Method for simultaneously extracting starch and protein and application thereof

Abstract

The invention discloses a method for simultaneously extracting starch and protein and application thereof. The invention belongs to the technical field of corn deep processing. The invention aims to solve the technical problems that the existing method is low in production efficiency and the obtained corn starch and corn protein are poor in processing characteristic and digestion characteristic. The method comprises the following steps: (1) performing vacuum low-temperature alkalization cooking on corn kernels in a calcium hydroxide solution; (2) performing ultrasonic-high static pressure cooperative treatment after cooking, and then soaking; (3) performing coarse grinding on the soaked corn kernels, then performing fine grinding, and performing enzymolysis with compound protease; and (4) finely grinding, filtering, standing, centrifuging, washing with water, precipitating, respectively collecting a lower-layer white part and an upper-layer yellow part, and freeze-drying to respectively obtain the corn starch and the corn protein. The method improves the processing characteristics of starch and the digestion characteristics of protein, and can be applied to development and production of high-quality corn starch or corn protein-based food.

Description

Technical Field

[0001] The invention belongs to the technical field of corn deep processing, and particularly relates to a method for simultaneously extracting starch and protein and application thereof. Background Art

[0002] The main component of corn kernels is starch, which accounts for about 70% of the total weight of the kernels, followed by protein, which accounts for about 10%. Deep processing of corn in my country is mainly used to extract starch, while obtaining a large amount of protein-rich byproducts - corn yellow powder. However, the starch and protein in the corn endosperm are not free, but tightly bound together. The protein matrix wraps the elliptical or polygonal starch granules in a network-like manner, and the starch granules are also connected by flocculent proteins. The two exist in the form of a composite structure in corn kernels, so it is difficult to completely separate the two.

[0003] At present, corn kernels are mainly processed by wet milling to prepare starch and protein. The soaking process is the first step of corn wet milling, which directly affects the yield and quality of the finished starch products and their by-products during processing. The traditional corn soaking process generally uses a 0.2%-0.3% concentration of sulfurous acid solution at 48-53°C for soaking, and the soaking time is about 48 hours. The traditional wet milling process has the disadvantages of long soaking time, high production cost, low production efficiency, high energy consumption, large wastewater discharge, and environmental pollution. The obtained corn starch and corn protein have poor processing and digestion characteristics and cannot meet the needs of food processing. Therefore, it is urgent to improve the wet milling process to solve the above problems. At present, there are few reports on the research of promoting starch and protein extraction and improving its processing quality and digestion characteristics by improving the corn wet process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for extracting starch and protein simultaneously and application thereof.

[0005] One of the objects of the present invention is to provide a method for extracting starch and protein simultaneously, said method is carried out according to the following steps:

[0006] (1) vacuum low-temperature alkalization cooking of corn kernels in a calcium hydroxide solution;

[0007] (2) After cooking, ultrasonic treatment is performed first, followed by high static pressure treatment, and then soaking;

[0008] (3) The soaked corn kernels are firstly coarsely ground to remove the germ, and then finely ground by a colloid mill to remove the fiber, and then a composite protease is added to the resulting slurry for enzymatic hydrolysis, and then the enzyme is boiled to inactivate the enzyme after enzymatic hydrolysis;

[0009] (4) The corn slurry after enzymatic hydrolysis is finely ground in a ball mill, and the filtrate after filtering with filter cloth is allowed to stand for a certain period of time, and then centrifuged and washed with water to precipitate, and the lower white part and the upper yellow part are collected separately, and after freeze-drying, corn starch and corn protein are obtained respectively.

[0010] It is further defined that in step (1), the mass ratio of corn kernels to water in the calcium hydroxide solution is 1:(1-3).

[0011] It is further defined that the mass of calcium hydroxide in step (1) is 0.5-1.5% of the total mass of corn kernels and calcium hydroxide solution.

[0012] It is further defined that in step (1), the vacuum degree is 0.06-0.08 MPa, the cooking temperature is 50-70° C., and the cooking time is 10-20 min.

[0013] It is further defined that in step (2), the ultrasonic power is 100-200 W, the ultrasonic time is 20-30 min, the high static pressure is 100-300 MPa, and the high static pressure time is 10-20 min.

