Method of extracting proteins from a protein-rich raw material

Abstract

The invention relates to a method of extracting proteins from a protein-rich raw material, comprising the steps of - treating the raw material (F1) with an alkaline solution (L1, L2) such as to obtain a mixture (M1, M2) comprising a solid phase (R1, R2) and a protein-rich liquid phase (EXT1, EXT2) containing the proteins, - separating the protein-rich liquid phase (EXT1, EXT2) from the solid phase (R1, R2), - lowering the pH in the protein-rich liquid phase (EXT1, EXT2, M3), thereby causing precipitation of the proteins to obtain a further mixture (M4, M5) comprising a further liquid phase and a protein-rich solid phase, - separating the precipitated proteins from the mixture (M4, M5) to obtain a protein extract (R4). The method according to the invention is characterized in that the pH in the protein-rich liquid phase (EXT 1, EXT 2, M3) is lowered using a carbon dioxide-containing gas (G3) which is supplemented by a residual amount of inorganic and / or organic acids needed to attain a pH lower than 6.5, and in that the carbon dioxide-containing gas (G3) results from a fermentation of the solid phase (R1, R2) obtained after the raw material (F1) has been treated with the alkaline solution (L1, L2).

Description

[0001] Process for extracting proteins from protein-rich raw materials

[0002] The present invention relates to a method for extracting proteins from a protein-rich raw material, in particular from a residue of beer production, especially from brewer's spent grains.

[0003] Given the need to feed the world's ever-growing population, extensive research and work is being carried out to develop food from nutrient-rich waste products from a wide range of industrial processes.

[0004] The present invention is particularly concerned with the production of a protein-rich product from a protein-rich waste product of the food industry, such as residues from bakeries, fruit processing, confectionery production, and in particular waste products from distilleries and breweries.

[0005] The following will focus in particular on the production of a protein-rich product from brewer's spent grains, but the explanations also apply analogously to other protein-rich raw or waste materials.

[0006] In the EU, breweries generate approximately 3.4 million tons of waste products annually, of which brewer's spent grain (BSG) accounts for approximately 85%. The protein content of brewer's spent grain, for example, can be as high as 19-30% (Wen et al., A Mini-Review on Brewer's Spent Grain Protein, J. of Food Science 84 (12) 2019, 3330-3340).

[0007] Other protein-rich waste products from breweries are spent yeast and hot trub (Rodriguez et al., Protein recovery from brewery solid wastes, J. Foodchem, 2023 (407), 134810).

[0008] The extraction of proteins from such protein-rich raw materials can be carried out in various ways, whereby in the case of brewer's spent grains, the methods of alkaline extraction, extraction with organic solvents (especially ethanol), enzymatic extraction, all optionally supported by pretreatment with ultrasound, can be mentioned in particular.

[0009] Further background information on the processing of brewer's spent grain, in particular the extraction of proteins from it, can be found in WO 2021 / 028405 and the literature cited therein, as well as Vieira et al., Valuation of brewer's spent grain using a fully recyclable integrated process for extraction of proteins and arabinoxylans, Industrial Crops and Products 52 (2014) 136-143.

[0010] The present invention relates to the alkaline extraction of proteins from the above-mentioned protein-rich raw materials, followed by precipitation of the proteins by lowering the pH value.

[0011] The extraction of proteins from protein-rich raw materials or brewer's grains—a residue from beer production—is typically carried out using alkaline solutions such as sodium hydroxide or potassium hydroxide at a pH above 9-10. The subsequent extraction of the proteins is usually achieved—among other methods—by lowering the pH to the isoelectric point. This causes the proteins to flocculate, allowing them to be separated, for example, by filtration or centrifugation. For the alkaline extract from brewer's grains, for example, a pH below pH 4 must be achieved.

