Process for preparing starch with reduced amount of contaminants

Abstract

A process for preparing starch having a reduced amount of contaminants is described. The purified starch is obtained by a process comprising the step of providing a slurry containing particulate starch and contaminants and having a pH of 5.0-11.0. Thereafter, the contaminants are at least partially washed away from the slurry with water in a plurality of nozzle centrifuges provided in series, where the slurry is added to the first centrifuge in the series and wash water is added to the last centrifuge in the series; and wherein each nozzle centrifuge separates the incoming slurry stream into a light fraction comprising wash water and a washed portion of the contaminant and a heavy fraction comprising starch and an unwashed portion of the contaminant. The slurry may be dried after washing and optionally ground to obtain starch.

Description

Field of the Invention

[0001] The present invention relates to a method for preparing starch having a reduced amount of contaminants.The starch composition having a reduced amount of contaminants may alternatively be referred to as a purified starch composition.

[0002] background

[0003] Starch is widely used in the food manufacturing industry, for example as a food thickener or stabilizer.Starch can be in different forms, and the present invention is not limited to any particular type of starch.

[0004] Starches may also be chemically and / or physically modified to provide improved processing resistance or better properties.

[0005] The term physically modified starch includes starches that have been subjected to heat / moisture treatment, annealing, heat inhibition, alkaline roasting, etc. Physically modified starches (such as heat inhibited starches) have the advantage of not being considered chemically modified starches. These starches do not need to be labeled with an EU 'E' number or equivalent (such as an INS number in the United States), and can therefore be part of a 'clean label' approach to food product ingredients.

[0006] Chemically modified starches may include, but are not limited to, cross-linked starches, acetylated starches, hydroxyethylated and hydroxypropylated starches, inorganic esterified starches, cationic starches, anionic starches, oxidized starches, zwitterionic starches, and combinations thereof. During the manufacture of such chemically modified starch compositions, chemicals may be used to obtain certain desired effects or properties, such as cross-linking. Starches (whether modified or not) may also contain contaminants that are not intentionally added.

[0007] Starch can also be modified by enzymes.

[0008] As used herein, the term contaminant indicates compounds whose presence in starch is undesirable in view of the (potential) use of the starch, regardless of the nature of the characteristics of the compound itself.

[0009] Relatively high levels of contaminants are undesirable because they may negatively affect useful properties. For example, rheological properties may be affected in two ways: the stability of the starch at higher temperatures and its viscous behavior after the starch is subjected to relatively high levels of shear or low pH (as may occur during the preparation of a food product).

[0010] In order to at least partially remove the contaminants, the starch (eg bleached starch or heat-inhibited starch) may be subjected to a washing step resulting in the formation of a slurry which must then be dried, since the starch is usually supplied to the market in powder form.

[0011] WO 2022 / 159719 relates to a dry and wet milling method for producing starch, in particular pure starch slurry. The starch / gluten slurry is separated using a nozzle centrifuge. The obtained starch fraction is further washed using a starch washing hydrocyclone using a multi-stage countercurrent starch washing process.

[0012] EP 0486260 relates to a disc nozzle centrifuge provided with a return conduit for recirculating the underflow. The removal of impurities from starch modified by treatment with sodium sulphate and from starch modified by treatment with hydrochloric acid is described.

[0013] A disadvantage of this known process is that washing / slurry formation and subsequent drying may also result in a partial loss of properties present in the starch or imparted to the starch by modification. One such property is the so-called shear stability, i.e. the ability of the heat-inhibited starch to provide high viscosity in food products such as sauces which require exposure to high levels of shear during the preparation process.

[0014] It is an object of the present invention to provide a process for preparing purified starch in which partial losses of properties are reduced or even avoided.

[0015] Furthermore, it is an object of the present invention to provide a process for the preparation of purified starch having an improved pollutant removal efficiency and / or a reduced water and / or energy consumption. SUMMARY OF THE INVENTION

[0017] Will further wish to provide a kind of improvement method for the preparation of the starch of the desired functional characteristic loss with the amount of pollutants reduced and / or reduced.This improvement can for example be in the removal efficiency of the pollutant in the amount of the pollutant that can be removed and the consumption of some consumables (such as energy, wash water etc.).

[0018] According to the present invention, a method for preparing starch according to claim 1 is provided. The method of the present invention comprises the following steps:

[0019] a) providing a slurry containing granular starch and contaminants and having a pH between 5.0 and 11.0;

[0020] b) washing the contaminants from the slurry with water in a plurality of nozzle centrifuges provided in series, wherein the slurry is added to the first centrifuge in the series and fresh wash water is added to the last centrifuge in the series; and wherein each nozzle centrifuge separates the incoming slurry flow into a light fraction and a heavy fraction, the light fraction comprising wash water and the washed portions of the contaminants, and the heavy fraction comprising starch and the unwashed portions of the contaminants.

[0021] It has been shown that washing the slurry in a multiple nozzle centrifuge as claimed and at a slurry pH below a threshold as claimed not only provides improved efficiency of removing contaminants from the slurry, but also can reduce or even avoid partial loss of properties.

