RO119469B1 - Process for obtaining a starch hydrolysate with high content of dextrose - Google Patents

Abstract

The invention relates to a process for obtaining a starch hydrolysate with high content of dextrose, which consists in: a) liquefying a starch milk by means of an alpha-amylase so as to obtain a liquid starch milk; b) saccharifying the liquefied starch milk by means of a glucogenic enzyme, in order to obtain a saccharified hydrolysate; c) molecular by selecting the mentioned saccarified hydrolysate, to obtain a hydrolysate with high content of dextrose; and it is characterized by the fact that, between the stage a) and the stage b) there is a stage of inhibiting the alpha-amylase.

Description

The invention relates to a process for obtaining a starch hydrolyzate with high dextrose content.

The object of the invention is also a process for obtaining sorbitol, starting from a starch hydrolyzate with a high dextrose content, obtained by applying the process according to the invention.

It is known to manufacture starch hydrolysates, for which the value of the dextrose equivalent (reducing power expressed in dry matter glucose, hereinafter referred to as DE) is from 2 to 98 and which, according to this value, may contain up to 96% true dextrose. Different qualities of starch hydrolysates are obtained, by choosing the conditions of starch hydrolysis starting. The nature of hydrolysis is also involved, ie it is acidic or enzymatic.

Starch hydrolysates rich in dextrose, although they have many fields of application, serve mainly as a raw material for the manufacture of crystallized dextrose or as a substrate for the manufacture of fructose by isomerization. For these two applications, the highest possible conversion is sought, that is, as much dextrose content as possible, with a minimum content of impurities.

The starch conversion processes, which use an acid, lead to starch hydrolysates whose dextrose content does not exceed 85 ... 90%. Indeed, these processes promote concurrent reactions of dextrose reversal and internal dehydration.

Starch conversion processes, which use both an acid and an enzyme (generally glucoamylase), result in starch hydrolysates whose dextrose content is never higher than 93%. Indeed, in these processes, acid hydrolysis of starch produces strongly branched sugars, which are resistant to the action of glucoamylase.

Starch hydrolysates obtained by double enzymatic conversion with amylase and amyloglucosidase (or glucoamylase) generally contain between 93 and 95% true dextrose and contain between 5 and 7% residual oligosaccharides and polysaccharides, most of which are made up of disaccharide. maltose and isomaltose).

These hydroxylates are classically obtained by liquefying starch up to a DE value of 12-20, followed by a saccharification of amyloglucosidase, but under these conditions, the true dextrose content may not exceed 94-95%.

In order to reach a higher content of true dextrose, several methods are proposed, either to improve the conversion of starch by limiting the formation of by-products, or to improve the efficiency of the separation between dextrose and by-products (oligosaccharides and polysaccharides).

Thus, a first process consists in performing the liquefaction and sugaring stages at a very low content of dry matter (of the order of 5-10%). But even at these small values of dry matter, the true dextrose content does not exceed 95 - 97% in addition, such a process is not economically profitable, due to the energy required to evaporate the water.

Another process is to carry out the sugars in the presence of an enzyme that hydrolyzes the 1-6 bonds of the starch, but even in this case, the dextrose content is only maximum 96 - 97%.

Another process is to separate, in a manner known per se, the dextrose of oligosaccharides and polysaccharides by passing the hydrolyzate through a column comprising a molecular sieve, such as a cationic resin. In such a process, the aqueous starch hydrolyzate, which has previously undergone pretreatment, such as concentration, filtration and / or discoloration, is adsorbed on the column, the by-products (polysaccharides and part oligosaccharides) recovering. -is in the refined excluded from the sieve. Dextrose is further absorbed by

EN 119469 Β1 elution with water, the latter being then partially or totally eliminated to form a concentrated solution of dextrose or crystallized dextrose.

Another process, based on the same principle as mentioned above, consists in separating dextrose from oligosaccharides and polysaccharides by passing starch hydrolysate on membranes with tangential filtration. Such a process is described in EPA-452238, US-A-4429122 and US-A-4511654. 55

These last two processes actually allow to obtain a starch hydrolyzate, having a high content of true dextrose, higher than 98 - 99%, but the obtained yields are unfortunately too small (in the order of 60 - 65%) to justify from the point industrially and economically such processes.

