Method for improving solubility of quinoa protein

Abstract

The invention discloses a method for improving the solubility of quinoa protein. The method comprises the following steps: (1) degreasing chenopodium quinoa seeds, and sequentially carrying out alkali dissolution, acid precipitation and water washing to obtain chenopodium quinoa protein; (2) mixing the quinoa protein and an acid solution, heating in a water bath, cooling to room temperature, adding alkali to adjust the pH value to 4.5, and centrifuging to obtain acidolysis quinoa protein; and (3) mixing the acidolyzed quinoa protein with water, and washing with water to remove soluble salt in the acidolyzed quinoa protein. By adopting the method, the solubility of the chenopodium quinoa protein can be greatly improved, the operation is simple, the cost is low, and specifically, the solubility of the chenopodium quinoa protein is improved to 75%.

Description

Technical Field

[0001] The invention belongs to the technical field of plant proteins, and particularly relates to a method for improving the solubility of quinoa protein. Background Art

[0002] The long-established eating habits have determined the preference of Chinese consumers for meat products. However, due to the large population base in my country, the production capacity of meat products does not match the consumption scale. In addition to increasing the direct production capacity of meat products, we can also find substitutes to alleviate the contradiction between supply and demand. In recent years, plant-based foods have entered the public eye. They are based on plant protein and are prepared through certain technical means. Compared with red meat, they are rich in protein, lower in cholesterol, and easy to digest, which meets the needs of consumers for healthy diets.

[0003] One of the main raw materials of plant-based foods, plant protein, has a much lower impact on the environment than animal protein, but the quality of plant protein is often lower than that of animal protein, and plant protein often coexists with starch, dietary fiber, polysaccharides, phytic acid, etc. Some of these factors will also affect protein digestion and the body's absorption of minerals such as calcium and magnesium. At present, soy protein and pea protein are relatively low in price and have good emulsification, gelation, water retention and fat binding properties. They are widely used in commercially available plant-based foods. However, soy protein has anti-nutritional factors and potential allergies, and soy protein brings many food safety problems due to genetically modified issues; pea protein has weak gelation ability, and the prepared plant-based food has a softer taste and poorer elasticity. Therefore, researchers began to pay attention to new plant protein resources. Although it has been reported that quinoa protein has a better essential amino acid content than soy protein, its structural potential and application potential have not yet been clarified.

[0004] Quinoa is an annual herbaceous flowering plant that has been cultivated in South America for more than 7,000 years. Since 2008, my country has begun to cultivate quinoa on a large scale, and the current planting area has reached 3333hm 2 Among them, Shanxi Province is the first province in the country to carry out large-scale quinoa cultivation, with a quinoa planting area of ​​about 1,500 hm 2 Quinoa has a higher nutritional profile than most cereals due to its higher content of essential amino acids, especially lysine, tryptophan and cysteine, vitamins (vitamin E, B, C), and minerals such as calcium, iron, manganese, magnesium, copper and potassium.

[0005] The protein content of quinoa seeds varies from 12% to 23% depending on the variety. Although quinoa proteins have high nutritional value due to the high quality of amino acids, their use as food ingredients depends largely on their functional properties. The solubility of quinoa protein in water is its most basic functional property. Good solubility is the prerequisite for studying other functional properties, and good functional properties are the prerequisite for the development and utilization of proteins. However, the quinoa protein obtained by alkali dissolution and acid precipitation has poor solubility, and only about 40% of the protein components are soluble in water. The existing technology uses enzymatic hydrolysis, ultrasound and other treatments to improve the solubility of quinoa protein, but the reagents and equipment used in enzymatic hydrolysis, ultrasound and other treatments are all expensive. Therefore, how to improve the solubility of quinoa protein is an important issue currently faced. Summary of the invention

[0006] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a method for improving the solubility of quinoa protein. The method of the present application can greatly improve the solubility of quinoa protein, and the operation is simple and the cost is low. Specifically, the solubility of quinoa protein is increased to 75%.

[0007] In one aspect of the present invention, the present invention provides a method for improving the solubility of quinoa protein. According to an embodiment of the present invention, the method comprises:

[0008] (1) defatting quinoa seeds, then performing alkali dissolution, acid precipitation and water washing in sequence to obtain quinoa protein;

[0009] (2) mixing the quinoa protein and the acid solution, heating in a water bath, cooling to room temperature, adding alkali to adjust the pH to 4.5, and centrifuging to obtain acid-hydrolyzed quinoa protein;

[0010] (3) Mixing the acid-hydrolyzed quinoa protein with water and washing the mixture with water to remove soluble salts in the acid-hydrolyzed quinoa protein.

