A method for preparing colorless carbohydrates or colorless carbohydrate crystals.

Abstract

A process involving, or consisting of, the following steps is proposed for the production of colorless carbohydrates or colorless carbohydrate crystals: (a) ensuring an aqueous carbohydrate solution with a purity of >90% based on the total dry matter content of the solution; (b) Concentration of the aqueous solution from step (a) by a thermal evaporation step to obtain an aqueous concentrate; (c) The aqueous concentrate from step (b) is brought into contact with at least one adsorbent to obtain a decolorized concentrate, where the adsorbent is selected from the following: (i) activated carbon granules and (ii) organic synthetic resins or other materials. ion exchangers; (d) Optional concentration of the decolorized concentrate from step (c); (e) Crystallization of the concentrate obtained from step (d) and subsequent drying of the crystals as desired.

Description

AREA OF INVENTION

[0001] The invention is in the field of food technology and relates to a process for decolorizing aqueous carbohydrate solutions, namely aqueous allulose preparations. TECHNOLOGICAL BACKGROUND

[0002] Sugar substitutes include sweeteners and sugar alcohols. Sweeteners can be produced naturally or synthetically. They are characterized by having no or negligible nutritional value, which makes them particularly attractive to people on diets.

[0003] Sweeteners are excreted by the body either completely or almost entirely unchanged. They are found in many light and diet products. Sugar substitutes are carbohydrates that cause only a slight increase in blood sugar and insulin levels. Their sweetness is 40 to 70 percent that of regular table sugar. The proportion of sugar substitutes in foods and beverages has increased steadily in recent years. Within the scope of the present invention, the term "low calorie" A calorific value of no more than 10, preferably no more than 5 and in particular of 1 to 2 kcal is understood to be.

[0004] The most industrially important sugar substitutes are acesulfame K and aspartame. These are synthetic substances that some studies have identified as potentially carcinogenic. However, these findings, which have not yet been confirmed, reinforce the general trend towards… "natural" Sugar substitutes.

[0005] In recent years, steviosides have gained widespread attention because their constituent compounds, such as rebaudioside A, are up to 1000 times sweeter than table sugar and are calorie-free. However, a disadvantage is that steviosides generally have a harsh, metallic aftertaste and have therefore not yet been able to establish themselves as sugar substitutes.

[0006] This gap could be closed by the so-called "rare sugars" such as tagatose, cellobiose or allulose (which is also synonymously referred to as psicose).

[0007] Allulose (psicose) is a low-calorie sugar with a similar sweet taste to regular sugar. Allulose is one of many different sugars that occur naturally in very small amounts. Originally identified in wheat, allulose has since been found in certain fruits such as jackfruit, figs, and raisins. It is naturally present in small amounts in a variety of sweet foods, including caramel sauce, maple syrup, and brown sugar. Allulose is absorbed by the body but not metabolized, making it virtually calorie-free.

[0008] Due to the growing interest of a large part of the population in "healthy diet" and "healthy lifestyle" In general, allulose, as a calorie-free sugar, has attracted great interest in the food industry and the scientific community.

[0009] Allulose is often commercialized in the form of crystals. RELEVANT STATE OF THE TECHNOLOGY

[0010] H. Itoh et al, Journal of Fermentation Bioengineering, 80(1), 1995, pp. 101-103, published the production of D-psicose from D-fructose by immobilized D-tagatose 3-epimerase.

[0011] N. Wagner et al. in Organic Process Research Development 2012, 16, pp. 323-330, discusses practical aspects of the integrated operation of biotransformation and simulated moving bed separation (SMB) for fine chemical synthesis. D-Psicose is produced from D-fructose using D-tagatose epimerase-catalyzed epimerization.

[0012] N. Wagner et al, in Chemical Engineering Science 137 (2015) pp. 423-435 refers to the model-based cost optimization of an integrated process for the enzymatic production of psicose at elevated temperatures.

[0013] Bosshart et al, in Biotechnology Bioengineering 2016, 113(2), p. 349-58 refers to the production of the rare sugars D-psicose and L-tagatose by two artificially produced D-tagatose epimerases.

