EP4352069A1

EP4352069A1 - System and method for crystallizing d-allulose from d-allulose solution

Info

Publication number: EP4352069A1
Application number: EP22806995.1A
Authority: EP
Inventors: Rahul Raju KANUMURU; Muthuvaduganathan NAGASUNDRAM; Binay Kumar Giri
Original assignee: Petiva Private Ltd
Current assignee: Petiva Private Ltd
Priority date: 2021-05-08
Filing date: 2022-05-08
Publication date: 2024-04-17
Also published as: WO2022239026A1

Abstract

The present disclosure relates to a system and a method for crystallizing allulose from an allulose solution.

Description

Title: SYSTEM AND METHOD FOR CRYSTALLIZING D-ALLULOSE FROM

D-ALLULOSE SOLUTION

RELATED APPLICATION

This application claims the benefit of Indian provisional patent application number 202141007126 filed on May 8, 2021; the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present subject matter disclosed herein, in general, relates to a system and method for crystallizing sugars having high solubility in water. In particular, the subject matter relates to a system and method for crystallizing D-allulose from D-allulose solution.

BACKGROUND

D-allulose (known as D-psicose), a rare sugar and C-3 epimer of fructose, is an ideal sugar substitute and has sweetness similar to dextrose or 70 % to sucrose. Allulose when metabolized by human body, does not raise blood sugar or insulin levels and thereby providing minimal calories. A caloric value of allulose is 0.2 kcal per gram and prevents the formation of body fat in the human body. Further, it has been reported that allulose is non-cariogenic. Thus, allulose is of great interest in the nutraceutical applications as well as in various other applications.

Although, allulose attracts the attention for its properties, however its utilization is restricted due its scarce availability in nature and difficulty in current production methods and systems.

Allulose can be produced by chemical or enzymatic methods. However, it is difficult to produce D-allulose via chemical method as only a trace amount of D-allulose is produced from fructose at high temperatures. Whereas enzymatic methods yield a very low of D-allulose, for example, the amount of D-fmctose transformed into D-allulose after epimerization is generally less than 30% and thus it is necessary to isolate D-allulose at high purity. To isolate D-allulose from the mixture, chromatography is generally carried out to prepare a high pure liquid followed by crystallization to get high purity sugar product. However, there is presently no industrially applicable method for producing D-allulose.

Typically, allulose syrup and allulose powders are available in the market. Allulose syrups, are generally used for manufacturing food and/or pharmaceutical products.

Allulose powders can be prepared using atomization technique or granulation technique. The atomized powders generally contain large number of impurities and have low amounts of sugars in crystalline form. Further, they are highly hygroscopic and thus having reduced shelf life. Also, such products are disadvantageous in food industries due to low flowability. Allulose has a very high solubility (291 g per 100 g water at 25 °C and about 85% w/w at 60 °C) which makes crystallization a difficult process. Therefore, the crystals formed are very small, typically, 100 pm and needle shaped which makes it difficult to separate them from the mother liquor. Further, viscosity of the mother liquor is also very high, typically 100 cp and combined with a small density difference between the allulose crystals and the mother liquor poses difficulty in separation.

US8524888 (herein after ‘888 patent) discloses a method of producing D-psicose crystals. The method comprises the steps of removing impurities from a D-psicose solution to obtain a purified D-psicose solution; concentrating the purified D-psicose solution; and crystallizing D-psicose from the concentrated D-psicose solution in a supersaturated state under a metastable zone. ‘888 patent mentioned that progress of crystallization in the crystallizing may be monitored by collecting a sample at a predetermined interval to observe the sample with the naked eye or by using a microscope or analyzing a sugar concentration in a supernatant obtained by centrifugation of the sample. In accordance with the result, the temperature or concentration of D-psicose may be controlled. Moreover, the yield was low. Further, initial rates of crystal growth are slow, requiring larger crystallizers. In addition, the process is a batch process which requires considerable down time and holding tanks.

Hence, there need exists for a system and a process for producing pure D-psicose (D-allulose), in the form of crystals to seek to mitigate one or more above shortcomings. Consequently, those skilled in the art will appreciate the present disclosure that provides many advantages and overcomes all the above and other limitations. SUMMARY

The present disclosure relates to a system and a method for crystallizing allulose from an allulose solution. In an aspect, the system comprises comprises a feed tank, a primary crystalliser, and at least one separating device and an evaporator.

In an aspect, the present disclosure relates to a system for crystallising a D- allulose solution. The system comprises a feed tank to store and supply concentrated D- allulose solution. Further, one or more crystallizers are fluidly connected to the feed tank. Each of the one or more crystallizers are configured to selectively receive the concentrated D-allulose solution from the feed tank to crystallize received concentrated D- allulose solution for obtaining D-allulose massecuite. A separating device is fluidly connected to the one or more crystallizers to continuously receive the D-allulose massecuite and to continuously separate a plurality of D-allulose crystals and mother liquor present in the D-allulose massecuite. Further, an evaporator is fluidly connected to the separating device and the feed tank. The evaporator is being configured to receive the mother liquor from the separating device concentrate the mother liquor to form super saturated D- allulose solution. The super saturated D- allulose solution is recycled and supplied into the feed tank. Furthermore, at least one drying device is fluidly connected to the separating device to wash and dry the D-allulose crystals.

