A method for purifying astaxanthin

Abstract

The invention discloses a method for purifying astaxanthin. The method comprises the following steps: taking an extracted oil phase containing astaxanthin as a purification raw material, adopting 3-methyl-5-(2,6,6-trimethyl-3-oxo-4-hydroxy-1-cyclohexenyl)-2,4-pentadienyl triphenylphosphine halide and 2,7-dimethyl-2,4,6-octatriene dialdehyde as raw materials to synthesize astaxanthin under alkaline conditions, adding acid for neutralization after reaction, washing with water, extracting with a non-polar solvent to obtain an extracted oil phase, and adding R to the extracted oil phase during purification. 1 ‑OH, after the mixed system reaches or approaches saturation, cool it down to the preset crystallization temperature, and start adding R 2 ‑OH, continue crystallization after addition, separate the crystals, dry them, R 1 , R 2 Independently selected from alkyl groups with a carbon number of 3 or 4; the astaxanthin product obtained by this method not only has a high content of trans-astaxanthin, but also has a low content of by-products, especially triphenylphosphine oxide, semi-astaxanthin and astaxanthin.

Description

Technical Field

[0001] The invention relates to the field of synthesis technology, in particular to the preparation of astaxanthin, and specifically to a method for purifying astaxanthin. Background Art

[0002] Astaxanthin, also known as astaxanthin, is a fat-soluble carotenoid. Its English name is Astaxanthin. Its chemical name is 3,3'-dihydroxy-4,4'-diketo-β,β'-carotene. Its molecular formula is C 40 H 52 O4, molecular weight 596.839, reddish brown to brown powder, strong heat resistance, poor light resistance. It has unique coloring function and anti-oxidation, anti-cancer, anti-ultraviolet damage and other functions, and is widely used in food, feed, cosmetics and medicine. Its chemical structure is a six-membered ring structure composed of four isoprene units connected in the form of conjugated double bonds, and two isoprene units at both ends. The structure is as follows:

[0003]

[0004] As a non-vitamin A source carotenoid, astaxanthin cannot be converted into vitamin A in animals, but has the same antioxidant effect as carotenoids. Its ability to quench singlet oxygen and capture free radicals is more than 10 times higher than that of β-carotene and more than 100 times stronger than vitamin E. People also call it "super vitamin E". At the same time, astaxanthin is also a good colorant that can improve the pigmentation of aquatic products, livestock and poultry skin and eggs. It is the main pigment of salmon and other fish and can improve product quality. Astaxanthin also has an important immunomodulatory effect and can be used as an immunopotentiator to improve the body's immunity. It is also of great value in aquatic and poultry farming. Astaxanthin can improve the survival rate and reproduction rate of aquatic animals, and plays an extremely important role in the normal growth and healthy breeding of aquatic animals. It has a good application in the breeding of precious aquatic products such as salmon. Astaxanthin can increase the survival rate of poultry and livestock, reduce the infection rate, and it can also increase the fertilization rate and egg production rate of poultry eggs. At present, astaxanthin has been officially approved by the US FDA as a food additive.

[0005] Most of the astaxanthin is produced by chemical synthesis. The industrial synthesis process routes are basically the same, using C9+C6→C15, 2C15+C10→C40 synthesis process routes. This process route has a great technical defect, that is, when using C15-bromophosphonium salt and C10-dialdehyde to prepare astaxanthin by WITTIG reaction, a large amount of by-product triphenylphosphine oxide (TPPO, ). At the same time, the WITTIG reaction in an alcohol system is a process of crystallization while reacting, which results in TPPO attached to the surface of the astaxanthin crystals or wrapped inside, which is difficult to remove; and the TPPO residue in feed-grade astaxanthin crystals is required to be ≤100ppm, which leads to the need to strictly remove TPPO when using C15-bromophosphonate and C10-dialdehyde to prepare astaxanthin, which also makes post-processing very troublesome;

[0006] The synthetic route of C15-bromophosphonate and C10-dialdehyde is as follows:

[0007]

[0008] At present, for the reaction mixture after the WITTIG reaction of C15-bromophosphonate and C10-dialdehyde to prepare astaxanthin, the prior art generally adopts a heating total reflux method. For example, in the patent document CN114369048, the reaction mixture is extracted and concentrated, and then ethanol is added, and total reflux is performed under boiling point conditions. After the reflux is completed, the filter is filtered, the filter cake is washed, and dried to obtain an astaxanthin product. However, although the content of trans-astaxanthin in the astaxanthin product obtained by this method is improved to a certain extent, there are other by-products in the product, such as a large amount of semi-astaxanthin and astaxanthin, which is not conducive to improving the product quality and there is an obvious problem of losing one thing while gaining another. Summary of the invention

