Process for preparing starch with reduced impurities

Abstract

A process for preparing starch with reduced impurities is described. The refined starch is obtained by a process that includes the step of providing a slurry containing granular starch and impurities, with a pH of 5.0 to 11.0. The impurities are then at least partially removed from the slurry by washing with water in a series of nozzle centrifuges, the slurry is added to the first centrifuge of the series, the washing water is added to the last centrifuge of the series, and each nozzle centrifuge separates the supplied slurry flow into a light fraction containing the washing water and the fractions removed by washing the impurities, and a heavy fraction containing the starch and the fractions not removed by washing the impurities. The slurry is dried after washing and optionally milled to obtain starch.

Description

[Technical Field]

[0001] This invention relates to a process for preparing starch with reduced impurities. A starch composition with reduced impurities may also be called a refined starch composition. [Background technology]

[0002] Starch is widely used in the food manufacturing industry, for example, as a food thickener or stabilizer. Starch can be provided in various forms, and the present invention is not limited to any particular type of starch.

[0003] Starch can also be chemically and / or physically processed to provide greater process tolerance or better properties.

[0004] The term "physically modified starch" includes starch that has undergone heating / humidification, annealing, heat suppression, alkaline roasting, etc. Physically modified starch, such as heat suppressed starch, has the advantage of not being considered chemically modified starch. These do not require the display of a European Union "E" number or equivalent, such as a US INS number, and therefore can be included in "clean label" compliance for food ingredients.

[0005] Chemically modified starches may include, but are not limited to, crosslinked starches, acetylated starches, hydroxyethyl and hydroxypropyl starches, inorganic esterified starches, cationic, anionic, oxidized starches, zwitterionic starches, and combinations thereof. During the manufacture of such chemically modified starch compositions, chemicals are used, for example, to crosslink, in order to obtain specific desired effects or properties. Starches may also contain impurities that are not intentionally added, whether processed or not.

[0006] Starch can also be modified by enzymes.

[0007] As used herein, "impurity" refers to a compound whose presence in starch is undesirable in the (possible) use of starch, regardless of the properties of such compound.

[0008] Relatively high levels of impurities are undesirable because they can adversely affect beneficial properties. For example, flow properties can be affected in terms of both the stability of the starch at higher temperatures and its viscous behavior after exposure to relatively high levels of shear or low pH, which can occur during food preparation, etc.

[0009] To remove contaminants, at least partially, starch, such as bleached starch or heat-suppressed starch, may be subjected to a washing step, resulting in the formation of a slurry, which then must be dried, as starch is usually sold in powder form.

[0010] International Publication No. 2022 / 159719 relates to dry and wet milling processes for producing starch, particularly high-purity starch slurry. The starch / gluten slurry is separated using a nozzle-type centrifuge. The resulting starch fraction is further washed using a multi-stage backflow starch washing process with a starch washing hydrocyclone.

[0011] European Patent No. 0486260 relates to a disk-nozzle type centrifuge with a return line for recirculating underflow. It describes the removal of impurities from starch modified by treatment with sodium sulfate and starch modified by treatment with hydrochloric acid.

[0012] A known drawback of the process is that washing / slurry formation and subsequent drying may partially impair properties present in the starch or imparted to the starch through modification. One such property is so-called shear stability, i.e., the ability of heat-suppressed starch to provide high viscosity in foods such as sauces when subjected to high levels of shear during the preparation process. [Overview of the project]

[0013] An object of the present invention is to provide a process for preparing purified starch that reduces and further avoids partial loss of properties.

[0014] Furthermore, an object of the present invention is to provide a process for preparing purified starch in which the efficiency of removing contaminants is improved and / or the consumption of water and / or energy is reduced.

Means for Solving the Problems

[0015] Furthermore, it would be desirable to provide an improved starch preparation process in which the amount of contaminants is reduced and / or the loss of desired functional properties is reduced. The improvement can be made, for example, in terms of the amount of contaminants that can be removed and the efficiency of removing contaminants in terms of the consumption of specific consumables such as energy and washing water.

[0016] According to the present invention, there is provided a process for preparing starch according to claim 1. The process of the present invention a) providing a slurry containing granular starch and contaminants, having a pH of 5.0 to 11.0; and b) removing contaminants from the slurry by washing in a plurality of nozzle-type centrifuges provided continuously, wherein the slurry is added to a continuous first centrifuge and fresh washing water is added to a continuous last centrifuge, and each nozzle-type centrifuge separates the supplied slurry flow into a light fraction containing washing water and the fraction removed by washing the contaminants, and a heavy fraction containing starch and the fraction not removed by washing the contaminants.

[0017] Washing the slurry with a plurality of nozzle-type centrifuges as claimed, and having the pH of the slurry lower than a threshold as claimed, has been shown not only to improve the efficiency of removing contaminants from the slurry, but also to reduce partial loss of properties and even avoid such loss.

[0018] To the extent intended herein, a plurality of nozzle centrifuges includes nozzle centrifuges in which the removal of contaminants by washing is performed at least partially. Thus, the last centrifuge in a sequence is the last nozzle centrifuge in which the removal by washing is performed. Other centrifuges or separation devices may be included in the claimed process for purposes other than removal by washing. Such centrifuges or separation devices are not included in a sequence of nozzle centrifuges.