In another aspect, one or more crystallizers comprises a primary crystallizer to crystallize the concentrated D- allulose solution for obtaining the D-allulose massecuite. A secondary crystallizer increases a crystal growth of existing plurality of D-allulose crystals present in the D-allulose massecuite obtained from the primary crystallizer.

In yet another aspect, the present disclosure relates to a method for continuously producing D-allulose crystals from a D-allulose solution. The method comprises the steps of: a) providing a D-allulose solution; b) removing impurities from the D-allulose solution to obtain a purified D- allulose solution; c) concentrating the purified D-allulose solution and storing in a feed tank; d) cooling the concentrated D-allulose solution from about 55-65 °C to about 25-35 °C through a heat exchanger; e) continuously introducing the cooled D-allulose solution having a temperature of about 25-35 °C into a primary crystalliser; f) performing crystallisation of D-allulose in the primary crystalliser to obtain D-allulose massecuite; g) continuously withdrawing the D-allulose massecuite from the primary crystalliser and introducing into a separation device to separate D- allulose crystals and the mother liquor from the D-allulose massecuite; h) continuously introducing the separated mother liquor into an evaporator; i) concentrating the mother liquor in the evaporator to obtain supersaturated solution of D-allulose; j) recycling the supersaturated solution of D-allulose to the feed tank; and k) washing and drying the separated D-allulose crystals to obtain pure D- allulose crystals.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features and characteristics of the disclosure are explained herein. The embodiments of the disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, regarding the accompanying drawing in which:

FIG. 1 is an illustration of a system for crystallizing D-allulose from D-allulose solution.

FIG.2schematically illustrates a process for producing allulose according to an embodiment of the present disclosure;

FIG. 3 illustrates D-allulose crystal size and length distribution from Phase contrast Microscopic (PCM) during continuous crystallization. FIG. 4 illustrates PCM view of D-allulose crystals during continuous crystallization.

FIG. 5 illustrates HPLC chromatogram of crystallizer feed.

FIG. 6 illustrates HPLC chromatogram of D-allulose crystals after crystallization.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structure and mechanism illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other assemblies for carrying out the same purposes of the present disclosure. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

The present disclosure relates to a system and a method for crystallizing allulose from an allulose solution. The system generally identified by reference numeral 100. The system 100 is more particularly, but not exclusively used for producing pure D-allulose in a crystal form from D-allulose solution. It is believed that those skilled in the art will readily recognize that as the description proceeds, such systemlOO may be utilized also for continuously obtaining pure D-allulose in a crystal form from D-allulose solution.

The system 100 comprises a feed tank 10, one or more crystallisers20,50, and at least one separating device 30 and an evaporator 40.

Referring to figure 1, the system 100 comprises a feed tank 10 configured to store and supply concentrated D-allulose solution. The concentrated D-allulose solution may be referred as a stock solution of D-allulose. The feed tank 10 is provided with an agitating device 12 disposed within the feed tank 10 to stir the concentrated D-allulose solutionin a predetermined way. In an embodiment, the agitating device 12 is suspended from an upper portion of the feed tank 10. The agitating device 12 includes a longitudinal shaft defined with a first end and second end as shown in Fig.l. Further, a plurality of stirring blades are coupled radially along the shaft and / or to the second end portion of the shaft. In an embodiment, the stirring blades are fixedly or movably coupled to the shaft using any fastening means. In another embodiment, the stirring blades are integrally formed on the shaft. The shaft is rotatably coupled to a rotary unit at the first end to facilitate the shaft to rotate along a rotational axis of the agitating device 12. In an embodiment, the agitating device 12 rotates at 100 -200 rpm, preferably at 150rpm.The rotation of the agitating device 12 facilitates uniform blending of the concentrated D-allulose solution, thereby preventing formation of deposits within the feed tank 10. In an embodiment, the feed tank 10 is surrounded by a jacket 11. The jacket 11 is in the fluid flow communication with an auxiliary tank (not shown in Figures). The auxiliary tank stores and circulates hot fluid into the jacket 11 that aids in maintaining a temperature of the feed tank 10 at a desired temperature (e.g., about 50-70 °C) in order to keep the D- allulose solution in liquid form.