[0012] A disadvantage of this method is that a significant amount of acid is required to change from the initially strongly alkaline pH range to a strongly acidic pH. If mineral acids such as hydrochloric acid, phosphoric acid, or sulfuric acid are used for this purpose, they also introduce foreign elements such as chlorine, phosphorus, or sulfur, which can affect the properties, color, and taste of the precipitated protein concentrate. Therefore, a subsequent washing step is necessary to remove the resulting salts and acid residues.

[0013] If organic acids such as citric acid are used, they are usually expensive, often come from non-biogenic sources and also influence the taste of the final concentrate.

[0014] Further prior art is known from US 3,846,397, FR 3 085 680 and from Chetrariu et al., Brewer's Spent Grains: Possibilities of Valorization, a Review, Applied Sciences 16 (2020) 5619.

[0015] The object of the present invention is to overcome the disadvantages of the known processes for obtaining proteins from protein-rich raw materials, in particular brewer's spent grains, and to provide an improved process.

[0016] This object is achieved by a process comprising the steps of - treating the raw material with an alkaline solution, whereby a mixture is obtained which comprises a solid phase and a protein-rich liquid phase containing the proteins

[0017] - Separation of the protein-rich liquid phase from the solid phase,

[0018] - lowering the pH value in the protein-rich liquid phase, whereby the proteins are precipitated and a further mixture is obtained which comprises another liquid phase and a protein-rich solid phase,

[0019] - separating the precipitated proteins from the mixture to obtain a protein extract, and which is characterized in that a carbon dioxide-containing gas is used to lower the pH in the protein-rich liquid phase, which gas is supplemented by a residual amount of inorganic and / or organic acids necessary to achieve a pH lower than 6.5, and in that the carbon dioxide-containing gas originates from a fermentation of the solid phase obtained after treating the raw material with the alkaline solution.

[0020] SHORT DESCRIPTION OF THE CHARACTERS

[0021] Figure 1 shows schematically as a flow diagram an embodiment of the method according to the invention.

[0022] DETAILED DESCRIPTION OF THE INVENTION

[0023] It has been found that by at least partially replacing the above-described inorganic or organic acids for precipitating the proteins present in the liquid phase after alkaline extraction with carbon dioxide, the known processes can be improved in several respects:

[0024] Firstly, the need for acids / chemicals can be reduced, which also means a reduction in costs. Furthermore, the accumulation of reaction products that are difficult to process, such as salts, can be reduced. Likewise, the disadvantages described above, such as the unpleasant taste of the resulting protein extract, etc., can be reduced, as can the washing effort. Since the use of carbon dioxide alone only allows a reduction in the pH to approximately 6.5, the carbon dioxide is supplemented in a conventional manner during the precipitation step with a residual amount of inorganic and / or organic acids necessary to achieve a lower pH.

[0025] Acids that can be used include hydrochloric acid, phosphoric acid, citric acid, ascorbic acid, lactic acid, fruit acids and mixtures thereof.

[0026] In the process according to the invention, the pH value is preferably reduced to a value <5, particularly preferably 3.5 to 4.5, particularly when processing brewer's spent grains.

[0027] In the process according to the invention, the carbon dioxide-containing gas used to precipitate the proteins comes from a biogenic source, in particular from a fermentation.

[0028] The process according to the invention is characterized, among other things, by the fact that the carbon dioxide-containing gas originates from a fermentation of the solid phase obtained after treating the raw material with the alkaline solution. During the reaction of the alkali with the raw material, the biogenic CO2 contained in the raw material is bound. This alone contributes to the reduction of climate-damaging gases.

[0029] To increase the solubility of CO2, the temperature of the protein-rich liquid phase can be lowered to below 20°C, preferably below 15°C, in particular to 10 to 4°C, during the addition of CO2.

[0030] In addition, the solubility of the CO2 can be increased by pressurizing the protein-rich liquid phase during the addition of the CO2, in particular below 10 bar, preferably below 6 bar, in particular from 2 to 5 bar.

[0031] By using overpressure, a static mixer or a pipe section can be used instead of a mixing container to dose and mix the CO2.

