Method for preparing protein powder by extracting protein from walnut meal

Abstract

The invention provides a method for preparing protein powder by extracting protein from walnut meal. The method comprises the following steps: (1) crushing the walnut meal to obtain walnut meal powder; (2) mixing the walnut meal powder with water, stirring at 57-59 DEG C and 150-200RPM, adjusting the pH value to 10.5-11.5, performing ultrasonic-assisted treatment for 0.8-1.5 h with 250-350W and 15-25kHz, centrifuging at room temperature, taking a middle clear liquid layer, adjusting the pH value to 4.8-5.2, centrifuging, taking precipitate, adding a sodium hydroxide solution, adjusting the pH value to be neutral, and centrifuging and collecting the precipitate; and (3) carrying out vacuum freeze drying on the collected precipitate to obtain protein powder. According to the method, through systematic optimization of the whole technological process and operation conditions, the yield is remarkably increased on the premise that the product quality is not sacrificed, collaborative optimization of the yield and the quality is truly achieved, and the method is suitable for industrial application and popularization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of protein powder preparation, and particularly relates to a method for extracting protein from walnut meal to prepare protein powder. BACKGROUND

[0002] Walnut meal is a by-product of walnut oil processing, usually accounting for more than 50% of the dry weight of walnuts. The traditional utilization of walnut meal is mainly limited to feed or fertilizer, and the economic value is low. Walnut meal is rich in high-quality protein (content can reach 30%-50%), and its amino acid composition is comprehensive, containing all 18 amino acids required by the human body, among which the proportion of 8 essential amino acids is balanced. Walnut protein has good potential as a nutritional supplement and functional food ingredient in the food industry.

[0003] In recent years, with the growth of demand for plant protein and the deepening of the concept of sustainable development, the extraction of high-value protein powder from walnut meal has become a research hotspot. Existing walnut protein extraction methods mainly include solvent extraction, alkali extraction, enzyme extraction and reverse micelle extraction. Among them, solvent extraction is difficult to promote in the food industry due to food safety risks, and enzyme extraction and reverse micelle extraction are limited in their industrial application due to high cost. The main problem of alkali extraction method is that in the pursuit of high extraction rate, the natural structure, nutritional value and functional properties of protein are often sacrificed, that is, it is difficult to balance the yield and quality of the product. To solve this problem, ultrasonic-assisted alkali extraction technology emerged as the times require, in order to realize efficient and mild extraction by using its physical field effect, so as to reduce chemical damage. However, the industrial application of this improved route has not been as rapid as expected, and it is faced with problems such as scale-up effect and complex process parameter interaction mechanism, which makes it difficult to stably reproduce the extraction effect when the scale is expanded, and the synchronous improvement of protein product yield and functional properties has not been fully realized. Therefore, further optimization of ultrasonic-alkali extraction process is the key prerequisite for promoting its transition from laboratory to industrialization. SUMMARY

[0004] The purpose of the present application is to provide a method for extracting protein from walnut meal to prepare protein powder, which can effectively balance the yield and quality of protein powder.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is: A method for extracting protein from walnut meal to prepare protein powder, characterized in that it comprises the following steps: (1) grinding the walnut meal to obtain walnut meal powder; (2) the walnut meal powder is mixed with water in a ratio of 1 g: (38-45) mL, while maintaining stirring, the pH is adjusted to 10.5-11.5 at 57-59°C, and the mixture is treated with 250-350 W, 15-25 kHz ultrasonic assistance for 0.8-1.5 h, the obtained mixture is centrifuged at 3500-4500 r / min for 10-20 min at room temperature, the middle supernatant layer is taken, the pH of the middle supernatant layer is adjusted to 4.8-5.2, the mixture after acid adjustment is centrifuged at 3500-4500 r / min for 10-20 min, the precipitate is mixed with a sodium hydroxide solution with a pH of 7.8-8.5, a sodium hydroxide solution with a concentration of 0.08-0.12 mol / L is used to adjust the pH to neutral, and the mixture after neutral adjustment is centrifuged at 3500-4500 r / min for 10-20 min, and the precipitate is collected; (3) the precipitate finally collected in step (2) is freeze-dried under a vacuum degree of 0.1-0.2 mbar to obtain the protein powder.

[0006] In some embodiments, in step (1), the walnut meal is crushed and passed through a 30-50 mesh screen.

