm / s, with an irradiation intensity of 42 mW / cm² and an irradiation time of 20 s.

[0029] Step (10): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.4 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 12% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0030] Example 2: Step (1): 100 kg of corn starch was mixed with 700 kg of 0.9% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 52°C for a constant temperature hydrolysis reaction for 2.1 hours. After the reaction was completed, 220 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 8500 r / min for 18 minutes. The supernatant was collected as the hydrolyzate.

[0031] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.035. The temperature was controlled at 30±0.3°C. Sterile air was introduced to maintain the dissolved oxygen content at 26%. After fermentation for 63 h, the pH was adjusted to 7.1 using 10% sodium hydroxide solution.

[0032] Step (3): 1.4% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.25, the temperature was raised to 78°C and kept warm for 50 min, and the mycelium was removed by centrifugation at 9500 r / min for 18 min to obtain a crude vitamin C solution.

[0033] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 7.5:1) at a flow rate of 1.7 BV / h, and washed with 3.2 BV of deionized water, 2.1 BV of 0.1 mol / L NaOH solution, and 2.1 BV of 0.05 mol / L HCl solution in sequence. Finally, a 7.0% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 16-21 mS / cm was collected.

[0034] Step (5): The eluate was concentrated under reduced pressure at 43°C to a solid content of 58%, 0.045% by mass of seed crystals was added, and the temperature was lowered to 5±0.3°C at a rate of 0.9°C / min. After crystallization for 11 hours, the crystals were separated by centrifugation.

[0035] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.085 MPa, and dry them in three stages: preheat at 28°C for 0.5 h in the first stage, dry at 49°C for 2.7 h in the second stage, and dry at a constant temperature of 35°C for 7.3 h in the third stage.

[0036] Step (7): The dried product was classified through a 280-mesh vibrating sieve to collect particles with a particle size of 85-145 μm.

[0037] Step (8): The particles were dispersed in ultrapure water to form a 13% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.17 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.29 MPa. The feed liquid temperature was controlled at 13 °C.

[0038] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 17 cm / s, with an irradiation intensity of 45 mW / cm² and an irradiation time of 18 s.

[0039] Step (10): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.35 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 10% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0040] Example 3: Step (1): 100 kg of corn starch was mixed with 650 kg of 0.85% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 51°C for a constant temperature hydrolysis reaction for 2.05 h. After the reaction was completed, 210 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 8200 r / min for 16 min. The supernatant was collected as the hydrolyzate.

[0041] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.042. The temperature was controlled at 30±0.4°C, sterile air was introduced to maintain the dissolved oxygen content at 25.5%, and after fermentation for 62.5 h, the pH was adjusted to 7.05 using 10% sodium hydroxide solution.

[0042] Step (3): 1.35% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.22, the temperature was raised to 76°C and kept warm for 48 minutes, and the mycelium was removed by centrifugation at 9200 r / min for 19 minutes to obtain a crude vitamin C solution.

[0043] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 7.2:1) at a flow rate of 1.75 BV / h, and rinsed with 3.1 BV of deionized water, 2.05 BV of 0.1 mol / L NaOH solution, and 2.05 BV of 0.05 mol / L HCl solution in sequence. Finally, a 6.9% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 15.5-20.5 mS / cm was collected.

[0044] Step (5): The eluate was concentrated under reduced pressure at 42.5°C to a solid content of 56%, 0.042% by mass of seed crystals was added, and the temperature was lowered to 5±0.4°C at a rate of 0.85°C / min. After crystallization for 10.5 hours, the crystals were separated by centrifugation.

[0045] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.088 MPa, and dry them in three stages: preheat at 26°C for 0.5 h in the first stage, dry at 48.5°C for 2.75 h in the second stage, and dry at a constant temperature of 35°C for 7.25 h in the third stage.

[0046] Step (7): The dried product was classified through a 260-mesh vibrating sieve to collect particles with a particle size of 88-142 μm.

[0047] Step (8): The particles were dispersed in ultrapure water to form a 12.5% ​​suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.175 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.285 MPa. The feed liquid temperature was controlled at 12.5 °C.

[0048] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 17.5 cm / s, with an irradiation intensity of 43 mW / cm² and an irradiation time of 19 s.

[0049] Step (10): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.38 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 11% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0050] Example 4: Step (1): 100 kg of corn starch was mixed with 680 kg of 0.95% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 53°C for a constant temperature hydrolysis reaction for 2.15 hours. After the reaction was completed, 230 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 8800 r / min for 17 minutes. The supernatant was collected as the hydrolyzate.

