Process for removing calcium citrate from liquid dairy stream

Abstract

The present invention relates to a method for removing calcium citrate from a liquid dairy stream. Specifically, the present invention relates to a process for removing calcium citrate from a liquid dairy product stream wherein the liquid dairy product stream has a pH of less than 6.2 or is optionally adjusted to a pH of less than 6.2, and wherein the liquid dairy product stream having a pH of less than 6.2 is subjected to a calcium citrate precipitation step. Subsequently, the precipitated calcium citrate may be separated.

Description

Technical Field

[0001] The present invention relates to a method for removing calcium citrate from a liquid dairy stream. In particular, the present invention relates to a method for removing calcium citrate from a liquid dairy stream, wherein the liquid dairy stream has a pH below 6.2 or is optionally adjusted to a pH below 6.2, and wherein the liquid dairy stream having a pH below 6.2 is subjected to a calcium citrate precipitation step. Subsequently, the precipitated calcium citrate can be separated. Background Art

[0002] During the production of crystalline lactose from dairy streams, such as a) permeate obtained from ultrafiltration of dairy products or b) whey, the presence of minerals may precipitate during the lactose production process or co-precipitate with lactose during the lactose crystallization process, resulting in a crystalline lactose product with more ash and reduced value.

[0003] Regarding lactose production, calcium, citric acid and phosphorus have a significant impact on several steps in lactose production:

[0004] - High levels of calcium, citric acid and phosphorus can cause scaling of membrane equipment

[0005] - High levels of calcium, citric acid and phosphorus can cause evaporator scaling

[0006] - High contents of calcium, citric acid and phosphorus lead to high ash content in the obtained lactose powder because:

[0007] The calcium phosphate and calcium citrate formed can serve as nuclei for the lactose crystallization process and are therefore difficult to wash away from the lactose crystals during the washing step,

[0008] • During processing, calcium phosphate and citrate particles formed travel with the decanter and centrifuge slurry and therefore cannot be removed from the lactose crystals by separation and washing processes.

[0009] Dairy products contain high levels of soluble calcium, often in combination with anions such as citrate and phosphate. The presence of free calcium and anions results in the production of calcium citrate precipitates and calcium phosphate precipitates, which can be problematic for the efficient production of lactose crystals. Therefore, in order to improve the quality of the lactose product, calcium phosphate precipitates are often produced and removed from the dairy stream used to make lactose crystals. Calcium phosphate is typically removed from the dairy stream by raising the pH of the dairy stream to above pH 7.0 and then heating the pH adjusted dairy stream to precipitate the calcium phosphate, which can be separated from the dairy stream before lactose crystallizes, thereby improving the quality of the lactose crystal product.

[0010] WO 2016 / 135172A1 discloses a method for separating calcium phosphate from whey permeate by adjusting the pH to about 7.2 by adding caustic Mg(OH)2 or NaOH and then heating the whey permeate to about 80° C. The precipitated calcium phosphate is then removed by centrifugation or membrane filtration.

[0011] WO 2016 / 193138 A1 discloses a method for obtaining crystalline lactose from one or more aqueous solutions, the aqueous solution comprising lactose from whey or whey permeate. The method involves demineralizing the lactose solution, whey or whey permeate, and the demineralization is performed by nanofiltration.

[0012] Typically, if the stream / portion obtained from the dairy product is used for lactose production, the addition of citric acid to the dairy product is avoided. However, citric acid or citrate can be added to milk during cheese production, resulting in an ultrafiltration permeate containing citric acid / citrate and acid whey. Typically, this acid-containing ultrafiltration permeate and acid whey are used as animal feed. Citric acid can be added to the dairy product during the preparation of cheese to separate the calcium bound to the casein micelles into free calcium. Calcium and citric acid form calcium citrate, the presence of which is problematic for the efficient production of lactose crystals.

[0013] The inventors of the present invention have found that known methods for removing calcium phosphate from dairy streams are not suitable for effectively removing calcium citrate.

[0014] It is important to remove calcium phosphate and calcium citrate from dairy streams because calcium phosphate and calcium citrate will co-precipitate with lactose during the lactose crystallization process, thereby reducing the lactose crystal yield. In addition, the lactose crystallization product will be high in impurities if calcium phosphate and calcium citrate are present.

[0015] Furthermore, if the dairy product is concentrated to a high solids content, scaling problems of membranes or heating elements are often observed during the concentration of the dairy solution. Scaling of membranes and heating elements is problematic because it results in the need for more frequent cleaning.

[0016] Therefore, a method of removing calcium citrate from dairy streams would be advantageous, and in particular a method of effectively removing calcium citrate without requiring improved cleaning of membranes and heating elements used for concentration would be advantageous. Summary of the invention

[0017] It is therefore an object of the present invention to provide a method for the efficient removal of calcium citrate from a liquid dairy stream. In particular, the present invention relates to a method for the efficient removal of calcium citrate from a dairy stream with minimal fouling of membranes and heating elements.

[0018] In the production of lactose, there is usually a decalcification step. The inventors of the present invention surprisingly found that lactose production is facilitated by first precipitating calcium citrate at a low pH and then precipitating calcium phosphate at a higher pH.

[0019] In particular, the object of the present invention is to provide a method that solves the above-mentioned problems of the prior art that calcium citrate is not removed and the membrane and heating element are scaled.

[0020] Therefore, one aspect of the present invention relates to a method for removing calcium citrate from a liquid dairy stream, wherein the method comprises the following steps:

[0021] i) providing a liquid dairy stream comprising a) calcium and b) citric acid and / or a citrate, and wherein the liquid dairy stream has a pH below 6.2;

[0022] ii) concentrating the liquid dairy stream until the Brix is ​​in the range of 5°Bx to 24°Bx, wherein the concentration is performed by using one or more of nanofiltration and reverse osmosis;

[0023] iii) subjecting the concentrated liquid dairy stream to a precipitation step to precipitate calcium citrate, the precipitation step comprising the precipitation in step A) or the precipitation in step B):

[0024] A) heating the concentrated liquid dairy stream to a temperature of 40°C to 85°C for at least 5 minutes to precipitate calcium citrate;

[0025] B) The concentrated liquid dairy stream is inoculated and stored at a temperature of 10°C to 40°C.

[0026] storing concentrated liquid dairy streams after inoculation;

[0027] iv) optionally, cooling the heat-treated concentrated liquid dairy product;

[0028] v) separating the precipitated calcium citrate from the heat treated liquid dairy product stream by using one or more devices for mechanically separating the precipitated calcium citrate from the liquid dairy product stream.

[0029] Another aspect of the present invention relates to a method for preparing crystalline lactose, wherein the method comprises the following steps:

[0030] A) providing a liquid dairy product stream from which calcium citrate has been removed according to the invention or a liquid dairy product stream from which calcium citrate and calcium phosphate have been removed according to the invention;

[0031] B) adjusting the pH to within the range of 5.5 to 6.2;

[0032] C) concentrating the pH adjusted liquid dairy product stream of step B) at a temperature of 50°C to 80°C until the Brix is ​​in the range of 55°Bx to 65°Bx;

[0033] D) cooling to a temperature of 5° C. to 20° C. to obtain crystalline lactose and a mother liquor;

[0034] E) separating lactose crystals from the mother liquor;

[0035] F) Optionally, washing the lactose crystals with water. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The indices of different nutrients of "high calcium ultrafiltration (UF) permeate" and "low calcium UF permeate" are shown.

[0037] Figure 2 Shown is the calcium content as a percentage of the total solids content in different samples of "High Calcium UF Permeate" and "Low Calcium UF Permeate" concentrated to different Brix levels.

[0038] Figure 3 The phosphorus content as a percentage of the total solids content in different samples of "high calcium UF permeate" and "low calcium UF permeate" concentrated to different Brix levels is shown.

[0039] Figure 4 The content of citric acid as a percentage of the total solids content in different samples of "High Calcium UF Permeate" and "Low Calcium UF Permeate" concentrated to different Brix levels is shown.

[0040] Figure 5 Flux data are shown as a measure of scaling tendency for "UF Permeate High Calcium" and "UF Permeate Low Calcium" samples subjected to continuous reverse osmosis (RO) concentration from 5° Bx to 16° Bx.

[0041] Figure 6 Flux data are shown as a measure of scaling tendency for "UF Permeate High Calcium" and "UF Permeate Low Calcium" samples that were continuously RO concentrated from 16° Bx to 27° Bx.

[0042] Figure 7 Shown is the calcium content of the total solids content in "high calcium UF permeate" samples which have been adjusted to different pH values ​​and then heated.

[0043] Figure 8 Shown is the citric acid content of the total solids content in samples of "high calcium UF permeate" which had been adjusted to different pH values ​​and then heated.

[0044] Fig. 9Shown is the phosphorus content of the total solids content in samples of "high calcium UF permeate" which have been adjusted to different pH values ​​and then heated.

[0045] Fig.10 Shown is the calcium content of the total solids content in "low calcium UF permeate" samples which have been adjusted to different pH values ​​and then heated.

