Use of water-soluble lignin for stabilising emulsions

Abstract

The invention relates to the use of lignin that is soluble in an aqueous medium in order to formulate oil-water emulsions. Water-soluble lignin has advantageous properties for various industrial applications, in particular as a sustainable, biodegradable and environmentally friendly emulsifying and / or stabilising agent. Said water-soluble lignin can be obtained enzymatically without organic solvent.

Description

[0001] USE OF WATER-SOLUBLE LIGNIN FOR THE STABILIZATION OF EMULSIONS

[0002] Technical field

[0003] The invention relates to the use of lignin soluble in aqueous medium for the formulation of oil / water emulsions.

[0004] Water-soluble lignin has attractive properties for various industrial applications, including as a sustainable, biodegradable and environmentally friendly emulsifying and stabilizing agent.

[0005] Said water-soluble lignin can be obtained enzymatically in the absence of organic solvent.

[0006] Water-soluble lignin-based emulsions can be used in many industrial sectors, such as, for example, the cosmetic, pharmaceutical and food industries.

[0007] State of the art

[0008] To date, 44% of surfactants and emulsifiers used worldwide are of petro-based origin, and 52% are partly derived from biomass and mainly from oleochemical products that are only partially renewable, biodegradable and bio-based. Only 4% of surfactants are entirely derived from biomass through chemical production methods. Surfactants, and more generally formulation agents, are used in a wide variety of applications ranging from cosmetic emulsions to detergent products, including ink stabilization, pigment dispersion and cement plasticization.

[0009] Thus, we see that bio-based surfactants currently represent only a small share of the surfactant market. Nevertheless, this market is growing strongly due to consumer demand for products that are more respectful of humans and nature, as well as new environmental standards.

[0010] Lignin is a natural polymer (or biopolymer) that is one of the main components of wood along with cellulose and hemicelluloses. It is available in large quantities, particularly as a by-product of the paper industry. The use of chemically modified lignin in the field of emulsions has been described. In particular, the use of lignosulfonates, obtained by chemical treatment and functionalization, to stabilize emulsions has been studied (1).

[0011] However, lignosulfonates contain a significant amount of sulfur, which can pose health risks according to international chemical safety data sheets. These risks make lignosulfonates unsuitable for industrial uses.

[0012] Other chemical derivatives of lignin have been studied, such as derivatives oxidized with ozone to form carboxyl groups in lignin (2), or amine derivatives of lignin used as cationic emulsifiers (3).

[0013] However, chemical modifications of lignin can be costly, have an impact on the environment and result in a loss of its natural properties.

[0014] The use of lignin as an additive in the presence of other bio-sourced components, such as hemicellulose with which it interacts to stabilize emulsions in different industrial applications has also been described (4).

[0015] However, these different uses do not solve the problem of the concomitant use of other emulsifying or stabilizing agents that may not be bio-sourced. Furthermore, some of these derivatives, due to their functionalization, can only be used in specific pH ranges.

[0016] The limitation of lignin use in industries is mainly due to its insolubility in water. In particular, the formulation of an emulsion is generally achieved by dissolving a soluble emulsifier in the continuous phase. Thus, effective stabilization of an oil / water emulsion requires a water-soluble emulsifying agent.

[0017] So far, the only lignin soluble in water at neutral pH is lignosulfonate, which contains, as mentioned above, sulfonate, and therefore has a high level of toxicity. Lignosulfonate is obtained by chemical functionalization and results in the presence of significant amounts of sulfur impurities. Lignin is also soluble in water at high pH, ​​above 10, but these very basic solutions are limited for many applications. There is therefore a need for bio-based, water-soluble emulsifying and / or emulsion-stabilizing agents that can be used alone, or possibly in combination with other emulsifying and / or stabilizing agents to form oil / water emulsions, under pH conditions compatible with the desired applications.

