EP1041161B1 - Process for preparing an alpha crystalline anhydrous dextrose of high purity - Google Patents

Abstract

Anhydrous crystalline alpha -dextrose (I) is prepared by preparing a starch hydrolyzate; subjecting the product to nanofiltration on a membrane, to give a syrup of high glucose content as permeate; concentrating the syrup to solids and crystallizing by evaporation to give (I) crystals. Preparation of anhydrous crystalline alpha -dextrose (I) involves: (a) preparing a starch hydrolyzate; (b) subjecting the product to nanofiltration on a membrane, to give a syrup of high glucose content as permeate; (c) concentrating the syrup to a solids content of at least 70 wt. % glucose at 50-110 degrees C; (d) crystallizing by evaporation and stirring to give a crystalline mass containing at least 30 wt. % crystals; and (e) separating, recovering and drying the obtained (I) crystals.

Description

The present invention relates to a method of high crystalline anhydrous dextrose α preparation purity from a starch hydrolyzate.

More particularly, the invention relates to a process for the preparation of an anhydrous crystalline dextrose which consists in subjecting a starch hydrolyzate to a nanofiltration to prepare a syrup with a high content of glucose, then evaporate the syrup of glucose thus obtained to obtain crystals of high purity anhydrous dextrose α.

Dextrose can come in three forms crystalline, hydrated form or α monohydrate form, and two anhydrous forms, i.e. α anhydrous and β anhydrous.

Solid dextrose is conventionally produced by crystallization of supersaturated syrups with a high content of glucose, and the crystals collected are crystals of dextrose α monohydrate. This process is also described in US Patent 3,039,935.

Anhydrous dextrose α is classically obtained by dissolving crystals of dextrose α monohydrate in water, then by crystallizing at temperatures between 60 and 65 ° C and in vacuum evapo-crystallization operating conditions carefully set.

• le procédé décrit dans le brevet US 3.197.338, consistant à concentrer un hydrolysat d'amidon à une matière sèche en dextrose d'au moins 95 % sur sec, de préférence d'au moins 98 % sur sec, à le cristalliser par malaxage à une température comprise entre 75 et 110°C, et à l'extruder sous la forme d'un ruban dans une zone qui refroidit le produit à une température inférieure à 65,5 °C,
• le procédé décrit dans le brevet US 3.236.687, consistant à concentrer un hydrolysat d'amidon à une matière sèche en dextrose d'une valeur comprise entre 93 et 96 % sur sec et à le soumettre à un fort cisaillement en présence de gaz pour former de très petits cristaux de dextrose,
• le procédé décrit dans le brevet US 4.059.460, consistant à préparer un concentré fondu d'un sirop de glucose ayant une concentration de 85 à 93 % sur sec, à une température supérieure à 110°C. Le sirop de glucose concentré est ensuite mélangé par cisaillement et refroidi à une température inférieure à 95 °C. Le sirop est enfin maintenu à une concentration inférieure à 93 % et à une température supérieure à la température de cristallisation du dextrose α monohydrate, puis façonné et transformé en masse solide. Cette masse solide est alors granulée et déshydratée à une teneur en eau inférieure à 2 %.

There are also a number of processes allowing the manufacture of anhydrous dextrose from starch hydrolysates, for example:

• the process described in patent US Pat. at a temperature between 75 and 110 ° C, and extruding it in the form of a ribbon in an area which cools the product to a temperature below 65.5 ° C,
• the process described in patent US Pat. form very small dextrose crystals,
• the process described in US Pat. No. 4,059,460, consisting in preparing a molten concentrate of a glucose syrup having a concentration of 85 to 93% on a dry basis, at a temperature above 110 ° C. The concentrated glucose syrup is then mixed by shearing and cooled to a temperature below 95 ° C. The syrup is finally maintained at a concentration of less than 93% and at a temperature above the crystallization temperature of the dextrose α monohydrate, then shaped and transformed into a solid mass. This solid mass is then granulated and dehydrated to a water content of less than 2%.

