Method for recovering small molecular protein peptide and lactic acid from corn soaking water

Abstract

The invention discloses a method for recovering small molecular protein peptide and lactic acid from corn soaking water, which comprises the following steps: filtering phytic acid corn soaking water by using a ceramic membrane to obtain permeate liquid I; adding tartaric acid into the permeate I, adjusting the pH value of the solution, slowly cooling and precipitating, and filtering to obtain supernate; concentrating the supernate by adopting a nanofiltration membrane to obtain trapped fluid II and permeated fluid II; concentrating the trapped fluid II, slowly cooling and crystallizing, filtering and collecting filtrate I and a filter cake I; performing spray drying on the filtrate I to obtain small molecular protein peptide; concentrating the permeate liquid II, slowly cooling and crystallizing, and filtering to obtain a filter cake II and filtrate II; mixing the filter cake I and the filter cake II, adding water, chloroform and petroleum ether, heating and stirring until solids are dissolved, cooling and crystallizing, filtering the filter cake, and drying to obtain lactic acid. According to the method, high-content lactic acid and small-molecule protein peptide are obtained from the phytic acid-removed solution by adjusting the pH, crystallization conditions and the like of the solution in each stage, the process is simple, and the energy consumption is low.

Description

Technical Field

[0001] The invention relates to the technical field of resource recycling, and in particular to a method for recovering small molecule protein peptides and lactic acid from corn soaking water. Background Art

[0002] In the wet production process of corn starch, a large amount of corn soaking water is produced, which contains a large amount of sugars, proteins, phytic acid, etc. Phytic acid, also known as inositol hexaphosphate, is a light yellow or light brown liquid. Phytic acid is widely used in food, medicine, paints and coatings, and daily chemicals as a chelating agent, antioxidant, and preservative. Therefore, how to effectively recover phytic acid from corn soaking water has received widespread attention.

[0003] The patent with application number 202211615973.7 provides a processing method for extracting potassium phytate from corn soaking water, including: filtering and removing impurities from the collected corn soaking liquid to obtain corn soaking clear liquid; using anion resin to extract crude phytic acid, preparing crude potassium phytate liquid, and preparing potassium phytate. The patent with application number 202210339124.7 provides a new process for preparing phytic acid, including the following steps: using weak alkaline anion resin to adsorb clarified corn soaking water, washing with hydrochloric acid solutions of different concentrations in turn, collecting the effluent, heating, concentrating, and decolorizing the effluent after concentrating it, and continuing to heat and concentrate to obtain a phytic acid product. The above-mentioned prior art can effectively recover phytic acid in corn soaking water, but a large amount of waste liquid will be generated after recovering phytic acid. The waste liquid contains a certain amount of protein and lactic acid as effective ingredients. How to recover the above-mentioned effective ingredients is of great significance. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, a method for recovering small molecule protein peptides and lactic acid from corn soaking water is provided. The method uses dephytic acid corn soaking water as a raw material, first removes calcium ions and magnesium ions in the solution, then concentrates it under certain conditions, preliminarily separates the small molecule protein peptides from the lactic acid, and then controls the concentration and crystallization to respectively recover the high-content small molecule protein peptides and lactic acid, thereby greatly improving the economic value of the dephytic acid corn soaking water.

[0005] In order to solve the above technical problems, the technical solution of the present invention is:

[0006] A method for recovering small molecule protein peptides and lactic acid from corn soaking water comprises the following steps:

[0007] (1) Using a ceramic membrane to filter the corn soaking water to remove phytic acid, and collecting the permeate;

[0008] (2) adding tartaric acid to the permeate, adjusting the pH of the solution to 5-5.5, slowly cooling the solution to allow precipitation, and removing the precipitate from the feed solution after the precipitation is complete to obtain a supernatant;

[0009] (3) using a nanofiltration membrane to concentrate the supernatant in step (2) to obtain a second retentate and a second permeate;

[0010] (4) concentrating the retentate solution 2, then slowly cooling and crystallizing, filtering after the crystallization is completed, and collecting the filtrate 1 and the filter cake 1;

[0011] (5) spray drying the filtrate to obtain a small molecule protein peptide;

[0012] (6) concentrating the second permeate and then slowly cooling it down for crystallization, filtering the crystallization liquid to obtain a second filter cake and a second filtrate;

[0013] (7) Filter cake 1 and filter cake 2 are mixed, a mixed solvent consisting of water, chloroform and petroleum ether is added, the temperature is raised and stirred until the solid is dissolved, and then the temperature is lowered to crystallize, the crystallized liquid is filtered, and the filter cake is dried to obtain lactic acid.

