METHOD FOR EXTRACTING PROTEIN FROM RASPBERRY CAKES

Description

[0001] The present invention relates to a process for obtaining proteins from rapeseed press cake, comprising the following steps: Separation of hull components from the rapeseed press cake; suspension of the purified fraction after separation of the hull components in an aqueous solution; mixing of this first suspension at an elevated temperature of at least 31 °C to dissolve proteins; cooling of the protein solution or the suspension to a temperature of less than 5 °C with precipitation of a first protein-rich sediment and separation of the first protein-rich sediment.

[0002] Rapeseed is a plant species from the Brassicaceae family and, due to its high oil content, is classified as a soft seed. Compared to cereals, rapeseed is almost entirely free of endosperm tissue; nutrients are stored in a structured manner within the cells. For the extraction of proteins with water, the amphiphilic properties of the proteins and their solubility are important. Rapeseed oil is primarily stored in oleosomes. The oleosome membranes contain proteins. The smaller the average oleosome diameter, the larger the membrane surface area and thus the higher the protein content in the rapeseed. These storage proteins make up 90% of the total protein content of rapeseed and can be divided into three main types: 40% Globulins 40% Albumins 10% Oleosin

[0003] The proteins to be extracted are therefore mainly globulins and albumins.

[0004] The proteins contained in rapeseed have different solubilities due to their varying structures. These are primarily the 12S globulin cruciferin and the 2S albumin napin. The solubility of cruciferin in water depends mainly on the pH of the solution. Its isoelectric point (IEP) is approximately 4.5. Solubility increases with increasing pH, starting from the IEP. At a pH of 4.5, cruciferin is at its isoelectric point, is therefore nonpolar, and thus poorly soluble in water, while its solubility increases in alkaline conditions.

[0005] Rapeseed oil is extracted in oil mills either by hot pressing and extraction or by cold pressing. After pressing, in which the rapeseed oil is mostly, but not completely, extracted, a protein- and energy-rich rapeseed mass remains with a residual oil content of, for example, approximately 10% to 20% by weight. This rapeseed mass is called "rapeseed meal" or "canola meal" (also known as "rapeseed extraction meal" or "canola meal") after hot pressing and extraction. The residue remaining after cold pressing is called "rapeseed press cake."

[0006] Rapeseed consists of a rapeseed kernel (cotyledon) and black hulls, which are removed in some processes. If only the kernel remaining after hull removal is pressed, cold pressing yields rapeseed kernel oil. However, cold pressing for oil extraction usually involves pressing the whole or partially hulled rapeseed, so the resulting rapeseed press cake still contains the hulls.

[0007] Regarding the starting materials for rapeseed protein production, a distinction must be made between rapeseed meal and rapeseed press cake, whose composition and properties differ significantly. Rapeseed meal, which is produced during the extraction of rapeseed with solvents, typically contains a maximum of approximately 2.5% oil, about 11.5% water, for example, about 32% protein, and about 13% crude fiber. When extracting rapeseed oil, the hulls are usually removed first. Solvents such as hexane are used in the extraction process, and higher temperatures are employed. For this reason, and because of the subsequent toasting to drive off the solvent, the protein content in rapeseed meal is denatured and therefore less valuable for human nutrition.

[0008] Rapeseed press cake, on the other hand, is the solid press residue obtained as a byproduct of cold pressing or, in some cases, hot pressing of rapeseed oil. Rapeseed press cake has a significantly higher oil content than rapeseed meal, ranging from approximately 10% to 20%, or around 15%, depending on the pressing method. The protein content of rapeseed press cake is approximately 26% to 38%, or around 33%, for example. The fiber content is approximately 7.8% to 13%, or around 9%, for example. The moisture content is 5% to 12%, or around 8%, for example. Rapeseed press cake also differs from rapeseed meal in its hull content. Furthermore, after cold pressing, rapeseed press cake is produced in a lumpy or granular form, and to extract the protein, it must first be ground. This can be achieved, for example, by wet grinding in suspension.

[0009] German patent DE 10 2016 115 911 B4 describes a process in which, according to one variant, a mixture of already de-oiled rapeseed (press cake) is used. This press cake is then crushed, the crushed mixture dispersed, and the pH of the resulting pulp is adjusted to an alkaline range with a pH greater than 9.5 by adding lye. Ethanol, a water-soluble organic solvent, is then added to separate the hulls from the cotyledon. The solid phase containing the hulls is separated, the pH is adjusted to the acidic range using dilute hydrochloric acid, and the resulting multiphase mixture is separated in a decanter, yielding a polyphenol-albumin liquid phase to which the enzyme laccase is added. The enzyme reacts the aqueous sinapic acid-containing phase.In addition to the aqueous sinapic acid phase, a protein curd precipitates during acidification, which can be separated and thus obtained as a byproduct of this known process. This document contains no information on different solubilities of the proteins at different temperatures.

