NL2004533C2

NL2004533C2 - Particle preparation by centrifugal dispersing.

Info

Publication number: NL2004533C2
Application number: NL2004533A
Authority: NL
Inventors: Albert Thijs Poortinga
Original assignee: Friesland Brands Bv
Priority date: 2010-04-09
Filing date: 2010-04-09
Publication date: 2011-10-11
Also published as: EP2555639A1; WO2011126368A1

Description

P91031NL00

Title: particle preparation by centrifugal dispersing

The invention relates to a method for preparing particles, to particles obtainable by a method according to the invention, to a food product comprising said particles, and to the use of said particles.

Particles have been defined and classified in various different ways 5 depending on their specific structure, size, or composition. As used herein, particles are broadly defined as micro- or nanoscale particles which are typically composed of at least one solid, semi-solid or liquid material. Typically, the weight-average diameter of such particles range from approximately 10 nm to approximately 1000 pm, as may be determined by microscopy (fight microscopy, or electron microscopy, depending on 10 the size, as will be understood by the skilled person). More in particles, the term is used herein for particles having an average particle diameter between about 0.5 pm and 100 pm.

Particles may have a homogeneous structure or a heterogenous structure. Homogenous particles in general consist of a material in a single phase (state of 15 matter), e.g. one liquid phase or a material in a single solid state of matter Particles with a heterogeneous structure wherein two or more states of matter (phases) are distinguishable may be referred to as hierarchical particles. Hierarchical particles in particular include particles comprising an inner core and an outer layer (a coating or shell or the like), such as nano- and microcapsules. They further include particles 20 formed by the colloidal association of small molecules, especially of amphiphilic molecules, or other complex structures, such as liposomes, lipoplexes, lipid complexes, and lipospheres.

Particles are used in many fields. For instance, particles comprising an active substance, such as a medicine or a nutrient, are used in pharmaceutical 25 respectively food applications.

Particles with a hierarchical structure have various uses. For instance, particles of an active substance, such as a medicinal product or a nutrient, can be surrounded by a protective layer (as by means of encapsulation) to protect the active substance from undesired effects from the environment and/or to protect the 2 environment from the active substance. A protective layer surrounding a pharmaceutically active ingredient or a food ingredient may also serve to alter a release pattern of said ingredient, after administration to an individual. For instance, enteric coatings are known to provide sustained release preparations that delay 5 release of an active substance until the orally administered preparation has passed the stomach.

It is also possible to provide hierarchical particles wherein the outermost phase (the phase forming the surface of the particles) is an active phase providing a desired property to the particles. The core may also comprise an active substance or 10 be an inert phase (e.g. water). For example, in many food products fat particles contribute to an appreciated property of the product, for instance a pleasant mouth feel or a desirable texture. Fat particles may also act as a structuring agent, e.g. in a cream or foam. However, from a health image perspective, there is a large demand for products that are relatively low in fat. By providing particles of which only the outer 15 part is formed by fat and wherein the core is fat-free or low in fat, a similar effect as with full-fat particles may be achieved, whilst the fat content of the product is reduced.

Various techniques of preparing particles are available in the art, each with its own advantages and drawbacks.

20 A common technique for preparing particles is spray-drying is a conventional technique. With spray-drying, typically, wet emulsions or dispersions are sprayed under pressure in a spray tower and then contacted with hot air.

However, spray-drying can cause problems as a result of a high thermal load of the product, which can lead to quality loss, in particular if the product contains a 25 component which is heat-sensitive. Also, problems can occur with the controllability of the product properties such as particle size distribution, form and/or solubility; there is the risk of dust explosions. Further, the high energy consumption is a problem. In addition it is generally difficult to produce core-shell particles, especially small (10 micron or smaller) particles. Moreover particularly a need exist for particles with a 30 hydrophobic {e.g. fat) shell in water. Producing these by spray-drying, e.g. in air, would imply that a subsequent dispersion step in water is needed which is impractical and may again destroy the particles. In many cases also one does not want the core and or the shell to be solid whereas spray-drying inherently leads to solid particles.

3

Colloidosomal particles can be prepared with the aid of an emulsion of the water-in-oil type or the oil-in-water type, see e.g. WO 02/47665. To obtain water-filled colloidosomes, colloidal particles are dissolved in a hydrophobic continuous phase (such as toluene), after which water is added as a discontinuous phase. The examples 5 all use a synthetic polymer, such as polystyrene or polymethyl methacrylate. After allowing aggregation of the particles, if desired, the hydrophobic continuous phase may be replaced by water after the colloidosomes have been formed. Here, the colloidosomes need to be prevented from breaking as a result of the great forces exerted on the colloidosomes, for instance as a result of the surface tension. To this 10 end, the colloidosomes are washed first with octanol and then added to an aqueous solution of a surface-active substance. To keep the colloidosomes intact, the particles are usually strongly bonded to one another, for instance by sintering. Further, it is generally difficult to produce colloidosomes with a closed fat or oil shell. Known preparation techniques generally yield products wherein a substantial fraction of the 15 particles do not have an essentially closed shell.

Particles in the form of core-shell double emulsion droplets can be produced using microfluidic methods (e.g. WO 2007/030501). Using these methods it is however difficult to produce small double emulsions droplets, e.g. smaller than 10 micron, since this requires microfluidic devices with very small features which will give rise to 20 larger pressure drops, greater susceptibility to fouling, larger influence of the (difficult to control) wetting behaviour of the used fluids and smaller production rates. At the same time, up-scaling seems difficult since it requires massive parallelization of generally complicated fluid streams. It is generally also difficult to apply these methods to encapsulate particles, especially of variable size, since these may block the 25 microfluidic channels. In general, methods to encapsulate small (<100 microns) particles in an apolar shell, are very rare.

It is an object of the invention to provide a novel method that can be used for preparing particles with a hierarchical structure, in particular particles having one or more cores at least substantially surrounded by a surrounding phase, and that 30 can be used as an alternative to known methods of producing particles.

It is in particular an object of the invention to provide such a method that overcomes one or more of the above identified drawbacks. One or more further objects that may be addressed by the invention will follow from the description hereinbelow.

4

It has now been found possible to prepare particles having a core, composed of a first phase, at least partially surrounded by a second phase, making use of centrifugal force.

