WO2009004153A1

WO2009004153A1 - Method for producing families of galacturonic acid oligomers and use thereof

Info

Publication number: WO2009004153A1
Application number: PCT/FR2008/000717
Authority: WO
Inventors: Patrice Pheulpin; Stéphanie ROSSARD; Maximilien Barbier; José KOVENSKY; Bernard Courtois; Josiane Courtois-Sambourg
Original assignee: Université de Picardie Jules Verne
Priority date: 2007-05-25
Filing date: 2008-05-26
Publication date: 2009-01-08
Also published as: FR2916447B1; FR2916447A1

Abstract

The invention relates to a method for producing galacturonic acid oligomers, said method being of the type that comprises providing a mixture of galacturonic acid polymers. According to the invention, the method further comprises the following steps: bringing said mixture to a predetermined temperature and pressure for degrading said galacturonic acid polymers in order to obtain a oligomer mixture containing galacturonic acid oligomers having a polymerisation degree dp substantially between 2 and 40; and recovering said galacturonic acid oligomers having a polymerisation degree dp substantially between 2 and 40; in this way, it is possible to obtain oligomers in a predetermined percentage and with a polymerisation degree dp essentially between 2 and 40.

Description

Process for the production and use of qalacturonic acid oligomer families

The present invention relates to a process for producing a family of galacturonic acid oligomers and to a use of such a family of oligomers.

Oligosaccharides are a broad family of compounds among which many molecules have biological activities that can be used in a variety of applications. Certain derivatives of these oligosaccharides may be developed in order to inhibit the development of infectious processes, for example in plants.

Plants are precisely an important source of biologically active oligosaccharides and most of them are obtained by fragmenting pectins, pectins from flax, for example, or from any other plant. Pectins correspond to a major constituent of the plant cell wall.

The pectins consist essentially of homogalacturonans and rhamnogalacturonans type RG I and type RG II. The homogalacturonans consist of 100% of partially methylated C6 and C2 and / or C3 acetylated galacturonic acid. The rhamnogalacturonans type RG I consist mainly of rhamnose, galacturonic acid and galactose, arabinose and sometimes xylose. RG II-type rhamnogalacturonans, which are less important in pectins, consist of galacturonic acid, glucuronic acid, rhamnose, galactose, arabinose, fucose, apiose, KDO, a derivative of heptulosuric acid and xylose.

Methods have been implemented to degrade these pectins in order to obtain oligomers of galacturonic acid. These methods proceed from the enzymatic degradation of pectins and then from the purification of galacturonic acid oligomers. The article by L. Bedouet et al. ("Methods for obtaining neutral and acid oligosaccharides from flax pectins", Biotechnology Letters (2005) 27: 40), in which there is described an enzymatic method for obtaining neutral and acidic oligosaccharides from partially substituted flax pectins. C6 methyl and / or C2 / C3 acetyl. The purification of 100% neutral oligosaccharide (oligogalactan, oligoarabinogalactan) or 100% oligosalacturonan (or partially anionic) oligosaccharide families requiring purification by anion exchange chromatography. Reference can also be made to Japanese patent application JP 10 226 701, which also describes a method for decomposing crude pectins to obtain galacturonic acid oligomers. The method consisting in carrying out a hot extraction (60 to 100 ^° C.) of said pectin and then subjecting the extract to enzymatic degradation using pectinase. The enzymes used make it possible to cut the polymer chains into oligomers. These polymer chains naturally have acetyl substituents, the oligogalacturonane preparation described in the process is naturally contaminated with non-100% anionic oligomers since the hot extraction necessarily results in neutral osmotic fractions of low molecular weight, article by L. Bedouet (Changes in esterified pectins in the flax stems and leaves Carbohydrate Polymers 65, (2006) 165-173); the oligomers resulting from this enzymatic degradation exhibit antibacterial activity

Although interesting, the methods described in these documents are relatively complex to implement, and therefore expensive. Furthermore, the structure of the oligomers obtained depends strongly on the origin of the pectins, in particular the substitution, in particular by the acetates, which varies from one plant to another, but also as a function of the stage of growth of the plant (Bedouet et al. al, 2006, Carbohydrate Polymers 65, 165-173). Also, a problem that arises and that the present invention aims to solve is to provide a less expensive method of producing oligomers, consisting solely of galacturonic acid, unsubstituted or acetylated. Another problem, which the invention solves, is to provide a process which makes it possible to obtain oligomers having the same structure (not contaminated with oligomers containing neutral oses), whatever the origin of the pectins used, these oligomers which may be unsubstituted or acetylated by a given percentage.

