Walnut concentrated protein powder

Abstract

The invention provides walnut concentrated protein powder. The walnut concentrated protein powder is prepared by adopting the following method: (1) squeezing walnut kernels with seed coats at low temperature to prepare oil; (2) crushing the walnut cake meal, and degreasing through a subcritical extraction technology, so that the residual oil rate of the cake meal is reduced to 1-3%; (3) preliminarily removing seed coats in the walnut cake meal; and 4) finely separating the seed coat fragments from the walnut concentrated protein powder. The method provided by the invention adopts a normal-temperature dry method for preparation, realizes efficient and sufficient separation of walnut kernel seed coats and proteins in a powder state, obtains the walnut concentrated protein powder with the protein content of more than 70%, has the advantages of high efficiency, no pollution, water saving, energy saving and the like, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of agriculture and relates to an improved walnut protein powder, in particular to a concentrated walnut protein powder. Background Art

[0002] Walnut deep processing plays a vital role in the high-quality development of the walnut industry. Walnut protein accounts for 15%-20% of walnut kernels and is rich in 18 kinds of amino acids, including 8 essential amino acids for the human body. Its lysine to arginine ratio is low, and it is a high-quality protein. Walnut protein powder is mostly separated from the cake after walnut oil production, and the protein content accounts for about 30%-50% of the cake.

[0003] In actual production, oil-making technologies such as screw pressing and organic solvent extraction are prone to denaturation of protein or residual organic solvents in the cake, which affects the utilization of protein and reduces the utilization rate of walnut oil byproducts. Oil-making technologies such as hydraulic cold pressing can obtain high-quality walnut oil while further utilizing the byproduct walnut cake to develop products such as walnut defatted powder. However, the prerequisite is that the walnut kernels are first de-coated. This is because the presence of walnut kernel seed coat polyphenols will bring three adverse effects: (1) the oxidative browning of seed coat polyphenols makes the walnut cake brown, affecting the appearance quality of walnut defatted powder; (2) seed coat polyphenols can covalently bind to proteins, resulting in a significant decrease in the water solubility of walnut protein in a neutral environment, affecting the solubility of walnut defatted powder; (3) giving the product a bitter taste. It has been reported that the "walnut kernel full utilization technology" removes the kernel seed coat by hot alkali method, and then produces oil, prepares walnut defatted powder and walnut skim milk to avoid the adverse effects of walnut kernel seed coat. However, although the hot alkali method has the advantages of large processing capacity, good removal effect and high efficiency, its disadvantages are also very obvious: (1) The hot alkali method requires a large amount of NaOH solution in the pre-treatment stage. Not only will the waste liquid cause environmental pollution, but the subsequent raw materials also need a large amount of clean water to repeatedly rinse to remove the residual alkali solution, resulting in a waste of water resources; (2) If the alkali solution is not thoroughly cleaned, it will also pose a potential risk to food safety and food quality; (3) A large amount of polyphenols contained in the seed coat are discarded along with the removal of the seed coat. (4) After washing, the walnut kernels need to be dried at low temperature to a water content of 4%, which takes a long time and causes additional energy consumption during the baking process.

[0004] Walnut protein concentrate generally requires a protein content of more than 65% to meet the requirements of preparing special walnut protein products, high-purity walnut protein peptides, etc. Walnut protein concentrate and walnut protein isolate with higher protein content are mainly prepared by alkali dissolution and acid precipitation or alcohol precipitation. The preparation process produces wastewater and waste liquid, and the waste of walnut kernel seed coat resources is wasted. Therefore, through process technology innovation to achieve the preparation of walnut protein concentrate powder with high protein content, and explore the technology of replacing alkali dissolution and acid precipitation or alcohol precipitation to purify walnut protein, it will save a lot of production costs, improve product quality, reduce environmental pollution, and avoid resource waste.