The system 100 includes one or more crystallisers 20, 50 fluidly connected to the feed tank 10. Each of the one or more crystallizers 20, 50 is configured to selectively receive the concentrated D-allulose solution from the feed tank 10 to crystallize received concentrated D- allulose solution for obtaining D-allulose massecuite. In an embodiment, the one or more crystallisers 20, 50 comprises a primary crystalliser 20 and a secondary crystalliser 50. The primary crystalliser 20 is in fluid flow communication with the feed tank 10. The primary crystalliser 20 is configured to continuously receive the concentrated D- allulose solution. The concentrated D-allulose solution is supplied into the primary crystalliser 20 via at least one pump70a. Further, the supply of concentrated D-allulose solution is into the primary crystalliser 20 is controller and regulated by a valve 80a.The primary crystalliser 20 after receiving the concentrated D- allulose solution performs crystallisation to provide a D-allulose massecuite. The “massecuite” refers to a mixture of sugar crystals (D-psicose crystals) and solution (mother liquor) obtained during crystallization. The primary crystalliser 20 is provided with an agitating device 22 disposed within the to stir the concentrated D- allulose solution in a predetermined way. In the embodiment, the agitating device 22, is similar to the agitating device 11 disposed within the feed tank 10 from an upper portion of the primary crystalliser 20. The rotation of the agitating device 22 facilitates no or minimal local concentration and temperature gradients while feeding the concentrated D-allulose solutioninto the primary crystallizer 20. This further causes a higher crystallization rate thereby providing higher concentration of the massecuite leading to a higher crystal yield. In certain embodiments, speed of the agitating device 22 in the primary crystallizer 20 is about 80-100 RPM. In an embodiment, the primary crystalliser 20 is a vessel with a cone-shaped bottom having an apex that is pointed downwardly, so that a lower portion of the primary crystalliser 20 tapers to an outlet from which the D-allulose massecuite is withdrawn. The reason for providing cone-shaped bottom in primary crystalliser 20 is that by rotating the concentrated D-allulose solution a plurality of D-allulose crystals tend to form and be retained in the centre of the vessel, and in order to control crystal growth, these crystals must be maintained in motion throughout the process and prevent congregating or stagnation at any point. In crystallization reaction with a rotating concentrated D- allulose solution, the conical- shaped bottom of the vessel facilities collection of the plurality of crystals, such that from the apex of the downwardly pointing cone precludes capturing of the plurality of crystals. The requirement for the cone-shaped extension of the vessel, also, results in a considerable increase in the height of the crystallizer vessel, with concomitant requirement for structural support and enclosure. Moreover, the plurality of the crystals formed may have different sizes. In an embodiment, an average size of the plurality of crystals formed is about 125m. In an embodiment, the primary crystalliser 20 is surrounded by a jacket 21. The jacket 21 may be in the fluid flow communication with the auxiliary tank (not shown in figures). The auxiliary tank stores and circulate fluid of desired temperature into the jacket 21 thereby aids in maintaining the temperature of the primary crystalliser 20 at a desired temperature. In certain embodiments, the primary crystallizer 20 is maintained at about 10°C to about 35 °C with blending that is sufficient to ensure no local concentration and temperature gradients at the time of feeding the concentrated D-allulose solution. Further, continuous out flow at the same rate as that of feeding rate is maintained to keep a constant volume in the primary crystallizer 20. The primary crystallizer 20 operates at steady state in a metastable zone where a rate of crystal growth matches with the difference in inlet and outlet allulose concentrations. The metastable zone prevents spontaneous nucleation of the formed crystals. In certain embodiments, the higher concentration of allulose in the stock solution gets deposited on to the plurality of crystals in the primary crystallizer thereby increasing the total crystal size.

Further, at least one heat exchanger 60 is disposed in fluid flow communication between with the feed tank 10 and the one or more crystallisers 20, 50. In an embodiment, the heat exchanger 60 is disposed between with the feed tank 10 and the primary crystalliser 20. The heat exchanger 60 is configured to maintain the concentrated D- allulose solution at a predetermined temperature. The heat exchanger 60 receives the concentrated D-allulose solution via at least one pump 70a. The heat exchanger 60 receives the concentrated D-allulose solution to heat/cool the stock solution to a pre determined temperature. In an embodiment, the heat exchanger60 of the present disclosure cools the concentrated D-allulose solution pre-determined temperature being about 25-35 °C. This allows the crystallisation of concentrated D-allulose solution. Further, the temperature of the concentrated D-allulose solution is accurately controlled by the heat exchanger 60 in order to prevent local heating during crystallisation, thereby promoting increase and growth of a size of the plurality of crystals and increasing a growth kinetics of the plurality of crystals.

The system 100 further comprises a separation device 30. The separating device 30 is in fluid flow communication with the one or more crystalliser 20, 50 to receive the D-allulose massecuite and to continuously separate the plurality of D-allulose crystals and mother liquor. In an embodiment, the separating device 30 is in fluid flow communication with the primary crystalliser 20 via a pump 70b. The D-allulose massecuite is supplied to the separating device 30 via a valve 80b. The separating device 30 in configured to recover plurality of D-allulose crystals which is at least about 99% pure from mother liquor. The plurality of D-allulose crystals is recovered via an outlet and the mother liquor supplied to another system for further processing. In an embodiment, the separating device 30 is any suitable device that can be used to separate the plurality of crystals from the mother liquor. In certain embodiments, the separating device 30 is a centrifuge device. The centrifuge device is at least one of filters, centrifuges, hydro cyclones gravity settlers and any suitable device to separate. In another embodiment, the centrifuge device used in the system of the present disclosure is Pusher - centrifuge.