[0007] In some embodiments, in step (2), the neutral pH is 6.8-7.2.

[0008] In some embodiments, in step (2), the walnut meal powder is mixed with water in a ratio of 1 g: (38-42) mL under stirring at a stirring speed of 170-190 RPM, while maintaining stirring, the pH is adjusted to 10.8-11.2 at 57.5-58.5°C, and the mixture is treated with 280-320 W, 18-22 kHz ultrasonic assistance for 0.8-1.2 h, the obtained mixture is centrifuged at 3500-4500 r / min for 14-16 min at room temperature, the middle supernatant layer is taken, and the pH thereof is adjusted to 4.9-5.1, the mixture after acid adjustment is centrifuged at 3500-4500 r / min for 14-16 min, the precipitate is mixed with a sodium hydroxide solution with a pH of 7.8-8.2, a sodium hydroxide solution with a concentration of 0.08-0.12 mol / L is used to adjust the pH to neutral, and the mixture after neutral adjustment is centrifuged at 3500-4500 r / min for 14-16 min, and the precipitate is collected.

[0009] Further preferably, in step (2), the walnut meal powder is mixed with water at a ratio of 1g: (39-41) mL under stirring at a stirring speed of 170-190 RPM, while maintaining stirring, the pH is adjusted to 10.9-11.1 at 57.8-58.2°C, and the obtained mixture is subjected to ultrasonic-assisted treatment at 290-310 W, 19-21 kHz for 0.9-1.1 h, the obtained mixture is centrifuged at 3900-4100 r / min for 14-16 min at room temperature, the middle clear liquid layer is taken, the pH value of the middle clear liquid layer is adjusted to 4.9-5.1, the mixture after the pH adjustment is centrifuged at 3900-4100 r / min for 14-16 min, the precipitate is mixed with a sodium hydroxide solution with a pH value of 7.9-8.1, the pH value of the mixture is adjusted to neutral by using a sodium hydroxide solution with a concentration of 0.09-0.11 mol / L, and the mixture after the pH adjustment is centrifuged at 3900-4100 r / min for 14-16 min, and the precipitate is collected.

[0010] In some embodiments, in step (2), the pH is adjusted to 10.5-11.5 by using a sodium hydroxide solution, and the pH of the middle clear liquid layer is adjusted to 4.8-5.2 by using a hydrochloric acid solution.

[0011] In some specific and preferred embodiments, the concentrations of the hydrochloric acid solution and the sodium hydroxide solution are independently 0.8-1.2 mol / L.

[0012] In some embodiments, in step (3), the temperature conditions of the freeze-drying are as follows: first, -55--45°C is maintained for 8-12 h, then the temperature is raised to -25--15°C at a rate of 0.8-1.2°C / h and maintained for 8-12 h, and then the temperature is raised to 22-28°C at a rate of 1.5-2.5°C / h and maintained for 2-6 h.

[0013] Further preferably, in step (3), the temperature conditions of the freeze-drying are as follows: first, -52--48°C is maintained for 9-11 h, then the temperature is raised to -22--18°C at a rate of 0.9-1.1°C / h and maintained for 9-11 h, and then the temperature is raised to 24-26°C at a rate of 1.8-2.2°C / h and maintained for 3-5 h.

[0014] In some specific embodiments, the obtained freeze-dried product can be optionally sieved through a 80-150 mesh sieve at room temperature to obtain the protein powder product.

[0015] In some specific and preferred embodiments, the walnut meal has a crude protein content of 30%-50% and a water content of 11%-13%.

[0016] Thanks to the above technical solution, the present application has the following advantages compared with the prior art: The application can better balance the protein extraction rate, product yield and product quality through the synergistic effect of alkali extraction and ultrasonic auxiliary treatment, combined with the system optimization of the whole process and operation conditions. The obtained protein powder is natural light yellow without browning phenomenon, indicating that the structural integrity of the protein is well maintained during the processing, thereby ensuring a high digestibility. Compared with the traditional method, the application significantly improves the yield without sacrificing the product quality, truly realizes the synergistic optimization of yield and quality, has obvious advantages in comprehensive performance, and is more suitable for industrialization promotion and application. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The protein powder prepared in Example 1 is shown. DETAILED DESCRIPTION

[0018] The technical solutions and technical effects of the present application will be further illustrated below in combination with specific examples and comparative examples. The examples provided below are for illustrative purposes only and are not intended to limit the present application unless otherwise specified. Therefore, the present application should not be considered limited to the following examples, but should be understood to include any and all obvious variations as a result of the teachings provided herein.