[0022] As described herein, a plurality of nozzle centrifuges include nozzle centrifuges in which washing of contaminants occurs at least in part. Therefore, the last centrifuge in the series connection is the last nozzle centrifuge in which washing occurs. For other purposes other than washing, other centrifuges or separation equipment may be included in the claimed method. Such centrifuges or separation equipment are not included in the nozzle centrifuges in the series connection.

[0023] As used herein, unless otherwise indicated, the terms 'substantially', 'essentially', 'consisting essentially of', 'substantially all' and their equivalents in relation to a composition or a process step have the ordinary meaning that deviations may occur in the composition or process step, but only to the extent that the essential characteristics and effects of the composition or process step are not substantially affected by such deviations.

[0024] As used herein, the term "cause it to" or its equivalents in relation to a parameter such as, for example, the pH or moisture content of a system has the meaning that the parameter may be caused to increase, decrease, or remain unchanged, depending on the circumstances.

[0025] Raw starch can be obtained from any natural source. Unless otherwise specifically distinguished, the reference to starch in this specification does not include its corresponding flour, which still contains some protein, such as protein content of>4wt.% relative to the weight of flour, such as wheat gluten. Typical sources of starch are cereals, tubers, roots, beans, fruit starch and mixed starch. Suitable sources include but are not limited to corn, quinoa, peas, potatoes, sweet potatoes, sorghum, bananas, barley, wheat, rice, sago, Amaranth, cassava, arrowroot, Canna. The preferred source is rice. Suitable starch can also be derived from the plant obtained by breeding techniques, which include hybrid breeding, translocation, inversion, conversion or gene or chromosome engineering to include any other method of its variation. In addition, the starch derived from the plant (which can be produced by known standard mutation breeding methods) grown by artificial mutation and variation of the above general composition is also suitable in this article.

[0026] In an embodiment of the claimed method, the starch is selected from the group consisting of potato starch, maize (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 a combination of two or more of these.

[0027] According to the present invention, a slurry is provided, which contains granular starch and contaminants and has a pH of 5.0-11.0. The slurry can be provided in any known manner. For example, the slurry can be provided by a slurrying step of combining dry starch powder with an aqueous phase to form a slurry. The slurry can also be provided as a result of a method for preparing starch. For example, an extraction step in such a starch preparation method can produce a slurry suitable for use in the method claimed in the present invention. As described herein, the term slurry has the following general meaning: a system having a liquid as a continuous phase and containing solid particles, while being able to flow and transport in a manner similar to a liquid at a temperature between 5°C and 60°C. For some starches (such as rice starch), a maximum temperature of 60°C may be too high due to the risk of gelatinization. In such cases, the maximum temperature can be 50°C or even 40°C. It is well known that the maximum weight percentage of solid particles that can be included in the slurry while still maintaining flowability and transportability characteristics will depend on the exact nature of the particles. In the case of thermally inhibited or chemically modified starches, it is preferred that the solids content of the slurry is between 5 and 60, more preferably between 5 and 40 wt.%, even more preferably between 10 and 35 wt.% and more preferably between 15 and 30 wt.%. Preferred slurries contain rice starch having a solids (or dry matter DM) content between 10 and 30 wt.%.

[0028] Starch preferably constitutes a substantial part of the material present in the slurry. In addition to contaminants, starch can also be present in the form of a mixture with other compounds. In the case of a mixture, starch is the largest dry matter component in the mixture, preferably accounting for at least 40%, 50%, 60%, 70%, 80%, 90% or at least 95% of the mixture present in the slurry. Examples of possible other compounds in the mixture are starches modified differently from the main starch, small amounts of pregelatinized starch, other carbohydrates and lipids (but at low levels). As already mentioned above, suitable starches may contain residual amounts of proteins, such as less than 4wt.%, preferably less than 1wt.% relative to the total weight of the starch in dry form.

[0029] The slurry may be provided before the actual washing step, for example by a slurrying step. As known to the person skilled in the art, the slurry may also come from a starch preparation process.

[0030] The liquid or aqueous phase in the slurry preferably has water as its continuous phase and main component. Other compounds except water may also be present, and indeed in industrial applications such as the present invention, process water or other available and suitable water streams are used in industrial applications. The same applies to the claimed washing steps, which will be further explained below. Preferably, the aqueous phase is substantially free of, preferably free of, other solvents, such as ethanol. The aqueous phase preferably contains at least 80, 85, 90 or even at least 95, 96, 97 or 98 wt.% of water. In an embodiment of the present invention, the aqueous phase is substantially composed of water or even composed of water.

[0031] The temperature of the aqueous phase can vary over a wide range and is preferably between 5°C and 50°C, more preferably between 10°C and 30°C, or even between 15°C and 25°C. This applies to the step of providing the slurry as well as the washing step. The starch is preferably kept in a native / granular state during its preparation. In this case, the temperature of the slurry during its preparation and during the washing is preferably kept below the gel point of the starch. Since the exact gel point of the starch in the slurry depends on various parameters, the gel point as described herein is such a temperature that no significant gelatinization can be observed later or even no gelatinization can be observed at all - as evidenced by the presence of the well-known Maltese cross when observed under a polarized light microscope, preferably when the starch granules have been stained with iodine. In a preferred embodiment, it is ensured that the temperature of the slurry does not exceed 60°C, more preferably does not exceed 50°C during its preparation and during the washing step. If necessary, a cooling device can be provided.