Accordingly, the present invention relates to a method for preparing 5 particles, comprising a) providing a dispersion comprising a continuous phase composed of at least a first liquid, and dispersed in the continuous phase a dispersed material, wherein the continuous phase has a density that is different from the density of the dispersed material; 10 b) providing a second liquid, that is at least substantially immiscible with the first liquid and that has a density that is different from the density of the first liquid; c) providing the dispersion and the second liquid in a centrifugation chamber; and d) subjecting the centrifugation chamber provided with the dispersion and the 15 second liquid to centrifugation, whereby said material together with a fraction of the first liquid at least partially surrounding said material, migrates from said dispersion into the second liquid, thereby forming particles of said material and said fraction of the first liquid at least partially surrounding said material, in the second liquid; and e) collecting the particles.

20 Further, the invention relates to particles obtainable by a method according to the invention. These particles are in general hierarchical particles. The invention is in particular directed to a method for preparing core-shell particles. The core-shell particles according to the invention are particles having at least one solid, liquid or gaseous core and an outer phase formed of the first liquid or solidified first 25 liquid, at least substantially surrounding the core or cores. A core-shell particle having a single core (2) and a single shell (1) is schematically shown in Figure 1. Herein the first liquid generally is present in the form of a layer on the surface of the core. Figure 2 shows a particle with multiple cores (2) in a surrounding first liquid (1). Herein, the first liquid generally not only forms a shell at least partially surrounding 30 the assembly of cores but may also form layers between the individual cores and/or at least partially fill interstitial spaces between the cores.

Further, the invention relates to a food product, comprising particles according to the invention.

5

Further, the invention relates to the use of particles according to the invention as a fat substitute.

The invention in particular is suitable for preparing edible particles. Herein, "edible" is particularly understood to mean "suitable for human consumption", 5 more in particular suitable for use in a food, including beverages, such as for instance in a dairy product, soup or a beverage.

The term “or” as used herein is defined as “and/or” unless specified otherwise.

The term “a” or “an” as used herein is defined as “at least one” unless 10 specified otherwise.

When referring to a noun (e.g. a compound, an additive, etc.) in the singular, the plural is meant to be included. Thus, when referring to a specific moiety, e.g. "compound", this means "at least one" of that moiety, e.g. "at least one compound", unless specified otherwise.

15 When referred herein to a solid, a liquid or gaseous state of a substance m this state under the existing method conditions is meant, unless specified otherwise. As is generally known, in case a material is a pure compound, the compound will be a solid below the melting point and liquid between the melting point and the boiling point, and a gas above the boiling point (at a given pressure). Mixtures of compounds 20 do not always have a specific melting point, but may rather have melting ranges (e.g. fats). In particular where a physical state of matter cannot adequately be defined by the melting point or boiling point, the following definitions apply herein.

The term ‘solid’ is used herein in particular in relation to a method according to the invention means to indicated that a substance under the existing 25 method conditions is essentially shape and volume stable, e.g. a material in a solid state of matter or an edible solid material such as a spice, herb, mineral, peptides, amino acids, cells, etc.. If the term ‘solid’ is used in another context (e.g. that particles are solid at room temperature), this will be specified.

The term ‘liquid’ is used herein in particular in relation to a method 30 according to the invention means to indicated that a substance under the existing method conditions is able to flow and take the shape of a container, but, like a solid, it resists compression and does not disperse to fill every space of a container, and maintains a fairly constant density. Thus, liquids include in particular liquids in the 6 sense of one of the three classical states of matter. A liquid may be formed of a single compound or a mixture of several compounds. If the term ‘liquid’ is used in another context (e.g. that a lipid is liquid at room temperature), this will be specified.

The term “fat” is generally used herein as a generic term for carboxylate 5 esters of glycerine (glycerides); in particular triglycerides are fats. The term "fat" includes compounds that are solid at room temperature and compounds that are liquid at room temperature (20 °C).

The term ’’oil” is used to describe that the fat is liquid. For instance, the oil in the oil in water emulsion comprises one or more fats which form a liquid phase at 10 the processing temperature during at least part of the method.

With ‘at least substantially is in particular meant ‘for 50-100 %’, more in particular ‘for 80-100 %’, more in particular ‘for 90-100 %’ or ‘for 85-100 %’.

Depending upon the melting points of the liquids used, a method of the invention may be employed at a relatively low temperature, e.g. around room 15 temperature, which is advantageous with respect to energy consumption and/or in case the particles are prepared from a heat-sensitive material, or at an elevated temperature, e.g. between room temperature and the boiling point of the liquids.

A method of the invention is suitable to collect hierarchical particles, optionally dispersed in a collection phase in a relatively pure form, if desired. With 20 relatively pure form is meant that the collected particles are at least substantially free of droplets consisting of the first liquid (or solidified first liquid) and material that has not been provided with a layer formed of the first liquid (or solidified first liquid).

In addition, a method of the invention can be employed adequately at a 25 high production capacity, and is advantageous in that respect compared to at least some known methods, such as the use of microfluidic devices.

Further, a method according to the invention allows preparation of hierarchical particles with a high encapsulation efficiency, at least compared to some other encapsulation techniques, e.g. a known technique wherein the particle 30 formation is (primarily) done by emulsification/dispersing.

Furthermore, a method according to the invention is advantageous in that it allows the preparation of core-shell particles with (essentially) complete enclosure of the core or cores by a shell.

7

Moreover, a method according to the invention advantageously allows fine-tuning in a controlled manner of thickness of the shell, in case core-shell particles are prepared.

In principle, in a method according to the invention said dispersion 5 comprising dispersed material and the first liquid may be dispersed into the second liquid prior to the centrifugation. This is generally done by gentle mixing under conditions wherein no substantial microparticle formation occurs, e.g. by shaking manually. During centrifugation the dispersed first fluid and the dispersed material dispersed therein will be pulled in an opposite direction by the centrifugal force. As a 10 result the dispersed material will be dragged out of the droplets of the first fluid towards the second fluid therewith taking along a thin layer of first fluid surrounding the dispersed particles. This is illustrated schematically in Figure 9B.

