GB2480730A

GB2480730A - Capsules comprising a hydrophilic core, intermediate oil layer and polymer shell

Info

Publication number: GB2480730A
Application number: GB1106947A
Authority: GB
Inventors: Piotr Garstecki; Marcin Izydorzak; Jacek Michalski; Dominika Ogonczyk
Original assignee: Instytut Chemii Fizycznej of PAN
Current assignee: Instytut Chemii Fizycznej of PAN
Priority date: 2010-05-28
Filing date: 2011-04-27
Publication date: 2011-11-30
Anticipated expiration: 2031-04-27
Also published as: PL391361A1; PL216320B1; GB2480730B; GB201106947D0

Abstract

Capsules are disclosed that comprise a hydrophilic core, an intermediate oil layer and a polymer shell formed from an aqueous polymer solution, characterised in that the said intermediate oil layer contains a hydrophobic substance with a melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C. Also disclosed is a method for producing said capsules, comprising introducing into solution composite droplets composed of at least three layers, where the external layer is made of an aqueous polymer solution, the intermediate layer is an oil and the droplet core is hydrophilic, characterised in that the said intermediate layer contains a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C.

Description

Capsules with hydrophilic core and polymer shell and method for producing thereof The subject matter of the invention are capsules with a hydrophilic core and a polymer shell and a method for producing thereof. The invention relates to capsules or mini-capsules. The capsule's core may contain dissolved (or suspended) additional organic and inorganic substances providing for appropriate taste, odour and consistency, as well as for proper action of active substances.

The state of the art knows basically two different methods for producing capsules and multiple capsules (i.e., capsules consisting of more than two layers). The first one, disclosed, e.g., in patents US 4,202,908; US 4,362,748 or in patent application WO 2005/060769 Al, consists in: * preparation of the core by introducing droplets of polymer solution (essentially aqueous phase) into a chilled oil, * washing oil rests with water, * coating the core prepared beforehand with successive coatings by successively bathing in polymer solutions and solutions containing cross-linking agents, e.g., biva lent metal ions.

This is a multi-stage method and obviously a complex one. It allows to produce capsules with hydrophilic core, the core, however, contains a polymer, which -when not protected by additional protective layers, gelatinizes with time forming an elastic granule. It may also get dry forming a hard and rigid sphere (or granule), unsuitable, e.g., in production of capsules -the caviar-like ones or in other applications.

The second method, disclosed, e.g., in patents us 5,260,002; us 4,375,481; us 3,962,383; us 4,695,466 or in application WO 2007/103186, leads to formation of capsules or multiple capsules in one stage: * a droplet composed of multiple layers formed beforehand in a set of coaxially aligned nozzles is introduced to a bath containing a polymer cross-linking agent (temperature, metal ions -most frequently calcium, etc.). Depending on the complication of presented systems, the number of nozzles varies from two to five.

These solutions are used mainly to form capsules with purely oil filling. In spite of being a one-stage one, the method is not entirely free of drawbacks in formation of capsules containing hydrophilic core. One of them, in the solutions known so far, is a necessity to use one or more polymers in the core. These polymers are used as substances preventing moisture escape from the inside of the capsule. Gelatine is often used; it is a substance of animal origin, produced from bones and cartilages, mainly of domestic pig. Therefore, gelatine may be not used by some individuals for religious or dietetic reasons. Polymer or other substances are necessary according to methods known from the state of the art, because otherwise water would be removed from the capsule during drying. The polymer is also used as an internal framework, providing the core with required rigidity in the structure of multiple capsules (e.g., US patent 4,695,466).

An additional shortcoming of the above solutions is lacking compatibility of polymers with many substances or components. Some polymers, such as alginates, can not be used to prepare acidic solutions. Using the solutions mentioned above one can not encapsulate components that contain substances with acidic reaction.

Therefore, production of capsules which do not have to contain in their core polymers or other components preventing escape of moisture still remains a problem. At the same time, a challenge is also to produce capsules with hydrophilic core that maintain elasticity during long term storage. Then, a problem is to prevent gelatinization of capsule core so that the gelatinized layer forms only a shell for fluid interior. Encapsulation of components with acidic reaction is also problematic. It turned unexpectedly out that it is possible to produce capsules which do not contain polymers or other water binding substances with a method according to the invention. The method according to the invention allows also encapsulating acidic components or those containing acidic substances.