[0032] Through the reaction of biogenic CO2 with the OH ion of the lye used for alkaline extraction, this carbonates are bound and can also be physically separated from the mixture during the separation of the precipitated proteins. This results in the separation and storage of the CO2. The solid phase resulting from the alkaline extraction is processed by fermentation to produce biogas. According to the invention, the carbon dioxide produced during fermentation is now used to precipitate the proteins after the alkaline extraction. This internal recycling enables further savings and increased efficiency of the overall process (no use of external carbon dioxide, shortened transport routes). This results in an elegant coupling of two previously separate processes.Obtaining the CO2 required to lower the pH of the protein-rich phase from the processing of a residue from the same plant leads to technical and economic advantages.

[0033] Some steps of the process according to the invention can be repeated and combined to further increase efficiency:

[0034] Thus, the solid phase obtained after treating the raw material with the alkaline solution can be treated again with an alkaline solution, resulting in a further mixture comprising another solid phase and another liquid phase containing a further portion of proteins. The further liquid phase containing proteins can be combined with the first liquid phase obtained containing proteins before precipitation.

[0035] The pH lowering step for protein precipitation can also be repeated. For example, the carbon dioxide-containing gas can be added in a first pH lowering step, and in a subsequent step, the amount of organic and / or inorganic acids required to achieve a lower pH, possibly mixed with additional carbon dioxide, can be added.

[0036] Physical methods such as static settling, centrifugation or membrane filtration, preferably centrifugation e.g. using a disc separator, can be used to separate and concentrate the precipitated proteins.

[0037] DETAILED DESCRIPTION OF THE FIGURE

[0038] According to Figure 1, in one embodiment of the present invention, a protein-rich raw material, e.g., brewer's spent grains, is fed as feed Fl to a first extraction unit EA1. An alkaline liquid extractant LI is fed to the extraction unit EA1. The resulting first mixture MI comprises a liquid phase EXTI containing a high proportion of proteins and a solid phase RI. These two phases are separated from each other in a conventional manner.

[0039] As shown in Figure 1, the solid phase RI is treated in a further extraction unit EA2 with further alkaline or neutral (e.g. water) extraction agent L2, whereby a further mixture M2, whose liquid phase EXT 2 contains a further portion of proteins, is obtained.

[0040] The two phases R2 and EXT2 of the mixture M2 are again separated from each other in a conventional manner.

[0041] The two resulting protein-rich liquid phases EXTI and EXT2 are mixed in a first mixer MIX1 to form a mixture M3.

[0042] The mixture M3 is mixed with carbon dioxide-containing gas G3 in another mixer MIX2 and thus acidified.

[0043] The carbon dioxide-containing gas G3 originates, as shown in Figure 1, from a fermentation FERM of the solid residue R2 for the production of biogas. The raw biogas G1 produced in the fermentation is separated in a conventional manner into a methane-rich stream G2 and the carbon dioxide-rich stream G3. The solid residue from the fermentation R3 is discharged from the process.

[0044] For further acidification, the further mixture M4 obtained after adding the carbon dioxide-containing gas G3 to the mixture M3 can be mixed, for example, in a further mixer MIX3 with inorganic and / or organic acid L3 until the desired pH value is reached.

[0045] The resulting mixture M5 contains the proteins precipitated by acidification in a solid phase R4. This protein-rich phase R4 can be separated again from the resulting liquid phase L4 in a conventional manner and, if necessary, washed with washing medium W in two washing steps W1 and W2. A washed protein extract R5 is obtained, which can be used for further purposes. EXAMPLES

[0046] Example 1 :

[0047] 50.05 g of an alkaline NaOH-extracted extract M3 with a pH of 11.9 was adjusted to pH 2.1 with 4.5 g of 1M HCl. 53.697 g of the solution was transferred to a centrifuge tube, and the resulting precipitate was separated for 5 minutes at 4000 rpm and weighed out at 5.478 g. After drying overnight at 105°C, 0.53 g of dry concentrate was obtained.