[0014] It is further defined that the soaking temperature in step (2) is 40-60° C. and the soaking time is 6-10 h.

[0015] It is further defined that in step (3), the composite protease is composed of neutral protease and trypsin in a mass ratio of 1:1, and the composite protease is 500-1500 U / g.

[0016] It is further defined that in step (3), the enzymatic hydrolysis pH is 6.5-8.5, the enzymatic hydrolysis temperature is 40-60° C., and the enzymatic hydrolysis time is 20-40 min.

[0017] It is further defined that in step (4), the filtrate is allowed to stand for 2-4 hours.

[0018] A second object of the present invention is to provide a corn starch obtained by the above method.

[0019] The third object of the present invention is to provide a zein obtained by the above method.

[0020] A fourth object of the present invention is to provide an application of the above method in corn deep processing.

[0021] Compared with the prior art, the present invention has the following significant effects:

[0022] (1) The present invention uses vacuum low-temperature alkalization cooking to soften the cortex of corn kernels, reduce thermal damage and oxidation of proteins and lipids, reduce water loss in the cooking materials, promote water to enter the interior of the corn kernels, shorten the soaking time, destroy the starch-protein composite structure inside the kernels, and facilitate the separation of starch and protein;

[0023] (2) Ultrasound-high static pressure synergistic treatment is used to shorten the soaking time by utilizing the cavitation effect of ultrasound and the strong pressure of high static pressure, thereby destroying the interaction between starch and protein, resulting in partial gelatinization of starch and proper denaturation of protein, which is beneficial to the subsequent initial crushing of corn and enzymatic hydrolysis of compound protease;

[0024] (3) The enzymatic hydrolysis of the composite enzyme composed of neutral protease and trypsin can destroy the protein matrix wrapped around the outside of starch granules, effectively break the chemical bonds between starch and protein, and release starch from the protein network matrix to the greatest extent, which is beneficial to the subsequent fine grinding of corn, improves the separation efficiency and extraction rate of starch and protein, and improves the processing characteristics of starch; in addition, after the composite protease hydrolyzes the protein, its water solubility and digestibility are improved, which promotes its absorption and utilization by the body.

[0025] (4) The method of the present invention shortens the soaking time of the traditional wet process for preparing corn starch and protein from 48 hours to less than 10 hours, shortens the processing time by about 80%, and significantly improves the extraction rate of corn starch and protein. It has the characteristics of being green and safe, having high production efficiency and low cost. At the same time, it improves the processing characteristics of starch and the digestion characteristics of protein, and can be applied to the development and production of high-quality corn starch or corn protein-based foods. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A is the corn starch extraction rate of the methods of Example 1 and Comparative Examples 1-4;

[0027] Figure 1B is the corn protein extraction rate of the methods of Example 1 and Comparative Examples 1-4;

[0028] Figure 2A The gelatinization properties of corn starch obtained by the methods of Example 1 and Comparative Examples 1-4;

[0029] Figure 2B The texture characteristics of corn starch obtained by the methods of Example 1 and Comparative Examples 1-4;

[0030] Figure 2C The storage modulus G' of corn starch obtained by the methods of Example 1 and Comparative Examples 1-4;

[0031] Figure 2D is the loss modulus G" of corn starch obtained by the methods of Example 1 and Comparative Examples 1-4;

[0032] Figure 3A The solubility of zein obtained by the methods of Example 1 and Comparative Examples 1-4;

[0033] Figure 3BThe free amino acid content of corn protein obtained by the methods of Example 1 and Comparative Examples 1-4;

[0034] Figure 3C The hydrolysis degree of corn protein obtained by the methods of Example 1 and Comparative Examples 1-4;

[0035] Figure 3D The digestibility of corn protein obtained by the methods of Example 1 and Comparative Examples 1-4. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0038] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0039] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0040] The endpoints and any values ​​of the ranges disclosed in the invention 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 regarded as specifically disclosed in this article.