[0014] N. Wagner, et al., in Journal of Chromatography A 2015, 1398, p. 47-56 discloses a method for the economical production of d-psicose by simulated moving bed chromatography.

[0015] From EP 2552241 B1, a one-stage process for concentrating aqueous allulose solutions is known, in which a supersaturated sugar solution is evaporated into the solution at a temperature of 60 to 70 °C. However, the process requires a high energy input. Furthermore, long residence times in the evaporator are necessary, which, at the temperatures involved, leads to Maillard reactions. The resulting products therefore often exhibit undesirable discoloration, which makes marketing difficult.

[0016] Document EP 2 552 241 B1 discloses a process for producing high-purity D-allolose crystals with a purity of 98% (w / w) or more and a particle size of MA200 or more, comprising: removing impurities from a D-allolose solution to obtain a purified D-allolose solution; concentrating the purified D-allolose solution; cooling the concentrated D-allolose solution to 30°C to 40°C by means of a heat exchanger; seeding the D-allolose solution at 30°C to 40°C, and subsequent crystallization.

[0017] Document US 4,950,332 discloses a method for decolorizing an aqueous sugar solution containing dyes. The method includes the step of contacting an aqueous sugar solution with an effective amount of an adsorbing resin to adsorb dyes from the aqueous sugar solution onto the adsorbing resin.

[0018] EP 3564250 A2 recommends treatment with activated carbon powder for the decolorization of discolorations in allulose solutions.

[0019] The subject of WO 2018 087261 A1 (PFEIFER&LANGEN) is a process for the synthesis of a simple sugar, preferably D-allolose, from a starting material, preferably D-fructose, under heterogeneous or homogeneous catalysis, which includes chemical and / or enzymatic catalysis, wherein the synthesis is carried out in at least two reactors connected in series and the reaction product exiting the first reactor is subjected to chromatographic separation before entering the second reactor. Preferably, the chromatographic separation is integrated into a simulated moving bed.

[0020] The EP 3 006 568 A1 , WO 2018 / 081557 and EP 3 210 478 A1 disclose further compositions which contain carbohydrates. TASK OF INVENTION

[0021] As a result of the temperature stress during the concentration of liquid allulose preparations, which occur as intermediates and are either sold as such ( "Allulose syrup" If the carbohydrates are subjected to oxidation or crystallization, for example through the Maillard reaction, they can become discolored. The end products then have a brownish hue, which makes marketing difficult because consumers interpret this as an indication of inferior quality.

[0022] The object of the present invention was therefore to improve the decolorization processes known from the prior art, so that colorless carbohydrates, in particular allulose, with excellent taste properties can be obtained.

[0023] Another object of the present invention was therefore to provide a method for producing colorless allulose crystals, such that the resulting allulose crystals are free-flowing, readily soluble in water and have an impeccable taste. DESCRIPTION OF THE INVENTION

[0024] The invention is defined by the attached claims.

[0025] The following description is subject to this limitation. All aspects and embodiments not covered by the claims are merely aspects of the present disclosure and not part of the invention.

[0026] The present invention relates to a process for producing colorless allulose or colorless allulose crystals, comprising or consisting of the following steps: (a) Providing an aqueous allulose solution with a purity >90% based on the total dry matter content of the solution, wherein the allulose solution has a fructose content of no more than 10 wt% based on the total dry matter content of the solution; (b) Concentrating the aqueous solution from step (a) by a thermal evaporation step to obtain an aqueous concentrate having a dry matter content of 60 to 85 wt%; (c) Contacting the aqueous concentrate from step (b) with adsorbent to obtain a decolorized concentrate, wherein at least two adsorption columns are connected in series, filled with different adsorbents selected from (i) activated carbon granules and (ii) organic synthetic resins orion exchangers; (d) optional concentration of the decolorized concentrate from step (c); (e) optional crystallization of the concentrate from step (d) and subsequent optional drying of the crystals.

[0027] Surprisingly, it was found that granulated activated carbon and adsorbent resins are not only more suitable means for decolorizing sugar solutions in general and allulose evaporator concentrates in particular in short times with high throughput, but that the resulting decolorized products also have taste advantages and increased storage stability.