For this purpose, the present invention provides a rapid and inexpensive process for the production of acetylated or unsubstituted galacturonic acid oligomers, said process being of the type in which a mixture of galacturonic acid polymers is provided; and according to the invention this process further comprises the following steps: a) adjusting the pH of said mixture of galacturonic acid polymers to acidic conditions between 4 and 5; b) said mixture is brought to a temperature above 110 ^° C. and at a pressure determined to degrade said galacturonic acid polymers so as to obtain a mixture of oligomers comprising oligomers of galacturonic acid whose degree of polymerization dp is essentially between 2 and 40; and, c) recovering said galacturonic acid oligomers of dp substantially between 2 and 40; in this way oligomers are obtained which will be acetylated according to a given percentage and having a degree of polymerization dp substantially between 2 and 40. Thus, a characteristic of the invention lies in the implementation of a polymer mixture of galacturonic acid which is thermally degraded in a controlled manner to obtain oligomers of a limited degree of polymerization of between 2 and 40, for example between 5 and 25. A description will be given in greater detail in the following description of an embodiment of the invention. wherein the degree of polymerization dp is essentially between 4 and 11.

It will be observed that the subject of the present invention has hydrolysis conditions different from the aforementioned document by L. Bedouet et al, since the degradation of the crude pectin described in this document is carried out in the presence of 0.1 M of HCI 12 M; and under these conditions, the pH of the solution is of the order of 1 and the temperature applied is 80 ° C.

Said mixture of galacturonic acid polymers is advantageously brought to a temperature higher than 110 ° C in an autoclave, and therefore, according to the Regnault table, said mixture of galacturonic acid polymers is brought to a pressure greater than 0, 5 bar.

Preferably, a temperature of less than 130 ° C., for example 121 ° C., is applied for a period of time of between 30 and 60 minutes, whereas according to the aforementioned prior art the reaction lasts 24 hours, which is greatly less profitable, and moreover in this case, does not lead to the same results. For example, the mixture is placed in an autoclave for 40 minutes. Under these conditions of temperature, 121 ° C, and pressure corresponding and close to 1 bar, essentially unsubstituted galacturonic acid oligomers are obtained.

Advantageously, and according to a step d), after step c), an acetic compound is reacted on said galacturonic acid oligomers recovered in a controlled manner in order to graft acetate groups in a determined percentage onto said recovered galacturonic acid oligomers. ; in this way, acetylated galacturonic acid oligomers are obtained without modifying the degree of polymerization. In this way, the galacturonic acid polymers which are naturally partially acetylated, but according to a variable rate which depends on their origin, are first completely free of their substituents and then be acetylated in a totally controlled manner. In this way we can get rid of the origin of polymers.

Moreover, and according to yet another embodiment, said oligomers are advantageously substituted with groups selected from the group consisting of, alkyl, aryl, acyl, phosphate and sulphate, according to a percentage determined so as to confer properties on them. special. These oligomers will then be treated with an acetylation reagent, and preferably a reagent that is easy to eliminate at the end of the reaction, such as acetic anhydride, will be chosen. In the case of sulfated galacturonic acid oligomers, they will preferably be obtained using an SO ₃ -DMF complex.

According to a particularly advantageous embodiment of the invention, said galacturonic acid polymers are obtained by hydrolyzing pectins derived from plants of any nature whatsoever. Such a source of supply is almost infinite, and therefore very cost-effective. Also, not only is the raw material of low cost, but in addition the method of implementation, is relatively simple and does not use expensive methods of enzymatic degradation. Moreover, the processes for preparing oligogalacturonans enzymatically require the elimination of the protein so that the oligogalacturonan fraction is pure. The method which is the subject of the present invention is freed from this deproteinization step.