[0041] Embodiment 1: The method for extracting starch and protein simultaneously in this embodiment is carried out according to the following steps:

[0042] (1) placing corn kernels in a calcium hydroxide solution, vacuum low-temperature alkalization cooking for 15 min at a vacuum degree of 0.07 MPa and a temperature of 60° C., wherein the mass ratio of corn kernels to distilled water is 1:2, and the mass of calcium hydroxide is 1.0% of the total mass of corn kernels and distilled water;

[0043] (2) After cooking, the mixture was ultrasonically treated at an ultrasonic power of 150 W for 25 min, subjected to high static pressure treatment at a pressure of 200 MPa for 15 min, and then soaked at 50 °C for 8 h;

[0044] (3) The soaked corn kernels were first placed in a tissue crusher for coarse grinding to remove the germ, and then finely ground in a colloid mill to remove the fiber, and then 1000 U / g of a composite protease was added to the resulting slurry, wherein the composite protease consisted of a neutral protease and trypsin in a mass ratio of 1:1, and the enzymatic hydrolysis was performed at an enzymatic hydrolysis pH of 7.5 and an enzymatic hydrolysis temperature of 50°C for 30 minutes, and then the enzymatic hydrolysis was boiled for 5 minutes to inactivate the enzyme;

[0045] (4) The corn slurry after enzymatic hydrolysis was finely ground in a ball mill and filtered using a 200-mesh filter cloth. The filtrate was allowed to stand for 3 hours and then centrifuged at 4000 rpm for 10 minutes. The precipitate was washed with distilled water, and the lower white part and the upper yellow part were collected and freeze-dried to obtain corn starch and corn protein, respectively.

[0046] This method significantly shortens the soaking time of traditional wet processing of corn and improves the extraction rate of corn starch and protein. It has the characteristics of green and safety, high production efficiency and low cost. At the same time, it improves the processing characteristics of starch and the digestion characteristics of protein. It can be applied to the development and production of high-quality corn starch or corn protein-based foods.

[0047] Embodiment 2: The method for extracting starch and protein simultaneously in this embodiment is carried out according to the following steps:

[0048] (1) The corn kernels are placed in a calcium hydroxide solution and vacuum-cooked at low temperature for 10 min at a vacuum degree of 0.06 MPa and a temperature of 50° C., wherein the mass ratio of the corn kernels to the distilled water is 1:1, and the mass of the calcium hydroxide is 1.5% of the total mass of the corn kernels and the distilled water;

[0049] (2) After steaming, the mixture was ultrasonically treated at an ultrasonic power of 100 W for 30 min, subjected to high static pressure treatment at a pressure of 150 MPa for 20 min, and then soaked at 50 °C for 8 h;

[0050] (3) The soaked corn kernels were first placed in a tissue crusher for coarse grinding to remove the germ, and then finely ground in a colloid mill to remove the fiber, and then 500 U / g of a composite protease was added to the resulting slurry, wherein the composite protease consisted of a neutral protease and trypsin in a mass ratio of 1:1, and the enzymatic hydrolysis was performed at an enzymatic hydrolysis pH of 8.0 and an enzymatic hydrolysis temperature of 45°C for 40 minutes, and then the enzymatic hydrolysis was boiled for 5 minutes to inactivate the enzyme;

[0051] (4) The corn slurry after enzymatic hydrolysis was finely ground in a ball mill and filtered using a 200-mesh filter cloth. The filtrate was allowed to stand for 3 hours and then centrifuged at 4000 rpm for 10 minutes. The precipitate was washed with distilled water, and the lower white part and the upper yellow part were collected and freeze-dried to obtain corn starch and corn protein, respectively.

[0052] This method significantly shortens the soaking time of traditional wet processing of corn and improves the extraction rate of corn starch and protein. It has the characteristics of green and safety, high production efficiency and low cost. At the same time, it improves the processing characteristics of starch and the digestion characteristics of protein. It can be applied to the development and production of high-quality corn starch or corn protein-based foods.