[0051] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.038. The temperature was controlled at 31±0.4°C. Sterile air was introduced to maintain the dissolved oxygen content at 27%. After fermentation for 64 h, the pH was adjusted to 7.15 using 10% sodium hydroxide solution.

[0052] Step (3): 1.45% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.28, the temperature was raised to 77°C and kept warm for 55 minutes, and the mycelium was removed by centrifugation at 9800 rpm for 17 minutes to obtain a crude vitamin C solution.

[0053] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 7.8:1) at a flow rate of 1.85 BV / h, and rinsed with 3.3 BV of deionized water, 2.15 BV of 0.1 mol / L NaOH solution, and 2.15 BV of 0.05 mol / L HCl solution, respectively. Finally, a 7.1% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 17-22 mS / cm was collected.

[0054] Step (5): The eluate was concentrated under reduced pressure at 44°C to a solid content of 59%, 0.048% by mass of seed crystals was added, and the temperature was lowered to 5±0.2°C at a rate of 0.95°C / min. After crystallization for 11.5 hours, the crystals were separated by centrifugation.

[0055] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.092 MPa, and dry them in three stages: preheat at 29°C for 0.5 h in the first stage, dry at 49.5°C for 2.65 h in the second stage, and dry at a constant temperature of 35°C for 7.35 h in the third stage.

[0056] Step (7): The dried product was classified through a 290-mesh vibrating sieve to collect particles with a particle size of 82-147 μm.

[0057] Step (8): The particles were dispersed in ultrapure water to form a 14% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.19 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.295 MPa. The feed liquid temperature was controlled at 14 °C.

[0058] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 19 cm / s, with an irradiation intensity of 48 mW / cm² and an irradiation time of 22 s.

[0059] Step (10): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.42 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 13% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0060] Example 5: Step (1): 100 kg of corn starch was mixed with 720 kg of 1.0% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 54°C for a constant temperature hydrolysis reaction for 2.2 hours. After the reaction was completed, 240 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 9000 r / min for 16 minutes. The supernatant was collected as the hydrolyzate.

[0061] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.048. The temperature was controlled at 31±0.5°C. Sterile air was introduced to maintain the dissolved oxygen content at 28%. After fermentation for 65 h, the pH was adjusted to 7.2 using 10% sodium hydroxide solution.

[0062] Step (3): 1.5% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.3, the temperature was raised to 80°C and kept warm for 60 minutes, and the mycelium was removed by centrifugation at 10,000 rpm for 15 minutes to obtain a crude vitamin C solution.

[0063] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 8:1) at a flow rate of 2.0 BV / h, and washed with 3.5 BV of deionized water, 2.2 BV of 0.1 mol / L NaOH solution, and 2.2 BV of 0.05 mol / L HCl solution in sequence. Finally, a 7.2% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 18-23 mS / cm was collected.

[0064] Step (5): The eluate was concentrated under reduced pressure at 45°C to a solid content of 60%, 0.05% by mass of seed crystals was added, and the temperature was lowered to 5±0.5°C at a rate of 1.0°C / min. After crystallization for 12 hours, the crystals were separated by centrifugation.

[0065] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.1 MPa, and dry them in three stages: preheat at 30°C for 0.5 h in the first stage, dry at 50°C for 3 h in the second stage, and dry at a constant temperature of 35°C for 7.5 h in the third stage.

[0066] Step (7): The dried product was classified through a 300-mesh vibrating sieve to collect particles with a particle size of 80-150 μm.

[0067] Step (8): The particles were dispersed in ultrapure water to form a 15% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.2 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.3 MPa. The feed liquid temperature was controlled at 15 °C.

[0068] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 20 cm / s, with an irradiation intensity of 50 mW / cm² and an irradiation time of 25 s.

[0069] Step (10): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.5 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 15% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0070] Comparative Example 1: Step (1): 100 kg of corn starch was mixed with 500 kg of 0.5% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 45°C for a constant temperature hydrolysis reaction for 1.5 hours. After the reaction was completed, 150 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 6000 r / min for 10 minutes. The supernatant was collected as the hydrolyzate.

[0071] Step (2): The hydrolyzate and common black Aspergillus species were added into a 50 m³ fermentation tank at a volume ratio of 1:0.03, the temperature was controlled at 28°C, sterile air was introduced to maintain the dissolved oxygen content at 20%, and after fermentation for 48 h, the pH was adjusted to 6.8 using 10% sodium hydroxide solution.

