Process for the preparation of D-allulose crystals

Description

Field of invention

[0001] The invention relates to a new process for producing D-allulose crystals which allows continuous operation and high yield. The invention also relates to new D-allulose crystals. Another subject of the invention relates to the use of a nanofiltration unit in a D-allulose crystal production circuit to improve the overall yield of D-allulose crystals.

[0002] The invention is defined by the appended claims. Prior art

[0003] D-allulose (or D-psicose) is a rare sugar with a sweetening power equal to 70% of that of sucrose. Unlike the latter, D-allulose does not cause weight gain because it is not metabolized by humans. It has a very low caloric value (0.2 kcal per gram) and thus prevents fat gain. In addition, studies have shown that D-allulose is non-cariogenic, even anti-cariogenic. These properties have recently generated significant interest from the food and pharmaceutical industries.

[0004] Although it is possible to obtain D-allulose chemically, for example by reacting an aqueous glucose solution in an acidic medium in the presence of an ammonium molybdate catalyst, D-allulose is generally obtained enzymatically, by reacting an aqueous D-fructose solution with a D-psicose epimerase as described, for example, in application WO2015 / 032761 A1 in the name of the Applicant. In both cases, the reaction is not complete. For example, the amount of D-fructose transformed into D-allulose after epimerization is generally less than 30%.

[0005] Thus, at the end of the epimerization reaction, it is necessary to carry out a step of separation of D-allulose, to increase the richness of the resulting D-allulose composition. To carry out this separation, chromatography of the composition resulting from the epimerization reaction is very generally carried out, for example by continuous chromatography of the simulated moving bed type.

[0006] Document JP2001354690 A describes a process for manufacturing a D-allulose syrup starting from a mixture of fructose and D-allulose, said process comprising a separation step consisting of a continuous chromatography step using a particular sequence of samples of the different products of the mixture. A fraction rich in D-allulose (whose D-allulose richness can reach 98%) and a fraction rich in fructose are recovered. The recovery yield in the fraction rich in D-allulose is 96%.

[0007] At the end of the separation steps mentioned above, liquid compositions rich in D-allulose are obtained. This is how these liquid compositions, generally called syrups, are used for the manufacture of food or pharmaceutical products.

[0008] For example, application WO 2015 / 094342 also in the name of the Applicant describes the manufacture of solid food products comprising a D-allulose syrup, comprising from 50 to 98% of D-allulose and a native protein. It is mainly in this form of syrups that various companies have announced the marketing of D-allulose to date.

[0009] D-allulose is also marketed in powder form. However, as explained below, their manufacture can be quite complex.

[0010] It is possible to produce powders using, for example, atomization techniques. However, atomized powders, whose composition depends on the atomized raw material, generally contain large quantities of impurities. Furthermore, these atomized powders are weakly crystalline; they are very hygroscopic and this therefore causes problems with water resistance. This also creates generally more significant caking phenomena.

[0011] Due to these difficulties, the atomization of D-allulose has been little described in the literature. For example, EP1860195 can be cited, which describes the atomization of a mixture comprising D-allulose and D-allose. With regard to the enantiomer of D-allulose, L-allulose, JP 4761424 can be cited, which describes the atomization of a massecuite of L-allulose.

[0012] It is also possible to produce powders using granulation techniques, as described for example in application WO2016 / 012853 in the name of the Applicant.

[0013] Another form of powders concerns crystals obtained by crystallization of a mother solution of D-allulose.

[0014] A method for manufacturing D-allulose crystals has been described in document CN 104447888 A. This document describes more particularly in the examples a method comprising a step of manufacturing a D-allulose solution from glucose using a molybdate catalyst then a step of decolorizing this solution using activated carbon then filtration to remove the activated carbon, a step of deionization by electrodialysis, a step of separation by continuous chromatography to form a D-allulose solution having a purity ranging from 70 to 90%, a step of concentrating said solution to obtain a concentrated D-allulose solution, followed by a step of crystallization in ethanol to obtain a crystalline D-allulose product having a limited purity, at most 99%. No crystallization yield is indicated in this document.

[0015] Another crystallization process has also been described in WO 2011 / 119004 in the name of CJ Cheiljedang in which the crystallization yield is of the order of 50%. This process for manufacturing D-allulose crystals comprises a step of providing a D-allulose solution, a step of purifying this solution, a step of concentrating the D-allulose solution to provide a stock solution and a step of crystallizing this stock solution, in which the crystallization step is carried out while maintaining the stock solution in its metastable zone. The purification step described in this document is a chromatographic separation step, which makes it possible to separate D-allulose from fructose. This document, however, recognizes that the manufacture of powders in the form of crystals is difficult to implement: First of all, this crystallization is difficult to control as indicated in paragraph

[36] , in which it is specified that the crystallization must be carried out carefully, by continuous observation of the crystals, also measuring the concentration of the supernatant, in order to regulate the temperature in the crystallizer. However, this document is silent on the reasons why it is difficult to carry out this crystallization. In addition, the crystals obtained have a size of less than 200 µm (see paragraph

[89] ) and are therefore, due to their small size, difficult to separate from the crystallization mother liquors during centrifugation. The recovered crystals are also difficult to handle during subsequent use.

[0016] WO 2016 / 064087, also in the name of CJ Cheiljedang, also describes in Example 3 a process for producing D-allulose crystals in which a mother solution is introduced into a crystallizer at four separate times. Between each introduction, four heating and cooling cycles are carried out, resulting in a process lasting more than 80 hours. Compared to the process described in WO 2011 / 119004, the crystallization yield is not improved (it is 52.8%). The crystals obtained have a larger average size (mean aperture equal to 374 µm). However, the crystals obtained contain impurities. Furthermore, the crystals marketed by the company CJ Cheiljedang have a needle shape, which leads to a flow that is not entirely satisfactory.

[0017] It appears from the above that many problems still remain in the manufacture of D-allulose crystals.

[0018] First of all, the overall yield of D-allulose crystals is excessively low. By "overall yield of D-allulose crystals" is meant the ratio, expressed in dry mass, of the mass of D-allulose crystals obtained to the mass of D-fructose introduced. This low yield, of the order of 15% compared to D-fructose, is essentially linked to the yields of the epimerization (less than 30%) and crystallization (generally of the order of 50%) stages.

[0019] In order to improve the efficiency of the processes, it is therefore imperative to carry out “recycling steps”. By “recycling step” in a process is meant the reuse in a previous step of the process of a fraction of product obtained during a separation step. By “separation step” in the present Application is meant any step making it possible to separate a composition comprising a product A and a product B into at least a first fraction richer in product A and a second fraction richer in product B. The fraction may be in any form, for example in solid form, in liquid form, or even in the form of a solid suspension in a liquid. A separation step may be of any type, for example a chromatography step, in which the liquid composition is separated into at least two liquid fractions, or a crystallization step where a liquid composition is separated into a solid fraction and a liquid fraction.

[0020] Steps for recycling fructose-rich fractions have already been described with a view to improving the yield of the D-allulose syrup manufacturing process. In particular, the previously mentioned document JP2001354690 A describes the recycling of the fructose-rich fraction obtained during the chromatography step to subject it to the epimerization step. This makes it possible to improve the yield of D-allulose in the form of a liquid composition.

[0021] It was by seeking to apply the teachings of this document in a process for manufacturing D-allulose crystals (such as for example that described in document WO 2011 / 119004) that the Applicant was able to observe that these were not simply transposable.

[0022] In fact, when recycling the fructose-rich fraction (see Figure 1), the Applicant was able to observe that the mother solution obtained becomes increasingly difficult to crystallize. After a certain time, this crystallization even becomes impossible as demonstrated in the Examples section.

[0023] Furthermore, still with the aim of improving the overall yield of D-allulose crystals from the process, the Applicant has also attempted to recycle the crystallization mother liquors (i.e. the D-allulose-rich solution which is obtained after separation of the crystals obtained during the crystallization step) by mixing them with a D-allulose composition to form, after concentration, a new mother solution (see Figure 2 ). She was able to observe (see Examples section) that this recycling of mother liquors caused the same difficulties, and this even more quickly than in the case of recycling the fructose-rich fraction.

[0024] In these two cases described above, stops in the production of D-allulose crystals must therefore be made.

[0025] Furthermore, the Applicant was able to observe that, even without carrying out recycling, by transposing the teachings described above into a continuous industrial process for manufacturing D-allulose crystals, “instabilities” are observed. These instabilities result in crystal massecuites inexplicably exhibiting a variable appearance during the process. This is particularly troublesome because the crystal massecuites can be centrifuged and then non-centrifuged at certain times, and this without any a priori prediction of its behavior being able to be made. There is then a need to remelt the massecuites obtained if it is desired to reuse them in the process and this makes the process impractical and less economical.

[0026] However, in order to accelerate the industrial development of D-allulose, which is currently mainly marketed in the form of syrup, it is imperative on an industrial scale to be able to carry out a continuous and stable process for manufacturing D-allulose crystals, in order to be able to supply them at a competitive price.

[0027] After extensive research, the Applicant has succeeded in obtaining a process for manufacturing D-allulose crystals in which the problems mentioned above can be solved.

[0028] Due to improved process stability, the production of crystals does not require systematic control as for example indicated in WO 2011 / 119004, which makes it possible to carry out a continuous process for the production of D-allulose crystals.

[0029] Furthermore, since the method of the invention also allows for numerous recycling steps, the efficiency of the method can be greatly increased.

[0030] It was by conducting extensive research that the Applicant was able to observe that, in a process for manufacturing D-allulose crystals, specific impurities are formed during the various stages of the process for preparing the mother solution. These impurities have, to the best of the Applicant's knowledge, never been reported in the literature. They were able to be identified by the Applicant using a particular gas chromatography (GC) technique. Without being bound by any theory, the Applicant believes that these impurities are D-allulose dimers which are formed by condensation throughout the process.

[0031] The Applicant was also able to show that these D-allulose dimers, unlike other impurities such as glucose or D-fructose, have a very significant anti-crystallizing effect.

[0032] Surprisingly, the Applicant has succeeded, by carrying out a process for manufacturing D-allulose crystals in which a particular separation step is carried out, in eliminating this problem of difficult crystallization of D-allulose. This separation step consists of a nanofiltration step, which allows the elimination of these anti-crystallizing impurities.

[0033] This new process represents a major step forward for the industrial development of D-allulose crystals, as it allows for an overall yield exceeding 25% compared to the D-fructose introduced, advantageously exceeding 50%, or even exceeding 65%. This makes it possible to envisage the production of D-allulose crystals at a competitive price as well as the commercial development of such crystals on a larger scale.

[0034] Furthermore, the Applicant noted that the presence of these impurities is a factor which influences the shape of the crystals, in particular when seeking to produce large crystals, in particular when their average size exceeds 200 µm.

[0035] During its research, the Applicant also succeeded in manufacturing new D-allulose crystals using a specific crystallization process using, among the manufacturing steps, the nanofiltration step mentioned above. These crystals, which are another aspect of the present invention, have in particular the particularity of comprising a very low mass percentage of D-allulose dimer. The crystals obtained can also have a different shape and improved flow. These shape and flow properties are directly linked to the fact that the dimers are present in the crystals in very small quantities.On the contrary, when it is desired to produce large crystals, the significant presence of D-allulose dimers in the mother solution during crystallization leads to D-allulose crystals comprising significant quantities of these dimers; moreover, the elongation of these crystals to form needles is observed. However, these needle-shaped crystals may exhibit less flow than the crystals of the invention. Summary of the invention

[0036] The invention thus relates to a method for manufacturing D-allulose crystals as defined in claim 1 comprising: a step of providing a composition rich in D-allulose, a step of nanofiltration of said composition rich in D-allulose to provide a retentate and a permeate, the nanofiltration step being carried out with a membrane having a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da; a step of recovering the nanofiltration permeate; a step of concentrating this permeate to provide the mother solution of D-allulose; a step of crystallization of the mother solution to form crystals of D-allulose and mother liquors.