[0046] Fig.11 Shown is the citric acid content of the total solids content in samples of "low calcium UF permeate" which had been adjusted to different pH values ​​and then heated.

[0047] Fig.12 Shown is the phosphorus content of the total solids content in samples of "low calcium UF permeate" which had been adjusted to different pH values ​​and then heated.

[0048] Fig.13 Shown are the calculated solubility products in "High Calcium UF Permeate" and "Low Calcium UF Permeate" samples adjusted to different pH values.

[0049] Fig.14 Shown are the calculated solubility products in "High Calcium UF Permeate" and "Low Calcium UF Permeate" samples adjusted to different pH values.

[0050] Fig.15 Shown is the change in calcium and citric acid concentration per unit of total solids in the supernatant fraction of an inoculated "High Calcium UF Permeate" versus an uninoculated "High Calcium UF Permeate" over a period of time.

[0051] Fig.16 Shown are heat transfer coefficient measurements for "High Calcium UF Permeate" samples heated to different temperatures.

[0052] Fig.17 Shown is the pressure drop for "High Calcium UF Permeate" samples heated to different temperatures.

[0053] Fig.18 Shown is the calcium content of the total solids content in "High Calcium UF Permeate" samples concentrated to different Brix levels.

[0054] Fig.19 Shown is the citric acid content of the total solids content in the "High Calcium UF Permeate" samples concentrated to different Brix levels.

[0055] Fig. 20 Shown is the phosphorus content of the total solids content in "High Calcium UF Permeate" samples concentrated to different Brix levels.

[0056] Fig.21The contents of calcium, phosphorus and citric acid in the "high calcium UF permeate" samples concentrated from 5°Bx to 16°Bx and 27°Bx, respectively, are shown, and the calcium citrate is separated by using ultrafiltration.

[0057] Fig. 22 The contents of calcium, phosphorus and citric acid in the "high calcium UF permeate" samples concentrated from 5°Bx to 16°Bx and 27°Bx, respectively, are shown, and the calcium citrate is separated by using a clarifier.

[0058] Fig.23 The contents of calcium, phosphorus and citric acid in the "high calcium UF permeate" samples concentrated from 5°Bx to 16°Bx and 27°Bx, respectively, are shown, and the calcium citrate is separated by using a clarifier and ultrafiltration.

[0059] Fig.24 Shown are flux data as a measure of the scaling tendency of a "high calcium UF permeate" sample concentrated to 27° Bx, a reference UF permeate of milk (no citric acid added), and a high calcium UF permeate sample without calcium citrate removal.

[0060] The present invention will now be described in more detail hereinafter. DETAILED DESCRIPTION

[0061] definition:

[0062] Before discussing the present invention in further detail, the following terms and conventions will first be defined:

[0063] All references to singular features or limitations of the invention shall include the corresponding plural features or limitations and vice versa unless otherwise specified or clearly implied to the contrary by the context of the reference.

[0064] The term "Brix" refers to the amount of soluble components in an aqueous solution. Brix may also be referred to as "°Bx". In the dairy industry, Brix is ​​used as an indicator of the soluble dry matter content of ultrafiltration permeate. Soluble components such as lactose, protein and minerals all contribute to the measurement of Brix.

[0065] The measurement of "Brix" is therefore an alternative method of measuring dissolved solids in a liquid, i.e. the solids content of a liquid. 1 °Bx is equal to approximately 1 gram of sugar (such as sucrose or lactose) in 100 grams of solution, expressing the concentration of the solution as a mass percentage. However, in the liquid dairy stream used in the method of the present invention, other dissolved solids (including minerals and citric acid) in addition to pure lactose are dissolved therein. Therefore, °Bx is not equivalent to solids content, but is close to solids content. In the context of the present invention, Brix has been measured to express solids content because the method of measuring °Bx is faster than the method of measuring total solids content.

[0066] In the context of the present invention, 1°Bx corresponds to 0.9 g to 1.0 g of solids in 100 g of liquid dairy product flow. In particular, 1°Bx corresponds to 0.92 g to 0.99 g of solids in the liquid dairy product flow.

[0067] Liquid Dairy Flows:

[0068] The liquid dairy stream is any liquid dairy stream comprising calcium and citric acid and / or citrate, and should not be limited to any particular stream.

[0069] However, in one embodiment of the invention the liquid dairy stream is selected from the group consisting of whey, ultrafiltration permeate, microfiltration permeate and whey protein concentrate.

[0070] The ultrafiltration permeate is generally a permeate stream obtained by ultrafiltration of a liquid dairy product. For example, the ultrafiltration permeate may be a permeate stream obtained by ultrafiltration of milk. The ultrafiltration permeate may also be a permeate obtained after ultrafiltration of whey associated with cheese curd production. Furthermore, the ultrafiltration permeate may be a permeate obtained after ultrafiltration of milk to which a coagulant enzyme such as rennet and a chemical acidulant such as citric acid and lactic acid have been added.

[0071] The microfiltration permeate is typically a permeate stream obtained by microfiltration of a liquid dairy product. For example, the microfiltration permeate may be a permeate obtained by microfiltration of milk, which may be referred to as whey protein concentrate.

[0072] In the context of the present invention, the term "milk serum proteins" or "serum proteins" refers to proteins found in milk serum. Milk serum proteins typically include β-lactoglobulin, α-lactalbumin, bovine serum albumin, immunoglobulins and osteopontin, as well as lactoferrin and lactoperoxidase. Milk serum proteins may also contain significant amounts of β-casein when the milk feed is stored at low temperatures (4°C) without subsequent heat treatment.

[0073] The term "whey" refers to the liquid obtained after casein has been precipitated and filtered from milk.

[0074] For example, the precipitation of casein can be obtained by using a coagulant, such as chymosin. In other methods known in the art, coagulation is due to acidification or a combination of acidification and the addition of a coagulant. The whey obtained by precipitating casein using a coagulant is commonly referred to as sweet whey, and the whey obtained by acid precipitation of casein micelles is commonly referred to as acid whey or sour whey.

[0075] Whey protein concentrate is obtained by concentrating whey protein.

[0076] Usually, due to the presence of acid, the pH value is low and the use of acid whey is limited. In contrast, sweet whey can be further processed into various products, such as whey protein products or lactose products. However, according to the present invention, acid whey can also be used to produce lactose products. Acid whey can be obtained by chemically acidifying whey and / or adding acid-producing microorganisms.

[0077] The milk used to obtain the ultrafiltration permeate and / or microfiltration permeate can be, for example, whole milk, low-fat milk, reduced-fat milk, fat-free milk, reconstituted milk powder, heat-treated milk (such as pasteurized milk and UHT milk), raw unfiltered milk, homogenized milk, mineral-reduced milk, whey protein-reduced milk and combinations thereof.

[0078] Preferably, the milk is pasteurized milk, in particular pasteurized bovine milk. When referring to pasteurized milk, in principle any type of pasteurized milk product as described above can be used, such as pasteurized whole milk, low-fat milk, reduced-fat milk, fat-free milk, raw unfiltered milk, homogenized milk, mineral-reduced milk and whey protein-reduced milk.

[0079] The milk from which the ultrafiltration permeate and / or microfiltration permeate is obtained may be based on the milk of a mammal, such as a cow, buffalo, goat, sheep, yak, pig, horse, ewe, mare or a combination thereof. In a preferred embodiment of the invention, the milk is from a cow, i.e. bovine milk. The terms "bovine milk" and "cow's milk" refer to the same thing.

[0080] The pH of the liquid dairy stream should be below pH 6.2. If the pH of the liquid dairy stream is above 6.2, calcium citrate will be removed only in very small amounts. In a preferred embodiment of the present invention, the pH of the liquid dairy stream is in the range of 5.0 to 6.2. The pH of the liquid dairy stream should preferably be above 5.0, because a lower pH results in reduced removal of calcium citrate. Therefore, if the pH of the liquid dairy stream is below 5.0, less calcium is precipitated in the form of calcium citrate, and when preparing a crystalline lactose product, it is not desirable to have such a high amount of citrate in the product. In another preferred embodiment of the present invention, the pH of the liquid dairy stream is in the range of 5.2 to 6.1, for example in the range of 5.5 to 6.1. Most preferably, the pH of the liquid dairy stream is in the range of 5.6 to 6.0.

[0081] In addition, in one embodiment of the present invention, the pH of the liquid dairy product stream can be adjusted to within the range of 5.5 to 6.0. In the method for removing calcium citrate according to the present invention, pH adjustment is preferably performed after step i) and before step ii). For example, if an ultrafiltration (UF) permeate with a pH of 6.1 is used, the pH of the liquid dairy product can be adjusted to within the range of 5.5 to 6.0 to increase the formation of calcium citrate precipitates, thereby improving the efficiency of removing calcium citrate. When the pH of the liquid dairy product stream is within the range of 5.0 to 6.2, calcium citrate can be removed. However, when the pH is within the range of 5.5 to 6.1, calcium citrate is most effectively removed, and when the pH is within the range of 5.7 to 6.0, calcium citrate is more effectively removed. The pH of the liquid dairy product stream can be adjusted by adding a base or an acid, depending on whether the pH should be increased or decreased.