[0018] Statement of the invention

[0019] The invention relates to the use of water-soluble lignin as an emulsifying and / or stabilizing agent for oil / water emulsions, said water-soluble lignin being obtained enzymatically. The invention also relates to the oil / water emulsions formulated from said water-soluble lignin, as well as their applications.

[0020] Brief description of the figures

[0021] Figure 1 represents the variation of dynamic viscosity (Pa.s) as a function of shear rate (1 / s) for different concentrations of lignin having undergone enzymatic treatment.

[0022] Figure 2a and Figure 2b represent the variation of interfacial tension in 3 environments (air, mineral oil and peanut oil) a) for pure water, b) for 10% lignin solution.

[0023] Figure 3a and Figure 3b represent the droplet size distribution of water-soluble lignin-based oil / water emulsions as a percentage of the same sample: a) on the day of preparation, b) after a period of 3 months.

[0024] Figure 4 represents the droplet size distribution of an emulsion comprising enzymatically obtained lignin (treated with BOD) before and after a 72-hour treatment at 60°C.

[0025] Figure 5a and Figure 5b respectively represent the droplet size distribution of emulsions stabilized a) by SDS, b) by a lignin obtained by enzymatic treatment (treated by BOD), after centrifugation at different forces from 5,000 to 80,000 g for 30 min.

[0026] Figure 6 represents an aqueous solution comprising raw Kraft lignin (Fig. 6A) or Kraft lignin obtained after enzymatic treatment (BOD-treated) (Fig. 6B). Figure 7a and Figure 7b represent, respectively, optical microscopy images of oil / water emulsions formed with a) BOD-treated lignin, b) raw lignin.

[0027] Detailed description

[0028] It has now been found that lignin obtained by enzymatic treatment, making it water-soluble, can be used as a sustainable, biodegradable and environmentally friendly stabilizing and / or emulsifying agent for the creation of direct emulsions (oil / water) while giving these emulsions very good stability properties, allowing their use in many industrial fields.

[0029] Indeed, it has now been found that aqueous solutions of lignin can stabilize oil droplets in water and can be used to create direct emulsions. Without wishing to tie the invention to a theory, it can be hypothesized that the lignin adsorbed at the interface of the oil droplets prevents the latter from coalescing.

[0030] The subject of the invention is therefore the use of lignin as a stabilizing and / or emulsifying agent in an oil / water emulsion, said lignin being obtained enzymatically and soluble in water at a pH greater than or equal to 4.

[0031] An "emulsifying agent" means an agent that promotes the fragmentation of one liquid phase into droplets in another liquid phase, thereby promoting the formation of the emulsion.

[0032] By "stabilizing agent" we mean an agent which limits the coalescence of the droplets formed.

[0033] In the present invention, the terms "droplets" and "drops" are used interchangeably.

[0034] Preferably, said lignin being obtained by enzymatic means is soluble in water at a pH greater than or equal to 5, preferably greater than or equal to 6, preferably greater than or equal to 7, and at a pH less than or equal to 13, preferably less than or equal to 12, preferably less than or equal to 11, preferably less than or equal to 10. In particular, said lignin obtained by enzymatic means is soluble in water at a pH between 4 and 12, in particular between 5 and 9, and more particularly between 6 and 8.

[0035] The lignin that can be used for the purposes of the invention can be obtained enzymatically as described, in particular, in application WO2019 / 076893.

[0036] The enzymatic treatment is carried out using at least one enzyme of the bilirubin oxidase (BOD) type. Briefly, the enzymatic production process comprises bringing a lignin into contact, in water, optionally in the presence of a buffering agent, with at least one enzyme, for example of the bilirubin oxidase type, optionally in the presence of a redox mediator, and recovering the lignin solution.

[0037] Advantageously, the soluble lignin thus obtained has a sulfur content 70% lower than known soluble lignins.

[0038] For example, the soluble lignin obtained by enzymatic means may have a sulfur content of less than or equal to 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1.80%, 1.75%. The soluble lignin obtained by enzymatic means has a sulfur content preferably less than 4%, very preferably less than or equal to 2%.