[0053] Embodiment 3: The method for extracting starch and protein simultaneously in this embodiment is carried out according to the following steps:

[0054] (1) The corn kernels are placed in a calcium hydroxide solution and vacuum-cooked at low temperature for 20 minutes at a vacuum degree of 0.08 MPa and a temperature of 70° C., wherein the mass ratio of the corn kernels to the distilled water is 1:3, and the mass of the calcium hydroxide is 0.5% of the total mass of the corn kernels and the distilled water;

[0055] (2) After steaming, the mixture was ultrasonically treated at an ultrasonic power of 200 W for 20 min, subjected to high static pressure treatment at a pressure of 250 MPa for 10 min, and then soaked at 50 °C for 8 h;

[0056] (3) The soaked corn kernels were first placed in a tissue crusher for coarse grinding to remove the germ, and then finely ground in a colloid mill to remove the fiber, and then 1500 U / g of a composite protease was added to the resulting slurry, wherein the composite protease consisted of a neutral protease and trypsin in a mass ratio of 1:1, and the enzymatic hydrolysis was performed at an enzymatic hydrolysis pH of 7.0 and an enzymatic hydrolysis temperature of 55°C for 20 minutes, and then the enzymatic hydrolysis was boiled for 5 minutes to inactivate the enzyme;

[0057] (4) The corn slurry after enzymatic hydrolysis was finely ground in a ball mill and filtered using a 200-mesh filter cloth. The filtrate was allowed to stand for 3 hours and then centrifuged at 4000 rpm for 10 minutes. The precipitate was washed with distilled water, and the lower white part and the upper yellow part were collected and freeze-dried to obtain corn starch and corn protein, respectively.

[0058] This method significantly shortens the soaking time of traditional wet processing of corn and improves the extraction rate of corn starch and protein. It has the characteristics of green and safety, high production efficiency and low cost. At the same time, it improves the processing characteristics of starch and the digestion characteristics of protein. It can be applied to the development and production of high-quality corn starch or corn protein-based foods.

[0059] Comparative Example 1:

[0060] The corn kernels and distilled water are fully mixed in a mass ratio of 1:3, sulfurous acid is added in an amount of 0.2% of the total mass of the corn kernels and the distilled water, and the mixture is soaked at 50°C for 48 hours. The soaked corn kernels are firstly placed in a tissue crusher for coarse grinding to remove the germ, then finely ground in a colloid mill to remove the fiber, and then finely ground in a ball mill. The corn slurry is filtered through a 200-mesh filter cloth, the filtrate is allowed to stand for 3 hours, and then centrifuged at 4000 rpm for 10 minutes. After washing the precipitate with distilled water, the lower white part and the upper yellow part are respectively collected, and after freeze-drying, corn starch and corn protein are obtained respectively.

[0061] Comparative Example 2:

[0062] The difference between this comparative example and Example 1 is that the ultrasonic treatment and high static pressure treatment in step (2) are omitted, and the mixture is directly immersed at 50° C. for 8 hours. The compound protease enzymatic hydrolysis in step (3) is also omitted. The other steps and parameters are the same as those in Example 1.

[0063] Comparative Example 3:

[0064] The difference between this comparative example and Example 1 is that the compound protease enzymatic hydrolysis in step (3) is omitted. The other steps and parameters are the same as those in Example 1.

[0065] Comparative Example 4:

[0066] The difference between this comparative example and Example 1 is that the vacuum low-temperature cooking in step (1) is omitted, and step (2) is directly performed after adding calcium hydroxide. The other steps and parameters are the same as those in Example 1.

[0067] Detection test (I)

[0068] Determination of corn starch and protein extraction rate: The starch content was determined using the starch kit method of Megazyme, Ireland; the protein content was determined according to the Kjeldahl nitrogen determination method in GB5009.5-2016. The extraction rates of the two were calculated based on the percentage of the extracted starch and protein in the total starch and total protein, respectively.

[0069] Figure 1 shows the extraction rates of corn starch and protein. For Comparative Sample 1, the soaking time required for preparing corn starch and protein by the traditional wet milling process is as long as 48 hours, while the soaking time is shortened to less than 10 hours by Comparative Samples 2-4 and the method of Example 1, and the processing time is shortened by about 80%, which significantly improves the production efficiency of corn starch and protein. The starch and protein extraction rates of Comparative Sample 1 are 88.97% and 86.54%, respectively. Compared with Comparative Sample 1, the starch (89.87%) and protein (87.83%) extraction rates of Comparative Sample 2 do not change significantly, while the starch and protein extraction rates of Comparative Sample 3 are increased to 91.54% and 89.33%, respectively, and the starch and protein extraction rates of Comparative Sample 4 are increased to 92.84% and 90.07%, respectively. Compared with all the control samples, Example 1 has higher starch and protein extraction rates, reaching 95.58% and 92.48% respectively, which indicates that the combined action of vacuum low-temperature alkalization cooking, ultrasound, high static pressure and composite protease is conducive to the effective separation of starch and protein, and further improves the extraction rate of corn starch and protein.