In an advantageous embodiment, said dispersion and the second liquid are applied into the centrifugation chamber as separate layers prior to or during 15 centrifugation (the latter in particular in case of continuous centrifugation). In case the dispersion has a lower density than the second liquid, the first layer comprising the dispersion and a second layer comprising the second liquid are then in general applied such that during centrifugation the first layer is situated closer to the centre of rotation than the second layer. In case the dispersion has a higher density than the 20 second liquid, the first layer comprising the dispersion and a second layer comprising the second liquid are then in general applied such that during centrifugation the first layer is situated more remote from the centre of rotation than the second layer. This is illustrated schematically in Figure 9A.

In accordance with the invention, the hierarchical particles are formed 25 during centrifugation. During centrifugation, the centrifugation chamber typically rotates around a centre of rotation (the rotational axis). During centrifugation, the dispersion (comprising the first liquid) and the second liquid rotate in separate layers around the centre of rotation. The particle preparation in accordance with the invention is based on the insight that it is possible to employ a centrifugal force to 30 move the dispersed material out of the phase wherein it has been dispersed (at least comprising the first liquid) into the second liquid. When the material actually migrates into the second liquid, it will at least substantially be surrounded by a film comprising the first liquid.

8

Depending on the density of the dispersed material relative to the continuous phase in which it is dispersed, a second liquid with a specific density is selected.

In case the density of the material is higher than the density of the 5 continuous phase, a second liquid is generally provided that has a density that is higher than the density of the first liquid yet lower than the density of said material. During centrifugation the dispersion of the dispersed material in the first liquid will then be positioned (in a first layer) closer to the centre of rotation than the second liquid (in a third layer). Thus, the material be able to leave the first liquid and also to 10 penetrate into the second liquid, whereby particles are formed of said material, at least substantially surrounded by a film comprising the first liquid. Such embodiment is in particular useful for various liquid materials or (dense) solid materials.

In case the density of the material is lower than the density of the continuous phase, a second liquid is generally provided that has a density that is 15 lower than the density of the continuous phase yet higher than the density of said material. During centrifugation the dispersion of the dispersed material and the first liquid will then be positioned more remote from the centre of rotation than the second liquid. Thus, the material be able to leave the first liquid and also to penetrate into the second liquid, whereby particles are formed of said material, at least substantially 20 surrounded by a film comprising the first liquid. In such an embodiment the dispersed material may for example be a gas or low-density solid particles (such hollow particles comprising internal voids filled with gas).

The skilled person will be able to choose suitable densities and viscosities of the different phases based on the information disclosed herein, common general 25 knowledge and optionally a limited amount of routine testing.

As a rule of thumb, densities and viscosities may be chosen in such a way that: 1) the dispersed material will, under the influence of the centrifugal force, move from the first fluid phase to the interface with the second fluid within an acceptable time.

30 This condition is generally easily fulfilled as will be seen later.

2) the centrifugal force working on the dispersed particle/droplet is strong enough to overcome the interfacial pressure trying to keep the particle/droplet inside the first fluid phase. Not wishing to be bound by this model, the above can be described by a 9 simple model, in which we assume that the shell has a thickness negligible compared to the diameter of the core: 4/3nR3g(#g)\(pc -p2)| > 4nR1 ^

K

5

In which R is the radius of the core (m), g the gravitational constant (m/s2), #g the number of g’s applied, pc the density of the core phase (kg/m3), p2 the density of the second fluid phase (kg/m3) and y the interfacial tension between the first and the second fluid (N/m).

10

The above formula is used to calculate the lower line in Fig. 3. It should be noted that this model, when compared with experimental observations, tends to overestimate the number of g’s required to produce core-shells with a certain size. It can be seen that to produce 15 micron core-shell particles with a liquid core about 10 000 g is needed.

15 This means that according to Stokes’ law: v_2 R2g(#g)(pc-P2) 9tj (In which r\ is the viscosity of the first fluid phase in mPas, which will usually be about 102 mPas (being the order of magnitude of the viscosity of oil), the core will 20 travel through the first fluid towards the interface at a speed v in the order of 1 mm/s. This means that for a practical height of the first liquid phase of a few centimeters the cores need up to 1 min to travel to the interface between the first in the second fluid where they will form a core-shell. This is a very practical time, such that condition 1 is fulfilled.

25 The skilled person will be able to provide a suitable dispersion and a suitable second liquid. In practice, in order to let the dispersed material migrate out of the continuous phase into the second liquid at an advantageous rate, the density of the dispersed material in the dispersion is usually at least 1.05 times, in particular at least 1.10 times the density of the continuous phase, if the dispersed material is more 30 dense, respectively up to 0.95 times, in particular up to 0.90 times the density of the continuous phase if the dispersed material is less dense.

10

The differences in density between the first liquid and the second liquid are not particularly critical. In particular, the difference in density may be 2 % or more.

The differences in density between the dispersed material (or of the formed 5 particles, if those have a substantially different density) and the second liquid are not particularly critical. In particular, the difference in density may be 2 % or more.

In principle, the maximum difference is not critical, the higher the difference, the lower the centrifugal force needed to prepare the particles at a specific rate. The density of the more dense of the dispersed material and the continuous 10 phase, respectively the first and the second liquid respectively the dispersed material and the second liquid is not particularly critical, it may for instance be up to 5 times, up to 3 times, up to 1.5 times, or up to 1.25 times the density of the less dense of these two phases. Regarding the density difference of the second liquid and the dispersed material (or of the formed particles, if those have a substantially different density) it 15 is observed that in particular if the second liquid serves as a collection phase a relatively small difference can be advantageous for collecting purposes. Also a relatively small difference may be advantageous with respect to avoiding disruption of the formed particles, while centrifugation is continued.

A minimum centrifugal force to cause the dispersed material to move out 20 of the continuous phase can be determined based on the information disclosed herein, common general knowledge and optionally a limited amount of testing. In general, centrifugation will be carried out at 50 g or more, in particular at 250 g or more, more in particular at 1000 g or more. A suitable maximum limit is determined by the centrifugal force at which the prepared particles are disrupted to an unacceptable 25 extent. Depending on the specific dispersed material and liquids used the maximal centrifugal force may be 100 000 or more, 500 000 or more, or even 1 000 000 or more, whilst still obtaining particles in accordance with the invention. However, good results can be obtained with a method wherein the centrifugal force is less than 50 000 g, less than 25 000 g , or less than 10 000 g.