[0039] In one embodiment, the lignin is of the kraft type (or alkaline lignin). Kraft lignin is used when it is obtained by a kraft process (also known as "kraft pulping" or sulfate process), which is a process for converting wood into paper pulp. The kraft process involves treating wood chips with a hot mixture of water, sodium hydroxide, and sodium sulfide, breaking the wood fibers and separating the lignin and hemicellulose from the cellulose. This technique includes mechanical and chemical steps, including impregnation and cooking. In one embodiment, the lignin is of the organosolv type.

[0040] The enzyme used may be a bilirubin oxidase (BOD) of fungal origin, for example a BOD described in international application WO 2012 / 160517 (BOD EC 1.3.3.5. of Magnaporthe oryzae origin).

[0041] According to another variant, the BOD is of bacterial origin, in particular a BOD described in international application WO 2011 / 117839 (BOD EC 1.3.3.5. of Bacillus pumilus origin). According to one embodiment, the lignin obtained after enzymatic treatment can be subjected to an ultrasound treatment so as to optimize and accelerate its dissolution, and to denature the enzyme at the end of incubation.

[0042] The lignin obtained after enzymatic treatment in aqueous solvent is separated from the salts, for example by dialysis or centrifugation. After centrifugation, the supernatant containing the soluble lignin can be used as is or subjected to lyophilization in powder form for further use.

[0043] Soluble lignin is soluble in water at a concentration of up to 90% by mass relative to the mass of the solution.

[0044] The oils used can be chosen from any type of oil, such as for example vegetable oils, mineral oils such as vaseline oil; synthetic oils such as hydrogenated polyisobutene, esters of fatty acids and fatty alcohols (Ce-Cso), fatty alcohol ethers (C4 to C30 saturated and / or branched); silicone oils, in particular volatile silicone oils such as cyclomethicones (cyclotetradimethylsiloxane or cyclotetramethicone, cyclopentadimethylsiloxane or cyclopentamethicone, cyclohexadimethylsiloxane or cyclohexamethicone); fluorinated oils and mixtures thereof.

[0045] Vegetable oils may be chosen, for example, from argan oil, avocado oil, linseed oil, sunflower oil, palm oil, saw palmetto oil, coconut oil, grapeseed oil, black mustard oil, poppy seed oil, shea butter oil, sweet almond oil, soybean oil, peanut oil, cottonseed oil, sesame oil, olive oil, corn oil, cocoa oil, castor oil, Moringa oil (or Ben oil), rapeseed oil, annatto oil, wheat germ oil, safflower oil, walnut oil, hazelnut oil, rapeseed oil or mixtures thereof.

[0046] Vegetable oil can also be produced synthetically, for example by preparing oils with a similar chemical composition, for example by preparing oils including glycerides.

[0047] Emulsions using said soluble lignin can be prepared in the usual manner in the field of oil / water emulsions.

[0048] Said oil / water emulsions can, for example, be obtained according to conventional preparation methods classically used in cosmetics, by gradually incorporating the oily phase into the aqueous phase and homogenizing the whole with stirring. For example, a high-shear mixer can be used for this stirring.

[0049] The aqueous phase (containing water-soluble lignin) like the oily phase, may also possibly contain additives, depending on their hydrophilic or lipophilic nature, prior to mixing the two phases.

[0050] Advantageously, the mass fraction of said lignin in water is from 0.05 to 20%, preferably from 0.5% to 20%, in particular from 0.5% to 15% and more particularly from 1 to 10%, and the mass fraction of oil is from 0.1% to 80%, in particular from 1% to 50%, in particular from 1% to 30%, and more particularly from 5% to 20%, expressed relative to the total weight of the emulsion.