• celui d'utiliser directement des hydrolysats d'amidon qui contiennent, outre le glucose, des proportions non négligeables d'autres sucres de degré de polymérisation (D.P.) supérieur, par exemple des D.P. 2 (tel le maltose) et D.P. 3 (tel le maltotriose). Ces sucres de D.P. supérieur résultent de l'hydrolyse non totale, qu'elle soit chimique ou enzymatique, dudit hydrolysat d'amidon.
• celui de conduire à des mélanges des deux formes anhydres du dextrose, au mieux en proportion équivalentes, voire favorisant la forme β anhydre, et s'accompagnant parfois de la présence de dextrose α monohydrate, résultant de l'incorporation de l'humidité résiduelle en eau de recristallisation.

However, all of these methods have two major drawbacks:

• that of directly using starch hydrolysates which contain, in addition to glucose, significant proportions of other sugars with a higher degree of polymerization (DP), for example DP 2 (such as maltose) and DP 3 (such as maltotriose). These higher DP sugars result from the non-total hydrolysis, whether chemical or enzymatic, of said starch hydrolyzate.
• that of leading to mixtures of the two anhydrous forms of dextrose, at best in equivalent proportions, even favoring the anhydrous β form, and sometimes accompanied by the presence of dextrose α monohydrate, resulting from the incorporation of residual moisture into recrystallization water.

The crystalline dextroses obtained by these processes have a strong tendency to agglomerate, which makes handling all the more difficult. Their flow characteristics are otherwise particularly poor.

To solve the first and main drawback described above and lead to obtaining a dextrose of more homogeneous crystal structure, it has been proposed in FR 2,483,427 to concentrate a starch hydrolyzate to a glucose dry matter of about 92 to 99%, from preferably about 95 to 99% in a layer evaporator thin and at a temperature between 90 and 135 ° C.

But the product obtained still has more than 50% of anhydrous β form with the anhydrous α form, and a content in non-negligible amorphous structure.

The anhydrous character is obtained in this process thanks to at the particularly high temperatures used, but these operating conditions also have the consequence direct to increase the proportion in anhydrous β form which naturally crystallizes at said temperatures.

As for the problem linked to sugar contamination of D.P. higher starch hydrolysates, it has been proposed two solutions.

The first is to optimize the process of preparation of said starch hydrolyzate.

However, if this solution reduces the share of sugars from D.P. 2 and D.P. 3 remarkably, it is particularly difficult to obtain contents residuals less than 5%.

The second solution consists in implementing a nanofiltration process which removes all traces of these superior PDs, as described in the request for Patent FR 2,762,616 of which the Applicant company is holder, or US patent 5,869,297.

From all of the above, however, it follows that there is an unmet need for a dextrose high purity α-anhydrous lens.

Indeed, all the processes of the prior art do not allow to have only solid dextrose constituted a mixture of anhydrous α and β forms, or even forms monohydrates, associated with relatively large amounts significant of D.P. 2, D.P. 3, or even D.P. higher.

The invention therefore aims to remedy this situation, and to propose a process that responds better than those that already exist to the various constraints of the convenient.

Indeed, it appears clearly in the state of technique than conventional processes for preparing anhydrous dextrose which require for example the work of two successive crystallization techniques, take place in areas of high temperature which invariably lead to mixtures of forms α and β crystals.

The Applicant company thus succeeded in bringing point a process for obtaining an anhydrous dextrose high purity crystalline from high syrup glucose content prepared by nanofiltration of a starch hydrolyzate.

Within the meaning of the invention, the term “dextrose anhydrous α crystalline of high purity ", a content of anhydrous dextrose α of approximately 100% by weight.

(a) prépare un hydrolysat d'amidon ;

(b) nanofiltre sur membranes ledit hydrolysat d'amidon de manière à obtenir un perméat de nanofiltration constituant un sirop à haute teneur en glucose et un rétentat de nanofiltration ;

(c) concentre ledit sirop à haute teneur en glucose à une matière sèche d'au moins 70 % en poids de glucose et à une température comprise entre 50 et 110°C ;

(d) cristallise ledit sirop concentré par évaporation et agitation de manière à obtenir une masse cristalline renfermant au moins 30 % en poids de cristaux ;

(e) sépare, récupère et sèche les cristaux de dextrose α anhydre ainsi obtenus.