[0070] Detection test (II)

[0071] (1) Determination of corn starch gelatinization properties: 3 g corn starch sample and 25 mL distilled water were added to the aluminum box of a rapid visco analyzer (RVA), stirred at 160 r / min, kept at 50 °C for 1 min, then heated to 95 °C at a rate of 4 °C / min, kept at 95 °C for 5 min, and then cooled to 50 °C at the same rate and kept for 5 min to form a starch paste and analyze the gelatinization properties of the sample.

[0072] Depend on Figure 2A It can be seen that the peak viscosity and final viscosity of comparative sample 1 are 2873 and 2834 cp, respectively. Compared with comparative sample 1, the peak viscosity of comparative samples 2-4 increases to 3405, 3686 and 3695 cp, respectively, and the final viscosity increases to 3388, 3632 and 3664 cp, respectively. There is no significant difference in viscosity between comparative samples 3 and 4. The peak viscosity and final viscosity of Example 1 are higher than all comparative samples, reaching 3834 and 3746 cp, respectively, indicating that the combination of multiple technologies in Example 1 can effectively improve the gelatinization properties of starch. In addition, compared with comparative sample 1, comparative samples 2-4 reduce the gelatinization temperature of starch from 73.45°C to 72.53, 70.85 and 70.72°C, respectively. Example 1 has the lowest starch gelatinization temperature (69.22°C), indicating that the starch crystalline structure is destroyed and the starch is more easily gelatinized. The improvement of gelatinization properties may also be related to indicators such as starch granule size, straight branch ratio, and damaged starch content.

[0073] (2) Determination of corn starch gel texture properties: The starch paste prepared by RVA was sealed and stored at 4°C for 12 h to form a gel, and the gel texture properties were analyzed using a TPA texture analyzer. Parameter settings: pre-test rate, test rate, and post-test rate were all 1 mm / s, the compression rate was 40%, the trigger force was 5 g, and a P / 0.5 probe was selected.

[0074] Depend on Figure 2B It can be seen that the gel hardness and elasticity of comparison sample 1 are 322.5g and 0.923 respectively. Compared with comparison sample 1, the gel hardness of comparison samples 2-4 increases to 356.5, 372.8 and 375.4g respectively, and the gel elasticity increases to 0.994, 1.098 and 1.094 respectively. The texture properties of Example 1 are further improved compared with all comparison samples, and its gel hardness and elasticity are increased to 389.7g and 1.134 respectively. This improvement is due to the synergistic effect of alkali, physical field and biological enzymes.

[0075] (3) Determination of rheological properties of corn starch: The gelatinized corn flour sample was refrigerated at 4°C overnight to form a gel. The gel was placed between the plates of the rheometer with a distance of 1 mm. The strain was set to 2%, the temperature was set to 25°C, and the frequency scanning range was 0.1-70 Hz. The changes in storage modulus (G') and loss modulus (G") with frequency were recorded.

[0076] The storage modulus (G') and loss modulus (G") of corn starch vary with angular frequency as shown in Figure 2C -D. G'( Figure 2C ) and G”( Figure 2D ) have similar changing trends. With the increase of frequency, both G' and G" increase, and G' is much larger than G", indicating that all corn starches exhibit typical weak gel viscoelastic behavior. The final G' and G" obtained by frequency scanning for comparison sample 1 are 1060 and 112Pa, respectively. Compared with comparison sample 1, the G' of comparison samples 2-4 increases to 1132, 1211 and 1223Pa, respectively, and G" increases to 124, 137 and 139Pa, respectively. In addition, Example 1 has higher G' and G" than all comparison samples, reaching 1280 and 145Pa, respectively, indicating that the corn starch in Example 1 has the strongest gel structure and viscoelasticity, and exhibits the best rheological properties. Different soaking processes will cause differences in the degree of damage and particle size distribution of corn starch particles, resulting in different strengths of the three-dimensional network structure formed when the starch molecules are heated, thereby affecting its viscoelasticity. Therefore, the corn starch prepared by the method of the present invention has better gelatinization properties, texture properties and rheological properties, and effectively improves the processing properties of starch.