[0051] Stability can be assessed, for example, by observing good dispersion of the oil phase in the aqueous phase and the absence of clusters of oily drops. The behavior of the emulsion can, for example, be analyzed by diluting the emulsion with water, followed by its observation under a microscope. The emulsion is considered unstable if it exhibits heterogeneity created by the presence of large oil drops. Otherwise, good dispersion of the oil drops and good stability of the emulsion, which is homogeneous, are observed. The size of the drops can be measured, for example, under a microscope.

[0052] Advantageously, in the emulsions prepared using the water-soluble lignin according to the invention, stabilization and notable absence of coalescence were observed over several months.

[0053] According to one embodiment of the invention, said soluble lignin obtained enzymatically is used as the sole stabilizing and / or emulsifying agent of the emulsion.

[0054] According to another embodiment, said water-soluble lignin obtained enzymatically is used with at least one other stabilizing and / or emulsifying agent of the emulsion.

[0055] The invention also relates to oil / water emulsions containing said water-soluble lignin, obtained enzymatically and soluble in water at pH greater than or equal to 4 as a stabilizing and / or emulsifying agent, as well as the use of said emulsions in usual industrial applications, such as, for example and without being exhaustive, in the preparation of cosmetic products (creams, lotions, emulsions, etc.), pharmaceutical products (formulations for topical application, formulations for oral administration, etc.), or agri-food products (sauces, seasoning products, dairy products, etc.).

[0056] As is known, emulsions may also contain usual additives depending on the field of application considered, such as solvents, active ingredients, preservatives, antioxidants, complexing agents, perfumes, fillers, bactericides, odor absorbers, coloring matters, etc.

[0057] Examples

[0058] Example 1: Study of enzymatically treated water-soluble lignin

[0059] 1) Preparation of the lignin solution

[0060] On the first day, 3 g of Kraft sigma lignin (CAS 8068-05-1) are introduced into a three-necked flask equipped with a magnetic stirrer. 100 mL of 50 mmol borate at pH 10 are then added to the lignin. The solution is heated and stirred at 250 rpm using a magnetic bar at 60°C in the presence of oxygen. The bacterial bilirubin oxidase (BOD) enzyme, from Bacillus pumilus in liquid form, is incorporated into the solution at 60°C, at a rate of 10 mg of enzyme per 3 g of lignin for 18 hours. Then a dialysis step is initiated by preparing a large 5L beaker containing distilled water. The solution is transferred into this container and dialysis continues for one day, using Spectra / Por 7 Pretreated Regenerated Cellulose (RC) Tubing dialysis bags with a MWCO molecular weight cutoff of 10kD, with two water changes performed after 4 hours and 18 hours.Finally, after the last dialysis, the solution is centrifuged at 4297 g for 15 minutes at room temperature and placed in the freezer (-80°C) for 3 hours, before being lyophilized.

[0061] 2) Rheology

[0062] Rheology experiments were carried out on treated aqueous lignin solutions using an AR2000 rheometer equipped with a 4 cm diameter cone-plate system and a 2 degree angle. A series of dilutions were subjected to these measurements, with volume percentages varying between 20 and 1%. All these measurements were carried out after overnight sample preparation, keeping them under stirring with a magnetic stirrer during this period.

[0063] The variation of dynamic viscosity (Pa.s) as a function of shear rate (1 / s) was measured for aqueous solutions at different lignin concentrations obtained by enzymatic treatment, ranging from 20% to 1% (in water), with intermediate concentrations of 16, 13, 10, 8, 5, 3%.

[0064] The results shown in Figure 1 show that for high concentrations, the lignin solution exhibits thixotropic characteristics, as well as a high viscosity for the most concentrated samples. This increase in viscosity, due to the increase in molecular weight of the BOD-treated lignin, compared to its initial molecular weight, is an asset for the production of emulsions.

[0065] 3) Interfacial tension

[0066] To measure interfacial tension, drop shape analyses were performed using the Teclis Tracker device. These analyses were carried out in 3 different media: air, mineral oil (paraffin oil CAS 8020-83-5) and peanut oil, using lignin volume fractions ranging from 0 to 10%. The drop volume was set between 10 and 15 pL, with a measurement duration of 4 hours.