[0010] WO 2019 / 048695 A1 describes a process for extracting protein from rapeseed or other oilseeds, in which the rapeseed is first dehulled, leaving only a comparatively low hull content and thus a low fiber content. The dehulled rapeseed is then mechanically defatted by pressing, and the water bound in the press cake is largely removed, resulting in a water content of less than 2%. This is followed by extraction with an organic solvent such as methanol, ethanol, propanol, hexane, or supercritical CO₂. In this known process, the pressing takes place at a temperature of 70 °C, the subsequent drying is carried out under vacuum at 80 °C, and then the extraction with the organic solvent is performed at a relatively high temperature of 60 °C.

[0011] US Patent 9,040,098 B2 describes the production of a soluble rapeseed protein isolate by adding an aqueous sodium chloride solution to rapeseed meal and stirring the mixture at room temperature. The insoluble portion of the rapeseed meal is removed, and the resulting protein solution is centrifuged, filtered for clarification, concentrated across a membrane, and then pasteurized at 60 °C. Subsequently, the concentrated solution is treated with calcium chloride, and the resulting precipitates are separated by centrifugation. This known process always proceeds with the retentate, that is, with those proteins that dissolve in an aqueous saline solution at room temperature. The starting material used is "rapeseed meal," so it can be assumed that it is a rapeseed extraction meal as described above.Furthermore, this known process includes a step in which the concentrated rapeseed protein solution is acidified with hydrochloric acid to a pH value of 2.5 to 4.

[0012] EP 1 389 921 B1 also discloses a process for obtaining proteins from rapeseed flour, in which the flour is dissolved using a room-temperature NaCl solution, yielding an aqueous protein solution. After separating the remaining rapeseed flour and clarifying the solution by centrifugation, as well as adding activated carbon, the protein extract solution is concentrated by ultrafiltration. The concentrated solution is then diluted with water at 4 °C, forming a precipitate in the form of a white cloud. The viscous, sticky mass obtained after removal of the water is then dried without further treatment.

[0013] US2007 / 0004909 A1 discloses the extraction of rapeseed proteins from rapeseed meal oil using an aqueous salt solution, heat treatment of the separated rapeseed protein solution, and precipitation of the proteins.

[0014] The aforementioned publications show that prior art includes methods for extracting proteins from rapeseed oilseed, both of which start with rapeseed meal (rapeseed extraction meal) and those that attempt to extract proteins from the rapeseed press cake obtained by cold pressing. However, these methods often employ organic solvents to dissolve the proteins and / or adjust the pH of the protein solution by adding alkali or acid. A disadvantage of using alkali is the subsequent need to add acid to bring the pH to a near-neutral level. Other methods involve adding salts such as NaCl or CaCl₂ to increase protein solubility or to separate certain substances, necessitating subsequent removal of these salts through washing or similar processes.

[0015] Some known methods involve many separation steps and are therefore complex, or they use comparatively expensive separation steps such as ultrafiltration. In the method known from EP 1 389 921 B1, the process of dissolving proteins from rapeseed flour is carried out by stirring at room temperature with the addition of sodium chloride. Investigations related to the present invention have shown that at room temperature (approx. 20 °C) only a portion of the proteins dissolve, as protein solubility increases with temperature. On the other hand, excessively high temperatures applied during the dissolution process or other steps in the treatment of the rapeseed are also counterproductive, as they lead to protein denaturation.

[0016] Based on the aforementioned disadvantages of the prior art, the object of the present invention is to provide a process for obtaining proteins from rapeseed press cake with the aforementioned features, which is less complex, does not require the use of organic solvents and acids, alkalis or salts, uses methods that are gentle on the proteins and nevertheless enables the recovery of a comparatively high proportion of the proteins contained in the rapeseed press cake.

[0017] The solution to the aforementioned problem provides a method for obtaining proteins from rapeseed press cake with the features of claim 1.

[0018] According to the invention, a process with the features mentioned above is provided in which the first protein-containing sediment obtained after separation is subsequently mixed with water to produce a further suspension. This further suspension is cooled to a temperature of less than 5 °C, and the second protein-rich sediment obtained is separated. The process according to the invention has the following advantages: Firstly, it provides for the dissolution of the proteins without the addition of organic solvents. An aqueous suspension of the purified fraction is produced after separation of the shell components. However, the suspension and mixing of the suspension take place at a higher temperature than in the prior art, preferably at a temperature of at least about 31 °C. Due to this higher temperature, a larger proportion of the proteins dissolves when an aqueous medium is used as the solvent.

[0019] Since, according to the invention, the use of salts in the process of dispersing the rapeseed press cake and dissolving protein components is dispensed with, the process is simpler overall, as the removal of salts can be dispensed with and thus further subsequent purification steps can be omitted.