[0032] The pollutants in the slurry may be present in the liquid continuous phase in a dissolved state and / or they may exist as undissolved solid particles. In the context of the present invention, pollutants may include all components (naturally occurring or non-naturally occurring) that may be present in the original source material of starch, such as heavy metals, pesticides, etc., but do not include protein fractions and fiber fractions, both of which have been removed to a considerable extent before the method claimed in the present invention. In the context of the present invention, the definition of pollutants further includes (residual) components of chemical adjuvants or excipients used during the starch production process before the claimed method, such as chlorates, chlorides, acetic acid... Other chemical modifiers such as phosphorus oxychloride, sodium trimetaphosphate, acetic anhydride, succinic anhydride, propylene oxide, hydrochloric acid, sulfuric acid, hydrogen peroxide, sodium hypochlorite, calcium hypochlorite, etc. are also included in the definition of pollutants. The chemical adjuvants and / or modifiers mentioned above may have been at least partially consumed in the chemical reactions that occur during the starch production process, and these chemical reactions may also produce the reaction products of the reagents. Therefore, pollutants may also include the reaction products of the reagents.

[0033] It is further noted that when the wording 'starch' is used in this application, this is not intended to include 'flour'. As is known, starch may contain residual amounts of protein.

[0034] According to the invention, the slurry is provided so that it has a pH of 5.0 to 11.0. This can be achieved by bringing the pH of the aqueous phase to a value such that the slurry reaches the desired pH value before it enters the slurrying step. Alternatively, the desired pH of the slurry can be achieved by adjusting the pH of the slurry after it has been formed, preferably immediately after the slurry has been formed. It is also possible to first adjust the pH of the aqueous phase and then also adjust the pH value of the slurry.

[0035] Adjustment of the pH is familiar per se to the person 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 with the aid of a buffer such as a citrate buffer.

[0036] As used herein, the pH of solid materials like starch is at 21°C and is determined as follows: the test material to be measured is added to a beaker containing at least 100 ml of demineralized water, followed by stirring to form a slurry. The amount of the test material is selected so that the dry matter content of the slurry is 24 wt.%. The pH of the slurry is then measured by using a calibrated standard pH measuring device. The measured pH is considered to be the pH of the test material.

[0037] The pH of the slurry according to the present invention should be at least 5.0, and in preferred embodiments, the pH of the slurry is at least 6.0, 6.5, or even at least 7.0 to facilitate removal of contaminants.

[0038] The pH of the slurry according to the invention should be at most 11.0, as it has been found that the properties of the slurry dried starch are beneficially affected when the pH of the slurry is below 11.0. More preferably, the pH of the slurry is at most 10.5, 10.0, 9.5, or even at most 9.0.

[0039] 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, most preferably 8.5 to 9.5.

[0040] According to the present invention, a plurality of nozzle centrifuge stages arranged in series are used to carry out a continuous washing process. Granular raw material (granular starch) is fed into the first nozzle centrifuge together with a liquid medium (such as water) - forming a slurry also containing (dissolved) pollutants, and (fresh) wash water is continuously fed into the last nozzle centrifuge in the series connection. As disclosed above, the nozzle centrifuge in series is defined as a centrifuge limited to washing. However, other centrifuges or separation equipment that are not washed can be used additionally. Wash water preferably flows countercurrently with the flow of the slurry to remove a portion of pollutants.

[0041] Although wash water is continuously fed to the last nozzle centrifuge in the series, this does not exclude the further addition of wash water to additional nozzle centrifuges in the series other than the last nozzle centrifuge.

[0042] A nozzle centrifuge (also known as a disc nozzle centrifuge) is a device for classifying / separating or sorting particles in a liquid suspension or slurry based on the density of the particles. A nozzle centrifuge typically has a closed body, such as metal (mainly steel), ceramic or plastic, comprising a conical section (i.e., a separation chamber) provided with a stack of rotatable separation discs forming a separation channel. The body rotates at high speed around a central rotation axis. The slurry containing starch and contaminants is typically fed from the top and directed to the separation channel, where the slurry to be washed is propelled outwardly under the action of the centrifugal force generated by the rotation. The angle and length of the conical section may affect the operating characteristics. Water is typically fed from the bottom of the body and forced to flow countercurrently with the slurry into the separation channel. The nozzle size of the nozzle through which the purified starch slurry leaves the separation channel - for example, between 1.0 and 2.5 mm - may also affect the operating characteristics, such as the wash water flow rate (in m 3 / h). The water flowing in the separation channel in a countercurrent manner with the slurry at least partially removes contaminants from the slurry, and the water now also containing contaminants leaves through a wash water outlet, which is typically arranged at the top of the centrifuge body and is located at the end of the separation channel connected to its fluid. The at least partially purified slurry leaves the separation channel through a common purified slurry outlet connected to the separation channel fluid via a nozzle. Therefore, the nozzle centrifuge is able to separate the incoming slurry flow into a light fraction and a heavy fraction (also represented as heavy phase in this application), the light fraction containing wash water and the washed portion of contaminants, and the heavy fraction containing starch and the unwashed portion of contaminants. The light fraction leaves the nozzle centrifuge through the wash water outlet (also called the light fraction outlet). The heavy fraction leaves the nozzle centrifuge through the purified slurry outlet (also called the high fraction outlet). The light fraction may contain a small amount of starch; these small amounts are typically regarded as losses.