[0082] If an acid is added to adjust the pH, a food grade acid such as citric acid, lactic acid, acetic acid, hydrochloric acid, carbon dioxide or glucono-delta-lactone is preferred. If the pH of the liquid dairy stream is low, the pH can be raised by adding a base such as sodium hydroxide, calcium hydroxide, potassium hydroxide or magnesium hydroxide.

[0083] Concentration of liquid dairy streams:

[0084] The liquid dairy stream is concentrated to a Brix in the range of 5°Bx to 24°Bx. It is preferred to concentrate the liquid dairy stream to at least 5°Bx because increased concentration results in higher supersaturation, higher driving force for precipitation, and reduces the volume that needs to be heated. However, the liquid dairy stream should not be concentrated to a Brix above 24°Bx because higher concentrations can cause scaling of membranes and heating elements.

[0085] In one embodiment of the invention the liquid dairy stream is concentrated to a Brix in the range of 8 to 22°Bx, such as 10 to 20°Bx, preferably 12 to 18°Bx, even more preferably 12 to 16°Bx.

[0086] In the method of the present invention, the concentration of the liquid dairy product stream is one or more selected from reverse osmosis and nanofiltration. Thus, the concentration of the liquid dairy product is obtained by subjecting the liquid dairy product stream to one or more concentration methods selected from reverse osmosis and nanofiltration. In the method of the present invention, evaporation is not used.

[0087] Most preferably, the concentration is performed by using reverse osmosis.By using reverse osmosis, water is removed from the permeate, but the solid components remain in the retentate.

[0088] During the concentration of the liquid dairy product stream, the liquid dairy product stream should preferably not be heated. Since evaporation at temperatures above 50°C results in rapid precipitation of calcium citrate, the use of heat for evaporation is not preferred. It is undesirable to have precipitated calcium citrate in the evaporator. Furthermore, vacuum evaporation is not preferred. Vacuum evaporation allows the liquid to be concentrated at a lower temperature than evaporation without a vacuum. Although the liquid can boil at a lower temperature, the temperature is still too high to avoid precipitation of calcium citrate. As previously mentioned, it is undesirable to precipitate calcium citrate during the concentration step. Instead, it is desirable to control the precipitation of calcium citrate, which can be achieved by the method of the present invention.

[0089] In the context of the present invention, the term "nanofiltration" (NF) refers to nanofiltration as commonly understood by the skilled person. Thus, in the context of the present invention, NF refers to separation by membrane filtration using a membrane with a molecular weight cut-off (MWCO) in the range of 20 Daltons (Da) to 1000 Daltons (Da), which corresponds to 90% of the molecular weight (MW) of a known substance (such as dextran or polyethylene glycol) being retained by the membrane in the separation step.

[0090] In one embodiment of the present invention, the MWCO of the NF membrane used is in the range of 100 Da to 800 Da, most preferably 200 Da to 400 Da.

[0091] In the context of the present invention, the term "reverse osmosis" (RO) refers to reverse osmosis as commonly understood by the skilled person. Thus, in the context of the present invention, RO refers to the separation of water from solids by membrane filtration using a membrane with a molecular weight cut-off (MWCO) of less than 50 Da. A reverse osmosis membrane will retain 95% to >99% of the sodium chloride.

[0092] During the concentration step, the pH of the liquid dairy product stream will typically decrease slightly. Thus, the pH of the liquid dairy product stream after concentration is typically in the range of 5.0 to 5.9, such as 5.3 to 5.8. Preferably, the pH of the liquid dairy product stream after the concentration step is in the range of 5.5 to 5.75.

[0093] Precipitation steps:

[0094] In the method according to the invention, the concentrated liquid dairy stream is subjected to a precipitation step to precipitate calcium citrate, the precipitation step comprising the precipitation in step A) or the precipitation in step B).

[0095] Step A) comprises precipitating calcium citrate by heating the concentrated dairy product stream to a temperature of 40°C to 85°C for at least 5 minutes. The higher the temperature, the shorter the time required for precipitation of calcium citrate. If the temperature is below 40°C, precipitation of calcium citrate takes a long time. For example, if the temperature is 10°C, it takes 24 hours or more to precipitate a small amount of calcium citrate.

[0096] The temperature at which the concentrated dairy product stream is heated should preferably be in the range of 50 to 80°C, more preferably in the range of 55 to 72°C, even more preferably in the range of 60 to 70°C.

[0097] Since temperature and time are interdependent, the time period should not be considered limiting. However, the time for carrying out the precipitation in step A) is generally in the range of 5 minutes to 2 hours, for example 10 minutes to 1.5 hours, preferably 15 minutes to 60 minutes. If the temperature is in the range of 60° C. to 70° C., the time for precipitation is generally in the range of 15 minutes to 60 minutes.

[0098] The precipitation may also be performed by using a precipitation step B). The precipitation step B) involves inoculating the concentrated liquid dairy stream and storing the inoculated concentrated liquid dairy stream at a temperature of 10°C to 40°C.

[0099] The precipitation in step B), i.e. at a lower temperature, increases the lag time for spontaneous nucleation and is not feasible without inoculation because precipitation would take too long. However, when the concentrated dairy stream is inoculated and stored at 10°C to 40°C, precipitation of calcium citrate takes about 2 hours to 24 hours.

[0100] In the context of the present invention, the term "nucleation" refers to nucleation as generally understood, i.e. the formation of a thermodynamically new phase or structure. Nucleation is a mechanism for producing phase changes and is the beginning of the process of forming a new thermodynamic phase. In the present invention, seeding accelerates the phase change of the precipitated calcium citrate.

[0101] In one embodiment of the invention, the inoculation in step iii) B) is selected from direct inoculation and indirect inoculation. Direct inoculation is inoculation by calcium citrate, and indirect inoculation is by mechanical nucleation. Mechanical nucleation overcomes the activation energy of nucleation, for example, mechanical nucleation can be achieved by using ultrasound, kinetic energy or thermal energy. Direct inoculation with calcium citrate is preferred.

[0102] Therefore, in a preferred embodiment of the present invention calcium citrate crystals are added to the concentrated liquid dairy product stream prior to the precipitation in step iii) B).

[0103] Precipitation step A) with precipitation at higher temperature is preferred, since precipitation of calcium citrate is obtained faster. Therefore, precipitation step A) is more feasible than precipitation step B).

[0104] In the precipitation step, the concentrated dairy product stream may be heated by using one or more devices selected from the group consisting of a heat exchanger, a steam injection device, and a direct steam injection device.

[0105] The heat exchanger may be selected from a tubular heat exchanger and a plate heat exchanger (PHE).

[0106] In a preferred embodiment, the heat treatment in step iii) A) is carried out as a two-step heat treatment, wherein the concentrated dairy product is first heated in a heat exchanger to a temperature of up to 50° C. and subsequently heated with direct steam injection or steam injection to a temperature of up to 85° C. It is undesirable to use direct steam injection or steam injection entirely for heating due to steam consumption and dilution of the dairy liquid stream.

[0107] For the thermal treatment of liquid dairy streams with high solids content (Brix), such as those above 12°Bx, it is advantageous to partially use direct steam injection or steam injection. Therefore, it is desirable to first heat to about 40°C to 50°C using a heat exchanger and then heat to higher temperatures by direct steam injection or steam injection. If the solids content is too high, heating to temperatures above 40°C to 50°C in the heat exchanger can lead to fouling of the heat exchanger. This should be avoided. The higher the solids content, the lower the temperature required for rapid fouling in the heat exchanger. For example, a dairy liquid stream with a solids content of 10°Bx will not lead to heat exchanger fouling until the temperature reaches about 50°C. In contrast, a liquid dairy stream concentrated to 16°Bx or higher will lead to heat exchanger fouling if heated to temperatures above 40°C.

[0108] However, in one embodiment of the present invention, the heat treatment in step iii) A) is performed by direct steam injection or steam injection, at a temperature of up to 85°C.

[0109] Optional cooling:

[0110] In one embodiment of the invention, the concentrated and heat treated liquid dairy product stream may be cooled. The cooling in step iv) may, for example, be to a temperature in the range of 5°C to 15°C. The cooling step may be performed to reduce the risk of microbial growth. The cooling is more preferably performed at a temperature in the range of 5°C to 10°C.

[0111] Cooling can be performed before separation step v) or during separation step v). For example, cooling can be performed between two separation steps using different separation devices.

[0112] Isolation of precipitated calcium citrate:

[0113] In step v) of the method according to the invention, the precipitated calcium citrate is separated from the concentrated liquid dairy product stream by using one or more devices for mechanically separating the precipitated calcium citrate from the liquid dairy product stream. In one embodiment of the invention, the one or more devices for separation in step v) are one or more selected from the following devices: clarifiers, centrifuges, decanters, filters and cyclone separators. The present invention should not be limited to the separation device, as all types of devices known in the art suitable for separation can be used. Filters include different types of filters, including membrane filtration, such as ultrafiltration.