[0020] The use of alkalis in the dispersing step of the rapeseed press cake is avoided whenever possible, and according to the invention, this step is preferably carried out at a native pH value. "Native" pH value refers to the pH value obtained when the rapeseed press cake is dispersed in water without the addition of an alkali or other basic medium. According to the invention, the pH value is therefore approximately in the neutral range. This has the advantage of ensuring gentle treatment of the proteins contained in the rapeseed press cake and preventing denaturation by an alkaline medium. Furthermore, it is advantageous that no subsequent neutralization of the alkaline medium is necessary, thus avoiding the addition of acids and simplifying the entire process.

[0021] The process according to the invention is further based on the understanding that the solubility of the proteins contained in the rapeseed press cake in aqueous solution depends on the temperature of the water. The difference in solubility increases with the temperature difference. For example, if the rapeseed press cake is dispersed with water at a temperature of approximately 31 °C and the aqueous medium in which a portion of the proteins has dissolved is subsequently cooled to a temperature of, for example, 4 °C, then a temperature difference of 27 °C already results. Alternatively, if the rapeseed press cake is dispersed at a temperature of, for example, 38 °C and the protein-containing solution is subsequently cooled to, for example, 1 °C, then the temperature difference is already 37 °C.Such temperature differences cannot be nearly achieved if the rapeseed press cake is dispersed at room temperature, as is the case with prior art methods, because in this case a maximum temperature spread of only about 20 °C would be possible, since the temperature cannot be lowered below freezing during protein precipitation. Nevertheless, the inventive method avoids excessively high temperatures when dissolving the proteins, for example, 60 °C or above, because there would be a risk that the proteins would at least partially denature, thus reducing the value of the final product.

[0022] According to the invention, by significantly cooling the protein-rich solution by lowering the temperature to less than 5 °C, proteins precipitate. This protein mass, referred to in the invention as the "first protein-rich sediment," is then mixed with water in at least one subsequent step to produce a further suspension. This further suspension is cooled to a temperature of less than 5 °C, and the resulting second protein-rich sediment is then separated. This method according to the invention has the advantage of producing a washing effect, since substances that dissolve and remain in solution under these conditions can be separated and removed during the subsequent separation process.These can be, for example, components of the rapeseed press cake that negatively affect the sensory properties of the protein-containing target product, which is intended for use in food or animal feed. By removing unwanted substances from the sediment during this washing process, the relative protein content in the sediment increases.

[0023] A further advantage is that the aforementioned measure is a comparatively simple process step that does not require increased equipment, such as ultrafiltration, which is used in the prior art. Thus, the process according to the invention is superior to known methods, is considerably more cost-effective, and therefore advantageous, particularly when the production of rapeseed press cake on an industrial scale in large quantities is planned.

[0024] Thus, the present invention provides a method which, with less equipment than previous methods, enables the extraction of a comparatively high proportion of the proteins contained in the rapeseed press cake in a gentle manner.

[0025] As mentioned earlier, rapeseed press cake, unlike rapeseed extraction meal, generally still contains a portion of the hull, since the rapeseed is pressed with the hulls during cold pressing to obtain rapeseed oil. Assuming rapeseed press cake from cold pressing, the process according to the present invention offers two alternative methods for removing the hulls. One can either separate the hulls using a dry process, removing them before the rapeseed press cake is dispersed with water, or the rapeseed press cake is first dispersed in water, and then the hulls are removed from this dispersion; in other words, this is essentially a wet separation process.In this variant of wet separation, according to a preferred embodiment of the invention, shell fragments can be separated from the suspension by filtration or decantation, for example, using vibrating screens, rotary filters, a filter press, or the like – optionally in several stages and with combined separation systems. This yields a shell-rich filter cake, which can optionally be redispersed with water to obtain further proteins from the resulting suspension. After separation of the filter cake, a protein-rich liquid remains, containing all proteins that dissolve under the conditions of suspension with water at a given temperature of at least 31 °C. This protein-rich liquid is then cooled in the next step to precipitate the proteins.

[0026] In the alternative dry separation of the hulls, the rapeseed press cake is first crushed, for example, by milling. Various milling methods are suitable, such as impact mills, pin mills, cross-mills, roller mills, or similar devices. This crushing is necessary because the rapeseed press cake is usually in larger pieces or chunks after pressing. After crushing, the hulls can be separated, for example, by sieving and / or air classification. Air classification is a mechanical separation process in which particles are separated based on the ratio of inertial force (gravity) to flow resistance in a gas stream. During vertical air classification, the lighter hulls rise to the top, while the particles, where gravity exceeds flow resistance, settle to the bottom.Sieving involves separation based on particle size.

[0027] After the dark hulls of the rapeseed are removed using a dry process, a lighter fraction remains, containing the core of the rapeseed (the cotyledon) and possibly some remaining hull fragments. In the process according to the invention, this lighter fraction of the rapeseed press cake is then suspended in water and mixed to dissolve the protein components. Thus, in the dry separation process, the hulls are first removed, and then the hull-free fraction is suspended in water, whereas in the wet separation process described above, the crushed rapeseed press cake is first suspended in water, and then the hulls are removed from the suspension.An advantage of wet separation is that the entire rapeseed press cake is subjected to the suspension, thus avoiding the loss of parts of the rapeseed kernel adhering to the hulls, and therefore some of the proteins to be recovered, which would occur during mechanical dry separation of the hulls.