[0005] Therefore, developing the process of pressing walnut kernels with seed coat to produce oil, separating the by-product walnut cake from the seed coat and walnut powder through technological innovation, and further developing a technology for preparing high-protein walnut concentrated protein powder without chemical methods have become urgent issues to be solved in production. Summary of the invention

[0006] In order to solve the above problems, the object of the present invention is to provide a walnut concentrated protein powder, which has high protein content and is green and efficient.

[0007] In order to achieve the above object, the present invention provides a walnut protein concentrate powder, which is prepared by the following steps:

[0008] 1) Walnut kernel with seed coat is pressed at low temperature to make oil

[0009] Shelling the walnuts, selecting walnut kernels without mildew and with a seed coat color of light yellow to light amber, using a hydraulic cold pressing method to produce oil, separating the walnut oil, and obtaining walnut cake, wherein the residual oil content of the walnut cake is controlled to be 8%-20%;

[0010] 2) Crushing and defatting of walnut cake

[0011] The walnut cake is crushed by a hammer crusher into particles with a side length of 1-5 mm, and then subcritical extraction and degreasing are performed to reduce the residual oil rate in the walnut cake to 1%-3%;

[0012] 3) Preliminary removal of the seed coat from walnut cake

[0013] Grinding the defatted walnut cake particles to remove most of the seed coat to obtain coarse powder;

[0014] 4) Finely separate the seed coat debris to obtain walnut protein concentrate powder with high protein content

[0015] The coarse powder is further freed of seed coat debris by using an airflow specific gravity separator, so that the seed coat residue rate in the obtained powder is less than 0.1%, the protein content reaches more than 70%, and the obtained powder accounts for more than 56% of the coarse powder.

[0016] Furthermore, the conditions for the hydraulic cold pressing method of oil production in step 1) are: pressing pressure 50-70MPa, pressing time 30min-60min, pressing temperature 40-50°C, and cyclic pressing 2-3 times.

[0017] The hydraulic cold pressing method can avoid thermal denaturation of protein in walnut cake and significantly increase the protein yield compared with other oil pressing methods.

[0018] Furthermore, the process parameters of the subcritical extraction in step 2) are: butane as solvent, extraction pressure of 0.5 MPa, extraction temperature of 45° C., extraction time of 40 min, and extraction 1-3 times.

[0019] Subcritical extraction can reduce the residual oil rate in walnut cake to 0.5%-2%, and the residual oil removal rate can reach 90-97%.

[0020] Furthermore, the grinding in step 3) adopts an impact mill, a high-impact loose powder mill or a roller mill.

[0021] Furthermore, the grinding adopts a roller mill, and the operating steps of the roller mill are as follows: a) first round of grinding and removing the seed coat: adjusting the height of the feeding door of the roller mill to 5-8mm, the feeding system includes a front feeding roller and a feeding roller, the speed range of the front feeding roller is 60-300r / min, and the speed ratio of the front feeding roller to the feeding roller is 1.5:1-2.5:1; the speed range of the fast roller is 450-650r / min, the speed ratio of the fast roller and the slow roller is set to 1.25:1-2.5:1, and the rolling distance between the fast roller and the slow roller is adjusted to 0.5-0.8mm; the number of grinding roller teeth is 15-25 teeth, the angle of the grinding teeth is (60°-80°) / (25°-45°), and the inclination is 1:6-1:1 2. Create an air pressure difference through a fan, and successively transfer the walnut cake meal powder particles to 30-mesh and 80-mesh sieves for seed coat separation, and carry out the next round of grinding to remove the seed coat for the material that does not pass through the 30-mesh sieve; b) Second and third rounds of grinding to remove the seed coat: the opening height of the feeding door is reduced to 0.5-5mm; the rolling distance between the grinding rollers of the roller mill is adjusted to 0.1-0.4mm, and the material that does not pass through the 30-mesh sieve in step a) is subjected to the second and third rounds of grinding to remove the seed coat, and create an air pressure difference through a fan, and successively transfer the walnut cake meal powder particles to 30-mesh and 80-mesh sieves for further seed coat separation; finally, the coarse powder mixed with a small amount of seed coat debris is collected through the 80-mesh sieve.