[0009] The object of the present invention is to overcome one or more deficiencies of the prior art and to provide an improved method for purifying astaxanthin, wherein the astaxanthin product obtained by the method not only has a high content of trans-astaxanthin, but also has a low content of by-products, especially triphenylphosphine oxide, semi-astaxanthin and astaxanthin.

[0010] Based on the problem of neglecting one thing while focusing on another in the process of purifying the extracted oil phase containing astaxanthin in the prior art, the inventors of the present invention unexpectedly discovered through a large number of experimental studies that the use of an alkyl alcohol with a carbon number of 3 or 4 as a crystallization solvent in combination with a non-polar solvent in the extracted oil phase, and the addition of an alkyl alcohol with a carbon number of 3 or 4 in stages and at specific time points, not only reduces the solubility of astaxanthin in the system and maximizes the precipitation, but also significantly improves the content of trans-astaxanthin in the astaxanthin product, and increases the solubility of the system for by-products, thereby achieving the mutual separation of the target product and by-products, and in particular, substantially no unexpected by-products are produced.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for purifying astaxanthin, the method using an extracted oil phase containing astaxanthin as a purification raw material, the preparation method of the extracted oil phase comprising: using 3-methyl-5-(2,6,6-trimethyl-3-oxo-4-hydroxy-1-cyclohexenyl)-2,4-pentadienyltriphenylphosphine halide and 2,7-dimethyl-2,4,6-octatriene dialdehyde (C10-dialdehyde) as raw materials to synthesize astaxanthin under alkaline conditions, adding acid for neutralization after the reaction, washing with water, and extracting with a non-polar solvent to obtain an extracted oil phase, wherein:

[0013] The purification method comprises: adding R1-OH to the extraction oil phase, making the mixed system reach or approach saturation, then cooling until a preset crystallization temperature is reached, starting to add R2-OH during the cooling process, continuing crystallization after the addition is completed, separating crystals after the crystallization is completed, and drying, wherein R1 and R2 are independently selected from alkyl groups with 3 or 4 carbon atoms.

[0014] According to some specific aspects of the present invention, the 3-methyl-5-(2,6,6-trimethyl-3-oxo-4-hydroxy-1-cyclohexenyl)-2,4-pentadienyltriphenylphosphonium halide can be 3-methyl-5-(2,6,6-trimethyl-3-oxo-4-hydroxy-1-cyclohexenyl)-2,4-pentadienyltriphenylphosphonium bromide (C15-bromophosphonium salt).

[0015] In the present invention, both C15-bromophosphonium salt and C10-dialdehyde can be prepared according to existing literature.

[0016] According to some specific aspects of the present invention, the alkaline condition can be formed by adding an alkaline substance, for example, sodium hydroxide or an ethanol solution of sodium hydroxide can be added.

[0017] According to some specific aspects of the present invention, the extraction oil phase is prepared by WITTIG reaction of C15-bromophosphonate and C10-dialdehyde, followed by neutralization of the reaction mixture with formic acid, washing with water, and extraction with a non-polar solvent.

[0018] Furthermore, the reaction system of C15-bromophosphonium salt and C10-dialdehyde uses alcohols, a mixture of different alcohols, or a mixture of alcohol and an immiscible non-polar solvent as a reaction solvent.

[0019] Furthermore, the WITTIG reaction in an alcohol system is a process of crystallization while reacting. Although the solubility of astaxanthin and TPPO generated by the reaction in the system can be different to a certain extent by controlling the type of reaction solvent, thereby precipitating the generated astaxanthin and dissolving TPPO in the system, thereby achieving preliminary separation, at the same time, TPPO will also be attached to the surface of the precipitated astaxanthin crystals or wrapped inside, which further increases the difficulty of removing TPPO. In the prior art, total reflux is used to separate TPPO, but there are other by-products in the product, such as a large amount of semi-astaxanthin and astaxanthin, which is not conducive to improving product quality. The above method of the present invention better solves the above problem.

