Method for separating walnut kernel seed coats through normal-temperature dry method

Abstract

The invention provides a method for separating walnut kernel seed coats by a normal-temperature dry method. The method comprises the following steps: (1) squeezing walnut kernels with seed coats at low temperature to prepare oil; 2) crushing and degreasing the walnut cake meal; (3) preliminarily removing seed coats in the walnut cake meal; and (4) finely removing seed coats. According to the method provided by the invention, the seed coats are separated and collected by adopting a normal-temperature and dry method, so that the walnut kernel seed coats can be efficiently and sufficiently removed and collected in a powder state on the premise of obtaining high-quality walnut oil, and meanwhile, the problems that wastewater is generated in a seed coat removing process in a kernel form, a polyphenol structure of the seed coats is damaged, and energy is consumed in washing and re-drying are avoided; and resource reutilization is facilitated, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the agricultural field and relates to a method for separating walnut kernel seed coats, and specifically to a method for separating walnut kernel seed coats by a room-temperature dry method. Background Art

[0002] Walnut is one of the woody grain and oil tree species that the country supports. In 2022, my country's total walnut production has reached 5.93 million tons. Deep processing of walnuts plays a vital role in the high-quality development of the walnut industry. Walnut kernel seed coat removal is a by-product of walnut deep processing. Especially in the processing of walnut milk, walnut powder and other products, the polyphenols contained in the walnut kernel seed coat will bring astringency and browning to the processed products and need to be fully removed; in the walnut oil production process, the walnut kernel seed coat is also a by-product of walnut oil production, which is often discarded along with the walnut cake and cannot be reused. On the other hand, polyphenols in walnut kernel seed coat are an important bioactive component. Their excellent free radical scavenging ability has not only been confirmed by in vitro antioxidant tests, but also has potential application value in regulating intestinal flora and improving gastrointestinal function. In vivo tests on organisms have more accurately shown that walnut kernel seed coat polyphenols have physiological and medical activities such as inhibiting the proliferation of human renal cancer cell lines (A-498 and 769-P) and colon cancer cell lines (Caco-2) and maintaining 8-hydroxydeoxyguanosine (8-OHdG) at a low level in diabetic mouse models. Previous studies have shown that polyphenols in walnut kernels are mainly concentrated in the inner seed coat. 17 phenolic acids were detected in walnut kernel seed coat, with gallic acid being the highest content. Eight flavonoids were detected, and rutin content was the highest in the standard sample, at 187.6 mg / 100 g dry sample. Although walnut kernel seed coat polyphenols have high content and obvious functional activity, due to the lack of reasonable seed coat removal technology, walnut kernel seed coat cannot be collected in large quantities, which limits the utilization of walnut kernel seed coat polyphenols. At the same time, as a by-product of walnut kernel processing, walnut kernel seed coat is mostly discarded, resulting in a waste of resources.

[0003] The commonly used method for removing the seed coat in industrial production is the hot alkali method, which has the advantages of large processing capacity and good removal effect, but there are disadvantages such as the generation of alkaline wastewater containing waste residues, large water consumption for repeated washing, and the loss and abandonment of beneficial polyphenol resources in the seed coat of walnut kernels. The high-pressure water washing method removes the seed coat of walnut kernels by strong washing, which also causes the abandonment of the seed coat of walnut kernels, and the additional energy consumption caused by repeated drying. In addition to the two wet methods for removing the seed coat of walnut kernels, the technology of removing the seed coat of walnut kernels by temperature-changing methods is also more common, including baking, blanching, freeze-thaw and other seed coat removal technologies, among which baking and blanching destroy the biological activity of polyphenols due to temperature increase, resulting in waste of walnut seed coat polyphenol resources, while the freeze-thaw method consumes a large amount of energy through quick freezing and temperature increase, and the processing capacity is also limited, thereby limiting its industrial application.

[0004] Therefore, it is an urgent problem to develop an efficient, energy-saving and water-saving method for separating walnut kernel seed coats, so as to achieve efficient and large-scale collection of walnut kernel seed coats, a by-product of walnut processing, and promote the reuse of polyphenol components in walnut kernel seed coats. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a method for separating walnut kernel seed coat by dry method at room temperature. The method adopts room temperature and dry method to separate the seed coat. On the premise of obtaining high-quality walnut oil, the kernel seed coat in the walnut oil processing by-product - walnut cake can be separated and collected, laying a foundation for the reuse of walnut kernel seed coat polyphenols, while avoiding the energy consumption of removing the seed coat, washing and re-drying the complete walnut kernel.