30 The centrifugal force that is actually employed is usually mainly determined by the average particle size of the desired particles. In general a certain minimum centrifugal force is needed to achieve formation of the shell around the core with a good degree of coverage. The minimum centrifugal force that is needed is 11 higher as the size of the dispersed particles or droplets decreases. In Figure 3 a relation between centrifugal force and particles size of core-shell particles is illustrated for particles wherein the core is liquid. The line ‘g min’ shows which centrifugal force according to the above exemplary model is needed to produce core-5 shell particles with the diameter shown at the x-axis. Depending on the specific method conditions (nature of the used material and liquids, etc.) a different centrifugal force may be applied in order to obtain a desired average particle size. It should be noted that the size of the obtained core-shell particles is primarily determined by the size of the material (e.g. solid particles or liquid droplets) dispersed 10 in the first liquid provided that the applied centrifugal force is large enough to transfer these through the interface between the first and second liquid. This is in fact one of the prowess of the present invention. The invention thus provides an encapsulation method for preparing core-shell particles that adjusts itself to whatever is provided as the material for the core (the dispersed material). For instance, if a 15 material for the cores is provided with a specific particle size distribution, this usually essentially determines the particle size distribution of the formed core-shell particles, which may be essentially maintained. This can be very handy, e.g. for encapsulation of specific medicaments, minerals, biological cells.

A relatively high centrifugal force may also be preferred for an increased 20 particle production rate.

On the other hand, above a threshold centrifugal force, the pressure that the core and the shell exert on each other in the centrifugal field may become so high that it overcomes the stabilising pressure (also known as disjoining pressure) of the used emulsifiers and the shell may rupture (Significant deformation of the core-shell 25 particles may occur, or droplets of first liquid that are free of said dispersed material may form, e.g. due to disruption of prepared particles. This may be undesired. Thus, a maximum value of a centrifugal force in a specific embodiment may be determined by the maximally allowable concentration of droplets of first liquid that are free of said dispersed material, in the collected particles.). Thus, the centrifugal force is usually 30 chosen to be less than the force of the disjoining pressure, which may be determined by routine testing.

The line ‘g max’ in Figure 3 shows such threshold centrifugal force for an exemplary model embodiment, wherein the core for the particles (which may be 12 droplets) have been stabilised using an emulsifier. Depending on the specific method conditions (nature of the used material and liquids, etc) the ‘g-max’ line will be different. For instance, it is contemplated that with particulate stabilisers (e.g. fat nanoparticles) the ‘g max’ line will be at least 10-100 times higher.. A preferred 5 centrifugal force depends on factors like particle size of the dispersed material (for liquid dispersed material), desired thickness of the film formed of first liquid at least partially surrounding the material migrating out of the continuous phase, the nature of the dispersed material and the first liquid, e.g. density, physical/chemical interaction between said material and the first liquid, physical state of the dispersed 10 material (liquid/solid/gas), viscosity of the first liquid and the dispersed material (if liquid), the presence of additives that stabilise the formed particles.

The centrifugation may be carried out in a continuous manner or in a batch manner.

In particular when batch-centrifugation is used the dispersion (comprising 15 the first liquid and the dispersed material), the second liquid, and if used the collection phase may be applied to the centrifugation chamber in separate layers prior to centrifugation, wherein the phase with the highest density (the second liquid or the collection phase) is applied as the bottom layer and the phase with the lowest density as the top layer (the dispersion). In principle it is also possible to apply two or more of 20 the phases simultaneously and allow the phases to settle, thereby forming the separate layers, prior to or during the initial phase of centrifugation.

Surprisingly, a method according to the invention is also particularly suitable to be carried out in a continuous manner. In a continuous centrifuge, the dispersion, the second liquid, and - if used - a separate collection phase, are applied 25 to the centrifuge continuously or intermittently while continuing the centrifugation and particles are collected continuously or intermittently while centrifugation is continued. Continuous centrifugation is particularly useful for preparing particles at a large scale, (see e.g. Perry’s handbook of chemical engineering (1984), fig. 19-120a or Perry’s handbook of chemical engineering (20th edition), fig. 18-154a or fig 18-155.

30 The centrifugation is continued as long as is needed to obtain the particles in a desirable yield. A suitable centrifugation time (or average residence time in the case of continuous centrifugation) can be routinely determined with the help of the information disclosed herein and common general knowledge, and may . in particular 13 be at least 10 sec, at least 25 sec at least 1 min, up to 10 min or more, up to 30 min or more or up to 1 hr or more. Preferably the centrifugation time is chosen just long enough to achieve the particles formation at a desirable yield, to minimise the risk of a substantial portion of the formed particles being disrupted by the centrifugal field.

5 A suitable time can be determined depending upon the specific situation, based on the information disclosed herein and common general knowledge. An advantage of the use of a continuous centrifuge may be that formed core-shell particles are transported out of the centrifugal field soon after they are formed, which reduced risk of deteriorating, and provides a high yield of particles with the desired structure.

10 The particles may be collected as a dispersion of the second liquid or isolated from the second liquid.

It is also possible to provide a collecting-phase for the particles in the centrifugation chamber. In case a collection phase is used, this phase is chosen to have a density that will allow the particles to migrate from the second liquid into the 15 collection phase. In general, the collection phase has a density that is higher than the density of the second liquid if the particles have a higher density than the second liquid respectively a density lower than the second liquid if the particles have a lower density than the second liquid. A density of the collection phase that is about the same as the density of the prepared particles is in particular advantageous to collect 20 particles because this will (essentially) stop the core-shell particles from continuing to move into the centrifugal field. Also, unlike when the core-shells are stopped by the presence of a wall, this will prevent the core-shells from being substantially deformed. Deformation is unwanted since it will increase the chances of shell rupture. The concentration of the particles when collected in the second liquid or the collection 25 phase is not critical; they may be collected in a relatively low concentration in the second liquid or the collection phase, e.g. in a concentration of 1-10 % a, based on the total weight of the collected product, if desired the particles may be collected at a higher concentration, e.g. of more than 10 %, in particular up to 50 %, based on total weight. A relatively low concentration is considered advantageous with respect to 30 maintaining particle shape and integrity, in particular in case the particles have a liquid core and/or liquid outer layer. It may also be advantageous to collect at a relatively low concentration in order to avoid or at least reduce coalescence of the outer phase (which may still be liquid).