[0037] As mentioned above, the Applicant has been able to observe that, systematically, in a process for manufacturing D-allulose crystals, particular impurities are formed during the process. These have, to the best knowledge of the Applicant, never been reported in the literature. This is explained by the fact that, by the high-performance liquid chromatography (HPLC) technique conventionally used to measure the purity of D-allulose, these impurities are not detected on the chromatograms (see Figures 7 and 8 ). It was by using a gas chromatography technique that the Applicant was able to detect their presence (see Figures 9 and 10 ).

[0038] These impurities were identified by the Applicant as being D-allulose dimers. The Applicant was also able to show that these dimers, unlike other impurities such as glucose or D-fructose, have a very significant anti-crystallizing effect. However, as these D-allulose dimers are formed during the process, their presence can limit the yield of a continuous process for manufacturing D-allulose crystals by purely and simply preventing this crystallization, by forming non-centrifugable massecuites, if the quantities of these dimers are too high. Furthermore, in a continuous industrial process for manufacturing D-allulose crystals where numerous successive steps are carried out, the quantity of these impurities can vary over time. This makes the process unstable over time, the massecuites sometimes being centrifugeable, sometimes not centrifugeable.

[0039] It is to the Applicant's credit that they identified these specific impurities and managed to eliminate them by carrying out a separation step consisting of at least partially separating these D-allulose dimers by nanofiltration.

[0040] Using the method of the invention which makes the crystallization step very stable, it is then possible to carry out the process continuously but also to drastically increase the overall yield of D-allulose crystals. This is made possible by being able to provide a D-allulose stock solution having a very low quantity of D-allulose dimers, thanks to the aforementioned nanofiltration step.

[0041] Another merit of the Applicant is to have succeeded in providing new D-allulose crystals using this mother solution, in a particular crystallization process which also limits the in-situ formation of said dimers. This results in crystals whose mass percentage of D-allulose dimers is lower than those of the prior art. Another subject of the invention thus relates to D-allulose crystals as defined in claim 13 comprising a mass content of D-allulose dimer, determined by gas chromatography (GC), of less than 0.5%, and having a volume average size D4.3 greater than 200 µm, advantageously ranging from 210 to 800 µm, preferably from 220 to 350 µm, and for a given volume particle size D4.3 chosen in the range from 200 to 400 µm, a Feret min / Feret max ratio greater than 0.60, advantageously ranging from 0.62 to 0.90, for example from 0.63 to 0.80.

[0042] With regard to the crystals described in document WO2011119004 A2, as they have a very fine size, they are difficult to separate from the crystallization mother liquors. These mother liquors comprise large quantities of D-allulose dimers and the content of dimers in the crystals recovered after separation is therefore significant, much higher than that of the crystals of the invention. Furthermore, comparative example 3 of the present Application (see examples sections) demonstrates that even by further improving the process described in this document, the Applicant has not succeeded in obtaining the crystals of the invention.

[0043] As for the crystals described in WO 2016 / 064087, they have impurities, which may be D-allulose dimers in quantities greater than the crystals of the invention. Without being bound to any theory, the presence of these dimers can be explained by the fact that the D-allulose solution is kept warm before being introduced into the crystallizer, iefor a period of up to 60 hours. Furthermore, this document is completely silent on how to prepare the mother solution, in particular with regard to the conditions of the concentration step. However, as appears in the remainder of the description, the choice of conditions for the crystallization and concentration steps have a significant impact on the quantity of D-allulose dimers formed. Thus, the choice of these conditions makes it possible to limit the quantities of dimers formed during the process and thus reduce the contents of D-allulose dimers in the D-allulose crystals obtained. As the choice of conditions for the steps of preparation of the mother solution have a major impact on the quantity of D-allulose dimers in it, this document describes neither the mother solution useful for the preparation of the crystals of the invention, nor the crystals themselves.

[0044] Document EP1860195 describes complex tubular-type crystalline compositions of D-allose and D-allulose where D-allulose is in the minority and not D-allulose crystals.

[0045] For the crystalline compositions obtained by crystallization in ethanol described in document CN 104447888 A, this document is silent on many process conditions for manufacturing the crystalline compositions and in particular on the step of concentrating the mother solution. It is therefore impossible to reproduce these tests for manufacturing the crystalline compositions. However, it is useful to note that the crystallization must be specifically done in an organic solvent such as ethanol. However, it is known that crystallization in this type of solvent is used only if necessary. Indeed, water is generally preferred for obvious cost and environmental reasons.A selected organic solvent (ethanol in the case of D-allulose), although more expensive and difficult to reprocess, has the advantage of facilitating crystallization, making possible crystallization that would be impossible in water. This therefore confirms that the D-allulose stock solution includes large quantities of D-allulose dimer-type impurities and this can be explained by the fact that no special precautions for the various steps of preparation of the stock solution seem to have been taken (in particular, no conditions are indicated for the concentration step). Furthermore, in terms of purification, crystallization from ethanol may be less effective in obtaining high-purity crystals of D-allulose than crystallization from water (when this is possible) because these dimers of a chemical nature close to D-allulose are also poorly soluble in ethanol and also precipitate.Finally, other impurities, also numerous, are found in the crystalline compositions as demonstrated by the low purities obtained in this document. Crystalline compositions obtained by crystallization in ethanol are also described in the publication of Takeshita et al. (Mass production of D-psicose from D-fructose by a continuous bioreactor system using immobilized D-tagatose 3-epimerase, Journal of bioscience and bioengineering, Vol.90 No.4, January 2000, pages 453-455). This document focuses on the first step of preparation of D-allulose and not on the manufacture of D-allulose crystals, which are also very little detailed. Since the choice of the conditions of the preparation steps of the stock solution have a major impact on the quantity of D-allulose dimers in it, this document describes neither the stock solution useful for the preparation of the crystals of the invention, nor the crystals themselves.Furthermore, in this document, it is specified that this crystallization is carried out in ethanol to facilitate the solidification of D-allulose, which demonstrates the significant quantity of non-crystallizing impurities and confirms the impossibility of crystallizing the D-allulose mother solution of this document in water. Moreover, the crystallization in question in this document is in reality an uncontrolled “precipitation” by the addition of ethanol, inevitably leading to impure crystalline solid compositions.

[0046] Other crystalline compositions are also mentioned in document CN 103333935 A but without any details of their preparation since no conditions for preparing the mother solution or crystallization (not even solvent) are indicated. Furthermore, this document does not include a preparation test per se. Since the choice of conditions for the preparation steps of the mother solution have a major impact on the quantity of D-allulose dimers in it, this document describes neither the mother solution useful for preparing the crystals of the invention, nor the crystals themselves. Furthermore, the low purities of the crystalline compositions obtained (98%) in this document seem to indicate that the crystalline compositions are very impure.

[0047] Another object of the invention also relates to the use as defined in claim 16 of a nanofiltration unit in a circuit for producing D-allulose crystals to improve the overall yield of D-allulose crystals, the membrane used for nanofiltration having a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da. Brief description of the Figures

[0048] Figure 1 : There Figure 1 schematically represents a D-allulose crystal production circuit in which the D-fructose-rich chromatography raffinate is recycled to be mixed with the fructose at the head of the epimerization reaction. Figure 2 : There Figure 2 schematically represents a circuit for the production of D-allulose crystals in which the crystallization mother liquors are recycled to be mixed with the D-fructose / D-allulose composition resulting from the epimerization reaction. Figure 3 : There Figure 3schematically represents a circuit for producing D-allulose crystals comprising a nanofiltration unit useful in the process of the invention. Figure 4 : There Figure 4 represents an example of an adiabatic vacuum crystallizer-evaporator useful for a variant of the process of the invention. Figure 5 : There Figure 5 represents an example of a vertical crystallizer useful for a variant of the process of the invention. Figure 6 : There Figure 6 represents the permeation curve relative to the nanofiltration stage, i.e. the flow rate as a function of the volume concentration factor. Figure 7 : There Figure 7 represents an HPLC chromatogram of a composition rich in D-allulose taken in the process of the invention (see Figure 3 ), that is, before nanofiltration. Figure 8 : There Figure 8 represents an HPLC chromatogram of a permeate taken in the process of the invention (see Figure 3 ), that is to say after nanofiltration. Figure 9 : There Figure 9 represents a CPG chromatogram, in the characteristic zone of the dimers, of a composition rich in D-allulose taken in the process of the invention (see Figure 3 ), that is, before nanofiltration. Figure 10 : There Figure 10 represents a CPG chromatogram, in the characteristic zone of the dimers, of a permeate taken in the process of the invention (see Figure 3 ), that is to say after nanofiltration. Figure 11 : There Figure 11 represents a snapshot obtained by optical microscopy of comparative D-allulose crystals. Figure 12 : There Figure 12 represents two photographs obtained by optical microscopy of D-allulose crystals according to the invention. Figure 13 : There Figure 13 represents a photograph obtained by optical microscopy of D-allulose crystals manufactured and marketed by the company CJ CheilJedang Food Ingredient. Figure 14 : There Figure 14represents the ratio of Feret min / Feret max diameters as a function of particle size in volume D4.3 for two types of D-allulose crystals. Figure 15 : There Figure 15 represents the Feret min and Feret max diameters of a model particle. Detailed description of the invention

[0049] A process for manufacturing D-allulose crystals typically comprises: a step of concentrating a composition rich in D-allulose to provide the mother solution to be crystallized; a step of crystallizing the mother solution to form D-allulose crystals and mother liquors; a step of separating the mother liquors and the D-allulose crystals.

[0050] The method of the invention has the particularity of comprising a nanofiltration step.

[0051] This nanofiltration step makes it possible to limit the quantity of D-allulose dimers in the stock solution provided in the process of the invention. This nanofiltration step takes place in a step prior to the step of concentrating the composition rich in D-allulose. This step therefore makes it possible to provide a stock solution of D-allulose whose content of D-allulose dimers is lower than that obtained from the same process not using this nanofiltration step.

[0052] In the nanofiltration step, which is essential to the process of the invention, two fractions are formed when a D-allulose composition is subjected to nanofiltration: a permeate, which is depleted in D-allulose dimers; as well as a retentate, which is enriched in D-allulose dimers.

[0053] In the Figure 3which represents a crystal production circuit useful in the process of the invention, Stream 6 represents the permeate and Stream 12 represents the retentate. For illustrative but not limiting reasons, the Streams indicated in the remainder of the description refer to the flows of the production circuit of this Figure 3 .

[0054] Nanofiltration permeate is an intermediate enabling the production of this mother solution.

[0055] The terms "depleted in D-allulose dimers" and "enriched in D-allulose dimers" are obviously relative to the content of D-allulose oligomers in the composition to be nanofiltered. By "D-allulose dimer" is meant a compound comprising a D-allulose condensed with at least one second identical or different monosaccharide. These dimers are for example dimers of the D-allulose-D-allulose type.

[0056] These dimers could be detected by GC and could not be detected during HPLC analysis, as demonstrated in the examples section. It follows that the mass quantities of the different constituents, expressed as dry mass, are systematically determined in the present application by GC. To determine the quantities of each of the species in the composition, the sample generally undergoes a treatment step in order to transform the different species present into trimethylsilylated methoxime derivatives. The mass quantities of each of the species are expressed in the present Application, unless otherwise stated, relative to the total dry mass.

[0057] The amounts of glucose, fructose and allulose can be determined in a gas chromatograph equipped with an injector heated to 300°C, a flame ionization detector (FID) heated to 300°C and equipped with a 40 meter DB1 capillary column, having an internal diameter of 0.18 mm and a film thickness of 0.4 µm, the column temperature being programmed as follows: from 200°C up to 260°C at a rate of 3°C / min, then from 260°C up to 300°C at 15°C / min, holding at 300°C for 5 min. The amount of D-allulose dimers is defined as the difference between the total amount of dimers in a sample, as determined by GC, and the amount of any known dimers present, which are glucose-glucose dimers such as maltose and isomaltose. However, the amount of these glucose-glucose dimers is usually very low or nonexistent.For example, in the mother solution useful for the invention, the mass quantity of glucose-glucose dimers is generally less than 0.2%, often less than 0.1%. The same applies to the crystals of the invention.