[0006] In order to achieve the above object, the present invention provides a method for separating walnut kernel seed coat by dry method at room temperature, comprising the following steps:

[0007] 1) Walnut kernel with seed coat is pressed at low temperature to make oil

[0008] 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%;

[0009] 2) Crushing and defatting of walnut cake

[0010] The walnut cake is crushed by a hammer crusher into particles with a side length of 1-5 mm, and then degreased by subcritical extraction or CO2 supercritical extraction, so that the residual oil rate in the walnut cake is reduced to 0.5%-3%;

[0011] 3) Preliminary removal of seed coat from walnut cake

[0012] Grinding the defatted walnut cake particles to remove most of the seed coat to obtain coarse powder;

[0013] 4) Fine removal of seed coat

[0014] The coarse powder is further subjected to the removal of seed coat debris by an airflow specific gravity separator, so that the seed coat residue rate in the obtained powder is less than 0.1%.

[0015] 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℃, and cyclic pressing 2-3 times.

[0016] 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.

[0017] 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.

[0018] Subcritical extraction can reduce the residual oil rate in walnut cake to 1%-3%, and the residual oil removal rate can reach 90-97%.

[0019] Furthermore, the process parameters of the CO2 supercritical extraction in step 2) are: the walnut cake particles are loaded into the extraction kettle, and the extraction is carried out at 20-40MPa, the pressure of separator I is set to 8MPa and the temperature is 40°C, the pressure of separator II is set to 5-6MPa and the temperature is 30°C, the extraction time is 120min, and the CO2 flow rate is 4L / min.

[0020] CO2 supercritical extraction can reduce the residual oil rate in walnut cake to 0.5%-2%, and the residual oil removal rate can reach 93-98%.

[0021] Furthermore, the grinding in step 3) adopts an impact mill, a high-impact loose powder mill or a roller mill.

[0022] Furthermore, it is preferred that 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 front feeding roller speed range is 60-300r / min, and the speed ratio of the front feeding roller to the feeding roller is 1.5:1 to 2.5:1; the main grinding roller of the roller mill includes a fast roller and a slow roller, the fast roller speed range is 450-650r / min, the fast and slow roller speed ratio is set to 1.25:1 to 2.5:1, and the rolling distance between the two grinding rollers is adjusted to 0.5-0.8mm; the number of grinding roller teeth is 15-25 teeth, the grinding tooth angle is: (60°~80°) / (25°~45°), and the slope is 1:6-1 : 12; The air pressure difference is created by the fan, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sachlon-type powder extractors for seed coat separation, and the materials that do not pass through the 30-mesh sieve are subjected to the next round of grinding to remove the seed coat; b) The second and third rounds of grinding and removing 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 materials that do not pass through the 30-mesh sieve in step a) are subjected to the second and third rounds of grinding and removing the seed coat, and the air pressure difference is created by the fan, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sachlon-type powder extractors for further seed coat separation;; Finally, the coarse powder mixed with a small amount of seed coat debris is collected through the 80-mesh sachlon-type powder extractor, and the seed coat removal rate in the coarse powder reaches 98%.

[0023] 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.

[0024] 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 low seed coat residual powder at the discharge port B.

[0025] 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.

[0026] The present invention can significantly reduce energy consumption: baking, freeze-thaw and other methods involve high temperature or freezing and heating treatment, which consumes relatively high energy. Taking the treatment of 1 ton of walnut kernels with seed coat as an example, the present invention can reduce power consumption by about 400 degrees because it does not involve high temperature and variable temperature treatment.

[0027] The present invention can avoid wastewater discharge and reduce environmental pollution: 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 consumption of electric energy is required during re-drying. However, the present invention does not have the problems of water consumption and water pollution, and avoids the problem of energy consumption for re-drying.

[0028] The present invention lays a foundation for the reuse of walnut kernel seed coat resources: walnut has the reputation of "king of antioxidants", and the polyphenol components in walnut kernels have high antioxidant activity and multiple functional activities such as lowering blood sugar, preventing cardiovascular diseases, and inhibiting the development of cancer cells. 90% of the polyphenols in walnut kernels are concentrated in the walnut kernel seed coat, but in the process of "baking method" to remove the seed coat, the polyphenol structure and functional activity are destroyed. In the process of hot alkali method and high-pressure water washing method to remove the seed coat, the seed coat polyphenols are discharged and discarded with wastewater and cannot be reused. 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, and the polyphenol components in the seed coat are better preserved, laying a foundation for the reuse of walnut kernel seed coat polyphenols.

