METHOD FOR THE COUPLED PROCESSING OF SWEET WHEY AND LACTIC ACID FROM ACID WHEY

Description

AREA OF INVENTION

[0001] The invention is in the field of the dairy industry and relates to a process for the coupled production of sweet whey and lactic acid from acid whey. BACKGROUND OF THE INVENTION

[0002] Whey is the watery, greenish-yellow residue produced during cheesemaking. It is the liquid portion that can be separated after the milk has coagulated into cheese or curd. There are two types of whey: the sweet whey (also rennet whey), which is produced when milk is thickened with rennet to make cheese, and which Sour whey which is produced when milk is fermented by lactic acid bacteria.

[0003] Whey consists of 94% water, 4 to 5% lactose, and is virtually fat-free. It also contains lactic acid, vitamins B1, B2 (which gives it its greenish color), and B6, as well as potassium, calcium, phosphorus, and other minerals, but most importantly, 0.4 to 1% whey protein. Whey contains significantly less protein than milk. In particular, unlike milk, it contains no casein. Casein is the main protein in milk. Sweet whey has a pH value of 5.6 or higher, while acid whey has a pH of 5.1 or lower.

[0004] While whey, and especially sweet whey, represent valuable dairy products with diverse applications, sour whey, due to its high lactic acid and mineral content, is a waste product suitable at best for animal feed.

[0005] There have been various approaches to deacidifying whey, but corresponding separation processes have so far proven to be either too complex or too incomplete. RELEVANT STATE OF THE TECHNOLOGY

[0006] From US patent 3,615,663 A (ALFA LAVAL) a process for the production of non-hygroscopic whey powder is known in which the whey is first pasteurized, evaporated to a dry matter content of 35 to 52 wt.%, the concentrate is cooled until crystals are deposited and the product is finally spray-dried.

[0007] An analogous procedure is also known in GB 2293825 B2 (WATERFORD).

[0008] The subject of US Patent 2015 150275 A1 (US AGRICULTURE) is a process for processing acid whey, comprising treating the acid whey solution with alpha-galactosidase and / or beta-galactosidase at a pH of approximately 3.2 to approximately 5.2 for approximately 20 minutes to approximately 16 hours at approximately 20°C to approximately 60°C to produce an acid whey solution containing at least approximately 40 percent less lactose than the original acid whey solution, and filtering the acid whey solution. The resulting retentate is enriched with proteins, and the permeate contains essentially the lactose, which can be separated from it. The retentate can then be spray-dried and textured.

[0009] The subject of EP 0712381 B1 (FRAUNHOFER) is a process for purifying dairy wastewater by anaerobic conversion and separation of the resulting reaction products, comprising the following steps: (a) pretreating the wastewater with base, (b) introducing the pretreated wastewater into a fermenter, anaerobic fermentation of the lactose present in the wastewater to lactic acid, and further purification of the fermentation broth formed in the fermenter; (c) concentrating the lactate in the wastewater and concentrating the lactic acid and base using bipolar electrodialysis. This document has no connection to whey.

[0010] EP 1320410 B1 (ELECTROSYNTHESIS) proposes a bipolar membrane electrodialysis process for the salt splitting of polyvalent metal salts, in which the metal cation forms essentially insoluble precipitates in the presence of hydroxyl ions. The introduction of an acid into the chamber, where metal hydroxides would otherwise form, inhibits their evolution or neutralizes any solids formed, allowing the salt splitting to continue. The process is used to produce concentrated and purified acids, such as 2-keto-L-gluconic acid, H₂ (KLG), a key intermediate in the production of ascorbic acid.

[0011] From EP 2598468 B1 (PFEIFER UND LANGEN) a process for recovering an auxiliary substance used in a fermentation process for the production of a product, which has been added to a fermentation broth and from which another substance is formed by means of a chemical reaction in the fermentation broth, is known, wherein the following steps are carried out: the fermentation broth is subjected to a first process step in which the auxiliary substance used in the fermentation process is an acidic ion exchanger, a mineral hydroxide, or a mineral acid selected from the group consisting of sodium hydroxide, ammonia, potassium hydroxide, hydrochloric acid, sulfuric acid, or phosphoric acid, and the resulting other substance is selected from the group consisting of sodium chloride, potassium chloride, ammonium chloride, sodium chloride, potassium chloride, ammonium phosphate, sodium chloride, potassium chloride,- Ammonium sulfate and / or at least partially exhausted acidic ion exchangers are separated by at least one chromatographic method into fraction A from the at least one product obtained in the fermentation process, and the latter is obtained in fraction B, fraction A is subjected to bipolar electrodialysis in a second process step in order to generate the auxiliary substance, such as the acids / alkalis corresponding to the salts, from other substances such as salts contained in fraction A.

