Capsule drying method

Abstract

The present invention relates to a method for drying a capsule having a shell formed by a gelled casing mainly composed of biopolymer, and a method for rehydrating said capsules. The present invention also relates to the dehydrated capsules obtained by said drying method as well as to the rehydrated capsules obtained following the rehydration method.

Description

[0001] DESCRIPTION

[0002] TITLE: Capsule drying process

[0003] The present invention relates to a method for drying capsules having a shell formed from a gelled envelope mainly composed of biopolymer and a method for rehydrating these capsules. The present invention also relates to the dehydrated capsules obtained by this drying method, and to the rehydrated capsules obtained following the rehydration method.

[0004] Capsule formulations are increasingly used in a wide variety of technical fields because they offer numerous advantages. Drying these capsules could facilitate their storage and transport, particularly by reducing their volume and weight, but also improve the stability of the product during storage.

[0005] The invention relates herein to a capsule drying method in which the capsule comprises a shell and a core, in which the core of the capsule is aqueous, or of the oil-in-water emulsion type, or of the water-in-oil emulsion type, in which the shell is a gelled envelope mainly composed of at least one biopolymer; in which the shell has a thickness of at least 10 μm; in which said drying method comprises a step of fluidized bed drying and / or freeze-drying.

[0006] The invention also relates to a dehydrated capsule capable of being obtained by the drying process according to the invention.

[0007] Secondly, the capsules can be rehydrated, preferably before use, especially if their effectiveness is greater in hydrated form.

[0008] Thus the invention also relates to a method for rehydrating dehydrated capsules, comprising suspending the dehydrated capsules in an aqueous medium.

[0009] Finally, the invention relates to the rehydrated capsule capable of being obtained by the rehydration process of the invention. detailed description of the invention

[0010] Capsule

[0011] By "capsule" is meant here a capsule comprising at least a core and a shell. Such capsules preferably comprise a liquid core encapsulated by a substantially solid gelled shell. This type of capsule has applications in numerous technical fields. The shell encompasses one or more concentric or non-concentric compartments. Preferably, the capsules according to the invention comprise only a single core coated by the shell. Preferably, the capsules according to the invention have an average diameter of less than 10 mm in hydrated form.

[0012] These capsules are therefore very different from beads, because beads are mainly made up of a solid or gelled matrix comprising multiple small inclusions.

[0013] The use of capsules rather than beads also allows a larger volume of core to be confined.

[0014] According to a preferred embodiment of the invention, the capsules have a core volume to total capsule volume ratio greater than 20%. These capsules thus make it possible to protect a large volume of core and therefore possibly of active agent, for a given shell volume.

[0015] Preferably, the capsules have a core / shell volume ratio of between 0.2 and 3, and more preferably between 0.5 and 2, before drying.

[0016] Capsules are well known to those skilled in the art and can be formed by different techniques and have different shell compositions.

[0017] Typically, the capsules used in the context of the invention are produced according to the manufacturing process described in French patent no. 2939012.

[0018] As described below, the capsules according to the invention can be dehydrated. However, when they are in hydrated form, such as for example in suspension in an aqueous solution, the capsules according to the invention have an average diameter of between 50 and 4000 μm, preferably between 100 and 2000 μm, more particularly between 200 and 1000 μm, advantageously between 200 and 600 μm. This average diameter can be measured by various techniques well known to those skilled in the art, such as particle size analysis based on laser light diffraction, sieve fractionation or optical microscopy imaging. In one embodiment, the capsules according to the invention further comprise an intermediate layer between the core and the shell. Preferably, this layer is composed of at least one biopolymer in the form of a solution or hydrogel.

[0019] The heart

[0020] The core of the capsules according to the invention may be aqueous, or in the form of an oil-in-water (O / W) emulsion or a water-in-oil (W / O) emulsion. In one embodiment of the invention, the core is an oil-in-water microemulsion.

[0021] The core of the capsules according to the invention is preferably a liquid core. Preferably the viscosity of the core is less than 2000 mPa.s.

[0022] By "aqueous core" we mean a core based on a predominantly aqueous phase.

[0023] In the case where the capsule core is in the form of an oil-in-water (O / W) emulsion or a water-in-oil (W / O) emulsion, oil or a mixture of oils may be used, preferably oils of vegetable, mineral or synthetic origin or a mixture thereof. "Oil" means a fatty substance that is liquid at room temperature (25°C) and atmospheric pressure.

[0024] The hull

[0025] The capsules according to the invention preferably comprise at least one core encapsulated by a substantially solid gelled envelope called the shell.