14

If desired, at least part of the layer comprising the first liquid of the prepared particles is solidified before, during or after collecting the particles. Solidification may usually be accomplished by extracting a solvent from the first liquid (e.g. when the first liquid is a polymer solution) or by cooling the particles to a 5 temperature below the solidification temperature (or range) of the first liquid. This may be done after centrifugation or during centrifugation, e.g. by maintaining the dispersion layer at a temperature above the solidification temperature (or solidification range) of the first liquid and maintaining the second liquid, or (if present) the collection phase at a temperature below the solidification temperature (or 10 solidification range).

The collected particles may be further treated, e.g. subjected to a concentration step. The concentration may for instance be carried out by filtration (e.g. tangential flow filtration) or a further (gentle) centrifugation step. A suitable centrifugal force is usually lower than the centrifugal force needed during formation 15 of the core-shells (see Fig. 3), preferably at least 10 times lower, in order to (nearly) completely rule out substantial destruction of the core-shells. The minimum required force depends on the particle size, particle density, density of the fluid in which the particles are dispersed and viscosity of said fluid, and can be determined routinely.

The collected particles may be used whilst dispersed in the second liquid, 20 the collection phase, or yet another phase, or may be isolated there from, prior to further use.

As the first liquid in particular a liquid lipid can be used, more in particular an edible fat that is liquid under the centrifugation conditions. Edible fats in particular include triglycerides. These are usually provided as a mixture of 25 different triglycerides. The fat may be of vegetable or animal nature. In particular the first liquid may comprise one or more fats selected from the group of milk fat, corn oil, cottonseed oil, canola oil, olive oil, peanut oil, safflower oil, soybean oil, sunflower oil, oils from nuts, oils from fruit seeds, and fractions of any of these fats and oils. The melting range of the first liquid can be altered by changing the triglyceride 30 composition. The skilled person will be able to do so, based on common general knowledge. The centrifugation is in general carried out at a temperature above the melting range of the first liquid, but after the particles have been formed, the first liquid surrounding the inner material may be allowed to solidify, by reducing the 15 temperature to a value at which the liquid or part thereof solidifies, if desired. This may be done during centrifugation, by maintaining the first liquid at a higher temperature than the second liquid (or at a higher temperature then a further phase, wherein the particles may be collected, see below). The first fluid may also consist of a 5 polymer solution or a polymer melt.

As the second liquid in particular a polar liquid may be used that does not or at least not substantially form a single dissolved phase with the first liquid. Particularly suitable, especially when a lipid is used as the first liquid, is water or an aqueous liquid as the second liquid. An aqueous liquid is a liquid that comprises 10 water as a major constituent. Usually at least 50 wt. %, in particular at least 80 %, more in particular at least 90 wt. % of the aqueous liquid is water. In addition, the aqueous liquid may comprise one or more other polar liquids, e.g. ethanol, glycerol. Such liquids may e.g. be used to alter the viscosity and/or the density of the second liquid and its interfacial tension with the first liquid. When the first liquid is a 15 polymer solution one could use a solvent that is at least partially miscible with a collection phase. In that case one could use a second fluid that is not miscible with this solvent, or one could already saturate the second fluid with this solvent. In that case, in the collection phase the solvent will be extracted from the polymer solution shell such that it solidifies.

20 A separate collection phase for the particles, which may be used in addition to the second liquid, may have largely the same composition as the second liquid, with the proviso that it is modified to keep the collection phase phase-separated from the second liquid. In particular, the density and/or viscosity may be altered. For instance, the collection phase may be a gel composed of the second liquid 25 (or another liquid) and a gelling agent.

The first, the second or - if present - the third liquid may comprise one or more additives. Such additives may in particular be selected from viscosity modifiers, density modifiers, gelling agents, dispersants, stabilising agents that stabilise the layer provided by the first liquid. It is also possible to influence the production of 30 particles with either single or multiple cores e.g. by choosing the surfactant in the second phase in combination with the number of g’s applied. If the combination of interfacial tension and g force is such that single core can not be drawn through the interface, multiple cores will collect the interface until the cumulative g-force becomes 16 large enough to pull them through the interface therewith forming a multiple core particles. This can be seen in Example 3.

Viscosity modifiers and gelling agents are generally known in the art and include various polymers, e.g. polysaccharides (such as starch, cellulose, pectin, 5 maltodextrins, derivatives of any of these), proteins.

Density modifiers are generally known in the art and include other solvents like glycerol, ethanol, solutes like carbohydrates, proteins, salts or nano-/microparticles.

It is particularly advantageous to increase the density of the dispersed 10 droplets by using water in which solutes are dissolved. Specifically when using solutes with a relatively high molecular weight (> 500 g/mol) the osmotic pressure of the dispersed droplet will remain low which prevents swelling of the core-shells. Alternatively, very small particles may be dispersed in the core phase to increase its density.

15 Dispersants are generally known in the art and include surface active agents, in particular emulsifiers, such as monoglycerides, diglycerides, polymeric emulsifiers, such as polysorbates (e.g. Tweens).

Dispersants may be used to stabilise the particles. It is contemplated that in particular spacer particles or particles that stabilise the interface between the layer 20 formed by the first liquid and the material the layer at least partially surrounds and/or the interface between the layer of the first liquid and the environment are advantageous. Such particles may be selected from fat particles (crystals, nanoparticles). Suitable stabilising fat particles generally have a melting temperature or range above the melting temperature or range of the first liquid, and 25 preferably a melting temperature or range above the temperature at which the particles are prepared. Obviously, the particle size of such particles will be less than the desired size of the layer formed by the first liquid. Such particles are e.g. known from N. Garti et al., JAOCS 76 (1999) 383-389). Stabilising fat particles (fat crystals, fat nanoparticles) are in particular considered advantageous to stabilise the interface 30 of the material forming the core(s) of the particles and the layer of the first liquid in case said material is water or an aqueous liquid and the first liquid is an oil. Spacer particles may also be used to modify the thickness of the shell of a core-shell particle.