[0077] Detection test (III)

[0078] (1) Determination of corn protein solubility: 100 mg corn protein was dissolved in 10 mL deionized water, and the protein solution was adjusted to pH 7.0 with 1 M NaOH / HCl solution. Centrifuged at 10,000 g for 15 min, 1 mL of the supernatant was added to 9 mL of buffer solution (50 mM EDTA and 8 M urea, pH 10.0), and the absorbance of the solution was measured at 280 nm and recorded as A1, while the absorbance of the suspension before centrifugation was recorded as A2.

[0079]

[0080] Changes in the solubility of zein Figure 3A As shown. Compared with control sample 1 (7.15%), the protein solubility of control samples 2-4 increased to 8.51%, 11.57% and 11.85%, respectively, and Example 1 had a higher protein solubility than all control samples, up to 14.81%. Physical field treatments such as alkaline cooking, ultrasound and high static pressure reduce the protein particle size, expose more hydrophilic groups, and make the protein structure more flexible, thereby improving its solubility. In addition, compound protease hydrolysis can make the protein structure more relaxed, change its surface hydrophilicity / hydrophobicity, and hydrolyze the protein into small polypeptides, which will also improve the protein solubility.

[0081] (2) Determination of corn protein digestibility: Corn protein was prepared into a 5 mg / mL solution, and the pH of the sample solution was adjusted to 2.0 with 1 M HCl, and then pepsin was added to a concentration of 0.5 mg / mL, and the mixture was digested at 37°C and 100 rpm under continuous shaking conditions for 1 h. After the gastric digestion, the pH of the sample solution was adjusted to 7.0 with 1 M NaOH, and then trypsin was added to a concentration of 0.5 mg / mL. The mixture was digested for another 1 h under the same conditions (37°C, 100 rpm continuous shaking), and the sample was placed in an ice bath to cool to terminate the intestinal digestion. Samples were collected at the end of gastric and intestinal digestion, respectively, and centrifuged at 10,000 g for 15 min. The supernatant obtained was stored at 4°C for further analysis.

[0082] Prepare OPA solution: First, dissolve 80 mg of OPA in 2 mL of methanol, then add 50 mL of 0.1 mol / L borax solution, 1 mg of sodium dodecyl sulfate (SDS), and 200 μL of β-mercaptoethanol. Finally, add distilled water to the mixture to bring the total volume to 100 mL. The entire operation process was completed under light-proof conditions. Take 0.4 mL of the protein solution to be tested and add it to 3 mL of OPA solution. After reacting for 2 minutes, measure its absorbance at 340 nm, and determine the FAA content according to the leucine standard curve. The formula for calculating protein hydrolysis degree and digestibility is as follows:

[0083]

[0084]

[0085]

[0086] Where: h is the number of peptide bonds broken during hydrolysis, h hot is the total number of peptide bonds (h hot A is the absorbance of the sample at 340 nm; M is the molecular weight of the protein (Da); d is the dilution factor; ε is the extinction coefficient at 340 nm (6000 mol -1 cm -1 ); c is the protein concentration (g / L). m1 is the protein content of the supernatant after in vitro digestion (mg); m2 is the total protein amount after in vitro digestion (mg).

[0087] Changes in free amino acid content of corn protein Figure 3B As shown. In the first 10 minutes of gastrointestinal digestion, the free amino acid content increased rapidly and then tended to be flat. Compared with comparative sample 1, the free amino acid content of comparative samples 2-4 increased significantly in both the gastric digestion stage and the intestinal digestion stage. The free amino acid content of gastric digesta increased from 1.26 mg / mL to 2.15, 2.32 and 2.90 mg / mL, respectively, and the free amino acid content of intestinal digesta increased from 2.49 mg / mL to 3.26, 3.52 and 4.25 mg / mL, respectively. Example 1 has a higher free amino acid content than all comparative samples, and its free amino acid content of gastric and intestinal digesta is as high as 4.11 and 5.31 mg / mL, respectively, indicating that the technical solution of Example 1 promotes the release of free amino acids during protein digestion.