According to the invention, the capsules with hydrophilic core and polymer shell, comprising an external layer formed from an aqueous polymer solution, an intermediate oil layer and a hydrophilic core are characterised in that the said intermediate layer contains a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C. For example, the said hydrophobic substance is selected from the group consisting of isopropyl palmitate, butyl palmitate, propyl palmitate, ethyl palmitate, isoamyl palmitate, ethyl myristate, methyl myristate, butyl stearate and methyl anthranilate and mixtures thereof.

More preferably, the said intermediate layer contains additionally a surface active agent (surfactant), e.g. lecithin. The surfactant is dissolved in the hydrophobic substance in concentration from 3 to 50% per weight, and more preferably from S to 30% per weight.

Preferably, the said polymer contained in the shell is sodium alginate.

In a preferred embodiment, the said hydrophilic core comprises of pure water, aqueous solution, aqueous emulsion or suspension.

The invention covers also a method for producing capsules with hydrophilic core and polymer shell, comprising of introducing into solution composite droplets composed of at least three layers, where the external layer is made of a polymer aqueous solution, the intermediate layer is an oil one and contains the hydrophobic substance, whereas the core is hydrophilic.

Preferably, the said droplets composed of at least three layers are formed by pumping fluids A, B and C through a nozzle containing 3 coaxially aligned tubes, where the external layer (C) contains a polymer solution, preferably polysaccharide, more preferably alginate, and most preferably sodium alginate, the intermediate layer (B) contains a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C, and the internal layer -(A) is pure water, aqueous solution, aqueous emulsion or suspension.

In a preferred embodiment of the invention, the said nozzle includes additionally a fourth tube, surrounding three tubes mentioned above and aligned coaxially with them; the fourth tube is used to pump the most external fluid layer (D) and to control correct formation of droplets with the flow of the fluid (D).

In one of the variants of the invention, the said fluid (D) is gas, preferably air.

Preferably, the said fluids are pumped under pressure.

Preferably, the fluid flows from 1 to 100 mI/h are used, preferably from 2 to 50 mI/h, and most preferably from 3 to 35 mI/h.

According to the invention, the gas (D) overpressure ranges from 0 to 300kPa, more preferably from 5 to l5OkPa, and most preferably from 20 to lOOkPa.

In a preferred embodiment of the invention, the droplets produced are subsequently gelatinized in a bath containing a cross-linking agent.

The temperature of the chilling bath is lower than the melting point of the said intermediate oil layer. More preferably, the temperature of the chilling bath ranges from 0°C to 25°C and is lower than the melting point of the intermediate oil layer by not less than 5°C, and not more than 20°C.

Preferably, the said cross-linking agent is bivalent metal ions, preferably strontium or barium, more preferably zinc, and most preferably calcium ions.

Preferably, the said bivalent metal ions are introduced into solution in the form of water soluble salts, preferably in concentration from 0.2 to 2% per weight, and more preferably from 0.5 to 1.5% per weight.

According to the invention, the gelatinization time ranges from 2 to 300 minutes, more preferably from 5 to 50 minutes, and most preferably from 15 to 30 minutes.

During gelatinization, the liquid in the tank is stirred preferably with rotation speed from 50 to 1000 rotations/mm; more preferably between 100 and 300 rotations/mm.

Preferably, said capsules are stored in a tight container under oil or water, or in air. Storage temperature ranges from 4°C to 10°C.

The capsules according to the invention are comprised of an external layer formed from an aqueous polymer solution, e.g., sodium alginate, an intermediate oil layer and a core composed of an aqueous phase, i.e. pure water or aqueous solution or aqueous emulsion or suspension, where said intermediate oil layer is stabilized with a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C. For example, the hydrophobic substances may be: isopropyl palmitate, butyl palmitate, propyl palmitate, ethyl palmitate, isoamyl palmitate, ethyl myristate, methyl myristate, butyl stearate and methyl anthranilate and mixtures thereof.