[0067] The results are shown in Figures 2a and 2b). Figure 2a shows the variation of interfacial tension in the three environments, and Figure 2b shows the variation of interfacial tension for 10% lignin solutions. The results show that the presence of lignin leads to a decrease in interfacial tension of approximately 15 mN / m in all three environments.

[0068] Example 2: Creation and analysis of emulsions

[0069] The emulsions were made with a mixer (Silverson L4RT). The mixer speed was set at a constant speed between 7500 and 7700 rpm. Three types of oil were used: peanut oil, olive oil, and mineral oil (paraffin oil CAS 8020-83-5).

[0070] The total volume of oil added is 10% of the total volume of emulsion made, equivalent to 100 pL. The oil addition is gradual, with incorporation in 25 pL increments. At each addition, an emulsion is created by mixing for 1 minute. This methodology was repeated with 5 concentrations of 1 mL lignin solutions in 4 mL pill bottles, namely 1%, 3%, 5%, 8% and 10%.

[0071] Analysis method:

[0072] All samples were examined on the same day of their preparation, under an optical microscope (Leica DM2500P) with a 10x objective. Dimensional analyses of the emulsions were performed using Image J software, and a curve illustrating the size distribution was generated using OriginPro software. Analyses are performed on optical microscopy images. Observations show the formation of emulsion drops with various sizes.

[0073] The size distributions were performed by measuring approximately 10,000 drops. The stability of the samples was examined in the same way after 3 months, after storage at room temperature, according to the method explained previously. Figures 3a and 3b illustrate the droplet size distribution of an emulsion based on a 5% mass fraction lignin solution in water and mineral oil (paraffin oil CAS 8020-83-5) at the date of their creation and after 3 months. The results show that the size distribution remains constant, with emulsion droplet diameters between 0 and 40 pm. Significantly, the majority of the drops are between 5 and 10 pm, representing the highest percentage.

[0074] Example 3: Study of the stability of the emulsion at temperature

[0075] An aqueous lignin solution is prepared as in Example 1 from enzymatically obtained lignin (in the presence of BOD) dissolved in milliQ water. The concentration of lignin in the aqueous solution is 3% by mass. 10% by mass of mineral oil (paraffin oil CAS 8020-85-5) is then added to the aqueous solution. The resulting suspension is stirred at high shear in a Siverson L4RT mixer operating at 75,000 rpm for 20 min.

[0076] An oil / water emulsion is thus obtained, the oil being in the form of drops.

[0077] The temperature resistance of the emulsion was analyzed by placing this emulsion for 72 hours at 60°C. No change in macroscopic appearance was detected after treatment.

[0078] The microscopic appearance of the emulsion, including the emulsion droplet size distribution, was characterized using a Malvern Mastersizer 2000 particle size analyzer. The droplet size distributions before and after treatment at 60°C are shown in Figure 4.

[0079] Figure 4 shows that the size distributions of the emulsion drops before and after treatment exhibit two peaks characteristic of two main populations of drops, each of these peaks changing very little with temperature.

[0080] These results show that the coalescence of the emulsion is very limited at high temperature and that the emulsion is stable at high temperature.

[0081] These results show that lignin obtained by enzymatic means promotes the formation of an emulsion and limits the coalescence of the oil drops formed even at high temperature.

[0082] Example 4: Comparison with a commonly used surfactant, sodium dodecyl sulfate (SDS)

[0083] An oil / water emulsion stabilized by a soluble lignin obtained by an enzymatic treatment as in Example 1 (in the presence of BOD) is compared to an oil / water emulsion stabilized by sodium dodecyl sulfate (SDS, CAS 151-21-3, Sigma).