[0014] Preferably, in step (1), the pore size of the ceramic membrane is 40-60 nm.

[0015] Preferably, in step (2), the amount of tartaric acid added is 0.5%-1% of the volume of the permeate; and sodium hydroxide is used to adjust the pH of the solution.

[0016] Preferably, in step (2), the process of slow cooling and precipitation is: cooling to 20°C at a rate of 10°C / h and precipitation for 2-4h.

[0017] Preferably, in step (3), the molecular weight cutoff of the nanofiltration membrane is 300 Da, the operating pressure of the membrane during concentration is 3 MPa, and the temperature is 40-50°C.

[0018] Preferably, in step (4), the retentate is concentrated to a solid content of 58-63 wt %; and the slow cooling crystallization process is cooling to 25° C. at a rate of 10° C. / h and crystallizing for 10-12 h.

[0019] Preferably, in step (6), the permeate is concentrated to a solid content of 55-60%; the slow cooling crystallization process is: cooling to 20°C at a rate of 10°C / h and crystallizing for 4-8h.

[0020] Preferably, in step (7), the amount of the mixed solvent added is 2-3 times the volume of the solid; the volume ratio of water, chloroform and petroleum ether in the mixed solvent is (6-7): (2.5-3): (0.1-1).

[0021] Preferably, in step (7), the temperature of heating and stirring is 50-55°C.

[0022] Preferably, in step (7), the process of cooling and crystallizing is: cooling to 25°C at a rate of 10°C / h and crystallizing for 12-16h.

[0023] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. The present invention provides a method for recovering small molecule protein peptides and lactic acid from corn soaking water. The method uses dephytic acid corn soaking water as raw material. In order to avoid the influence of calcium ions and magnesium ions in the solution on the subsequent lactic acid recovery, tartaric acid is firstly added, and the pH value and precipitation temperature of the solution are effectively adjusted to fully remove the calcium ions and magnesium ions in the solution, thereby ensuring the smooth separation of subsequent lactic acid and protein.

[0025] 2. In order to separate the small molecule protein peptides in the solution, the present invention first uses a nanofiltration membrane to concentrate the supernatant to remove the salt substances in the supernatant, and then concentrates the retentate to a certain solid content, and obtains a high content of small molecule protein peptides under controlled cooling and crystallization conditions.

[0026] 3. In order to remove salt substances in lactic acid, the present invention preliminarily concentrates the permeate II and then controls the cooling and crystallization conditions to precipitate lactic acid; then the lactic acid recovered from the small molecule protein peptide is mixed with the lactic acid obtained in this step, and a mixed solvent consisting of water, chloroform and petroleum ether is used for crystallization purification to obtain high-content lactic acid.

[0027] 4. The method provided by the present invention is simple to operate, generates little waste liquid in the whole process, has low cost and high production efficiency. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0029] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0030] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0031] Protein peptide yield (%) = [(protein peptide product mass × protein peptide content in protein peptide product) / (permeate mass × protein peptide content in permeate)] × 100%.

[0032] Lactic acid yield (%) = [(mass of lactic acid product × lactic acid content in lactic acid product) / (mass of permeate × lactic acid content in permeate)] × 100%.

[0033] Example 1

[0034] A method for recovering small molecule protein peptides and lactic acid from corn soaking water comprises the following steps:

[0035] (1) using a ceramic membrane with a pore size of 50 nm to filter the corn soaking water to remove phytic acid, and collecting 50 kg of permeate 1; the permeate 1 has a protein content of 5.83 wt%, a lactic acid content of 2.75 wt%, a calcium content of 50 ppm, and a magnesium content of 1500-2000 ppm;

[0036] (2) Adding tartaric acid to the permeate 1 (the amount of tartaric acid added is 0.5% of the volume of the permeate 1), and then adding sodium hydroxide to adjust the pH of the solution to 5, and then cooling to 20° C. at a rate of 10° C. / h for precipitation for 2 h. After the precipitation is completed, the precipitate in the feed liquid is removed to obtain a supernatant;