[0114] In a preferred embodiment of the present invention, the one or more devices for separation are clarifiers or ultrafiltration or a combination of clarifiers and ultrafiltration.

[0115] Two-step precipitation of calcium citrate and calcium phosphate:

[0116] In one embodiment of the invention, the method involves a two-step precipitation and separation, first precipitating and isolating calcium citrate, and then precipitating and isolating calcium phosphate.

[0117] Therefore, in one embodiment of the present invention, the method according to the present invention comprises a method for removing calcium phosphate from the liquid dairy product stream obtained after separation of calcium citrate in step v), the method comprising the following steps:

[0118] a) concentrating the liquid dairy product stream until the Brix is ​​in the range of 15°Bx to 30°Bx;

[0119] b) heating the concentrated liquid dairy product stream to a temperature in the range of 40°C to 85°C;

[0120] c) adding an alkaline compound to the concentrated liquid dairy stream to adjust the pH to at least 6.5 and maintaining at 40° C. to 85° C. for at least 5 minutes to precipitate calcium phosphate;

[0121] d) optionally cooling the heat treated concentrated liquid dairy stream;

[0122] e) separating the precipitated calcium phosphate from the heat treated liquid dairy product stream by using one or more devices for mechanically separating the precipitated calcium phosphate from the liquid dairy product stream.

[0123] The concentration of the liquid dairy product can be carried out by the previously described concentration methods, i.e. one or more of reverse osmosis and nanofiltration. Preferably the concentration is carried out by using reverse osmosis.

[0124] Heating may also be performed by any heating device as described above, such as one or more selected from a heat exchanger, a steam injection device, and a direct steam injection device.

[0125] The temperature and time of the heating step are similar to the temperature and time disclosed above for precipitating calcium citrate using heating (Step A).

[0126] An alkaline compound is added to the liquid dairy product stream to raise the pH to above 6.5. Preferably, the pH should be in the range of 6.5 to 8.0, more preferably in the range of 6.8 to 7.8. Most preferably, the pH should be adjusted to a range of 7.0 to 7.5. The alkaline compound may typically be sodium hydroxide, but other alkaline compounds commonly used for pH adjustment of foods may also be used.

[0127] The conditions of the cooling step are also similar to the cooling step of the calcium citrate precipitation method, for example, the cooling step can be performed at a temperature ranging from 5°C to 15°C.

[0128] The one or more devices for separation are also similar to the one or more devices for separation described previously for separation of calcium citrate. Thus, the one or more devices for separation can be selected from one or more of the following devices: a clarifier, a centrifuge, a decanter, a filter, and a cyclone separator. The present invention should not be limited to the separation device, as all types of devices known in the art suitable for separation can be used. Filters include different types of filters, including membrane filtration, such as ultrafiltration.

[0129] In a preferred embodiment of the present invention, the one or more devices for separation are clarifiers or ultrafiltration or a combination of clarifiers and ultrafiltration.

[0130] Preparation of lactose crystals:

[0131] The present invention also relates to a method for preparing crystalline lactose, wherein the method comprises the following steps:

[0132] A) providing a liquid dairy product stream from which calcium citrate has been removed according to the invention or a liquid dairy product stream from which calcium citrate and calcium phosphate have been removed according to the invention;

[0133] B) adjusting the pH to within the range of 5.5 to 6.2;

[0134] C) concentrating the pH adjusted liquid dairy product stream of step B) at a temperature of 50°C to 80°C until the Brix is ​​in the range of 55°Bx to 65°Bx;

[0135] D) cooling to a temperature of 5° C. to 20° C. to obtain crystalline lactose and a mother liquor;

[0136] E) separating lactose crystals from the mother liquor;

[0137] F) optionally washing the lactose crystals with water.

[0138] In one embodiment, the concentration in step C) is performed by using an evaporator.

[0139] In another embodiment, the lactose crystals are separated from the mother liquor by using a decanter.

[0140] The lactose crystals separated from the mother liquor can be optionally washed. In a preferred embodiment, the lactose crystals are washed with water.

[0141] The washed lactose crystals can then be separated from the wash water. For example, this can be achieved using a centrifuge, ultrafiltration or a clarifier.

[0142] pH adjustment is usually achieved by adding food grade acid. The acid used can be the same as previously disclosed.

[0143] In one embodiment of the present invention, the pH adjusted liquid dairy product stream obtained in step B) may be subjected to a decolorization step before being concentrated in step C). The decolorization step is any known decolorization step, for example activated carbon may be used.

[0144] In another embodiment, the lactose crystals can be dried to obtain lactose powder. Drying is preferably achieved by using a fluidized bed dryer.

[0145] The method for preparing crystalline lactose can also be implemented by using a liquid dairy stream in which calcium phosphate has been removed as described above, but calcium citrate has not been removed by the method of the present invention. If a liquid dairy stream without added citric acid is used, it may be relevant to use a dairy stream from which only calcium phosphate has been removed.

[0146] It should be noted that embodiments and features described in the context of one aspect of the invention may also be applicable to other aspects of the invention.

[0147] The invention will now be described in more detail in the following non-limiting examples.

[0148] Example

[0149] Example 1: Analysis of calcium, citric acid and phosphorus content in different ultrafiltration permeates for lactose production

[0150] The purpose of this example is to show that the ultrafiltration permeate can have different amounts of calcium, citric acid and phosphorus. The amounts of calcium, citric acid and phosphorus depend on how the ultrafiltration permeate is obtained.

[0151] The following methods were used:

[0152] - The content of calcium, potassium, magnesium, sodium, phosphorus and chloride was measured using standard method AOAC 984.27, mod.

[0153] - Determination of chloride content using potentiometric titration, ISO 5943 / IDF 88, 4th edition, 2006.

[0154] - Ash content was measured using the NMKL 173 method, 2nd edition, 2005.

[0155] - Total protein content was measured using the Kjeldahl method, ISO 8968-3:2004(E) / IDF 20-3:2004: Determination of nitrogen content, block digestion method (semi-micro rapid routine method), ISO 8968-3:2007 / IDF 20-3:2007.

[0156] - Non-protein nitrogen is measured using ISO 8968-2001 / IDF 20-4:2001: Determination of nitrogen content, Determination of non-protein nitrogen content.

[0157] - Total solids content was measured using a modified version of ISO 6731:2010E / IDF21:2020E “Milk, cream and condensed milk - Determination of total solids content”.

[0158] - The citric acid content was determined by the method of Boehringer Mannheim, test kit, catalog number 10139076035.

[0159] - Lactose and galactose content was measured using DS / ISO 5765-2:2002, IDF 79-2, first edition 2002-09-01, “Milk powder, dry ice mix and processed cheese – Determination of lactose content, enzymatic method, Boehringer Mannheim, test kit, catalog number 176303. Modification – Carrez I and II, NaOH method

[0160] In the following table 1, the calcium, phosphorus, citric acid and lactose contents of two different ultrafiltration permeates are shown. The first ultrafiltration permeate (10 samples used), called "high calcium UF permeate", was obtained during the preparation of cheese whey, wherein citric acid had been added to the skim milk before ultrafiltration. The "high calcium UF permeate" is the ultrafiltration permeate obtained from the ultrafiltration of skim milk, which had been pH adjusted with citric acid before concentration.

[0161] The second ultrafiltration permeate (5 samples used) called "low calcium UF permeate" was obtained in combination with UF concentration of sweet whey. For these samples, the whey was not pH adjusted with citric acid before ultrafiltration. The "low calcium UF permeate" was obtained from cheese milk subjected to rennet treatment, separation of curds from whey and ultrafiltration of the whey obtained.

[0162] Prior to analysis, samples of the UF permeate were concentrated to 25% solids content using reverse osmosis.

[0163] Table 1: Weight percentage of total solids content of various nutrients in UF permeate

[0164]

[0165]

[0166] *TS refers to total solid content

[0167] **NPN refers to non-protein nitrogen

[0168] ***Stdev refers to standard deviation

[0169] Thus, Table 1 shows that the calcium content in the ultrafiltration permeate obtained after the addition of citric acid to skim milk is higher (calcium content 1.369 wt% of TS) compared to the calcium content in the ultrafiltration permeate of whey (no citric acid was added before ultrafiltration of whey; calcium content 0.730 wt% of TS).

[0170] Furthermore, Table 1 shows that the phosphorus content in the ultrafiltration permeate obtained after adding citric acid to skim milk is higher (phosphorus content is 1.096 wt% of TS) compared to the calcium content in the ultrafiltration permeate of whey (phosphorus content is 0.855 wt% of TS).

[0171] Furthermore, the citric acid content in the ultrafiltration permeate obtained after the addition of citric acid to skim milk was higher compared to the citric acid content in the ultrafiltration permeate of whey (5.385% vs. 2.959%).