[0022] Preferably, the speed ratio of the fast roller and the slow roller is 1.5:1; the speed ratio of the front feeding roller and the feeding roller is 2:1; the number of teeth of the grinding roller is 20, the angle of the grinding teeth is 70° / 35°, and the inclination is 1:9.

[0023] Furthermore, the step of further removing the seed coat in step 4) is as follows: the coarse powder is put into the feeding port of the airflow specific gravity separator, and the powder particles and seed coat debris with high density and easy sedimentation are collected at the discharge port A by adjusting the equipment parameters of the airflow specific gravity separator, and the powder particles with low density and easy floating are collected at the discharge port B; then the powder collected at the discharge port B is fed for the second time to further remove the seed coat debris and collect the walnut concentrated protein powder at the discharge port B.

[0024] Furthermore, the equipment parameters of the airflow specific gravity separator are as follows: the adjustment frequency of the frequency converter controller of the feeder of the airflow specific gravity separator is 8.0-16.0 Hz, and the feeding speed is controlled to be 40-90 kg / hour; the frequency conversion adjustment range of the frequency converter controller of the airflow specific gravity separator is 40-90 Hz, and the frequency conversion frequency of the frequency converter in the induced draft fan of the airflow specific gravity separator is 40-60 Hz; the secondary air volume is adjusted by adjusting the air regulating valve of the airflow specific gravity separator, so that the aperture of the induced draft duct of the induced draft fan in the airflow specific gravity separator varies within the range of 5-10 cm.

[0025] Plant protein concentrate is mainly made from plant-based raw materials by using the properties of protein such as dissolving in alkaline solutions, precipitating at isoelectric points, and being insoluble in ethanol, etc. Both preparation methods are chemical methods that consume chemical reagents, bring environmental pollution pressure, consume water and energy, and use dry methods at room temperature to increase protein content. Plant protein concentrate products are still rare.

[0026] The invention provides a walnut concentrated protein powder, which achieves walnut protein powder enrichment based on the physical scales of protein particles and seed coat debris components through volume screening dominated by air flow pressure difference and different drift distances caused by differences in specific gravities of powder particles.

[0027] The present invention can avoid wastewater discharge and reduce environmental pollution: in the preparation of walnut protein powder, the conventional method usually first uses a hot alkali method and a high-pressure water washing method to remove the walnut kernel seed coat to avoid the influence of seed coat polyphenols on the color, flavor and other aspects of the walnut protein. Taking the treatment of 1 ton of walnut kernels with seed coat as an example, the hot alkali method commonly used in production will discharge 5-8 tons of alkaline wastewater with a high NaOH content, and the high-pressure water washing method will consume 4-6 tons of water, and secondary power consumption is required during re-drying, while the present invention does not have the problem of water consumption and water pollution.

[0028] The invention adopts a physical method to increase the protein content, avoids chemical methods such as alkali dissolution, acid precipitation and alcohol precipitation, does not use chemical reagents, avoids pollution and product quality problems caused by the introduction of chemical reagents, is more environmentally friendly, and is conducive to improving product quality.

[0029] The present invention can separate the walnut kernel seed coat while preparing the walnut concentrated protein powder, laying a foundation for the reuse of walnut kernel seed coat resources: 90% of the polyphenols in the walnut kernel are concentrated in the walnut kernel seed coat, but in the process of removing the seed coat by the hot alkali method and the high-pressure water washing method, the seed coat polyphenols are discharged and discarded with the wastewater. The present invention is carried out under normal temperature and dry conditions throughout the process. Compared with the existing method, the walnut kernel seed coat can be separated and enriched, laying a foundation for the reuse of the walnut kernel seed coat polyphenols.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a walnut concentrated protein powder, the protein content of which can reach more than 70%, and the powder can be used as a food raw material or auxiliary material for application in different product scenarios, so as to develop walnut protein products with various forms. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a process flow chart for preparing the walnut protein concentrate powder.