Preferably, the pH of the oligomer mixture is lowered after step b) to precipitate the acid oligomers. galacturonique whose degree of polymerization dp is greater than 40 or preferably greater than 25, so as to recover in step c) a supernatant containing said galacturonic acid oligomers of degree of polymerization dp, between 2 and 40 or else preferably, between 2 and 25 and essentially between 5 and 25. Then, said supernatant is treated so as to recover oligomers of dp substantially between 5 and 25, either by precipitation or by ultrafiltration; it may advantageously be mixed with an alcohol to precipitate said galacturonic acid oligomers whose degree of polymerization dp is essentially between 5 and 25. In the case of filtration, it is advantageous to use an IkDa cut-off membrane, the oligomers of dp essentially between 5 and 25 are recovered in the retentate, this filtration method further allows to concentrate the oligomer solution which can be freeze-dried. And in step d), acetic anhydride is advantageously reacted with the recovered galacturonic acid oligomers to graft acetate groups. In this way, the acetylation process is relatively mild and thus does not cause a change in the degree of polymerization. There is no further degradation of the oligomers.

According to a particular embodiment, in step d), the acetic compound and said oligomers of galacturonic acid form a reaction mixture, and the acetylation reaction is interrupted by adding a given amount of water to said reaction mixture. Then, said reaction mixture supplemented with said quantity of water given is dialyzed after reaction to recover said acetylated oligomers in solution in water. Advantageously, said acetylated oligomers in solution in water are lyophilized to be isolated. Preferably, they are frozen before lyophilization.

In another aspect, the present invention relates to the oligomers obtained according to the production method described above. In yet another aspect, the present invention provides the use of acetyl oligomers according to the method described above for use as an antimicrobial agent.

Other features and advantages of the invention will emerge from a reading of the description given below of particular embodiments of the invention. the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which:

FIG. 1 is a proton nuclear magnetic resonance spectrum ( ¹ H NMR) of a compound obtained according to the process according to the invention and having a first degree of substitution; and,

- Figure 2 is a spectrum of this same compound having a second degree of substitution.

Neutral osse sequences are acid-sensitive in contrast to uronic acid sequences. In neutral acid medium, neutral oles and oligomers of neutral osues are soluble, while acidic oligomers form a precipitate. The neutral osse sequences will therefore be eliminated by controlled acid hydrolysis, while the acidic osse sequences will remain intact; we will then obtain polymers of galacturonic acid (PGA).

The method used to degrade galacturonic acid polymers (PGA) to galacturonic acid oligomers (OGA) corresponds to an autohydrolysis, under acidic conditions at a pH of between 4 and 5 and preferentially at a pH of 4.4. of these galacturonic acid polymers (PGA) caused by heating in an autoclave at 121 ^° C. (1 atm) for 40 minutes. It will be specified here that an autoclave is a thick-walled and hermetically sealed container, forming a sealed enclosure. If one refers to the Regnault table, giving the approximate temperature of the water vapor alone in an autoclave according to the pressure, when the temperature is 121 ° C, the internal pressure of the autoclave reached about 1 atmosphere, more precisely, 1 bar for 120.42 ⁰ C; and when the temperature is 134 ⁰ C, the pressure reaches about 2 atmospheres, precisely, 2 bar for 133.69 ° C. Also according to the Regnault table at 144 ° C the pressure is about 4 atmospheres. Also, in an autoclave, the values of pressure and temperature are bound by physical laws. Therefore, when using an autoclave to degrade the polymers, according to the invention, the only temperature value imposed on the inside, conditions the degradation pressure. Method:

The oligomers of pectin are obtained by degradation of crude pectins, which contain acidic oses (galacturonic acid) and neutral oses. The ratio of neutral to acidic acids varies according to the origin of the pectins. It is respectively 75/25 for flax, 80/20 for apple, or 82/18 for lemon. The method applied to degrade the pectins according to which they are subjected to an acid treatment and then are brought to at least 120 ^° C., makes it possible to eliminate all the substituents present on the polymer and in particular the acetyl groups. After purification, the oligomers of galacturonic acid (OGA) thus obtained, whose degree of polymerization DP is essentially between 5 and 25 units are therefore nonacetylated.

On the other hand, other methods than thermal degradation, in particular enzymatic degradation by commercial pectinases, can lead to the production of acetylated galacturonic acid oligomers (OGAs), since the galacturonic acid polymers are naturally acetylated and that the enzymatic degradation simply consists in cutting the polymer into oligomers. However the exploitation of such a process can lead to a heterogeneity of the samples since the substitution rate of the pectins varies according to the plant, but also according to its stage of development. And above all, these methods are more expensive.

Likewise, the ratio of neutral to acidic acids varies according to the plants and their stage of growth and the exploitation of raw pectins would lead to a variability of composition which could be detrimental to the reproducibility of the properties in the case of the application of these molecules.