The process for preparing a crystalline anhydrous α dextrose according to the invention is therefore characterized by the fact that:

(a) prepares a starch hydrolyzate;

(b) nanofilter on membranes, said starch hydrolyzate so as to obtain a nanofiltration permeate constituting a syrup with a high glucose content and a nanofiltration retentate;

(c) concentrating said syrup with a high glucose content at a dry matter of at least 70% by weight of glucose and at a temperature between 50 and 110 ° C;

(d) crystallizes said concentrated syrup by evaporation and stirring so as to obtain a crystalline mass containing at least 30% by weight of crystals;

(e) separates, collects and dries the crystals of anhydrous α dextrose thus obtained.

• liquéfaction d'un lait d'amidon à l'aide d'une α-amylase de façon à obtenir un lait d'amidon liquéfié,
• saccharification dudit lait d'amidon liquéfié à l'aide d'une enzyme glucogénique de manière à obtenir un hydrolysat saccharifié brut, et
• éventuellement, microfiltration dudit hydrolysat saccharifié brut de manière à recueillir un perméat de microfiltration comprenant ledit hydrolysat d'amidon brut et un rétentat de microfiltration.

According to a first embodiment of the process according to the invention, said starch hydrolyzate is a crude starch hydrolyzate obtained by:

• liquefaction of a starch milk using an α-amylase so as to obtain a liquefied starch milk,
• saccharification of said liquefied starch milk using a glucogenic enzyme so as to obtain a crude saccharified hydrolyzate, and
• optionally, microfiltration of said crude saccharified hydrolyzate so as to collect a microfiltration permeate comprising said crude starch hydrolyzate and a microfiltration retentate.

• liquéfaction d'un lait d'amidon à l'aide d'une α-amylase de façon à obtenir un lait d'amidon liquéfié,
• saccharification dudit lait d'amidon liquéfié à l'aide d'une enzyme glucogénique de manière à obtenir un hydrolysat d'amidon saccharifié brut d'une richesse d'au maximum 80 % en poids, et de préférence d'au maximum 75 % en poids, et
• microfiltration de l'hydrolysat saccharifié brut de manière à recueillir un perméat de microfiltration comprenant ledit hydrolysat d'amidon brut et un rétentat de microfiltration.

According to a second embodiment of the process according to the invention, said starch hydrolyzate is a crude starch hydrolyzate obtained by:

• liquefaction of a starch milk using an α-amylase so as to obtain a liquefied starch milk,
• saccharification of said liquefied starch milk using a glucogenic enzyme so as to obtain a crude saccharified starch hydrolyzate with a richness of at most 80% by weight, and preferably at most 75% by weight, and
• microfiltration of the crude saccharified hydrolyzate so as to collect a microfiltration permeate comprising said crude starch hydrolyzate and a microfiltration retentate.

For the purposes of the present invention, the term “ raw saccharified starch hydrolyzate, a hydrolyzate starch free of insoluble matter and not undergone no purification treatment aimed at eliminating soluble matter (enzymes, proteins, amino acids, dyes, salts, ...).

So unlike the state teaching of technique which classically provides, at the end of saccharification, a step of inhibiting the enzyme saccharification (to avoid the formation of reversion), we therefore seek on the contrary in this invention to maintain enzymatic activity saccharifying within the starch hydrolyzate saccharified.

We also seek, in the present invention, to maintain the presence of fillers within the hydrolyzate saccharified starch. In conventional methods of the state of the art, these charges are conventionally eliminated by passage of the saccharified starch hydrolyzate on carbon black and on a resin of demineralization. In the present invention, the hydrolyzate is not demineralized.

It is preferable, advantageously in the conforming process to the invention, carry out a controlled hydrolysis of milk starch so as to obtain a liquefied starch milk at low transformation rate.

Thus, in the process according to the invention, one preferably leads the liquefaction stage to a DE between 2 and 10, and more particularly up to a DE between 4 and 8.

Preferably, the liquefaction stage is carried out in two sub-stages, the first consisting in heating, for a few minutes and at a temperature included between 105 and 108 ° C, starch milk in the presence of the enzyme (type THERMAMYL 120L sold by the company NOVO) and a calcium activator, the second consisting in heating the starch milk thus treated, to a temperature between 95 and 100 ° C for one to two hours.