[0028] In accordance with the disclosure, the carbohydrates used in step (a) of the process according to the invention are in particular low-calorie mono- and / or disaccharides with preferably 6 to 12 carbon atoms.

[0029] According to the invention, the aqueous solution of step (a) is an aqueous solution of allulose.

[0030] As already mentioned, the aqueous solution of step (a) has a purity >90%, based on the total TS content of the solution.

[0031] The dry matter content (TS content) of the aqueous solution of step (a) is in the range of 8-35%, preferably 9-30%, more preferably 9-28%, more preferably 9-26%, more preferably 9-25%, and particularly preferably in the range of 20-23%.

[0032] In a preferred embodiment, the aqueous solution of step (a) has a purity >91%, preferably >92%, preferably >93%, preferably >94%, preferably >95%, preferably >95%, preferably >96%, preferably >97%, preferably >98% and preferably >99%, based on the total TS content of the solution.

[0033] In a preferred embodiment, the aqueous solution of step (a) has a purity >93%, based on the total solids content of the solution, wherein the TS content of the solution is in the range of 9-30%.

[0034] According to the invention, the aqueous solution of step (a) is an aqueous solution of allulose.

[0035] The production of psicose / allulose by rearrangement of fructose in the presence of an epimerase represents state of the art and dates back to work at Kagawa University in 1994. Ken Izumori discovered that D-tagatose 3-epimerase is able to convert D-fructose into D-psicose. ( Biosci. Biotechnol. Biochem., 1994, 58:12, 2168-2171 ). The present invention also includes racemates, stereoisomers of individual carbohydrates and mixtures of different carbohydrates, without each being specifically mentioned again below.

[0036] Since the aqueous solution from step (a) is an aqueous allulose solution, it is possible that other byproducts, mainly resulting from the enzymatic conversion of fructose to psicose, are also present in the solution. These byproducts are primarily fructose and salts.

[0037] In a preferred embodiment of the process according to the invention, the aqueous solution of step (a) is an allulose solution having a fructose content of at most about 5 wt.%, preferably at most about 4 wt.%, preferably at most about 3 wt.%, preferably at most about 2 wt.%, preferably at most about 1 wt.%, preferably at most about 0.5 wt.%, and particularly preferably at most 0.1 wt.%, based on the total TS content of the solution.

[0038] In a further preferred embodiment of the process according to the invention, the aqueous solution of step (a) is an allulose solution having a salt content of at most about 2 wt.%, preferably at most about 1 wt.%, preferably at most about 0.9 wt.%, preferably at most about 0.8 wt.%, preferably at most about 0.7 wt.%, preferably at most about 0.6 wt.%, preferably at most about 0.5 wt.%, and particularly preferably at most 0.1 wt.%, based on the total TS content of the solution.

[0039] In a further preferred embodiment of the process according to the invention, the aqueous solution of step (a) is an allulose solution having a purity >95% and a fructose content of at most 5 wt.% and a salt content of at most 0.1 wt.%, each based on the total TS content of the solution.

[0040] In step (b) of the process according to the invention, the aqueous solution of step (a) is concentrated by a thermal evaporation step.

[0041] According to the present invention, various evaporators are suitable for carrying out the concentration step (b), for example steam boilers, thin-film evaporators, falling-film evaporators, boiler evaporators, coaxial evaporators, natural circulation evaporators, plate evaporators, or forced circulation evaporators. These devices are well known to those skilled in the art and therefore do not require further explanation.

[0042] The evaporation process typically takes place either in one or in two to three evaporators connected in series; preferably falling film evaporators or plate evaporators are used.

[0043] By step (b) of the process according to the invention, an aqueous concentrate is obtained which has a dry matter content of 60 to 85 wt.%, preferably of about 65 to about 80 wt.%, more preferably of about 70 to about 80 wt.%, and particularly preferably of about 70 to about 78 wt.%.