[0019] It should be appreciated that modifications that do not materially affect the activity of various embodiments of the application can also be encompassed by the definition of the application provided herein. Therefore, the following examples are intended to illustrate the present application but not to limit the present application.

[0020] In the present application, unless otherwise specified, the operation methods involved in the examples and comparative examples are conventional methods in the art.

[0021] In the present application, unless otherwise specified, the materials, reagents and devices and equipment involved in the examples and comparative examples are commercially available products.

[0022] In the present application, unless otherwise specified, the water used in the examples and comparative examples meets the "Drinking Water Health Standards" (GB 5749-2022).

[0023] In the present application, room temperature refers to (20±5)℃.

[0024] In the present application, unless otherwise specified, "%" represents mass percentage (wt%).

[0025] In the present application, the walnut meal (also known as walnut residue) used for extracting protein is the waste part after walnut kernel oil is pressed, and the water content is (12±0.5)%. The total nitrogen content is determined according to the Kjeldahl method in "GB 5009.5-2016 Food Safety National Standards Determination of Protein in Food", and the crude protein content (%) = total nitrogen content (%) x conversion factor (6.25) is measured to be 46.18%.

[0026] In the present application, the protein extraction rate detection method of the following examples and comparative examples is as follows: the protein concentration of the intermediate supernatant layer is determined by using the Bradford method (with bovine serum albumin BSA as the standard protein), and the protein extraction rate (%) = (protein concentration of the intermediate supernatant layer x volume of the intermediate supernatant layer) / (mass of walnut meal powder x 46.18%) x 100%.

[0027] The protein powder product yield (recovery rate) (%) = mass of the protein powder product / (mass of the walnut meal powder x 46.18%) x 100%.

[0028] The shape of the protein powder product is mainly judged by observing its color. The ideal color is light yellow, indicating that the protein structure has not changed significantly, and the digestibility and amino acid (especially lysine) effectiveness are guaranteed. If the color is too deep (such as brown or brown), it indicates that the quality of the protein powder product is poor, browning occurs, the protein structure is denatured, which will lead to a decrease in digestibility and amino acid effectiveness. The deeper the color, the higher the degree of browning, and the poorer the quality of the protein powder product.

[0029] Example 1 The present embodiment provides a method for extracting protein from walnut meal to prepare protein powder, which is specifically as follows: (1) Pretreatment: the walnut meal is crushed and passed through a 40-mesh screen to obtain walnut meal powder.

[0030] (2) Ultrasonic extraction: in a temperature-controlled extractor, the walnut meal powder and water are fed in a ratio of 1:40 (g / mL), and are mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature is raised to (58±0.2)℃, and the pH value of the mixture is adjusted to 11±0.05 using a 1 mol / L sodium hydroxide solution, while being assisted by ultrasonic treatment at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture is centrifuged at 4000 r / min for 15 min to remove the bottom precipitate layer and a small amount of oil layer on top, and the intermediate supernatant layer is taken. At room temperature, the pH value of the intermediate supernatant layer is adjusted to 5±0.05 using a 1 mol / L HCL solution, while stirring at a stirring speed of 90 RPM. The acid-adjusted mixture is centrifuged at 4000 r / min for 15 min, and the precipitate is mixed with 1 times the volume of the precipitate of a 8±0.05 pH value sodium hydroxide solution for re-dissolution, and the pH value is adjusted to neutral (7±0.1) using a 0.1 mol / L sodium hydroxide solution. The neutral-adjusted mixture is centrifuged at 4000 r / min for 15 min, and the precipitate is taken.

[0031] (3) Freeze-drying: freeze-dry the precipitate collected in step (2) under a vacuum of 0.1-0.2 mbar, first at -50°C for 10 h, then at a temperature increase of 1°C / h to -20°C and maintain for 10 h, and then at a temperature increase of 2°C / h to 25°C and maintain for 4 h, and the obtained freeze-dried product is the protein powder product, which can be optionally sieved through a 100-mesh screen at room temperature.

[0032] The protein extraction rate in this example is 68.64%, and the yield of the protein powder product is >60%, and the protein powder product is uniform light yellow Figure 1 ), without browning, and has good quality.