To ensure the perfect reproducibility of batches, we are particularly interested in the fraction containing only the acidic oses. The galacturonic acid (PGA) polymers can be extracted from pectins isolated from plants of any kind. It will also be possible to use galacturonic acid polymers sold as such commercially. In both cases, it is intended to obtain oligomers of galacturonic acid (OGA). Example 1

A process for preparing galacturonic acid polymers from a determined amount of pectin is described below. First, 10 g of pectin are provided, which is dissolved in water, and advantageously in ultra-pure water. Such a quality of water can be obtained by means of a commercial device, for example the PURELAB UHQ system. Then, 4 molar hydrochloric acid is added to the solution, then the mixture is brought to 50 ^° C. and stirred for a period of 2 to 4 hours, advantageously the treatment is treated for 3 hours at 50 ^° C. In this way, the neutral osse sequences are hydrolysed while the bonds between the uronic acids are not degraded. After this stirring phase, the mixture is neutralized with sodium hydroxide

12 times molar. Then 2 volumes of isopropanol are added to the mixture. Thus, only high average mass molecules precipitate with isopropanol, while low mass molecules (mono and oligosaccharides) remain in solution. The mixture is then introduced into tubes of a centrifuge. The precipitate is then recovered in the pellet of said tubes, after centrifugation of the mixture brought to 4 ° C. and 15,000 g for 30 minutes, while the supernatant is removed. In this way, polymers of galacturonic acid are obtained. EXAMPLE 2 The precipitate obtained according to Example 1 is then re-dissolved in UHQ ultrapure water. The pH of the solution is then adjusted to 4.4 with 0.1 molar hydrochloric acid. In this way, the carboxylic functions of the galacturonic acid polymer (PGA) are predominantly in the ionized COO ^- H ^{+ form, which} improves self-degradation when the mixture is heated to 121 ° C. in an autoclave for 40 minutes. A reduction in the duration of the treatment reduces the degradation of the polymer, whereas conversely an increase in the duration of the treatment at 121 ^° C. increases the degradation of the polymer and leads to oligomers of galacturonic acid whose dp are in average, depending on the case mainly higher or smaller than those obtained by treatment for 40 minutes.Through this heat treatment and the conditions of application, on the one hand, all the substituents of the polymer are eliminated, in particular the acetyl substituents, and on the other hand, in particular galacturonic acid oligomers are obtained whose degree of polymerization dp is mainly between 2 and 25 units. Moreover, when comparing the elution profiles in ion exchange chromatography (DEAE-Sepharose), galacturonic acid polymers obtained according to example 1 above and oligomers of galacturonic acid obtained by the treatment thermal described above, we observe for the second, an elution that not only starts earlier, but also that is more spread than the first. This is indicative of the degradation of polymers, since the elution of small molecules is faster and the elution of larger molecules.

The mixture of galacturonic acid oligomers mentioned above is then rapidly cooled. Then, the pH of this cooled mixture is adjusted to 2.0 with acetic acid. This adjustment then causes the precipitation of the molecules of average mass which can result from an incomplete degradation.

Thus, after centrifugation of the mixture at 15,000 g for 30 minutes and at a temperature of 4 ° C., the supernatant which is neutralized with ammonia and which consists of small molecules is recovered, while the base of the Centrifuge tubes containing the above-mentioned medium mass molecules are removed.

Here again, the ion exchange chromatography elution of the supernatant in comparison with the two other elution profiles described above, shows a profile that starts a little earlier and, above all, attenuates rather than the profile of the oligomers of galacturonic acid after heat treatment. This shows the elimination of high molecular weight compounds by precipitation at pH 2 in the presence of acetic acid.

Small molecules consisting of oligosaccharides are then recovered, either by precipitation in the presence of an alcohol, sbit by ultrafiltration membrane IkDa cutoff threshold; in both cases, the oligomers can be dried by lyophilization. In the case of the alcoholic precipitation, a treatment with 7 volumes of isopropanol is preferentially chosen. The mixture is again centrifuged under the same conditions and the tubes, galacturonic acid oligomer fractions, are then recovered in the pellet. To do this, the precipitate recovered in the pellet is dried, for example by evaporation. Then, the dry precipitate can advantageously be solubilized in UHQ water (10 g of galacturonic acid oligomers per liter) then freeze-dried. Lyophilization improves the conditioning of galacturonic acid oligomers (OGA).

Reference is made to Table I below, in which appears the percentage of galacturonic acid oligomer fractions obtained by precipitation in isopropanol, depending on the degree of polymerization.