[0029] The existing "dry peeling" process has a peeling rate of about 82%. The "normal temperature dry peeling" technology provided by the present invention can increase the peeling rate of walnut kernels to 99.95%, basically achieving the complete removal of the walnut kernel seed coat, with a subversive peeling effect, and can provide technical support for the recycling of walnut cake protein and seed coat resources.

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

[0031] The present invention provides a method for separating walnut kernel seed coat by dry method at room temperature, wherein the method extracts oil from walnut kernel with seed coat and defats it, and at the same time when the cake is crushed and ground into powder, the seed coat fragments are separated and collected by air flow pressure difference. In the whole method, walnut oil, low seed coat residual powder and high seed coat residual powder can be obtained. Compared with the conventional technology for directly removing seed coat from walnut kernel, the method avoids the problems of high energy consumption and destruction of seed coat polyphenols existing in "variable temperature" seed coat removal technologies such as baking and freeze-thaw, and solves the problems of water consumption and pollution existing in "wet method" seed coat removal technologies such as hot alkali method and high-pressure water washing commonly used in production, laying a foundation for realizing the reuse of walnut kernel seed coat resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a process flow chart of a method for separating walnut kernel seed coat by dry method at room temperature.

[0033] Figure 2 The present invention provides a photograph of walnut kernel seed coat fragments and coarse powder collected after grinding in the process of the method for separating walnut kernel seed coat by dry method at room temperature.

[0034] Figure 3 Comparative photos of powder discharged from discharge ports A and B of each group after the first feeding in the process of airflow specific gravity sorting in the method for separating walnut kernel seed coat by dry method at room temperature provided by the present invention.

[0035] Figure 4 The following are comparison photos of powder discharged from T6 discharge port A and discharge port B after the second feeding of airflow specific gravity separation in the process of the method for separating walnut kernel seed coat by dry method at room temperature provided by the present invention.

[0036] Figure 5 The present invention provides a method for separating walnut kernel seed coats by dry method at room temperature provided by the present invention. The present invention provides a method for separating walnut kernel seed coats by dry method at room temperature provided by the present invention. The present invention provides a method for separating walnut kernel seed coats by dry method at room temperature provided by the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] The commonly used methods for removing the walnut kernel seed coat in production are mainly hot alkali method and high-pressure water washing method, and there are also research reports on removing the seed coat by baking, freeze-thaw and other methods. The present invention uses normal temperature and dry method to separate the seed coat, avoiding the problems of high energy consumption and destruction of seed coat polyphenols in "variable temperature" seed coat removal technologies such as baking and freeze-thaw, and solves the problems of water consumption and pollution in "wet method" seed coat removal technologies such as hot alkali method and high-pressure water washing commonly used in production, laying a foundation for realizing the reuse of walnut kernel seed coat resources.

[0039] Example 1

[0040] according to Figure 1 The process flow chart of the method for separating walnut kernel seed coat by dry method at room temperature is shown to process walnuts: the specific steps are as follows:

[0041] 1) Walnut kernel with seed coat is pressed at low temperature to make oil

[0042] 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%.

[0043] The residual oil rate: crude fat mass in cake / cake mass × 100%, where crude fat is determined by referring to the method of GB / T5009.6 2016 “National Food Safety Standard - Determination of Fat in Food”.

[0044] 2) Crushing and defatting of walnut cake

[0045] The walnut cake is crushed by a hammer crusher into particles with a size of about 1-5 mm, and then degreased by subcritical extraction or CO2 supercritical extraction, so that the residual oil rate in the walnut cake is reduced to 0.5%-3%.

[0046] Subcritical extraction degreasing has a larger processing capacity than CO2 supercritical extraction, lower cost, and is more suitable for industrial production. Therefore, this embodiment uses subcritical extraction for subsequent operations, and the residual oil rate in the walnut cake is reduced to 1%.

[0047] 3) Preliminary removal of seed coat from walnut cake

[0048] The defatted walnut cake particles are ground to remove most of the seed coat to obtain coarse powder.

[0049] 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%.

[0050] Table 1 The effect of three kinds of equipment on removing seed coat

[0051] 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

[0052] As can be seen from Table 1, the walnut kernel seed coat removal rate of the impact mill is lower than that of the strong impact loose powder machine and the roller mill per unit time. 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. Considering the walnut kernel seed coat removal rate and flour extraction rate, the roller mill is selected as the preferred treatment method.

[0053] 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.

[0054] 4) Fine removal of seed coat

[0055] After the initial 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 to remove the walnut kernel seed coat to the maximum extent.