[0037] (3) using a nanofiltration membrane with a molecular weight cutoff of 300 Da to concentrate the supernatant in step (2) at a membrane operating pressure of 3 MPa and a temperature of 40° C. to obtain a retentate II and a permeate II;

[0038] (4) concentrating the retentate II to a solid content of 58 wt %, then slowly cooling to 25° C. at a rate of 10° C. / h for crystallization for 10 h, filtering after the crystallization, and collecting the filtrate I and the filter cake I;

[0039] (5) spray drying the filtrate to obtain 3.53 kg of small molecule protein peptides with a protein peptide content of 71% and a yield of 86%;

[0040] (6) Concentrating the permeate II to a solid content of 55%, slowly cooling the temperature to 20°C at a rate of 10°C / h for crystallization for 4h, filtering the crystallization liquid to obtain filter cake II and filtrate II;

[0041] (7) Filter cake 1 and filter cake 2 were mixed, and a mixed solvent consisting of water, chloroform and petroleum ether was added (the volume ratio of water, chloroform and petroleum ether in the mixed solvent was 6:3:1; the amount of the mixed solvent added was twice the volume of the solid), the temperature was raised to 50°C and stirred until the solid dissolved, and then the temperature was lowered to 25°C at a rate of 10°C / h for crystallization for 12h, the crystallized liquid was filtered, and the filter cake was dried to obtain 1.15kg of lactic acid with a lactic acid content of 80.2% and a yield of 67%.

[0042] Example 2

[0043] A method for recovering small molecule protein peptides and lactic acid from corn soaking water comprises the following steps:

[0044] (1) using a ceramic membrane with a pore size of 50 nm to filter the corn soaking water to remove phytic acid, and collecting 50 kg of permeate 1; the permeate 1 has a protein content of 5.83 wt%, a lactic acid content of 2.75 wt%, a calcium content of 50 ppm, and a magnesium content of 1500-2000 ppm;

[0045] (2) Adding tartaric acid to the permeate 1 (the amount of tartaric acid added is 0.5% of the volume of the permeate 1), and then adding sodium hydroxide to adjust the pH of the solution to 5, and then cooling to 20° C. at a rate of 10° C. / h for precipitation for 3 hours. After the precipitation is completed, the precipitate in the feed liquid is removed to obtain a supernatant;

[0046] (3) using a nanofiltration membrane with a molecular weight cutoff of 300 Da to concentrate the supernatant in step (2) at a membrane operating pressure of 3 MPa and a temperature of 40° C. to obtain a retentate II and a permeate II;

[0047] (4) concentrating the retentate II to a solid content of 63 wt %, then slowly cooling to 25° C. at a rate of 10° C. / h for crystallization for 12 h, filtering after the crystallization, and collecting the filtrate I and the filter cake I;

[0048] (5) spray drying the filtrate to obtain 3.47 kg of small molecule protein peptides with a protein peptide content of 72.3% and a yield of 86.1%;

[0049] (6) Concentrating the permeate II to a solid content of 55%, slowly cooling the temperature to 20°C at a rate of 10°C / h for crystallization for 6h, filtering the crystallization liquid to obtain filter cake II and filtrate II;

[0050] (7) Filter cake 1 and filter cake 2 were mixed, and a mixed solvent consisting of water, chloroform and petroleum ether was added (in the mixed solvent, the volume ratio of water, chloroform and petroleum ether was (6-7):3:(0.1-1)7:2.5:0.5; the amount of the mixed solvent added was 3 times the volume of the solid), the temperature was raised to 55°C and stirred until the solid dissolved, and then the temperature was lowered to 25°C at a rate of 10°C / h for crystallization for 16 hours, the crystallized liquid was filtered, and the filter cake was dried to obtain 1.1 kg of lactic acid with a lactic acid content of 81.7% and a yield of 65.4%.