[0011] According to the method for improving the solubility of quinoa protein of the present invention, quinoa seeds are first defatted and then subjected to alkali dissolution, acid precipitation and water washing in sequence to obtain quinoa protein, and then the obtained quinoa protein is mixed with an acid solution and heated in a water bath, and then cooled to room temperature, and then the pH is adjusted to 4.5 and centrifuged to obtain acid-hydrolyzed quinoa protein. By mixing the acid-hydrolyzed quinoa protein and the acid solution and heating in a water bath, the structure of the protein can be deamidated, and covalent bonds such as peptide bonds and disulfide bonds within and between protein molecules can be broken and non-covalent bonds such as hydrogen bonds can be distorted. Specifically, deamidation usually occurs at asparagine and glutamine in the protein. On the amide residue, the amide side group is replaced by a carboxyl group, forming and breaking the intramolecular cyclic imide intermediate, resulting in the release of ammonia, thereby changing the internal structure of the protein molecule, and therefore the change in the internal structure of the protein molecule and the breaking or distortion of the chemical bonds within and between the protein molecule, in addition, protein acid hydrolysis causes the rupture of some peptide bonds to form polypeptides, which can self-assemble under certain conditions to form new aggregates with higher solubility, effectively improving the solubility of the protein, and finally mixing the quinoa protein after acid hydrolysis with water for washing, thereby removing the soluble salts in the quinoa protein after acid hydrolysis, avoiding the influence of soluble salts on the solubility of the protein. Thus, the solubility of quinoa protein can be greatly improved using the method of the present application, and it is simple to operate and low in cost, and specifically, the solubility of quinoa protein is increased to 75%.

[0012] In addition, the method for improving the solubility of quinoa protein according to the above embodiment of the present invention may also have the following technical features:

[0013] In some embodiments of the present invention, in step (1), the quinoa seed defatting comprises: drying the quinoa seeds and grinding them into quinoa powder, and then mixing with an organic solvent for defatting. In this way, the quinoa seeds can be defatted.

[0014] In some embodiments of the present invention, in step (1), the drying temperature is 35-45°C.

[0015] In some embodiments of the present invention, in step (1), the water activity of the quinoa seeds after drying is 8.5%-10.5%.

[0016] In some embodiments of the present invention, in step (1), the mass ratio of the quinoa powder to the organic solvent is 1:(2.5-5). Thus, the quinoa seeds can be defatted.

[0017] In some embodiments of the present invention, in step (1), the alkali dissolution and acid precipitation comprises: mixing defatted quinoa seed powder with water, adding alkali, centrifuging and collecting the supernatant, and then mixing the supernatant with acid and centrifuging and collecting the precipitate. In this way, quinoa protein can be obtained.

[0018] In some embodiments of the present invention, in step (1), the mass ratio of the defatted quinoa seed powder to the water is 1:(7-13).

[0019] In some embodiments of the present invention, in step (1), the process of adding alkali comprises: adding 1 mol / L-12 mol / L NaOH solution to adjust and maintain the pH value between 8.5-9.5 for 60 min-120 min.

[0020] In some embodiments of the present invention, in step (1), the concentration of the acid is 1 mol / L-12 mol / L, and the acid adjusts the pH of the supernatant to 4.4-4.6.

[0021] In some embodiments of the present invention, in step (2), the mass ratio of the quinoa protein to the acid in the acid solution is 1g: (0.0033mol-0.0167mol). Thus, the solubility of the quinoa protein can be improved.

[0022] In some embodiments of the present invention, in step (2), the concentration of the acid solution is 2 mol / L-10 mol / L, thereby improving the solubility of quinoa protein.

[0023] In some embodiments of the present invention, in step (2), the acid of the acid solution includes at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

[0024] In some embodiments of the present invention, in step (2), the water bath heating temperature is 85°C-95°C, the time is 1.5h-8h, and the shaking rate is 100rpm-120rpm. Thus, the solubility of quinoa protein can be improved.

[0025] In some embodiments of the present invention, in step (2), the concentration of the base is 1 mol / L-10 mol / L.

[0026] In some embodiments of the present invention, in step (2), the base includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

[0027] In some embodiments of the present invention, in step (3), the mass ratio of the acid-hydrolyzed quinoa protein to the water is 1:(2-5). Thus, the soluble salts in the acid-hydrolyzed quinoa protein can be removed.