[0026] Preferably, the shell of the capsules according to the invention is mainly composed of a biopolymer having gelling properties, this biopolymer in the majority proportion in the shell is hereinafter called the main biopolymer. Such biopolymers having gelling properties are for example alginate, gellan gum, xanthan gum, pectin, chitosan, agar or carrageenan.

[0027] The materials that make up the shell are preferably biodegradable and bio-sourced. The shell is preferably semi-permeable to gases and low molecular weight molecules.

[0028] The gels forming the shell can be physical or chemical, i.e. formed by coacervation or by polymerization.

[0029] The gelling of these biopolymers can be achieved by a variation in temperature (gellan gum), a variation in pH (chitosan, pectin) or ionic (alginate, carrageenan). Preferably, the shell of the capsules according to the invention is mainly composed of a biopolymer having gelling properties by ionic or temperature variation.

[0030] Preferably, the shell of the capsules according to the invention is mainly composed of alginate.

[0031] The shell may further comprise one or more other biopolymers than the main biopolymer such as starch (in its various forms, for example amylose, pregelatinized starch), potato protein, or another biopolymer than the main biopolymer having gelling properties, such as for example alginate, gellan gum, xanthan gum, pectin, chitosan, agar or carrageenan.

[0032] Preferably, the shell of the capsules according to the invention comprises a gel containing water, one or more biopolymers having gelling properties, and optionally a surfactant resulting from its manufacturing process.

[0033] Preferably, the shell of the capsules according to the invention comprises a gel containing water, alkaline alginate, and optionally a surfactant resulting from its manufacturing process.

[0034] Preferably, the alkaline alginate is a sodium alginate or a potassium alginate. Alginates are produced from brown algae called laminaria, known by the English term "sea weed". Such alginates advantageously have an aL-guluronate content greater than approximately 50%, preferably greater than 55%, or even greater than 60%.

[0035] The surfactant is advantageously an anionic surfactant, a non-ionic surfactant, a cationic surfactant or a mixture thereof. The molecular weight of the surfactant is between 150 g / mol and 10000 g / mol, advantageously between 250 g / mol and 1500 g / mol.

[0036] In the case where the surfactant is an anionic surfactant, it is for example chosen from an alkyl sulfate, an alkyl sulfonate, an alkylarylsulfonate, an alkali metal alkylphosphate, a dialkylsulfosuccinate, an alkaline earth metal salt of saturated or unsaturated fatty acids. These surfactants advantageously have at least one hydrophobic hydrocarbon chain having a number of carbons greater than 5, or even 10, and at least one hydrophilic anionic group, such as a sulfate, a sulfonate or a carboxylate linked to one end of the hydrophobic chain. In the case where the surfactant is a cationic surfactant, it is for example chosen from an alkylpyridium or alkylammonium halide salt such as n-ethyldodecylammonium chloride or bromide, cetylammonium chloride or bromide (CTAB).These surfactants advantageously have at least one hydrophobic hydrocarbon chain having a number of carbons greater than 5, or even 10, and at least one hydrophilic cationic group, such as a quaternary ammonium cation. In the case where the surfactant is a non-ionic surfactant, it is for example chosen from polyoxyethylenated and / or polyoxypropylenated derivatives of fatty alcohols, fatty acids, or alkylphenols, arylphenols, or from alkyl glucosides, polysorbates, cocamides.

[0037] In one embodiment, the surfactant is sodium lauryl sulfate (LSS) also called sodium dodecyl sulfate and / or polyoxyethylene sorbitan monooleate (Polysorbate 80).

[0038] Preferably, the surfactant is polyoxyethylene sorbitan monooleate (Polysorbate 80).

[0039] In one embodiment, the mass content of surfactant in the shell is greater than 0.001% and is advantageously greater than 0.1%. Advantageously, the mass concentration of surfactant is about 0.03%.

[0040] The shell may also include other compounds that can, in particular, enhance its resistance to drying. These compounds include, for example, biochar. Preferably, the biochar is present in a proportion of 0.1 to 20% by volume fraction in the shell, advantageously 0.5 to 15% by volume fraction in the shell, and preferably 1 to 10% by volume fraction in the shell.

[0041] In the case of a capsule with an oily core, the shell may comprise a sedimentation agent, i.e. an inert agent, preferably mineral, making it possible to make the capsule heavier. Indeed, in the case of capsules with an oily core, these have a tendency to rise to the surface when they are included in an aqueous liquid, thus the addition to the shell of a sedimentation agent makes it possible to make them heavier, preferably so that the capsules are suspended in the liquid containing them. For example, a sedimentation agent according to the invention may be chosen from talc and / or silica. In this case, the sedimentation agent is present at a rate of 1 to 30% in volume fraction in the shell, advantageously at a rate of 5 to 20% in volume fraction in the shell. However, depending on the density of the capsules and the liquid containing them, a person skilled in the art is able to estimate the quantity of sedimentation agent necessary to obtain the desired effect.