[0033] Example 2: This example provides another method for extracting protein from walnut meal to prepare a protein powder, which is basically the same as Example 1, except that the ultrasonic-assisted treatment time in step (2) is extended to 1.5 h. The protein extraction rate in this example is 74.27%, and the protein powder product is uniform light yellow, without obvious color difference from the protein powder product of Example 1, without browning, and has good quality.

[0034] Comparative Example 1: This comparative example provides another method for extracting protein from walnut meal to prepare a protein powder, which is as follows: (1) Pretreatment: crush the walnut meal and pass it through a 40-mesh screen to obtain walnut meal powder.

[0035] (2) Ultrasonic extraction: in a temperature-controlled extractor, walnut meal powder and water are fed at a ratio of 1:40 (g / mL), and are mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature is raised to (65±0.2) °C, and the pH value of the mixture is adjusted to 10±0.05 using a 1 mol / L sodium hydroxide solution, while ultrasonic-assisted treatment is performed at 300 W and 20 kHz for 1.5 h. At room temperature, the treated mixture is centrifuged at 4000 r / min for 15 min to remove the bottom precipitate layer and a small amount of oil layer on top, and the middle clear liquid layer is taken. At room temperature, the pH value of the middle clear liquid layer is adjusted to 5±0.05 using a 1 mol / L HCL solution, while stirring is performed at a stirring speed of 90 RPM. The acid-adjusted mixture is centrifuged at 4000 r / min for 15 min, and the precipitate is mixed with 1-fold volume of a 8±0.05 pH value sodium hydroxide solution, and the pH value is adjusted to neutral (7±0.1) using a 0.1 mol / L sodium hydroxide solution. The neutral-adjusted mixture is centrifuged at 4000 r / min for 15 min, and the precipitate is taken.

[0036] (3) Freeze-drying: the final collected precipitate of step (2) is first kept at -50°C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed to -20°C at a rate of 1°C / h and maintained for 10 h, and then warmed to 25°C at a rate of 2°C / h and maintained for 4 h, and the obtained freeze-dried product is the protein powder product, which can be optionally sieved through a 100-mesh screen at room temperature.

[0037] The protein extraction rate in the present comparative example is 50.24%. The protein powder product is uniform light yellow, and has no obvious color difference from the protein powder product of Example 1.

[0038] Comparative Example 2: The present comparative example provides another method for extracting protein from walnut meal to prepare a protein powder, which is specifically as follows: (1) Pretreatment: the walnut meal is crushed and passed through a 40-mesh screen to obtain walnut meal powder.

[0039] (2) Ultrasonic extraction: in a temperature-controlled extractor, the walnut meal powder and water are fed at a ratio of 1:40 (g / mL), and are mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature is raised to (45±0.2) °C, and the pH value of the mixture is adjusted to 11±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while the mixture is treated with ultrasonic assistance at 300 W and 20 kHz for 1 h. The treated mixture is centrifuged at 4000 r / min for 15 min at room temperature, and the bottom precipitate layer and a small amount of oil layer on top are removed, and the middle clear liquid layer is taken. The pH value of the middle clear liquid layer is adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment is centrifuged at 4000 r / min for 15 min, and the precipitate is mixed with 1-fold volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value is adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization is centrifuged at 4000 r / min for 15 min, and the precipitate is taken.

[0040] (3) Freeze-drying: the final collected precipitate of step (2) is first kept at -50°C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed to -20°C at a rate of 1°C / h and maintained for 10 h, and then warmed to 25°C at a rate of 2°C / h and maintained for 4 h, and the obtained freeze-dried product is the protein powder product, which can be optionally sieved through a 100-mesh screen at room temperature.

[0041] The protein extraction rate in the present comparative example is 57.16%. The protein powder product is uniform light yellow, and has no obvious color difference from the protein powder product of Example 1.

[0042] Comparative Example 3: This comparative example provides another method for preparing protein powder from walnut meal by extracting protein, specifically as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40-mesh screen to obtain walnut meal powder.