Board

As can be seen, the oligomers galacturonic acid whose degree of polymerization is between 4 and 11 represent nearly 95% of all the compounds obtained by this process. On the other hand, almost 78% of the compounds have a degree of polymerization of between 5 and 10. Therefore, the method used here is extremely selective.

In the case of the recovery of galacturonic acid oligomers by membrane ultrafiltration with a cut-off 1 kDa, the retentate containing the oligomers of dp predominantly between 5 and 25 will be recovered; these oligomers concentrated in the retentate are lyophilized. Moreover, these oligomers are unsubstituted because of the elimination of the acetates and methylated during the preparation process described above. In addition, the fractions are free of neutral oste. Of course, oligomers of galacturonic acid may be obtained according to the method of preparation proposed in Example 2 above from commercially available galacturonic acid polymers.

The process according to the invention aims to obtain partially acetylated galacturonic acid oligomers just as are the galacturonic acid polymers present in the plant, but with a determined acetylation level. To do this, a method of acetylation has been developed. Thus, according to this technique, starting from unsubstituted oligomers, the acetylation of the galacturonic acid oligomer fractions can be controlled.

Galacturonic acid oligomers are supplemented with acetic anhydride and the acetylation is very soft and non-denaturing, that is to say, it does not degrade the oligomers. Example 3: a treatment cycle

To 1 g of galacturonic acid oligomers is added 10 ml of 0.1 molar acetic anhydride in four times. The mixture is then stirred gently for 24 hours and at room temperature. Then, the acetylation process is stopped by the addition of 50 ml UHQ ultra pure water. Then the mixture is dialyzed to remove the reagents and freeze-dried. Before lyophilization, the mixture is advantageously frozen. In this way, an end product is obtained containing acetylated galacturonic acid oligomers in 100% yield relative to the starting oligomers, that is to say that all the oligomers have acetyl substituents.

On the other hand, on average, for a first treatment cycle, 10% acetylation is obtained, relative to all the possible substitutions, without decreasing the degree of polymerization dp. Reference may be made to the proton nuclear magnetic resonance spectrum ( ¹ H NMR) shown in FIG. 1, which illustrates the method of calculating the acetylation rate. This is because the ratio of the integration of the signals corresponding to the protons of the acetates of the region ranging from 2.5 to 3 ppm, to the integration of the signals 12 corresponding to the protons of the galacturonic acid residues of the region ranging from 3.8 to 6 ppm makes it possible to determine the level of acetylation. A second cycle leads to approximately 30% acetylated galacturonic acid oligomers (OGA). The proton nuclear magnetic resonance spectrum shown in FIG. 2 shows the progression of the signals corresponding to the protons of the acetates of the region, 2.5 to 3 ppm compared with those of the region corresponding to the galacturonic acid residues. 3.8 to 6 ppm.

Also, a third cycle in accordance with the first treatment cycle mentioned above leads to approximately 40% acetylated OGAs without modifying the degree of polymerization dp. The spectrum of the molecules thus produced is not represented.

The acetylation rate of the oligomers of galacturonic acid to which the treatment of the aforementioned type has been subjected is reproducible. Example 4

The galacturonic acid oligomers (OGA) thus obtained were applied to microorganisms to demonstrate their activities. Thus, OGAs were introduced into culture media inoculated with Gram-positive (Staphylococcus aureus, Listha innocuita) and Gram-negative (Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa) bacteria at 10 ⁷ colony-forming units (CFUs). ) per milliliter for E. coli, L. innoccua, S. aureus and S. typhimurium, and 5 x 10 ⁷ CFU per milliliter for P. aeruginosa. The development of these microorganisms in the presence of OGAs was carried out in a liquid mixture for 6 hours at 37 ° C. with stirring. The measurement of galacturonic acid oligomer activity is measured by measuring the optical density of the mixture at 600 nm. The results presented in Table I below correspond to the average of 4 separate trials. The growth of microorganisms in the presence of OGA is compared to a control without OGA. The percentage growth inhibition is determined by the ratio of the standard optical density of the non-OGA control at 600 nm minus the optical density of the assay, all divided by the standard optical density and multiplied by 100: OD ₆ o Standard - DO ₆ oo tests / OD ₆ oo Standard x 100. Table II

Thus, it is shown that for the microorganisms Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa and Staphylococcus aureus, galacturonic acid oligomers acetylated at a rate of 10%, and having a degree of polymerization of between 5 and 25, slow down the development of these microorganisms with greater efficiency than nonacetylated galacturonic acid oligomers of the same degree of polymerization.