In an embodiment, the separation device 30 is in fluid flow communication with a washing fluid tank via at least one pump. The separating device 30 is provided with a first inlet to receive the D-allulose massecuite and a second inlet to receive washing fluid to wash the plurality of crystals obtained.

After separation of the crystals and the mother liquor, the plurality of crystals are washed with the washing fluid supplied from the washing fluid tank to obtain about 99% pure D-allulose crystals. In an embodiment, the washing fluid is water.

The system comprises at least one drying device fluidly connected to the separating device 30 to dry the washed crystals to yield pure D-allulose crystals without any residue. The drying device is any suitable drying device using the required method to obtain the desired purity of the D-allulose crystals. In certain embodiments, the drying of the crystals is a fluidized bed dryer or a vacuum dryer.

The one or more crystalliser comprising the secondary crystalliser 50 is disposed in fluid flow communication between the primary crystallizer 20 and the separating device 30 via at least one pump 70b. The secondary crystalliser 50 receives the D-allulose massecuite obtained from the primary crystalliser 20 to perform further crystallization. The secondary crystallizer 50 increase the crystal growth of existing plurality of D- allulose crystals present in the D-allulose massecuite obtained from the primary crystallizer 20. The massecuite obtained from the primary crystallizer 20 is further introduced in the secondary crystallizer 50 in order to provide more time for further crystal growth of the small crystals of D-allulose obtained and retained from the primary crystalliser 20. The secondary crystalliser 50 is provided with an agitating device 52 disposed within to stir the massecuite having smaller crystals than the plurality crystals obtained from the primary crystalliser 20, in a predetermined way. In an embodiment, the agitating device 52, is similar to the agitating device 11 disposed within the feed tank 10 from an upper portion of the secondary crystalliser 50. In an embodiment, the agitating device 52 may rotate at about 50-100 rpm, preferably at about 80 rpm. The rotation of the agitating device 52 facilitates no or minimal local concentration and temperature gradients while feeding the D-allulose massecuite into the secondary crystallizer 50, similar to the function of the agitating device 11. It may further facilitate a higher crystallization rate thereby providing higher concentration of the massecuite leading to the higher crystal yield. In an embodiment, the secondary crystalliser 50 is a vessel with a cone-shaped bottom having an apex that is pointed downwardly, so that a lower portion of the secondary crystalliser 50 tapers to an outlet from which the D-allulose massecuite is withdrawn. The reason for providing cone-shaped bottom in primary crystalliser 50 is that by rotating the concentrated D-allulose solution crystals tend to form and be retained in the centre of the vessel, and in order to control crystal growth, these crystals must be maintained in motion throughout the process and prevent congregating or stagnation at any point. In crystallization reaction with a rotating concentrated D-allulose solution and / or the D-allulose massecuite, the conical- shaped bottom of the vessel facilities collection of the crystals, such that from the apex of the downwardly pointing cone precludes capturing of the crystals. The requirement for the cone-shaped extension of the vessel, also, results in a considerable increase in the height of the crystallizer vessel, with concomitant requirement for structural support and enclosure

Further, the grown crystals from the secondary crystalliser along with the mother liquor will be supplied to the separating device 30 for separating D-allulose crystals and mother liquor. The centrifuge device 30 is in fluid flow communication with the secondary crystalliser 50 via a pump 70c. The D-allulose massecuite of the secondary crystalliser 50 is supplied to the centrifuge device via a valve 80d. In an embodiment, the secondary crystalliser 50 is surrounded by a jacket 51. The jacket 51 may be in the fluid flow communication with the auxiliary tank. The auxiliary tank stores and circulate fluid of desired temperature into the jacket 51 to maintain the temperature of the secondary crystalliser 50 at a desired temperature such as 50-70 °C.

The system further includes an evaporator 40 that is coupled to the centrifuge 30 to receive the separated mother liquor via at least one pump 70d to produce a supersaturated D-allulose solution. The produced supersaturated D-allulose solution is recycled and supplied to the feed tank 10. In an embodiment, the mother liquor received is evaporated in the evaporator 40 to get a supersaturated D-allulose solution. Each of the feed tank 10, the primary crystalliser 20, the second crystalliser 50, the evaporator 40 are provided with plurality of valve. This plurality of valves may be control valves being located in immediate vicinity of feed tank 10, the primary crystalliser 20, the second crystalliser 50, the evaporator 40 to control or regulate the supply of at least one of the concentrated D-allulose solution from the feed tank 10, D- allulose massecuite from the primary crystalliser 20, and the second crystalliser 50, the mother liquor from the evaporator 40. In an embodiment, the valves may be manually operated or actuator-controlled e.g., programmable logic controller (PLC).