17

Further and emulsifier may be used to create a lamellar phase and therewith form multiple layers around the dispersed material, in case the dispersed material are droplets of water or an aqueous liquid, see e.g. Modern aspects of emulsion science (1998, B.P. Binks (ed)) p 236 for details on this principle. Further, an 5 emulsifier that forms inverse micelles in the continuous phase in order to induce ‘stratification’ may be used, see e.g. Modern aspects of emulsion science (1998, B.P. Binks (ed)) p 336 or p345) for details on this principle.

The dispersed material may in principle be any substance of combination of substances. The material may be selected from the group of gases (such as CO2, 10 nitrogen, oxygen, air, a gaseous aroma) , liquids (water, aqueous liquids, emulsions), solids, mixtures of a solid and a liquid, mixtures of a solid and a gas, mixtures of a liquid and a gas and mixtures of a solid, a liquid and a gas.

In a specific compound the dispersed material comprises a compound selected from the group of proteins, other peptides, carbohydrates, vitamins, minerals 15 (e.g. iron containing minerals), probiotics, prebiotics, salts, flavourings; aromatic substances, (phospho-)lipids, herbs, pharmaceuticals and spices. Such materials may be protected by a surrounding layer of the first liquid (which may have been solidified), e.g. against detrimental influences of the environment during storage. Further, the presence of a surrounding may be desirable to achieve a desirable release 20 pattern, before, during or after consumption.

The concentration of dispersed material as a weight percentage of the dispersion (comprising the first liquid as continuous phase) can chosen within wide limits. Usually the concentration is 0.1 wt. % or more, in particular 0.5 wt. % or more, more in particular 1.0 wt. % or more. The concentration may e.g. be 50 wt. % or less, 25 in particular 24 wt. % or less. A relatively low concentration of dispersed material is considered advantageous for allowing the centrifugal force to cause migration of the dispersed material (the cores for the core-shell particles that are formed) into the second liquid at an advantageous rate, especially if use is made of a method wherein the dispersion of the first liquid and material for the cores of the core-shell particles to 30 be formed is dispersed in the second liquid prior to centrifugation. Therefore, it is specifically preferred that the concentration of dispersed material in the continuous phase comprising the first liquid is 20 wt. % or less, in particular 10 wt. % or less, or 5 wt. % or less.

18

In a further embodiment the material (core) that is at least partially surrounded by the first liquid (that may have been solidified) serves as an (inert) carrier for the surrounding layer, which may in particular be a fat layer (provided by an oil used as the first liquid). E.g. water, aqueous liquids, but also peptides, 5 carbohydrates, dietary fibres, minerals, vitamins and other materials other than lipids may be used to that purpose. Thus particles are provided that can be used to partially substitute fat in a food product.

A method according to the present invention is highly suitable to provide hierarchical particles wherein the outer phase (the phase comprising the first liquid 10 or solidified first liquid) forms a relatively small volume fraction of the total particle. In particular, the particles may comprise 80-99.5 vol. % of said material and 0.5-20 vol. % may be formed of said first liquid which first liquid may have been solidified, based on total weight, more in particular 85-99 vol. % of said material and 1-15 vol. % of said first (solidified) liquid, based on total weight, even more in particular 90-98 15 vol. % of said material and 2-10 wt. % of said (solidified) first liquid, based on total weight. Corresponding weight percentages can be determined based on the respective densities. A low volume fraction for the outer layer is in particular advantageous if the surface of the particles is of primary importance for the function of the particles, and wherein the outer phase is expensive, scarce, or wherein it is desired that the 20 particles comprise little of the outer phase for health reasons (e.g. if the particles are used as a fat substitute).

The particle size of the particles according to the invention can be chosen within a wide range. Usually, the particles have a volume-to-surface mean particle diameter d32 of at least 0.5 pm, in particular of at least 2 pm, at least 3 pm or at 25 least 5-10 pm. Usually, the particles have a volume-to-surface mean particle diameter d32 in the range of less than 500 pm, preferably of 100 pm or less, in particular of 50 pm or less, more in particular 20 pm or less, or 10 pm or less. The particles size can be determined using (dynamic) light scattering.

In a specific embodiment, the particles of the invention are oil-in-water or 30 oil in aqueous liquid emulsion droplets, which droplets are surrounded by an oil layer. The oil phases can in particular be selected from the oils mentioned above for the first liquid. In a further specific embodiment, the particles comprise a shell that comprises a fat phase that is solid at 25 °C (such as fat crystals, e.g. milk fat crystals) 19 and a fat phase that is liquid at 25 °C. In a further specific embodiment, the particles comprise a shell that comprises spacer particles. In a further specific embodiments that particles comprise one or more cores comprising a mineral, such as an iron containing mineral, like iron pyrophosphate. The core-shell structure contributes to a 5 controlled release pattern of the particles in food or pharmaceutical application, in particular after ingestion into the gastro-intestinal tract.

Particles according to the invention may in particular be used for the preparation of food products. In particular particles with a non-fat core and a fat-outer surface may provide the food product with fat-like organoleptic properties, 10 whilst less fat is needed than when full-fat particles are used.

Accordingly, the invention is further directed to food product comprising edible particles according to the invention. Such food product may in particular be selected from the group of foods comprising a gelled-structure, with dispersed therein the particles; whippable/whipped creams; cheeses; yoghurts; mousses; puddings; 15 bakery creams; desserts; dairy beverages; ice creams; creamers (for coffee, soup or the like); toppings; cream bases; and meringues.

Further, the invention is directed to a method for preparing a food product, wherein edible particles obtained in or obtainable by a method according to the invention are combined with one or more further food ingredients in a process for 20 preparing the food in a manner that is otherwise known per se, e.g. it may be combined with one or more other food ingredients which combination can then be further processed to product the food product of interest.

For example, particles according to the invention (in the phase wherein it has been collected or isolated there from) may be used in the preparation of a 25 whippable cream by combining the particles with other cream ingredients (e.g. sugar, dairy protein, fat globules). Upon whipping the cream, the particles become part of the network structure of the whipped cream, thereby stabilising the whipped product. Natural dairy cream is widely used in food industries. Cream is a three phase system, which, depending on numerous system parameters, can be transformed into a four 30 phase system upon introducing air by whipping. Natural cream has in general good whipping characteristics in terms of whipping time, stability, overrun and firmness.