[0084] An aqueous solution of soluble lignin obtained by enzymatic treatment as in Example 1 at 3% by mass and an aqueous solution of SDS at 3% by mass are prepared. 10% by mass of mineral oil (paraffin oil CAS 8020-83-5) is then added to each aqueous solution. The suspensions obtained are vigorously stirred in an IKA UltraTurrax Tube Drive mixer operating at 6000 rpm for 30 minutes. Stable emulsions consisting of small oil droplets are thus obtained.

[0085] These emulsions are then centrifuged at high speed to be destabilized. Different speeds (from 5,000 to 80,000g) are used for 30 min. The oil droplet size distributions are measured with a Malvern MasterSizer 2000 particle size analyzer. Figure 5a represents the oil droplet size distribution in the SDS-stabilized emulsion while Figure 5b represents the oil droplet size distribution in the water-soluble lignin-stabilized emulsion.

[0086] Figure 5a shows that with increasing centrifugation force from 5000 to 80,000 g, the peak of the oil droplet size distribution decreases in height and shifts to smaller sizes while a new peak appears and increases for very large sizes with emulsion oil droplet diameter greater than 10 microns.

[0087] These results show that when the emulsion is stabilized by SDS, it evolves in a non-homogeneous manner and very large drops appear in the emulsion. These results show the pronounced coalescence of the emulsion stabilized by SDS: the small diameter drops disappear to form very large diameter drops.

[0088] Conversely, Figure 5b shows that the emulsion stabilized by water-soluble lignin treated with BOD evolves homogeneously and without the appearance of very large drops.

[0089] Furthermore, for the SDS-stabilized emulsion, an oil film on the surface of the emulsion is visible as soon as a centrifugation force of 20,000 g is applied, whereas the oil film only forms on the surface of the lignin-stabilized emulsion at much higher centrifugation forces of the order of 100,000 g.

[0090] Thus, this accelerated aging test by application of a centrifugation force shows that the emulsion stabilized by soluble lignin obtained by enzymatic means is more stable than the emulsion stabilized by SDS.

[0091] Example 5: Comparison with untreated Kraft lignin

[0092] An aqueous solution of soluble lignin obtained by enzymatic treatment with BOD as in Example 1 at 3% by mass and an aqueous solution of crude (untreated) Kraft lignin (CAS 8068-05-1) at 3% by mass are prepared.

[0093] Figure 6 shows the untreated raw Kraft lignin aqueous solution (Fig. 6A) and the Kraft lignin aqueous solution after enzymatic treatment with BOD (Fig. 6B). Figure 6 shows that raw lignin does not dissolve in water and sediments at the bottom of the sample. Conversely, enzymatically processed lignin dissolves rapidly in water and forms a homogeneous aqueous solution.

[0094] 10% by mass of mineral oil (paraffin oil CAS 8020-83-5) is then added to each of the aqueous solutions. The suspensions are vigorously stirred in an IKA UltraTurrax Tube Drive mixer operating at 6000 rpm for 5 min. The emulsion drops are observed under a Leica DM2500P optical microscope with the 10X objective.

[0095] Figure 7 shows the optical microscopy images of oil / water emulsions formed with enzymatically treated lignin (Figure 7a) or formed with raw lignin (Figure 7b). The scale bar shown in Figure 7 corresponds to 100 microns.

[0096] The results shown in Figure 7 show that the oil droplets in the emulsion with BOD-treated lignin are much smaller than the oil droplets in the emulsion with raw lignin. Indeed, these microscopic images show that the droplets formed in the emulsion with treated lignin have a diameter of less than 100 microns or even 10 microns, while the droplets formed in the emulsion with raw lignin have a diameter of more than 100 microns and coalesce.

[0097] A macroscopic observation of the emulsions was also carried out.

[0098] After a few hours, a layer of large oil drops appears on the surface of the emulsion containing crude lignin. After 5 hours, a film of oil is observed on the surface of this emulsion. These characteristics reflect the destruction of the emulsion containing crude lignin by the coalescence of drops.