The system 100 includes at one controller coupled to at least one pump 70a, 70b, 70c, 70d, to actuate the pumps to supply, concentration-allulose solution in the feed tank 10, D-allulose massecuite from the primary crystalliser 20 and the secondary crystalliser 50 to separating device 30, recycled supersaturated and / or stock solution from the evaporator 40 to feed tank 10, respectively.

In an embodiment, the rotation rates vary for each agitating device 12, 22, 52. In an embodiment, rotational speed of agitating device 12 in the feed tank 10 is about 150 rpm. Further, rotational speed of agitating device 22, 52 in the primary crystallizers 20 and the secondary crystallizers 50 is about 50-100 RPM including 60-100 RPM, 70-100 RPM, 80-100 RPM. The rotational rates of the agitating devices are maintained in such a way that the uniform concentration gradient can be maintain throughout the primary and secondary crystallizers 20, 50, to enhance the crystal growth kinetics.

In an embodiment, design and dimensions of components of the system 100 such as the feed tank 10, primary crystalliser 20, secondary crystalliser 50, centrifuge 30, evaporator 40, heat exchanger 60etc., can be altered based on the requirements/application.

The present disclosure also provides a method for continuously producing D- allulose crystals. The method comprises the following steps: a) providing a feed stream comprising D-allulose solution; b) feeding the feed stream into a primary crystalliser (20); c) performing crystallisation of D-allulose in the primary crystalliser (20) to obtain D-allulose massecuite; d) continuously withdrawing the D-allulose massecuite from the primary crystalliser and introducing into a separation device (30) to separate D- allulose crystals and the mother liquor from the D-allulose massecuite; e) continuously introducing the separated mother liquor into an evaporator (40); f) concentrating the mother liquor in the evaporator to obtain supersaturated solution of D-allulose; g) recycling the supersaturated solution of D-allulose to the feed stream; and h) washing and drying the separated D-allulose crystals to obtain pure D- allulose crystals.

The D-allulose solution can be obtained by any method known in the art. In some instances, the D-allulose stock solution used in the present disclosure is obtained by the process comprising the following steps (see figure 2):

(i) mixing a sugar source with water or with an aqueous liquid and adjusting the concentration of dissolved sugar, preferably sucrose thereby providing a first solution of sugar source;

(ii) converting the sugar source to glucose and fructose thereby providing a second solution comprising glucose and fructose

(iii) separating the sugar products from the solution by simulated moving bed (SMB) chromatography thereby providing fraction 1 (rich in glucose) and fraction 2 (rich in fructose);

(iv) concentrating the glucose fraction is concentrated and passing through enzymatic bed for conversion of glucose into fructose and sending to SMB for separation of glucose and fructose

(v) converting the fructose in the solution to allulose;

(vi) separating sugar products from the solution by SMB chromatography thereby providing fraction 1 (rich in fructose) and fraction 2 (rich in allulose);

(vii) producing liquid allulose or solid allulose from the fraction 2;

(viii) returning the fraction 1 (rich in fructose) to bioconversion process after concentration.

In certain embodiments, according to step (i), water is added to sugar source such that the final concentration of sugar source, preferably sucrose, is about 30% w/v to 60% w/v. In certain embodiments, the final concentration of sugar source is about 35% w/v or 40% w/v or 45% w/v or 50% w/v or 55% w/v or 60% w/v. In certain embodiments, sugar source is ‘sucrose source’ and denotes any medium, solid or liquid containing sucrose in different concentrations, in particular from about 1 to about 100% of sucrose.

The conversion of the sugar source to glucose and fructose can be done using conventional methods. In certain embodiments, the sugar source is converted to glucose and fructose under heterogeneous or homogeneous catalysis which includes chemical and/or enzymatic catalysis. In some instances, the conversion of the sugar source to glucose and fructose according to step (ii) is performed using a strong cation exchange resin. Suitable resins for a given conversion are known to a skilled person and commercially available. Examples of resins include, but are not limited to, PK216H (Mitsubishi chemicals), C124SH (Purolite; Indion) and 225H (Ion exchange).

In certain embodiments, the mixture of sugars is separated efficiently by using six column SMB. Suitable resins for separation are known to a skilled person and commercially available. Examples of resins include, but are not limited to, UBK 555 (Mitsubishi chemicals), PCR642Ca++(Purolite).

Any suitable enzyme can be used in the process of step (iv). In certain embodiments, the conversion according to step (iv) is performed under enzymatic catalysis by immobilized glucose isomerase enzyme. The conversion of glucose to fructose is carried out at a temperature of about 50-55 °C, at a pH of about 8-9 and with a residence time of about 10-15 min. The enzyme may be freely dissolved or immobilized on a solid carrier. In certain embodiments, the enzyme may be present in dissolved state and may be retained in the reactor by membranes. In yet other embodiments, the enzyme may be immobilized on a solid support. In certain embodiments, the enzyme may be present in microorganisms that in turn are retained in the reactor by membranes. In certain embodiments, the enzyme may be present in microorganisms that in turn are immobilized on a solid support. Examples of solid support materials include, but are not limited to, resins, plastics and glass. The enzyme may also be encapsulated by the solid support material, e.g., in form of alginate beads.