[0044] Evaporation is generally carried out at a temperature of approximately 50 to 75 °C. If the process step is not carried out in a single stage, but in two or three stages, it has proven advantageous for energy reasons to omit the temperature range between 59 and 71 °C, i.e., to operate the evaporators in temperature ranges above and below this range.

[0045] In step (c) of the process according to the invention, the aqueous concentrate of step (b) is decolorized.

[0046] For decolorization, the aqueous concentrates are brought into contact with the decolorizing agents, i.e., either the activated carbon granules or the organic synthetic resins and ion exchangers, for a sufficient period of time.

[0047] The activated carbon granules preferably have a particle size distribution in which 90% of the particles have a diameter of approximately 0.5 to approximately 1 mm. Particularly preferred is a granulate from Cabot with an average particle diameter of approximately 0.65 mm, available under the name Norit GAC 1240.

[0048] Die bevorzugten Adsorptionsmittel stellen makroporöse Harze dar, wie sie im Folgenden exemplarisch aufgeführt sind: Lewatit A 365, Lewatit A 8071, Lewatit A 8072, Lewatit A 8072 PLUS, Lewatit A 8073, Lewatit AF 5, Lewatit S 1567, Lewatit S 1568, Lewatit S 1668, Lewatit S 2328, Lewatit S 2568, Lewatit S 2568 H, Lewatit S 4228, Lewatit S 4268, Lewatit S 4328, Lewatit S 4468, Lewatit S 4528, Lewatit S 5128, Lewatit S 5221, Lewatit S 5228, Lewatit S 5328, Lewatit S 5528, Lewatit S 6268, Lewatit S 6368, Lewatit S 6368 A, Lewatit S 6368 A OH, Lewatit S 6368 A SO4, Lewatit S 6368 Sulfate, Lewatit S 7468, Lewatit S 7968, Lewatit S 8107, Lewatit S 8223, Lewatit S 8227, Lewatit S 8227 Ca, Lewatit S 8227 Mg, Lewatit S 8229, Lewatit S 8229 Plus / Ag, Lewatit S 8229 PLUS X, Lewatit S 8528, Lewatit S 9167, Dowex HCR-S / S, Dowex HCR-S / S FF, Dowex HCR-W2, Dowex-HGR-NG, Dowex Marathon C 10, Dowex Monosphere C 350, Dowex Monosphere C 400, Dowex Marathon C , Dowex Marathon MSC, Dowex Marathon 1200,Dowex Marathon 1300 H, Dowex 88, Dowex 88 MB, Dowex Monosphere 88 MB, Dowex Monosphere C 600 B, Dowex 66, Dowex Monosphere 66, Dowex 22, Dowex Optipore SD 2, Dowex Optipore L493, Dowex Optipore V493, Dowex Optipore V502, XUS 43565.01, Dowex Optipore V323, Dowex N 406, Dowex Marathon A, Dowex Marathon A LB, Dowex Marathon A2, Dowex Marathon MSA, Dowex Marathon 11, Dowex Marathon MSA - , Dowex NSR-1, Dowex-PSR-2, Dowex Marathon 4200 CI, Treverlite IXC100, Treverlite IXC110, Treverlite IXC200, Treverlite IXC201, Treverlite IXC210, Treverlite IXC230, Treverlite IXC330, Treverlite IXA300, Treverlite IXA310, Treverlite IXA510, Treverlite IXA600, Treverlite IXA610, Treverlite IXA620, Treverlite IXA710, Treverlite CHE710, Treverlite CHE720, Treverlite CHE730, Treverlite XS100200, Treverlite XS103500, Treverlite XS106500, Treverlite XS122400. The corresponding decolorizing resins are commercial products manufactured by Lanxess,These materials can be obtained from Dow and Chemra. Particularly good results were achieved with ion exchangers whose matrix consists of styrene-divinylbenzene copolymers, cross-linked polystyrenes, cross-linked phenol-formaldehyde condensate, or mixtures thereof. Suitable cationic groups include primarily tertiary and quaternary amines, while sulfonic acids and sulfonates are the most appropriate anionic groups.

[0049] According to the invention, the decolorization takes place in adsorption columns.