[0072] Step (3): add 1.0% by volume of citric acid to the fermentation broth, adjust the pH to 2.0, heat to 70°C and keep warm for 30 minutes, centrifuge at 7000 r / min for 10 minutes to remove the mycelium, and obtain a crude vitamin C solution.

[0073] Step (4): The crude product solution was passed through a conventional cation exchange resin column (column height-to-diameter ratio 5:1) at a flow rate of 1.0 BV / h, and washed sequentially with 2 BV of deionized water, 1 BV of 0.1 mol / L NaOH solution, and 1 BV of 0.05 mol / L HCl solution. Finally, a gradient elution was performed with a 5% ammonium sulfate solution, and the eluate with a conductivity in the range of 10-15 mS / cm was collected.

[0074] Step (5): The eluate was concentrated under reduced pressure at 40°C to a solid content of 50%, 0.02% by mass of seed crystals was added, and the temperature was lowered to 4°C at a rate of 0.5°C / min. After crystallization for 8 hours, the crystals were separated by centrifugation.

[0075] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.08 MPa, and directly heat to 50°C and dry for 4 hours.

[0076] Step (7): The dried product was classified through a 200-mesh vibrating sieve to collect particles with a particle size of 70-180 μm.

[0077] Step (8): The particles were dispersed in ultrapure water to form a 10% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.1 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.2 MPa. The feed liquid temperature was controlled at 5°C.

[0078] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 10 cm / s, with an irradiation intensity of 30 mW / cm² and an irradiation time of 10 s.

[0079] Step (10): The sterilized solution is packaged into ordinary aluminum foil packaging bags (oxygen permeability 1.0 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 20% RH, filled with 99.9% nitrogen, and then heat-sealed and stored away from light.

[0080] Comparative Example 2: Step (1): 100 kg of corn starch was mixed with 800 kg of 1.2% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 55°C for a constant temperature hydrolysis reaction for 2.5 hours. After the reaction was completed, 300 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 10,000 r / min for 20 minutes. The supernatant was collected as the hydrolyzate.

[0081] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.05. The temperature was controlled at 32°C, sterile air was introduced to maintain the dissolved oxygen content at 30%, and after fermentation for 72 h, the pH was adjusted to 7.2 using 10% sodium hydroxide solution.

[0082] Step (3): add 2.0% by volume of citric acid to the fermentation broth, adjust the pH to 2.5, heat to 80°C and keep warm for 60 minutes, centrifuge at 12000 r / min for 25 minutes to remove the mycelium, and obtain a crude vitamin C solution.

[0083] Step (4): The crude product solution was passed through a sulfonic acid cation exchange resin column (column height-to-diameter ratio 10:1) at a flow rate of 3.0 BV / h, and rinsed with 5 BV of deionized water, 3 BV of 0.1 mol / L NaOH solution, and 3 BV of 0.05 mol / L HCl solution in sequence. Finally, a 10% ammonium sulfate solution was used for gradient elution, and the eluate with a conductivity in the range of 25-30 mS / cm was collected.

[0084] Step (5): The eluate was concentrated under reduced pressure at 50°C to a solid content of 70%, 0.1% by mass of seed crystals was added, and the temperature was lowered to 6°C at a rate of 2.0°C / min. After crystallization for 15 hours, the crystals were separated by centrifugation.

[0085] Step (6): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.12 MPa, and directly heat to 60°C and dry for 2 h.

[0086] Step (7): The dried product was classified through a 350-mesh vibrating sieve to collect particles with a particle size of 50-200 μm.

[0087] Step (8): The particles were dispersed in ultrapure water to form a 20% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.3 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.5 MPa. The feed liquid temperature was controlled at 25 °C.

[0088] Step (9): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 30 cm / s, with an irradiation intensity of 60 mW / cm² and an irradiation time of 40 s.

[0089] Step (10): The sterilized solution is packaged into ordinary aluminum foil packaging bags (oxygen permeability 0.2 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 5% RH, filled with 99.99% nitrogen, and then heat-sealed and stored away from light.

[0090] Comparative Example 3: Step (1): 100 kg of corn starch was mixed with 600 kg of 0.8% hydrochloric acid solution, placed in a hydrolysis reactor, and heated to 50°C for a constant temperature hydrolysis reaction for 2 h. After the reaction was completed, 200 L of anhydrous ethanol was added to terminate the reaction, and the mixture was centrifuged at 8000 r / min for 15 min. The supernatant was collected as the hydrolyzate.

[0091] Step (2): The hydrolyzate and Aspergillus niger strain AS3.758 were added to a 50 m³ fermentation tank at a volume ratio of 1:0.04. The temperature was controlled at 30±0.5°C. Sterile air was introduced to maintain the dissolved oxygen content at 25%. After fermentation for 62 h, the pH was adjusted to 7.0 using 10% sodium hydroxide solution.