[0020] According to some preferred aspects of the present invention, the R1-OH and the R2-OH are independently selected from one or more combinations of n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol, and 2-methylpropanol.

[0021] According to some preferred and specific aspects of the present invention, the R1-OH is the same as the R2-OH.

[0022] According to some preferred aspects of the present invention, the R1-OH and R2-OH are added by dropwise addition.

[0023] Furthermore, the dropping speeds of the R1-OH and the R2-OH are controlled to be 0.03-0.15 L / h, preferably 0.06-0.1 L / h.

[0024] In the present invention, by further controlling the ratio of the total feed volume of the R1-OH and the R2-OH to the volume of the non-polar solvent contained in the extraction oil phase, the precipitation of astaxanthin in the system can be better regulated, the precipitation of by-products such as TPPO can be reduced, and better separation can be achieved.

[0025] Further, according to some preferred aspects of the present invention, the ratio of the total feed volume of the R1-OH and the R2-OH to the volume of the non-polar solvent contained in the extraction oil phase is controlled to be 1-2:1.

[0026] Further preferably, the ratio of the total feed volume of the R1-OH and the R2-OH to the volume of the non-polar solvent contained in the extraction oil phase is controlled to be 1.1-1.6:1.

[0027] According to some preferred aspects of the present invention, the volume ratio of the R1-OH to the R2-OH is controlled to be 1-2.5:1.

[0028] More preferably, the volume ratio of the R1-OH to the R2-OH is controlled to be 1.1-2:1.

[0029] According to some preferred aspects of the present invention, the non-polar solvent is a combination of one or more selected from dichloromethane, chloroform, ethyl acetate, acetone, acetonitrile, and n-propyl acetate.

[0030] According to a preferred and specific aspect of the present invention, the non-polar solvent is dichloromethane.

[0031] According to some preferred aspects of the present invention, the preset crystallization temperature is controlled to be -30 to 0° C. Further, the preset crystallization temperature is controlled to be -20 to -5° C.

[0032] According to some preferred aspects of the present invention, the cooling rate is controlled to be 30-50° C. / h.

[0033] According to some preferred aspects of the present invention, the purification method further comprises the step of concentrating the extracted oil phase before adding R1-OH.

[0034] In some embodiments of the present invention, the purification method includes: slowly adding R1-OH to the extracted oil phase at room temperature, controlling the dropping time to 0.5-2h, cooling the astaxanthin mixed solution to a preset crystallization temperature after the dropping is completed, controlling the cooling time to 0.5-2h, and slowly adding R2-OH during the cooling process, controlling the dropping time to 0.5-3.5h, and after the dropping is completed, continuing to stir for 1-10h at the preset crystallization temperature, filtering after stirring, rinsing the filter cake with R1-OH several times, and then drying it in a vacuum drying oven with a vacuum degree of less than -0.8MPa and a temperature of 70-90°C for 3-15h to obtain an astaxanthin product.

[0035] The present invention also provides a method for synthesizing astaxanthin, which comprises the above-mentioned method for purifying the extracted oil phase.

[0036] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0037] 1. The method of the present invention has a better effect of removing TPPO, and the quality of astaxanthin is higher and the yield is also higher. TPPO≤15ppm, the content of astaxanthin in the finished product is ≥98%, and the yield is also 98%;

[0038] 2. The method of the present invention is easy to operate, has high safety, has a wide range of raw material sources, and is highly economical;

[0039] 3. The method of the present invention substantially does not produce any undesirable by-products such as semi-astaxanthin and astaxanthin. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1This is the HPLC spectrum of the astaxanthin product obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The above scheme is further described below in conjunction with specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions adopted in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0042] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0043] Example 1

[0044] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0045] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0046] At room temperature, slowly add 100 mL of n-propanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of n-propanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-propanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0047] Yield: 20.36 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 99.06%); according to high performance liquid chromatography, the trans-astaxanthin content is 98.07%, the TPPO content is 7 ppm, the semi-astaxanthin content is 0.8%, and the astaxanthin content is 0.1%.

[0048] Example 2

[0049] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0050] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0051] At room temperature, slowly add 100 mL of n-propanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. In the cooling process, slowly add 120 mL of n-propanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-propanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0052] Yield: 19.51 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 94.93%); according to high performance liquid chromatography, the trans-astaxanthin content is 98.07%, the TPPO content is 3 ppm, the semi-astaxanthin content is 0.76%, and the astaxanthin content is 0.11%.