[0028] According to a preferred embodiment of the present invention, the purified fraction is suspended in a salt-free aqueous solution. This has the advantage that the protein solution obtained in this step is salt-free, thus eliminating the need to remove the dissolved salts in a subsequent step. Furthermore, it can be advantageous to avoid any interaction between the salts used and the proteins contained in the solution.

[0029] To dissolve protein components from the crushed rapeseed press cake, the invention states that the press cake is dispersed with water at a temperature of at least approximately 31 °C. The rapeseed press cake can be mixed with warm water or, optionally, with cold water, and the resulting dispersion is then heated to the desired temperature. The resulting dispersion is stirred or otherwise thoroughly mixed to dissolve the proteins. According to a preferred embodiment of the invention, the dispersion or mixing of the first suspension takes place at a temperature in the range of approximately 31 °C to approximately 55 °C, particularly at a temperature between approximately 35 °C and approximately 50 °C, and most preferably at a temperature in the range of approximately 35 °C to approximately 45 °C.

[0030] The previously described heating of the aqueous suspension aims to dissolve as many of the proteins contained in the crushed press cake as possible. In the next step, this suspension is cooled, preferably to a temperature in the range of approximately 4 °C to 0 °C. During cooling, the temperature can be brought close to freezing, but care must be taken to ensure that the aqueous solution does not freeze, as this would impair the subsequent separation process. A precipitate forms during cooling, presumably because the initially dissolved proteins become insoluble at the low temperature and thus precipitate out. The resulting protein-rich sediment can then be separated.

[0031] This sediment, which precipitates after cooling the dispersion, is referred to in the present application as the "first protein-rich sediment". According to the invention, the separated first protein-rich sediment is then mixed with water again to produce a further suspension, this further suspension is then cooled to a temperature of less than 5 °C and the second protein-rich sediment obtained can again be separated.

[0032] According to a preferred embodiment of the invention, the separation of the first and / or second protein-rich sediment is carried out under the influence of a centrifugal or gravitational field. This means that the separation is effected by rotation in a suitable device in which such a centrifugal field is generated, for example in a decanter, a separator, or a centrifuge.

[0033] According to a preferred embodiment of the invention, the first suspension has a native pH value in the range of at least approximately 6.5 to 6.8. A native pH value is understood to be the pH value that results when the rapeseed press cake is dissolved in water without the addition of an acid or base. The resulting pH value thus depends only on the nature of the rapeseed press cake and the pH value of the added water, which can naturally fluctuate, particularly when tap water is added, as tap water can have a pH value within a certain range depending on the region. According to a possible alternative embodiment of the process, however, the addition of an alkaline medium can optionally be provided, by means of which the dispersion is brought to a neutral or slightly alkaline pH value in the range of approximately 6.5 to approximately 9.

[0034] According to the present invention, a solution is obtained by precipitating and separating the first protein-rich sediment, which is referred to herein as the "protein-poor supernatant". According to a possible preferred embodiment of the process according to the invention, it is possible to further process this protein-poor supernatant, which also contains the other substances soluble in water upon dispersion but which do not precipitate upon significant cooling to less than 5 °C, after the separation of the first protein-rich sediment. For example, it is conceivable to recover further valuable substances contained in the rapeseed press cake from this protein-poor supernatant. Examples include glucosinolates, sinapic acid, a phenolic acid present in rapeseed in significant quantities, or phytic acid, a phosphoric acid ester found in rapeseed.It is also conceivable to obtain further proteins from the supernatant during processing, which do not precipitate during the strong cooling but remain dissolved in the supernatant.

[0035] Finally, in some cases it is also useful to purify the protein-poor supernatant in a suitable way, for example to remove harmful substances, before discharging the supernatant into the wastewater to avoid contamination of the wastewater with these substances.

[0036] The same process steps listed above for the protein-poor supernatant after separation of the first protein-rich sediment can optionally also be carried out with the protein-poor supernatant from the second protein-rich sediment. When the first protein-rich sediment is resuspended in water, substances dissolve that remain at least partially dissolved in the protein-poor supernatant even after cooling and separation of the second protein-rich sediment. This second supernatant can be processed in the same way as the first protein-poor supernatant after separation of the first protein-rich sediment. However, it may be advantageous from a process engineering perspective to combine the second supernatant with the first and then process these solutions together.

[0037] According to a preferred embodiment of the inventive method, the conditions for producing a further suspension by adding water to the first protein-rich sediment can be varied compared to the conditions for the first suspension of the rapeseed press cake in an aqueous solution, in particular with regard to the composition or pH value or temperature of the aqueous medium used for suspension, and / or the conditions for cooling the further suspension can be varied compared to the conditions for cooling the first protein solution, in particular with regard to the temperature to which the respective suspension is cooled.In this way, for example, it is possible to dissolve different proportions of the rapeseed press cake in the preparation of the further suspension than in the first suspension, or to precipitate different proteins in the subsequent precipitation by cooling than in the first precipitation by cooling.