[0088] The hydrolysis degree of corn protein varies as follows Figure 3C The trend of protein hydrolysis degree is similar to that of free amino acid content. The corn protein of Example 1 has the highest hydrolysis degree, and the hydrolysis degree of its gastric and intestinal digesta increases from 7.79% and 14.76% to 14.62% and 20.41%, respectively.

[0089] Digestibility of corn protein varies as Figure 3DAs shown. In the gastric digestion stage, the protein digestibility of comparison sample 1 was 10.86%, and the protein digestibility of comparison samples 2-4 and Example 1 was between 15.5% and 16.3%, all higher than that of comparison sample 1, but there was no significant difference between them. In the intestinal digestion stage, the protein digestibility of comparison samples 1-4 was 24.43%, 32.38%, 35.22% and 38.73%, respectively, and the protein digestibility of Example 1 reached the highest of 42.08%, indicating that the combined effects of vacuum low-temperature alkaline cooking, ultrasound, high static pressure and composite protease promoted the digestion and hydrolysis of corn protein. The synergistic effect of alkali, physical field and biological enzymes loosens the structure of corn protein and reduces the particle size, improves the solubility of protein, increases its contact area with pepsin and trypsin, makes the protein polypeptide chain more easily broken, shows a higher free amino acid content, protein hydrolysis degree and digestibility, and improves the nutritional value and digestibility of corn protein.

[0090] In summary, the method of the present invention improves the extraction rate of corn starch and protein, shortens the extraction time, improves the processing characteristics of corn starch such as gelatinization properties, texture properties and rheological properties, promotes the protein digestion behavior of corn protein such as solubility, free amino acid content, hydrolysis degree and digestibility, and provides technical support for the development and industrial application of high-quality corn starch or corn protein-based foods.

[0091] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for simultaneously extracting starch and protein, characterized in that: The method: (1) vacuum low-temperature alkalization cooking of corn kernels in a calcium hydroxide solution; (2) After cooking, ultrasonic treatment is performed first, followed by high static pressure treatment, and then soaking; (3) The soaked corn kernels are firstly coarsely ground to remove the germ, and then finely ground by a colloid mill to remove the fiber, and then a composite protease is added to the resulting slurry for enzymatic hydrolysis, and then the enzyme is boiled to inactivate the enzyme after enzymatic hydrolysis; (4) The corn slurry after enzymatic hydrolysis is finely ground in a ball mill, and the filtrate after filtering with filter cloth is allowed to stand for a certain period of time, and then centrifuged and washed with water to precipitate, and the lower white part and the upper yellow part are collected separately, and after freeze-drying, corn starch and corn protein are obtained respectively.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of corn kernels to water in the calcium hydroxide solution is 1:(1-3), and the mass of calcium hydroxide is 0.5-1.5% of the total mass of the corn kernels and the calcium hydroxide solution.

3. The method according to claim 1, characterized in that In step (1), the vacuum degree is 0.06-0.08 MPa, the cooking temperature is 50-70° C., and the cooking time is 10-20 min.

4. The method according to claim 1, characterized in that: In step (2), the ultrasonic power is 100-200 W, the time is 20-30 min, the high static pressure is 100-300 MPa, and the time is 10-20 min.

5. The method according to claim 1, characterized in that In step (2), the soaking temperature is 40-60° C. and the soaking time is 6-10 hours.

6. The method according to claim 1, characterized in that In step (3), the composite protease is composed of neutral protease and trypsin in a mass ratio of 1:1, the composite protease is 500-1500 U / g, the enzymatic hydrolysis pH is 6.5-8.5, the enzymatic hydrolysis temperature is 40-60° C., and the enzymatic hydrolysis time is 20-40 min.

7. The method according to claim 1, characterized in that The filtrate in step (4) is allowed to stand for 2-4 hours.

8. The corn starch obtained by the method described in any one of claims 1 to 7.

9. Zein obtained by the method according to any one of claims 1 to 7.

10. Application of the method according to any one of claims 1 to 7 in corn deep processing.

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