[0033] Figure 2 The present invention provides a photograph of walnut kernel seed coat and coarse powder collected after grinding in the process of preparing the walnut concentrated protein powder provided by the present invention.

[0034] Figure 3 The present invention provides a comparative photograph of powder discharged from discharge port A and discharge port B of T4 after the first feeding of airflow specific gravity separation in the process of preparing the walnut concentrated protein powder provided by the present invention.

[0035] Figure 4 The present invention provides a comparative photograph of powder discharged from discharge port A and discharge port B of T6 after the second feeding of airflow specific gravity separation in the process of preparing the walnut concentrated protein powder provided by the present invention. DETAILED DESCRIPTION

[0036] The embodiments of the present invention will be described in detail and comprehensively below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0037] Example 1

[0038] according to Figure 1 The process flow chart of walnut concentrated protein powder shown in the figure has the following specific steps:

[0039] 1) Walnut kernel with seed coat is pressed at low temperature to make oil

[0040] The walnuts are shelled, and walnut kernels without mildew and with a seed coat color of light yellow to light amber are selected. The oil is produced by a hydraulic cold pressing method to separate walnut oil and walnut cake, wherein the residual oil rate of the walnut cake is controlled to be 8%-20%.

[0041] The residual oil rate: fat mass in cake / mass of cake × 100%, where fat is determined by referring to the method of GB / T5009.62016 "National Food Safety Standard - Determination of Fat in Food".

[0042] 2) Crushing and defatting of walnut cake

[0043] The walnut cake is crushed by a hammer crusher into particles with a size of about 1-5 mm, and then subcritical extraction and degreasing are performed to reduce the residual oil rate in the walnut cake to 1%-3%.

[0044] 3) Preliminary removal of walnut seed coat and preparation of coarse powder

[0045] The defatted walnut cake particles are ground to remove most of the seed coat to obtain coarse powder.

[0046] The removal of seed coat by grinding is achieved by an impact mill, a strong impact loose powder machine or a roller mill, and the effects of removing seed coat of the above three types of equipment are compared, and the results are shown in Table 1. Among them, the walnut kernel seed coat removal rate is the mass of walnut kernel seed coat removed from walnut cake / the total seed coat mass in walnut cake × 100%, and the total seed coat mass of walnut cake is the sum of the mass of removed seed coat and the mass of residual seed coat in cake powder. The flour extraction rate is the mass of walnut powder obtained by grinding / the mass of walnut cake × 100%.

[0047] Table 1 The effect of three kinds of equipment on removing seed coat

[0048] Device Name Walnut kernel seed coat removal rate (%) Flour yield (%) Separation effect Impact mill 85.5 71.1 better Strong impact powder loosening machine 89.2 68.9 good Roller mill 98.0 69.5 very good

[0049] As can be seen from Table 1, in terms of mass percentage, the roller mill has the highest walnut kernel seed coat removal rate per unit time, which can reach 98.0%, and the walnut kernel seed coat removal effect is the best. The flour extraction rate reflects the scraping effect of the crushing equipment on the walnut defatted powder attached to the walnut kernel seed coat during the grinding and seed coat removal process. The better the scraping effect, the higher the flour extraction rate. As can be seen from Table 1, the flour extraction rates of the three types of equipment are not much different, and the flour extraction rate of the impact mill is slightly higher. However, considering the walnut kernel seed coat removal rate and flour extraction rate, the roller mill is selected as the preferred processing method.