Step (v) can be performed using conventional methods. In certain embodiments, fructose to allulose is done by enzymatic catalysisin the solution to allulose Any suitable enzyme can be used in the process. In certain embodiments, the conversion according to step (v) is performed under enzymatic catalysis by immobilized D-tagatose 3-epimerase. The conversion of fructose to allulose is carried out at a temperature of about 50-55 °C, at a pH of about 8-9 and with a residence time of about 10-15 min. The enzyme may be freely dissolved or immobilized on a solid carrier. In certain embodiments, the enzyme may be present in dissolved state and may be retained in the reactor by membranes. In yet other embodiments, the enzyme may be immobilized on a solid support. In certain embodiments, the enzyme may be present in microorganisms that in turn are retained in the reactor by membranes. In certain embodiments, the enzyme may be present in microorganisms that in turn are immobilized on a solid support. Examples of solid support materials include, but are not limited to, resins, plastics and glass. The enzyme may also be encapsulated by the solid support material, e.g., in form of alginate beads.

Thereafter, the sugar products like glucose and fructose mixture in step(iii) or fructose and allulose mixture in step(vi) are separated by simulated moving bed (SMB) chromatography .

In certain embodiments of method for continuously producing D-allulose crystals, to obtain D-psicose crystals from a D-psicose solution, impurities that may affect the purification and crystallization of D-psicose may be removed. The impurities can be removed by any method known in the art. In certain embodiments, column chromatography may be used for removing the impurities. In certain embodiments, the amount of D-allulose in a D-allulose solution is about 70% to 95% or more.

The D-allulose solution (feed stream) is continuously feed into the primary crystalliser 20 to perform crystallisation thereby providing D-allulose massecuite. In certain embodiments, the feed temperature is about 50-60 °C, or about 55-60 °C. In further embodiments, the crystallization temperature is about 10-35°C. The cooling of D- allulose solution to about 10-35°C or about 25-35 °C prevents local heating during crystallisation, thereby promoting growth size of the crystals and increasing a growth kinetics of the crystals. In certain embodiments, D-allulose solution in the crystalliser is seeded with D-allulose for crystal seeding. In certain embodiments, about 0.5-2% or about 1% seeds are added for crystal seeding. In certain embodiments, the cooled D- allulose solution is introduced into the primary crystallizer 20 at an average feed flow rate of about 15-30 ml/min. In certain embodiments, average feed flow rate is about 20-30 ml/min, or about 20-25 ml/min. The primary crystalliser 20 is provided with an agitating device 22 to stir the stock solution in a predetermined way. The agitation is such that it facilitates no or minimal local concentration and temperature gradients while feeding the stock solution into the primary crystallizer 20. The agitation may further facilitate a higher crystallization rate thereby providing higher concentration of the massecuite leading to a higher crystal yield. In certain embodiments, stirrer speed in the crystallizer is about 80-100 RPM. In certain embodiments, incubation time of D-allulose solution for crystal growth is 30-45 h or about 35-40 h. In further embodiments, the primary crystalliser 20 is a vessel with a cone-shaped bottom having an apex that is pointed downwardly, so that a lower portion of the primary crystalliser tapers to an outlet from which the D-allulose massecuite is withdrawn. The cone-shaped bottom in the primary crystalliser aids in retaining the crystals in the centre of the vessel, and to prevent congregating or stagnation at any point. The cone-shaped extension of the vessel may also result in a considerable increase in the height of the crystallizer vessel, with concomitant requirement for structural support and enclosure. The temperature in the primary crystalliser is maintained through a jacket 21 surrounding the primary crystalliser 20. In certain embodiments, the primary crystallizer 20 may be maintained at a temperature of about 10-35 °C or about 20-25 °C with stirring that is sufficient to ensure no or minimal local concentration and temperature gradients at the time of feeding the stock solution. Further, continuous out flow at the same rate as that of feeding rate is maintained to keep a constant volume in the primary crystallizer 20. The primary crystallizer 20 operates at a steady state in a metastable zone where a rate of crystal growth matches with the difference in inlet and outlet allulose concentrations. The metastable zone prevents spontaneous nucleation of the formed crystals. In certain embodiments, the higher concentration of allulose in the stock solution gets deposited on to the crystals in the crystallizer thereby increasing the total crystal size.

The D-allulose massecuite obtained in the primary crystalliser 20 is continuously withdrawn and introduced into a separation device 30 to separate D-allulose crystals and the mother liquor from the D-allulose massecuite. In certain embodiments, average crystal withdrawn rate is about 15-30 ml/min or about 20-30 ml/min. The separated D- allulose crystals are washed with water and dried in a drying device to obtain pure D- allulose crystals. In certain embodiments, the drying device is a fluidized bed dryer or a vacuum dryer. In some instances, the obtained D-allulose crystals have a purity of about 99 %, and a grain size of 100 m tol50 m. Any suitable device that can be used to separate the crystals from the mother liquor can be used in the method. In certain embodiments, the separation device 30 is a centrifuge device. The separation device 30 may be selected from the group comprising filters, centrifuges, hydro cyclones and gravity settlers. In another embodiment, the centrifuge used in the system of the present disclosure is Pusher - centrifuge.