Fractions of galacturonic acid oligomers (OGA) which significantly reduce the growth of pathogenic bacteria such as Staphylococcus and Pseudomonas, as well as Salmonella, and which have a low activity against Escherichia coli are of great interest for the treatment of bacteria. human nutrition. Indeed, if they were incorporated into the diet in the form of food supplements for example, they could reduce the growth of pathogens by having a very low activity on saprophytes and Escherichia coli in particular. Ultimately, there may be extinction of the pathogenic flora. In addition, OGAs could be used in the field of cosmetics for skin applications. In this case, there would be, as in the previous case, a decrease in the pathogenic flora, especially Staphylococci and Pseudomonas.

Claims

A process for producing galacturonic acid oligomers, said method being of the type in which a mixture of galacturonic acid polymers is provided; characterized in that it further comprises the following steps: a. the pH of said mixture of galacturonic acid polymers is adjusted to acidic conditions between 4 and 5; b. said mixture is brought to a temperature above 110 ^° C. and at a pressure determined to degrade said galacturonic acid polymers so as to obtain a mixture of oligomers comprising oligomers of galacturonic acid whose degree of polymerization dp is essentially understood between 2 and 40; and, c. said galacturonic acid oligomers of dp are recovered substantially between 2 and 40; whereby oligomers are obtained according to a given percentage and having a degree of polymerization dp essentially between 2 and 40.

2. Process for producing galacturonic acid oligomers according to claim 1, characterized in that said mixture of galacturonic acid polymers is brought to a temperature above 110 ^° C. in an autoclave, whereby said mixture of polymers of galacturonic acid is brought to a pressure higher than 0.5 bar.

3. A process for producing galacturonic acid oligomers according to claim 1 or 2, characterized in that said mixture is brought to a temperature above 110 ⁰ C and at a determined pressure for a period of time between 30 and 60 minutes.

4. Process for producing galacturonic acid oligomers according to any one of claims 1 to 3, characterized in that the degree of polymerization dp is essentially between 4 and 11.

5. Process for producing galacturonic acid oligomers according to any one of claims 1 to 4, characterized in that the degree of polymerization dp is essentially between 5 and 25.

6. Process for producing galacturonic acid oligomers according to any one of claims 1 to 5, characterized in that according to a step d, after step c, an acetic compound is reacted on said oligomers of acid. galacturonic acid recovered in a controlled manner to graft acetate groups at a given percentage onto said recovered galacturonic acid oligomers so as to obtain acetylated oligomers.

7. A process for producing galacturonic acid oligomers according to any one of claims 1 to 6, characterized in that said oligomers are substituted with groups selected from the group consisting of, alkyl, aryl, acyl, phosphate and sulphate. .

8. A process for producing galacturonic acid oligomers according to any one of claims 1 to 7, characterized in that said galacturonic acid polymers are obtained by hydrolyzing pectins from plants.

9. A process for producing galacturonic acid oligomers according to any one of claims 1 to 8, characterized in that the pH of the oligomer mixture is lowered after step b, to cause the precipitation of the oligomers of galacturonic acid so as to recover in step c a supernatant containing said oligomers of galacturonic acid.

A process for producing galacturonic acid oligomers according to claim 9, characterized in that said supernatant is mixed with an alcohol to precipitate said oligomers of galacturonic acid.

11. Process for producing galacturonic acid oligomers according to claim 1, wherein in step d, acetic anhydride is reacted with said recovered galacturonic acid oligomers. .

A process for producing galacturonic acid oligomers according to any one of claims 1 to 11, characterized in that in step d, the acetic compound and said galacturonic acid oligomers form a reaction mixture, and in that the acetylation reaction is stopped by adding a given amount of water to said reaction mixture.

13. A process for producing galacturonic acid oligomers according to claim 12, characterized in that said reaction mixture supplemented with said quantity of water given is dialyzed after reaction to recover said acetyl oligomers dissolved in water.

14. A process for producing galacturonic acid oligomers according to claim 12 or 13, characterized in that said acetylated oligomers in solution in water are lyophilized to be isolated.

15. Galacturonic acid oligomers obtained according to the process according to any of claims 1 to 14.

16. Use of oligomers according to claim 14 for use as an antimicrobial agent.