Once the liquefaction stage is complete, within dry matter content, pH, rate conditions enzyme and calcium well known to those skilled in the art and after advantageously inhibiting the liquefying enzyme (by proceeding, for example, out of liquefaction to a thermal shock of a few seconds at a temperature greater than or equal to 130 ° C), we proceed to the step of saccharification of liquefied starch milk.

During this step, the starch milk is subjected liquefied by the action of a glucogenic enzyme, in particular chosen from the group consisting of amyloglucosidase, the glucoamylase or any other glucogenic enzyme.

To avoid reversion reactions and formation in particular of disaccharides (maltose, isomaltose) by repolymerization of glucose, it can be interesting to associate with the glucogenic enzyme a hydrolyzing enzyme specifically the α-1,6 bonds of starch. Of preferably, this debranching enzyme is isoamylase or pullulanase.

The saccharification stage is carried out in conditions and in a manner known in themselves, during approximately 12 hours to no more than 24 hours, so as to obtain a final hydrolyzate with a richness of between 50%, preferably 75%, and 95% by weight.

• α-amylase : 20 à 2.000 KNU (Kilo Novo Units) par kilogramme de substrat sec, température de 80 à 150°C, durée d'action de 2 à 15 minutes.
• amyloglucosidase : 4.000 à 400.000 unités internationales par kilogramme de substrat sec, température de 50°C à 60°C, durée d'action de 12 à au maximum 24 heures, pH de 4 à 6.
• pullulanase : 150 à 15.000 unités ABM.

The quantities and the conditions of action of the different enzymes used in the process according to the invention are chosen from the following:

• α-amylase: 20 to 2,000 KNU (Kilo Novo Units) per kilogram of dry substrate, temperature from 80 to 150 ° C, duration of action from 2 to 15 minutes.
• amyloglucosidase: 4,000 to 400,000 international units per kilogram of dry substrate, temperature from 50 ° C to 60 ° C, duration of action from 12 to maximum 24 hours, pH from 4 to 6.
• pullulanase: 150 to 15,000 ABM units.

The enzymes used can be of origin bacterial or fungal.

The hydrolyzate thus saccharified is then preferably filtered preferably by microfiltration on membranes so as to collect a permeate microfiltration comprising the crude saccharified hydrolyzate and a microfiltration retentate. The conditions of this treatment, especially in terms of temperature, are chosen to maintain activity saccharifying enzyme within the starch hydrolyzate saccharified. This is why, according to an embodiment preferred of the invention, the microfiltration of raw saccharified hydrolyzate at a lower temperature or equal to the enzyme inhibition temperature glucogenic (the enzyme of saccharification) and, advantageously, at a substantially equivalent temperature at the saccharification temperature. So if the saccharification temperature is between 50 ° C and 60 ° c, microfiltration must be carried out at a temperature between 50 ° C and 60 ° C.

The microfiltration membrane used in the process according to the invention, advantageously presents a porosity between 50 nm and 200 nm, said porosity preferably being of the order of 50 nm. The operating temperature is between 50 ° C and 60 ° C and the pressure (transmembrane) is between 1 and 2 bars. An advantageously put microfiltration membrane used in the process according to the invention is that marketed by the company SCT (channels with a diameter of 4 mm).

We then carry out on this saccharified hydrolyzate raw, possibly microfiltered but not demineralized, a separation by nanofiltration on membranes so as to collect a nanofiltration permeate constituting the syrup with high glucose content, of higher richness 97% and more preferably still greater than 99%, and a nanofiltration retentate.

Against all expectations, the Applicant Company has effect observed, under the same operating conditions, better enrichment of the permeate with glucose when the hydrolyzate saccharified to nanofiltrate was not demineralized. Without want to be linked to any theory, Society Applicant thinks that this better enrichment is due to the formation of a larger polarization layer at the surface of the membrane, the formation of this layer of additional filtration to obtain a richness into higher permeate glucose.

According to a preferred embodiment, the separation on membranes is carried out under conditions of temperatures between 30 ° C and 60 ° C, preferably between 40 ° C and 50 ° C and pressures included between 15 and 35 bars, and preferably between 20 and 30 bars. So the nanofiltration membrane advantageously implemented in the process according to the invention is of the NF40 type marketed by the company FILMTEC or DESAL 5 DL 3840 type marketed by DESALINATION SYSTEMS.