[0019] As used herein, the terms “substantially,” “essentially,” “essentially consisting of,” and “essentially all,” and their equivalents, have the usual meaning with respect to a composition or process step, that differences may occur within the composition or process step, but such differences do not substantially affect the fundamental characteristics and effects of the composition or process step.

[0020] As used herein, the term "~is set to" or its equivalent, relating to parameters such as the pH or water content of a system, means that the parameter is increased, decreased, or kept constant, depending on the specific circumstances.

[0021] Raw starch can be obtained from any natural source. Unless otherwise specified, references to starch herein refer to their corresponding flours and do not include flours containing any protein, such as wheat gluten, for example, flours with a protein content >4 wt.% relative to the weight of the flour. Typical sources of starch are cereals, tubers, root vegetables, legumes, fruit starches, and hybrid starches. Suitable sources include, but are not limited to, maize, quinoa, peas, potatoes, sweet potatoes, sorghum, bananas, barley, wheat, rice, sago, amaranth, tapioca, arrowroot, and canna. A preferred source is rice. Suitable starch can also be obtained from plants obtained by breeding techniques including crossbreeding, translocation, inversion, transformation, or any other process to incorporate their mutations, such as genetic or chromosome engineering. In addition, starches obtained from plants grown from artificial mutations or mutations of the above-mentioned comprehensive compositions, which can be produced by known standard mutation methods, are also suitable in the present invention.

[0022] In one embodiment of the claimed process, the starch is selected from the group consisting of potato starch, corn starch, tapioca starch, barley starch, rice starch, wheat starch, rye starch, oat starch, amaranth starch, quinoa starch, sago starch, bean starch, pea starch, waxy potato starch, waxy corn starch, waxy tapioca starch, waxy barley starch, waxy rice starch, waxy sorghum starch, waxy wheat starch, waxy pea starch, and high amylose starch, or two or more combinations thereof.

[0023] The present invention provides a slurry containing granular starch and impurities, with a pH of 5.0 to 11.0. The slurry can be provided by any known method. For example, the slurry can be provided by a slurrying step in which dry starch powder is combined with an aqueous phase to form the slurry. The slurry can also be provided as a result of a process for producing starch. For example, an extraction step in such a starch production step can provide a slurry suitable for use in the process claimed herein. The term slurry as intended herein has the usual meaning of a system having a liquid as a continuous phase, containing solid particles, and on the other hand being able to flow and be transported like a liquid at temperatures of 5°C to 60°C. The maximum temperature of 60°C may be too high for some starches, such as rice starch, due to the risk of gelation. In such cases, the maximum temperature may be 50°C, or even 40°C. The maximum weight percentage of solid particles that can be included in the slurry and still maintain its fluidity and transportability depends, as is known, on the precise properties of the particles. In the case of heat-suppressed or chemically processed starch, the solid content of the slurry is preferably 5 to 60, more preferably 5 to 40 wt.%, even more preferably 10 to 35 wt.%, and most preferably 15 to 30 wt.%. A preferred slurry contains rice starch with a solid (or dry matter DM) content of 10 to 30 wt.%.

[0024] Starch preferably constitutes a substantial portion of the substances present in the slurry. In addition to impurities, starch may exist in the form of a mixture with other compounds. In the case of a mixture, starch is the largest dry component in the mixture and preferably accounts for at least 40, 50, 60, 70, 80, 90, or at least 95% of the mixture present in the slurry. Examples of other possible compounds in the mixture include starch processed to be different from the main starch, albeit at low levels, small amounts of pregelatinized starch, other carbohydrates, and lipids. As already mentioned above, suitable starch may contain a specific protein residue, such as less than 4 wt.%, preferably less than 1 wt.%, with respect to the total weight of starch in dry form.

[0025] The slurry may be provided, for example, by a slurrying step, before the actual washing step. The slurry may also be obtained from a starch production process, as is known to those skilled in the art.

[0026] The liquid or aqueous phase in the slurry preferably has water as its continuous phase and as its main component. Other compounds other than water may be present, which is actually the case in the industrial applications of the present invention that utilize process water or other suitable water streams available on-site. The same applies to the claimed cleaning step, which will be further explained later. The aqueous phase is essentially free of other solvents such as ethanol, and preferably not at all. The aqueous phase preferably contains at least 80, 85, 90, and even more specifically, at least 95, 96, 97, or 98 wt.% water. In some embodiments of the present invention, the aqueous phase is essentially water, or even more specifically, water.

[0027] The temperature of the aqueous phase can vary over a wide range, preferably 5–50°C, more preferably 10–30°C, and even more preferably 15–25°C. This is maintained for the step of providing the slurry and for the washing step. The starch is preferably left in its original / granular state during its preparation. In such cases, the temperature of the slurry, both during its preparation and washing, is preferably kept below the gelation point of the starch. Since the precise gelation point of starch in the slurry depends on various parameters, the gelation point, as intended herein, is the temperature at which no significant gelation, or even any gelation at all, can be observed thereafter, as evidenced by the presence of the well-known Maltese cross when viewed under a polarizing microscope, preferably when the starch granules are stained with iodine. In a preferred embodiment, the temperature of the slurry is ensured not to exceed 60°C, more preferably 50°C, during its preparation and washing steps. Cooling means may be provided as needed.