[0038] According to a preferred embodiment of the process according to the invention, the second protein-rich sediment obtained from the further suspension can be treated again with water to produce a further suspension, which is then cooled again to a low temperature in the range of less than 5 °C, so that a further purified protein-rich sediment is obtained, and after its separation, a further protein-poor supernatant. Optionally, the cycle of these steps can be repeated two or more times in order to further purify the protein, further increase the relative protein content in the sediment, and improve the overall yield of the process.For example, it is also possible in these further process cycles to vary the conditions during the production of the aqueous suspension, such as the pH value and / or the conditions during the precipitation of the protein-rich sediment by cooling, such as the temperature at which precipitation takes place, in order to obtain further protein fractions contained in the starting product.

[0039] The invention and its technical context are explained in more detail below with reference to the figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations explained in the figures and combine them with other components and findings from the present description and / or figures. It should be noted in particular that the figures, and especially the depicted proportions, are only schematic. The same reference numerals denote the same objects, so that explanations from other figures can be consulted as needed. The figures show: Figure 1 a schematic representation of an exemplary first variant for the processing of the rapeseed press cake according to the inventive method, in which the hulls are separated in a dry process; Figure 2 a schematic representation of a second variant for the processing of the rapeseed press cake according to the inventive method, in which the hull separation takes place after the rapeseed press cake has been suspended with water; and Figure 3 a schematic representation of the protein extraction from the processed rapeseed press cake according to the inventive method.

[0040] The following section will first describe the procedural scheme of Figure 1Reference is made to, and a first possible variant for processing the rapeseed press cake according to the inventive method is explained in more detail based on this illustration. In this dry variant of the method, a rapeseed press cake 10 from the cold pressing of rapeseed is used, which is crushed by means of an impact mill to a particle size in the range of, for example, about 200 µm to about 1500 µm, preferably in the range of about 500 µm to about 1200 µm. From this crushed material 11 of the rapeseed press cake, the dark hulls of the rapeseed are then separated by air classification 12, resulting in two separate fractions, namely an inner light fraction 13 and the separated hulls 14. The further treatment of the hull-free light fraction 13 then takes place according to the process scheme shown. Figure 3 It will be explained in more detail there.

[0041] The following section will first describe the procedural scheme of Figure 2Reference is made to, and the processing of the rapeseed press cake according to the inventive method is explained in more detail. In this variant of the method, a rapeseed press cake 10 is used, which is mixed with water 15 to produce a suspension 16 with a concentration of approximately 5% in water. This suspension is stirred and mixed in a mixing tank at an elevated temperature of, for example, approximately 40 °C. The suspension 16 has a native, nearly neutral pH value of approximately 6.5 to 6.7. Heating the suspension 16 causes the proteins contained in the rapeseed press cake to dissolve. The suspension is then filtered 17 by being pressed through a French press. This produces a protein-rich liquid 18 and a filter cake rich in hulls. Thus, in this variant of the method, the hulls are not separated beforehand, but only from the rapeseed press cake suspension in water.

[0042] The shell-rich filter cake 19 obtained during filtration 17 can be mixed again with water 15 to produce another suspension 20 in a mixing tank, which is mixed at a temperature of, for example, approximately 6.5 and approximately 40 °C. This further suspension 20 can then be subjected to another filtration 21 in a filter press, again yielding a protein-rich liquid 22 and a shell-rich filter cake 23. The protein-rich liquid 22 is directed to protein extraction according to arrow 24, as is the protein-rich liquid 18 obtained during the first filtration 17. The further treatment of the protein-rich liquids is described below with reference to the Figure 3explained in more detail. The shell-rich filter cake 23 obtained as residue during filtration can be used for further purposes according to arrow 25, for example as animal feed, to which further components from this or other processes such as rapeseed extraction meal or the like may be added.

[0043] The following are, with reference to the Figure 3 The further steps according to an exemplary variant of the method according to the invention are explained in more detail. In this process, the following is described in the process scheme of Figure 3 either starting from the shell-free inner light fraction 13, which is obtained during the dry separation of the shells according to the variant of Figure 1 was received and according to Figure 3 with water 15 or it is assumed that the protein-rich liquid 18 or 22 is used in the wet separation in the process variant according to Figure 2The suspension 26, or the protein-rich liquid, is cooled in a mixing tank to a temperature of, for example, approximately 0 °C, and the pH of this suspension or solution is adjusted to 4.5 by adding acid. The cooling by approximately 40 °C causes the proteins contained in the suspension or protein-rich liquid to precipitate. These sedimented proteins can then be separated in a centrifugal field 27, for example, in a centrifuge, whereby the temperature of the solution may rise slightly, for example, to a temperature in the range of approximately 4–5 °C.