[0028] In some embodiments of the present invention, the soluble salt content in the acid-hydrolyzed quinoa protein after the water washing is not higher than 10 mmol / L, thereby reducing the effect of soluble salt on the solubility of quinoa protein.

[0029] In some embodiments of the present invention, in step (3), the mixing includes mixing by ultrasound or mixing by shearing.

[0030] In some embodiments of the present invention, the mixing and shearing has a rotation speed of 8000 r / min-12000 r / min and a time of 2 min-5 min, thereby removing soluble salts in the quinoa protein after acid hydrolysis.

[0031] In some embodiments of the present invention, the frequency of the mixed ultrasound is 20 khz-30 khz, and the time is 5 min-15 min. Thus, the soluble salt in the quinoa protein after acid hydrolysis can be removed.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 is an electron microscope image of quinoa protein in solution before acid hydrolysis in an embodiment of the present invention;

[0035] Figure 2 is an electron micrograph of quinoa protein prepared in Example 2 of the present invention in a solution;

[0036] Figure 3 is an electron micrograph of quinoa protein prepared in Example 3 of the present invention in a solution;

[0037] Figure 4 This is an electron microscope image of the quinoa protein prepared in Example 5 of the present invention in solution. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described in detail below, which are intended to explain the present invention but should not be construed as limiting the present invention.

[0039] In one aspect of the present invention, the present invention provides a method for improving the solubility of quinoa protein. According to an embodiment of the present invention, the method comprises:

[0040] S100: After degreasing, quinoa seeds are dissolved in alkali, acid precipitated and washed with water.

[0041] In this step, the quinoa seeds are washed and dried at a temperature of 35-45° C. to a water activity of 8.5%-10.5%, and then ground and sieved. The sieved quinoa seed powder is mixed with an organic solvent at a mass ratio of 1: (2.5-5), shaken in a shaker at 28-33° C. and 180-250 r / min for 1-1.5 hours, filtered, and defatted 2-4 times, and dried to obtain defatted quinoa seed powder; the defatted quinoa seed powder is mixed with water at a mass ratio of 1: (7-13), 1 mol / L-12 mol / L NaOH solution is added to adjust and maintain the pH between 8.5 and 9.5 for 60 min-120 min, and then the mixed liquid is heated at room temperature at 8000-100 00rpm for 13-17min, pass the supernatant through a 150-250 mesh nylon cloth to collect the supernatant, repeat the centrifugal filtration 2-4 times to collect the supernatant; adjust the pH of the obtained supernatant to between 4.4 and 4.6 with 1mol / L-12mol / L hydrochloric acid, centrifuge at 8000-10000rpm for 13-18min at room temperature, collect the protein precipitate, and then wash the protein precipitate 2-4 times with deionized water, wherein the mass ratio of the protein precipitate to water in each washing is 1:(2-5), and shear the protein precipitate with a shearing machine at 8000rpm-12000rpm for 2-5min, and finally shear the precipitate again to adjust the solution to neutral, freeze-dry, and obtain quinoa protein.

[0042] S200: Mix quinoa protein and acid solution, heat in a water bath, cool to room temperature, add alkali to adjust pH to 4.5, and centrifuge

[0043] In this step, the quinoa protein obtained in S100 and the acid solution are mixed and heated in a water bath, then cooled to room temperature, and then 1 mol / L-10 mol / L of alkali is added to adjust the pH to 4.5 and then centrifuged to obtain a quinoa protein precipitate after acid hydrolysis. Figure 1Before quinoa protein is mixed with an acid solution, a single quinoa protein exists as an aggregate in the solution as a sphere with a radius of 10 nm. By mixing quinoa protein and an acid solution and heating them in a water bath, the structure of the protein can be deamidated, and covalent bonds such as peptide bonds and disulfide bonds within and between protein molecules can be broken and non-covalent bonds such as hydrogen bonds can be distorted. Specifically, deamidation usually occurs on asparagine and glutamine residues, and the amide side group is replaced by a carboxyl group to form and break an intramolecular cyclic imide intermediate, resulting in the release of ammonia, thereby changing the internal structure of the protein molecule. Because of the change in the internal structure of the protein molecule and the breaking or distortion of the chemical bonds within and between the protein molecules, in addition, the acid hydrolysis of the protein breaks some peptide bonds to form polypeptides. Under certain conditions, these polypeptides can self-assemble to form new aggregates with higher solubility, so the solubility of the protein is effectively improved. It should be noted that the above-mentioned acids and bases are commonly used reagents in the art, and those skilled in the art can select specific types according to actual conditions. For example, the acid includes at least one of hydrochloric acid, sulfuric acid and phosphoric acid; the base includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