[0058] The possible amount of glucose-glucose dimers can be determined under the same conditions as those described previously for glucose, fructose and D-allulose: by carrying out a hydrolysis of the glucose-glucose dimers of the sample; by determining the quantity of total glucose in the same chromatograph and under the same conditions, said total glucose comprising the initial so-called free glucose and the glucose resulting from the hydrolysis of the glucose-glucose dimers; by subtracting, from this quantity of total glucose, the quantity of initial glucose of the sample.

[0059] The total amount of dimers can be determined in a gas chromatograph under the same conditions as described above, except that the column used is a 30-meter DB1 capillary column with an internal diameter of 0.32 mm and a film thickness of 0.25 µm, and the column temperature is programmed as follows: from 200°C to 280°C at a rate of 5°C / min, held at 280°C for 6 min, then from 280°C to 320°C at 5°C / min, held at 320°C for 5 min.

[0060] The method is described in more detail in the Examples section.

[0061] To carry out the nanofiltration step useful in the invention, the composition to be nanofiltered is passed over a nanofiltration membrane. It generally has a dry matter content ranging from 5 to 15%.

[0062] The temperature of this composition to be nanofiltered can range from 10 to 80°C, generally from 15 to 50°C, often around 20°C.

[0063] The skilled person will know how to choose the membrane useful for this separation. This nanofiltration membrane has a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da. Ideally, the membrane has a MgSO4 rejection rate of at least 98%. It may in particular be a Dairy DK or Duracon NF1 type membrane manufactured by GE ®< .

[0064] The pressure applied to the membrane can also vary widely and can range from 1 to 50 bars, preferably from 5 to 40 bars, most preferably from 15 to 35 bars.

[0065] This nanofiltration step can be accompanied by a diafiltration phase.

[0066] Preferably, the volume concentration factor (VCF) of the nanofiltration ranges from 2 to 20. This volume concentration factor is easily adjusted by those skilled in the art.

[0067] This nanofiltration step can be carried out continuously.

[0068] According to the invention, the step of providing a composition rich in D-allulose may comprise: a step of providing a composition comprising D-fructose (Stream 1 or 1'); an epimerization step to form a composition comprising D-fructose and D-allulose (Stream 2); a chromatography step to provide a composition rich in D-allulose (Stream 5) and a raffinate, which is a composition rich in D-fructose (Stream 14).

[0069] Preferably, the nanofiltration step is carried out between the step of providing the D-allulose-rich composition (Stream 5) and the concentration step to provide the D-allulose stock solution (Stream 7). The nanofiltration step of said D-allulose-rich composition provides a retentate (Stream 12) and a permeate (Stream 6). Thus, the method according to the invention comprises: a step of providing a composition rich in D-allulose; a step of nanofiltration of said composition rich in D-allulose to provide a retentate and a permeate, the nanofiltration step being carried out with a membrane having a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da; a step of recovering the nanofiltration permeate; a step of concentrating this permeate to provide the mother solution of D-allulose; a step of crystallization of the mother solution to form crystals of D-allulose and mother liquors.

[0070] In the process of the invention, the nanofiltration step is thus advantageously carried out on the D-allulose-rich composition resulting from the chromatography step, just before the concentration step which provides the mother solution. It is in this configuration that the process makes it possible to most effectively limit the quantity of D-allulose dimers in the mother solution to be crystallized, and therefore to most significantly increase the overall yield of D-allulose crystals.

[0071] By composition rich in D-allulose, we generally mean a composition having a dry mass content of D-allulose greater than 80%, advantageously ranging from 80 to 99%, preferably from 82 to 98%.

[0072] As regards the permeate obtained, its dry matter can vary, for example in the range from 3 to 15%. The permeate can in particular comprise, in addition to D-allulose, D-fructose and glucose, as well as other sugars possibly present. The composition of this filtrate can be very different and depends on the composition to be nanofiltered. At the end of this nanofiltration step, the recovered permeate can comprise, relative to its dry mass, from 0 to 1.2% of D-allulose dimers, for example from 0.1 to 1.0%, in particular from 0.15 to 0.5%. The permeate can be subjected to one or more steps such as a step of mixing with an additional product, a separation step, a purification step, an epimerization step or a concentration step.

[0073] As for the obtained retentate, its dry matter can also vary widely, for example in the range from 15 to 40%. It can mainly comprise D-fructose, D-allulose, glucose and D-allulose dimers. Alternatively, the retentate is recovered, possibly mixed with an additional D-allulose composition, to provide, after a possible concentration step, a D-allulose syrup.

[0074] In the preferred variant where the composition rich in D-allulose which comprises D-allulose dimers is subjected to a nanofiltration step, the permeate obtained (Stream 6), called “preferred permeate”, preferably comprises in dry mass: 80 to 99% D-allulose; 0 to 20% D-fructose; 0 to 10% glucose; 0 to 1.2% D-allulose dimers.

[0075] As indicated above, this preferred permeate can be directly subjected to a concentration step to obtain the mother solution to be crystallized (Stream 7).

[0076] It is specified that in the present Application, apart from the D-allulose crystals, all of the compositions are generally aqueous compositions. In other words, the solvent of the dry constituents comprises water. The solvent of the compositions generally consists of water or a mixture of water and alcohol such as, for example, ethanol. Preferably, the solvent of the compositions is water.

[0077] Thus, the D-allulose stock solution useful in the invention generally consists of an aqueous solution of D-allulose. The stock solution generally has a dry matter of at least 75%, for example 80 to 95%, preferably 81 to 92%, most preferably 83 to 89%.

[0078] To achieve this dry matter, it is necessary to carry out a concentration step. This step can be carried out on a composition rich in D-allulose, the only requirement is that this composition rich in D-allulose has been obtained by a process comprising, in a previous step, the nanofiltration step useful for the invention. This composition rich in D-allulose subjected to the concentration step can thus be the preferred permeate described above, but also a composition rich in D-allulose obtained by chromatography, or even a mixture of a permeate with an additional composition rich in D-allulose. Preferably, the composition rich in D-allulose subjected to the concentration step is the preferred permeate.

[0079] Since the formation of D-allulose dimers also occurs during the concentration step, it is preferable to select conditions that limit the quantities formed in these dimers. The concentration step is thus generally carried out under vacuum, for example at a pressure of 5 to 100 mbar, preferably ranging from 20 to 70 mbar. This vacuum makes it possible to reduce the temperature necessary for evaporation and to reduce the duration of this concentration step. It can be carried out at a temperature ranging from 30 to 80°C, advantageously from 34 to 70°C, preferably from 37 to 50°C. This concentration step can be carried out in a single-stage evaporator, a multiple-stage evaporator, for example a double-stage evaporator. At the end of the concentration step, the stock solution of D-allulose useful for the invention is obtained.

[0080] This concentration step can be carried out continuously.

[0081] The mother solution obtained can comprise in dry mass: from 80 to 99% of D-allulose, preferably from 85 to 98%; from 0 to 20% of D-fructose, preferably from 0.5 to 15%; from 0 to 10% of glucose, preferably from 0 to 5%; from 0 to 1.5% of D-allulose dimers, for example from 0.1 to 1.2%, preferably from 0.4 to 1.1%.

[0082] The method according to the invention further comprises a step of crystallizing said D-allulose mother solution to form a suspension of D-allulose crystals. This suspension comprises crystals and crystallization mother liquors which are also formed during this step.

[0083] This crystallization step can be of any type. It can in particular be a cooling crystallization step or an evaporative crystallization step. Those skilled in the art will be able to find the implementation conditions which are described in particular in document WO 2011 / 119004. However, it should be noted that the crystallization steps described in these documents are made easier to carry out due to the particular preparation of the mother solution useful for the invention.

[0084] At the end of the crystallization step, from the crystal suspension (Stream 9) the crystals (Stream 10) are separated from the mother liquors (Stream 13), in particular by a filtration and / or centrifugation step. This separation step is preferably carried out in batch.

[0085] Mother liquors (Stream 13) generally have a dry matter content ranging from 70 to 80%. They can include in dry mass: from 80 to 99% of D-allulose, preferably from 82 to 95%; from 0 to 20% of D-fructose, preferably from 0.5 to 15%; from 0 to 10% of glucose, preferably from 0 to 5%; from 0 to 3% of D-allulose dimers, for example from 0.1 to 2.9%, in particular from 1 to 2.5%.

[0086] The crystals obtained may be subjected to a clearing step with cold water and / or alcohol, particularly ethanol. These crystals may then be dried (Flow 11) by a drying step which may be carried out in any suitable type of dryer. The D-allulose crystals have a water content of less than 5%, preferably less than 1%.

[0087] This crystallization step can be carried out continuously, in particular using a vertical crystallizer, an example of which is shown in Figure 5 .

[0088] According to a most preferred embodiment, the crystallization step comprises an adiabatic evaporation-cooling stage, carried out in an adiabatic vacuum crystallizer-evaporator to form a massecuite (Stream 8), followed by a crystallization stage by cooling said massecuite to provide a suspension of crystals (Stream 9). Adiabatic evaporation-cooling causes immediate cooling of the mother solution to be crystallized. Preferably, the crystallizer-evaporator is equipped with a condenser and the water condensed during this stage is continuously reinjected along the walls at the top of the crystallizer to keep the dry matter stable. This preferred crystallization step comprising two distinct stages, combined with the nanofiltration step in a particular configuration of the process of the invention, made it possible to continuously obtain the crystals of the invention which are described below in the description.This is linked to the fact that this preferred crystallization step, in particular the evaporation-cooling stage, also makes it possible to significantly limit the in-situ formation of D-allulose dimers. Without being bound by any theory, the Applicant explains this by the fact that the mother solution can be cooled almost instantaneously upon its introduction into the crystallizer-evaporator, unlike the already known crystallization processes for D-allulose which describe the natural cooling of the mother solution, or even by a cooling ramp using a heat exchanger as described in application WO2016 / 064087. The crystals according to the invention have improved purity and properties, although the first stage of the crystallization step is an instantaneous evaporation-cooling stage, which shortens the duration of the crystallization step.However, this is contrary to what the person skilled in the art would have envisaged, for whom obtaining improved crystals requires an increased crystallization time.

[0089] During the evaporation-cooling stage, the temperature can range from 30 to 40°C, preferably from 33 to 37°C, for example around 35°C. This temperature is easily reached by a person skilled in the art by determining the appropriate vacuum to be applied. Thus, the pressure in the crystallizer-evaporator can range from 30 to 50 mbar. An adiabatic crystallizer can in particular be a DT type draft tube crystallizer (for Draft Tube) or DTB type (for Draft Tube Baffle),with forced circulation or indirect forced circulation (IFC ®< ). Preferably, this evaporation-cooling stage is continuous. During this stage, the primers are continuously generated by spontaneous nucleation in the evaporation-crystallizer by the supersaturation created by the rapid cooling; thus, there is no introduction of primers strictly speaking in this case. As a non-limiting example, one possibility of carrying out this evaporation-cooling stage continuously is described in the Examples section and in the Figure 4, where a fraction of the crystals formed during the evaporation-cooling stage (Stream 7d) is mixed into the feed Stream 7b of the crystallizer-evaporator, which makes it possible to obtain a Stream 7c which comprises, at the time of introduction into the crystallizer-evaporator, crystals which will be able to grow further during this new passage in the crystallizer-evaporator. According to this example, Stream 7b can be obtained from a mixture of Stream 7 and Stream 7a, which consists of a supersaturated syrup of D-allulose recovered in the crystallizer-evaporator, which comprises “fines”, i.e. the finest crystals of D-allulose in the crystallizer. According to this variant, Stream 7 can advantageously, before mixing, pass through a heat exchanger, this passage making it possible to heat Stream 7 almost immediately before mixing it immediately with Stream 7a.This then allows the fines of Flux 7a to be remelted and Flux 7 to be cooled to obtain a Flux 7b free of these fines.