A first object of the invention is, therefore, to propose a process of 60 obtaining a starch hydrolyzate with a high dextrose content, which will overcome the limits and disadvantages of the known processes of the prior art.

Another object of the invention is to propose a process for obtaining a starch hydrolyzate with a high dextrose content, over 97%, preferably over 98% and even more preferably more than 99%. 65

Another object of the invention is to propose such a process, simple and economically efficient, that will allow to obtain, with very satisfactory yields, hydrolysates with such a high content of true dextrose.

For this purpose, the invention proposes a process for obtaining a high dextrose starch hydrolyzate, comprising the steps consisting of: 70

a) performing a hydrolysis of a starch milk using an α-amylase, so as to obtain a liquefied starch milk;

b) performing a sugarification of liquefied starch milk, with the help of a glycogen enzyme, to obtain a sugary hydrolyzate;

c) performing a molecular sorting of said sugary hydrolyzate to obtain a high dextrose hydrolyzate;

this process being characterized in that, between step (a) and step (b), a step of α-amylase inhibition is performed.

The process of obtaining a high dextrose starch hydrolyzate according to the invention is based in fact on the neglected finding that a good separation technique, whether chromatographic or otherwise, is only effective. if, respectively, the characteristics of the product separately, in themselves, effectively allow its separation by the technique or techniques envisaged.

In the present case, an effective separation can only be obtained from a starch hydrolyzate having a particular composition, having, in particular, a bimodal carbohydrate spectrum 85, that is, having, in addition to a high content of true dextrose, a content. significantly reduced by disaccharides and trisaccharides and, on the contrary, a high content of polysaccharides slightly separated by dextrose.

It is therefore within the scope of the invention that impurities should be in the form of polysaccharides with long chains and as little as possible in the form of disaccharides or 90 oligosaccharides with a molecular mass close to that of dextrose.

The particular bimodal carbohydrate spectrum of starch hydrolysate is obtained, according to the process of the invention, by inhibition of α-amylase at the end of the liquefaction step.

This inhibition of α-amylase can preferably be done thermally by applying a thermal shock of 95 seconds at a temperature higher than or equal to 130 ° C when exiting the liquefaction step. ____

This inhibition of the liquefying enzyme avoids the continuation of its action during the sugar phase, thus favoring the formation of disaccharides (maltose, isomycosis) which

EN 119469 Β1 are difficult to separate from dextrose, in favor of branched polysaccharides (degree of polymerization DP = 7) resistant to amyloglucosidase and slightly separated from dextrose.

In order to enhance the bimodal distribution of starch hydrolysate, it is preferred, in the process according to the invention, to perform a light hydrolysis of starch milk so as to obtain liquefied starch milk with a low conversion rate.

Thus, in the process according to the invention, the liquefaction step (a) is preferably conducted up to a coefficient of DE between 2 and 10 and in particular up to a coefficient of DE between 4 and 8.

Making liquefaction, starch milk up to a very low DE coefficient, between 2 and 10 (and preferably between 4 and 8), combined with the inhibition of the liquefying enzyme at the end of liquefaction, favors obtaining a final hydrolyzate having the desired characteristics, that is, presenting an increased dextrose content and a particular non-dextrose composition, which results essentially from the presence of polysaccharides and not di- or oligosaccharides.

Preferably, the liquefaction stage is carried out in two sub-stages: the first is the heating, for several minutes and at a temperature between 105 and 108 ° C, of starch milk in the presence of the enzyme (of type THERMAMYL 120L, marketed by the company NOVO ) and a calcium-activating agent, and the second consists of heating the starch milk thus treated at a temperature between 95 and 100 ° C, for one or two hours.

Once the liquefaction step is completed, under the conditions of dry matter content, pH, enzyme and calcium content well known to the person skilled in the art, and after inhibition of the liquefying enzyme, proceed to step (b) of starch milk sugars. liquefied.