In natural cream, an oil-in-water emulsion, the emulsion droplet surface is covered by a milk fat globule membrane (MFGM) and the fat phase contains milk fat. Both the 20 MFGM and the milk fat plays a crucial role in creating a whipped cream. To be able to create a whipped cream partial coalescence of the emulsion droplets should occur upon whipping. Hereafter spreading of liquid fat on the oil/air interface and creation of a solid fat network stabilizes the air bubbles. The occurrence of partial coalescence 5 is influenced by the stability of the interfacial layer (e.g. a MFGM or proteins) by the ratio liquid/solid fat and most likely by the fat morphology (shape, size, stability, degree of sintering). Also structural aspects of the milk fat globule (MFG) such as spatial orientation and distribution of the crystals with respect to the MFGM seem to be involved. The particles according to the present invention are thought to provide a 10 unique structural alternative for partial coalescence. During whipping the particles collide with each other (and included air bubbles), followed by coalescence of the shell phases of both particles involved. The presence of the cores restricts the coalescence to the thickness of the shell layers due to spatial interference, limiting the coalescence to partial coalescence. This mechanism provides a structural alternative for the partial 15 coalescence occurring as known for natural dairy cream. In order to allow this mechanism to proceed well it is important that the ratio between the core and the shell dimensions can be accurately tuned, particularly in the region where the shell thickness is thin in comparison to the diameter of the core. The present invention allows such fine-tuning.

20 The particles may also advantageously be used in a gelled food product, e.g. cheese or a cheese analogue, wherein the particles are dispersed in a gel-matrix {e.g. gelled protein or carbohydrate) and act as structure disruptors. Thus, the particles may be used to tune the mechanical bulk properties.

The particles are in particular suitable to impart a food product with a 25 sensory quality that resembles a food product wherein fat is fully or predominantly present in the form of full-fat globules, having a higher fat content than the food product of the invention. Compared to a fat-free food product, the particles are in particular suitable to impart a fat-associated sensory quality to the product, whilst requiring less fat than when use would be made of full fat particles.

30 Said sensory qualities may for instance be selected from - "cheese oral texture", i.e. the similarity to yellow cheese in the mouth of the product; - "crumbliness": the amount of particles, without taking crystals into account 21 (crumbliness may be divided in "direct crumbliness": i.e. after chewing briefly and "later crumbliness", i.e. just before swallowing); - "fatty oral texture": an indication of how fatty the oral texture is perceived - "firmness": a measure for how the product feels when biting through (a product 5 being more firm the higher resistance when biting through); - "meltability": ease with which the product solves/falls apart in the mouth; - "rubberiness:": the extent to which the product has a rubber-like oral texture during chewing; - "stickiness": the extent to which the product tends to stick to palate and teeth; 10 - "creamy mouthfeel".

In addition or alternatively one or more other sensory quality may be altered, in particular one ore more attributes selected from elasticity, hardness, dryness, graininess, smoothness, remainings, fracturability and fatty impression.

Manners to determine such sensory qualities are generally known in the 15 art or may be based on the methods described or referred to in EP-A 1 884 166.

In a specific embodiment, the particles of the invention may be used for preparing a soft-solid food product - in particular a soft-solid dairy food product, such as a cheese product or a cheese analogue 20 product - comprising - providing a mixture comprising particles according to the invention (e.g. a dispersion thereof in water or an aqueous liquid) and a gel, said gel comprising a protein; - fragmenting the gel; 25 - regenerating the gel; and - shaping a product from the mixture, wherein the product comprises a gel phase comprising the protein, said gel phase having a relatively low fat content, and inhomogeneously distributed outside the gel phase a plurality of particles according to the invention. Details of suitable conditions may be based on EP-A 1 884 166.

30 The invention is illustrated by the following examples.

22

Example 1 A 50 wt% solution of maltodextrin 33DE (Roquette) was emulsified at a concentration of 1 wt,% in sunflower oil containing 5-10% Admul WOL (PGPR) as an 5 emulsifier. Emulsification was such that water droplets of about 20 micron were formed. This emulsion was placed on top of a two layer system with the bottom layer containing 1 wt.% Tween 20, 30 wt.% maltodextrin and 1.5 wt% HM Pectin (CP kelco) and the top layer containing just 1 wt.% Tween 20.

Typically centrifuge tubes with a diameter of 3 cm were used. Each of the three fluid 10 phases (the w/o emulsion at the top, the emulsifier solution in the middle, and the maltodextrin+pectin+emulsifier solution at the bottom) had a height of about 1 cm. Centrifugation was done for 30 seconds at 1000 to 3000g.

At the end of the experiment microscopic images of the bottom layer were taken (see Figure 4, showing a core-shell double emulsion, 400x magnification). It can 15 be seen that particles are present having a core-shell structure with a very thin shell of oil. This has also been confirmed with CSLM, which provided additional evidence that the core material (solution of maltodextrin) was present in the particles and surrounded by the shell.

20 Example 2

An experiment similar to Example 1 was done, except that the w/o emulsion was replaced by a 1 wt.% ferric pyrophosphate (particle size of 1-2 micron) dispersion in sunflower oil containing 10 wt% Admul WOL. Figure 5 shows the 25 obtained particles. Oil droplets are seen that are fully packed with ferric pyrophosphate. If, for comparison, a 40% ferric pyrophosphate dispersion in oil containing Admul is emulsified at a 5% concentration in water containing Tween 20 using a turrax, image shown in Figure 6 is obtained. The oil droplets are seen to hardly contain any ferric pyrophosphate anymore. It can be concluded that the 30 emulsification by centrifugation is an encapsulation method with a very high encapsulation efficiency.

23

Example 3

Example 3 was carried out as Example 1, but with the middle phase replaced by a 1% sodium caseinate solution. Here capsules with multiple water cores 5 were formed, as shown in Figure 7.

Example 4

Example 3 was carried out as Example 1, but replacing the sunflower oil with a molten fractionated palm oil (melting point of 53°C), using a warm (60°C) middle 10 layer and a cold (5°C) bottom layer. Results are shown in Figure 8. Herein the liquid palm oil surrounding the aqueous core is solidified in the bottom layer, also serving as the collecting phase.