[0044] According to an embodiment of the present invention, the mass ratio of quinoa protein to the amount of acid in the acid solution is 1g: (0.0033mol-0.0167mol). The inventor found that if the mass ratio of quinoa protein to the amount of acid in the acid solution is too small, quinoa protein is not easy to undergo acid hydrolysis, and the solubility of quinoa protein is very low; if the mass ratio of quinoa protein to the amount of acid in the acid solution is too large, the hydrolyzed solution will show obvious color changes, that is, the solution is yellow-brown. In this process, it is mainly because the protein is decomposed into small molecular compounds, and its amino group begins to react with sugar carbonyl, which eventually causes the protein to lose many functional properties, such as the stability of the interface, which is very unfavorable for later applications. Thus, the mass ratio of quinoa protein in the present application to the amount of acid in the acid solution is 1g: (0.0033mol-0.0167mol), which is conducive to the improvement of protein solubility without producing obvious color changes. Further, the concentration of the acid solution is 2mol / L-10mol / L, which is conducive to improving the solubility of quinoa protein.

[0045] According to an embodiment of the present invention, the temperature of the water bath heating is 85°C-95°C, the time is 1.5h-8h, and the rate of oscillation is 100rpm-120rpm. The inventors found that if the water bath heating time is too short, the quinoa protein will be mainly aggregated and precipitated under the action of high temperature, and the quinoa protein solubility is low; if the water bath heating time is too long, the solution will show obvious color changes. If the temperature of the water bath heating is small, the solubility of the quinoa protein will be improved less. Therefore, the present application adopts a water bath heating condition with a temperature of 85°C-95°C, a time of 1.5h-8h, and an oscillation rate of 100rpm-120rpm, which can improve the solubility of quinoa protein.

[0046] S300: Mix the acid-hydrolyzed quinoa protein with water for washing

[0047] In this step, the mass ratio of the acid-hydrolyzed quinoa protein obtained in S200 to water is 1: (2-5) and mixed, ultrasonic or sheared, and washed with water for 1-2 times to remove the soluble salts in the acid-hydrolyzed quinoa protein and avoid the influence of soluble salts on the solubility of the protein. Specifically, the soluble salt content in the acid-hydrolyzed quinoa protein after washing is not higher than 10mmol / L, and finally the quinoa protein after acid hydrolysis of the washed quinoa is freeze-dried for standby use. It should be noted that the mixing and ultrasonic or shearing is to allow the acid-hydrolyzed quinoa protein to be fully dispersed and to remove the soluble salts in the acid-hydrolyzed quinoa protein as much as possible, such as the mixing and shearing speed 8000r / min-12000r / min, time 2min-5min; the frequency of the mixed ultrasound is 20khz-30khz, and the time is 5min-15min; by adopting the above-mentioned ultrasonic or shearing conditions, the soluble salts in the acid-hydrolyzed quinoa protein are removed as much as possible.

[0048] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0049] Example 1

[0050] The quinoa seeds were washed to remove saponins, dried at 40°C to a water activity of 9.5%, then ground and sieved through a 60-mesh sieve. In a fume hood, quinoa powder and n-hexane were mixed at a mass ratio of 1:3, shaken in a shaker at 30°C and 220r / min for 1h, filtered, and degreased three times. The defatted powder was placed in a fume hood overnight for 12h to remove the residual n-hexane. The defatted quinoa powder was added to water at a mass ratio of 1:10, and the pH was adjusted and maintained at 9.0 with a 6mol / L NaOH solution for 90min. The feed solution was centrifuged at room temperature at 10000r / min for 15min, and the supernatant was passed through a 200-mesh nylon cloth to collect the supernatant. The supernatant was centrifuged and filtered twice to collect the supernatant. The pH of the supernatant was adjusted to 4.5 with 6mol / L hydrochloric acid, centrifuged at 10000r / min for 15min at room temperature, and the precipitate was collected. The precipitate was washed three times with deionized water to remove soluble salts, with a precipitate: water ratio of 1:3, and the precipitate was sheared for 3 minutes with a shearing machine at 10,000 r / min to make the precipitate uniformly dispersed in the water. The above precipitate was sheared again at 10,000 r / min for 3 minutes, with a precipitate: water ratio of 1:1.5, and the pH was adjusted and maintained at 7.0 with a 1 mol / L NaOH solution and stabilized for 30 minutes, and lyophilized to obtain quinoa protein.