Advantageously, then a saccharification of at least part of the retentate of nanofiltration so as to obtain a retentate of saccharified nanofiltration. This saccharification secondary (with reference to primary saccharification intervening upstream of the microfiltration stage) is possible because throughout the process according to the invention, the necessary was made to maintain a saccharifying enzymatic activity within the hydrolyzate especially at the level of the saccharification stage in not inhibiting the glucogenic enzyme at the end of hydrolysis and at the microfiltration stage by working in temperature conditions similar to that of step - of saccharification.

According to a variant of the process according to the invention, at least part of the retentate is recycled nanofiltration upstream of the separation step by nanofiltration on membranes. More specifically, we mixes at least part of the nanofiltration retentate with microfiltration permeate to form a mixture which is then advantageously saccharified. This secondary saccharification (here before the stage of separation by nanofiltration on membranes) is carried out for a period such that the saccharified mixture presents a glucose richness of at most 80%, and preferably 75% by weight.

In the case of secondary saccharification intervened upstream of the nanofiltration stage, we then performs a tertiary saccharification of the retentate nanofiltration so as to obtain a retentate of saccharified nanofiltration. The duration of this tertiary saccharification is approximately 48 hours.

It is then possible to perform on this saccharified nanofiltration retentate (obtained after implementation of secondary saccharification or tertiary), which can be rich in glucose up to 90%, molecular sieving so as to collect a fraction enriched in glucose and a fraction depleted in glucose.

This molecular sieving step can consist, for example, in a chromatographic separation step or in a separation step on membranes.

The chromatographic fractionation step is carried out in a manner known per se, discontinuously or continuous (simulated moving bed), on adsorbents of the type cationic resins, or on strongly acidic zeolites, preferentially charged using alkaline ions or alkaline earth such as calcium or magnesium but more preferably using sodium ions.

According to a preferred embodiment, the chromatographic fractionation is carried out using the process and the apparatus described in the patent American US-A-4,422,881 of which the applicant company is holder. Whatever the chromatographic process selected, recourse is preferably made to the adsorbent, to a strong cationic resin used under sodium or potassium form and crosslinked with about 4 to 10 % of divinylbenzene. The resins are advantageously of homogeneous particle size and between 100 and 800 micrometers.

In place of the separation step chromatographic it is possible in the process according to the invention, to implement a step of separation by nanofiltration on membranes, of the type of the one described above.

The fraction enriched in glucose obtained at the outlet of the chromatography step can then be mixed with the syrup with high glucose content previously obtained.

The following stages of the process according to the invention then consists in evapo-crystallizing the high glucose syrup thus obtained to obtain a high purity anhydrous α crystalline dextrose.

The third step (c) of the process according to the invention therefore consists in concentrating the syrup at high glucose content in a dry matter of at least 70% in weight.

This concentration step is carried out so known per se, for example by evaporation of water under vacuum at a temperature of the order of 70 ° C.

Temperature and dry matter conditions are thus specifically fixed to place the syrup glucose in the crystallization domain of the α form Anhydrous.

It is in fact known to those skilled in the art that for a high purity glucose solution, dextrose α anhydrous crystallizes in a temperature range included between 50 and 110 ° C, for an M.S. greater than 70%.

In the process according to the invention, the concentration of syrup enriched with glucose can reach a value of around 80% in M.S. Preferably, we then places at a temperature of the order of 70 ° C.

In a first preferential mode in accordance with the invention, crystallization is initiated by the addition of anhydrous dextrose α in concentrated glucose syrup and under agitation.

In a second mode of the process in accordance with the invention, spontaneous nucleation is carried out by any method known per se by a person skilled in the art, for example by shearing said concentrated solution.

The fourth step (d) of the process according to the invention consists in continuing crystallization by evaporation and stirring of said concentrated syrup so as to obtain a crystalline mass containing at least 30% by weight of crystals.

The residence time in the evaporator-crystallizer is around 5 to 8 hours, preferably for 6 hours, at a temperature of the order of 70 ° C.

In a preferred embodiment according to the invention, the evapo-crystallization is carried out in a rotary evaporator where a relatively high vacuum is established, of the order of 6.67 10 ³ Pa (50 mm Hg).