[0042] The shell of the capsules has a thickness of at least 10 μm. Indeed, the inventors have shown that such a shell thickness gives the capsule better resistance to drying. If the membrane of the shell were thin, the capsule would be weakened and would not withstand the shear forces / mechanical stresses applied during the handling of the capsules by the operator for example or the conditions of agitation of the capsules during physicochemical treatments and would be at high risk of breaking.

[0043] However, a membrane that is too thick would lose its appeal.

[0044] In particular, the shell of the capsules therefore has a thickness of between 10 pm and 1200 mm, advantageously between 20 pm and 800 pm, and more particularly between 20 pm and 400 pm.

[0045] In particular, relative to the diameter of the capsule, the shell of the microcapsule preferably has a thickness of between 0.1% and 30%, advantageously between 1% and 20%, and more particularly between 10% and 20% of the diameter of the capsule.

[0046] Drying process

[0047] The invention relates to a capsule drying method in which the capsule comprises a shell and a core, in which the core of the capsule is aqueous, or of the oil-in-water emulsion type, or of the water-in-oil emulsion type, in which the shell is a gelled envelope mainly composed of at least one biopolymer; in which said drying method comprises a step of fluidized bed drying and / or freeze-drying.

[0048] By "fluidized bed drying" is meant a process of bringing a rising gas into contact with a bed of particles (here the capsules), where the weight of the capsules is compensated by the current due to the gas flow. The capsule bed then behaves like a fluid. This technique makes it possible to increase the gas-capsule surface area to facilitate drying. The fluidized bed drying according to the invention can be on a simple fluidized bed, a vibrated fluidized bed, or a fluidized bed with an internal exchanger.

[0049] Preferably, before drying on a fluidized bed, the capsules according to the invention are coated with an anti-agglomerate agent.

[0050] The term "anticaking agent" means an agent that limits or prevents capsule clumping or capsule lump formation. Anti-clumping agents are well known to those skilled in the art and include, but are not limited to, calcium carbonate, tricalcium phosphate, calcium silicate, magnesium silicate, calcium stearate, magnesium stearate, magnesium carbonate, magnesium oxide, silicon dioxide, sodium aluminosilicate, sodium ferrocyanide, potassium ferrocyanide, and mixtures thereof.

[0051] Preferably, the anti-caking agent is calcium carbonate. By "coating" is meant the application of a layer of powder to the surface of the capsules.

[0052] "Lyophilization" means dehydration by sublimation of water. Preferably, the capsules are immersed in a co-formulant bath, then frozen to at least -80°C and then lyophilized.

[0053] By "co-formulant" we mean an additional compound, without any biological activity of its own, used to facilitate the handling of capsules or to limit the degradation of capsules.

[0054] For example, a co-formulant may be a cryoprotectant. Cryoprotectants that may be used in the context of the invention are glycerol, poly-L-lysine, lactose, trehalose, inulin, glutamate, sodium ascorbate, magnesium sulfate, sodium bicarbonate, sucrose, maltodextrin, milk powder and mixtures thereof.

[0055] In a preferred embodiment, the capsules are immersed in a bath of co-formulant comprising sucrose and more preferably comprising a concentration of between 50 and 500 g / L of sucrose.

[0056] In a preferred embodiment, the capsules are immersed in a bath of co-formulant comprising maltodextrin and more preferably comprising a concentration between 50 and 500g / L of maltodextrin.

[0057] In a preferred embodiment, the capsules are immersed in a bath of co-formulant comprising milk powder and more preferably comprising a concentration between 20 and 150 g / L.

[0058] The freezing step at -80°C is carried out until the core of the capsules is in a solid state. Preferably, the capsules are frozen at -80°C for at least 6 hours, and more preferably for at least 12 hours.

[0059] The drying process according to the invention makes it possible to obtain capsules in dehydrated form.

[0060] Preferably, the drying process makes it possible to reduce the humidity by weight of the capsules by at least 70%, at least 80% and more particularly at least 90%.

[0061] Preferably, the dehydration is partial, and the capsules obtained have a humidity level of less than 10%, measured by a humidity analyzer after dehydration.

[0062] The invention also relates to a dehydrated capsule obtainable by any of the dehydration methods of the invention.