[0099] Conversely, no oil film is observed on the surface of the emulsion containing the enzymatically treated lignin.

[0100] These results therefore show that enzymatically obtained lignin promotes the formation of oil droplets in the aqueous phase and limits the coalescence of the formed droplets. The presence of lignin obtained after treatment with BOD stabilizes an oil / water emulsion. Enzymatically obtained lignin with BOD is therefore a better emulsifying and stabilizing agent for an oil / water emulsion than raw Kraft lignin. References

[0101] (1 ) Ruwoldt, J. Emulsion Stabilization with Lignosulfonates. In Lignin Sand, A., Tuteja, J., Eds.; IntechOpen: Rijeka, 2022 https: / / doi.org / 10.5772 / intechopen.107336.)

[0102] (2) Shi, C.; Zhang, S.; Wang, W.; Linhardt, R. J.; Ragauskas, A. J. Preparation of Highly Reactive Lignin by Ozone Oxidation: Application as Surfactants with Antioxidant and Anti-UV Properties. ACS Sustain. Chem. Eng. 2020, 8 (1 ), 22-28, https: / / doi.org / 10.1021 / acssuschemeng.9b05498)

[0103] (3) Yuliestyan, A.; Partal, P.; Navarro, F. J.; Martin-Sam pedro, R.; Ibarra, D.; Eugenio, M. E. Emulsion Stabilization by Cationic Lignin Surfactants Derived from Bioethanol Production and Kraft Pulping Processes. Polymers 2022, 14 (14). https: / / doi.Org / 10.3390 / polym 14142879)

[0104] (4) Mikkonen, K. S. Strategies for Structuring Diverse Emulsion Systems by Using Wood Lignocellulose-Derived Stabilizers. Green Chem 2020, 22 (4), 1019-1037. https: / / doi.Org / 10.1039 / C9GC04457D)

Claims

Claims 1. Use of lignin obtained by enzymatic means as a stabilizing and / or emulsifying agent in an oil / water emulsion, said lignin being soluble in water at a pH greater than or equal to 4 and the enzymatic treatment of said enzymatic pathway being carried out using at least one bilirubin oxidase type enzyme.

2. Use according to claim 1, wherein said lignin is soluble in water at pH greater than or equal to 5, preferably greater than or equal to 6, preferably greater than or equal to 7, and pH less than or equal to 13, preferably less than or equal to 12, preferably less than or equal to 11, preferably less than or equal to 10.

3. Use according to claim 1, in which said lignin is soluble in water at a pH between 4 and 12, in particular between 5 and 9, and more particularly between 6 and 8.

4. Use according to one of claims 1 to 3, in which said lignin is obtained by a process comprising bringing a lignin, in water, in the presence or absence of a buffering agent, into contact with at least one bilirubin oxidase type enzyme, in the presence or absence of a redox mediator, and recovering the lignin solution.

5. Use according to one of claims 1 to 4, in which the mass fraction of said lignin in water is from 0.05 to 20%, preferably from 0.5% to 20%, in particular from 0.5% to 15% and more particularly from 1 to 10%, and the mass fraction of oil is from 0.1% to 80%, in particular from 1% to 50%, in particular from 1% to 30%, and more particularly from 5% to 20%, expressed relative to the total weight of the emulsion.

6. Use according to any one of claims 1 to 5, wherein said oil is chosen from vegetable oils, mineral oils and silicone type oils.

7. Use according to any one of claims 1 to 6, wherein said soluble lignin obtained enzymatically is used as the sole stabilizing and / or emulsifying agent of the emulsion.

8. Use according to any one of claims 1 to 6, wherein said water-soluble lignin obtained enzymatically is used with at least one other stabilizing and / or emulsifying agent of the emulsion.

9. Use according to any one of claims 1 to 8 for stabilizing emulsions in the preparation of cosmetic, pharmaceutical or agri-food products.

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