[0028] Contaminants in the slurry may be present in the liquid continuous phase solution and / or may exist as undissolved solid particles. Contaminants according to the present invention may include all components that may be present in the raw materials of starch (whether naturally occurring or not), such as heavy metals and pesticides, but exclude protein and fiber fractions, both of which are substantially removed before the process claimed in this application. Furthermore, the definition of contaminants according to the present invention also includes (residual) components of chemical additives or excipients used in the starch production process prior to the method claimed in this application, such as chlorates, chlorides, and acetic acid. Other chemical modifiers such as phosphorus oxychloride, sodium trimethane, acetic anhydride, succinic anhydride, propylene oxide, hydrochloric acid, sulfuric acid, hydrogen peroxide, sodium hypochlorite, and calcium hypochlorite are also included in the definition of contaminants. The aforementioned chemical additives and modifiers may be consumed at least partially in the chemical reactions that occur during the starch production process, and these chemical reactions may also generate reaction products of the aforementioned activators. Therefore, the impurities may also include reaction products of the aforementioned activators.

[0029] Furthermore, please note that when the term "starch" is used in this application, it does not include "powdered goods." As is well known, starch may contain protein residues.

[0030] According to the present invention, the slurry is provided with a pH of 5.0 to 11.0. This can be achieved by setting the pH of the aqueous phase to a value that reaches the required pH of the slurry before proceeding to the slurry formation step. Alternatively, the required pH of the slurry can be achieved by adjusting its pH after the slurry has been formed, preferably immediately after its formation. It is also possible to adjust the pH of the aqueous phase first and then adjust the pH value of the slurry.

[0031] pH adjustment is known to those skilled in the art and can be achieved, for example, by adding a base such as sodium hydroxide or an acid such as sulfuric acid, or by using a buffer such as citrate buffer.

[0032] As used herein, the pH of solid substances such as starch is determined at 21°C by the following procedure: The test substance to be measured is placed in a beaker containing at least 100 ml of demineralized water, and then stirred to form a slurry. The amount of test substance is selected such that the dry content of the slurry is 24 wt.%. The pH of the slurry is then measured using a calibrated standard pH meter. This measured pH is considered to be the pH of the test material.

[0033] The pH of the slurry according to the present invention should be at least 5.0, and in a preferred embodiment, the pH of the slurry is at least 6.0, 6.5, or even at least 7.0 to facilitate the removal of contaminants.

[0034] The pH of the slurry according to the present invention should be at most 11.0, because it has been found that a favorable effect on the properties of the slurry-dried starch is obtained when the pH of the slurry is less than 11.0. More preferably, the pH of the slurry is at most 10.5, 10.0, 9.5, or even at most 9.0.

[0035] Preferably, the pH of the slurry according to the present invention is in the range of 6.5 to 10.5, more preferably 7.5 to 10.0, and most preferably 8.5 to 9.5.

[0036] According to the present invention, multiple stages of nozzle-type centrifuges arranged in sequence are used to perform a continuous washing process. A particulate feed material (granular starch) is combined with a liquid medium such as water to form a slurry containing (dissolved) impurities, which is fed into the first nozzle-type centrifuge, and washing water (fresh water) is continuously supplied to the last nozzle-type centrifuge in the sequence. As already disclosed above, the sequence of nozzle-type centrifuges is defined as being limited to the centrifuges on which washing is performed. However, other centrifuges or separation devices that do not perform washing may be used in addition. The washing water preferably flows as a backflow of the slurry to remove some of the impurities.

[0037] The washing water is continuously supplied to the last nozzle-type centrifuge in the sequence, but this does not preclude further addition of washing water to any centrifuge other than the last nozzle-type centrifuge in the sequence.

[0038] Nozzle centrifuges, also known as disk-nozzle centrifuges, are devices that classify / separate or sort particles in a liquid suspension or slurry based on their specific gravity. Nozzle centrifuges typically have a closed body, usually made of metal (mostly steel), ceramic, or plastic, containing a conical section, i.e., a separation chamber, and a stack of rotatable separation disks forming a separation channel. This body is rotated at high speed around a central axis. The slurry, containing starch and impurities, is typically fed from above and guided into the separation channel, where the slurry to be washed is moved outward by the centrifugal force generated by the rotation. The angle and length of the conical section can affect the operating characteristics. Water is typically supplied from the bottom of the body and forced into the separation channel as a backflow with the slurry. The nozzle through which the refined starch slurry flows into the separation channel, for example, with a nozzle size of 1.0–2.5 mm, also affects the flow rate of the washing water provided (m³). 3 This can affect operating characteristics such as (in units of / h). The water flowing as a backflow of the slurry in the separation channel removes at least partially the impurities from the slurry, and the water, which at this point also contains impurities, exits through a wash water outlet located at the end of the separation channel, which is typically located at the top of the centrifuge and is in fluid communication with it. The at least partially purified slurry exits the separation channel through a common purified slurry outlet, which is in fluid communication with the separation channel via a nozzle. The nozzle-type centrifuge can therefore separate the supplied slurry flow into a light fraction containing wash water and the fractions removed by washing the impurities, and a heavy fraction (also called the heavy phase in this application) containing starch and the fractions not removed by washing the impurities. The light fraction exits the nozzle-type centrifuge through a wash water outlet (also called the light fraction outlet). The heavy fraction exits the nozzle-type centrifuge through a purified slurry outlet (also called the heavy fraction outlet). The light fraction may contain small amounts of starch, which are typically treated as losses.