The separated mother liquor is then introduced into an evaporator 40 and concentrated to obtain a supersaturated solution of D-allulose. The supersaturated solution of D-allulose is recycled to the feed tank to continue the process of recrystallisation.

In certain embodiments, prior to introducing the D-allulose massecuite from the primary crystalliser 20 into the separation device 30, it may be introduced into a secondary crystallizer 50 to perform further crystallization to provide D-allulose massecuite. The further crystallisation in the secondary crystallizer 50 provides more time for further crystal growth of the small crystals of D-allulose obtained from the primary crystalliser 20. The features of secondary crystalliser 50 are similar to those described for the primary crystalliser 20. The D-allulose massecuite obtained in the secondary crystalliser 50 is continuously withdrawn and introduced into the separation device30 to separate D-allulose crystals and the mother liquor from the D-allulose massecuite. Then, the separated D-allulose crystals are washed with water and dried in a drying device to obtain pure D-allulose crystals. In some instances, the obtained D-allulose crystals have a purity of about 99%, and a grain size of about 100-150p.The separation device is same as described above.

The separated mother liquor is then introduced into an evaporator 40 and concentrated to obtain supersaturated solution of D-allulose. The supersaturated solution of D-allulose is recycled to the feed tanklO to continue the process of recrystallisation as described herein.

The present disclosure is further described with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the present disclosure in any manner.

EXAMPLES

In a typical example, the crystallization system comprises two tanks, one for crystallizer and other for storage tank of concentrated solution. The concentrated solution temperature in the storage tank is maintained by circulating hot water in jacket (approx temperature of 55 °C). Approx 54 liters of concentrated Honeytose (also called as D- allulose 85% w/w) from the collection tank is pumped to the crystallizer. The temperature of the solution entering the crystallizer is approx 55 °C. The contents in the crystallizer are cooled to 40 °C and Honeytose seed crystals are added. The amount of seed added is 1.0% of the total Honeytose present in the solution. After seed addition the contents are gently mixed with stirrer RPM 85 and the temperature is reduced to 25 °C. The contents are then held at this temperature for a total residence time of approx 38 hours. After 38 hours, the feed and product withdrawn pumps are started simultaneously. Feed pump is adjusted to give the flow rate approx 20.68 ml/min. The flow rate of input and output are adjusted in such a way that the average residence time for crystallization is maintained same. The output is transferred to the centrifuge for separation of crystals from the mother liquor. The mother liquor obtained is collected in a mother liquor collection tank. The crystals in the centrifuge are washed with cold DM water (6 °C). The solution obtained during the washing step is also collected in the ML collection tank. The crystals are then discharged from the centrifuge and sent to the crystal drying section. The solution in the ML collection tank is pumped to ML evaporator for concentration and the concentrated solution is joining with feed storage tank for further crystallization.

A small amount of sample was collected from online and filtered under vacuum condition in order to separate the mother liquid from crystals. The crystal was dried in oven at the temperature 40°C. Sample was analyzed by using HPLC and the crystal size was checked under microscope. Phase contrast Microscopic (PCM) view of D-allulose crystalsduring continuous crystallisation is shown in figures 3-4. Figure 3 shows D- Allulose crystal size and length distribution from PCM during the continuous crystallization. HPLC chromatogram of crystallizer feed and D-allulose crystals after crystallization are shown in figures 5 and 6 respectively.

Process conditions for continuous crystallization:

Crystallization temperature 22 -25 °C Stirrer speed in crystallizer 85-100 RPM Starting volume 54 Ltrs Amount of seed added 1% of total Allulose Incubation time for crystal growth 35-40 h Feed temperature 55 °C EXAMPLE 1:

• Average Feed flow rate : 20.68 ml/min (approx)

• Average Crystal withdrawn rate : 23.16ml/min (approx) EXAMPLE 2:

• Average Feed flow rate : 28.34 ml/min (approx)

• Average Crystal withdrawn rate : 28.2 ml/min (approx)

Advantages of the present disclosure are illustrated herein:

The present disclosure relates to a method and a system that is simple, easy to operate and affordable.

The method and system according to the present disclosure is easy and inexpensive to manufacture.

The method and system according to the present disclosure enables withdrawal of D- allulose crystals continuously.