[0063] Preferably, the capsules obtained have a moisture content of less than 10% by weight, measured by a moisture analyzer after dehydration. In dehydrated form, the average diameter of the capsule tends to decrease. Preferably, the capsule according to the invention has an average diameter of between 10 μm and 4 mm in dehydrated form.

[0064] Rehydration process

[0065] The present invention relates to a method for rehydrating dehydrated capsules, preferably dehydrated capsules according to the invention, said method comprising suspending the dehydrated capsules in an aqueous medium.

[0066] Preferably, the aqueous medium is composed mainly of water, preferably purified water such as ultrapure water. The aqueous medium may be physiological water, i.e. purified water comprising 0.9% (m / v) sodium chloride.

[0067] In particular, the aqueous medium can be water supplemented with surfactant, for example with tween.

[0068] Thus, in one embodiment of the invention, if the dehydrated capsule does not comprise any living being or microorganisms, the rehydration method comprises suspending the dehydrated capsules in ultrapure water.

[0069] In another embodiment of the invention, if the dehydrated capsule comprises bacteria and / or viruses, the rehydration method comprises suspending the dehydrated capsules in physiological saline.

[0070] In another embodiment of the invention, if the dehydrated capsule comprises fungi or spores, the rehydration method comprises suspending the dehydrated capsules in an aqueous medium supplemented with surfactant, preferably in physiological water supplemented with Tween.

[0071] Preferably the dehydrated capsules are suspended in the aqueous medium for at least 30 minutes, preferably from 30 minutes to 1 hour. Preferably the dehydrated capsules are suspended at room temperature, i.e. between 10 and 25°C. Preferably the suspension is promoted by stirring.

[0072] The invention also relates to a rehydrated capsule obtainable by the rehydration method of the invention.

[0073] In the following description and examples, unless otherwise indicated, percentages are percentages by weight and ranges of values ​​expressed as "between ... and ...", "from ... to ...", or "greater than ..." include the limits specified. Throughout the application, the wording "comprising a" or "comprising a" means "comprising at least one" or "comprising at least" one unless otherwise specified.

[0074] The following examples are presented for illustrative purposes and are not intended to limit the scope of the invention.

[0075] Example 1: Freeze-drying test of capsules and their rehydration

[0076] Two alginate capsule prototypes are tested in which the biochar included in the capsule core serves as a probe to estimate and / or quantify the number of degraded capsules and / or the amount of probe lost during freeze-drying and rehydration. The first prototype (prototype 1) includes biochar only in the capsule core. The second prototype includes biochar in both the core and the shell. The biochar incorporated in the capsule shell serves here to stiffen the shell.

[0077] Alginate capsule prototypes are formed under the following production conditions:

[0078] The nozzle diameter of the injector is 200 μm. The total flow rate of the core and shell fluid, named Qtot, is 450 mL / h, the flow rate ratio between the core and shell fluid, named Rq, is 0.8, and gives a membrane thickness of at least 30 μm.

[0079] The capsules are produced by immersion in a calcium chloride bath. A sample of the calcium chloride bath is taken for the determination of the biochar present in this bath. This is the proportion of biochar that has not been encapsulated (the encapsulation yield is slightly less than 100%). The capsules are then collected and washed with water to remove the biochar that would be deposited on the surface of the capsules.

[0080] A sample of wet capsules is taken for the determination of the biochar contained in the capsule. For this, the capsules are incubated in a PBS / EDTA solution to solubilize the alginate shell and thus release the contents. The addition of PBS allows to maintain the physiological conditions of ionic strength and pH of the solution. The rest of the capsules are then incubated in a co-formulant bath (SM-Sucrose, i.e. a bath comprising 300 g / L of sucrose) and frozen at -80°C.

[0081] Then these capsules are freeze-dried. After freeze-drying, the capsules are washed by suspending them in an ultrapure water solution to allow release into the continuous phase and then to measure the biochar resulting from the rupture of the capsules during the freezing / freeze-drying step. After the washing step, a sample is taken for the measurement of the biochar contained in the capsules.

[0082] The columns named "hydrated capsules" and "dehydrated capsules" include the measurement of the OD (optical density) and the estimation of the quantity of biochar found after dissolution of the capsules. This dissolution is carried out by solubilization of the alginate hydrogel which composes the shell of the capsules. For this, a solution of PBS / EDTA (phosphate buffer saline / Ethylene Diamine Tetraacetic Acid) is used and allows the contents of the capsules to be released into the continuous phase. EDTA in fact allows the calcium ions present in the shell to be chelated.

[0083] The columns named "calcium bath" and "wash buffer" include the amount of probe lost in these baths or buffers.