[0039] Other types of separators, such as hydrocyclones, are also available, but the process claimed in this application uses a nozzle-type (or disk-nozzle type) centrifuge. These have proven superior in achieving the objectives of the present invention, namely, efficiently removing impurities from the starch slurry and, optionally, retaining the desired properties of the resulting starch after drying.

[0040] The concentration of solids in the provided slurry, along with other parameters such as the centrifuge dimensions, outlet and nozzle dimensions, feedwater pressure, and the relative properties of starch particles and liquid, can all or separately affect the efficiency of the process. However, the inventors have found that certain parameters have a greater impact on separation than others, which will be explained further later.

[0041] For example, in a preferred embodiment, a process is provided in which at least one, and preferably all, nozzle diameters of nozzle-type centrifuges are in the range of 1.0 to 4.0 mm, more preferably to 2.6 mm, even more preferably 1.4 to 2.2 mm, and most preferably 1.6 to 2.0 mm. These ranges are particularly preferred when rice slurry is used as the feed material to the continuous nozzle-type centrifuges. Furthermore, it should be noted that the nozzle size may depend on the desired cleaning capacity and the dry matter content of the slurry. The higher the desired cleaning capacity and the higher the dry matter content of the slurry, the larger the nozzle size that can be selected.

[0042] More specifically, a preferred embodiment of the present invention is the total wash water flow rate m added to at least one of the centrifuges, preferably the last centrifuge. 3 The ratio of / h to the flow rate T / h (tons per hour) of dry matter (DM) starch added to the first centrifuge is at least 0.1m 3 / T and a maximum of 5m 3 / T, more preferably up to 4.5m 3 / T, most preferably up to 4m 3Relates to a process that is / T. With such a limited washing water flow rate, it has been demonstrated that contaminants can be substantially removed from the starch slurry by a relatively limited number, for example, 3 or 4 nozzle type centrifuges. The washing water flow rate m added to the last centrifuge 3 The preferred minimum ratio of / h to the flow rate T / h of dry matter (DM) starch added to the first centrifuge is 0.5m 3 / T, more preferably 1m 3 / T, even more preferably 1.5m 3 / T, most preferably 2m 3 / T. As already disclosed, the total washing water flow rate can be added to the last centrifuge, which is preferred, but it can be added to any combination of two or more centrifuges in the series, including the last centrifuge.

[0043] More specifically, in a preferred embodiment of the present invention, the normalized water quantity ratio defined as the total washing water flow rate m 3 / h divided by the flow rate T / h of dry matter starch and the number of centrifuges used is preferably 0.2 - 2.0, more preferably 0.25 - 1.75. This results in an optimal combination of the water flow rate to be used (which should be as small as possible), the production rate (the amount of dry matter starch that can be added to the process, which should be as large as possible), and the number of centrifuges used. The specific value of the normalized water quantity ratio can be adjusted considering the pH value of the supplied slurry.

[0044] In an embodiment of the present invention, a process is provided in which the pH of the slurry is adjusted before entering the first centrifuge.

[0045] Other embodiments relate to a process in which the pH of the slurry is adjusted before entering a random nozzle type centrifuge other than the first one in the series, more preferably before entering any nozzle type centrifuge other than the first one in the series.

[0046] Another preferred embodiment relates to a process according to a patent claim, wherein the number of nozzle-type centrifuges in a series is 2 to 8, more preferably 3 to 7.

[0047] According to the present invention, nozzle-type centrifuges are provided in a continuous configuration. This allows the heavy fraction outlet of a centrifuge in the continuous configuration to be fluidically connected to the slurry inlet of an adjacent centrifuge in the continuous configuration. In this way, the heavy fraction from the preceding centrifuge can be further purified in the next centrifuge. In other embodiments, the heavy fraction can be diluted before or during its entry into the next centrifuge. By positioning them as a continuous configuration, the light fraction outlet of one centrifuge in the continuous configuration can also be fluidically connected to the wash water inlet of a centrifuge located immediately before the aforementioned centrifuge in the continuous configuration.

[0048] Therefore, in one embodiment of the process, the wash water for at least one centrifuge, excluding the last nozzle centrifuge, is obtained from the light fraction of the subsequent nozzle centrifuge, preferably from only the light fraction of the subsequent nozzle centrifuge.

[0049] In other embodiments of the process, the wash water for all centrifuges except the last nozzle centrifuge is obtained from the light fraction of the subsequent nozzle centrifuge, preferably from only the light fraction of the subsequent nozzle centrifuge.

[0050] It should be noted that the cleaning water for the final nozzle-type centrifuge can be obtained from multiple sources, such as a water supply network, one or more containers containing process water, or piping connected to other parts of the industrial environment. In one embodiment, the cleaning water added to the final nozzle-type centrifuge is passed through an ion exchange resin to remove ions present in the water, such as Ca 2+ and Mg 2+ It may be advantageous to provide a process that reduces the amount of ions. This can prevent, or at least hinder, corrosion, such as the buildup of calcium on the walls of reactors, centrifuges, and / or conduits used in the claimed process, but not limited to these.