[0043] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were added in a ratio of 1:30 (g / mL) and mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature was raised to (58±0.2) °C, and the pH of the mixture was adjusted to 10±0.05 using a 1 mol / L sodium hydroxide solution, while being assisted by ultrasonic treatment at 300 W and 20 kHz for 1.5 h. The treated mixture was centrifuged at 4000 r / min for 15 min at room temperature to remove the bottom precipitate layer and the small amount of oil layer on top, and the middle clear liquid layer was taken. At room temperature, the pH of the middle clear liquid layer was adjusted to 5±0.05 using a 1 mol / L HCL solution, while stirring at a stirring speed of 90 RPM. The acid-adjusted mixture was centrifuged at 4000 r / min for 15 min, and the precipitate was mixed with 1 times the volume of the precipitate of a pH 8±0.05 sodium hydroxide solution, and the pH was adjusted to neutral (7±0.1) using a 0.1 mol / L sodium hydroxide solution. The neutral-adjusted mixture was centrifuged at 4000 r / min for 15 min, and the precipitate was collected.

[0044] (3) Freeze-drying: The precipitate collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100-mesh screen at room temperature.

[0045] The protein extraction rate in this comparative example was 52.40%. The protein powder product was uniform light yellow, with no significant color difference from the protein powder product of Example 1.

[0046] Comparative Example 4: This comparative example provides another method for preparing protein powder from walnut meal by extracting protein, specifically as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40-mesh screen to obtain walnut meal powder.

[0047] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:30 (g / mL), and mixed under the stirring speed of 180 RPM. While maintaining the stirring speed of 180 RPM, the temperature was raised to (58±0.2) °C, and the pH value of the mixture was adjusted to 9±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and the top small amount of oil layer were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was mixed with 1 times the precipitate volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value was adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0048] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0049] The protein extraction rate in this comparative example was 47.42%. The protein powder product was uniform light yellow, and there was no obvious color difference with the protein powder product of Example 1.

[0050] Comparative Example 5: This comparative example provides another method for extracting protein from walnut meal to prepare protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain walnut meal powder.

[0051] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:35 (g / mL), and mixed under the stirring speed of 180 RPM. While maintaining the stirring speed of 180 RPM, the temperature was raised to (58±0.2) °C, and the pH value of the mixture was adjusted to 9±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1.5 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and the top small amount of oil layer were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was taken and mixed with 1 times the precipitate volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value was adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0052] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0053] The protein extraction rate in this comparative example was 50.02%. The protein powder product was uniform light yellow, and there was no obvious color difference with the protein powder product of Example 1.

[0054] Comparative Example 6: This comparative example provides another method for extracting protein from walnut meal to prepare protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain walnut meal powder.

[0055] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:35 (g / mL), and mixed under the stirring speed of 180 RPM. While maintaining the stirring speed of 180 RPM, the temperature was raised to (55±0.2) °C, and the pH value of the mixture was adjusted to 9±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and the top small amount of oil layer were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was mixed with 1 times the precipitate volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value was adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0056] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0057] The protein extraction rate in this comparative example was 50.23%. The protein powder product was uniform light yellow, and there was no obvious color difference with the protein powder product of Example 1.

[0058] Comparative Example 7: This comparative example provides another method for extracting protein from walnut meal to prepare protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain walnut meal powder.

[0059] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:40 (g / mL), and mixed under the stirring speed of 180 RPM. While maintaining the stirring speed of 180 RPM, the temperature was raised to (55±0.2) °C, and the pH value of the mixture was adjusted to 10±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1.5 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and the top small amount of oil layer were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was taken and mixed with 1 times the precipitate volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value was adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0060] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0061] The protein extraction rate in this comparative example was 56.73%. The protein powder product was uniform light yellow, and there was no obvious color difference with the protein powder product of Example 1.

[0062] Comparative Example 8: This comparative example provides another method for extracting protein from walnut meal to prepare protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain walnut meal powder.

[0063] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:30 (g / mL), and mixed under the stirring speed of 180 RPM. While maintaining the stirring speed of 180 RPM, the temperature was raised to (45±0.2) °C, and at this temperature, the pH value of the mixture was adjusted to 10±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and a small amount of oil layer on top were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was mixed with 1 times the precipitate volume of sodium hydroxide solution with a pH value of 8±0.05, and the pH value was adjusted to neutral (7±0.1) using a sodium hydroxide solution with a concentration of 0.1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0064] (3) Freeze-drying: The precipitate collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h. The obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0065] The protein extraction rate in this comparative example was 54.56%. The protein powder product was uniform light yellow, and there was no obvious color difference with the protein powder product of Example 1.

[0066] Comparative Example 9: This comparative example provides another method for extracting protein from walnut meal to prepare protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain walnut meal powder.