[0051] Example 3

[0052] A method for recovering small molecule protein peptides and lactic acid from corn soaking water comprises the following steps:

[0053] (1) using a ceramic membrane with a pore size of 50 nm to filter the corn soaking water to remove phytic acid, and collecting 50 kg of permeate 1; the permeate 1 has a protein content of 5.83 wt%, a lactic acid content of 2.75 wt%, a calcium content of 50 ppm, and a magnesium content of 1500-2000 ppm;

[0054] (2) Adding tartaric acid to the permeate 1 (the amount of tartaric acid added is 1% of the volume of the permeate 1), and then adding sodium hydroxide to adjust the pH of the solution to 5.5, and then cooling to 20° C. at a rate of 10° C. / h for precipitation for 4 hours. After the precipitation is completed, the precipitate in the feed liquid is removed to obtain a supernatant;

[0055] (3) using a nanofiltration membrane with a molecular weight cutoff of 300 Da to concentrate the supernatant in step (2) at a membrane operating pressure of 3 MPa and a temperature of 40° C. to obtain a retentate II and a permeate II;

[0056] (4) concentrating the retentate II to a solid content of 58 wt %, then slowly cooling to 25° C. at a rate of 10° C. / h for crystallization for 10 h, filtering after the crystallization, and collecting the filtrate I and the filter cake I;

[0057] (5) spray drying the filtrate to obtain 3.48 kg of small molecule protein peptides, with a protein peptide content of 72.6% and a yield of 86.7%;

[0058] (6) Concentrating the permeate II to a solid content of 60%, slowly cooling the temperature to 20°C at a rate of 10°C / h for crystallization for 8h, filtering the crystallization liquid to obtain filter cake II and filtrate II;

[0059] (7) Filter cake 1 and filter cake 2 were mixed, and a mixed solvent consisting of water, chloroform and petroleum ether was added (the volume ratio of water, chloroform and petroleum ether in the mixed solvent was 6:3:1; the amount of the mixed solvent added was twice the volume of the solid), the temperature was raised to 50°C and stirred until the solid dissolved, and then the temperature was lowered to 25°C at a rate of 10°C / h for crystallization for 12h, the crystallized liquid was filtered, and the filter cake was dried to obtain 1.12kg of lactic acid with a lactic acid content of 81.3% and a yield of 66.5%.

[0060] Example 4

[0061] A method for recovering small molecule protein peptides and lactic acid from corn soaking water comprises the following steps:

[0062] (1) using a ceramic membrane with a pore size of 50 nm to filter the corn soaking water to remove phytic acid, and collecting 50 kg of permeate 1; the permeate 1 has a protein content of 5.83 wt%, a lactic acid content of 2.75 wt%, a calcium content of 50 ppm, and a magnesium content of 1500-2000 ppm;

[0063] (2) Adding tartaric acid to the permeate 1 (the amount of tartaric acid added is 1% of the volume of the permeate 1), and then adding sodium hydroxide to adjust the pH of the solution to 5.5, and then cooling to 20° C. at a rate of 10° C. / h for precipitation for 4 hours. After the precipitation is completed, the precipitate in the feed liquid is removed to obtain a supernatant;

[0064] (3) using a nanofiltration membrane with a molecular weight cutoff of 300 Da to concentrate the supernatant in step (2) at a membrane operating pressure of 3 MPa and a temperature of 40° C. to obtain a retentate II and a permeate II;

[0065] (4) concentrating the retentate II to a solid content of 63 wt %, then slowly cooling to 25° C. at a rate of 10° C. / h for crystallization for 12 h, filtering after the crystallization, and collecting the filtrate I and the filter cake I;

[0066] (5) spray drying the filtrate to obtain 3.54 kg of small molecule protein peptides with a protein peptide content of 71.9% and a yield of 87.3%;

[0067] (6) Concentrating the permeate II to a solid content of 60%, slowly cooling the temperature to 20°C at a rate of 10°C / h for crystallization for 8h, filtering the crystallization liquid to obtain filter cake II and filtrate II;

[0068] (7) Filter cake 1 and filter cake 2 were mixed, and a mixed solvent consisting of water, chloroform and petroleum ether was added (the volume ratio of water, chloroform and petroleum ether in the mixed solvent was 7:2.5:0.5; the amount of the mixed solvent added was 3 times the volume of the solid), the temperature was raised to 55°C and stirred until the solid dissolved, and then the temperature was lowered to 25°C at a rate of 10°C / h for crystallization for 16h, the crystallized liquid was filtered, and the filter cake was dried to obtain 1.12kg of lactic acid with a lactic acid content of 82.6% and a yield of 67.3%.