[0090] At the end of this stage, a massecuite of D-allulose crystals (Stream 8) is recovered, i.e. a suspension of crystals, generally of a small size. The average residence time of the massecuite during this evaporation-cooling stage can be between 5 and 15 hours. The average volume size D4.3 of the crystals suspended in the massecuite generally ranges from 50 to 200 µm.

[0091] The cooling crystallization stage is carried out in a conventional manner by cooling the massecuite obtained during the evaporation-cooling stage (Stream 8). The duration of this crystallization stage can range from 25 to 50 hours. The crystallization start temperature generally depends on the temperature of the massecuite introduced and can in particular range from 30 to 40°C, preferably from 33 to 37°C, for example approximately 35°C. This stage is generally carried out with mechanical stirring. Preferably, during crystallization by cooling, the temperature is reduced at a rate ranging from 0.3 to 0.5°C per hour. Figure 5represents an example of a vertical crystallizer with, on the sides, different heat exchangers allowing the temperature in the crystallizer to be regulated. During this operation, it is preferable that the temperature difference between the massecuite and the water in the exchanger does not exceed 5°C. The cooling crystallization stage can preferably be carried out continuously, in particular in a vertical crystallizer.

[0092] Thus, a preferred variant of the method of the invention comprises: a step of providing a composition rich in D-allulose (Stream 5); a step of nanofiltration of said composition rich in D-allulose to provide a retentate (Stream 12) and a permeate (Stream 6); a step of recovering the nanofiltration permeate; a step of concentrating this permeate to provide the mother solution of D-allulose (Stream 7); a crystallization step comprising: i. an adiabatic evaporation-cooling stage, carried out in an adiabatic crystallizer-evaporator under vacuum to form a massecuite (Stream 8), ii. followed by a crystallization stage by cooling of said massecuite to form a suspension of crystals (Stream 9).

[0093] Apart from the advantages related to the crystals themselves, an advantage of this preferred variant of the process of the invention is that the crystals obtained can be even more easily separated from the mother liquors of crystallization and more easily dried. This is mainly related to the shape of the crystals obtained.

[0094] To start a crystallization step, D-allulose primers are usually introduced into the selected crystallizer. These D-allulose primers consist of small D-allulose crystals, for example, 10 to 100 µm in size. The mass quantity of primer can vary widely depending on the type of crystallizer used. It can range from 0.001 to 1%, often 0.01 to 0.7%, usually 0.05 to 0.5% relative to the mass of D-allulose in the stock solution. These quantities are particularly suitable when performing a cooling crystallization step from a D-allulose stock solution. As mentioned above, it is also possible to create primers in situ when using an evaporative cooling step.

[0095] Preferably, the crystallization step is carried out less than one hour after the concentration step, preferably less than 30 minutes after. Most preferably, the crystallization step is carried out immediately after the concentration step. This makes it possible to further limit, at the time of the crystallization step, the quantity of dimers in the mother solution to be crystallized.

[0096] Once recovered after drying, the crystals can also be subjected to an additional sieving step, which makes it possible to screen these crystals and, depending on the fraction recovered after sieving, to increase or decrease the size of the crystals. For example, this additional step makes it possible, compared to the size of the crystals subjected to the sieving step, to recover a fraction of smaller average size in volume D4.3 of D-allulose crystals passed through the sieve as well as a fraction of larger average size in volume D4.3 of D-allulose crystals remaining in the sieve. To modify the population of crystals and obtain the desired fraction D4.3, the person skilled in the art simply has to select the mesh size of the sieve.

[0097] It goes without saying that the process according to the invention may comprise other steps, such as the other steps appearing in the conventional process described above and which will be described in detail below. The process according to the invention may also comprise additional purification steps and also intermediate dilution or concentration steps in order to adjust the dry matter and thus carry out the various steps of the process of the invention under the best conditions. All of these steps may be carried out continuously.

[0098] The D-fructose composition provided (Stream 1) for carrying out the epimerization step may be a D-fructose syrup, which may be obtained by dissolving D-fructose crystals in water or a glucose / D-fructose syrup. Preferably, this composition comprises a glucose / D-fructose syrup which comprises at least 90% by dry weight of D-fructose, preferably at least 94% of fructose. In a preferred embodiment which will be explained later in the description, the D-fructose composition provided for carrying out the subsequent epimerization step is a mixture (Stream 1') of this D-fructose syrup with at least one recycled fraction which may be the raffinate in whole or in part (Stream 14 or 16), this recycled fraction being able to comprise a higher quantity of D-allulose.

[0099] The composition of D-fructose subjected to the epimerization step may include: 0 to 10% D-allulose; 70 to 100% D-fructose; 0 to 10% glucose; 0 to 15% D-allulose dimer.

[0100] The epimerization step is carried out from the D-fructose composition provided previously, optionally after adjusting the dry matter. This step is generally carried out at a dry matter ranging from 30 to 60%, often from 45 to 55%. An enzyme of the D-psicose epimerase type or a composition comprising this enzyme is introduced into this composition. The composition comprising this enzyme may be a lyophilisate of a host microorganism synthesizing D-psicose epimerase, this being able to be the Bacillus subtilis,in particular that described in application WO2015 / 032761 A1. The pH is adjusted according to the enzyme used, for example at a pH ranging from 5.5 to 8.5. The reaction can be carried out by heating to a temperature ranging from 40 to 70°C, often from 45 to 60°C. The reaction can last from 0.1 to 100 hours, for example from 0.2 to 60 hours. This reaction can for example be carried out on an enzymatic column, which has the advantage of also working continuously on this step. It is also possible to work sequentially with several reactors to operate continuously. To carry out this epimerization step, it is possible in particular to use the teaching of document WO 2015 / 032761 A1.

[0101] At the end of the reaction, a composition comprising D-fructose and D-allulose is formed, generally according to a D-fructose / D-allulose mass ratio ranging from 85 / 15 to 55 / 45, often according to a D-fructose / D-allulose mass ratio ranging from 80 / 20 to 60 / 40. This ratio depends on the epimerization parameters used and, of course, on the quantity of D-allulose and D-fructose in the D-fructose composition provided in the epimerization step; the quantity of D-allulose in this composition may be particularly greater in the case of recycling.

[0102] At the end of this epimerization step, if necessary, a filtration step can be carried out to recover any cellular debris that may be present, particularly when a lyophilisate of a host microorganism is used. This step may consist of a microfiltration step.

[0103] In the Figure 3, the microfiltered composition corresponds to Flow 3 and the cellular debris is recovered in Flow 17.

[0104] In the process of the invention, additional purification steps may also be carried out. Generally, before the chromatography step, a step of demineralization of the composition comprising D-fructose and D-allulose (Stream 3) is carried out, which may be carried out by passing through one or more cationic ion exchange resins (for example a cationic resin of the Dowex 88 type), anionic ion exchange resins (for example an anionic resin of the Dowex 66 type) and a cationic-anionic mixture. In the Figure 3, this composition corresponds to Flow 4. The composition comprising D-fructose and D-allulose obtained is then demineralized and generally has a resistivity greater than 100 kΩ.cm -1< . It is also possible to carry out, before this demineralization step, a step of decolorization of the composition comprising D-fructose and D-allulose, for example by passing it over a column comprising activated carbon.

[0105] The composition comprising D-fructose and D-allulose (Stream 4) can then be subjected to a chromatography step to provide at least one composition rich in D-allulose and one composition rich in D-fructose. In a preferred embodiment which will be explained in detail later in the description, the composition comprising D-fructose and D-allulose subjected to the chromatography step is a mixture (Stream 4') of the composition resulting from the epimerization step (Stream 4) and at least one recycled fraction, this recycled fraction being able to comprise a higher quantity of D-allulose.

[0106] The composition subjected to the chromatography step may comprise, in relation to its dry mass: 22-45% D-allulose, usually 25-37%; 45-75% D-fructose, usually 46-70%; 0-10% glucose; 2-10% D-allulose dimer.

[0107] To carry out this chromatography step, any type of continuous chromatography can be used, in particular simulated moving bed chromatography. (Simulated Moving Bed SMB), of type Improved Simulated Moving Bed (ISMB), of type Divide Improved Simulated Moving Bed (DISMB), Sequential Simulated Moving Bed (SSMB) or type Nippon Mitsubishi Chromatography Improved (NMCI). Water is generally used as the eluent. The chromatography may be equipped with several columns in series, for example, 4 to 8 columns. The columns comprise ion exchange resin, for example, a cationic calcium ion exchange resin. The dry matter of the composition comprising D-fructose and D-allulose may range from 40 to 70%, generally around 50%. The temperature of the composition during chromatography generally ranges from 40 to 80°C, preferably from 55 to 65°C. This chromatography lasts until satisfactory separation is obtained and may last several hours.

[0108] At the end of this step, a composition rich in D-allulose (Stream 5) is obtained which may comprise, relative to its dry matter, at least 80% of D-allulose, advantageously at least 90% of D-allulose. This composition rich in D-allulose may have a dry matter ranging from 5 to 15%. At the end of this step, a raffinate (Stream 14) is also obtained, which generally comprises, relative to its dry matter, at least 75% of D-fructose, often at least 80% of D-fructose. This raffinate generally has a dry matter ranging from approximately 15 to 30%.

[0109] The composition rich in D-allulose obtained at the end of the chromatography (Flow 5) can thus include, in relation to its dry mass: 80 to 98% D-allulose; 0 to 20% D-fructose; 0 to 10% glucose; 1.5 to 5% D-allulose dimer.

[0110] The raffinate can include, in relation to its dry mass: 1 to 10% D-allulose; 70 to 99% D-fructose; 0 to 10% glucose; 5 to 20% D-allulose dimer.

[0111] Unlike a conventional process where, relative to the D-fructose introduced, the overall yield of D-allulose crystals is less than 15%, the yield of the process of the invention may be greater than or equal to 25%. Advantageously, the overall yield of D-allulose crystals is greater than or equal to 50%, for example greater than or equal to 60%, or even greater than or equal to 65%. This particularly improved yield is made possible by the fact that it is possible to carry out recycling steps without disturbing the crystallization step.

[0112] Thus, the method of the invention can comprise at least one recycling step.

[0113] According to a preferred embodiment, this recycling step may consist of a step of recycling at least part of the raffinate from the chromatography step (Stream 14). This raffinate may optionally have been concentrated before being mixed. It may advantageously be recycled, in whole or in part, to be mixed with D-fructose (Stream 1), for example in the form of the D-fructose glucose syrup described above, to provide the D-fructose composition (Stream 1'). It is then this D-fructose composition, which is generally richer in D-allulose than the D-fructose syrup, which is subjected to the epimerization step.

[0114] This recycling step may consist of a step of recycling at least part of the mother liquors (Stream 13). These mother liquors may advantageously be recycled, in whole or in part, to be mixed with the composition comprising D-fructose and D-allulose (Stream 4). It is then this mixture (Stream 4') which is subjected to the chromatography step. These mother liquors may optionally have been diluted before being mixed.

[0115] This recycling step may consist of a step of recycling at least part of the retentate (Stream 12). This retentate may advantageously be recycled, in whole or in part, to be mixed with the composition comprising D-fructose and D-allulose (Stream 4) and possibly the recycled mother liquors. It is then this mixture (Stream 4') which is subjected to the chromatography step. This retentate may possibly have been concentrated before being mixed. In the case where the mixing is done with the retentate and mother liquor fractions, it may not be necessary to concentrate or dilute these fractions. It should be noted that the recycling of the retentate and mother liquor fractions, which are two fractions having relatively large quantities of D-allulose, makes it possible to increase the richness in D-allulose (and consequently reduce the quantity of D-fructose) of the composition subjected to the chromatography step.To carry out the possible stages of concentration of the recycled fractions, it is possible to use the same equipment and conditions described for the concentration stage allowing the manufacture of the mother solution.