[0050] The roller mill is a commercial product, mainly composed of a feeding system, a roller grinding system, a wind conveying system, and a screening and powder extraction system. In the first round of grinding and removing the seed coat of each batch of raw materials, the mill is equivalent to a skin mill. The height of the feeding door of the roller mill is adjusted to 5-8mm. The feeding system includes a front feed roller and a feeding roller. The speed range of the front feed roller is 60-300r / min, and the speed ratio of the front feed roller to the feeding roller is 1.5:1 to 2.5:1, preferably 2:1; the rollers of the roller mill include a fast roller and a slow roller. The different speeds of the rollers can separate the seed coat and the powder by grinding. The speed range of the fast roller is 450-650r / min, and the speed ratio of the fast roller and the slow roller is set to 1.25 : 1-2.5:1, preferably 1.5, the rolling distance between the fast roller and the slow roller is adjusted to 0.5-0.8mm; the number of teeth of the grinding roller (the number of grinding teeth within 1 inch along the circumference of the grinding roller, reflecting the arrangement density of grinding teeth on the surface of the grinding roller): 15-25 teeth, preferably 20 teeth, the angle of the grinding teeth (the angle between the two inclined surfaces of the grinding teeth): (60°-80°) / (25°-45°), preferably 70° / 35°, the inclination (the axial grinding teeth of the grinding roller are inclined at an angle to the center line of the grinding roller, the distance between the two ends of the same grinding tooth on the circumference of the grinding roller surface, and the grinding The ratio of the centerline length of the roller, that is, the slope) is 1:6-1:12, preferably 1:9; the air flow pressure difference is created by the fan, and the walnut cake powder particles are successively transferred to the 30-mesh and 80-mesh shakron powder extractors for seed coat separation. Under the action of the fan, negative pressure is formed in the shakron powder extractor and wind direction rotation is generated, and the materials that do not pass through the 30-mesh sieve (including seed coat fragments and powder blocks, etc.) are subjected to the next round of grinding and seed coat removal; then the raw materials enter the second and third rounds of grinding and seed coat removal stages, the mill is equivalent to a core mill, and the opening height of the feeding door is reduced to 0.5- 5mm; adjust the grinding roller speed by the feeding speed control hand wheel, and adjust the rolling distance between the grinding rollers to 0.1-0.4mm by the rolling distance adjustment hand wheel; the mixture of powder and seed coat fragments passing through the 30-mesh shakron powder extractor is transported to the 80-mesh shakron powder extractor for further separation under the action of airflow pressure difference, and the seed coat fragments that do not pass through the 80-mesh shakron powder extractor are separated and collected, and finally the powder mixed with a small amount of seed coat fragments (finer seed coat fragments) passing through the sieve of the 80-mesh shakron powder extractor has a yield of 69.5%, and the seed coat removal rate can reach 98%. The above-mentioned powder separated by the double-roller mill and still containing 2% seed coat fragments is used as coarse powder, and the seed coat fragments will be further separated by the airflow specific gravity separator. Collect the walnut kernel seed coat and coarse powder. At this time, the seed coat residue rate of the coarse powder is about 2%, Figure 2 Shown are photographs of walnut kernel seed coat fragments and coarse powder collected from Figure 2 It can be seen that the residual seed coat fragments are still scattered in the coarse powder, and visually there are obvious star-shaped light brown fragments distributed in the coarse powder.

[0051] 4) Finely separated high protein content walnut concentrated protein powder

[0052] After the preliminary removal of the walnut kernel seed coat, there is still a small amount (about 2%) of fine seed coat debris remaining in the coarse powder. The polyphenols contained in this part of the fragments will still affect the color and flavor of the defatted walnut powder. Therefore, an airflow specific gravity separator with good separation effect on fine particles is selected to further separate the coarse powder obtained in 3) to remove the walnut kernel seed coat to the maximum extent.