More preferably, the said intermediate layer contains additionally a surface active agent, e.g., lecithin. The surfactant is dissolved in the hydrophobic substance in concentration from 3 to 50% per weight, and more preferably from 5 to 30% per weight.

The method according to the invention consists in introducing into solution composite droplets composed of at least three layers, where the external layer, the intermediate layer and the core correspond to capsule layers as mentioned above.

The external layer is gelatinized -by forming a shell, for instance by bathing in a chilling solution containing bivalent metal ions.

The temperature of the chilling bath is lower than the melting point of the hydrophobic substance contained in the intermediate layer. Preferably, the temperature of the chilling bath is lower than the melting point of the intermediate oil layer by not less than 5°C, and not more than 20°C. Such method warrants simultaneous formation of the shell and solidification of the intermediate layer. Due to stabilisation of intermediate layer according to the invention an intermediate layer is obtained that maintains moisture inside the core. The method according to the invention leads thus to production of capsules with hydrophilic core, stable in time and durable outside the system where they are produced, even if the said core is entirely hydrophilic, i.e., does not contain polymers nor other water binding substances.

The capsules produced with the method described here may be particularly suitable in industrial applications: in food, pharmaceutical and cosmetic industries, in veterinary medicine or agricultural engineering.

The invention and its application are illustrated in an embodiment in attached figures, where: Fig. 1 shows a cross-section of coaxial nozzle system where a droplet is formed. Each nozzle contains fluid corresponding to another layer of the droplet. Fluid A in the internal nozzle forms the droplet core, fluid B in the intermediate nozzle forms the intermediate layer, and fluid C in the external nozzle forms the external layer of the droplet. Fluid D in the most external nozzle is responsible for formation of the entire multi-layered structure into a droplet of appropriate size, Fig. 2 shows a cross-section of a formed multi-layer droplet where the area A formed from fluid A represents the core of the droplet, the area B formed from the fluid B represents the intermediate layer of the droplet, and the droplet's external layer C formed from fluid C is the shell of the droplet.

The method for producing capsules with hydrophilic core according to the invention consists in: Pumping fluids A, B and C through a nozzle containing 3 coaxially aligned tubes (shown in Fig. 1) and forming a multi-layer droplet (Fig. 2). Subsequent layers of the droplet are characterized in that the external one (C) contains a polymer solution, preferably polysaccharide, and most preferably alginate in the form of sodium alginate. The intermediate layer (B) contains hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C. For example, the hydrophobic substances may be: isopropyl palmitate, butyl palmitate, propyl palmitate, ethyl palmitate, isoamyl palmitate, ethyl myristate, methyl myristate, butyl stearate and methyl anthranilate and mixtures thereof. More preferably, the said intermediate layer contains additionally a surface active agent, e.g., lecithin. The surfactant is dissolved in the hydrophobic substance in concentration from 3 to 50% per weight, and more preferably from 5 to 30% per weight.

The internal layer (A) is an aqueous solution or aqueous suspension or emulsion.

Preferably, the said nozzle includes also a fourth tube, surrounding three tubes mentioned above and aligned coaxially with them. The most external fluid layer (D) pumped through the fourth tube is used to form droplets of appropriate size by means of the flow of the fluid. Preferably, fluid (D) is gas, for instance air.

Any pumps used in the state of the art can be used to pump fluids: peristaltic, piston, syringe pumps, or preferably, the fluids are pumped under pressure. In a system with single nozzle, the fluid flow speeds range from 1 to lOOml/h, preferably from 2 to SOml/h, and most preferably from 3 to 35m1/h. Gas overpressure to form the droplets ranges from 0 to 300kPa, more preferably from S to lSOkPa, and most preferably from 20 to lOOkPa. In a multiple nozzle system designed according to the invention, the flow intensities multiply in proportion to the number of nozzles, and the overpressure is adjusted so as to reach the desired droplet size, from several millimetres to several tenths of millimetre.