[0172] Some citric acid will be present in the UF permeate of whey, as milk (from which whey is obtained) will contain small amounts of citric acid.

[0173] The lactose content in both ultrafiltration permeates was similar.

[0174] In the following Table 2, a comparison between the total solids composition of "High Calcium UF Permeate" and "Low Calcium UF Permeate" is shown. The index of the nutrients of "Low Calcium UF Permeate" is 100.

[0175] Table 2

[0176]

[0177]

[0178] As can be seen from Table 2, compared to "low calcium UF permeate", "high calcium UF permeate" usually contains:

[0179] -About 80% higher calcium content

[0180] - Phosphorus content is about 30% higher

[0181] - About 80% higher citric acid content

[0182] The indices shown in Table 2 are also Figure 1 shown.

[0183] In conclusion, different fractions of the ultrafiltration permeate obtained when making cheese may contain different amounts of calcium, citric acid, and phosphorus.

[0184] Example 2: Effect of feed type on membrane filtration and concentration performance

[0185] The purpose of this example is to show the difference in reverse osmosis performance of "high calcium UF permeate" and "low calcium UF permeate". "High calcium UF permeate" and "low calcium UF permeate" are the same ultrafiltration permeates used in Example 1.

[0186] The ultrafiltration permeate was collected and subjected to two reverse osmosis (RO) membrane filtration tests to concentrate the UF permeate to:

[0187] -RO concentration from 5°Bx to 16°Bx (26 bar transmembrane pressure)

[0188] -RO concentration from 16°Bx to 27°Bx (46 bar transmembrane pressure)

[0189] The pressure drop across the membrane was maintained at 0.8 bar. Each step was performed in a single cycle in continuous mode. The filtration unit was equipped with 2 tubes, each equipped with two 4” RO elements purchased from Toray.

[0190] The calcium, phosphorus and citric acid contents (wt % of total solids content) of the following samples were measured using the methods disclosed in Example 1:

[0191] - High calcium UF permeate as feed, 5°Bx

[0192] - Low calcium UF permeate as feed, 5°Bx

[0193] -RO retentate of high calcium UF permeate (Brix 5) as feed to RO concentrate to 16 Brix

[0194] - RO retentate of low calcium UF permeate (Brix 5) as feed to RO concentrate to 16 Brix

[0195] - High calcium UF permeate as feed, Brix 16

[0196] - Low calcium UF permeate as feed, Brix 16

[0197] -RO retentate of high calcium UF permeate (Brix 16) as feed to RO concentrate to 27 Brix

[0198] - RO retentate of low calcium UF permeate (Brix 16) as feed for RO concentration to 27 Brix

[0199] Figure 2 The percentage of calcium content in the total solid content of different samples is shown. Figure 2 It is shown that the sample with "high calcium UF permeate" contains more calcium than the sample with "low calcium UF permeate".

[0200] Figure 3 The phosphorus content of the different samples is shown as a percentage of the total solids content. Figure 3 It is shown that the sample with "high calcium UF permeate" contains more phosphorus than the sample with "low calcium UF permeate".

[0201] Figure 4 The content of citric acid in the different samples as a percentage of the total solid content is shown. As expected, the citric acid content in the "High Calcium UF Permeate" sample is higher than that in the "Low Calcium UF Permeate" sample. Figure 4 It is also shown that for samples with "high calcium UF permeate", the content of citric acid in the feed and RO retentate varies greatly. The variation in citric acid is believed to be due to the precipitation of calcium citrate during storage. Different samples were collected during the pilot test and stored under low temperature conditions until analysis. However, due to logistics reasons, the analysis of the samples could be performed after different residence times of the samples. It was observed that after storage, some samples contained precipitated material. To further analyze this, some feed and RO retentate samples were stored at room temperature and it was observed that the samples became turbid over time. An increase in turbidity over time is a sign of chemical precipitation. The inventors of the present invention believe that the precipitation is calcium citrate precipitation.

[0202] Example 3: Analysis of reverse osmosis (RO) membrane fouling

[0203] The flux data of the concentration on the RO membrane were analyzed for possible fouling of the membrane. The flux data of the continuous RO concentration from 5°Bx to 16°Bx of the "high calcium UF permeate" and "low calcium UF permeate" samples were analyzed. The RO concentration was continued for 4.5 hours at 26 bar TMP (transmembrane pressure). These flux data are shown in Figure 5 shown.

[0204] In addition, the flux data of continuous RO concentration from 16°Bx to 27°Bx for the “high calcium UF permeate” and “low calcium UF permeate” samples were analyzed. RO concentration was continued for 4.5 hours at 46 bar TMP. These flux data are shown in Figure 6shown.

[0205] Flux data are measured in L / h / element, where "element" refers to a "spiral wound membrane element".

[0206] Figure 5 It is shown that the flux data for the "high calcium UF permeate" and "low calcium UF permeate" are very similar when concentrating from 5°Bx to 16°Bx on the RO membrane. Fluxes of about 20-22 L / h / element were measured for both feeds, so there was no obvious sign of fouling in the 4.5 hour test.

[0207] Figure 6 The flux of "high calcium UF permeate" and "low calcium UF permeate" when concentrated from 16 ° Bx to 27 ° Bx is shown. The flux of the two UF permeates is about 14-15 L / h / element at the beginning (16 ° Bx), but the flux of "high calcium UF permeate" decreases significantly over time, which indicates that the membrane is severely scaled. After 4.5 hours, the flux of RO concentrated "high calcium UF permeate" is reduced to 3.5 L / h / element or only 25% of the initial flux. On the contrary, the flux of "low calcium UF permeate" concentrated from 16 ° Bx to 27 ° Bx is not significantly reduced, so no signs of scaling are shown.

[0208] Thus, this example shows that "high calcium UF permeate" is more susceptible to RO membrane fouling during RO concentration at high concentrations (high solids content) than "low calcium UF permeate". Therefore, "high calcium UF permeate" cannot be used directly in a process for producing lactose if the feed is concentrated to 27°Bx Brix without significantly reducing production capacity.

[0209] Furthermore, using a feed similar to "high calcium UF permeate", the RO process will be very expensive because the RO equipment will scale and need to be cleaned more frequently, and the membranes will need to be replaced more frequently, so the production cost will be very high.

[0210] Embodiment 4:

[0211] The purpose of this example is to show how to precipitate calcium citrate and calcium phosphate by controlling the pH.

[0212] The samples were analyzed using the method disclosed in Example 1.

[0213] The "low calcium UF permeate" and "high calcium UF permeate" were collected, frozen for approximately one week, and then thawed and used for analysis.

[0214] The method showing the effect / control of pH on precipitation of calcium citrate and calcium phosphate involves the following process:

[0215] Step 1: Heat the samples of "High Calcium UF Permeate" and "Low Calcium UF Permeate" in a water bath to 80°C

[0216] Step 2: Add 27% (w / w) sodium hydroxide to adjust the pH to different levels

[0217] Step 3: Keep the pH adjusted sample at 80°C for 60 minutes

[0218] Step 4: Centrifuge the sample at 3000G for 5 minutes

[0219] Step 5: Decant the supernatant obtained after centrifugation and cool to 8-10°C

[0220] The obtained supernatant was analyzed. In addition, the pH of the sample was measured after heating and after cooling the supernatant in step 1 (the pH of the sample to which NaOH was added was adjusted).

[0221] In Table 3 below, the pH and the contents of phosphorus, calcium and citric acid of "high calcium UF permeate" samples having different pH values ​​are shown.

[0222] Table 3

[0223]

[0224]

[0225] *“As-is sample” is “High calcium UF permeate” or “Low calcium UF permeate”

[0226] **pH measured after heating at 80°C - before centrifugation

[0227] *** pH of supernatant - measured at 10°C

[0228] Figure 7 The calcium content of the total solids content in the different samples is shown. Figure 8 Citric acid content of total solids content in different samples is shown. Fig. 9 The phosphorus content of the total solids content in the different samples is shown.

[0229] Table 3 and Figure 7 It is shown that for the "high calcium UF permeate", the calcium content in samples 2-7 is significantly reduced compared to the samples of the "high calcium UF permeate". Fig.10 As can be seen in Figure 2, the same is true for the sample with "low calcium UF permeate".

[0230] Table 3 and Figure 8It is shown that for the "high calcium UF permeate", the citric acid content in samples 2-6 is slightly reduced compared to the sample of "high calcium UF permeate". In sample 7, no sodium hydroxide was added, so the citric acid content was significantly reduced compared to the experiments 2-6 in which sodium hydroxide was added. Fig.11 , samples of "low calcium UF permeate" are shown, showing that the citric acid content is almost the same in all samples. Therefore, it can be concluded that citric acid is poorly removed in the form of calcium citrate at a pH of about 7-8, but is removed at a lower pH of about 5.