[0050] It has proven advantageous to carry out the decolorization continuously in two adsorption columns, which are operated alternately.

[0051] Accordingly, in a further preferred embodiment, the decolorization is carried out continuously in two adsorption columns, which are operated alternately.

[0052] The decolorizing resins or activated carbon granules can be stirred into the aqueous concentrate from step (b) and filtered off after a residence time of a few minutes to one hour. However, it has proven advantageous to carry out the decolorization continuously using adsorption columns filled with the granules or synthetic resins. The residence time can be controlled by adjusting the flow rate and column length so that a solution with the desired color reduction emerges at the end of the column(s). It is recommended to operate two rows of columns in parallel so that one can be purified alternately.

[0053] According to the invention, two or more columns are connected in series and filled with different adsorbents, in particular an adsorbent resin in the first column and activated carbon granules in the second column.

[0054] While the granules have the disadvantage of a smaller specific surface area compared to activated carbon powder, this is more than compensated for by the fact that the granules can be arranged in columns through which the aqueous concentrate from step (b) can flow. The granulation of the activated carbon, as well as the shape of the resin particles, results in a lower pressure drop when flowing through a packed column compared to the use of powdered agents, and therefore lower energy consumption. Furthermore, the use of packed columns has proven advantageous because the resin material or activated carbon granules are retained by the columns and do not need to be separated from the solution to be decolorized in an additional step. If resins are used, this also has the advantage that they can be easily chemically regenerated.In contrast, activated carbon requires a complex burn-off process once it has reached its decolorizing capacity. Furthermore, neither activated carbon granules nor synthetic resins produce fine dust.

[0055] The decolorized concentrate obtained in step (c) can be commercialized as such (“syrup”). Typically, the decolorized concentrate from step (c) (“syrup”) has a solids content of 55 to 90 wt.% (in the case of allulose concentrates according to the invention, of about 65 to about 85 wt.%).

[0056] In a preferred embodiment, the concentrate (allolose concentrate) of step (c) (“syrup”) has a TS content ≥70%, a purity based on the TS content ≥70%, a fructose content ≤10% based on the TS content, and a salt content of ≤0.04% based on the TS content, as well as an ICUMSA colour value ≤35 ([IE420] determined according to GS 9(1 / 2 / 3-8 (2011)).

[0057] The decolorized concentrate from step (c) can optionally also be used for crystallization.

[0058] If crystallization is desired, the concentrate from step (c) is optionally concentrated in an evaporator to a total solids (TS) content of at least 60 wt% and then seeded with crystals in the supersaturated region, near the saturation point. The supersaturation is then maintained by evaporation or slow cooling (0.1–1 K / h) until a crystal content of approximately 30 to approximately 50 wt% is reached.

[0059] According to the present invention, various evaporators are suitable for carrying out the optional concentration step, for example steam boilers, thin-film evaporators, falling-film evaporators, boiler evaporators, coaxial evaporators, natural circulation evaporators, plate evaporators, or forced circulation evaporators. These devices are well known to those skilled in the art and therefore do not require further explanation.

[0060] If crystallization occurs, the resulting colorless crystals are subjected to drying.

[0061] According to the present invention, various drying systems are suitable for carrying out the drying process according to step (e), for example, drum dryers, belt dryers, shaft dryers, cone dryers, convection dryers, vibrating fluidized bed dryers, fluidized bed dryers, tube bundle dryers, thin-film dryers, disk dryers, vacuum dryers, contact dryers, and microwave dryers. These drying systems are well known to those skilled in the art and therefore do not require further explanation.

[0062] However, carrying out the drying according to step (e) in a drying plant selected from the group consisting of fluidized bed dryers (continuous), vacuum dryers, belt dryers and thin-film dryers, in particular fluidized bed dryers and vacuum dryers, has proven to be particularly advantageous.

[0063] The water content of the crystals obtained is in the range of about 0.1 to about 0.5 wt.%, preferably from about 0.1 to about 0.3 wt.%, preferably from about 0.15 to 0.25 wt.%.