[0092] Step (3): 1.3% by volume of citric acid was added to the fermentation broth, the pH was adjusted to 2.2, the temperature was raised to 75°C and kept warm for 45 minutes, and the mycelium was removed by centrifugation at 9000 rpm for 20 minutes to obtain a crude vitamin C solution.

[0093] Step (4): The crude product solution was directly concentrated under reduced pressure to a solid content of 55%, 0.04% by mass of seed crystals were added, and the temperature was lowered to 5±0.5°C at a rate of 0.8°C / min. After crystallization for 10 hours, the crystals were separated by centrifugation.

[0094] Step (5): Place the crystals in a vacuum drying oven, control the vacuum degree to -0.09 MPa, and dry them in three stages: preheat at 25°C for 0.5 h in the first stage, dry at 48°C for 2.8 h in the second stage, and dry at a constant temperature of 35°C for 7.2 h in the third stage.

[0095] Step (6): The dried product was classified through a 250-mesh vibrating sieve to collect particles with a particle size of 90-140 μm.

[0096] Step (7): The particles were dispersed in ultrapure water to form a 12% suspension, passed through a 0.45 μm microfiltration membrane at an operating pressure of 0.18 MPa, and then passed through a 1000 Da ultrafiltration membrane at a transmembrane pressure difference of 0.28 MPa. The feed liquid temperature was controlled at 12 °C.

[0097] Step (8): The filtrate was passed through a 254 nm ultraviolet sterilization system at a transmission speed of 18 cm / s, with an irradiation intensity of 42 mW / cm² and an irradiation time of 20 s.

[0098] Step (9): The sterilized solution is packaged into aluminum foil composite film packaging bags (oxygen permeability 0.4 cm³ / (m²·24h·0.1MPa)) in a sterile environment with a humidity of 12% RH, filled with 99.999% high-purity nitrogen, and then heat-sealed and stored away from light.

[0099] Performance testing and data analysis: Key performance index tests were performed on the vitamin C products prepared in Examples 1-5 and Comparative Examples 1-3. The results are shown in Tables 1 and 2.

[0100] Table 1 Comparison of quality indicators of vitamin C products

[0101] Table 2 Comparison of production process parameters

[0102] 1. As shown in Table 1, the vitamin C products prepared in Examples 1-5 significantly outperformed the comparative examples in key indicators such as purity, residual solvent, heavy metal content, and microbial contamination. In particular, the residual solvent content in the Examples was kept below 2 ppm, while that in Comparative Examples 1-3 reached 15 ppm, 8 ppm, and 25 ppm, respectively. This is primarily due to the optimized resin purification process and staged drying technology employed in the Examples.

[0103] 2. The data in Table 2 show that the total yields of Examples 1-5 ranged from 75.3% to 78.4%, significantly higher than the 55.1% to 65.8% of Comparative Examples 1-3. Although Comparative Example 3 employed similar hydrolysis and fermentation processes as the Examples, the omission of the ion exchange resin purification step resulted in a decrease in total yield of approximately 10 percentage points and a significant increase in residual solvent, demonstrating the critical impact of the resin purification step on product quality and yield.

[0104] 3. Comparison of Example 5 and Comparative Example 2 reveals that, although both utilize relatively extreme process parameters, Example 5 achieves a better balance between product quality and yield by precisely controlling the parameter ranges of each step (e.g., hydrolysis temperature 54°C vs. 55°C, ammonium sulfate concentration 7.2% vs. 10%). This demonstrates that an optimized combination of process parameters is more important than the extreme values ​​of a single parameter.

[0105] 4. Stability testing results show that the 12-month content retention rates of the Example products were all above 99.5%, while those of the Comparative Examples were generally below 98%. This is primarily attributed to the comprehensive protective measures employed in the Examples, such as UV sterilization and nitrogen-filled packaging, which effectively slowed the oxidative degradation of vitamin C.

[0106] In summary, the low solvent residual vitamin C preparation method provided by this patent achieves a simultaneous improvement in product quality and yield through the coordinated optimization of process parameters in each step, especially the innovative combination of key technologies such as hydrolysis condition control, strain selection, resin purification and segmented drying. The solvent residual amount is significantly lower than that of conventional preparation methods.