[0231] Table 3 and Fig. 9 It is shown that for the "high calcium UF permeate", the phosphorus content in samples 2-6 is reduced compared to the samples with "high calcium UF permeate". In sample 7 without the addition of sodium hydroxide, phosphorus is not reduced to the same extent as in samples 2-6 with the addition of sodium hydroxide. The same reduction in phosphorus is observed for the samples with "low calcium UF permeate", see Tables 3 and Fig.12 Therefore, it can be concluded that phosphorus is removed in the form of calcium phosphate at a pH of about 7-8, but is poorly removed at lower pH (e.g., about 5).

[0232] Thus, this example demonstrates that the removal of calcium, citrate and phosphate can be controlled by pH, with calcium citrate precipitating at low pH and calcium phosphate precipitating at high pH.

[0233] Example 5: Effect of pH on precipitation product and reduction of scaling by precipitation in two steps

[0234] The purpose of this example is to show how pH can be used to control the precipitation product and to develop a method to reduce the evaporator fouling potential of the "high calcium UF permeate" to the same level as the "low calcium UF permeate", making the "high calcium UF permeate" suitable for lactose production.

[0235] The samples were analyzed using the analytical method described in Example 1.

[0236] The "Low Calcium UF Permeate" and "High Calcium UF Permeate" were collected, frozen for about a week, then thawed and used for analysis. The analysis was divided into two parts:

[0237] - Part 1: One-step precipitation

[0238] - Part 2: Two-step precipitation

[0239] Part 1: One-step precipitation

[0240] Precipitation with only one precipitation step involved screening the pH from 4.8 to 7.8 using "low calcium UF permeate" and "high calcium UF permeate".

[0241] A method for performing a precipitation step comprises:

[0242] a) Heat the sample in a water bath to 80°C

[0243] b) If necessary, add 27% (w / w) NaOH to the heated sample to adjust the pH

[0244] c) Keep the sample at 80°C for 60 minutes

[0245] d) Centrifuge the sample from step c) at 3000G for 5 minutes

[0246] e) Decant the supernatant and cool the supernatant to 8°C to 10°C

[0247] Part 2: Two-step precipitation

[0248] The first step of precipitation is:

[0249] i) Heat the sample in a water bath to 5°C, 15°C or 80°C

[0250] ii) Keep the sample at the specified temperature for 60 minutes

[0251] iii) Centrifuge the sample from step ii) at 3000G for 5 minutes

[0252] iv) Decant the supernatant and prepare it for the second precipitation step

[0253] The second step of precipitation is:

[0254] v) Heat the sample from step iv) in a water bath to 80°C

[0255] vi) If necessary, add 27% (w / w) NaOH or Ca(OH)2 to the heated sample to adjust the pH

[0256] vii) Keep the sample at 80°C for 60 minutes

[0257] viii) Centrifuge the sample from step vii) at 3000G for 5 minutes

[0258] ix) Decant the supernatant and cool the supernatant to 8°C to 10°C

[0259] In the second part, five different combinations of the first step precipitation and the second step precipitation were performed, as shown in Table 4 below.

[0260] Table 4

[0261]

[0262]

[0263] * "As is" pH was measured at 5.3

[0264] Ca(OH)2 was included in the analysis to investigate whether additional calcium would be beneficial for the precipitation of citrate and whether phosphorus levels could be further reduced. A target pH of 7 was achieved by adding NaOH and Ca(OH)2 at 80°C prior to precipitation.

[0265] In the production of lactose, the main concern regarding the processability of "high calcium UF permeate" is in the evaporator. Experience has shown that evaporator scaling usually consists of calcium citrate.

[0266] Therefore, to assess the fouling potential of the samples, the solubility product was calculated:

[0267] K=[Ca] 3 *[Citrate] 2

[0268] The density of a particular sample was not measured. Therefore, the unit used is mol / kg.

[0269] result

[0270] Part 1 – One-step precipitation

[0271] exist Fig.13 In the , the calculated solubility product corresponds to the pH measured in the cooled sample after separation of the precipitate. Samples of "high calcium UF permeate" and "low calcium UF permeate" are shown respectively.

[0272] like Fig.13 As shown, the solubility product of the "high calcium UF permeate" (squares) is higher than the solubility product of the "low calcium UF permeate" (circles). In addition, Fig.13 It is shown that the highest solubility product for the "high calcium UF permeate" is found at about pH 6, where the precipitate consists primarily of calcium phosphate, a large amount of citrate remains in the supernatant, and the calcium concentration is not as low as seen at higher pH values. At pH values ​​of about 7-8, the solubility product is lower because very little calcium remains in the supernatant for citrate to bind and precipitate as calcium citrate. At pH 5.5 and below, citrate precipitates with calcium, which affects the solubility product.

[0273] Therefore, it can be concluded that if precipitation is performed at pH around 6.5 and above, the scaling potential is high if “high calcium UF permeate” is used.

[0274] Part 2 - One-step and two-step precipitation

[0275] exist Fig.14 In the above equation, the calculated solubility product corresponds to the pH measured in the cooled sample after separation of the precipitate.

[0276] It shows:

[0277] -Two-step precipitation (triangle)

[0278] - One-step precipitation of "high calcium UF permeate"

[0279] - One-step precipitation of "low calcium UF permeate"

[0280] Fig.14 It is shown that a low solubility product is obtained in a two-step precipitation, where calcium citrate is first precipitated at 80°C with an unadjusted pH (pH about 5.3) feed, and then calcium phosphate is precipitated by adjusting the pH to 7 with NaOH.

[0281] In addition, the case of using Ca(OH)2 instead of NaOH for pH adjustment was also analyzed. In this analysis, precipitation at low pH was performed at 15°C instead of 80°C. Using Ca(OH)2 for pH adjustment also showed an acceptable solubility product, but the solubility product was slightly higher than precipitation at 80°C and pH adjustment with NaOH.

[0282] In summary, Example 5 shows that the precipitation of calcium citrate and calcium phosphate can be controlled by adjusting the pH of the feed. In addition, Example 5 shows that the use of a two-step precipitation of calcium citrate first at a low pH and then calcium phosphate at a higher pH results in a lower potential for scaling.

[0283] Example 6: Precipitation using low temperature and long residence time

[0284] The purpose of this example is to show how calcium citrate is precipitated at low temperatures and long residence times.

[0285] The feed used for this example was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk to which citric acid was added. The "High Calcium UF Permeate" feed was concentrated to 20 Brix by reverse osmosis (RO).

[0286] The feed was transferred to a reactor set at 15°C. The analysis lasted for 21 hours and samples were collected for analysis after 0, 4, 8 and 18 hours of storage. The samples were immediately separated by centrifugation at 3000 g for 5 minutes, diluted 1:1 with RO polished water, cooled to 5°C and sent for analysis.

[0287] Two reactors were used, one reactor contained only the feed, but in the second reactor 0.75 g of calcium citrate precipitate was seeded into 2 L of feed.

[0288] Interpolation between data points was performed by fitting a Weibull distribution but is provided for reference only. Slight extrapolation was performed to estimate the residence time required without seeding.

[0289] The results are as follows Fig.15 shown. Fig.15 The change in calcium and citric acid concentration per total solids in the supernatant fraction during the analysis period is shown. The two vertical axes are scaled to show how the decrease in calcium (right axis) and citric acid (left axis) concentrations are related.

[0290] For the inoculation test, after 4 hours, the concentrations of calcium (triangles) and citrate (squares) had already decreased significantly. Between the last two samples at 8 and 18 hours, the rate of change was lower, indicating that the concentrations were close to equilibrium.

[0291] For the uninoculated samples, the calcium concentration (crosses) began to decline only after 8 hours, and the citrate concentration (circles) measurements were actually higher than the feed at both 4 and 8 hours. The most likely explanation is that the feed sample had precipitated prior to analysis, which made some of the citrate unavailable for enzyme analysis. After 18 hours, the uninoculated run had precipitated only about one-third of the calcium and citrate, while the inoculated run had precipitated about half of the calcium and citrate. Weibull fits of the calcium and citrate measurements from the uninoculated run suggest that it would take 1 day or more to approach equilibrium concentrations.

[0292] In summary, this example shows that at 15°C, precipitation of calcium citrate requires a residence time of 1 day or more to reach equilibrium at 20°Bx, but by seeding the feed solution with previously precipitated calcium citrate, the required residence time can be shortened to 18 hours or less.

[0293] If samples with a Brix above 20° Bx are used, the settling time will be shorter, but the filtration equipment is more likely to foul due to the higher calcium content. Therefore, if the feed has a high calcium and citric acid content, i.e. a feed similar to a "high calcium UF permeate", it is preferred to perform the settling and remove the precipitated material before further concentration in the filtration equipment.

[0294] Example 7: Precipitation using high temperature and short residence time

[0295] The purpose of this example is to show how calcium citrate can be precipitated at high temperature and in a short time.

[0296] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk to which citric acid was added. The "High Calcium UF Permeate" feed was concentrated to 16 Brix by reverse osmosis (RO).