[0043] Although other types of separators are available, such as hydrocyclones, the claimed method uses a nozzle (or disc nozzle) centrifuge. These centrifuges have been shown to be excellent in achieving the objectives of the present invention, namely providing efficient removal of contaminants from a starch slurry and also retaining the desired properties of the resulting starch (optionally after drying).

[0044] The concentration of solids in the provided slurry, and other parameters such as centrifuge size, outlet and nozzle size, water feed pressure, and the relevant characteristics of starch granules and liquid can all or individually have an impact on the efficiency of the method. However, the inventors have found that certain parameters have a dominant effect on separation, as will be further explained below.

[0045] For example, in a preferred embodiment, a method is provided wherein at least one nozzle centrifuge and preferably the range of the nozzle diameter of all nozzle centrifuges is 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. When using rice starch slurry as the feeding to the nozzle centrifuge in series, these ranges are particularly preferred. It should be further noted that the nozzle size can depend on the desired washing power and the dry matter content of the slurry. The higher the desired washing power and the dry matter content of the slurry, the larger the nozzle size that can be selected.

[0046] More particularly, a preferred embodiment of the present invention relates to a method wherein the amount of m added to at least one centrifuge, preferably the last centrifuge, is 3 The ratio of the total wash water flow in T / h (tons / hour) to the dry matter (DM) starch flow in T / h (tons / hour) added to the first centrifuge is at least 0.1 m 3 / T and up to 5m 3 / T, more preferably at most 4.5m3 / T and more preferably at most 4m 3 / T. It has been determined that such limited wash water flow allows for substantial removal of contaminants from starch slurry with a relatively limited number of nozzle centrifuges (such as, for example, 3 or 4). 3 The preferred minimum ratio of the wash water flow in T / h to the dry matter (DM) starch flow in T / h added to the first centrifuge is 0.5 m 3 / T, more preferably 1m 3 / T, even more preferably 1.5m 3 / T and most preferably 2m 3 / T. As disclosed above, the total wash water flow can be added to the last centrifuge (which is preferred), but can also be added to any combination of two or more centrifuges in the series (including the last centrifuge).

[0047] More particularly, it has been determined that, in a preferred embodiment of the present invention, the amount of m added to at least one centrifuge, preferably the last centrifuge, is defined as 3 The normalized water ratio of the total wash water flow in T / h divided by the dry matter starch flow in T / h and the number of centrifuges used is preferably between 0.2-2.0, more preferably between 0.25-1.75. This provides the best combination of the water flow used (which should be as low as possible), the productivity (the amount of dry matter starch that can be added to the process, which should be as high as possible) and the number of centrifuges used. The specific value of the normalized water ratio can be adjusted taking into account the pH value of the incoming slurry.

[0048] In an embodiment of the present invention, a method is provided wherein the pH of the slurry is adjusted prior to entering the first centrifuge.

[0049] Another embodiment is directed to a method wherein the pH of the slurry is adjusted prior to entering a random nozzle centrifuge other than the first nozzle centrifuge in the series, more preferably prior to entering any nozzle centrifuge other than the first nozzle centrifuge in the series.

[0050] Another preferred embodiment relates to a method as claimed, wherein the number of nozzle centrifuges in the series is 2-8, more preferably 3-7.

[0051] According to the present invention, nozzle centrifuge is provided in series. This requires that the heavy fraction outlet of the centrifuge in the series connection be fluidically connected to the slurry inlet of the next centrifuge positioned in the series connection. In this way, the heavy fraction leaving the previous centrifuge can be further purified in the next centrifuge. In another embodiment, the heavy fraction can be diluted before or during entering the next centrifuge. The series positioning may also require that the light fraction outlet of the centrifuge in the series connection be fluidically connected to the wash water inlet of the centrifuge just positioned before the described centrifuge in the series connection.

[0052] Therefore, in an embodiment of the method, the wash water of at least one nozzle centrifuge other than the last nozzle centrifuge originates from the light fraction, preferably exclusively from the light fraction, of the subsequent nozzle centrifuges.

[0053] In another embodiment of the method, all wash water except the last nozzle centrifuge originates from the light fraction of the subsequent nozzle centrifuges, preferably only from the light fraction of the subsequent nozzle centrifuges.

[0054] It should be noted that the wash water for the last nozzle centrifuge can originate from a variety of sources, such as a water grid, one or more containers (e.g., containers holding process water), or a piping system connected to other parts of the industrial environment. In an embodiment, it may be beneficial to provide a method in which the wash water added to the last nozzle centrifuge is passed through an ion exchange resin to reduce the ions (e.g., Ca 2+) present in the water. 2+ and Mg 2+ This can prevent or at least hinder corrosion, such as but not limited to the deposition of calcium on the walls of the reactors, centrifuges and / or conduits used in the claimed method.

[0055] The method may also be characterized in that fresh wash water not originating from one of the centrifuges is added to at least one nozzle centrifuge other than the last nozzle centrifuge. This may further improve the removal of contaminants, particularly (but not limited to) when a relatively low number of nozzle centrifuges (e.g., 2-4) is used.