[0053] The airflow specific gravity separator is mainly composed of a feeder, an induced draft fan, a classifier, a discharge port A, a discharge port B, a frequency converter and other parts. The adjustment frequency of the feeder frequency converter is 8.0-16.0Hz, and the feeding speed is controlled at 40-90kg / hour, preferably 12.0Hz. The feeding speed is maintained at about 65kg / hour to ensure uniform feeding; the diameter of the classifier cavity is 40cm, and the classifier is adjusted by the frequency converter, and the frequency conversion adjustment range is 40-90Hz, so that the classifier speed is maintained at 1000-3000 rpm, and the air volume of the classifier cavity system is maintained at 3-5m / second. The air volume remains stable, and the coarse powder put into the feed port can be adjusted through the airflow pressure difference Transmission through the grading cavity; the diameter of the induced draft fan pipeline is 15cm, and the frequency conversion frequency of the frequency converter in the induced draft fan is 40-60Hz, preferably 45-50Hz, so that negative pressure is generated in the pipeline and the cavity, so that powders of different specific gravities fall at different distances; the discharge port A is close to the feeding port, and the discharged powder is particles with high density and irregular shapes and easy to settle seed coat debris, accounting for about 35%-40% of the added amount; the discharge port B is far from the feeding port, and the discharged powder is particles with low density and easy to float, accounting for about 60%-65% of the added amount. By adjusting the air regulating valve of the induced draft fan, the aperture of the induced draft pipeline can be changed within the range of 5-10cm, thereby adjusting the secondary air volume, controlling the coarseness ratio of the materials at the discharge ports A and B, and realizing the removal of trace walnut kernel seed coat debris. The influence of the airflow specific gravity sorting parameters of the first feeding on the separation effect is shown in Table 2, where the frequency conversion frequencies of different classifiers and induced draft fans are set in four groups: T1-T4, and the yield, protein content, chroma, and seed coat residual rate of the discharged powder from the discharge port A and the discharge port B are counted. Among them, the powder yield calculation method is: the mass of powder collected at the outlet / the mass of raw material powder × 100%; the protein content is determined by referring to the method of GB5009.5-2016 "Determination of Protein in Food in National Food Safety Standard"; the chroma (L value) is determined by Konica Minolta CM-5 spectrophotometer, and the L value is recorded; the seed coat residual rate is to manually screen the powder with a 100-200 mesh sieve, sort the residual seed coat debris and weigh it, and the seed coat residual rate = residual seed coat mass / total powder mass × 100%.

[0054] Table 2 Effect of airflow specific gravity separation parameters on separation effect of the first feeding

[0055]

[0056] As can be seen from Table 2, after the first feeding, under the condition of T4 processing classifier frequency of 50Hz and induced draft fan frequency of 50Hz, the powder yield of outlet B can reach 66.1%, the seed coat residual rate is 0.1%, and the protein content is the highest, reaching 70.90%, which has reached the protein content standard of concentrated protein. The protein content of powder obtained from outlet B of other test groups is less than 60%. Figure 3 The following are the coarse powder and the collected powder from T4 outlet A and outlet B. Figure 3 It can be seen that the powders obtained from T4 outlet A and outlet B have obvious differences in seed coat content. The seed coat fragments contained in the coarse powder are enriched in the powder from outlet A. The whiteness (L value) of the powder obtained from T4 outlet B is higher than that from outlet A. The selection of the frequency of the classifier and the induced draft fan takes into account the motor speed and the degree to which the powder is lifted. At the same time, the comprehensive effect of the induced draft fan should be considered, which is to ensure that the seed coat residual rate is reduced to a low level while taking into account the powder extraction rate. Therefore, T4 outlet B is selected for powder extraction for subsequent feeding.

[0057] The powder at outlet B of T4 was collected for the second feeding, and the classifier frequency and induced draft fan frequency were adjusted to obtain treatment groups T5 and T6. The results are shown in Table 3.