[0297] The concentrated feed was heated to 40°C in continuous mode on a plate heat exchanger (PHE). The heated concentrated feed was collected in a 1200L tank and stored for several hours. The product in the tank was then further heated to 60°C for about 12 minutes using direct steam injection. Samples were collected at different time points during the precipitation process. The samples were separated by centrifugation at 3000g for 5 minutes and cooled to 5°C. The citric acid content in the supernatant was measured using a Foss-Milkoscan FT1.

[0298] The plate heat exchanger used for all examples was from FH Scandibox A / S, serial number 115144.

[0299] In Table 5 below, the citric acid content measured in the different samples collected is shown.

[0300] Table 5:

[0301]

[0302]

[0303] *PHE refers to plate heat exchanger

[0304] **TS refers to total solid content

[0305] Table 5 shows that the precipitation of citric acid at 50°C is very slow, and the citric acid concentration only decreases by 0.08 g / 100 g within 2 hours of filling the tank at 40°C and heating it to 50°C. However, within the next 6 minutes of heating from 50°C to 60°C, the concentration of citric acid decreases by 0.28 g / 100 g. After heating at 60°C for 10 minutes, the concentration of citric acid decreases further, and after heating at 60°C for 60 minutes, the concentration of citric acid is only about 32% of the original concentration in the feed. In addition, it can be observed that after heating at 60°C for 10 minutes, the yield of citric acid is about 90%, and after heating at 60°C for 10 minutes, the precipitation becomes slow again.

[0306] In summary, this example shows that at 60°C, a residence time of 10-60 minutes is sufficient to achieve high removal rates of citric acid.

[0307] Example 8: Heating Analysis of "High Calcium UF Permeate"

[0308] The purpose of this example is to demonstrate the limitations of heating for products with a high potential for fouling.

[0309] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk with citric acid added. The "High Calcium UF Permeate" feed was concentrated to 16 Brix by reverse osmosis (RO). The concentrated feed was heated to different temperatures in a continuous mode on a plate heat exchanger (PHE) and sampled.

[0310] In a short period of about 30 minutes, the concentrated feed was heated to 30° C., 40° C., 50° C. and 60° C. The change from 50° C. to 60° C. was done without immediate purging.

[0311] For samples heated to different temperatures, the heat transfer coefficients for different residence times are calculated. The heat flow Q is determined by the industrial water flow Q w 、Heat capacity C p And the temperature change dT is calculated as:

[0312] Q=Q w *C p *dT

[0313] The heat transfer coefficient U is calculated from the low mean temperature LMDT and the plate area A.

[0314] Q=Q w *LMTD*A

[0315] Where LMDT = (dT1-dT2) / (ln(dT1)-ln(dT2)), dT1 and dT2 are the temperature differences between the fluids at each end of the plate heat exchanger.

[0316] In addition, pressure was measured.

[0317] Fig.16 shows the heat transfer coefficient of the samples measured in the analysis, while the pressure drop across the PHE can be found in Fig.17 Seen in.

[0318] Fig.16 and 17 It is shown that heating to 30°C (triangles) and 40°C (crosses) using a plate heat exchanger does not result in any changes in heat transfer coefficient or pressure drop. This indicates that these temperatures do not lead to fouling of the plate heat exchanger.

[0319] At 50°C (circles), the pressure drop increases, but the heat transfer coefficient does not change much over the 30-minute analysis time. At 60°C, the heat transfer coefficient immediately starts to decrease and the pressure drop increases more rapidly.

[0320] In summary, this example shows that heating a "high calcium UF permeate" concentrated to 16° Bx on a plate heat exchanger is stable with only a small amount of fouling up to 40°C. However, heating to 50°C in a plate heat exchanger will result in fouling and will require at least increased cleaning frequency. Heating to 60°C in a plate heat exchanger will result in rapid fouling.

[0321] Example 9: Two-step precipitation of calcium citrate and calcium phosphate

[0322] The purpose of this example is to show that calcium citrate can be precipitated from "high calcium UF permeate" at low pH in a first step (step 1) and calcium phosphate can be precipitated at a higher pH in a second step (step 2).

[0323] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk to which citric acid was added. The "High Calcium UF Permeate" feed was concentrated to 18° Bx by reverse osmosis (RO).

[0324] The precipitation method was performed as follows:

[0325] Step 1 Precipitation at low temperature and low pH:

[0326] - The "high calcium UF permeate" concentrated to 18° Bx was heated to 25°C on a plate heat exchanger and stored in a tank at 25°C for 16 hours.

[0327] - After 16 hours of storage, calcium precipitates were observed in the tanks.

[0328] -Ultrafiltration (UF1) of the stored “high calcium UF permeate” using an Alfa Laval GR82PE ultrafiltration membrane.

[0329] Step 2: Precipitation at high temperature and high pH:

[0330] - The UF permeate from UF1 was concentrated by reverse osmosis to a Brix of 24.8.

[0331] - The RO retentate at pH 4.88 at 7°C was stored in the tank for about 89 hours.

[0332] - The concentrated RO retentate with a Brix of 25.8 was heated to 80°C in a tank with live steam and after heating the pH was adjusted to 6.5 with 7% (w / w) NaOH. Due to the addition of NaOH and live steam, the Brix was 21.1.

[0333] - The pH adjusted RO retentate was maintained at 20°C.

[0334] - The pH adjusted and heated RO retentate was ultrafiltered using the same UF membrane as in step 1 and cooled to 3-5°C.

[0335] The contents of calcium, phosphorus, citric acid, ash, protein and pH were measured using the methods disclosed in Example 1. The data based on total solids content are shown in Table 6 below.

[0336] Table 6:

[0337]

[0338] Fig.18 shows the calcium content in the sample, Fig.19 The citric acid content is shown. Fig. 20 Phosphorus content is shown.

[0339] As shown in Table 6 and Figure 18-20 As shown, the removal of calcium citrate and calcium phosphate can be controlled by changing the pH. Calcium citrate is removed by heating the sample at a pH of about 5-6, and calcium phosphate is removed when the pH is adjusted to about 7 and heated.

[0340] Example 10: Precipitation and isolation of calcium citrate by ultrafiltration

[0341] The purpose of this example is to show that calcium citrate can be precipitated from a "high calcium UF permeate" having a concentration of 16° Bx and heated to 50°C in the precipitation step.

[0342] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples obtained from ultrafiltration of milk with addition of citric acid. The "High Calcium UF Permeate" feed was concentrated to 16 Brix at 7°C by reverse osmosis (RO).

[0343] The precipitation method was performed as follows:

[0344] - The feed "High Calcium UF Permeate" was concentrated by reverse osmosis (RO) at 7°C, i) from 5 to 16 Brix, ii) from 5 to 27 Brix.

[0345] - The RO retentate obtained from i) and ii) was heated to 50°C on a plate heat exchanger.

[0346] - The heated RO retentate was kept in a storage tank at 50°C for 60 minutes (time started when the tank was full).

[0347] - The obtained precipitate was separated by ultrafiltration of the RO retentate at 15°C.

[0348] The contents of calcium, phosphorus, citric acid, ash, protein and pH were measured using the methods disclosed in Example 1. The data based on total solids content are shown in Table 7 and Fig.21 shown.

[0349] Table 7:

[0350]

[0351] Table 7 and Fig.21 It is shown that when the pH during heating is 5.47, the calcium and citric acid contents are significantly reduced. In contrast, the phosphorus content is not reduced and therefore does not precipitate as calcium phosphate at pH 5.47.

[0352] In summary, calcium citrate precipitates at a pH of approximately 5-6 and can be isolated by ultrafiltration.

[0353] Example 11: Precipitation and isolation of calcium citrate using clarfier

[0354] The purpose of this example is to show that calcium citrate can be precipitated from a "high calcium UF permeate" having a concentration of 16 Brix and heated to 60° C. in a precipitation step. Furthermore, the purpose is to show that calcium citrate can be separated by using a clarifier.

[0355] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk to which citric acid was added. The "High Calcium UF Permeate" feed was concentrated to 16 Brix by reverse osmosis (RO).

[0356] The RO membrane used was DOW RO-3838 / 30-FF, and the RO was performed at 35 bar and 8°C.

[0357] The precipitation method was performed as follows:

[0358] - The feed "High Calcium UF Permeate" was concentrated by reverse osmosis (RO) at 8°C from 5 to 16 and 27 Brix, respectively.

[0359] - RO retentate is heated to 40°C in a plate heat exchanger

[0360] - When the RO retentate was at 40°C, the feed was further heated to 60°C by direct steam injection.

[0361] - The heated RO retentate was kept in a storage tank at 60°C for 60 minutes (time started when the tank was full).

[0362] - The precipitate was obtained by clarifying the RO retentate at 60°C in a SPX Seital Separation Technology model SE15XXQ3P2 of SPX Flow Technologies Santorso srl.

[0363] -Due to adjustments of some sparging settings on the clarifier during the clarification process, some sediment was carried over with the supernatant. Therefore, a second clarification step was performed.