[0051] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 2mol / L HCl solution, at this time, protein: acid = 1g:0.00334mol, put it in a shaking water bath, bathe it at 90℃ for 5h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 2mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0052] Add 20 ml of deionized water to the above-mentioned acid-hydrolyzed quinoa protein (the mass ratio of acid-hydrolyzed quinoa protein to water is 1g:4g), shear the acid-hydrolyzed quinoa protein with a shearing machine at 10000r / min for 3 minutes to fully disperse the acid-hydrolyzed quinoa protein in water, repeat water washing 3 times, and then freeze-dry to obtain quinoa protein powder.

[0053] Take 10 ml of deionized water, add 0.1 g of the quinoa protein powder directly, adjust the pH to 7, stir magnetically to dissolve for 2 hours, centrifuge at 10000 r / min for 15 minutes at room temperature, determine the protein content of the supernatant by Bradford method, and calculate the protein solubility. The measured protein solubility is 60.2%.

[0054] Example 2

[0055] The main differences between Example 2 and Example 1 are:

[0056] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 90℃ for 5h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0057] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 2 is 66.8%.

[0058] The electron microscope image of the quinoa protein prepared in Example 2 in the solution is as follows Figure 2 As shown, from Figure 2 It can be seen that the size of protein aggregates gradually decreases, and the components after acid hydrolysis form linear aggregates.

[0059] Example 3

[0060] The main differences between Example 3 and Example 1 are:

[0061] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 10mol / L HCl solution, at this time, protein: acid = 1g: 0.01667mol, put it in a shaking water bath, bathe it at 90℃ for 5h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 10mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0062] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 3 is 70.4%.

[0063] The electron microscopic image of the quinoa protein prepared in Example 3 in solution is as follows Figure 3 As shown, from Figure 3 It can be seen that as the amount of acid added increases, the size of the protein aggregates further decreases, the components formed after acid hydrolysis are smaller, and the overall dispersion becomes more uniform as the heating time increases.

[0064] Example 4

[0065] The main differences between Example 4 and Example 1 are:

[0066] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 90℃ for 1.5h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0067] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 4 is 58.8%.

[0068] Example 5

[0069] The main differences between Example 5 and Example 1 are:

[0070] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 90℃ for 8h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0071] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 5 is 71.7%.

[0072] The electron microscopic image of the quinoa protein prepared in Example 5 in solution is as follows Figure 4 As shown, compared with the electron micrograph of the quinoa protein prepared in Example 2, Figure 4 It can be seen that the protein in Example 5 is further reduced and the linear component is further increased, indicating that the solubility of quinoa protein is improved with the extension of the water bath time.

[0073] Example 6

[0074] The main differences between Example 6 and Example 1 are:

[0075] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 85℃ for 8h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0076] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 6 is 68.3%.

[0077] Example 7

[0078] The main differences between Example 7 and Example 1 are:

[0079] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 95℃ for 8h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0080] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 7 is 74.2%.

[0081] Example 8

[0082] The main differences between Example 8 and Example 1 are:

[0083] At room temperature, take 1g quinoa protein and dissolve it in 19.667ml deionized water, then add 0.333ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.002mol, put it in a shaking water bath, bathe it at 90℃ for 8h, and set the shaking rate to 120rpm / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000rpm, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0084] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 8 reaches 20.4%.

[0085] Example 9

[0086] The main differences between Example 9 and Example 1 are:

[0087] At room temperature, take 1g quinoa protein and dissolve it in 18.333ml deionized water, then add 1.667ml of 6mol / L HCl solution, at this time, protein: acid = 1g:0.01mol, put it in a shaking water bath, bathe it at 90℃ for 1h, and set the shaking rate to 120r / min. Take it out and cool it in ice water, then adjust the pH to 4.5 with 6mol / L sodium hydroxide solution, centrifuge it at room temperature, the centrifugal speed is 10000r / min, the centrifugal time is 15min, collect the precipitate, and obtain the quinoa protein after acid hydrolysis.

[0088] The test method of protein solubility is the same as that of Example 1. The protein solubility measured in Example 9 is 35.8%.