During this step, the liquefied starch milk is subjected to the action of a glycogen enzyme, especially selected from the group consisting of amyloglucosidase, glucoamylase or any other glycogen enzyme.

In order to avoid the reversal reactions and in particular the formation of disaccharides (maltose, isomaltose) by the de-extrolation of dextrose, the saccharification step is performed, under known conditions, so that a DE coefficient of the final hydrolyzate is obtained, not exceeding 95, in particular. greater than 90 and in particular between 80 and 90.

Indeed, the preferred substrate of glycogen enzymes has a high molecular weight, and the α-1.4 bonds of the starch are hydrolyzed much faster than the α-1.6 bonds. Therefore, at the beginning of saccharification, with large molecules and α-1,4 bonds predominating, dextrose production is extremely rapid over time, while the production of reversion products is very slow, due to the low concentration of dextrose in the reaction medium.

As sugars continue, small molecules and α-1.6 bonds become predominant, and dextrose production decreases progressively, while the production of reversible products (highly branched oligosaccharides) accelerates.

To combat this phenomenon, it may be of interest to associate with the glycogen enzyme an enzyme that specifically hydrolyzes the α-1.6 bonds of starch. This addition of a decomposition enzyme allows, on the one hand, to accelerate hydrolysis reactions without simultaneously accelerating the reversal reactions, and on the other, to reduce, the amount of strongly branched oligosaccharides that normally resist to the action of the glycogen enzyme. Preferably, the decomposing enzyme is isoamylase or pululanase.

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

- α-amylase: between 20 and 2000 KNU (Kilo Novo Units) per kilogram of dry substrate, temperature between 80 and 150 ° C, duration of action between 2 and 15 min;

RO 119469 Β1

- amyloglucosidase: between 4000 and 400,000 international units per kilogram of dry substrate, temperature between 50 and 60 ° C, duration of action between 30 and 72h, pH between 5.0 and 6.0;

- pululanase: between 150 and 15,000 ABM units.

The enzymes used may be of bacterial or fungal origin. 150

The sugar thus hydrolyzed is then filtered through the precoated filter or, preferably, by microfiltration on the membranes, after which it is demineralized.

Molecular sorting is performed on this sugary and purified hydrolyzate to separate dextrose from the oligosaccharides and polysaccharides in the composition and thus obtain a high dextrose starch hydrolyzate. 155

This molecular sorting step may, for example, consist of a chromatographic separation step or a membrane separation step.

The chromatographic fractionation step is performed in a manner known per se, discontinuously or continuously (simulated mobile layer), on cationic-type adsorbents, or on strongly acidic zeolites, preferably charged with alkaline or 160 alkaline ions. - earthy like calcium or magnesium, but more preferably with the help of sodium ions.

Examples of such processes are described above in US-A3044904, US-A-3416961, US-A-3692582, FR-A-2391754, FR-A-2099336, US-A-2985589, US-A-4024331 , US-A-4226977, US-A-4293346, US-A-4157267, US-A-4182633, US-A-165 4332623, US-A-4405455, US-A-4412866, US-A-4422881 and WO-A-92/12179.

According to a preferred embodiment, the chromatographic fractionation is performed using the method and apparatus described in US-A-4422881. Whatever the chromatographic process used, preferably, as regards the adsorbent, a strong cationic resin used in the form of sodium or potassium and cross-linked with about 4 - 170 was used.

10% Divinylbenzene. Advantageously, the resins are of homogeneous particle size and range from 100 to 800 µm.

Choosing the chromatographic fractionation parameters, among which are highlighted, the elution flow, the feed flow with the starting hydrolysate, the extraction flow of the fraction containing the high dextrose starch hydrolysate, the flow of the fraction containing the high impurities and the 175 computed areas. of desorption, adsorption and enrichment, is made so that to recover, with the best possible yield, the first fraction enriched with dextrose having a dextrose content greater than 99%.