[0064] Another object of the present invention is the use of the colorless concentrates or crystals obtained by means of the process according to the invention, namely colorless allulose concentrates or colorless allulose crystals, for the production of foodstuffs. EXAMPLES

[0065] The present invention will be easier to understand with reference to the following examples. Examples not covered by the scope of the claims are given for reference purposes.

[0066] However, these examples serve only to illustrate the invention and cannot be interpreted as limiting with regard to the scope of protection of the invention. EXAMPLE 1 (ACCORDING TO THE INVENTION)

[0067] An aqueous allulose solution with a total solids content (TS) of 23 wt% and a purity of 98%, a fructose content of 1 wt%, and a salt content of 0.5 wt%, all based on the total TS content of the solution, was prepared and concentrated using a plate evaporator. This resulted in an aqueous allulose solution with a TS content of 71 wt%. The stock solution had an ICUMSA color value (determined according to GS 9(1 / 2 / 3-8 (2011)) of approximately 9,000 IU) and was subsequently adjusted to a color value of 500 and 1,370 IU by adding water.

[0068] Two heated glass columns, each 100 cm long and 5 cm in diameter, were packed with different adsorbents, connected in series, and fed with a feed at a rate of 25 L / h. The color value was determined photometrically after each column exit. The change in color values ​​over the adsorbent's residence time is shown in Table 1 reproduced: Table 1A Decolorization in the Lewatit S 5221 / Norit GAC 1240 system Column I: Adsorber resin Column Column II: Activated carbon granules Stand time [h] 2 4 6 8 2 4 6 8 Color Count Feed [IE] 500 500 500 500 50 110 150 175 Color number product [IE] 50 110 150 175 25 (P1) 65 90 95 Table 1B Decolorization in the Lewatit S 5221 / Norit GAC 1240 system Column I: Adsorber har Column II: Activated carbon granules Stand time [h] 2 4 6 8 2 4 6 8 Color Count Feed [IE] 1.370 1.370 1.370 1.370 200 240 290 380 Color number product [IE] 200 240 290 380 100 110 140 170

[0069] After exiting the first column, the product obtained in both cases had a color value reduced to 10% of the initial value. Over a standing time of 8 hours, the value increased to approximately 20% of the initial color value. Using the second column ("polisher"), the color value could be reduced by a further 50% in each case. EXAMPLE 2 (Reference example)

[0070] An aqueous fructose solution (20 wt%) was prepared. The solution had a purity of 98% and a salt content of 0.5 wt%, both based on the total dry matter content of the solution. The solution was concentrated using a plate evaporator. This resulted in an aqueous fructose solution with a dry matter content of 60 wt%. The stock solution had an ICUMSA color value (determined according to GS 9(1 / 2 / 3-8 (2011)) of approximately 8,600 IU and was subsequently adjusted to a color value of 500 and 1,370 IU by adding water.

[0071] Two heated glass columns, each 100 cm long and 5 cm in diameter, were packed with different adsorbents, connected in series, and fed with a feed at a rate of 25 L / h. The color value was determined photometrically after each column exit. The change in color values ​​over the adsorbent's residence time is shown in Table 2 reproduced: Table 2A Decolorization in the Dowex Monosphere 88 MB / Norit GAC 1240 system Column I: Adsorber resin Column II: Activated carbon granules Stand time [h] 2 4 6 8 2 4 6 8 Color Count Feed [IE] 500 500 500 500 60 120 140 180 Color number product [IE] 60 120 140 180 30 70 85 90 Table 2B Decolorization in the Dowex Monosphere 88 MB / Norit GAC 1240 system Column I: Adsorber resin Column II: Activated carbon granules Stand time [h] 2 4 6 8 2 4 6 8 Color Count Feed [IE] 1.370 1.370 1.370 1.370 220 250 300 400 Color number product [IE] 220 250 300 400 110 120 150 160

[0072] After exiting the first column, the product obtained in both cases had a color value reduced to 10% of the initial value. Over a standing time of 8 hours, the value increased to approximately 20% of the initial color value. Using the second column ("polisher"), the color value could be reduced by a further 50% in each case. EVALUATION OF THE CONCENTRATES ("SIRUPS")

[0073] Syrup V1 was prepared by concentrating the aqueous allulose solution (60 wt%) from Example 1 to a total solids (TS) content of 75%. Syrup 1 was also prepared by concentrating the intermediate P1 from Table 1 to a total solids (TS) content of 75%.