[0051] Furthermore, this process may be characterized by the addition of a wash of fresh water obtained from one of the centrifuges to at least one nozzle centrifuge other than the last nozzle centrifuge. This can further improve the removal of contaminants, especially when using a relatively small number of nozzle centrifuges, such as 2 to 4, but not limited to these.

[0052] Preferably, the washing water is added to each nozzle-type centrifuge as a backflow of the stabilized starch slurry flow entering the nozzle-type centrifuge.

[0053] To further enhance the separation efficiency in each nozzle-type centrifuge and throughout the entire process, one embodiment of the present invention relates to a process in which a slurry added to a first centrifuge and a heavy fraction entering a subsequent nozzle-type centrifuge from a certain nozzle-type centrifuge are diluted with dilution water before entering the subsequent nozzle-type centrifuge.

[0054] In another preferred embodiment, the dilution water entering at least one nozzle centrifuge is obtained from the light fraction of a subsequent nozzle centrifuge, preferably from only the light fraction of a subsequent nozzle centrifuge. More preferably, the dilution water before entering all nozzle centrifuges is obtained from the light fraction of a subsequent nozzle centrifuge, preferably from only the light fraction of a subsequent nozzle centrifuge.

[0055] The degree of dilution can be adjusted within a wide range of limits. However, it has been proven that a process in which the slurry added to the first centrifuge and the heavy fraction entering the subsequent nozzle centrifuge from one nozzle centrifuge is diluted to a dry percentage of 5-30%, more preferably 8-20%, and most preferably 10-15%, achieves higher efficiency.

[0056] As previously disclosed, it is advantageous for this process to provide embodiments in which the washing is carried out at a temperature of 5 to 50°C, more preferably 5 to 40°C, even more preferably 10 to 30°C, or even more preferably 15 to 25°C.

[0057] After the washing step, a drying step may be performed to obtain starch. In one embodiment of the present invention, a process is provided in which the washed slurry is dried and starch is optionally obtained by milling.

[0058] In an optional drying step, at least a portion of the aqueous phase of the purified slurry exiting the final centrifuge is separated from the starch. This can be achieved by one or more operations known to themselves.

[0059] To the extent intended herein, the term "drying step" means not only operations that rely primarily on dehydration via physical force / displacement, such as centrifugal separation or filters or filter holders, but also operations that rely primarily on evaporative dehydration, such as spray drying, airflow drying, or oven drying. In a preferred embodiment of the present invention, the drying step consists of a combination of two or more operations, for example, a combination of one or more operations that rely primarily on dehydration via physical force / displacement and one or more operations that rely primarily on evaporative dehydration.

[0060] Preferably, one or more operations of the drying step are carried out until starch with a moisture content of 5-30 wt.% is formed. In other embodiments of the present invention, the drying step is carried out in such a way that gelation does not occur. Preferably, the present invention relates to a process for preparing granular starch, comprising the washing and drying steps outlined above in a single operation.

[0061] If the drying step is optional, the starch is typically recovered and further processed, for example, by packaging the starch.

[0062] It has been found that by applying the process of the present invention to prepare refined starch, impurities can be efficiently removed from the starch while the loss of properties such as the shear stability of the starch can be kept to a limited extent. The process of the present invention also allows for the efficient use of washing water and energy.

[0063] The present invention will be described in more detail here with reference to the drawings, but is not limited thereto. [Brief explanation of the drawing]

[0064] [Figure 1] Figure 1 shows a schematic cross-sectional view of a nozzle-type centrifuge used in one embodiment of the present invention. [Figure 2] Figure 2 shows a schematic flow diagram of a process according to one embodiment of the present invention. [Modes for carrying out the invention]

[0065] Referring to Figure 1, Nozzle-type centrifuge 1(C xA nozzle-type centrifuge (also known as a nozzle-type centrifuge) is schematically shown. The nozzle-type centrifuge 1 comprises a substantially closed steel body 10, which includes a conical portion 11 with a separation channel 12 inside. The body 10 is rotated at high speed around a central rotation axis 13. Slurry 2 containing starch and impurities is typically supplied from above through a slurry inlet 14 and led into the separation channel 12, where the slurry 2 is washed and moved outward by the centrifugal force generated by the rotation. The angle 15 and length 16 of the separation channel 12 may be selected to affect the operating characteristics. Wash water 3 is typically supplied from below the body 10 through a wash water inlet 17 and forced into the separation channel 12 as a backflow of the slurry 2 through a pump (not shown). Water 3 flowing into the separation channel 12 as a backflow of slurry 2 removes at least partially of the contaminants from slurry 2. The water 3+, which at this point also contains the contaminants, or at least a higher concentration of them, exits through a wash water outlet 18 located at the end of the separation channel 12, which is typically located at the top of the centrifuge body 10 and is fluidly connected to it. The at least partially purified slurry 2+ exits the separation channel 24 through a common purified slurry outlet or nozzle 19, which is fluidly connected to the separation channel 12. The nozzle-type centrifuge 1 can therefore separate the supplied slurry flow 2 into a light fraction containing wash water and the fractions removed by washing the contaminants, and a heavy fraction containing starch and the fractions not removed by washing. The light fraction exits the nozzle-type centrifuge 1 through the wash water outlet 18 (also called the light fraction outlet). The heavy fraction exits the nozzle-type centrifuge 1 through the purified slurry outlet or nozzle 19 (also called the heavy fraction outlet).