[0044] In this separation 27, a protein-rich sediment 28 is obtained, as well as a protein-poor supernatant 29, which contains the remaining substances from the suspension 26 that are soluble under these conditions. The protein-rich sediment 28, which has been separated, can then be mixed with water 15 to obtain a further suspension 30, so that the protein-rich sediment 28 is subjected to a washing process. This suspension is also carried out at low temperatures, for example, about 0 °C, to prevent the previously precipitated proteins from redissolving. The pH of this further suspension 30 is preferably in the range of about 4.5 to about 6.5.A further separation 31 takes place, for example in a decanter at a still low temperature and a pH value in the mentioned range, whereby washed-out substances that are undesirable in the protein as the target product are located in a protein-poor supernatant 32, which is shown in arrow 33 in . Figure 3 The sediment can either be further processed or discharged into the wastewater. The protein-rich sediment 34, purified by the washing process and separated at 31, can be further purified in one or more subsequent washing cycles, each of which comprises suspension with water 15 at low temperature to produce a suspension 30 and separation in a centrifugal field 31, so that a purified protein-rich sediment 34 is obtained as the target product.

[0045] The following examples illustrate the conditions for comminution and processing of the rapeseed press cake used for protein extraction on an industrial scale. shredding

[0046] The feed particle size of the rapeseed press cake to be ground was 30 mm, the bulk density was 520 g / l, the moisture content was 8.2%, and the quantity of feedstock supplied was 60 kg. An air vortex mill with a high-speed rotating ultra-rotor was used as the grinding device. In this type of mill, the rotary motion combined with a high airflow creates extremely fast air vortices. The soft to medium-hard materials are captured in this airflow, subjected to extreme turbulence, and ground at their natural fracture points by the impact of particles on each other, as well as on the grinding track and tools. The main rotor had a power output of 11 kW and its screening unit was equipped with an E650-type screen with a mesh size in the range of approximately 200 µm to 1500 µm, preferably in the range of approximately 500 µm to approximately 1200 µm.The mill's inlet temperature was 25 °C, the outlet temperature 41 °C. At the end of the milling process, 44.5 kg of fines and 8.4 kg of coarses were obtained. Processing for protein recovery (according to the invention)

[0047] The inventive method for obtaining proteins from rapeseed press cake is explained in more detail below using a specific example. While an example of the comminution of rapeseed press cake on an industrial scale was previously presented, the following example describes the comminution and subsequent experiments on a laboratory scale. The starting material was rapeseed press cake pressed into lumps. To enable further physical separation methods, the lumps first had to be comminuted. In this example, a hammer mill with a slot thickness of 5 mm was used for this purpose. Alternatively, experiments were also carried out using a so-called Stephan cutter for comminution, which, however, proved to be less effective.

[0048] Three kilograms of the pre-crushed rapeseed press cake were then placed in a zigzag air classifier. The heavier fraction, which had simply fallen through the chute, was fed a second time into the chute via the hopper. After this second pass, the bulk material was removed and separated into a lower-density fraction and a higher-density fraction. Both fractions were freeze-dried and analyzed for their protein content. The analyses were performed in duplicate. The separation of the dark, black hulls from the light yellow flour was also visually assessed. The lower-density fraction contained the processed, low-hull, high-protein rapeseed press cake, which was then further processed.The lower density fraction was light, primarily yellow, with small, black hull fragments and, when separated by air classification, usually made up about one third of the total weight of the rapeseed press cake, while the higher density bulk material, which consisted of dark, black and coarser hull fragments, made up about two thirds of the total weight.

[0049] The protein content of the entire crushed rapeseed press cake before separation by air classification was 30.8%, while that of the lighter-colored fraction with lower density, which was subsequently processed, was 32.2%. The protein percentages shown in the tables below were calculated as follows: Proteinanteil in % = Protein in g 30 , 8 g ⋅ 100

[0050] To extract the processed rapeseed press cake, it was suspended in water. A series of experiments was conducted in which three different parameters were varied: firstly, the pH of the aqueous solution used for suspension, which was once left at its native value and once adjusted to pH 9 (slightly alkaline); secondly, the temperature of the suspension was adjusted to either 20.5 °C or 40 °C; and thirdly, the concentration of rapeseed press cake in the suspension was adjusted to 5%, 8%, or 10%. After a reaction time of one hour, the solution was pressed in a French press. By pressing the filter onto the sample, the liquid supernatant was separated from the solid residue. The conditions of the individual experiments are shown in Table 1 below, with each sample being prepared in duplicate. Table 1: sample PH value temperature RPK concentration 1 native 20,5 °C 5 % 2 native 20,5 °C 8 % 3 native 20,5 °C 10 % 4 native 40 °C 5 % 5 native 40 °C 8 % 6 native 40 °C 10 % 7 9 20,5 °C 5 % 8 9 20,5 °C 8 % 9 9 20,5 °C 10 % 10 9 40 °C 5 % 11 9 40 °C 8 % 12 9 40 °C 10 % RPK = Rapeseed Press Cake

[0051] The liquid supernatant after pressing the suspension as described above contained the proteins that dissolved during extraction. The resulting solution was then cooled to 0 °C to precipitate the proteins, and the sediment formed was separated by centrifugation at 0 °C. In experiments where the pH had been previously adjusted to 9, the pH was lowered to 4.5 by adding 0.1 M hydrochloric acid, while in experiments where the pH had been adjusted to its native value (pH 6.7), the native pH was left unchanged.