[0056] Preferably, wash water is added to each nozzle centrifuge countercurrently to the flow of stabilized starch slurry entering the nozzle centrifuge.

[0057] In order to further improve the separation efficiency of each nozzle centrifuge, but also the separation efficiency of the complete method, an embodiment of the present invention relates to a method wherein the slurry added to the first centrifuge and the heavy fraction from the nozzle centrifuge entering the subsequent nozzle centrifuge are diluted with dilution water before entering the subsequent nozzle centrifuge.

[0058] In yet another preferred embodiment, the dilution water before entering at least one nozzle centrifuge is derived from the light fraction of a subsequent nozzle centrifuge, preferably only from the light fraction of a subsequent nozzle centrifuge. More preferably, the dilution water before entering all nozzle centrifuges is derived from the light fraction of a subsequent nozzle centrifuge, preferably only from the light fraction of a subsequent nozzle centrifuge.

[0059] The degree of dilution can be adjusted between wide limits. However, it has been shown that a method of diluting the slurry added to the first centrifuge and the heavy fraction from the nozzle centrifuge entering the subsequent nozzle centrifuge to a dry matter percentage between 5% and 30%, more preferably between 8% and 20% and most preferably between 10% and 15% results in improved efficiency.

[0060] As already disclosed previously, it is beneficial for the process to provide embodiments wherein washing is carried out at a temperature between 5°C and 50°C, more preferably between 5°C and 40°C, even more preferably between 10°C and 30°C, or even between 15°C and 25°C.

[0061] After the washing step, a drying step may be performed to obtain starch. In an embodiment of the present invention, a method is provided, wherein the slurry after washing is dried and optionally ground to obtain starch.

[0062] In an optional drying step, at least part of the aqueous phase of the purified slurry exiting from the last centrifuge is separated from the starch. This can be achieved via one or more operations known per se.

[0063] As described herein, the term drying step is meant to include not only operations that rely primarily on dehydration via physical force / displacement (such as centrifugation or filter press), but also operations that rely primarily on evaporative dehydration (such as spray drying, flash drying, or oven drying). In a preferred embodiment of the present invention, the drying step consists of a combination of two or more operations, such as 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.

[0064] The operation or operations in the drying step are preferably carried out to such an extent that a starch having a moisture content of between 5 wt.% and 30 wt.% is formed. In another embodiment of the invention, the drying step is carried out such that substantially no gelatinization occurs. Preferably, the present invention relates to a method for preparing starch in granular form, the method comprising in one operation the washing and drying steps as outlined above.

[0065] After the optional drying step is complete, the starch is typically recovered and further processed, for example by packaging the starch.

[0066] It has been found that by using the method for preparing purified starch of the present invention, it is possible to obtain the efficient removal of pollutants from starch while keeping the characteristic (such as shear stability) loss of starch limited. Due to the method of the present invention, wash water and energy can be used efficiently.

[0067] Detailed description of the invention and examples

[0068] The present invention will now be described in more detail with reference to the accompanying drawings, but the present invention is not limited thereto. In the drawings:

[0069] Figure 1 a schematic cross-sectional view showing a nozzle centrifuge as used according to an embodiment of the method of the present invention; and

[0070] Figure 2 A schematic flow chart showing a method according to an embodiment of the present invention.

[0071] refer to Figure 1 , schematically shows a nozzle centrifuge 1 (also referred to as C x ). The nozzle centrifuge 1 comprises a substantially closed steel body 10 including a conical section 11, which is provided with a separation channel 12 inside. The body 10 rotates at high speed around a central rotation axis 13. The slurry 2 containing starch and contaminants is typically fed from the top through a slurry inlet 14 and is led to the separation channel 12, where the slurry 2 to be washed is propelled outwardly under the action of the centrifugal force generated by the rotation. The angle 15 and length 16 of the separation channel 12 can be selected to affect the operating characteristics. Wash water 3 is typically fed from the bottom of the body 10 through a wash water inlet 17 and is forced to flow countercurrently with the slurry 2 (by a pump not shown) into the separation channel 12. The water 3 flowing in the separation channel 12 in a countercurrent manner with the slurry 2 at least partially removes contaminants from the slurry 2, and the water 3+ now also containing contaminants, or at least increased concentrations of contaminants, leaves through the wash water outlet 18, which is typically arranged at the top of the centrifuge body 10 and is located at the end of the separation channel 12 connected to the fluid. The at least partially purified slurry 2+ leaves the separation channel 24 through a common purified slurry outlet or nozzle 19 connected to the fluid of the separation channel 12. Therefore, the nozzle centrifuge 1 is capable of separating the incoming slurry flow 2 into a light fraction and a heavy fraction, the light fraction containing wash water and the washed portion of contaminants, and the heavy fraction containing starch and the unwashed portion of contaminants. The light fraction leaves the nozzle centrifuge 1 through the wash water outlet 18 (also called the light fraction outlet). The heavy fraction leaves the nozzle centrifuge 1 through the purified slurry outlet or nozzle 19 (also called the heavy fraction outlet).