[0066] Referring to Figure 2, a schematic process flow diagram according to one embodiment of the present invention is shown. The process involves multiple nozzle-type centrifuges C provided in a continuous manner. x This includes washing the contaminants from the supplied slurry 2 with water 3. In this specification, "x" corresponds to a desired number of centrifuges, for example, in the range of 2 to 20. Preferably, the diluted slurry 2 is added to the first centrifuge C1 in the sequence, and the washing water 3 is added to the last centrifuge C1 in the sequence.x It is added to the above. As mentioned above, each nozzle-type centrifuge C x The supplied slurry flow 2 is separated into a light fraction 3+ containing the wash water and the fraction removed by washing away impurities, and a heavy fraction 2+ containing the starch and the fraction not removed by washing away impurities.

[0067] As shown in Figure 2, nozzle-type centrifuge C i The function is provided as continuous, i = 2 ~ x. This gives us a centrifuge C in continuous form. i The heavy fraction outlet 19 is located next to centrifuge C in its continuum. i+1 The slurry inlet 14 of the first centrifuge C1 in the continuous is fluidly connected to the slurry inlet 14 of the adjacent centrifuge C2 in the continuous. i The heavy fraction 2+ that comes out is then processed in the next centrifuge C i+1 It can be further purified in multiple centrifuges C i Furthermore, centrifuge C in a continuous sequence C i+1 The light fraction outlet 18 is connected to the wash water inlet and the centrifuge C i+1 Centrifuge C is located in a straight line. i It communicates with the nozzle 17 and the fluid.

[0068] In the embodiment shown in the figure, the last nozzle-type centrifuge C x At least one centrifuge C other than i The washing water is then used in the subsequent nozzle-type centrifuge C i+1 Obtained from the light fraction 2+, preferably in a subsequent nozzle-type centrifuge C i+1 It is obtained solely from the light fraction 2+. As shown in Figure 2, the washing water for centrifuge C1 is obtained from the light fraction 3+ of the subsequent nozzle-type centrifuge C2.

[0069] However, as shown in Figure 1, each nozzle-type centrifuge C i The nozzle-type centrifuge C i An additional water inlet 20 may also be provided for introducing additional water 21.

[0070] The last nozzle-type centrifuge C x The cleaning water entering the system can be obtained from multiple sources, such as a water supply network, one or more containers holding process water, or piping connected to other parts of the industrial environment.

[0071] Each nozzle-type centrifugal separator C i To further improve the separation efficiency, slurry 2 is added to the first centrifuge C1 and nozzle-type centrifuge C i The subsequent nozzle-type centrifuge C is supplied from i+1 The heavy fraction 2+ that enters is then processed in the subsequent nozzle-type centrifuge C i+1 Before entering, it can be diluted with dilution water. This water can be introduced, for example, through the inlet 20 (water flow 21), or through the inlet and nozzle 17 and regulated by valve 22. In the latter option, a nozzle-type centrifuge C i The dilution water before entering the subsequent nozzle-type centrifuge C i+1 Obtained from the light fraction 3+, preferably followed by a nozzle-type centrifuge C i+1 It is obtained solely from the light fraction 3+. The degree of dilution can be adjusted, preferably to a dry percentage of 5-30%, more preferably 8-20%, and most preferably 10-15%. [Examples]

[0072] Several starch slurries were prepared. To do this, rice starch found to contain high levels of undesirable contaminants was used, and the slurry was formed by circulating it as an aqueous phase within a starch processing facility using industrial process water. The pH of the process water was 7.5–8.0. The weight ratio of the aqueous phase to the rice starch was adjusted to various values. The pH of the slurry was also adjusted to various values. These slurries were washed in multiple centrifuges.

[0073] To obtain the necessary starch properties, the purified slurry after washing was dehydrated by vacuum filtration. The resulting filtered cake was further dried using a fluidized bed dryer at a maximum air temperature of 50°C to an average moisture content of 12 wt.%.

[0074] The specific properties of slurry-forming dry starch were identified by preparing a gel with this slurry-forming dry starch. The gel was prepared in a Stephan UMSK 5 cooker equipped with a mixing insert having two rounded blades, using 135 g (dry weight) of starch, acidified to pH 3.6, citric acid and trisodium citrate for buffering, and enough water to make a total weight of 2,500 g. The citric acid and trisodium citrate were mixed with water, then the starch was added, and the mixture was prepared at 94°C and 300 rpm. After cooling to 25°C, the gel was subjected to a strong shearing action at 5,000 rpm for 1 minute using a Silverson L4RT mixer with a square-hole (2.4 mm) high-sear screen mixer head.

[0075] The tan σ of gels made from the relevant starches and subjected to initial strong shear action was determined at a temperature of 20°C using an Anton Paar Pheometer (parallel plate-plate configuration, plate diameter 40 mm). To the extent intended herein, the term tan σ is used in its general sense as the loss tangent in the linear viscoelastic region. This yields the ratio between the viscous and elastic properties of the system, indicating which is dominant. When the value of tan σ is 1, the elastic and viscous properties of the material are equal. The smaller the loss tangent, the higher the elasticity of the material. Tan σ was determined from the results of amplitude sweep measurements with the following properties: deformation 0.01–1000% and frequency 1 Hz.