[0052] The centrifuge rotated at 3000 revolutions per minute, and the centrifugation period lasted 10 minutes. The g-force (x times the force of gravity) during centrifugation was 1800 g.

[0053] Table 2 below shows the results for pressing the suspension using a French press as described above, with the subsequent extraction of the rapeseed press cake carried out at 40 °C according to the invention. The protein contents listed below were determined according to method L06.00-7 (Official Collection of Test Methods § 64 LFGB). The protein content is not determined directly, but calculated. For this purpose, the total nitrogen content is measured. The nitrogen content is determined by performing a Kjeldahl digestion to release the nitrogen. Table 2: (Extraction at 40 °C, precipitation of proteins at 0 °C) sample Concession PH value Protein content Protein per 100 g RPK in g proportion of protein obtained 1 5 9 59,32 % 13,70 44 % 2 5 9 56,41 % 14,18 46 % 3 10 9 54,47 % 12,25 40 % 4 10 9 53,99 % 12,43 40 %

[0054] Table 2 above shows that in the experiments where the rapeseed press cake (RPK) was suspended in water at a concentration of 5%, a higher proportion of proteins went into solution than in the cases where the suspension was prepared with a higher concentration of 10% in water. Comparative test 1

[0055] A first comparative experiment was carried out in which the extraction of the rapeseed press cake was not performed at a higher temperature (e.g., 40 °C) as per the invention, but at room temperature. The results are shown in Table 3 below. Table 3: (Extraction at room temperature, precipitation of proteins at 0 °C) sample Concession PH value Protein content Protein per 100 g RPK in g proportion of protein obtained 7 5 9 50,16 % 9,50 30 % 8 5 9 48,28 % 10,48 32 % 11 10 9 55,49 % 6,86 22 % 12 10 9 53,15 % 7,02 22 %

[0056] Comparison experiment 1 and Table 3 show that, under otherwise identical conditions (same pH and same concentrations when suspending the rapeseed press cake as in Table 2), the protein content in the solution and the proportion of protein recovered from the rapeseed press cake are considerably lower when extraction is carried out at room temperature. Furthermore, at a higher concentration in the suspension (10%), the proportion of recovered protein is again lower than at a lower concentration (5%). Comparison test 2

[0057] A second comparative experiment was conducted in which the extraction of the rapeseed press cake was not carried out at a higher temperature (e.g., 40 °C) as per the invention, but at room temperature. Furthermore, the precipitation of the proteins was also performed at room temperature and not at 0 °C. The results are shown in Table 4 below. Table 4: (Extraction at room temperature, precipitation of proteins at room temperature) sample Concession PH value Protein content Protein per 100 g RPK in g proportion of protein obtained 1 5 9 44,26 % 6,67 21 % 2 5 9 44,28 % 7,21 23 % 3 10 9 49,89 % 5,26 17 % 4 10 9 49,15 % 5,02 16 %

[0058] Comparison experiment 2 and Table 4 show that, under otherwise identical conditions (same pH and same concentrations when suspending the rapeseed press cake as in Table 2), even lower protein levels are obtained. This indicates that less protein can be precipitated at room temperature than at low temperatures.

[0059] In a further series of experiments, the effect of the number of washings of the first protein-rich sediment in the present application was investigated. The procedure was carried out under the conditions of the invention, i.e., extraction was performed at 40 °C and the subsequent precipitation of the first protein-rich sediment took place at a low temperature of 0 °C. The pH of the samples was adjusted to 9 for extraction, and the concentration during suspension of the rapeseed press cake was 5% in each case. The first protein-rich sediment was washed with water and then precipitated again at a low temperature. The results are shown in Table 5 below. For the first sample, the number of washings was 1, for the second sample it was two, and so on.The results in Table 5 show that the protein content of the sediment increases with the number of washes. This is because the protein purity increases as other unwanted substances are washed out. However, the proportion of recovered protein decreases slightly with each wash, as some protein is naturally redissolved during the process. The table shows, for example, that with three additional washes, the protein content of the washed and thus purified sample can be increased to 62.6%. Table 5: (Results of sediment analyses with increasing number of washes) sample Number of washes Protein content Protein per 100 g RPK in g proportion of protein obtained 1 1 54,9 % 11,21 36 % 2 2 58,7 % 10,22 33 % 3 3 60,3 % 9,93 32 % 4 4 62,6 % 9,74 32 % Example 2 (according to the invention)

[0060] The inventive process for obtaining proteins from rapeseed press cake is explained in more detail below using a further concrete example. While an example of protein extraction from rapeseed press cake on a laboratory scale was previously presented, the following example describes the comminution and further processing on a pilot scale. The starting product was rapeseed press cake pressed into lumps. To enable further physical separation methods, the lumps first had to be comminuted. In the present example, a hammer mill with an insert having a slot thickness of 5 mm was used for this purpose.