[0364] Calcium content, phosphorus content, citric acid content and pH were measured using the methods disclosed in Example 1. The data based on total solids content are shown in Table 8 and Fig. 22 shown.

[0365] Table 8:

[0366]

[0367] Table 8 and Fig. 22 It is shown that when heated to pH 5.6, the calcium and citric acid contents are significantly reduced. In contrast, the phosphorus content is not reduced and therefore does not precipitate as calcium phosphate at pH 5.6.

[0368] In summary, calcium citrate precipitates at a pH of approximately 5-6 and can be isolated by clarification.

[0369] Example 12: Precipitation of calcium citrate and removal of calcium citrate by clarifier and ultrafiltration

[0370] The purpose of this example is to show that calcium citrate can be precipitated from a "high calcium UF permeate" having a concentration of 17 Brix and heated to 60° C. in a precipitation step. Furthermore, the purpose is to show that calcium citrate can be separated by using a clarifier and ultrafiltration.

[0371] The feed used was "High Calcium UF Permeate" obtained by collecting ultrafiltration permeate samples of milk to which citric acid was added. The "High Calcium UF Permeate" feed was concentrated to 17 Brix by reverse osmosis (RO).

[0372] The RO membrane used was DOW RO-3838 / 30-FF, and the RO was performed at 35 bar and 8°C.

[0373] The precipitation method was performed as follows:

[0374] - The feed "High Calcium UF Permeate" was concentrated from 5 to 17 Brix by reverse osmosis (RO) at 8°C.

[0375] - RO retentate is heated to 40°C in a plate heat exchanger

[0376] - The heated RO retentate was kept in a storage tank at 40°C for 60 minutes (time started when the tank was full).

[0377] - The precipitate was obtained by clarifying the RO retentate in a clarifier at 60° C. The clarifier used was SPX Seital Separation Technology model SE15XXQ3P2 from SPX Flow Technologies Santorso srl.

[0378] -Some of the sparge settings on the clarifier were adjusted during the clarification process and some sediment came with the supernatant. Therefore, the supernatant was subjected to ultrafiltration.

[0379] Calcium content, phosphorus content, citric acid content and pH were measured using the methods disclosed in Example 1. The data based on total solids content are shown in Table 9 and Fig.23 shown.

[0380] Table 9:

[0381]

[0382]

[0383] Table 9 and Fig.23 It is shown that when heated to pH 5.47, the calcium and citric acid contents are significantly reduced. In contrast, the phosphorus content is not reduced and therefore does not precipitate as calcium phosphate at pH 5.6.

[0384] In summary, calcium citrate precipitates at a pH of approximately 5-6 and can be isolated by clarification and ultrafiltration.

[0385] Example 13: Analysis of preheating of "high calcium UF permeate"

[0386] The purpose of this example is to show the effect of preheating on scaling caused by using "high calcium UF permeate" as feed.

[0387] The feed used was "high calcium UF permeate" obtained by collecting a sample of the ultrafiltration permeate obtained by ultrafiltration of whey to which citric acid had been added.

[0388] The feed was heated to 40°C using a plate heat exchanger and then further heated to 60°C using live steam. Calcium citrate precipitated and clarification began after 23 minutes. Clarification took 40-50 minutes with an average residence time of 47 minutes at 60°C. The supernatant was further ultrafiltered to produce a clarified product. The clarified product was then concentrated to 27 Brix by reverse osmosis using an Alfa Laval HSRO membrane.

[0389] After concentration to 27° Bx, the flux data was analyzed as a fouling measure:

[0390] - High calcium UF permeate, where calcium citrate has been removed by using the method of the present invention

[0391] - Reference ultrafiltration permeate of milk (without added citric acid)

[0392] - High calcium UF permeate where calcium citrate is not removed.

[0393] Flux data are measured in L / h / element, where "element" refers to a "spiral wound membrane element".

[0394] The results are as follows Fig.24 shown.

[0395] Fig.24 It is shown that the concentration of the "high calcium UF permeate" (squares) from which calcium citrate has been removed according to the present invention is much more stable than the concentration of the "high calcium UF permeate" (circles) from which calcium citrate has not been removed. The flux of the "high calcium UF permeate" from which calcium citrate has been removed according to the present invention (squares) is slightly lower than the reference value (crosses).

[0396] Thus, this example demonstrates that the method of the present invention for removing calcium citrate from a liquid dairy stream eliminates or at least reduces scaling during RO filtration due to the presence of citric acid.

[0397] Example 14: Comparison of °Bx and dry matter measurements:

[0398] The differences between °Bx and dry matter content measured in different samples of milk UF permeate, UF permeate concentrated by RO and clarified UF permeate that has been concentrated by RO are illustrated by way of an example. The results are shown in Table 10 below.

[0399] Table 10:

[0400]

[0401]

Claims

1. A method for removing calcium citrate from a liquid dairy stream, wherein the method comprises the following steps: i) providing a liquid dairy stream comprising a) calcium and b) citric acid and / or a citrate, wherein the pH of the liquid dairy stream is below 6.2; ii) concentrating the liquid dairy stream until the Brix is ​​in the range of 5°Bx to 24°Bx, wherein the concentrating is performed by using one or more of nanofiltration and reverse osmosis; iii) subjecting the concentrated liquid dairy stream to a precipitation step to precipitate calcium citrate, said precipitation step comprising the precipitation in step A) or the precipitation in step B): A) heating the concentrated liquid dairy stream to a temperature of 40°C to 85°C for at least 5 minutes to precipitate calcium citrate; B) inoculating the concentrated liquid dairy product stream and storing the inoculated concentrated liquid dairy product stream at a temperature of 10° C. to 40° C.; iv) optionally, cooling the heat treated concentrated liquid dairy stream; v) separating the precipitated calcium citrate from the heat treated liquid dairy product stream by using one or more devices for mechanically separating the precipitated calcium citrate from the liquid dairy product stream.

2. The method of claim 1, wherein the liquid dairy stream is selected from the group consisting of whey, ultrafiltration permeate, microfiltration permeate and whey protein concentrate.

3. The method according to any one of claims 1 or 2, wherein the pH of the liquid dairy product stream after step i) and before step ii) is adjusted to a pH in the range of 5.5 to 6.

1.

4. The method according to any one of claims 1 to 3, wherein the heat treatment in step iii) A) is performed by using one or more selected from a heat exchanger, steam injection and direct steam injection.

5. The method according to claim 4, wherein the heat treatment in step iii) A) is carried out as a two-step heat treatment, wherein the concentrated dairy product is first heat treated in a heat exchanger to a temperature of up to 50°C and subsequently heated to a temperature of up to 85°C using direct steam injection or steam injection.

6. The process according to any one of claims 1 to 5, wherein the heat treatment in step iii) A) is performed by direct steam injection or steam injection at a temperature of up to 85°C.

7. The method according to any one of claims 1 to 6, wherein the one or more devices for separation in step v) are one or more selected from the following devices: a clarifier, a centrifuge, a decanter, a filter and a cyclone separator.

8. The method of claim 7, wherein the one or more devices for separation are a combination of a clarifier and ultrafiltration.

9. The method according to any one of claims 1 to 8, wherein the cooling temperature in step iv) is 5°C to 15°C.

10. The process according to any one of claims 1 to 9, wherein the cooling is performed before or during separation step v).

11. The method according to any one of claims 1 to 10, wherein the inoculation in step iii) B) is selected from direct inoculation and indirect inoculation.

12. The method according to any one of claims 1 to 11, wherein the liquid dairy stream obtained after separation of calcium citrate in step v) is subjected to a treatment for removing calcium phosphate, said treatment comprising the following steps: a) concentrating the liquid dairy stream until the Brix is ​​in the range of 15° Bx to 30° Bx; b) heating the concentrated liquid dairy product stream to a temperature in the range of 40°C to 85°C; c) adding an alkaline compound to the concentrated liquid dairy stream to adjust the pH to at least 6.5 and maintaining at 40° C. to 85° C. for at least 10 minutes to precipitate calcium phosphate; d) optionally, cooling the heat treated concentrated liquid dairy stream; e) separating the precipitated calcium phosphate from the heat treated liquid dairy product stream by using one or more devices for mechanically separating the precipitated calcium phosphate from the liquid dairy product stream.

13. A method for preparing crystalline lactose, wherein the method comprises the following steps: A) providing a liquid dairy product stream from which calcium citrate has been removed according to any one of claims 1 to 11 or a liquid dairy product stream from which calcium citrate and calcium phosphate have been removed according to claim 12; B) adjusting the pH to within the range of 5.5 to 6.2; C) concentrating the pH adjusted liquid dairy product stream of step B) at a temperature of 50°C to 80°C until the Brix is ​​in the range of 55°Bx to 65°Bx; D) cooling to a temperature of 5° C. to 20° C. to obtain crystalline lactose and a mother liquor; E) separating lactose crystals from the mother liquor; F) Optionally, washing the lactose crystals with water.

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