To achieve this result, these parameters are chosen as follows, when the chromatographic fractionation is performed using the process and apparatus 180 described in US 422881 and when the adsorbent used is a cationic resin of reduced particle size, cross-linked by 8% divinylbenzene and used. in sodium form:

- elution flow between 70 and 700 l / h / m ³ of adsorbent;

- feed flow with hydrolyzate starting from 10 to 100 l / h / m ³ of adsorbent;

- extraction rate of the dextrose-enriched fraction between 80 and 800 l / h / m ³ ; 185

- extraction rate of the dextrose-enriched fraction between 80 and 800 l / h / m ³ of adsorbent;

- flow rate of the fraction enriched with oligo- and polysaccharides between 20 and 200 l / h / m ² of adsorbent.

Instead of the chromatographic separation step, it is possible that a separation step by nanofiltration on membranes may be applied in the process according to the invention.

Membranes with different pore diameters are made from numerous polymers and copolymers of polysulfones, polyamides, polyacrylonitriles, polycarbonates, polyurethanes, etc.

Four classes of membranes are currently being marketed: reverse osmosis, nanofiltration, ultrafiltration and microfiltration.

195

RO 119469 Β1

Examples of use of such membranes are described above in EP-A 452238, US-A-4429122 and US-A-4511654.

According to a preferred embodiment, the membrane separation is carried out using a membrane with a porosity close to 10 A. Advantageously, the membrane applied in the process according to the invention is of the type FILMTEC NF 40, marketed by the company DOW.

According to an advantageous embodiment of the invention, the excluded part of the membranes or following the chromatography, comprising the impurities of high molecular weight, is recycled upstream of the saccharification step.

Thanks to the process, according to the invention, which enjoys both the benefits of the applied hydrolysis steps and those of the molecular sorting step, it is possible to obtain, with yields greater than 80%, a starch hydrolyzate whose dextrose content is greater than 99%. Such purity could only be achieved until now with crystallized dextrose reintroduced into the solution.

High dextrose starch hydrolysates, obtained by the process according to the invention, can then easily be catalytically hydrogenated.

The hydrogenation of such a hydrolyzate is carried out according to those known in the art and which lead, for example, to the production of sorbitol starting from glucose.

For this stage both ruthenium catalysts and Raney nickel catalysts can be used. However, it is preferred to use Raney nickel catalysts, which are less expensive.

In practice, between 1 and 10% by weight of the catalyst is used in relation to the dry matter of the hydrolyzate subjected to hydrogenation. Hydrogenation is preferably carried out on a hydrolyzate whose dry matter is between 15 and 50% (practically near 30 - 45%), under a hydrogen pressure of between 20 and 200 bar. It can be carried out continuously or discontinuously.

When operating discontinuously, the hydrogen pressure used is generally between 30 and 60 bar, and the temperature at which the hydrogenation takes place is between 100 and 150 ° C. The aim is to maintain the pH of the hydrogenation medium, by adding soda or sodium carbonate for example, but without exceeding a pH of 9.0. This way of working allows the avoidance of cracking or isomerization products.

The reaction is stopped when the reducing sugar content of the reaction medium has become less than 1%, preferably less than 0.5 and, in particular, less than 0.1%.

After cooling the reaction medium, the catalyst is removed by filtration and the sorbitol thus obtained is demineralized on cationic and anionic resins. At this stage, the syrups contain at least sorbitol and it is easy to purify it by crystallization after concentrating and cooling the solutions.

Other features and advantages of the invention will be clearly apparent from the presentation of the following examples. These are given here for illustrative purposes only and not in a limiting sense.

Example 1. A starch milk is usually liquefied using 2% THERMAMYL 120L (α-amylase marketed by NOVO), up to a DE coefficient of 6.5

The reaction medium is then heated for 140 seconds at 140 ° C to inhibit α-amylase.

It is then performed, in a manner known per se, the sugarification of the hydrolyzate with 35% dry matter, in the presence of 0.8% amyloglucosidase G990 marketed by the company ABM.