[0061] The resulting flour exhibited a specific particle size distribution. 40 kg of this flour were suspended in 760 L water at 45 °C with continuous stirring. After 30 minutes, this suspension was pumped through a two-stage vibrating sieve. The resulting filter cake was pressed using a juice press, and the resulting solution was combined with the remaining liquid. A protein solution and a filter cake were obtained. The protein solution was cooled to 0–1 °C. After 14 hours, this solution was separated using a disc separator (Westfalia Separator CA 20). The sediment was rehydrated, cooled to 0 °C, and centrifuged as previously described. Reference symbol list

[0062] 10 Rapeseed press cake 11 Grinding 12 Hull separation by air classification 13 Inner light fraction 14 Separated hulls 15 Water 16 Suspension 17 Filtration 18 Protein-rich liquid 19 Hull-rich filter cake 20 Suspension in mixing tank 21 Filtration 22 Protein-rich liquid 23 Hull-rich filter cake 24 For protein extraction 25 For further use, e.g., as animal feed 26 Suspension in mixing tank 27 Separation in centrifugal field 28 Protein-rich sediment 29 Protein-poor supernatant 30 Further suspension 31 Separation 32 Protein-poor supernatant 33 Arrow 34 Protein-rich sediment

Claims

1. Method for obtaining proteins from rapeseed press cake obtained by cold pressing or optionally by hot pressing, comprising the following steps: optionally separating peel fractions from the rapeseed press cake (10); suspending the rapeseed press cake (10) in an aqueous solution before or after separating the peel fractions; mixing this first suspension (16) at an elevated temperature of at least 31°C in order to bring proteins into solution; separating (17) the peel fractions from the solution, if these have not already been separated dry in advance; cooling the protein solution (18, 22) or the suspension (26) to a temperature of less than 5°C with precipitation of a first protein-rich sediment (28); separating (27) the first protein-rich sediment (28); wherein water (15) is then added again to the first protein-rich sediment to produce a further suspension (30), the further suspension (30) is cooled to a temperature of less than 5°C and the second protein-rich sediment (34) obtained in the process is separated.

2. Method for obtaining proteins from rapeseed press cake according to claim 1, characterized in that the peel fractions are separated by filtration (17) or in a gravity or centrifugal field, in particular by decantation.

3. Method for obtaining proteins from rapeseed press cake according to claim 1 or 2, characterized in that the suspended (26) of the purified peel-free fraction is carried out with a salt-free aqueous solution (15).

4. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 3, characterized in that the suspension or the mixing of the first suspension (16) is carried out at a temperature in the range from about 31°C to about 55°C, in particular at a temperature between about 35°C and about 50°C, particularly preferably at a temperature in the range from about 35°C and about 45°C.

5. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 4, characterized in that the protein solution (18, 22) or the suspension (26) is cooled to a temperature in the range from about 4°C to about 0°C.

6. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 5, characterized in that the first suspension (16) has a native pH in the range from at least about 6.5-6.8 or is brought to a neutral or weakly alkaline pH in the range from about 6.5 to about 9 by addition of an alkaline medium.

7. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 6, characterized in that the separation (27, 31) of the first (28) and / or second protein-rich sediment (34) is carried out under the action of a centrifugal field.

8. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 7, characterized in that further processing of the protein-poor supernatant (32) is provided after the separation of the first (28) or second protein-rich sediment (34).

9. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 8, characterized in that the separation of shell portions (14) from the rapeseed press cake comprises at least one step of comminution (11) and / or at least one subsequent step of sieving or air sifting (12), preferably before the suspension of the rapeseed press cake.

10. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 8, characterized in that the rapeseed press cake (10), optionally after or with comminution, is suspended with an aqueous solution (15) and the separation of shell portions (19) is carried out after the suspension (16) by filtration (17) or in a centrifugal field.

11. Method for obtaining proteins from rapeseed press cake according to one of claims 1 to 10, characterized in that the conditions during the production of a further suspension (30) by addition of water (15) to the first protein-rich sediment (28) are varied in comparison with the conditions during the first suspension (26) of the rapeseed press cake in an aqueous solution, in particular with regard to the composition or the pH or the temperature of the aqueous medium which is used for the suspension and / or in that the conditions during the cooling of the further suspension (30) are varied in comparison with the conditions during the cooling of the first protein solution (18, 22) or suspension (26), in particular with regard to the temperature to which the respective suspension is cooled.