[0056] 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 frequency converter of the feeder is adjusted at 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. The classifier speed 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. The air volume of the classifier cavity system is maintained at 3-5m / second, and the air volume is maintained stable. The coarse powder put into the feed port can be compressed by the airflow. Differential transmission passes 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, the aperture of the induced draft fan's induced draft pipeline changes 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%.

[0057] Table 2 Effect of airflow specific gravity separation parameters of the first feeding on the separation effect

[0058]

[0059] 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 at outlet B can reach 66.1%, the protein content can reach 70.90%, and the seed coat residual rate is 0.1%. The protein content of powder at outlet B of other test combination frequencies is lower than 60%. Figure 3 Shown are the coarse powder and the collected powder photos of the outlets A and B of T1-T4 for observing the color. Figure 3 It can be seen that at the same feeding stage, the powders obtained from outlet A and outlet B can obviously show differences in seed coat content. The seed coat debris contained in the coarse powder is enriched in the powder from outlet A. The whiteness (L value) of the powder obtained from outlet B in the corresponding group is higher than that of the powder 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 of powder being lifted, and also the comprehensive effect of the induced draft fan, which ensures that the seed coat residual rate is reduced to a low level while taking into account a higher powder extraction rate. Therefore, T4 outlet B is selected for powder extraction for subsequent feeding.

[0060] The powder discharged from the outlet B of the first feeding of T4 was collected for the second feeding, and the classifier frequency and the induced draft fan frequency were adjusted to obtain the T5 and T6 treatment groups. The results are shown in Table 3.

[0061] Table 3 Effect of airflow specific gravity separation parameters of the second feeding on the separation effect

[0062]

[0063] As can be seen from Table 3, in order to further remove the seed coat debris, the frequency of the classifier was increased to 58Hz and 60Hz respectively after the second feeding, so that the movement state of the powder changed, which was conducive to further separation of the walnut kernel seed coat. The protein content of the walnut powder obtained from the discharge port B was compared with the powder obtained from the discharge port B after the first feeding, and the color L value was slightly increased. At the same time, the powder yield can reach more than 85%, and the seed coat residual rate is reduced to 0.05%. Among them, the discharge port B treated with T6, in addition to obtaining a lower seed coat residual rate, has a higher powder yield than T5, so T6 treatment is selected for the next step. Figure 4 The following are photos of powder discharge from outlet B of T4 and outlet A and outlet B of T6. The powder from outlet B of T4 is used as the raw material for secondary feeding. Figure 4 It can be seen that the walnut kernel seed coat is further enriched and mainly concentrated in the powder at outlet A.

[0064] The powder collected at outlet B after the second feeding T6 was fed for the third time, in which the frequency of the classifier was increased to 89 Hz, and the frequencies of the induced draft fan were 47 Hz and 50 Hz, respectively. The results are shown in Table 4.

[0065] Table 4 Effect of airflow specific gravity separation parameters on separation effect of the third feeding

[0066]

[0067] As can be seen from Table 4, after the third feeding, most of the powder in treatments T7 and T8 fell to outlet A, with a powder yield of about 65-67%, and the powder yield at outlet B was only 33.8%-35.0%. The protein content increased compared with T5 and T6, but the increase was small, and the seed coat residual rate did not decrease significantly. Figure 5 The following are comparison photos of powder discharged from outlet A and outlet B of T8. Compared with the powder discharged from outlet B of T6, there is no obvious difference in color.

[0068] Comprehensively considering the powder yield of different treatment outlets B, starting from the coarse powder raw material, the actual total yield of the third feeding T8 treatment outlet B is about 19.9%, that is, the powder yield of 0.04% of the seed coat residue is 19.9% ​​of the coarse powder, and after the second feeding, the actual powder yield of the treatment T6 outlet B is about 56.98% of the coarse powder, and the seed coat residue is about 0.05%. After the first feeding, the actual powder yield of the treatment T4 outlet B is about 66.1% of the coarse powder, and the seed coat residue is about 0.1%. Taking into account the powder yield and seed coat residue, the second feeding is preferred as the better process solution.