[0012] US patent 4,855,056 A (HARJU) describes a process for obtaining demineralized whey, in which not only whey but also cations and anions are recovered. TASK OF INVENTION

[0013] A first object of the present invention has therefore been to provide a method by which acid whey can be deacidified in order to obtain sweet whey.

[0014] A second task is to provide a sweet whey with improved sensory properties, specifically a reduced mineral aftertaste and increased sweetness.

[0015] Finally, the new process should also make it possible to utilize the resulting by-products, i.e., to obtain lactic acid and also minerals in the highest possible purity. DESCRIPTION OF THE INVENTION

[0016] The invention relates to a process for the coupled production of sweet whey and lactic acid from acid whey, comprising or consisting of the following steps:

[0017] Continuous process for the coupled production of sweet whey and lactic acid from sour whey, comprising or consisting of the following steps: (a) Provision of acid whey; (b) Provision of water as a rinsing solution; (c) Provision of an electrodialysis apparatus comprising at least three cells arranged side by side and connected by semipermeable membranes; (d) Application of the acid whey to the central cell; (e) Application of the rinsing solution to the two cells flanking the central cell; (f) Electrodialysis of the acid whey in the central cell to obtain a deacidified diluate; (g) Provision of a reverse osmosis cell; (h) Application of the rinsing solution to the reverse osmosis cell to obtain a retentate and a permeate; (i) Return of the permeate to the dialysis cell; (j) Provision of a bipolar electrodialysis cell; and (k) Application of the retentate to the bipolar electrodialysis cell to obtain a diluate containing lactic acid and salt-rich fractions, which are combined to form the concentrate containing the minerals.

[0018] Surprisingly, it was found that sour whey can be converted into sweet whey in the manner described above, which also differs from a conventional comparison product in that it has an improved taste quality, namely more sweetness and no mineral, metallic aftertaste.

[0019] The rinsing solution is circulated and, upon exiting the electrodialysis system, is combined or mixed to ensure charge balance. Furthermore, it is advantageous to keep the concentration of the rinsing solution as low as possible so that the driving force does not have to work against a high charge concentration. Preferably, after continuous discharge, the rinsing solution is concentrated by reverse osmosis or bipolar electrodialysis, and the permeate is returned to the cycle, while the lactic acid can be recovered from the retentate or diluate, for example, by evaporation. Sour whey

[0020] Whey is the liquid component produced during the acidification of raw or skim milk with lactic acid bacteria. If pasteurized milk is used for acidification, subsequent pasteurization of the whey is unnecessary. If no pasteurization step precedes the production of the whey, it is pasteurized before further processing. This is typically done by passing the whey through a heat exchanger with a temperature gradient, where the product is heated to a temperature of approximately 70 to 80 °C, and particularly approximately 72 to 74 °C, for a residence time of at least 15 and at most 60 seconds, preferably about 30 seconds. Pretreatment; evaporation or ultra- or nanofiltration

[0021] Before electrodialysis, the whey can be pretreated, with one alternative being to increase the dry matter content by evaporation, for example to a content of about 15 to about 30 wt. For this purpose, the whey is dehydrated, for example in falling film evaporators.

[0022] In the second option, the whey can alternatively be subjected to ultrafiltration or, preferably, nanofiltration. Nanofiltration removes some of the existing lactate and mineral salts without reducing the valuable lactose content.

[0023] Ultrafiltration and nanofiltration are filtration processes from the field of membrane technology used to separate and concentrate macromolecular substances and small particles from a medium. Microfiltration, ultrafiltration, and nanofiltration are distinguished by the degree of separation. If the exclusion limit (or also "Cut-off"If the exclusion limit is 100 nm or above, it is called microfiltration. If the exclusion limit lies in the range between 2 and 100 nm, it is called ultrafiltration. In nanofiltration, the exclusion limit is below 2 nm. In each of these cases, these are purely physical, i.e., mechanical, membrane separation processes that operate on the principle of mechanical size exclusion: all particles in the fluids that are larger than the membrane pores are retained by the membrane. The driving force in both separation processes is the differential pressure between the inlet and outlet of the filter surface, which ranges between 0.1 and 10 bar.

[0024] The exclusion limits of ultrafiltration membranes are also expressed in the form of the NMWC (English: Nominal Molecular Weight Cut-Off, also MWCO,The Molecular Weight Cut-Off (NMWC), unit: Dalton, is specified. It is defined as the minimum molecular mass of globular molecules that are retained by the membrane at a rate of 90%. In practice, the NMWC should be at least 20% lower than the molecular mass of the molecule to be separated. Further qualitative statements about the filtration can be made based on the Flux (Water value) (transmembrane flow rate or percolation rate). Ideally, this is proportional to the transmembrane pressure and inversely proportional to the membrane resistance. These values ​​are determined by the properties of the membrane used, as well as by concentration polarization and any fouling that may occur. The percolation rate is expressed per 1 m² of membrane area. Its unit is l / (m² < h).