[0069] Comparative Example 1

[0070] Compared with Example 4, the difference is that in step (2), the amount of tartaric acid added is 0.3% of the volume of the permeate, and the other conditions are the same as those in Example 4, and 3.54 kg of small molecule protein peptides are obtained, with a protein peptide content of 71.3% and a yield of 86.5%; 1.04 kg of lactic acid is obtained, with a lactic acid content of 78.2% and a yield of 59%.

[0071] Comparative Example 2

[0072] Compared with Example 4, the difference is that in step (2), the amount of tartaric acid added is 2% of the volume of the permeate, and the other conditions are the same as those in Example 4, and 3.2 kg of small molecule protein peptides are obtained, with a protein peptide content of 72% and a yield of 79.1%; 1.13 kg of lactic acid is obtained, with a lactic acid content of 79% and a yield of 65.2%.

[0073] Comparative Example 3

[0074] Compared with Example 4, the difference is that in step (2), sodium hydroxide is added to adjust the pH of the solution to 4, and the other conditions are the same as those in Example 4, and 3.56 kg of small molecule protein peptides are obtained, with a protein peptide content of 68.8% and a yield of 84%; 1.13 kg of lactic acid, with a lactic acid content of 75.3% and a yield of 62%.

[0075] Comparative Example 4

[0076] Compared with Example 4, the difference is that in step (2), sodium hydroxide is added to adjust the pH of the solution to 6.5, and the other conditions are the same as those in Example 4, and 2.54 kg of small molecule protein peptides are obtained, with a protein peptide content of 65% and a yield of 56.7%; 1.14 kg of lactic acid is obtained, with a lactic acid content of 71.3% and a yield of 59%.

[0077] Comparative Example 5

[0078] Compared with Example 4, the difference is that in step (4), the retentate is concentrated to a solid content of 45wt%, and other conditions are the same as those in Example 4, obtaining 2.55kg of small molecule protein peptides with a protein peptide content of 74.4% and a yield of 65%; and 1.12kg of lactic acid with a lactic acid content of 81% and a yield of 65.9%.

[0079] Comparative Example 6

[0080] Compared with Example 4, the difference is that in step (4), the retentate is concentrated to a solid content of 70wt%, and other conditions are the same as those in Example 4, obtaining 4.17kg of small molecule protein peptides with a protein peptide content of 63% and a yield of 90.2%; and 1.12kg of lactic acid with a lactic acid content of 81.3% and a yield of 66%.

[0081] Comparative Example 7

[0082] Compared with Example 4, the difference is that in step (6), the permeate II is concentrated to a solid content of 45%, and the other conditions are the same as those in Example 4, obtaining 3.57 kg of small molecule protein peptides with a protein peptide content of 71% and a yield of 87%; and 0.62 kg of lactic acid with a lactic acid content of 84.8% and a yield of 38%.

[0083] Comparative Example 8

[0084] Compared with Example 4, the difference is that in step (6), the permeate II is concentrated to a solid content of 70%, and the other conditions are the same as those in Example 4, obtaining 3.55 kg of small molecule protein peptides with a protein peptide content of 71.1% and a yield of 86.6%; and 1.87 kg of lactic acid with a lactic acid content of 59% and a yield of 80.2%.

[0085] Comparative Example 9

[0086] Compared with Example 4, the difference is that in step (7), an equal amount of water is used to replace the mixed solvent described in Example 4, and other conditions are the same as Example 4, and 3.52 kg of small molecule protein peptides are obtained, with a protein peptide content of 70.9% and a yield of 85.7%; 0.34 kg of lactic acid, with a lactic acid content of 84% and a yield of 21%.

[0087] Comparative Example 10

[0088] Compared with Example 4, the difference is that in step (7), an equal amount of chloroform is used to replace the mixed solvent described in Example 4, and other conditions are the same as Example 4, and 3.52 kg of small molecule protein peptides are obtained, with a protein peptide content of 71% and a yield of 85.7%; 1.22 kg of lactic acid, with a lactic acid content of 71% and a yield of 63%.

[0089] Comparative Example 11

[0090] Compared with Example 4, the difference is that in step (7), an equal amount of petroleum ether is used to replace the mixed solvent described in Example 4, and other conditions are the same as Example 4, and 3.51 kg of small molecule protein peptides are obtained, with a protein peptide content of 71% and a yield of 85.5%; 1.56 kg of lactic acid, with a lactic acid content of 57% and a yield of 48%.