[0107] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing low-solvent residual vitamin C, characterized in that: The following steps are involved: Step (1) corn starch and a hydrochloric acid solution with a mass concentration of 0.5-1.2% are mixed in a mass ratio of 1:5-8, and hydrolysis reaction is carried out at 45-55° C. for 1.5-2.5 hours. After the reaction is completed, anhydrous ethanol is added to terminate the reaction, and the hydrolyzate is obtained by centrifugation; Step (2) adding the hydrolyzate and Aspergillus niger to a fermentation tank at a volume ratio of 1:0.03-0.05, controlling the temperature at 28-32°C, introducing sterile air to maintain a dissolved oxygen content of 20-30%, and adjusting the pH to 6.8-7.2 after fermentation for 48-72 hours; Step (3) adding citric acid to the fermentation broth to adjust the pH to 2.0-2.5, heating to 70-80°C and keeping warm for 0.5-1h, and centrifuging to remove mycelium to obtain a crude vitamin C solution; Step (4) passing the crude product solution through a cation exchange resin column, washing with deionized water, 0.1 mol / L NaOH solution, and 0.05 mol / L HCl solution in sequence, and then gradient eluting with 5-8% ammonium sulfate solution; Step (5) collecting the eluate and concentrating it under reduced pressure at 40-45°C to a solid content of 50-60%, adding seed crystals and cooling it to 4-6°C at a rate of 0.5-1°C / min, crystallizing for 8-12 hours, and then centrifuging to separate the crystals; Step (6) placing the crystals in a vacuum drying oven, controlling the vacuum degree to -0.08~-0.1MPa, heating to 50°C in stages and drying for 3-4h, then cooling to 35°C and drying for 6-8h; The dried product in step (7) is classified through a 200-300 mesh vibrating sieve to collect particles with a particle size of 80-150 μm; Step (8) dispersing the particles in ultrapure water to form a 10-15% suspension, and sequentially passing through a 0.45 μm microfiltration membrane and a 1000 Da ultrafiltration membrane; Step (9) the filtrate is sterilized by ultraviolet irradiation with an irradiation intensity of 30-50 mW / cm² and an irradiation time of 15-30 s; Step (10) The sterilized solution is packaged into aluminum foil composite film packaging bags in a sterile environment, and the bags are sealed with nitrogen and stored away from light.

2. The preparation method according to claim 1, wherein: In step (1), the concentration of the hydrochloric acid solution is 0.8-1.0%, the mass ratio of corn starch to the hydrochloric acid solution is 1:6-7, the hydrolysis temperature is 50±2° C., and the reaction time is 2-2.2 h.

3. The preparation method according to claim 1, wherein: In the step (2), the Aspergillus niger strain is AS3.758, the fermentation temperature is controlled at 30±0.5°C, the dissolved oxygen content is 25-28%, and the fermentation period is 60-65h.

4. The preparation method according to claim 1, wherein: In step (4), the cation exchange resin is a sulfonic acid resin, the resin column has a height-to-diameter ratio of 6:1-8:1, an elution flow rate of 1.5-2.0 BV / h, and the concentration of the ammonium sulfate solution is 6.5-7.2%.

5. The preparation method according to claim 1, wherein: In step (5), the amount of seed crystals added is 0.03-0.05% of the mass of the concentrated solution, the cooling rate is 0.8-1.0°C / min, and the crystallization endpoint temperature is 5±0.5°C.

6. The preparation method according to claim 1, wherein: The vacuum drying in step (6) is divided into three stages: the first stage is preheating at 20-30°C for 0.5h, the second stage is drying at 45-50°C for 2.5-3h, and the third stage is constant temperature drying at 35°C for 7-7.5h.

7. The preparation method according to claim 1, wherein: In step (8), the operating pressure of the microfiltration membrane is 0.15-0.2 MPa, the transmembrane pressure difference of the ultrafiltration membrane is 0.25-0.3 MPa, and the feed liquid temperature is maintained at 10-15°C.

8. The preparation method according to claim 1, wherein: In step (9), the wavelength of the ultraviolet light is 254 nm, the irradiation intensity is 40±5 mW / cm², and the transmission speed of the suspension is 15-20 cm / s.

9. The preparation method according to claim 1, wherein: In the step (10), the purity of the nitrogen filling is ≥99.999%, the oxygen permeability of the packaging bag is ≤0.5 cm³ / (m²·24h·0.1MPa), and the humidity of the packaging environment is ≤15%RH.

10. The preparation method according to claim 1, characterized in that: In step (3), the amount of citric acid added is 1.2-1.5% of the volume of the fermentation liquid, the pH value at the acidification end point is 2.2-2.3, and the centrifuge speed is 8000-10000 r / min.

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