[0067] (2) Ultrasonic extraction: In a temperature-controlled extractor, the walnut meal powder and water were fed according to the solid-liquid ratio of 1:30 (g / mL), and mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature was raised to (60 ± 0.2) °C, and the pH value of the mixture was adjusted to 11 ± 0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and the top small amount of oil layer were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5 ± 0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The mixture after acid adjustment was centrifuged at 4000 r / min for 15 min, and the precipitate was taken and mixed with 1 times the volume of water for re-dissolution, and the pH value was adjusted to neutral (7 ± 0.1) using a sodium hydroxide solution with a concentration of 1 mol / L. The mixture after neutralization was centrifuged at 4000 r / min for 15 min, and the precipitate was taken.

[0068] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then warmed up to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then warmed up to 25 °C at a rate of 2 °C / h and maintained for 4 h, and the obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100 mesh screen at room temperature.

[0069] The protein extraction rate in this comparative example was 66.91%. The freeze-dried product was distributed in patches with uneven color, and the patch color was slightly darker than that of the protein powder product of Example 1, suggesting that a slight browning might have occurred locally. The main reason was that the pH value was too high in the local area when the neutralization was directly performed using a 1 mol / L sodium hydroxide solution in step (2), and the quality of the protein powder product in this comparative example was slightly worse.

[0070] Comparative Example 10: This comparative example provides another method for extracting protein from walnut meal to prepare a protein powder, which is as follows: (1) Pretreatment: The walnut meal was crushed and passed through a 40 mesh screen to obtain a walnut meal powder.

[0071] (2) Ultrasonic extraction: In a temperature-controlled extractor, walnut meal powder and water were added according to a solid-liquid ratio of 1:30 (g / mL), and mixed under stirring at a stirring speed of 180 RPM. While maintaining the stirring at 180 RPM, the temperature was raised to (58±0.2) °C, and the pH value of the mixture was adjusted to 11±0.05 using a sodium hydroxide solution with a concentration of 1 mol / L, while using ultrasonic assistance at 300 W and 20 kHz for 1 h. At room temperature, the treated mixture was centrifuged at 4000 r / min for 15 min, and the bottom precipitate layer and a small amount of oil layer on top were removed, and the middle clear liquid layer was taken. At room temperature, the pH value of the middle clear liquid layer was adjusted to 5±0.05 using a HCL solution with a concentration of 1 mol / L, while stirring at a stirring speed of 90 RPM. The acid-adjusted mixture was centrifuged at 4000 r / min for 15 min, and the precipitate was taken, mixed with 2 times the volume of water, and centrifuged at 4000 r / min for 10 min, and the precipitate was taken, mixed with 2 times the volume of water again, and centrifuged at 4000 r / min for 10 min, and the precipitate was taken.

[0072] (3) Freeze-drying: The precipitate finally collected in step (2) was first maintained at -50 °C for 10 h under a vacuum degree of 0.1-0.2 mbar, then raised to -20 °C at a rate of 1 °C / h and maintained for 10 h, and then raised to 25 °C at a rate of 2 °C / h and maintained for 4 h, and the obtained freeze-dried product was the protein powder product, which could be optionally sieved through a 100-mesh screen at room temperature.

[0073] The protein powder product of the present comparative example was light brown, browned, and of poor quality.

[0074] In summary, the processes for extracting protein from walnut meal and preparing protein powder provided in Examples 1 and 2 can better balance the protein extraction rate, product yield, and product quality. The obtained protein powder product is naturally light yellow in color and has no browning phenomenon, indicating that the structural integrity of the protein is well maintained during the processing, thereby ensuring a high digestion rate. In contrast, Examples 1-10 only adjust the local operating conditions, which leads to different degrees of decline in protein extraction rate or product quality, making it difficult to balance the yield and quality of the protein powder. Production verification shows that the preparation methods of Examples 1 and 2 can be applied to the preparation of a single batch of 2 tons of protein powder product, achieving a good balance in extraction rate, yield, and product quality.

[0075] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for extracting protein from walnut meal to prepare protein powder, characterized in that, It includes the following steps: (1) The walnut meal is crushed to obtain walnut meal powder; (2) Under stirring at a speed of 150-200 RPM, the walnut meal powder and water are mixed at a ratio of 1 g:(38-45) mL. While maintaining stirring, the pH is adjusted to 10.5-11.5 at 57-59°C, and the mixture is treated with ultrasonic waves at 250-350 W and 15-25 kHz for 0.8-1.5 h. The resulting mixture is then centrifuged at 3500-4500 r / min for 10-20 min at room temperature. Take the intermediate clear liquid layer and adjust its pH to 4.8-5.