[0072] refer to Figure 2, schematically showing a process flow scheme according to an embodiment of the present invention. The method comprises a plurality of nozzle centrifuges C provided in series. x The contaminants are washed from the incoming slurry 2 with water 3. In this context, 'x' corresponds to the desired number of centrifuges, where x ranges from, for example, 2 to 20. The preferably diluted slurry 2 is added to the first centrifuge C in the series. 1 and the wash water 3 is added to the last centrifuge C in the series x As disclosed above, each nozzle centrifuge C x The incoming pulp stream 2 is separated into a light fraction 3+, which contains wash water and the washed portion of contaminants, and a heavy fraction 2+, which contains starch and the unwashed portion of contaminants.

[0073] like Figure 2 As shown in the figure, the multiple nozzle centrifuge C i is provided in series, where i = 2 to x. This requires the centrifuges C in the series to be i The heavy fraction outlet 19 is fluidly connected to the next centrifuge C positioned in series. i+1 The slurry inlet 14. For example, the first centrifuge C in the series 1 The heavy fraction outlet 19 is fluidly connected to the centrifuge C positioned next in the series. 2 The slurry inlet 14. In this way, the slurry leaving the previous centrifuge C i The heavy fraction 2+ can be centrifuged in the next centrifuge C i+1 Further purification in multiple centrifuges C i It is further arranged so that the centrifuges C in series i+1 The light fraction outlet 18 is fluidly connected to the centrifuge C located in series. i+1 Previous centrifuge C i The wash water inlet and nozzle 17.

[0074] In the embodiment shown, except for the last nozzle centrifuge C x At least one centrifuge C other than i The washing water comes from the subsequent nozzle centrifuge C i+1 The light fraction 2+, preferably originating only from the subsequent nozzle centrifuge C i+1 The light fraction is 2+. Figure 2 As shown in the centrifuge C 1 The washing water comes from the subsequent nozzle centrifuge C 2 The light grade is 3+.

[0075] However, if Figure 1 As shown in the figure, each nozzle centrifuge C iAn additional water inlet 20 may also be provided to introduce additional water 21 into the nozzle centrifuge C. i middle.

[0076] Enter the last nozzle centrifuge C x The wash water in the industrial environment may originate from a number of sources, such as a water grid, one or more containers (eg containers holding process water) or a pipe system connected to other parts of the industrial environment.

[0077] In order to further increase the C of each nozzle centrifuge i The separation efficiency in the first centrifuge C 1 The slurry 2 enters the subsequent nozzle centrifuge C i+1 From nozzle centrifuge C i The heavy fraction 2+ can enter the subsequent nozzle centrifuge C i+1 This water can be introduced, for example, via inlet 20 (water flow 21) or via inlet and nozzle 17, the flow rate of which is regulated by valve 22. In the latter option, the nozzle centrifuge C i The previous dilution water comes from the subsequent nozzle centrifuge C i+1 The light fraction 3+, preferably only originates from the subsequent nozzle centrifuge C i+1 The dilution can be adjusted and is preferably diluted to a dry matter percentage between 5%-30%, more preferably between 8%-20% and most preferably between 10%-15%.

[0078] Examples

[0079] Several starch slurries were prepared. In addition, rice starch that was found to have undesirably high levels of certain contaminants was used to form the slurry using industrial process water circulating in a starch modification facility as the aqueous phase. The process water had a pH of 7.5-8.0. The weight ratio between the aqueous phase and the rice starch was adjusted to different values. The pH of the slurry was also adjusted to different values. The slurry was washed in multiple centrifuges.

[0080] To obtain starch properties, the purified slurry after washing was then dewatered by means of vacuum filtration.The filter cake obtained was further dried to an average moisture content of 12 wt.% by means of drying using a fluidized bed dryer at a maximum air temperature of 50°C to form slurry dried starch.

[0081] Certain properties of the slurried dried starch were determined by preparing gels with the slurried dried starch. The gels were prepared at 94°C and 300 rpm using 135 g (dry matter) of starch, acidified and buffered to pH 3.6 using citric acid and trisodium citrate, and using sufficient water to obtain a total weight of 2,500 g, wherein the citric acid and trisodium citrate were combined with the water before the starch was added. After cooling to 25°C, the gels were subjected to intense shearing action at 5,000 rpm for 1 minute using a Silverson L4RT mixer using a square hole (2.4 mm) high shear mesh mixing head.

[0082] The tan δ of a gel prepared from the starch in question and first subjected to strong shearing is determined at a temperature of 20° C. with the aid of an Anton Paar rheometer (parallel plate-plate configuration; plate diameter 40 mm). As described herein, the term tan δ is used in its usual meaning as loss tangent in the linear viscoelastic region. It gives the ratio between the viscous and elastic properties of a system, showing which one is dominant. At a tan δ value of 1, the elastic and viscous properties of the material are equal. The smaller the loss tangent, the greater the elasticity of the material. tan δ is determined from the results of an amplitude sweep measurement with the following characteristics: deformation 0.01 to 1000%, frequency 1 Hz.

[0083] Other properties, such as Brabender viscosity during temperature sweeps, were obtained on the same slurry-dried starch according to the following method: The Brabender curve was determined at 6 wt.% dry matter in deionized water brought to pH 6.0-6.5 with sulfuric acid; the total weight was 500 g and the measuring speed was 75 rpm. The applied temperature profile started at 50°C, increased at 3°C / min to about 95°C, held at about 95°C for 15 minutes, and then cooled to 20°C at 3°C / min. From the viscosity curve obtained, the Δ95 value was calculated by subtracting the viscosity at the beginning of the 95°C interval from the viscosity at the end of the 95°C interval.