[0091] Comparative Example 12

[0092] Compared with Example 4, the difference is that in step (7), an equal amount of water is used to replace the chloroform described in Example 4, and the other conditions are the same as Example 4, and 3.54 kg of small molecule protein peptides are obtained, with a protein peptide content of 70.6% and a yield of 85.7%; 0.87 kg of lactic acid, with a lactic acid content of 74.4% and a yield of 47%.

[0093] Comparative Example 13

[0094] Compared with Example 4, the difference is that in step (7), an equal amount of water is used to replace the petroleum ether described in Example 4, and other conditions are the same as Example 4, and 3.53 kg of small molecule protein peptides are obtained, with a protein peptide content of 71% and a yield of 85.9%; 1.06 kg of lactic acid, with a lactic acid content of 72.8% and a yield of 56%.

[0095] Comparative Example 14

[0096] Compared with Example 4, the difference is that in step (7), the cooling rate is 20°C / h, and the other conditions are the same as those in Example 4, and 3.52 kg of small molecule protein peptides are obtained, with a protein peptide content of 71.2% and a yield of 86%; 1.26 kg of lactic acid, with a lactic acid content of 72% and a yield of 65.8%.

[0097] In summary, the present invention comprehensively utilizes a variety of purification methods such as ceramic membrane filtration, precipitation to remove metal ions, nanofiltration membrane concentration, crystallization, extraction, etc., and effectively adjusts the conditions during purification to obtain high-content protein peptides and lactic acid.

[0098] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for recovering small molecule protein peptides and lactic acid from corn soaking water, characterized in that: The following steps are involved: (1) Using a ceramic membrane to filter the corn soaking water to remove phytic acid, and collecting the permeate; (2) adding tartaric acid to the permeate, adjusting the pH of the solution to 5-5.5, slowly cooling the solution for precipitation, and removing the precipitate from the feed solution after the precipitation is completed to obtain a supernatant; (3) using a nanofiltration membrane to concentrate the supernatant in step (2) to obtain a second retentate and a second permeate; (4) concentrating the retentate solution 2, then slowly cooling and crystallizing, filtering after the crystallization is completed, and collecting the filtrate 1 and the filter cake 1; (5) spray drying the filtrate to obtain a small molecule protein peptide; (6) concentrating the second permeate and then slowly cooling it down for crystallization, filtering the crystallization liquid to obtain a second filter cake and a second filtrate; (7) Filter cake 1 and filter cake 2 are mixed, a mixed solvent consisting of water, chloroform and petroleum ether is added, the temperature is raised and stirred until the solid is dissolved, and then the temperature is lowered to crystallize, the crystallized liquid is filtered, and the filter cake is dried to obtain lactic acid.

2. A method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (1), the pore size of the ceramic membrane is 40-60 nm.

3. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (2), the amount of tartaric acid added is 0.5%-1% of the volume of the permeate; and sodium hydroxide is used to adjust the pH of the solution.

4. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (2), the process of slowly cooling and precipitating is: cooling to 20°C at a rate of 10°C / h and precipitating for 2-4h.

5. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (3), the molecular weight cutoff of the nanofiltration membrane is 300Da, the operating pressure of the membrane during concentration is 3MPa, and the temperature is 40-50°C.

6. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (4), the retentate II is concentrated to a solid content of 58-63 wt %; the slow cooling crystallization process is to cool to 25° C. at a rate of 10° C. / h and crystallize for 10-12 h.

7. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (6), the permeate is concentrated to a solid content of 55-60%; the slow cooling and crystallization process is: cooling to 20°C at a rate of 10°C / h and crystallizing for 4-8h.

8. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (7), the amount of the mixed solvent added is 2-3 times the volume of the solid; the volume ratio of water, chloroform and petroleum ether in the mixed solvent is (6-7): (2.5-3): (0.1-1).

9. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (7), the temperature of heating and stirring is 50-55°C.

10. The method for recovering small molecule protein peptides and lactic acid from corn soaking water according to claim 1, characterized in that: In step (7), the process of cooling and crystallizing is: cooling to 25°C at a rate of 10°C / h and crystallizing for 12-16h.