2. Centrifuge the acidified mixture at 3500-4500 r / min for 10-20 min. Take the precipitate and mix it with a sodium hydroxide solution with a pH of 7.8-8.

5. Adjust the pH to neutral using a sodium hydroxide solution with a concentration of 0.08-0.12 mol / L. Centrifuge the neutralized mixture at 3500-4500 r / min for 10-20 min and collect the precipitate. (3) The precipitate collected in step (2) is freeze-dried at a vacuum of 0.1~0.2 mbar to obtain the protein powder.

2. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, In step (1), the walnut meal is crushed and passed through a 30-50 mesh sieve.

3. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, In step (2), the neutral pH value is 6.8 to 7.

2.

4. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, In step (2), the walnut meal powder and water are mixed at a ratio of 1g:(38~42)mL while stirring at a speed of 170~190RPM. While maintaining stirring, the pH is adjusted to 10.8~11.2 at 57.5~58.5℃, and the mixture is treated with ultrasonic waves at 280~320W and 18~22kHz for 0.8~1.2h. The resulting mixture is then centrifuged at 3500~4500r / min for 14 hours at room temperature. After 16 minutes, take the intermediate clear liquid layer and adjust its pH to 4.9-5.

1. Centrifuge the acidified mixture at 3500-4500 r / min for 14-16 minutes. Take the precipitate and mix it with a sodium hydroxide solution with a pH of 7.8-8.

2. Adjust the pH to neutral using a sodium hydroxide solution with a concentration of 0.08-0.12 mol / L. Centrifuge the neutralized mixture at 3500-4500 r / min for 14-16 minutes and collect the precipitate.

5. The method for preparing protein powder from walnut meal according to claim 4, characterized in that, In step (2), the walnut meal powder and water are mixed at a ratio of 1g:(39~41)mL while stirring at a speed of 170~190RPM. While maintaining stirring, the pH is adjusted to 10.9~11.1 at 57.8~58.2℃, and the mixture is treated with ultrasonic waves at 290~310W, 19~21kHz for 0.9~1.1h. The resulting mixture is then centrifuged at 3900~4100r / min for 14 hours at room temperature. After 16 minutes, take the intermediate clear liquid layer and adjust its pH to 4.9-5.

1. Centrifuge the acidified mixture at 3900-4100 r / min for 14-16 minutes. Take the precipitate and mix it with a sodium hydroxide solution with a pH of 7.9-8.

1. Adjust the pH to neutral using a sodium hydroxide solution with a concentration of 0.09-0.11 mol / L. Centrifuge the neutralized mixture at 3900-4100 r / min for 14-16 minutes and collect the precipitate.

6. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, In step (2), the pH is adjusted to 10.5-11.5 using sodium hydroxide solution, and the pH of the intermediate clear liquid layer is adjusted to 4.8-5.2 using hydrochloric acid solution.

7. The method for preparing protein powder from walnut meal according to claim 6, characterized in that, The concentrations of the hydrochloric acid solution and the sodium hydroxide solution are independently 0.8~1.2 mol / L.

8. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, In step (3), the temperature conditions for freeze drying are as follows: first, maintain the temperature at -55~-45℃ for 8~12h, then increase the temperature at 0.8~1.2℃ / h to -25~-15℃ and maintain it for 8~12h, then increase the temperature at 1.5~2.5℃ / h to 22~28℃ and maintain it for 2~6h.

9. The method for preparing protein powder from walnut meal according to claim 8, characterized in that, In step (3), the temperature conditions for freeze drying are as follows: first, maintain the temperature at -52 to -48℃ for 9 to 11 hours, then increase the temperature at 0.9 to 1.1℃ / h to -22 to -18℃ and maintain it for 9 to 11 hours, and then increase the temperature at 1.8 to 2.2℃ / h to 24 to 26℃ and maintain it for 3 to 5 hours.

10. The method for preparing protein powder from walnut meal according to claim 1, characterized in that, At room temperature, the obtained freeze-dried product can be selectively passed through an 80-150 mesh sieve to obtain the protein powder product.

Images