[0116] According to a very preferred embodiment of the invention (the Figure 3 represents a production circuit for this preferred method of the invention), the method comprises: a) a step of providing a composition comprising D-fructose (Stream 1'); b) an epimerization step to form a composition comprising D-fructose and D-allulose (Stream 2); c) a chromatography step to provide a composition rich in D-allulose (Stream 5) and a raffinate consisting of a composition rich in D-fructose (Stream 14); d) a step of nanofiltration of the composition rich in D-allulose to form a permeate (Stream 6) and a retentate (Stream 12); e) a step of concentrating the permeate to form the mother solution to be crystallized (Stream 7); f) a step of crystallization of the mother solution (Stream 9) to form crystals (Stream 10) and mother liquors (Stream 13); and in which is carried out: a step of recycling at least a portion of the raffinate (Stream 14 or 16) to be mixed with D-fructose (Stream 1) and provide the composition (Stream 1') of step a); and / or a step of recycling at least a portion of the retentate (Stream 12) from the nanofiltration step to be mixed with the composition comprising D-fructose and D-allulose (Stream 4) from step b) to provide the composition (Stream 4') subjected to the chromatography step c); and / or a step of recycling at least a portion of the mother liquors (Stream 13) from the crystallization step to be mixed with the composition comprising D-fructose and D-allulose from step b) (Stream 4) to provide the composition (Stream 4') subjected to the chromatography step c).

[0117] The process comprises a purging step, this purging step being able to be a step of purging at least a part of at least one of the recycled fractions chosen from the raffinate, the retentate and the crystallization mother liquors. Indeed, for the system to remain stable, it is absolutely necessary to remove from the production circuit a part of the D-allulose dimers formed during the process. Generally speaking, the more the fractions are recycled, the more the quantity of D-allulose dimers increases in the circuit. Thus, one possibility of reducing the quantity of D-allulose dimers is to increase the purged quantities. However, this is then done to the detriment of the overall yield of D-allulose crystals. The process of the invention makes it possible to drastically increase the recycling of the different fractions obtained in the process, while still maintaining crystallization.

[0118] For example, in the most preferred process variant described above where all of the raffinate, retentate and crystallization mother liquor fractions are recycled, the raffinate recycling step is advantageously a partial recycling, for example 50 to 95% of this raffinate is recycled (Stream 16) and 5 to 50% is purged (Stream 15) to provide a D-fructose composition which comprises D-allulose dimers: in other words, the recycling rate of the D-fructose-rich composition ranges from 50 to 95%. Preferably, the recycling rate ranges from 70 to 92%. In this case, the other two recycles are advantageously total recycles.

[0119] The purged fractions can then be used to make syrups, possibly after a concentration step and / or mixing with other compositions and / or additives. Because the crystallization step remains stable over time, the process according to the invention is particularly advantageous because it can be continuous.

[0120] As explained above, according to the preferred variant of the invention combining the nanofiltration and crystallization step in an adiabatic vacuum crystallizer-evaporator, the Applicant has also succeeded in obtaining crystals having an improved quality. The crystals according to the invention have a mass content of D-allulose dimer of less than 0.50%, preferably less than 0.30%, or even less than 0.20%. These crystals may advantageously comprise a mass content of D-allulose dimer ranging from 0.01 to 0.48%, preferably ranging from 0.02 to 0.45%, for example ranging from 0.03 to 0.40%, in particular from 0.04 to 0.30%, particularly from 0.05 to 0.20%.

[0121] The crystals according to the present disclosure advantageously have a mass content of D-allulose greater than or equal to 99.00%, preferably greater than or equal to 99.50%, or even greater than or equal to 99.70%.

[0122] An advantage of the crystals of the invention is that these crystals have low amounts of D-allulose dimer. Without being bound by any theory, the Applicant explains this by the fact that the mother solution useful for the manufacture of these crystals comprises a very low content of D-allulose dimers and by the fact that the crystallization step implemented makes it possible to limit the formation of these dimers in situ. These crystals were thus able to be obtained by the Applicant by this process, by combining the nanofiltration step with the crystallization step comprising an adiabatic evaporation-cooling stage and a crystallization stage by cooling.

[0123] A disadvantage associated with prior art D-allulose crystals, which comprise a higher dimer content than those of the invention, is that an elongation of these crystals to have a shape close to needles is observed, especially when they are large.

[0124] The D-allulose crystals of the invention have a volume average size D4.3 greater than 200 µm, advantageously ranging from 210 to 800 µm, preferably from 220 to 350 µm.

[0125] The crystals of the invention, which have a lower D-allulose dimer content, have the advantage of having a more “stocky” shape, as demonstrated in the Figures 11, 12 And 13 .

[0126] This more squat shape can be reflected by the fact that the D-allulose crystals of the invention can have, for a given particle size in volume D 4.3 and chosen in the range from 200 to 400 µm, a Feret min / Feret max diameter ratio greater than 0.60, advantageously ranging from 0.62 to 0.90, for example from 0.63 to 0.80. The Feret diameter is a quantity well known to those skilled in the art. It is deduced from the projected area of a particle, using the principle of the caliper. The Feret min diameter consists of the smallest of the dimensions while the Feret max diameter consists of the largest of the dimensions. Figure 15 represents the principle of min and max Feret diameters on a given particle.

[0127] Preferably, the crystals of the invention have this Feret min / Feret max ratio across all particle sizes in the range of 200 to 400µm.

[0128] Alternatively and independently of the D-allulose dimer content, an object of the invention relates to D-allulose crystals which have a volume average size D4.3 greater than 200 µm, advantageously ranging from 210 to 800 µm, preferably from 220 to 350 µm and having, for a given volume particle size D4.3 chosen in the range from 200 to 400 µm, a Feret min / Feret max diameter ratio greater than 0.60, advantageously ranging from 0.62 to 0.90, for example from 0.63 to 0.80. Preferably, the crystals of the invention have this Feret min / Feret max ratio over all particle sizes in the range from 200 to 400 µm. These crystals of the invention comprise a mass content of D-allulose dimer of less than 0.50%, preferably less than 0.30%, or even less than 0.20%.These crystals may advantageously comprise a mass content of D-allulose dimer ranging from 0.01 to 0.48%, preferably ranging from 0.02 to 0.45%, for example ranging from 0.03 to 0.40%, in particular from 0.04 to 0.30%, particularly from 0.05 to 0.20%. These crystals advantageously have a mass content of D-allulose greater than or equal to 99.00%, preferably greater than or equal to 99.50%, or even greater than or equal to 99.70%.

[0129] The average volume size D4.3 and the Feret min / Feret max diameter ratio of the crystals are determined by a granulometer, in particular the QICPIC RODOS type granulometer from SympaTEC, such as the one used in the Examples section. Since the crystals are observed statistically in all directions in a granulometer, the values obtained by a granulometer for a population of crystals are different from the values obtained by calculation on a simple microscopic image of this population of crystals, the values obtained by granulometry being generally higher.

[0130] Preferably, the crystals are non-agglomerated (or individualized). The fact that the crystals are non-agglomerated can be verified by simple observation by optical microscopy. For example, the crystals of the Figure 13 are agglomerated, unlike those of Figures 11 and 12 .

[0131] This different shape translates on a macroscopic scale into improved flow of the crystals of the invention compared to crystals of the same average size. Also, these crystals can exhibit better caking behavior over time.

[0132] Thus, due to their properties, the crystals obtained by the preferred method of the invention can flow easily. This is how they have made it possible to obtain crystals with a flow never before achieved. They can thus be used advantageously, for example, as table sugar.

[0133] The D-allulose crystals of the invention can be used in the known applications of allulose and, in general, of sweeteners. Among the applications which can use the D-allulose crystals of the invention may be cited chewing gum in the form of tablets or dragees, candies and lozenges, biscuits, cookies, muffins, cakes, gelatin-based cakes, chewing pastes, in particular short-textured chewing pastes, icings and powdered drinks.

[0134] Another object of the invention also relates to the use of a nanofiltration unit in a D-allulose crystal production circuit to improve the overall yield of D-allulose crystals. This use is particularly advantageous when the raw material introduced into the circuit comprises D-fructose.

[0135] Another subject of the present disclosure also relates to the use of a nanofiltration unit in a D-allulose crystal production circuit to improve the quality of the crystals obtained. By improving the quality of the crystals obtained, it is meant in particular reducing the D-allulose dimer content and / or increasing the Feret min / Feret max diameter ratio of the D-allulose crystals.

[0136] By way of illustration, other embodiments of the process according to the invention, comprising a step of recycling the mother liquors and / or a step of recycling the raffinate and / or a step of recycling the retentate are presented below.

[0137] According to a first embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition rich in D-allulose; b) a concentration step to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a step of recycling at least a portion of the mother liquors; the nanofiltration step is carried out on these recycled mother liquors to form a permeate a retentate; the permeate is mixed with the composition rich in D-allulose provided in step a); and this mixture is subjected to the concentration step b) to provide the mother solution to be crystallized; at least a portion of the mother liquors and / or the retentate is purged.

[0138] According to a second embodiment, the method comprises: a) a step of providing a composition rich in D-allulose; b) a concentration step to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a step of recycling at least a portion of the mother liquors; these recycled mother liquors are mixed with the D-allulose-rich composition provided in step a); the nanofiltration step is carried out on this mixture to provide a permeate and a retentate; this permeate is subjected to the concentration step b) to provide the mother solution to be crystallized; and at least a portion of the mother liquors is purged.

[0139] According to a third embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-allulose and D-fructose; b) a chromatography step to provide a composition rich in D-allulose and a raffinate consisting of a composition rich in D-fructose; c) a step of concentrating the composition rich in D-allulose to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a step of recycling at least part of the mother liquors; the nanofiltration step is carried out on these recycled mother liquors to form a permeate and a retentate; the permeate is mixed with the composition provided in step a); this mixture is subjected to the chromatography step b); and at least part of the mother liquors is purged.

[0140] According to a fourth embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-allulose and D-fructose; b) a chromatography step to provide a composition rich in D-allulose and a composition rich in D-fructose; c) a concentration step to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a step of recycling at least part of the mother liquors; these recycled mother liquors are mixed with the composition provided in step a); the nanofiltration step is carried out on this mixture to provide a permeate and a retentate; this permeate is subjected to the chromatography step b); and at least part of the mother liquors is purged.

[0141] According to a fifth embodiment, the method comprises: a) a step of providing a composition comprising D-allulose and D-fructose; b) a chromatography step to provide a composition rich in D-allulose and a composition rich in D-fructose; c) a concentration step to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a step of recycling at least a portion of the mother liquors; these recycled mother liquors are mixed with the composition provided in step a); the chromatography step b) is carried out on this mixture; the nanofiltration step is carried out on the D-allulose-rich composition resulting from this chromatography step b), to provide a permeate and a retentate; this permeate is subjected to the concentration step c); and at least a portion of the mother liquors is purged.

[0142] According to a sixth embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and allulose; c) a step of chromatography of this composition to provide a composition rich in allulose and a raffinate consisting of a composition rich in D-fructose; d) a step of concentrating the composition rich in D-allulose to form the mother solution to be crystallized; characterized in that: at least one recycling step consists of a raffinate recycling step; the nanofiltration step is carried out on this raffinate to provide a permeate and a retentate; the permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture and; at least part of the raffinate is purged.

[0143] According to a seventh embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and D-allulose; c) a step of chromatography of this composition to provide a composition rich in allulose and a raffinate consisting of a composition rich in D-fructose; d) a concentration step to form the mother solution to be crystallized; characterized in that: a recycling step consists of a step of recycling the raffinate obtained in step c); a first nanofiltration step is carried out on this raffinate to provide a first permeate and a first retentate; the first permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture; a recycling step consists of a step of recycling at least a portion of the mother liquors; a second nanofiltration step is carried out on these recycled mother liquors to form a second permeate and a second retentate; the second permeate is mixed with the composition rich in D-allulose provided in step c); this mixture is subjected to the concentration step d) to provide the mother solution to be crystallized and; at least a portion of the raffinate and / or the mother liquors is purged.