[0025] Membranes with a pore diameter in the range of approximately 1,000 to 50,000 Daltons, and preferably approximately 5,000 to 25,000 Daltons, have proven particularly suitable for ultrafiltration. Nanofiltration preferably uses pore diameters in the range of 100 to 5,000 Daltons, and preferably approximately 500 to 2,000 Daltons.

[0026] The filter surface material – in both ultrafiltration and nanofiltration – can be stainless steel, polymers, ceramics, aluminum oxide, or textiles. Various filter element designs exist: candle filters, flat membranes, spiral-wound membranes, bag filters, and hollow fiber modules, all of which are fundamentally suitable for the purposes of the present invention. However, spiral-wound membranes made of polymers or candle filters made of ceramics or aluminum oxide are preferably used, with the first embodiment proving particularly advantageous for ultrafiltration and the second for nanofiltration.

[0027] Both ultrafiltration and nanofiltration can be carried out "hot" or "cold" according to the present invention, i.e., in the temperature range of about 10 to about 60 °C. However, it is preferred to operate at temperatures in the lower range of about 10 to about 20 °C.

[0028] It has also proven advantageous to include a pretreatment step in which the acid whey is passed through a cation exchanger, preferably a weakly acidic cation exchanger, before electrodialysis. This has the advantage that a significant portion of the divalent salts is already separated, which would otherwise only be captured by the electrolysis after the monovalent salts have been removed.

[0029] Of course, it is possible to combine evaporation and filtration, in particular to first evaporate the acid whey and then filter it, or vice versa. Electrodialysis

[0030] This is a membrane process driven by the application of an electric field, in which ion exchange membranes are used in combination with an electrical potential difference to separate ionic species from uncharged solvents or impurities by passing them across selective membranes. The following diagram illustrates the process; AM stands for anion exchange membrane and CM for cation exchange membrane:

[0031] In an electrodialysis separator, the space between two electrodes is divided by a stack of alternating anion and cation exchange membranes. Each pair of ion exchange membranes forms a separate "cell." In industrial systems, these stacks consist of more than two hundred membrane pairs. When a direct current voltage is applied to the electrodes, the anions migrate to the anode. The anions can easily pass through the positively charged anion exchange membranes, but they are stopped at the nearest negatively charged cation exchange membrane. Because the same thing happens with the cations (naturally with the opposite sign), the net effect of electrodialysis is an accumulation of salts in the odd-numbered cells (anion exchange membrane / cation exchange membrane), while the even-numbered cells (cation exchange membrane / anion exchange membrane) become depleted of salts.Solutions with increased salt concentration are combined to form the concentrate, while solutions with low salt concentration form the diluate.

[0032] In this way, the sour whey is not only freed from its lactic acid content, but the minerals also migrate into the rinsing liquid, which is circulated and gradually becomes enriched with lactic acid and minerals, while a diluate is obtained from the middle cell, which in its composition corresponds to a mineral-free or mineral-poor sweet whey.

[0033] The process is carried out continuously. Lactic acid recovery

[0034] In a further preferred embodiment, the process is interrupted as soon as the rinsing liquid has such a high lactic acid content that recovery is economically worthwhile; this limit can therefore vary.

[0035] For recovery, either all of the rinsing fluid or only a portion of it can be removed, with the missing amount then being replenished with fresh water. If necessary, this process can also be carried out continuously, meaning that while concentrate is being removed, a corresponding amount of fresh water is simultaneously added. Reverse osmosis

[0036] According to the invention, the concentrate is processed by reverse osmosis. Reverse osmosis is a physical membrane process for concentrating substances dissolved in liquids, in which the natural osmosis process is reversed by applying pressure.

[0037] The process principle is that the medium in which the concentration of a specific substance is to be reduced is separated from the medium in which the concentration is to be increased by a semipermeable membrane. This membrane is subjected to a pressure that must be higher than the pressure generated by the osmotic tendency for concentration equalization. This causes the solvent molecules to migrate against their "natural" osmotic direction. The process forces them into the compartment where the solutes are less concentrated. Typical pressures for reverse osmosis range from 3 to 30 bar (drinking water desalination) or up to 80 bar (seawater desalination).

[0038] The osmotic membrane, which only allows the carrier fluid (solvent) to pass through and retains the dissolved substances (solutes), must be able to withstand these high pressures. If the pressure difference more than compensates for the osmotic gradient, the solvent molecules pass through the membrane like a filter, while the "contaminant molecules" are retained. Unlike a conventional membrane filter, osmotic membranes do not have continuous pores. Instead, the ions and molecules migrate through the membrane by diffusing through the membrane material, as described by the solution-diffusion model: The osmotic pressure increases with increasing concentration difference. When the osmotic pressure equals the applied pressure, the process stops. At this point, osmotic equilibrium is reached. A continuous outflow of the concentrate can prevent this.At the concentrate outlet, the pressure is either controlled via a pressure regulator or used via a pressure exchanger to build up the pressure required in the system's inlet.