[0053] Example 3

[0054] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0055] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0056] At room temperature, slowly add 100 mL of n-propanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -15°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of n-propanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-propanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0057] Yield: 19.53 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 95.03%); according to high performance liquid chromatography, the trans-astaxanthin content is 98.07%, the TPPO content is 8 ppm, the semi-astaxanthin content is 0.68%, and the astaxanthin content is 0.13%.

[0058] Example 4

[0059] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0060] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0061] At room temperature, slowly add 100 mL of n-butanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of n-butanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-butanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0062] Yield: 20.12 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 97.90%); according to high performance liquid chromatography, the trans-astaxanthin content is 98.47%, the TPPO content is 5 ppm, the semi-astaxanthin content is 0.75%, and the astaxanthin content is 0.12%.

[0063] Example 5

[0064] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0065] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0066] At room temperature, slowly add 100 mL of tert-butanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of tert-butanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-butanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0067] Yield: 19.98 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 97.22%); according to high performance liquid chromatography, the trans-astaxanthin content is 98.03%, TPPO is 11 ppm, the semi-astaxanthin content is 0.76%, and the astaxanthin content is 0.13%.

[0068] Comparative Example 1

[0069] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0070] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0071] At room temperature, slowly add 100 mL of methanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of methanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of methanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0072] Yield: 16.97 g astaxanthin (82.57% calculated based on the C10-dialdehyde used); according to HPLC, the trans-astaxanthin content was 97.65%, the TPPO content was 23 ppm, the semi-astaxanthin content was 0.94%, and the astaxanthin content was 0.23%.

[0073] Comparative Example 2

[0074] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0075] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0076] At room temperature, slowly add 100 mL of ethanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of ethanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of ethanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0077] Yield: 17.85 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 86.85%); according to high performance liquid chromatography, the trans-astaxanthin content is 97.67%, the TPPO content is 47 ppm, the semi-astaxanthin content is 0.91%, and the astaxanthin content is 0.25%.

[0078] Comparative Example 3

[0079] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0080] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0081] At room temperature, slowly add 100 mL of n-pentanol to the concentrated oil phase, and control the dropping time for 1 hour. After the dropping is completed, cool the astaxanthin mixed solution to -20°C, and control the cooling time to 1 hour. During the cooling process, slowly add 200 mL of n-pentanol, and control the dropping time to 2 hours. After the dropping is completed, continue stirring at -20°C for 4 hours, and then filter after stirring. Rinse the filter cake twice with 50 mL of n-pentanol, and then dry it in a vacuum drying oven at 80°C with a vacuum degree of less than -0.8 MPa for 6 hours;

[0082] Yield: 20.05 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 97.56%); according to high performance liquid chromatography, the trans-astaxanthin content is 95.65%, the TPPO content is 109 ppm, the semi-astaxanthin content is 1.24%, and the astaxanthin content is 0.34%.

[0083] Comparative Example 4

[0084] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0085] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0086] Add 300 mL of n-propanol to the concentrated oil phase, place it in a heating device for heating, then extract 100 mL of solvent at (internal temperature is about 80°C, heat source is 120°C), add 100 mL of n-propanol, and then reflux for 3 hours at boiling point conditions. Cool the material to room temperature, filter it, rinse the filter cake with 50 mL of n-propanol twice, and then dry it in a vacuum drying oven at a vacuum degree of less than -0.8 MPa and 80°C for 6 hours;

[0087] Yield: 15.64 g astaxanthin (76.17% calculated based on the C10-dialdehyde used); according to HPLC, the trans-astaxanthin content was 94.03%, TPPO was 106 ppm, the semi-astaxanthin content was 2.03%, and the astaxanthin content was 1.02%.

[0088] Comparative Example 5

[0089] 40g C15-bromophosphonium salt, 5.65g C10-dialdehyde, 100g dichloromethane, and 40g ethanol were placed in a flask. When the mixed solution in the flask was cooled to -20°C, sodium hydroxide ethanol solution (5.2g sodium hydroxide, 70g ethanol) was added dropwise. After the addition was completed, the mixture was stirred and kept warm for 3h at -20°C. After the reaction was completed, 7.8g glacial acetic acid was used for neutralization. Then, the mixture was washed with 200mL water for 4 times. During the washing process, 50mL dichloromethane was used for extraction each time. The oil phases were separated, collected, and combined to obtain the extracted oil phase.