[0144] According to an eighth embodiment, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and allulose; c) a step of chromatography of this composition to provide a composition rich in allulose and a raffinate consisting of a composition rich in D-fructose; d) a concentration step to form the mother solution to be crystallized; characterized in that: a recycling step consists of a step of recycling the raffinate obtained in step c); a first nanofiltration step is carried out on this raffinate to provide a first permeate and a first retentate; the first permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture; a recycling step consists of a step of recycling at least a portion of the mother liquors; these recycled mother liquors are mixed with the composition rich in D-allulose provided in step c); a second nanofiltration step is carried out on this mixture to provide a second permeate and a second retentate; this second permeate is subjected to the concentration step d) to provide the mother solution to be crystallized and; at least a portion of the raffinate and / or the mother liquors is purged.

[0145] According to a ninth embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and D-allulose; c) a chromatography step to provide a composition rich in D-allulose and a raffinate consisting of a composition rich in D-fructose; d) a step of concentrating the composition rich in D-allulose to form the mother solution to be crystallized; characterized in that: a recycling step consists of a step of recycling the raffinate obtained in step c); a first nanofiltration step is carried out on this raffinate to provide a first permeate and a first retentate; the first permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture; a recycling step consists of a step of recycling at least a portion of the mother liquors; a second nanofiltration step is carried out on these recycled mother liquors to form a second permeate and a second retentate; the second permeate is mixed with the composition formed in step b); this mixture is subjected to the chromatography step c); and at least a portion of the raffinate and / or the mother liquors is purged.

[0146] According to a tenth embodiment not forming part of the present invention, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and D-allulose; c) a chromatography step to provide a composition rich in D-allulose and a raffinate consisting of a composition rich in D-fructose; d) a step of concentrating the composition rich in D-allulose to form the mother solution to be crystallized; characterized in that: a recycling step consists of a step of recycling the raffinate obtained in step c); a first nanofiltration step is carried out on this raffinate to provide a first permeate and a first retentate; the first permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture; a recycling step consists of a step of recycling at least a portion of the mother liquors; these recycled mother liquors are mixed with the composition formed in step b); a second nanofiltration step is carried out on this mixture to provide a second permeate and a second retentate; this second permeate is subjected to the chromatography step c); and at least a portion of the raffinate and / or the mother liquors is purged.

[0147] According to an eleventh embodiment, the method comprises: a) a step of providing a composition comprising D-fructose; b) an epimerization step to form a composition comprising D-fructose and allulose; c) a chromatography step to provide a composition rich in D-allulose and a raffinate consisting of a composition rich in D-fructose; d) a step of concentrating the composition rich in D-allulose to form the mother solution to be crystallized; characterized in that: a recycling step consists of a step of recycling the raffinate obtained in step c); a first nanofiltration step is carried out on this raffinate to provide a first permeate and a first retentate; the first permeate is mixed with the composition comprising D-fructose from step a); the epimerization step b) is carried out on this mixture; a recycling step consists of a step of recycling at least a portion of the mother liquors; these recycled mother liquors are mixed with the composition formed in step b); the chromatography step c) is carried out on this mixture; a second nanofiltration step is carried out on the composition rich in D-allulose resulting from this chromatography step b), to provide a second permeate and a second retentate; this second permeate is subjected to the concentration step d); and at least a portion of the raffinate and / or the mother liquors is purged.

[0148] In a non-limiting manner, the invention will now be detailed in order to illustrate its interest in the examples below. Examples Analytical methods Gas chromatography

[0149] The gas chromatograph used is a Varian 3800 type and is equipped with: A split-splitless injector (with or without dividers); A flame ionization detector (FID); A computer system for processing the detector signal; An automatic sampler (type 8400).

[0150] The various quantities are determined by gas chromatography in the form of trimethylsilylated methoxime derivatives, then quantified by the internal calibration method. Determination of D-allulose, D-fructose and glucose contents

[0151] The applied response coefficients are 1.25 for D-allulose and D-fructose and 1.23 for glucose. Other monosaccharides were not detected. Sample preparation

[0152] In a tare box, weigh 100 to 300 mg of the sample to be tested + 10 ml internal standard solution consisting of methyl α-D-glucopyranoside at 0.3 mg / ml in pyridine. In a 2 ml cup, take 0.5 ml from the tare box and evaporate to dryness under a stream of nitrogen. Add 20 mg of methoxylamine hydrochloride and 1 ml of pyridine. Stopper and leave in the Reacti-therm ®< type incubation system at 70°C for 40 min. Add 0.5 ml of N, O Bis (trimethylsilyl) trifluoroacetamide (BSTFA). Heat for 30 min at 70°C. Chromatographic conditions

[0153] Column: DB1 capillary 40 meters, internal diameter 0.18 mm, film thickness 0.4 µm, made of 100% dimethylpolysiloxane, non-polar (J&W Scientific ref.: 121-1043) Column temperature: 100°C programable up to 260°C at 3°C / min, then up to 300°C at 15°C / min, maintain 5 min at 300°C. Injector temperature: 300°C Detector temperature: 300°C (Range 10 -12< ) Pressure: 40 psi (constant flow rate) Carrier gas: Helium Injection mode: Split (Split flow rate: 100 ml / min) Injected volume: 1.0 µl

[0154] D-allulose, D-fructose, and glucose were detected in that order. D-allulose, which was unknown, had a retention time under these conditions of between 39.5 and 40 minutes. Determination of D-allulose dimers and glucose-glucose dimers contents

[0155] The applied response coefficients are 1.15 for D-allulose dimers and maltose, and 1.08 for isomaltose. Other glucose dimers were not detected. Sample preparation:

[0156] In a tare box, weigh 100 to 300 mg of the sample to be tested + 10 ml internal standard solution consisting of Phenyl beta-D-glucopyranoside at 0.3 mg / ml in pyridine.

[0157] In a 2 ml cup, take 0.5 ml from the tare box and evaporate to dryness under a stream of nitrogen. Take up with 0.5 ml of the 40 g / l hydroxylamine hydrochloride solution in pyridine, stopper, shake and leave for 40 min at 70°C.

[0158] Add 0.4 ml of BSTFA and 0.1 ml of N-Trimethylsilylimidazole (TSIM). Heat for 30 min at 70°C. Chromatographic conditions

[0159] Column: DB1 capillary 30 meters, internal diameter 0.32 mm, film thickness 0.25 µm (J&W Scientific ref.: 123-1032) Column temperature: 200°C programable up to 280°C at 5°C / min (hold 6 min), then up to 320°C at 5°C / min, hold 5 min at 320°C. Injector temperature: 300°C Detector temperature: 300°C (Range 10 -12< ) Pressure: 14 psi (constant flow) Carrier gas: Helium Injection mode: Split (Split flow rate: 80 ml / min) Injected volume: 1.2 µl Expression of results:

[0160] The content of the different constituents is expressed in g per 100 g of raw product and is given by the following equation: % constituant i = Si Se × Pe P × 100 Ki With : Si = area of the peak(s) of constituent i Se = area of the peak of the internal standard Pe = Weight of internal standard introduced into the beaker (in mg) P = weight of weighed sample (in mg) Ki = response coefficient of constituent i

[0161] If the percentage obtained (expressed here as crude) exceeds 20% for one of the constituents, the sample is diluted and the CPG analysis repeated in order to obtain a mass quantity less than 20%.

[0162] The mass quantities expressed in gross are then expressed in dry, by dividing for the dry matter of the sample tested.

[0163] The mass quantities of D-allulose, D-fructose and glucose are readily determined, with none of the characteristic peaks co-eluting.

[0164] The peak of maltose and D-allulose dimers can be co-eluted. It should be noted, however, that in the crystals of the invention and described in the examples below, maltose is never present.

[0165] If the characteristic peaks of maltose are not detected, the area Si of the D-allulose dimers is determined by integration of the unknown peaks, between 10 and 17 minutes. If the characteristic peaks of maltose are detected (which may be the case in the syrups of the invention), the quantities of maltose are determined and this quantity is subtracted from the total quantity of dimers.

[0166] To determine the total quantity of glucose-glucose dimers, the following protocol is carried out on a sample: • Hydrochloric hydrolysis

[0167] In a 15 ml hydrolysis tube with a Teflon screw cap, weigh approximately 50 to 500 mg of sample accurately (adjust the weighing according to the expected sugar content), add 2 ml of the internal standard solution (galactitol at 5 mg / ml in reverse osmosis water) with a two-mark pipette, add 3 ml of water and 5 ml of the 4N HCl solution.

[0168] Seal tightly, shake for 1 minute with a vortex mixer. Place the tube in a thermostatically controlled dry bath set at 100°C for 1 hour, vortexing occasionally. • Demineralization and concentration

[0169] After cooling, place the entire hydrolysis in a 50 ml beaker. Add 6 to 8 g of a 50 / 50 mixture of anionic resin AG4 X 4 and AG50 W 8. Leave under magnetic stirring for 5 minutes. Filter through paper. Collect the juice and repeat the demineralization step until a pH close to water is obtained. • Sample preparation

[0170] In a tare box, weigh 100 to 300 mg of the sample to be tested + 10 ml internal standard solution consisting of methyl α-D-glucopyranoside at 0.3 mg / ml in pyridine. In a 2 ml cup, take 0.5 ml from the tare box and evaporate to dryness under a stream of nitrogen. Add 20 mg of methoxylamine hydrochloride and 1 ml of pyridine. Stopper and leave in the Reacti-therm ® at 70°C for 40 min. Add 0.5 ml of BSTFA. Heat for 30 min at 70°C.

[0171] The total glucose quantity in the solution (which includes the initial so-called "free" glucose and the glucose resulting from hydrolysis and in particular linked to the presence of maltose and isomaltose) is determined by GC analysis of the glucose. The quantity of maltose can easily be deduced and, by difference with the total quantity of dimers attributed to the peaks between 10 and 17 minutes, the quantity of D-allulose dimers. Granulometer

[0172] The values of the average size in volume D 4.3 as well as the ratio of Feret min / Feret max diameters of the crystals are determined on a QICPIC RODOS type granulometer from SympaTEC, equipped with its powder dispersion module (dry method), following the technical manual and the manufacturer's specifications. Realization of processes continuous industrial crystal manufacturing D-allulose Example 1

[0173] Example 1 consists of a method for the continuous production of D-allulose crystals. The process steps used are detailed in the Figure 3 The composition and flow rate of the Fluxes after stabilization in the process are described in Tables 1a and 1b. Step 1 :

[0174] 13.1 tonnes of a mixture composed of 26% of a Fructamyl D-fructose syrup (Tereos) comprising 95% D-fructose at 50% dry matter (DM) (Stream 1), and 74% of Stream 16 brought back to 50% DM, are introduced into a 12m 3< useful stirred batch reactor. The whole (Stream 1') is maintained at 55°C. A lyophilisate of the strain is introduced into the tank. Bacillus subtilis host of the enzyme D-Psicose 3 Epimerase detailed in patent WO2015032761 in sufficient quantity to have 2.5*10 7< units of activity in the reactor. Five reactors are used sequentially so as to provide a syrup essentially composed of fructose and allulose (Stream 2) continuously at a flow rate of 1.3t / h. The reaction conditions are as follows: Temperature: 55°C pH=7 Reaction time 48h

[0175] At the end of the reaction, Flux 2 is obtained comprising a D-allulose richness approximately equal to 25% and a D-fructose richness approximately equal to 75%. Step 2:

[0176] Stream 2 passes through a microfiltration membrane during a batch operation. A Stream 3 free of cellular debris and a microfiltration retentate (Stream 17) comprising debris from the freeze-dried product are obtained. Bacillus subtilis which is purged from the circuit. The microfiltration parameters are as follows: Transmembrane pressure: 0-3 bar Pore size: 0.1 µm Temperature: 50°C Average flow rate: 15 l / h / m 2< Membrane: Sepro PS35 Volume Concentration Factor: 33 Table 1a: Flow rates and composition of the Flows of steps 1 to 5 of Example 1 Stage / Characteristics of Flows Flow Step 1 Stream 1 Stream 16 Stream 1' Mass flow rate (kg / h) 360 1005 1365 Dry Matter (%) 50 50 50 Fructose Richness (%) 94,5 75,5 80,5 Dextrose Richness (%) 2 6,6 5,4 Allulose Richness (%) 1 2,1 1,7 Di-Allulose Richness (%) 1 10,9 8,3 Other Wealth (%) 1,5 4,9 4,1 Step 2 / Step 3 Flux2 / 3 / 4 Stream 17 - Mass flow rate (kg / h) 1324 41 - Dry Matter (%) 50 50 - Step 4 Stream 4' Stream 14 Stream 5 Mass flow rate (kg / h) 1673 2061 2993 Dry Matter (%) 50,2 26,2 10 Fructose Richness (%) 49,6 75,5 2,8 Dextrose Richness (%) 4,5 6,6 0,6 Allulose Richness (%) 33,4 2,1 90,1 Di-Allulose Richness (%) 8,3 10,9 3,5 Other Wealth (%) 4,2 4,9 3 Step 5 Stream 5 Stream 6 Flux12 Mass flow rate (kg / h) 2993 2797 196 Dry Matter (%) 10 8,7 29 Fructose Richness (%) 2,8 2,7 3 Dextrose Richness (%) 0,6 0,6 0,7 Allulose Richness (%) 90,1 94,4 71,7 Di-Allulose Richness (%) 3,5 0,4 16,6 Other Wealth (%) 3 1,9 8 Table 1b: Flow rates and composition of the Flows of steps 6 to 9 of Example 1 Stage / Feature Flow Step 6 Stream 6 Stream 7 - Mass flow rate (kg / h) 2797 279 - Dry Matter (%) 8,7 87 - Fructose Richness (%) 2,7 2,7 - Dextrose Richness (%) 0,6 0,6 - Allulose Richness (%) 94,4 93,7 - Di-Allulose Richness (%) 0,4 1,1 - Other Wealth (%) 1,9 1,9 - Step 7a / 7b Flux7 / 8 / 9 - Mass flow rate (kg / h) 279 - - Dry Matter (%) 87 - - Step 8 Stream 9 Flux10 Stream 13 Mass flow rate (kg / h) 279 126 152 Dry Matter (%) 87 97 76,5 Fructose Richness (%) 2,7 0,1 5,4 Dextrose Richness (%) 0,6 0 1,2 Allulose Richness (%) 93,7 99,7 87,5 Di-Allulose Richness (%) 1,1 0,2 2,2 Other Wealth (%) 1,9 0 3,7 Step 9 Stream 10 Flux11 - Mass flow rate (kg / h) 126 122 - Dry Matter (%) 97 99,8 - Step 3:

[0177] Stream 3 is demineralized by passing through a strong cationic resin Dowex 88 then a weak anionic resin Dowex 66 at an average flow rate of 2BV / h. The cylinders are maintained at a temperature of 45°C and the resistivity of Stream 4 at the end of demineralization remains greater than 100kΩ.cm -1< at the outlet (Stream 4). Otherwise, the resins are regenerated. Step 4:

[0178] Stream 4 is mixed with Stream 12 (nanofiltration retentate) and Stream 13 (crystallization mother liquors) to form a Stream 4' which feeds the continuous simulated moving bed (SMB) chromatography (SCC ARI ®< equipped with 8 columns) of the circuit. The average feed flow rate is 1673kg / h at 50% DM.

[0179] The chromatography parameters are defined as follows: Volume / column: 2m 3< Resin: Dowex Monosphere 99Ca / 320 Temperature: 60°C Water flow rate / Flow 4' (vol. / vol.): 2.4 Load (Feed flow rate / resin volume): 0.09 h -1<

[0180] Two fractions are extracted: the SCC raffinate (Stream 14), the D-allulose-rich fraction (Stream 5) which goes towards stage 5. 7% of Stream 14 is purged (Stream 15) in order to remove the allulose dimers while the remainder (Stream 16) goes back to stage 1 after being brought back to a dry matter content of 50% via an evaporator. Step 5:

[0181] Stream 5 is processed on a nanofiltration plant in batch mode. The parameters are as follows: Transmembrane pressure: 30 bars Temperature: 20°C Membrane: GE Duracon NF1 8040C35 Volume Concentration Factor (FCV): 16

[0182] Allulose dimers concentrate in the retentate (Stream 12) and this retentate is recycled and mixed with Stream 4, while the permeate (Stream 6) is recovered. figure 6 gives details of the permeation of syrups as a function of FCV. Step 6:

[0183] Stream 6 passes through a two-stage evaporator with an internal pressure of 50 mbar. At the outlet of the first stage, the Stream is at a temperature of 38°C and has a dry matter content of 35%. At the outlet of the second stage, the Stream reaches a temperature of 48°C and has a dry matter content of 87%. The D-allulose stock solution (Stream 7) is obtained at the end of this stage. Step 7a:

[0184] The mother solution thus formed (Stream 7) is introduced immediately after being heated to 68°C by an exchanger, into an adiabatic vacuum crystallizer-evaporator of 3m 3< useful, inside which the pressure is maintained at 35mbars.

[0185] The operating principle of the adiabatic vacuum crystallizer-evaporator used here is detailed in Figure 4 : Stream 7a is composed of supersaturated D-allulose syrup at 35°C and the finest D-allulose particles. It is mixed with Stream 7 in a ratio such that the mixture is just below the solubility limit of the mixture (84% dry matter and 46°C) (Stream 7b). The fine particles are thus remelted. The massecuite is withdrawn from the adiabatic crystallizer-evaporator at a temperature of 35°C, at the same speed as the mixture, so as to maintain a constant level in the adiabatic crystallizer-evaporator. This recovered massecuite is separated into two streams: Stream 7d and Stream 8. Stream 7d is entrained with Stream 7b to form a Stream 7c comprising the D-allulose stock solution as well as crystallization primers. The mixing ratio is made so as to be again beyond solubility (85.5% dry matter and 42.7°C) so that the crystals can continue to grow.Flux 7c is then introduced into the adiabatic vacuum crystallizer-evaporator to prolong crystallization and form the massecuite. The water condensed during this stage is continuously reinjected along the walls at the top of the crystallizer.

[0186] The different flows during the evaporation-cooling stage in the adiabatic vacuum crystallizer-evaporator are reported in Table 2. Table 2: Characteristics of the different flows in the adiabatic vacuum crystallizer-evaporator Setting Stream 7 Flow 7a) Stream 7b) Stream 7c) Stream 7d) Stream 8 Mass flow rate (kg / h) 279 519 798 1203 405 279 Dry Matter (%) 87 83 84,1 85,1 87 87 Temperature (°C) 68,3 35 46 42,4 35 35 Step 7b:

[0187] The drawn massecuite is injected into the top of a vertical crystallizer with a useful volume of 8m 3 and equipped with an agitator and five cooling layers. The massecuite is brought from 35 to 20°C in 40 hours, i.e. a cooling ramp of approximately 0.4°C / h. The crystallizer diagram is shown in Figure 5 The temperature of the cooling water in the water tables is as follows: 1. 34°C inlet, 32°C outlet 2. 31°C inlet, 29°C outlet 3. 28°C inlet, 26°C outlet 4. 25°C inlet, 22°C outlet 5. 21°C inlet, 20°C outlet Step 8:

[0188] At the bottom of the crystallizer, the crystal suspension (Stream 9) is recovered and then centrifuged on a Rousselet Robatel SC 100KSA spin dryer. The crystal suspension is systematically centrifuged, which means that the process is very stable over time. The mother liquors (Stream 13) are recycled and mixed with Streams 4 and 12. The wet D-allulose crystals are recovered (Stream 10). An initial clarification with water and then a final clarification with ethanol of around 0.5% m / m is carried out to improve separation. The clarified crystals comprise 3% water. Step 9:

[0189] The wet crystals are passed through a rotary dryer and dried crystals are obtained, which comprise 0.4% water. Final cooling in a fluidized bed lowers the crystal temperature from 60 to 25°C. The final crystals are recovered (Stream 11) and then packaged. The overall yield of D-allulose crystals, which is the ratio expressed in dry mass of the mass of D-allulose crystals obtained to the mass of D-fructose introduced, is 72%. Example 2

[0190] Example 2 is identical to Example 1 except that no recycling is performed. Stream 7 comprises 0.7% D-allulose dimers. The crystal suspension of Stream 9 is still centrifugable over time. Although the overall crystal yield is only 12%, the process has the advantage of being stable, unlike the processes of the comparative examples, which do not use the nanofiltration step, which will be presented below. Comparative example 1

[0191] Comparative Example 1 is identical to Example 1 except: that no nanofiltration step is carried out, that no step of recycling the mother liquors is carried out, that the recycling of the raffinate (Stream 14) is recycled in its entirety to be mixed with Stream 1 of the D-fructose syrup, the crystallization step is carried out as follows: the mother solution formed (Stream 7) is introduced sequentially into three vertical crystallizers with a useful volume of 8m 3 < identical to that used for crystallization step 7b of example 1. The cooling ramp is 0.33°C / h up to 20°C. In each crystallizer, a D-allulose primer of D4.3 approximately equal to 60µm is introduced in mass quantities of 0.1%, this quantity being expressed relative to the dry weight of D-allulose introduced into the crystallizer.

[0192] The production circuit used (iethe different stages of the process used) is that corresponding to the Figure 1 .

[0193] Flux 7 comprises 1.9% D-allulose dimers. Flux 9 is recovered and is taken to step 8. This Flux 9 is a massecuite that is not always centrifuged. After one week, Flux 7 comprises 2.2% D-allulose dimers and the massecuite of Flux 9 even becomes systematically non-centrifugable (crystals too small). Comparative example 2

[0194] Comparative Example 2 is identical to Comparative Example 1 except that the mother liquors are completely recycled (Stream 13) to be mixed with the D-allulose-rich composition from the chromatography step (Stream 5) and that the raffinate (Stream 14) is not recycled and is purged from the circuit.

[0195] The production circuit used is that corresponding to the Figure 2 .

[0196] Stream 7 comprises 1.9% D-allulose dimers. Stream 9 is recovered and taken to step 8. This Stream 9 is a massecuite that is not always centrifuged. As soon as the mother liquors are recycled, Stream 7 comprises 2.4% D-allulose dimers and the massecuite of Stream 9 even becomes systematically non-centrifugable (crystals too small). Comparative example 3

[0197] Comparative Example 3 is identical to Comparative Example 1 except that the raffinate is not recycled.

[0198] The production circuit used is that corresponding to the Figure 1 .

[0199] Stream 7 comprises 1.9% D-allulose dimers. Stream 9 is recovered and is carried to step 8. This Stream 9 is a massecuite that is not always centrifuged. When it is centrifuged, the mother liquors separate from the allulose crystals, which can be recovered. But sometimes, Stream 9 consists of a mass of small, inseparable crystals, synonymous with spontaneous nucleation in the crystallizer. In this case, it is necessary to drain the Flux from the circuit. This makes the process unusable industrially.

[0200] The summary of the results obtained for these processes are reported in Table 3. The overall reported yield is an average over one week of use.