The droplets with size from below 1mm to over 6mm are subsequently gelatinized in a chilling bath containing a cross-linking agent; preferably containing bivalent metal ions.

The temperature of the chilling bath is lower than the melting point of the hydrophobic substance contained in the intermediate layer. Preferably, the temperature of the chilling bath is lower than the melting point of the intermediate oil layer by not less than 5°C, and not more than 20°C.

The gelatinization proceeds in a separate tank containing a cross-linking agent.

Preferably, the cross-linking agent may be bivalent metal ions: preferably strontium, barium, more preferably zinc, and most preferably calcium ions. They are introduced into a solution in the form of water soluble salts, preferably in concentration from 0.2% to 2% per weight, and more preferably from 0.5% to 1.5%. The cross-linking is carried out by allowing freshly formed capsules to stay for a specific period of time in a solution containing a cross-linking agent. Preferably, the cross-linking time ranges from 2 to 300 minutes, more preferably from 5 to 50 minutes, and most preferably from 15 to 30 minutes. The liquid in the tank is preferably stirred with rotation speed from 50 to 1000 rotations/mm; more preferably between 100 a 300 rotations/mm.

The capsules may be stored in tight containers under oil or water or in air. The storage temperature ranges from 4°C to 10°C.

Reagents Reagents: polymers used to prepare solutions, edible oils and other oils are common reagents available in retail trade. The surface active agents and the hydrophobic substances with an appropriate melting point are also commercially available reagents.

Preferable embodiments of the invention

Example 1

The following substances have been pumped simultaneously through a multiple nozzle composed of 4 coaxially aligned tubes: Nozzle A) water with pumping speed 30m1/h, nozzle B) isopropyl palmitate containing 25% per weight lecithin with pumping speed lOml/h and nozzle C) 1% sodium alginate solution with pumping speed 35m1/h, gas overpressure in nozzle D) was lOkPa.

Three-layered droplets with external diameter of about 5mm were collected in a 400m1 vessel containing a 1% calcium chloride solution, chilled beforehand to the temperature 4°C.

After 20 minutes of operation the flow was stopped and the capsules formed were stirred for another 15 minutes. Then, the capsules were filtered out and washed with water. So prepared capsules are suitable for direct use or may be stored for several months in a refrigerator.

Example 2

The following substances have been pumped simultaneously through a multiple nozzle composed of 4 coaxially aligned tubes: Nozzle A) water with pumping speed 40m1/h, nozzle B) butyl stearate containing 5% per weight lecithin with pumping speed lOml/h and nozzle C) 1% sodium alginate solution with pumping speed 35m1/h, gas overpressure in nozzle D) was lOkPa.

Three-layered droplets with external diameter of about 5mm were collected in a 400m1 vessel containing a 1% calcium chloride solution, chilled beforehand to the temperature 10°C. After 20 minutes of operation the flow was stopped and the capsules formed were stirred for another 15 minutes. Then, the capsules were filtered out and washed with water.

So prepared capsules are suitable for direct use or may be stored for several months in a refrigerator.

Example 3

The following substances have been pumped simultaneously through a multiple nozzle composed of 4 coaxially aligned tubes: Nozzle A) water with pumping speed 35m1/h, nozzle B) ethyl myristate with pumping speed 3m1/h and nozzle C) 1% sodium alginate solution with pumping speed 40m1/h, gas overpressure in nozzle D) was 2OkPa.

Three-layered droplets with external diameter of about 4mm were collected in a 400m1 vessel containing a 1% calcium chloride solution, chilled beforehand to the temperature 4°C.

After 10 minutes of operation the flow was stopped and the capsules formed were stirred for another 30 minutes. Then, the capsules were filtered out and washed with water. So prepared capsules are suitable for direct use or may be stored for several months in a refrigerator.