Claims

THE CLAIM:

1. A system (100) for crystallizing D-alluslose solution, the system (100) comprising: a feed tank (10) to store and supply concentrated D- allulose solution; one or more crystallizers (20, 50) fluidly connected to the feed tank (10), each of the one or more crystallizers (20,50) configured to selectively receive the concentrated D-allulose solution from the feed tank (10) and to crystallize the received concentrated D-allulose solution for obtaining D-allulose massecuite; and a separating device (30), fluidly connected to the one or more crystallizers (20,50), to continuously receive the D-allulose massecuite and to continuously separate a plurality of D-allulose crystals and mother liquor present in the D- allulose massecuite; an evaporator (40), fluidly connected to the separating device (30) and the feed tank (10), the evaporator (40) being configured to receive the mother liquor from the separating device (30) concentrate the mother liquor to form super saturated D- allulose solution, wherein the super saturated D- allulose solution is recycled to the feed tank (10); and at least one drying device, fluidly connected to the separating device (30), to wash and dry the D-allulose crystals.

2. The system (100) as claimed in claim 1, wherein one or more crystallizers (20, 50) comprises a primary crystallizer (20) to crystallize the concentrated D-allulose solution for obtaining the D-allulose massecuite, and a secondary crystallizer (50) to increase a crystal growth of existing plurality of D-allulose crystals present in the D-allulose massecuite obtained from the primary crystallizer (20).

3. The system as claimed in claim 2, wherein each of the one or more crystallizers (20, 50) comprises an agitating device (22) configured to stir the D-allulose solution to facilitate a higher rate of crystal growth formed therein.

4. The system as claimed in claim 3, wherein each of the one or more crystallizers (20, 30) is surrounded by a fluid circulation jacket (21, 51) for circulating a fluid to maintain the concentrated D-allulose solution at a temperature range of 25-35 °C during separation of the plurality of D-allulose crystals and mother liquor from the D-allulose massecuite.

5. The system (100) as claimed in claim 1, comprises at least one heat exchanger (60) disposed between the feed tank (10) and the one or more crystallizers (20, 50) maintain the concentrated D-allulose solution at a predetermined temperature.

6. The system (100) as claimed in claim 1, wherein separating device (30) is at least one centrifuge device, wherein the centrifuge device is at least one of filters, centrifuges, hydro cyclones and gravity settlers. . The system (100) as claimed in claim 1, wherein a plurality of pumps () are fluidly connected to the feed tank (10), the one or more crystallizers (20, 50), the separating device (30), the evaporator (60) and the drying device.

8. The system (100) as claimed in claim 1, wherein a plurality of valves () is fluidly connected to the feed tank (10), the one or more crystallizers (20, 50), the separating device (30), the evaporator (60) and the drying device to regulate a flow of concentrated D- allulose solution, D-allulose massecuite and mother liquor, respectively.

9. The system (100) as claimed in claim 1, comprises a washing fluid tank fluidly connected to the drying device for supplying a washing fluid to wash the plurality of D-allulose crystals.

10. The system as claimed in claim 1, whereon the feed tank (10) is having the agitator device (12) to uniformly stir the concentrated D-allulose solution.

11. A method for continuously producing D-allulose crystals, said method comprising: a) providing a feed stream comprising D-allulose solution; b) feeding the feed stream into a primary crystalliser (20); c) performing crystallisation of D-allulose in the primary crystalliser (20) to obtain D-allulose massecuite; d) continuously withdrawing the D-allulose massecuite from the primary crystalliser and introducing into a separation device (30) to separate D- allulose crystals and the mother liquor from the D-allulose massecuite; e) continuously introducing the separated mother liquor into an evaporator (40); f) concentrating the mother liquor in the evaporator to obtain supersaturated solution of D-allulose; g) recycling the supersaturated solution of D-allulose to the feed stream; and h) washing and drying the separated D-allulose crystals to obtain pure D- allulose crystals.

12. The method as claimed in claim 11, wherein the amount of D-allulose in the feed stream of D-allulose solution is about 70% to 95% or more.

13. The method as claimed in claim 11, wherein the feed temperature is about 50-60 °C.

14. The method as claimed in claim 11, wherein average feed flow rate is aboutl5-30 ml/min.

15. The method as claimed in claim 11, wherein the crystallization temperature is about 10-35°C.

16. The method as claimed in claim 11, wherein the crystallization temperature is about 20-25°C.

17. The method as claimed in claim 11, wherein stirrer speed in the crystallizer is about 80-100 RPM.

18. The method as claimed in claim 11, wherein incubation time for crystal growth is about 35-40 h.

19. The method as claimed in claim 11, wherein average crystal withdrawn rate is 15- 30 ml/min. 0. The method as claimed in claim 11, wherein the primary crystalliser (20) is a vessel with a cone-shaped bottom having an apex that is pointed downwardly, so that a lower portion of the primary crystalliser tapers to an outlet from which the D-allulose massecuite is withdrawn. 1. The method as claimed in claim 11, wherein continuous out flow at the same rate as that of feeding rate is maintained to keep a constant volume in the primary crystallizer (20). The method as claimed in claim 11, wherein the drying device is a fluidized bed dryer or a vacuum dryer. The method as claimed in claim 11, further comprising introducing the D-allulose massecuite from the primary crystalliser (20) into a secondary crystallizer (50) prior to introducing the D-allulose massecuite from the primary crystalliser 20 into the separation device (30).