[0084] The prepared slurry was subjected to washing in multiple nozzle centrifuges and the amount of contaminants was determined after each nozzle centrifugation stage (denoted as HP1, HP2, HP3, HP4, etc.). The acronym HP stands for 'Heavy Phase', which is also denoted as Heavy Fraction 2+ in the figure. The contaminant concentration is measured in this heavy phase.

[0085] The pH, Baumé and dry matter content (DM) of the incoming slurry (before dilution) entering the first centrifuge were measured according to the following methods:

[0086] • The pH of the slurry was measured using a WTW 3210 pH meter with a combined electrode WTW SenTix 81 under gentle stirring.

[0087] • Determine the Baume degree of the starch slurry by inserting a Baume meter (measuring range 10-20 Baume degrees) into a 500 mL cylinder filled to the top with the slurry. After the Baume meter is stable, read the value according to the scale on the Baume meter.

[0088] • Dry matter content (DM) was analyzed at 130°C with the aid of infrared moisture balance.

[0089] By obtaining the HP of the sample after each centrifugation stage i To measure the concentration of three pollutants (i.e. chlorate, chloride and sulfate) in the slurry flow. After formic acid methanol extraction according to EURL-SRM method QuPPe-PO, the chlorate concentration is measured by means of LC-MS / MS. Chloride and sulfate concentrations are measured according to DIN EN ISO 10304-1:2009-07 (a test method for measuring inorganic anions (chloride, nitrite, nitrate, phosphate, sulfate and oxalate) using ion chromatography (IC). The content of inorganic anions is given in mg / kg or mg / L, and the percentage reduction in % is calculated after washing. According to the principle of the method, inorganic anions are separated by elution on a latex anion exchange column and detected by conductivity determination after suppression. The concentration gradient required for the separation component is automatically generated by the eluent generator integrated in the IC system.

[0090] For sample preparation, prepare solutions by weighing samples or by dilution. The dry matter content of the solutions should not be higher than 10 g / 100 g. The sample solutions are then diluted as required. Further dilution steps are then carried out from these sample solutions as required to enable measurements within the calibration range of the components.

[0091] For the thick juice obtained after washing as claimed, samples were prepared by weighing 10 g of sample into a 100 mL volumetric flask, mixing with ultrapure water and filling to the mark at 20° C. Further dilutions were then prepared. (1:10 and 1:20 dilutions).

[0092] The following chromatographic conditions were used:

[0093] -Eluent: Potassium hydroxide gradient:

[0094] 0.0-2.0min: 1.0mM KOH

[0095] 2.0-16.0 min: 1.0 mM to 40.0 mM KOH

[0096] 16.0-16.1min: 40.0mM to 50.0mM KOH

[0097] 16.1-17.0min: 50.0mM KOH

[0098] 17.0-17.1min: 50.0mM to 1.0mM KOH

[0099] 17.1-25.0min: 1.0mM KOH

[0100] -Flow rate: 0.25mL / min

[0101] -Injection volume: 5μL

[0102] - Column oven temperature: 30°C

[0103] -ADRS suppressor current:

[0104] 0.0min-10.0min: 8mA

[0105] 10.0min-25.0min: 22mA

[0106] -Conductivity measurement cell temperature: 30°C

[0107] Anion concentrations were then calculated via appropriate software (Chromeleon) by comparing the peak areas of the standard and sample solutions using component-specific calibration functions.

[0108] The process conditions applied to each example are summarized in Table 1 below. The term '#c' refers to the number of centrifuges used. For ease of comparison, Example 4C was replicated as Example 7A.

[0109]

[0110]

[0111] Table 1: Process conditions for Examples 1 to 8

[0112] The results obtained are shown in the following table.

[0113]

[0114] Table 2: Results of Examples 1A and 1B

[0115] From Examples 1A and 1B, it can be inferred that for a fixed normalized ratio of wash water to DM starch, there is a more efficient contaminant removal at higher pH values ​​for all contaminants (chlorate, chloride, and sulfate), but there is also a certain degree of performance loss at the higher pH value of pH = 9.6, but it is still acceptable. For chlorate, this inference is confirmed in Examples 2A and 2B, as shown in Table 3.

[0116]

[0117] Table 3: Results of Examples 2A and 2B

[0118] It can be inferred from Examples 3A and 3B that for a fixed normalized ratio of wash water to DM starch, the contaminant removal efficiency in terms of chlorate and chloride increases at higher pH values, as shown in Table 4.

[0119]

[0120]

[0121] Table 4: Results of Examples 3A and 3B

[0122] For chlorate, this inference is confirmed in Examples 4A, 4B, and 4C, as shown in Table 5 below.

[0123]

[0124]

[0125] Table 5: Results of Examples 4A, 4B and 4C

[0126]

[0127] Table 6: Results of Examples 5A and 5B

[0128]

[0129] Table 7: Results of Examples 6A and 6B

[0130] This finding was also confirmed in Examples 7A and 7B for two different nozzle diameters of the nozzle centrifuges used at the same pH, wash water flow rate, and number of centrifuges. The nozzles of all centrifuges in Example 7A were identical in diameter. The nozzles of all centrifuges in Example 7B were also identical in diameter, and their diameters were 6% larger than the diameters of the nozzles in Example 7A. For ease of comparison, Example 4C was replicated as Example 7A.