Claims

Patent claims 1. Capsules with hydrophilic core and polymer shell, comprising an external layer formed from an aqueous polymer solution, an intermediate oil layer and a hydrophilic core, characterised in that the said intermediate layer contains a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C.
2. Capsules of claim 1, characterised in that the said hydrophobic substance is selected from the group consisting of isopropyl palmitate, butyl palmitate, propyl palmitate, ethyl palmitate, isoamyl palmitate, ethyl myristate, methyl myristate, butyl stearate and methyl anthranilate and mixtures thereof.
3. Capsules of claim 1 or 2, characterised in that the said intermediate layer contains a surface active agent.
4. Capsules of claim 3, characterised in that the said surface active agent is lecithin.
5. Capsules of claim 3 or 4, characterised in that the concentration of the said surface active agent ranges from 3 to 50% per weight, preferably from S to 30% per weight.
6. Capsules of any of the foregoing claims, characterised in that the said polymer is sodium alginate.
7. Capsules of any of the foregoing claims, characterised in that the said hydrophilic core comprises of pure water, aqueous solution, aqueous emulsion or suspension.
8. A method for producing capsules with hydrophilic core and polymer shell, comprising of introducing into solution composite droplets composed of at least three layers, where the external layer is made of a polymer aqueous solution, the intermediate layer is an oil one and the droplet core is hydrophilic, characterised in that the said intermediate layer contains a hydrophobic substance with melting point higher than S°C, and lower than 2S°C, preferably higher than 8°C, and lower than 1S°C.
9. The method of claim 8, characterised in that the said droplets composed of at least three layers are formed by pumping fluids A, B and C through a nozzle containing 3 coaxially aligned tubes, where the external layer (C) contains a polymer solution, preferably polysaccharide, more preferably alginate, and most preferably sodium alginate, the intermediate layer (B) contains a hydrophobic substance with melting point higher than 5°C, and lower than 25°C, preferably higher than 8°C, and lower than 15°C, and the internal layer (A) is pure water, aqueous solution, aqueous emulsion or suspension.
10. The method of claim 9, characterised in that the said nozzle includes additionally a fourth tube, surrounding three tubes mentioned above and aligned coaxially with them; the fourth tube is used to pump the most external fluid layer (D) and to control correct formation of droplets with the flow of the fluid (D).
11. The method of claim 10, characterised in that the said fluid (D) is gas, preferably air.
12. The method of any of the claims from 9 to 11, characterised in that the said fluids are pumped under pressure.
13. The method of any of the claims from 9 to 12, characterised in that the fluid flows from 1 to 100 mI/h are used, preferably from 2 to 50 mI/h, and most preferably from 3 to 35 mI/h.
14. The method of any of the claims from 10 to 13, characterised in that the gas (D) overpressure ranges from 0 to 300kPa, more preferably from S to lSOkPa, and most preferablyfrom 2Oto lOOkPa.
15. The method of any of the claims from 8 to 14, characterised in that the droplets produced are subsequently gelatinized in a chilling bath containing a cross-linking agent.
16. The method of claim 15, characterised in that the temperature of the said chilling bath is lower than the melting point of the said intermediate oil layer.
17. The method of claim 16, characterised in that the temperature of the said chilling bath is lower than the melting point of the said intermediate oil layer by not less than 5°C, and not more than 20°C. ii
18. The method of claim 16 or 17, characterised in that the temperature of the said chilling bath ranges from 0°C to 25°C.
19. The method of any of the claims from 15 to 18, characterised in that the said cross-linking agent is bivalent metal ions, preferably strontium or barium, more preferably zinc, and most preferably calcium ions.
20.The method of claim 19, characterised in that the said bivalent metal ions are introduced into solution in the form of water soluble salts, preferably in concentration from 0.2 to 2% per weight, and more preferably from 0.5 to 1.5% per weight.
21.The method of any of the claims from 15 to 20, characterised in that the gelatinization time ranges from 2 to 300 minutes, more preferably from 5 to 50 minutes, and most preferably from 15 to 30 minutes.
22.The method of any of the claims from 15 to 21, characterised in that during gelatinization the liquid in the tank is stirred preferably with rotation speed from 50 to 1000 rotations/mm; more preferably between 100 and 300 rotations/mm.
23. The method of any of the claims from 8 to 22, the said capsules are stored in a tight container under oil or water, or in air.
24. The method of claim 23, characterised in that the storage temperature ranges from 4°C to 10°C.