[0058] Table 3 Effect of airflow specific gravity separation parameters of the second feeding on the separation effect

[0059]

[0060] As can be seen from Table 3, after the second feeding, the classifier frequency was increased to 58Hz and 60Hz respectively, the protein content of the walnut powder obtained from the discharge port B was increased, the chromaticity L value was slightly increased, and the powder yield was more than 85%, among which the protein content of the powder obtained from the discharge port B by T5 treatment was increased to 72.6%, and the seed coat residue rate was reduced to 0.05%. Calculated from the coarse powder raw material, the powder obtained from the discharge port B by T5 treatment was 56.65% of the coarse powder. Combined with the protein content and seed coat residue rate, the treatment with high protein content was given priority, and the T5 treatment with higher protein content was selected as the preferred treatment for separating and preparing walnut concentrated protein powder.

[0061] like Figure 4 Shown are the collected powder photos of T4 processing outlet B, T5 outlet A and outlet B. Figure 4 It can be seen that the walnut kernel seed coat is further enriched in the powder discharged from outlet A, and the chromaticity value of the powder obtained from outlet B of T5 is significantly higher than that from outlet A.

[0062] The chemical composition of walnut kernels at different processing stages was further statistically analyzed, as shown in Table 4. Among them, the protein content was determined according to the method of GB5009.5-2016 "National Food Safety Standard for Determination of Protein in Foods"; the moisture content was determined according to the method of GB5009.3-2016 "National Food Safety Standard for Determination of Moisture in Foods"; the ash content was determined according to the method of GB5009.4-2016 "National Food Safety Standard for Determination of Ash in Foods"; the crude fiber content was determined according to the method of GB / T5009.10-2003 "Determination of Crude Fiber in Plant Foods"; and the fat content was determined according to the method of GB / T 5009.62016 "National Food Safety Standard for Determination of Fat in Foods".

[0063] Table 4 Chemical composition of walnut protein concentrate powder at different stages of preparation

[0064]

[0065] As can be seen from Table 4, from the cold-pressed walnut meal obtained by low-temperature pressing in step 1) to the walnut concentrated protein powder in step 4), the protein content gradually increases and the fat content effectively decreases.

[0066] As can be seen from the above embodiments, the present invention provides a walnut concentrated protein powder, which has a high protein content, is physically prepared throughout the entire processing process, preserves the natural nutrition of walnut protein, and is a good raw material for adding to a variety of foods and health products. The protein content of the walnut concentrated protein powder in the present invention can reach more than 70%, which is a potential raw material for plant-based vegetarian meat products and an important raw material for high-quality health protein powder. The higher protein concentration is of great value for the development of highly functional walnut peptides, and can also be widely used in daily staple food products and ham sausages, ice cream and other plant protein raw materials. Through technological innovation, the present invention makes full use of the walnut cake meal, a by-product of walnut oil production, to achieve green and efficient preparation, and improve the added value of walnut processing.

[0067] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A walnut protein concentrate powder, characterized in that: The walnut protein concentrate powder is prepared by the following steps: 1) Walnut kernel with seed coat is pressed at low temperature to make oil Shelling the walnuts, selecting walnut kernels without mildew and with a seed coat color of light yellow to light amber, using a hydraulic cold press method to produce oil, separating walnut oil and walnut cake, wherein the residual oil rate of the walnut cake is controlled to be 8%-20%; 2) Crushing and defatting of walnut cake The walnut cake is crushed by a hammer crusher into particles with a side length of 1-5 mm, and then subcritical extraction and degreasing are performed to reduce the residual oil rate in the walnut cake to 1%-3%; 3) Preliminary removal of the seed coat from walnut cake Grinding the defatted walnut cake particles to remove most of the seed coat to obtain coarse powder; 4) Finely separate the seed coat debris to obtain walnut protein concentrate powder with high protein content An airflow specific gravity separator is used to further remove seed coat debris from the coarse powder, so that the seed coat residue rate in the obtained powder is reduced to less than 0.1%, and walnut concentrated protein powder with a protein content of more than 70% is obtained, and the obtained powder accounts for more than 56% of the coarse powder.