[0084] [Table 1] Table 1: quantification of biochar at each stage of the treatment of prototype 1

[0085] Thus in proportions, the fraction [washing buffer of dehydrated capsules] represents 7% of the total quantity of biochar and the fraction [dehydrated capsules] represents 100- 7.06 = 92.94%.

[0086] The loss of biochar during the freeze-drying process is therefore estimated at only 7% with prototype 1. [Table 2] Table 2: quantification of biochar at each stage of the treatment of prototype 2

[0087] The loss of biochar during the freeze-drying process is therefore estimated at only 0.5% with prototype 2. The loss of biochar is therefore reduced in the presence of biochar in the capsule shell by a factor of 10, going from 7% to 0.5%

[0088] Example 2: freeze-drying test of capsules containing a bacteriophage and their rehydration

[0089] Two prototype alginate capsules are tested in which bacteriophages are embedded in the capsule core and serve as a living probe to quantify the number of degraded capsules and / or the amount of probe lost during lyophilization and rehydration.

[0090] The first prototype (prototype 1) does not include biochar. The second prototype (prototype 2) includes biochar in the shell.

[0091] Alginate capsule prototypes are formed under the following production conditions:

[0092] The total flow rate of core and shell fluid named Qtot is 500 mL / h, the flow rate ratio between core and shell fluid, named Rq is 0.8.

[0093] The average diameter of the two capsule prototypes is 462 pm with a coefficient of variation of 17% and 542 pm with a coefficient of variation of 18%, respectively. The shell thickness of these prototypes is at least 30 pm.

[0094] Bacteriophages of strain M13K07 are lytic bacteriophages that act selectively and specifically against the bacterial pathogen Escherichia coli. [Table 3] Table 3: Quantification of bacteriophages during capsule formation and drying

[0095] [Table 4] Table 4: Evaluation of bacteriophage losses during capsule drying

[0096] The calculations are carried out as follows:

[0097] The "encapsulation yield by the so-called calcium bath method" is calculated by measuring the quantity of bacteriophage remaining in the bath and therefore not encapsulated, compared to the quantity of bacteriophage used during the formation of the capsules.

[0098] [Table 5] Table 5: Bacteriophage encapsulation yields

[0099] The loss of survival of bacteriophages during lyophilization is estimated at 5%.

[0100] Example 3: Fluidized bed drying test of capsules

[0101] Fluidized air bed drying of a prototype alginate capsule containing a bacterial strain was tested. The prototype alginate capsule is formed under the following production conditions:

[0102] The nozzle diameter of the injector is 150 pm. The total flow rate of the core and shell fluid named Qtot is 350 mL / h, the flow rate ratio between the core and shell fluid, named Rq is 1, giving the capsules a membrane thickness of at least 20 pm.

[0103] Once produced and washed in physiological water, the capsules are mixed with calcium carbonate in mass proportions 1:1 before drying them in a fluidized air bed for 30 minutes. The temperature reached within the enclosure remains below 45°C.

[0104] Once dry, the capsules are washed by resuspension in physiological saline to remove calcium carbonate. A sample of capsules is taken to determine the bacterial concentration contained in the capsules.

[0105] Bacterial concentrations in wet and dry products are 5.48.10, respectively. 8 UFC / g and 4.11.10 5CFU / g. The inventors observed that the bacterial concentration of the prototype after drying in a fluidized air bed remains relatively high.

Claims

CLAIMS 1. A method of drying a capsule in which the capsule comprises a core and a shell, in which the core of the capsule is aqueous, or of the oil-in-water emulsion type, or of the water-in-oil emulsion type, in which the shell is a gelled envelope mainly composed of at least one biopolymer; in which the shell has a thickness of at least 10 μm; in which said drying method comprises a step of drying on a fluidized bed and / or lyophilization.

2. Capsule drying method according to claim 1, wherein the shell is mainly composed of alginate.

3. Drying method according to any one of claims 1 to 2 in which the capsule before drying has a core / shell volume ratio of between 0.5 and 2.

4. Drying method according to any one of claims 1 to 3 in which the capsules are immersed in a bath of co-formulant, then frozen to at least -80°C then lyophilized.

5. Drying method according to any one of claims 1 to 3 in which before drying on a fluidized bed the capsules according to the invention are coated with an anti-agglomerate agent.

6. Dehydrated capsule obtainable by any one of the processes according to claims 1 to 5.

7. A method of rehydrating dehydrated capsules according to claim 6, comprising suspending the dehydrated capsules in an aqueous medium.

8. Rehydrated capsule obtainable by the capsule rehydration process according to claim 7.

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