RO 119469 Β1

After 42 hours of sugaring, a hydrolyzate is obtained with the following carbohydrate spectrum: 245 glucose ................................. ................... 95.6%

DP2 ................................................. ....... 1.9%

DP3 ................................................. ....... 0.3%

Higher DP: .............................................. 2 , 2% where the abbreviation of DP designates degrees of polymerization. 250

The sugars thus hydrolyzed are further filtered by microfiltration on membranes, and then demineralized.

Then, the fractionation of the sugary and purified hydrolyzate is carried out, in the continuous chromatographic separation plant, whose construction and operation details are presented in US 4422881. 255

They are obtained as follows:

- a first fraction enriched with dextrose, with a yield greater than 87% by weight and having the following composition:

dextrose .................................................... 99.4%

DP2 ................................................. ....... 0.6%

- a second fraction enriched with oligo- and polysaccharides having the following composition:

dextrose .................................................... ... 70%

DP2 ................................................. ....... 10%

DP3 ................................................. ....... 2.3%

260

265

Higher DP ............................................... 17 7%

Example 2. Exactly the same stages of liquefaction and saccharification as in Example 1 above are performed on starch milk, except that a-amylase is not inhibited.

After 42 hours of sugaring, a hydrolyzate is obtained having the following carbohydrate spectrum: 270 glucose ................................. ................... 95.1%

DP2 ................................................. ........ 2.3%

DP3 ................................................. ....... 1.3%

Higher DP ............................................... 1 ,1%.

The sugar thus hydrolyzed is then filtered by microfiltration on membranes, and then demineralized.

After the chromatographic fractionation, it is recovered:

- a first fraction enriched with dextrose, with a yield of 7.8% by weight and having the following composition:

dextrose .................................................... ..99.4% 280

DP2 ................................................. ....... 0.5%

DP3 ................................................. ....... 0.1%

- a second fraction enriched with oligo- and polysaccharides having the following composition:

dextrose .................................................... ... 80% 285

DP2 ................................................. ....... 8.6%

DP3 ................................................. ....... 5.5%

Higher DP: ............................................... 5.9%

The chromatographic yield of 78% by weight obtained in this example should be compared with that of 87% by weight obtained in example 1 according to the invention. 290

Example 3. The dextrose-enriched fraction of Example 1, concentrated to a dry matter value of 45%, is subjected to catalytic hydrogenation in the presence of 5% by weight Raney nickel relative to the dry matter.

RO 119469 Β1

The operating conditions are as follows:

temperature................................................. 140 ° C pressure ............................................... .... 60 bar duration ........................................... ............ 2 hrs

The hydrogenation is stopped when the sugar content of the reaction medium is less than 600 ppm.

After cooling the reaction medium, remove the catalyst by filtration, then demineralize the syrup obtained and finally concentrate the syrup up to 70% dry matter.

The dry composition of the syrup thus obtained is as follows:

sorbitol ................................................. .... 98.8% mannitol ......................................... ............. 0.4% iditol and cracking products ............................ ........... 0.2%

Claims (6)

claims 1. Process for obtaining a high dextrose starch hydrolyzate, comprising the steps consisting of: a) performing a liquefaction of a starch milk with the help of an α-amylase, so as to obtain a liquefied starch milk; b) performing a sugarification of liquefied starch milk, with the help of a glycogen enzyme, to obtain a sugary hydrolyzate; c) performing a molecular sorting of said sugary hydrolyzate, to obtain a high dextrose hydrolyzate; characterized in that the step a) of liquefaction is led to a DE between 2 and 10, preferably between 4 and 8, and is passed between step a) and b) to a step of inhibition of α-amylase. 2. Process according to claim 1, characterized in that the step b) of sugaring is conducted up to a DE between 80 and 90. Process according to claim 1 or 2, characterized in that an enzyme which hydrolyzes the 1-6 bonds of the starch is associated with the glycogen enzyme. Process according to any one of claims 1 ... 3, characterized in that step c) is a chromatographic separation step. Process according to any one of claims 1 ... 4, characterized in that step c) is a step of separation by nanofiltration on the membrane. 6. Use of high dextrose starch hydrolysate, obtained by the process defined in claims 1 ... 5, to obtain sorbitol by hydrogenation.