2. The walnut protein concentrate powder according to claim 1, wherein The conditions for the hydraulic cold pressing method of oil production in step 1) are: pressing pressure 50-70MPa, pressing time 30min-60min, pressing temperature 40℃-50℃, and cyclic pressing 2-3 times.

3. The walnut protein concentrate powder as claimed in claim 1, characterized in that The process parameters of the subcritical extraction in step 2) are: butane as solvent, extraction pressure of 0.5 MPa, extraction temperature of 45° C., extraction time of 40 min, and extraction 1-3 times.

4. The walnut protein concentrate powder as claimed in claim 1, characterized in that Step 3) The grinding is carried out by using an impact mill, a strong impact loose powder mill or a roller mill.

5. The walnut protein concentrate powder as claimed in claim 4, characterized in that The grinding adopts a roller mill, and the operation steps of the roller mill are as follows: a) removing the seed coat in the first round of grinding: adjusting the height of the feeding door of the roller mill to 5-8mm, the feeding system comprises a front feeding roller and a feeding roller, the speed range of the front feeding roller is 60-300r / min, and the speed ratio of the front feeding roller to the feeding roller is 1.5:1-2.5:1; the speed range of the fast roller is 450-650r / min, the speed ratio of the fast roller to the slow roller is set to 1.25:1-2.5:1, and the rolling distance between the fast roller and the slow roller is adjusted to 0.5-0.8mm; the number of grinding roller teeth is 15-25 teeth, the angle of the grinding teeth is (60°-80°) / (25°-45°), and the slope is 1:6-1:12; The fan creates an air pressure difference, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sieves for seed coat separation, and the material that does not pass the 30-mesh sieve is subjected to the next round of grinding to remove the seed coat; b) The second and third rounds of grinding and seed coat removal: the opening height of the feed door is reduced to 0.5-5mm; the rolling distance between the grinding rollers of the roller mill is adjusted to 0.1-0.4mm, and the material that does not pass the 30-mesh sieve in step a) is subjected to the second and third rounds of grinding and seed coat removal, and the fan creates an air pressure difference, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sieves for further seed coat separation; finally, the coarse powder mixed with a small amount of seed coat debris is collected by the 80-mesh sieve.

6. The walnut protein concentrate powder as claimed in claim 5, characterized in that The speed ratio of the fast roller and the slow roller is 1.5:1; the speed ratio of the front feeding roller and the feeding roller is 2:1; the number of teeth of the grinding roller is 20, the angle of the grinding teeth is 70° / 35°, and the slope is 1:

9.

7. The walnut protein concentrate powder according to claim 1, characterized in that Step 4) The step of further removing the seed coat is as follows: the coarse powder is put into the feeding port of the airflow specific gravity separator, and the powder particles and seed coat debris with high density and easy sedimentation are collected at the discharge port A by adjusting the equipment parameters of the airflow specific gravity separator, and the powder particles with low density and easy floating are collected at the discharge port B; then the powder collected at the discharge port B is fed for the second time to further remove the seed coat debris, and the walnut concentrated protein powder at the discharge port B is collected.

8. The walnut protein concentrate powder as claimed in claim 7, characterized in that The equipment parameters for adjusting the airflow specific gravity separator are as follows: the adjustment frequency of the frequency converter controller of the feeder of the airflow specific gravity separator is 8.0-16.0 Hz, and the feeding speed is controlled to be 40-90 kg / hour; the frequency conversion adjustment range of the frequency converter controller of the airflow specific gravity separator is 40-90 Hz, and the frequency conversion frequency of the frequency converter in the induced draft fan of the airflow specific gravity separator is 40-60 Hz; the secondary air volume is adjusted by adjusting the air regulating valve of the airflow specific gravity separator, so that the aperture of the induced draft duct of the induced draft fan in the airflow specific gravity separator varies within the range of 5-10 cm.

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