[0201] The characteristics of the crystals obtained for examples 1, 2 and comparative example 3, as well as the D-allulose crystals marketed by the company CJ Cheiljedang Food Ingredient are reported in Table 4. Table 3: Comparison of the different circuits tested Example Circuit Recycling of Flow 14 (%) Recycling of Flow 13 (%) Recycling of Flow 12 (%) Overall yield of D-allulose crystals from the continuous process Comparative example 1 Figure 1 100 0 0 (no nanofiltration) Unstable then shutdown installation, does not work continuously Comparative example 2 Figure 2 0 100 0 (No nanofiltration) Unstable then shutdown installation, does not work continuously Comparative example 3 Figure 1 0 0 0 (no nanofiltration) Unstable, does not work continuously Example 1 Figure 3 93 100 100 Stable, 72% Example 2 Figure 3 0 0 0 Stable, 12%

[0202] The process of the invention makes it possible to obtain stable crystallization over time, which is demonstrated in the industrial process exemplified above (Examples 1 and 2). It also makes it possible to carry out very significant recycling and thus increase the overall yield of D-allulose crystals (see Example 2). By carrying out recycling without ensuring that the D-allulose dimers are separated by the nanofiltration step, the illustrative comparative examples 1 and 2 above demonstrated that the industrial crystallization process had to be stopped because the massecuite systematically becomes non-centrifugable (crystals of too small a size). Table 4: Characteristics of the crystals obtained Crystals Residual humidity D4.3 (µm) % D-allulose dimers (CPG) Feret min / Feret max at 200 µm Feret min / Feret max at 400 µm Example 1 0,3% 302 0,2% 0,63 0,68 Example 2 0,3% 285 <0,1% 0,68 0,76 Comparative example 3 0,3% 297 0,7% 0,55 0,53 Crystals marketed by CJ 0,5% 346 0,7% 0,53 0,50 Cheiljedang Food Ingredient

[0203] There Figure 14which represents, for the crystals of Example 2 and the crystals marketed by CJ of D-allulose, the ratio of the Feret min / Feret max diameters as a function of the particle size in volume D4.3, demonstrates that it is for populations of large size, greater than or equal to 200 µm (for example in the range from 200 to 400 µm), that clear differences in appearance are observed between the crystals according to the invention and the comparative crystals. Thus, in this range from 200 to 400 µm, the Feret min / Feret max ratios are, for the comparative crystals, always less than 0.55 whereas the crystals according to the invention have a ratio of at least 0.63. This difference is entirely in agreement with the optical microscopy images of the Figures 11 and 12 , which visually demonstrate that the crystals according to the invention have a much more stocky appearance than the comparative crystals. With regard to the CJ crystals of the Figure 13(optical microscopy images), we notice that these are crystals in the form of needles, not individualized.

[0204] Although comparative example 3 is not strictly identical to the teaching of document WO 2011119004 A2 with regard to the concentration step (in particular in that the Applicant has succeeded in carrying out the concentration step in a more optimal manner so as to further reduce the quantity of D-allulose dimers formed), the crystals obtained use a process of the same type as that used to manufacture the crystals described in example 6 of document WO 2011119004 A2 (in particular with regard to the crystallization being carried out exclusively by controlled cooling in water). This comparative test 3, producing crystals comprising 0.7% of D-allulose dimers, therefore clearly demonstrates that document WO 2011119004 A2 does not allow the crystals of the invention to be formed. Use of crystals of the invention in different applications

[0205] The crystals of Example 2 were used in the manufacture of the following products. Meal replacement drink manufacturing

[0206] The goal is to create a low-calorie meal replacement drink powder. This powdered drink must flow well and form few lumps when formulated. Formula :

[0207] Ingredients Percentages Allulose Sucrose Sugar 28,29 28,29 Milk protein concentrate 26,62 26,62 GLUCIDEX ®< 19 maltodextrin 22,63 22,63 NUTRIOSE ®< FM 06 Soluble fiber 10,82 10,82 Pea protein 9,98 9,98 Sodium caseinate 0,67 0,67 Vanilla cream flavor 0,50 0,50 Vanilla aroma 0,33 0,33 Cekol 10000 0,17 0,17 Total 100,00 100,00

[0208] After being weighed, the ingredients are vigorously mixed in a dry mixer.

[0209] The drink is then easily reconstituted by adding 210g of water to 30g of the formula, without forming lumps.

[0210] The formula using the crystals of the invention exhibits flow behavior quite similar to the formula comprising sucrose, while comprising far fewer calories. Making Yellow Cake

[0211] The objective is to provide a yellow cake with a satisfactory texture and appearance with a 25% reduced calorie content. Formula :

[0212] Ingredients Reference Invention Sucrose 24,10 0,00 Cake flour 27,09 25,24 Nutriose ®< FB06 0,0 1,75 Egg yolk 10,00 10,00 Butter 15,45 15,45 Milk 21,81 21,81 Salt 0,25 0,25 Baking powder 0,80 0,90 Vanilla 0,50 0,50 Allulose 0,00 24,10 Total 100,00 100,00 Method :

[0213] 1. Mix the flour, salt, Nutriose ®< and yeast; 2. Cream the butter with the sucrose or allulose; 3. Add the egg yolk and vanilla to the cream then add the milk to form a creamy mixture; 4. Add the flour mixture to the creamed mixture and mix in a mixer on slow (1 minute) then more briskly until the formula is well mixed; 5. Pour 600g of the batter into a greased 9-inch circular mold; 6. Bake at 180°C for 20 minutes.

[0214] The objective is achieved: the cake using the crystals of the invention has a very pleasant texture in the mouth (we speak of “crumb texture”) and the shape of the cake is maintained after baking. Making chocolate cookies

[0215] The following formulas were produced: Ingredients Reference Allulose Allulose + Nutriose ®< Wheat flour 25 25 23 Baking soda 0,14 0,14 0,14 Salt 0,17 0,17 0,17 Melted butter 14,16 14,16 14,16 Nutriose ®< FB06 0 0 2 Allulose 0 29,17 29,17 Brown sugar 20,35 0 0 Powdered sugar 8,82 0 0 Vanilla 1,14 1,14 1,14 Eggs 7 7 7 Chocolate chips 23,22 23,22 23,22 Total 100 100 100 Method :

[0216] 1. Mix the dry ingredients together; 2. Cream the butter with the sugars or allulose; 3. Add the eggs and vanilla to the creamed mixture; 4. Add the flour mixture to the creamed mixture and mix in a mixer on slow (1 minute) then more briskly until the formula is well mixed; 5. Add the chocolate chips and mix; 6. Weigh out 30g portions and bake at 160°C for 8 minutes.

[0217] The allulose-based cookie dough (column 2) spreads less than the sugar-based dough (column 1). However, the dough in column 3 spreads the same as the dough in column 1.

[0218] During baking, allulose cookies brown more quickly.

[0219] It should be noted that the cookies have a dome shape. The height of the cookie according to the invention is less swollen and it does not collapse after baking, unlike the sugar-based cookie, which allows it to keep a better appearance.

[0220] Allulose-based cookies have a good taste, although less sweet. The texture of the cookies according to the invention is softer and more moist than sugar-based cookies.

[0221] The water activity (wa) and humidity (M) of the cookies are measured over time: Date Reference Allulose Allulose + Nutriose ®< wa Humidity (%) wa Humidity (%) wa Humidity (%) Day 1 0,6429 7,62 0,5482 8,91 0,5027 8,69 Day 7 0,7531 9,42 0,5859 9,59 0,5472 8,82 Day 30 0,7633 8,33 0,5888 9,47 0,5563 9,11

[0222] Allulose-based cookies have better moisture stability. Making Oatmeal Cookies Formulas :

[0223] Ingredients Reference Invention Wheat flour 16,84 15,09 Nutriose ®< FB06 0,00 1,75 Baking soda 0,42 0,42 Yeast 0,27 0,27 Salt 0,44 0,44 Butter 14,53 14,53 Sucrose 14,08 11,30 Brown sugar 13,89 0,00 Allulose 0,00 16,67 Eggs 6,43 6,43 Vanilla 0,60 0,60 Oat flakes 19,35 19,35 Inclusions* 13,15 13,15 Total 100,00 100,00 *Inclusions include 50.0 grams of pecans, 20.0 grams of cranberries, and 18.6 grams of blueberries. Method:

[0224] 1. Mix the flour, Nutriose ®< , baking soda, yeast and salt; 2. Cream the butter with the sugars or allulose; 3. Add the eggs and vanilla to the creamed mixture; 4. Add the flour mixture to the creamed mixture and mix in a mixer on slow (1 minute) then more briskly until the formula is well mixed; 5. Add the oats and mix; 6. Add the inclusions and mix; 7. Weigh out 30g portions and bake at 160°C for 10 minutes.

[0225] Cookies made with allulose instead of sucrose are slightly browner and have a crispy texture after baking. Bubble gum manufacturing

[0226] A bubble gum was made with the recipe below: Ingredients Parts Flama T base eraser 24 Allulose 50 Lycasin ®< 85 / 55 10 Nutriose ®< FB06 13,4 Liquid flavoring 0,9 Powdered flavoring 1,2 Acidifier 0,5 Total 100

[0227] Bubble gum has a very satisfying appearance, similar to commercial bubble gum.

Claims

1. Method for producing D-allulose crystals comprising: • a step of providing a composition rich in D-allulose, • a nanofiltration step of said composition rich in D-allulose so as to provide a retentate and a permeate, said nanofiltration step being performed with a membrane having a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da; • a step of recovering the nanofiltration permeate; • a step of concentrating said permeate so as to provide a D-allulose stock solution; • a step of crystallising the stock solution so as to form D-allulose crystals and mother liquors.

2. Method according to claim 1, characterised in that the stock solution to be crystallised obtained after concentration comprises by dry mass: • 80 to 99% D-allulose, preferably 85 to 98%; • 0 to 20% D-fructose, preferably 0.5 to 15%; • 0 to 10% glucose, preferably 0 to 5%; • 0 to 1.5% D-allulose dimers, for example from 0.1 to 1.2%, preferably from 0.4 to 1.1%, the quantities being determined by gas chromatography (GC) according to the method described on page 12 line 22 to page 13 line 24 as well as on pages 36-39.

3. Method according to any one of the preceding claims, characterised in that the volume concentration factor of the nanofiltration ranges from 5 to 20.

4. Method according to one of the preceding claims, characterised in that the crystallisation step comprises: i. an adiabatic evaporative cooling stage, carried out in an adiabatic crystallizer evaporator under vacuum to form a massecuite, ii. followed by a stage of crystallisation by cooling of said massecuite so as to form crystals.

5. Method according to claim 4, characterised in that the temperature during the adiabatic evaporative cooling stage ranges from 30 to 40°C, preferably ranging from 33 to 37°C, for example about 35°C.

6. Method according to any one of the preceding claims, characterised in that it is continuous.

7. Method according to any one of the preceding claims, characterised in that it comprises at least one recycling step.

8. Method according to any one of the preceding claims, characterised in that it comprises a step of recycling at least one part of the mother liquors.

9. Method according to any one of the preceding claims, characterised in that it comprises a step of recycling at least one part of the retentate.

10. Method according to any one of the preceding claims, characterised in that the step of providing the composition rich in D-allulose comprises: • a step of providing a composition comprising D-fructose; • an epimerization step so as to form a composition comprising D-fructose and D-allulose; • a chromatography step so as to provide a composition rich in D-allulose and a composition rich in D-fructose.

11. Method according to claim 10, characterised in that it comprises a step of recycling at least one part of the composition rich in D-fructose.

12. Method according to claim 11 characterised in that the recycling rate of the composition rich in D-fructose ranges from 50 to 95%.

13. D-allulose crystals comprising a mass content of D-allulose dimer, determined by gas chromatography (GC) according to the method described on page 12 line 22 to page 13 line 24 as well as on pages 36-39, of less than 0.50%, and having a mean volume size D4.3 greater than 200 µm, advantageously ranging from 210 to 800 µm, preferably from 220 to 350 µm, and for a given and chosen volume particle size D4.3 ranging from 200 to 400 µm, a Feret min / Feret max ratio greater than 0.60, advantageously ranging from 0.62 to 0.90, for example from 0.63 to 0.80, the values of mean volume size D 4.3 as well as of Feret min / Feret max ratio being determined on a SympaTEC QICPIC RODOS granulometer, equipped with its powder dispersion unit.

14. D-allulose crystals according to claim 13, characterised in that they comprise a mass content of D-allulose dimer ranging from 0.01 to 0.48%, preferably ranging from 0.02 to 0.45%, for example ranging from 0.03 to 0.40%, in particular from 0.04 to 0.30%.

15. D-allulose crystals according to claim 14, characterised in that they have said Feret min / Feret max ratio over all volume particle sizes D4.3 in the range from 200 to 400 µm.

16. Use of a nanofiltration unit in a D-allulose crystal production circuit so as to improve the overall yield in D-allulose crystals, the membrane used for nanofiltration having a cut-off threshold of less than 300 Da, preferably ranging from 150 to 250 Da.