At the end of evapo-crystallization, the last stage of process according to the invention consists in separating, recover and dry the anhydrous dextrose crystals thus obtained.

The crystalline mass containing at least 30% of individualized crystals is then separated from the liquor mother by all known methods in themselves, by example by spinning or filtering the α dextrose syrup anhydrous crystallized.

Preferably, the crystals are then purified by clearing with water, then dried at a lower temperature at the melting point of anhydrous dextrose α, preferably at a temperature of around 60 ° C, by any method also known, for example in an oven, or on a fluidized bed.

The implementation of the process according to the invention produces crystals with a richness of the order of 100% in anhydrous α form.

Other characteristics and advantages of the invention will appear on reading the examples described below.

EXAMPLE 1

Starch milk is conventionally liquefied at using 0.5 per thousand THERMAMYL 120L (α-amylase marketed by the company NOVO) up to a DE of 6.5.

The reaction medium is then heated for a few seconds at 140 ° C. so as to inhibit the α-amylase.

Then, in a manner known per se, the saccharification of the hydrolyzate to 35% dry matter in the presence of 0.8 per thousand of amyloglucosidase G990 marketed by ABM (temperature: 60 ° C, pH = 4,5).

glucose : 93 %

DP2 : 2,5 %

DP3 : 0,5 %

DP supérieurs : 4 %

   étant entendu que l'abbréviation "DP" signifie degré de polymérisation.After 24 hours of saccharification, a hydrolyzate is obtained having the following carbohydrate spectrum:

glucose: 93%

DP2: 2.5%

DP3: 0.5%

Senior DP: 4%

it being understood that the abbreviation "DP" signifies degree of polymerization.

The enzymatic activity measured is 3 U / l.

The hydrolyzate thus saccharified is then filtered by microfiltration on membranes.

• Membrane SCT : 50nm
• Température : 60°C
• Pression : 2 bars

The operating conditions are as follows:

• SCT membrane: 50nm
• Temperature: 60 ° C
• Pressure: 2 bars

The enzymatic activity measured is 2.5 U / l

The hydrolyzate thus microfiltered is separated into two to form a hydrolyzate A and a hydrolyzate B.

The hydrolyzate A is not demineralized. Hydrolyzate B is demineralized by passing over black carbon and resin.

• Membrane DESAL 5 DL
• Température : 45°C
• Pression : 25 bars

Each of the hydrolysates A and B is subjected to nanofiltration under the following operating conditions:

• DESAL 5 DL membrane
• Temperature: 45 ° C
• Pressure: 25 bars

The characteristics of the nanofiltration permeates and retentates A and B of hydrolysates A and B are as follows: glucose / purity Enzymatic activity Permeate A 99.7% 0 U / l Retentate A 80% 7 U / l Permeate B 98.5% 0 U / l Retentate B 80% 0 U / l

EXAMPLE 2

Liquefaction and saccharification are carried out starch milk as described in Example 1.

glucose : 75,8 %

DP2 : 2,1%

DP3 et supérieurs : 20,1 %

After 12 hours of saccharification, a hydrolyzate is obtained having the following carbohydrate spectrum:

glucose: 75.8%

DP2: 2.1%

DP3 and above: 20.1%

The enzymatic activity measured is 3 U / l.

The hydrolyzate thus saccharified is then filtered by microfiltration on membranes, under the same conditions than example 1.

The enzymatic activity measured is 2.5 U / l

The hydrolyzate thus microfiltered is separated into two to form a hydrolyzate C and a hydrolyzate D.

The hydrolyzate C is not demineralized. Hydrolyzate D is demineralized by passing over black carbon and resin.

• Membrane DESAL 5 DL
• Température : 45°C
• Pression : 25 bars

Each of the hydrolysates C and D is subjected to nanofiltration under the following operating conditions:

• DESAL 5 DL membrane
• Temperature: 45 ° C
• Pressure: 25 bars

The characteristics of the C and D nanofiltration permeates and retentates of the C and D hydrolysates are as follows: glucose / purity Enzymatic activity Permeate C 99.4% 0 U / l Retentate C 50% 7 U / l Permeate D 97.9% 0 U / l Retentate D 50% 0 U / l

EXAMPLE 3

Permeate A of Example 1 (99.4% richness in glucose) is concentrated to 80% dry matter, by evaporation at 70 ° C, and placed in a rotary evaporator of 2 1 usable volume laboratory marketed by BÜCHI company.