[0131]

[0132]

[0133] Table 8: Results of Examples 7A and 7B

[0134] Examples 8A and 8B finally demonstrate again that for comparable normalized ratios of wash water to DM starch, there is more efficient contaminant removal for chloride ions at higher pH values. However, at higher pH, there is also an increased loss of properties or functionality, as indicated by the included Brabender Δ95 data. In addition, Examples 8A and 8C demonstrate that reducing the number of centrifuges (which is reflected in higher normalized wash water / DM starch ratios) may adversely affect contaminant removal.

[0135]

[0136]

[0137] Table 9: Results of Examples 8A, 8B and 8C. Note: The Δ95 viscosity increase as measured on the material used to prepare the feed slurry is considered to be 100%. If after washing the starch has a smaller Δ95 viscosity increase, it is recalculated as a percentage reduction compared to the Δ95 of the feed slurry starch. If there is even a decrease in viscosity, this translates into a Δ95 loss higher than 100%.

Claims

1. A method for preparing starch, comprising the following steps: a) providing a slurry containing granular starch and contaminants and having a pH of 5.0-11.0; b) washing said contaminants from said slurry with water in a plurality of nozzle centrifuges provided in series, wherein said slurry is added to the first centrifuge in said series and wash water is added to the last centrifuge in said series; and wherein each nozzle centrifuge separates an incoming slurry stream into a light fraction comprising wash water and a washed portion of said contaminants and a heavy fraction comprising starch and an unwashed portion of said contaminants.

2. The method according to claim 1, in, The slurry has a pH of 6.5-10.5, more preferably 7.5-10.0, even more preferably 8.5-9.5 before entering the first nozzle centrifuge in the series.

3. The method according to claim 1 or 2, in, Added to at least one of the centrifuges, preferably the last centrifuge, is m 3 The ratio of the washing water flow in T / h to the dry matter (DM) starch flow in T / h added to the first centrifuge is at least 0.1 m / h. 3 / T and up to 5m 3 / T.

4. A method as claimed in any one of the preceding claims, in, is defined as the amount of m added to at least one of the centrifuges, preferably the last centrifuge 3 The normalized water ratio of the wash water flow in T / h divided by the dry matter starch flow in T / h added to the first centrifuge and the number of centrifuges used is between 0.2-2.0, more preferably between 0.25-1.

75.

5. A method as claimed in any one of the preceding claims, in, The pH of the slurry is adjusted prior to entering a nozzle centrifuge in the series other than the first nozzle centrifuge.

6. A method as claimed in any one of the preceding claims, in, The number of nozzle centrifuges in the series is 2-8, more preferably 3-7.

7. A method as claimed in any one of the preceding claims, in, The wash water of at least one nozzle centrifuge other than the last nozzle centrifuge originates from the light fraction, preferably exclusively from the light fraction, of the subsequent nozzle centrifuges.

8. The method according to claim 7, in, The wash water of all nozzle centrifuges except the last nozzle centrifuge originates from the light fraction of the subsequent nozzle centrifuges, preferably only from the light fraction of the subsequent nozzle centrifuges.

9. A method as claimed in any one of the preceding claims, in, Wash water is added to each nozzle centrifuge countercurrently to the flow of stabilized starch slurry entering the nozzle centrifuge.

10. The method according to any one of the preceding claims, in, Fresh wash water not originating from one of the centrifuges is added to at least one nozzle centrifuge other than the last nozzle centrifuge.

11. A method as claimed in any one of the preceding claims, in, The slurry added to the first centrifuge and the heavy fraction from the nozzle centrifuge entering the subsequent nozzle centrifuge are diluted with dilution water before entering the subsequent nozzle centrifuge.

12. The method according to claim 11, in, The dilution water before entering at least one nozzle centrifuge originates from the light fraction of a subsequent nozzle centrifuge, preferably originates only from the light fraction of a subsequent nozzle centrifuge.

13. The method according to claim 12, in, The dilution water before entering all the nozzle centrifuges originates from the light fraction of subsequent nozzle centrifuges, preferably only from the light fraction of subsequent nozzle centrifuges.

14. The method according to any one of claims 11 to 13, in, The slurry added to the first centrifuge and the heavy fraction from the nozzle centrifuge entering the subsequent nozzle centrifuge are diluted to a dry matter percentage between 5%-30%, more preferably between 8%-20% and most preferably between 10%-15%.

15. A method as claimed in any one of the preceding claims, in, The contaminants include organic acids, bisulfites or hydrogen peroxide.

16. A method as claimed in any one of the preceding claims, in, The nozzle diameter of at least one of the nozzle centrifuges is in the range of 1.0 to 2.6 mm, more preferably 1.4 to 2.2 mm, most preferably 1.6 to 2.0 mm.

17. A method as claimed in any one of the preceding claims, in, The washing is carried out at a temperature between 5°C and 40°C.

18. A method as claimed in any one of the preceding claims, in, The slurry after washing is dried and optionally ground to obtain the starch.

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