[0090] The extracted oil phase is subjected to a reduced pressure recovery method to recover part of the dichloromethane, and when the dichloromethane remaining in the extracted oil phase is 200 mL, the recovery is stopped to obtain a concentrated oil phase;

[0091] The concentrated oil phase was cooled to -20°C, and the cooling time was controlled to be 1 hour. After cooling to -20°C, 300 mL of n-propanol was slowly added dropwise, and the dropping time was controlled to be 3 hours. After the dropping was completed, stirring was continued for 4 hours. After stirring, suction filtration was performed, and the filter cake was rinsed with 50 mL of n-propanol twice, and then dried in a vacuum drying oven at a vacuum degree of less than -0.8 MPa and 80°C for 6 hours;

[0092] Yield: 20.00 g astaxanthin (calculated based on the C10-dialdehyde used, the yield is 97.31%); according to high performance liquid chromatography, the trans-astaxanthin content is 97.05%, the TPPO content is 76 ppm, the semi-astaxanthin content is 0.91%, and the astaxanthin content is 0.25%.

[0093] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0094] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

Claims

1. A method for purifying astaxanthin, wherein the extraction oil phase containing astaxanthin is used as a purification raw material, and the preparation method of the extraction oil phase comprises: Astaxanthin is synthesized under alkaline conditions using 3-methyl-5-(2,6,6-trimethyl-3-oxo-4-hydroxy-1-cyclohexenyl)-2,4-pentadienyltriphenylphosphine halide and 2,7-dimethyl-2,4,6-octatriene dialdehyde as raw materials, followed by acid neutralization, water washing, and extraction with a non-polar solvent to obtain an extracted oil phase, which is characterized by: The purification method comprises: adding R1-OH to the extraction oil phase, making the mixed system reach or approach saturation, cooling down until reaching a preset crystallization temperature, starting to add R2-OH during the cooling process, continuing crystallization after the addition is completed, separating crystals after the crystallization is completed, and drying; Wherein, R1 and R2 are independently selected from alkyl groups with a carbon number of 3 or 4, and the feed volume ratio of the R1-OH to the R2-OH is controlled to be 1-2.5:1; and the preset crystallization temperature is controlled to be -30~0°C.

2. The method for purifying astaxanthin according to claim 1, characterized in that: The R1-OH and the R2-OH are independently selected from one or more combinations of n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol, and 2-methylpropanol.

3. The method for purifying astaxanthin according to claim 1 or 2, characterized in that: The R1-OH is the same as the R2-OH.

4. The method for purifying astaxanthin according to claim 1, characterized in that: The R1-OH and R2-OH are added dropwise.

5. The method for purifying astaxanthin according to claim 4, characterized in that: The dropping speeds of the R1-OH and the R2-OH are controlled to be 0.03-0.15 L / h respectively.

6. The method for purifying astaxanthin according to claim 5, characterized in that: The dropping speeds of the R1-OH and the R2-OH are controlled to be 0.06-0.1 L / h respectively.

7. The method for purifying astaxanthin according to claim 1, characterized in that: The ratio of the total volume of the R1-OH and the R2-OH to the volume of the non-polar solvent contained in the extraction oil phase is controlled to be 1-2:

1.

8. The method for purifying astaxanthin according to claim 7, characterized in that: The ratio of the total feed volume of the R1-OH and the R2-OH to the volume of the non-polar solvent contained in the extraction oil phase is controlled to be 1.1-1.6:

1.

9. The method for purifying astaxanthin according to claim 1, 7 or 8, characterized in that: The volume ratio of the R1-OH to the R2-OH is controlled to be 1.1-2:

1.

10. The method for purifying astaxanthin according to claim 1, 7 or 8, characterized in that: The non-polar solvent is a combination of one or more selected from dichloromethane, chloroform, ethyl acetate, acetone, acetonitrile, and n-propyl acetate.

11. The method for purifying astaxanthin according to claim 10, characterized in that: The non-polar solvent is dichloromethane.

12. The method for purifying astaxanthin according to claim 1, characterized in that: The preset crystallization temperature is controlled to be -20 to -5°C; and / or the cooling rate is controlled to be 30-50°C / h.

13. The method for purifying astaxanthin according to claim 1, characterized in that: The purification method further comprises the step of concentrating the extracted oil phase before adding R1-OH.

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