[0089] Comparative Example 1

[0090] Quinoa bioactive protein hydrolysate produced by pancreatin enzyme-functional and antioxidant properties (Daliri, H., et al., LWT, 2021.150:p.111853.)

[0091] In the article, for the quinoa protein obtained by alkali dissolution and acid precipitation, pancreatic enzyme (2.5%, w / w, enzyme / protein) was added to a 5% (w / v) protein solution, and enzymatic hydrolysis was carried out at 40°C, 200rpm for 4 hours. After the enzymatic hydrolysis was completed, the reaction was terminated at 95°C for 15 minutes, cooled to room temperature, freeze-dried, and re-dissolved at pH 7. The solubility of quinoa protein increased from 12.6% to 32.7%.

[0092] Comparative Example 2

[0093] Impact of high-pressure homogenization on physico-chemical,structural,and rheological properties of quinoa protein isolates.(Luo,L.,etal.,Food Structure,2022.32:p.100265.)

[0094] In the article, for the quinoa protein obtained by alkali dissolution and acid precipitation, a 1% (w / v) protein solution was prepared and the pH was adjusted to 7. A 20kHz ultrasonic instrument was used to sonicate for 5min / 15min in the 30s on / 30s off mode. During the entire ultrasonic treatment process, the glass bottle containing the sample was kept in a water ice bath to keep the temperature below 35°C. After freeze-drying and re-dissolving at pH 7, the solubility of quinoa protein increased from 14.7% to 45%.

[0095] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0096] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for improving the solubility of quinoa protein, characterized in that: include: (1) defatting quinoa seeds, then performing alkali dissolution, acid precipitation and water washing in sequence to obtain quinoa protein; (2) mixing the quinoa protein and the acid solution, heating in a water bath, cooling to room temperature, adding alkali to adjust the pH to 4.5, and centrifuging to obtain acid-hydrolyzed quinoa protein; (3) Mixing the acid-hydrolyzed quinoa protein with water and washing the mixture with water to remove soluble salts in the acid-hydrolyzed quinoa protein.

2. The method according to claim 1, characterized in that In step (1), the quinoa seed defatting comprises: drying the quinoa seeds and grinding them into quinoa powder, and then mixing with an organic solvent for defatting; Optionally, the drying temperature is 35-45°C; Optionally, the water activity of the quinoa seeds after drying is 8.5%-10.5%; Optionally, the mass ratio of the quinoa powder to the organic solvent is 1:(2.5-5).

3. The method according to claim 1, characterized in that In step (1), the alkali dissolution and acid precipitation comprises: The defatted quinoa seed powder is mixed with water, alkali is added, and the supernatant is collected by centrifugation. The supernatant is then mixed with acid, and the precipitate is collected by centrifugation.

4. The method according to claim 3, characterized in that The mass ratio of the defatted quinoa seed powder to the water is 1:(7-13); Optionally, the process of adding alkali includes: adding 1 mol / L-12 mol / L NaOH solution to adjust and maintain the pH between 8.5 and 9.5 for 60 min to 120 min; Optionally, the concentration of the acid is 1 mol / L-12 mol / L, and the acid adjusts the pH of the supernatant to 4.4-4.

6.

5. The method according to claim 1, characterized in that In step (2), the mass ratio of the quinoa protein to the acid in the acid solution is 1g: (0.0033mol-0.0167mol).

6. The method according to claim 1 or 4, characterized in that: In step (2), the concentration of the acid solution is 2 mol / L-10 mol / L; Optionally, in step (2), the acid in the acid solution includes at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

7. The method according to claim 1, characterized in that In step (2), the water bath heating temperature is 85°C-95°C, the time is 1.5h-8h, and the shaking rate is 100rpm-120rpm.

8. The method according to claim 1, characterized in that In step (2), the concentration of the base is 1 mol / L-10 mol / L; Optionally, the base includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

9. The method according to claim 1, characterized in that: In step (3), the mass ratio of the acid-hydrolyzed quinoa protein to the water is 1:(2-5); Optionally, the soluble salt content in the acid-hydrolyzed quinoa protein after the water washing is not higher than 10 mmol / L.

10. The method according to claim 1, characterized in that In step (3), the mixing includes mixing by ultrasound or mixing by shearing; Optionally, the mixing and shearing has a rotation speed of 8000 r / min-12000 r / min and a time of 2 min-5 min; Optionally, the frequency of the mixed ultrasound is 20 khz-30 khz, and the time is 5 min-15 min.

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