[0074] V1 and Syrup 1 were stored at room temperature for 7 months (protected from light and heat). After storage, V1 and Syrup 1 were evaluated by a panel of five experienced and trained testers with regard to their visual and gustatory properties (3 = pronounced, 2 = present, 1 = not detectable). The results are summarized in Table 3. Table 1 Examples blackout Metallic taste Syrup 1 x 1 Syrup V1 √ 3 x = not determinable; √ = present

[0075] The experimental data show that the syrups produced using the inventive method show improved results in terms of appearance and taste.

Claims

1. Method for producing colorless allulose or colorless allulose crystals, comprising or consisting of the following steps: (a) providing an aqueous allulose solution with a purity >90%, based on the total dry matter content of the solution, wherein the allulose solution has a fructose content of at most 10% by weight, based on the total dry matter content of the solution; (b) concentrating the aqueous solution from step (a) by means of a thermal evaporation step to obtain an aqueous concentrate having a dry matter content of 60 to 85% by weight; (c) bringing the aqueous concentrate from step (b) into contact with adsorbents to obtain a decolorized concentrate, wherein at least two adsorption columns are connected in series, which are filled with different adsorbents selected from (i) activated carbon granules and (ii) organic synthetic resins or ion exchangers; (d) optional concentration of the decolorized concentrate from step (c); (e) optional crystallization of the concentrate from step (d) and subsequent optional drying of the crystals.

2. Method according to claim 1, characterized in that the aqueous allulose solution has a salt content of at most 2% by weight based on the total dry matter content of the solution.

3. Method according to one of the preceding claims, characterized in that the aqueous allulose solution has a salt content of at most 1% by weight based on the total dry matter content of the solution.

4. Method according to one of the preceding claims, characterized in that the aqueous allulose solution has a salt content of at most 0.7% by weight based on the total dry matter content of the solution.

5. Method according to one of the preceding claims, characterized in that the aqueous allulose solution has a salt content of at most 0.5% by weight based on the total dry matter content of the solution.

6. Method according to one of the preceding claims, characterized in that the aqueous allulose solution has a salt content of at most 0.1% by weight based on the total dry matter content of the solution.

7. Method according to one of the preceding claims, characterized in that the aqueous allulose solution has a purity >95% and a fructose content of at most 5% by weight and a salt content of at most 0.1% by weight, in each case based on the total dry matter content of the solution.

8. Method according to one of the preceding claims, characterized in that the aqueous concentrate of step (b) has a dry matter content of 65 to 80% by weight.

9. Method according to one of the preceding claims, characterized in that the aqueous concentrate of step (b) has a dry matter content of 70 to 80% by weight.

10. Method according to one of the preceding claims, characterized in that the aqueous concentrate of step (b) has a dry matter content of 70 to 78% by weight.

11. Method according to one of the preceding claims, characterized in that the evaporation in step (b) is carried out at a temperature of 50 to 75 °C.

12. Method according to one of the preceding claims, characterized in that the evaporation is carried out in one or in two to three evaporators connected in series.

13. Method according to one of the preceding claims, characterized in that the evaporation is carried out in two or three stages and the temperature range between 59 and 71 °C is omitted during temperature control.

14. Method according to one of the preceding claims, characterized in that of the two adsorption columns connected in series, the first is filled with an organic synthetic resin and the other with activated carbon granules.

15. Method according to one of the preceding claims, characterized in that organic synthetic resins or ion exchangers are used which contain (i) as a matrix, styrene-divinylbenzene copolymers, cross-linked polystyrenes, cross-linked phenol-formaldehyde condensate or mixtures thereof, and / or (ii) as cationic groups, tertiary amines and / or quaternary amines, and / or (iii) as anionic groups, sulfonic acids and / or sulfonates.