[0076] Other properties of the same slurry-forming dry starch, such as Brabender viscosity during temperature sweeps, were also obtained using the following method: Brabender curves were identified in 6 wt.% dry material in deionized water with a pH of 6.0-6.5 using sulfuric acid, with a total weight of 500 g and a measurement speed of 75 rpm. The applied temperature profile started at 50°C, increased at 3°C / min to approximately 95°C, held at approximately 95°C for 15 minutes, and then cooled to 20°C at 3°C / min. From the resulting viscosity profile, the value of Delta 95 was calculated by subtracting the viscosity at the end of the 95°C interval from the viscosity at the start of the 95°C interval.

[0077] The prepared slurry was washed using multiple nozzle-type centrifuges, and the amount of impurities was identified after each nozzle-type centrifuge (indicated as HP1, Hp2, HP3, HP4, etc.). The abbreviation HP stands for "heavy phase," which is also shown as heavy fraction 2+ in the figure. The impurity concentration is measured in this heavy phase.

[0078] The pH, Baumé, and dry matter content (DM) of the feed slurry entering the first centrifuge were measured by the following method: The pH of the slurry was determined under slow stirring using a WTW 3210 pH meter with a WTW SenTix 81 combination electrode. The Baumé degree of the starch slurry was determined by inserting a Baumé meter (measuring range 10-20 Baumé) into a 500 mL cylinder filled to the brim with the slurry. After the Baumé meter stabilized, the value was read from the meter's scale. • The dry matter content (DM) was analyzed at 130°C using an infrared moisture meter.

[0079] The concentrations of the three contaminants in the slurry flow, namely chlorates, chlorides, and sulfuric acid, are measured at each centrifuge stage HP. i The measurements were taken by taking samples after the analysis. Chlorate concentrations were measured by LC-MS / MS after methanol extraction of formate using the EURL-SRM QuPPe-PO method. Chloride and sulfuric acid concentrations were measured using ion chromatography (IC) according to the test method for the identification of inorganic anions (chlorates, nitrites, nitrates, phosphates, nitrates, and oxalates) in DIN EN ISO 10304-1:2009-07. Inorganic anion content was given in units of mg / kg or mg / L, and the percentage reduction after washing was calculated. According to the principle of this method, inorganic anions were separated by elution in a latex anion exchange column, and after inhibition, detected by conductivity measurement. The concentration gradient required for component separation is automatically generated by an eluent generator incorporated into the IC system.

[0080] For sample preparation, solutions were prepared by weighing or diluting the sample. The dry substance content of the solution should be 10 g / 100 g or less. Subsequently, the sample solutions were diluted as needed. From these sample solutions, further dilution steps were performed as needed to enable measurement within the calibration range of the components.

[0081] For the highly concentrated saline obtained after the claimed washing, a 10 g sample was weighed and placed in a 100 mL volumetric flask, mixed with ultrapure water, and heated to the mark at 20°C to prepare the sample. Subsequently, other dilutions (1:10 and 1:20 dilutions) were prepared.

[0082] The following chromatography conditions were used: -Dilution: Potassium hydroxide gradient 0.0~2.0 min: 1.0mM KOH 2.0~16.0 mins: 1.0mM~40.0mM KOH • 16.0-16.1 min: 40.0mM-50.0mM KOH 16.1-17.0 minutes: 50.0mM KOH 17.0-17.1 min: 50.0mM-1.0mM KOH • 17.1~25.0 minutes: 1.0mM KOH -Flow rate: 0.25mL / min -Injection volume: 5μL - Column oven temperature: 30°C -Current ADRS suppressor: • 0.0 min to 10.0 min: 8mA ·10.0 minutes~25.0 minutes: 22mA - Conductivity measurement cell temperature: 30°C

[0083] Subsequently, the anion concentration was calculated using appropriate software (Chromeleon) by comparing the peak regions of the standard and sample solutions using calibration functions for each component.

[0084] The process conditions applied to each sample are summarized in Table 1 below. The column "#c" indicates the number of centrifuges used. Example 4C is reproduced as Example 7A for easier comparison. TIFF2026513090000001.tif214170

[0085] The results obtained are shown in the table below. TIFF2026513090000002.tif160170

[0086] From Examples 1A and 1B, it can be inferred that for all contaminants (chlorates, chlorides, sulfates), the higher the pH value, the higher the efficiency of contaminant removal when the normalization ratio of wash water to DM starch is constant. However, at a higher pH value of pH=9.6, although still acceptable, there is some loss of properties. This is confirmed for chlorates from Examples 2A and 2B, as shown in Table 3. TIFF2026513090000003.tif137170

[0087] From Examples 3A and 3B, as shown in Table 4, it can be inferred that when the normalization ratio of washing water to DM starch is constant, a higher pH value leads to higher efficiency in removing chlorate and chloride contaminants. TIFF2026513090000004.tif130170

[0088] This is confirmed for chlorates from Examples 4A, 4B, and 4C, as shown in Table 5 below. TIFF2026513090000005.tif197170TIFF2026513090000006.tif80170TIFF2026513090000007.tif79170