[0048] Example 2:

[0049] 50.05 g of an alkaline NaOH-extracted M3 extract with a pH of 11.5 is gassed with CO2 until a pH of approximately 6.5 is established. The solution is transferred to a centrifuge tube and centrifuged for 5 minutes at 4000 rpm. No precipitate forms. 48.06 g of the solution is transferred back to a stirred beaker with a pH meter. A pH of 2.3 is adjusted by adding 3.76 g of 1M HCl. 51.82 g of the solution is transferred to a centrifuge tube, and the resulting precipitate is separated for 5 minutes at 4000 rpm. The wet weight is determined to be 3.52 g.

[0050] After drying at 105°C overnight, 0.499 g of dry concentrate was obtained.

[0051] The acid reduction in Example 2 compared to Example 1 is approximately 11-12% based on the dried product. The dried product from Example 2 tastes pleasantly mildly sour and only slightly salty.

[0052] Example 3:

[0053] A process simulation was used to calculate the extent to which CO2 capture is possible in the process according to the invention and to achieve savings in the acid required for precipitation. The simulation is based on a model calculation using ChemCad and illustrates the magnitude of an industrial coupling of extraction and fermentation. The relevant output stream from a brewery was based on empirical values ​​with an annual output of 24,000 t of moist spent grain. The material flows are given in kilotons per year (kt pa):

[0054] The 24 kt of raw material (Fl) is extracted with a mixture of 51.22 kt of water and 0.54 kt of NaOH (50%) (LI + L2). After mechanical separation, this yields 55.65 kt of extract (M3) and 20.1 kt of extracted and dewatered residue (R2). The residue R2 is then subjected to fermentation, yielding approximately 1.8 kt of CEE (G2) and 1.9 kT of CO2 (G3) per year. The extracted CO2 (G3) is then added to the extract M3. Preliminary tests have shown that approximately 2.7 g / kg of CO2 can be bound per kilogram of extract. This results in an annual binding of approximately 0.15 kt of CO2, or approximately 8% of the total amount of CO2 produced.

[0055] Without the inventive addition of CO2, approximately 0.8 kt of 25% HCl would be required for acidification and precipitation, according to the simulation. From Examples 1 and 2, it is known that a saving of approximately 11% in the acid (L3) requirement for acidification can be expected. Based on the 0.8 kt of 25% HCl required for acidification and precipitation without the inventive addition of CO2, this results in a saving of 0.8 kt or 100 t of HCl per year.

[0056] This not only significantly reduces the acid required for precipitation, but also directly contributes to the capture of climate-damaging CO2. Since the captured CO2 comes from a renewable source, the described process has the potential to be a CO2-negative process.

Claims

Patent claims:

1. A process for extracting proteins from a protein-rich raw material, comprising the steps - treating the raw material (Fl) with an alkaline solution (LI, L2) to obtain a mixture (Ml, M2) comprising a solid phase (RI, R2) and a protein-rich liquid phase (EXT 1, EXT2) containing the proteins - Separation of the protein-rich liquid phase (EXT 1, EXT2) from the solid phase (RI, R2), - lowering the pH value in the protein-rich liquid phase (EXT 1, EXT 2, M3), whereby the proteins are precipitated and a further mixture (M4, M5) is obtained, which comprises another liquid phase and a protein-rich solid phase, - separating the precipitated proteins from the mixture (M4, M5) to obtain a protein extract (R4), characterized in that a carbon dioxide-containing gas (G3) is used to lower the pH in the protein-rich liquid phase (EXT 1, EXT 2, M3), which is supplemented by a residual amount of inorganic and / or organic acids necessary to achieve a pH lower than 6.5, and in that the carbon dioxide-containing gas (G3) originates from a fermentation of the solid phase (RI, R2) obtained after treating the raw material (Fl) with the alkaline solution (LI, L2).

2. Process according to claim 1, characterized in that the protein-rich raw material is a residue of beer production, in particular brewer's spent grains.

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