The temperature is maintained at 70 ° C, and the crystallization by adding 5 g of anhydrous dextrose.

Evapo-crystallization is carried out for 6 h, in continuously feeding with concentrated glucose syrup to 30% of M.S. at a flow rate of 1 l / h.

At the end of evapo-crystallization, 3 kg of a crystalline mass containing 50.8% by weight of crystals individualized.

The crystals are then separated from the mother liquor by centrifugation at 1000 g for 10 min with a laboratory wringer marketed by the company Rousselet.

During this centrifugation, clearing is carried out crystals with 200 ml of demineralized water.

The crystals are finally dried in a bed drier fluidized for 15 min at 60 ° C.

The crystallization yield is 56% by weight, expressed by weight of anhydrous dextrose α crystallized on the total dry matter weight.

The purity of the crystals recovered is 99.7% over dry. The water content is 0.2%.

Claims (9)

1. A process for preparing a crystalline α-anhydrous dextrose characterised in that:

   a) a starch hydrolysate is prepared;

   b) said starch hydrolysate is nanofiltered over membranes in such a way as to obtain a nanofiltration permeate consisting of a syrup with a high glucose content and a nanofiltration retentate;

   c) said syrup with a high glucose content is concentrated to a dry matter content of at least 70 wt.% of glucose, at a temperature in the range 50°C to 110°C;

   d) said concentrated syrup is crystallised by evaporation and agitation in such a manner as to obtain a crystalline mass containing at least 30 wt.% of the crystals;

   e) the crystals of α-anhydrous dextrose thus obtained are separated, recovered and dried.
2. A process according to Claim 1, characterised in that said starch hydrolysate is a crude starch hydrolysate obtained by:

   liquefaction of a starch milk using an α-amylase in such a way as to obtain a liquefied starch milk,

   saccharification of said liquefied starch milk using a glucogenic enzyme in such a manner as to obtain a crude saccharified hydrolysate, and

   optionally, microfiltration of said crude saccharified hydrolysate in such a manner as to recover a microfiltration permeate containing said crude starch hydrolysate and a microfiltration retentate.
3. A process according to Claim 1, characterised in that said starch hydrolysate is a crude starch hydrolysate obtained by:

   liquefaction of a starch milk using an α-amylase in such a way as to obtain a liquefied starch milk,

   saccharification of said liquefied starch milk using a glucogenic enzyme in such a manner as to obtain a crude saccharified starch hydrolysate with a maximum concentration of 80 wt.%, preferably a maximum concentration of 75 wt.%, and

   microfiltration of the crude saccharified hydrolysate in such a manner as to recover a microfiltration permeate containing said crude starch hydrolysate and a microfiltration retentate.
4. A process according to Claim 2 or Claim 3, characterised in that microfiltration of the saccharified crude starch hydrolysate is performed at a temperature less than or equal to the inhibition temperature of the glucogenic enzyme.
5. A process according to Claim 3 or Claim 4, characterised in that at least part of the nanofiltration retentate is mixed with the microfiltration permeate in order to form a mixture and that said mixture is saccharified.
6. A process according to any one of Claims 1 to 5, characterised in that:

   at least part of the nanofiltration retentate is saccharified in such a way as to obtain a saccharified nanofiltration retentate;

   said saccharified nanofiltration retentate is subjected to molecular sieving in such a manner as to obtain a fraction enriched in glucose, and

   said fraction enriched in glucose is mixed with said syrup containing a high concentration of glucose.
7. A process according to any one of Claims 1 to 6, characterised in that the syrup with a high glucose content has a glucose concentration greater than 97%, preferably greater than 99%.
8. A process according to any one of Claims 1 to 7, characterised in that the stage in which the syrup with a high glucose content is concentrated is performed by evaporation at a temperature of about 70°C.
9. A process according to any one of Claims 1 to 8, characterised in that the α-anhydrous dextrose crystals obtained after the stage in which the syrup with a high concentration of glucose is crystallised are collected by centrifuging and dried at a temperature of about 60°C.