[0069] From the above embodiments, it can be seen that the present invention selects a roller mill for processing, and the walnut kernel seed coat removal rate can reach 98.0%, and the seed coat removal effect is good. Further, an airflow specific gravity separator is used to separate and remove the walnut kernel seed coat. Under the conditions of a feeding speed of 65kg / h, a classifier frequency of 50Hz, and an induced draft fan frequency of 50Hz, the walnut powder with a higher protein content collected at the discharge port B is 66.1% of the coarse powder, and the residual rate of walnut kernel seed coat debris is reduced to 0.1%. Under corresponding conditions, the walnut protein content of the powder obtained at the discharge port A is 36.8%, and the residual rate of walnut kernel seed coat debris is about 3.2%. The powder obtained from the discharge port B was repeatedly fed under the condition of increasing the frequency of the classifier, that is, the second and third separations were carried out. After the second feeding, the powder yield of the discharge port B was about 56.98% of the coarse powder, and the seed coat residual rate was about 0.05%. After the third feeding, the powder yield of the discharge port B was about 19.9% ​​of the coarse powder, and the seed coat residual rate was about 0.04%. Comprehensively considering the powder yield and seed coat residual rate, the second feeding for airflow specific gravity separation is preferred as a better process solution.

[0070] The powder collected from discharge port A after multiple feedings is high in seed coat residue. This powder and the walnut kernel seed coat separated by the roller mill can be used to extract beneficial polyphenols in the seed coat, and can be used as raw materials for medicines or health foods. The powder collected from discharge port B after the second feeding is low in seed coat residue. The protein content is relatively high, and it can be used to produce products with high requirements for taste and color, and high requirements for protein content. The walnut oil obtained by hydraulic cooling and subcritical (CO2 supercritical) extraction in the previous steps can be used in the fields of food and cosmetics as a high-quality oil. While preparing walnut oil, the walnut kernel seed coat, a by-product of walnut processing, can be efficiently and massively collected, which can promote the development and utilization of components such as walnut kernel seed coat polyphenols.

[0071] The invention provides a method for separating walnut kernel seed coat by dry method at room temperature, which can realize efficient separation and collection of walnut kernel seed coat in a powder state, avoids the problems of wastewater generation, seed coat polyphenol structure destruction, water washing and re-drying energy consumption, etc. in the process of removing seed coat in the form of kernels, and the like. The invention is efficient, water-saving, energy-saving, and is conducive to the reuse of walnut processing by-product resources, and has good application prospects.

[0072] 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 method for separating walnut kernel seed coat by dry method at room temperature, characterized in that: The steps include: 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 degreased by subcritical extraction or CO2 supercritical extraction, so that the residual oil rate in the walnut cake is reduced to 0.5%-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) Fine removal of seed coat The coarse powder is further cleaned of seed coat debris by using an airflow specific gravity separator, so that the seed coat residue rate in the obtained powder is reduced to 0.1% or less.

2. The method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 1, characterized in that: 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.

3. The method for separating walnut kernel seed coat by dry method at room temperature 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 method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 1, characterized in that: The process parameters of the CO2 supercritical extraction in step 2) are: loading the walnut cake particles into the extraction kettle, extracting at 20-40MPa, setting the pressure of separator I to 8MPa and the temperature to 40°C, the pressure of separator II to 5-6MPa and the temperature to 30°C, the extraction time to 120min, and the CO2 flow rate to 4L / min.

5. The method for separating walnut kernel seed coat by dry method at room temperature 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.

6. The method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 5, characterized in that: The grinding adopts a roller mill, and the operation steps of the roller mill are as follows: a) first round of grinding and seed coat removal: 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 grinding rollers of the roller mill include a fast roller and a slow roller, 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 grinding angle is (60°-80°) / (25°-45°), and the slope is 1 :6-1:12; the air pressure difference is created by the fan, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sachlon powder extractors for seed coat separation, and the materials that do not pass through the 30-mesh sieve are subjected to the next round of grinding to remove the seed coat; b) the second and third rounds of grinding and removing 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 materials that do not pass through the 30-mesh sieve in step a) are subjected to the second and third rounds of grinding and removing the seed coat, and the air pressure difference is created by the fan, and the walnut cake powder particles are successively transferred to 30-mesh and 80-mesh sachlon powder extractors for further seed coat separation; finally, the coarse powder mixed with a small amount of seed coat debris is collected through the 80-mesh sachlon powder extractor.

7. The method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 6, 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 inclination is 1:

9.

8. The method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 1, characterized in that: Step 4) The step of further removing the seed coat is as follows: the coarse powder is fed into the feeding port of the airflow specific gravity separator for the first feeding, and by adjusting the equipment parameters of the airflow specific gravity separator, the powder particles and seed coat debris with high density and easy sedimentation are collected at the discharge port A, 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 low seed coat residual powder at the discharge port B.

9. The method for separating walnut kernel seed coat by dry method at room temperature as claimed in claim 8, characterized in that: 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.

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