[0089] Examples 7A and 7B confirm this finding for two different nozzle diameters of nozzle-type centrifuges used, with the same pH, wash water flow rate, and number of centrifuges. All centrifuges in Figure 7A had the same nozzle diameter. All centrifuges in Example 7B also had the same nozzle diameter, which was 6% larger than the nozzle diameter in Example 7A. Example 4C is reproduced as Example 7A for easier comparison. TIFF2026513090000008.tif139170

[0090] Tables 8A and 8B also demonstrate that, for chlorides, higher pH values ​​at equivalent wash water-to-DM starch normalization ratios result in higher contaminant removal efficiency. However, higher pH levels also lead to increased loss of properties or functionality, as shown by the included Brabender Delta 95 data. In addition, Examples 8A and 8C demonstrate the potential adverse effects of reducing the number of centrifuges on contaminant removal, which is evident at higher wash water / DM starch normalization ratios. TIFF2026513090000009.tif191170

Claims

1. In the process of preparing starch, a) A step of providing a slurry containing granular starch and impurities, with a pH of 5.0 to 11.0, b) A process comprising the step of removing the contaminants from the slurry by washing in a plurality of nozzle-type centrifuges provided in a series, wherein the slurry is added to the first centrifuge of the series, fresh water washing water is added to the last centrifuge of the series, and each nozzle-type centrifuge separates the supplied slurry flow into a light fraction containing the washing water and the fractions removed by washing the contaminants, and a heavy fraction containing starch and the fractions not removed by washing the contaminants.

2. A process according to claim 1, characterized in that the pH of the slurry before it enters the first centrifuge in the sequence is 6.5 to 10.5, more preferably 7.5 to 10.0, and even more preferably 8.5 to 9.

5.

3. In the process according to claim 1 or 2, the flow rate of washing water m added to the centrifuge, preferably the last centrifuge. ３ The ratio of the flow rate T / h of the dry matter (DM) starch added to the first centrifuge is at least 0.1 m ３ / T and a maximum of 5m ３ A process characterized by being / T.

4. In the process according to any one of claims 1 to 3, the flow rate m of the washing water added to at least one of the centrifuges, preferably the last centrifuge. ３ The process is characterized in that the normalized water ratio, defined as dividing / h by the flow rate T / h of the dried starch added to the first centrifuge and the number of centrifuges used, is 0.2 to 2.0, more preferably 0.25 to 1.

75.

5. A process according to any one of claims 1 to 4, characterized in that the pH of the slurry is adjusted before it enters a nozzle-type centrifuge other than the first of the continuous ones.

6. A process according to any one of claims 1 to 5, characterized in that the number of continuous nozzle-type centrifuges is 2 to 8, more preferably 3 to 7.

7. A process according to any one of claims 1 to 6, characterized in that at least one washing water other than the last nozzle-type centrifuge is obtained from the light fraction of a subsequent nozzle-type centrifuge, preferably from only the light fraction of a subsequent nozzle-type centrifuge.

8. The process according to claim 7, characterized in that all washing water other than that from the last nozzle-type centrifuge is obtained from the light fraction of the subsequent nozzle-type centrifuge, preferably only from the light fraction of the subsequent nozzle-type centrifuge.

9. A process according to any one of claims 1 to 8, characterized in that washing water is added to each nozzle-type centrifuge as a backflow of the stable starch slurry flowing into the nozzle-type centrifuge.

10. A process according to any one of claims 1 to 9, characterized in that the wash water of fresh water not obtained from one of the centrifuges is added to at least one nozzle-type centrifuge other than the last nozzle-type centrifuge.

11. A process according to any one of claims 1 to 10, characterized in that the slurry added to the first centrifuge and the heavy fraction entering a subsequent nozzle centrifuge from a certain nozzle centrifuge are diluted with diluent water before entering the subsequent nozzle centrifuge.

12. The process according to claim 11, characterized in that the dilution water before entering at least one nozzle-type centrifuge is obtained from the light fraction of a subsequent nozzle-type centrifuge, preferably from only the light fraction of a subsequent nozzle-type centrifuge.

13. The process according to claim 12, characterized in that the dilution water before entering all of the nozzle-type centrifuges is obtained from the light fraction of the subsequent nozzle-type centrifuge, preferably only from the light fraction of the subsequent nozzle-type centrifuge.

14. A process according to any one of claims 11 to 13, characterized in that the slurry added to the first centrifuge and the heavy fraction entering a subsequent nozzle centrifuge from a certain nozzle centrifuge are diluted to a dry percentage of 5 to 30%, more preferably 8 to 20%, and most preferably 10 to 15%.

15. A process according to any one of claims 1 to 14, characterized in that the impurity includes an organic acid, a bisulfite, or hydrogen peroxide.

16. A process according to any one of claims 1 to 15, characterized in that the diameter of at least one nozzle of the nozzle-type centrifuge is in the range of 1.0 to 2.6 mm, more preferably 1.4 to 2.2 mm, and most preferably 1.6 to 2.0 mm.

17. A process according to any one of claims 1 to 16, characterized in that the washing is performed at a temperature of 5 to 40°C.

18. A process according to any one of claims 1 to 17, characterized in that the slurry after washing is dried and optionally milled to obtain the starch.

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