[0039] A lactic acid concentrate is obtained that contains no impurities except for a small amount of minerals and is particularly suitable for polymerization, for example. The permeate serves as a rinsing liquid and is recycled back into the process. Bipolar electrodialysis

[0040] Subsequently, lactic acid and minerals are obtained from the retentate of reverse osmosis by bipolar electrodialysis.

[0041] Bipolar electrodialysis is a well-known separation process. It is an electrochemically driven membrane process in which ion exchange membranes are used in combination with an electrical potential difference to separate ionic species from uncharged solvents or impurities.

[0042] In an electrodialysis separator, the space between two electrodes is divided by a stack of alternating anion and cation exchange membranes. Each pair of ion exchange membranes forms a separate "cell." In industrial systems, these stacks consist of more than two hundred membrane pairs. When a direct current voltage is applied to the electrodes, the anions migrate to the anode. The anions can easily pass through the positively charged anion exchange membranes, but they are stopped at the nearest negatively charged cation exchange membrane. Because the same thing happens with the cations (naturally with the opposite sign), the net effect of electrodialysis is an accumulation of salts in the odd-numbered cells (anion exchange membrane / cation exchange membrane), while the even-numbered cells (cation exchange membrane / anion exchange membrane) become depleted of salts.

[0043] Solutions with increased salt concentrations are combined to form the concentrate, from which the minerals are extracted, while the solutions with low salt concentrations form the diluate containing lactic acid. The aqueous fractions can then be dried, for example by evaporation, spray drying, or freeze-drying. EXAMPLES EXAMPLE 1

[0044] An electrodialysis unit according to Figure 1 One cell was continuously fed with 100 L / h of acid whey (0.7 wt% lactic acid, 0.8 wt% minerals, pH 4.5). The two adjacent cells were operated with fresh water in a closed loop at the same flow rate. The diluate was continuously removed. A sweet whey was obtained that was practically free of lactic acid and minerals and had a pH of 5.9.

[0045] After 10 hours of operation, the lactic acid concentration in the rinse water reached 1.8 wt%. The rinse water from both cells was continuously drained and simultaneously replaced with an equal volume of fresh water. The two rinse water volumes were combined and applied to a reverse osmosis unit (concentration factor 10) at 20 °C. The resulting permeate was returned to the dialysis unit's detergent circuit, while the retentate was applied to a bipolar electrodialysis unit. The resulting saline and low-salt fractions were combined and then dehydrated. This process yielded lactic acid with a purity of 97.4% and a mineral concentrate consisting primarily of sodium chloride. EXAMPLE 2 Taste assessment

[0046] The sweet whey obtained according to the invention as described in Example 1 was tasted against conventional sweet whey from rennet cheese production by a panel of 5 experienced tasters and evaluated on a scale from (1) = slightly present to (5) = clearly pronounced. The results are presented in Table 1: Table 1 Sweet whey tasting Sweet whey according to the invention Standard sweet whey sweetness 4,5 3,0 Mineral aftertaste 2,0 3,5

[0047] The sweet whey according to the invention was characterized by higher sweetness and a lower mineral aftertaste.

Claims

1. Continuous process for the coupled production of sweet whey and lactic acid from sour whey, comprising or consisting of the following steps: (a) providing acid whey; (b) providing water as a rinsing solution; (c) providing an electrodialysis apparatus having at least three cells arranged side by side and connected by semipermeable membranes; (d) feeding the acid whey to the middle cell; (e) feeding the flush solution to the two cells flanking the middle cell; (f) electro-dialysing the acid whey in the middle cell to obtain a deacidified diluate; (g) providing a reverse osmosis cell; (h) applying the flush solution to the reverse osmosis cell to obtain a retentate and a permeate; (i) returning the permeate to the dialysis cell; (j) providing a bipolar electrodialysis cell; and (k) feeding the retentate to the bipolar electrodialysis cell to obtain a diluate containing the lactic acid and salt-rich fractions, which are combined to form the concentrate containing the minerals.

2. Process according to claim 1, characterised in that the acid whey is concentrated by evaporation prior to electrodialysis.

3. Process according to at least one of claims 1 to 2, characterised in that the acid whey is subjected to ultra- or nanofiltration prior to electrodialysis.

4. Process according to at least one of claims 1 to 3, characterised in that the acid whey is passed over a cation exchanger before electrodialysis.

5. Process according to at least one of claims 1 to 4, characterised in that the diluate and the concentrate from the bipolar electrodialysis are subsequently dewatered.