Example 5 15

Particles are continuously prepared in a continuous centrifuge, e.g a continuous disk-centrifuge bowl as shown in Perry’s handbook of chemical engineering (1984), fig. 19-120a. The dispersion (w/o emulsion) comprising the material for forming the core (droplets of aqueous liquid) of the particles and the first liquid (an oil forming the 20 continuous phase) is fed continuously into the centrifuge, thereby maintaining a first layer (a dispersion of the core in the continuous phase), said layer situated more remote to the centre of centrifugation. The second liquid (an aqueous phase) is continuously fed into the centrifuge, thereby maintaining a second layer, said layer situated more close to the centre of centrifugation. As the aqueous droplets migrate 25 from the first layer into the second layer they drag along a film of the first liquid into the second liquid, whereby particles of aqueous liquid surrounded by an oil film are obtained in the second liquid. Together with the second liquid these particles form a double emulsion (of the w/o/w type). At the exit of the centrifuge two streams are collected: 1) the heavier stream containing formed double emulsions, 2) a rest stream 30 partially or fully depleted from water, and rich in oil.

24

Reference list to figure 9A and 9B

Fig. 9A

5 - ref. 9.1 = 1st fluid - ref. 9.2 = 2nd fluid 10 - ref. 9.3 = Dispersed material (core) - ref. 9.4 = Interfacial force - ref. 9.5 = Centrifugal force 15

Fig. 9B

20 - ref. 9.6 = 1st fluid - ref. 9.7 = 2nd fluid - ref. 9.8 = Dispersed material 25 - ref. 9.9 = Centrifugal force on 1st flui - ref. 9.10 = Centrifugal force on dispersed material

Claims

A method for preparing particles, comprising a) providing a dispersion comprising a continuous phase composed of at least a first liquid, and, dispersed in the continuous phase, a dispersed material, wherein the continuous phase has a density that is 5 is different from the density of the dispersed material; b) providing a second liquid which is at least substantially immiscible with the first liquid and which has a density different from the density of the first liquid; c) providing the dispersion and the second liquid in a centrifugation chamber; and d) subjecting the centrifugation chamber provided with the dispersion and the second liquid to centrifugation, wherein said material, at least partially surrounded by a phase comprising first liquid, migrates from the first liquid into the second liquid. E) collecting the particles.

The method of claim 1, wherein the density of the first liquid is lower than the density of the dispersed material, the density of the second liquid is higher than the density of the first liquid and the density of the dispersed material is higher than the density of the dispersed material. density of the second liquid.

3. Method as claimed in claim 2, wherein in step c) a first layer comprising the dispersion and a second layer comprising the second liquid are provided in the centrifugation chamber, wherein the layers are provided such that during centrifugation the first layer nearer the center of rotation is then the second layer.

A method according to claim 3, wherein in step c) a third layer is applied, which layer has a density higher than the density of the second liquid, which third layer is applied such that during centrifugation the third layer is more removed from the center of rotation is located than the second layer, and in which layer the particles are collected during centrifugation.

The method of claim 4, wherein the third layer is composed of a gel or a polymer solution that has a higher viscosity than the second layer.

The method of claim 1, wherein the density of the first liquid is higher than the density of the dispersed material, the density of the second liquid is higher than the density of the first liquid and the density of the dispersed material is lower than the density of the dispersed material. density of the second liquid.

A method according to any one of the preceding claims, wherein the dispersed material is selected from the group of liquids, solids, mixtures of a solid and a liquid, mixtures of a solid and a gas, mixtures of a liquid and a gas and mixtures of a solid, a liquid, and a gas, or a method according to claim 6, wherein the dispersed material is a gas.

A method according to any one of the preceding claims, wherein the dispersed material is droplets, for example wherein the dispersed material in the first liquid is an emulsion.

A method according to any one of the preceding claims, wherein the dispersed material comprises a compound selected from the group of proteins, other peptides, phospholipids, other lipids, sugars, other carbohydrates, vitamins, minerals, probiotics, prebiotics, salts, flavorings; aromatic substances, herbs, water, aqueous liquids, pharmaceuticals and spices.

A method according to any one of the preceding claims, wherein the first liquid is a lipid, in particular an edible oil.

The method of any one of the preceding claims, wherein the dispersion comprises hydrophobic stabilizer particles, such as fat crystals.

The method of any one of the preceding claims, wherein the second fluid is water or an aqueous fluid.

A method according to any one of the preceding claims, wherein the first liquid, the second liquid, or both, comprise a dispersing agent.

14. Method as claimed in any of the foregoing claims, wherein the centrifugation is carried out using continuous centrifugation. Ti

A method according to any one of the preceding claims, wherein the collected particles are concentrated by filtration, a further centrifugation step or by another concentration technique.

A method according to any one of the preceding claims, wherein the particles that are collected comprise at least one core comprising said material (material that was previously dispersed in the continuous phase) wherein - on average - 50-100. %, in particular 90-100%, more in particular 95-100% of the surface of the core is covered with the first liquid.

The method of any one of the preceding claims, wherein the particles are 80-99.5 vol. % of said material and 0.5-20 vol. % of said first liquid or solidified first liquid, based on total weight, in particular 85-99 vol. % of said material and 1-15 vol. % of said first liquid or solidified first liquid, based on total weight, more in particular 90-98 vol. % of said material and 2-10 vol. % of said first liquid or solidified liquid, based on total volume.

18. A method according to any one of the preceding claims, wherein the particles that are collected have a volume-to-surface average particle diameter d32 in the range of 0.5-100 µm, in particular in the range of 3-20 µm, more particularly in the range of 5-10 µm.

19. Method as claimed in any of the foregoing claims, wherein the centrifugation comprises centrifugation at a centrifugal force in the range of 50 to 1000000 g, in particular in the range of 250 to 100000 g, more in particular in the range of 1000 to 25000 g.

A method according to any one of the preceding claims, wherein at least a portion of the layer comprising the first liquid is solidified before, during or after the collection of the particles.

21. Particles obtainable by a method according to any of the preceding claims.

Particles according to claim 21, wherein the particles have a liquid, non-gelled core or a gelled core and an at least substantially surrounded shell consisting of at least substantially one or more lipids.

23. A food product comprising particles according to claim 21 or obtained in a method according to any of claims 1-20.

The food product of claim 23, wherein the product is selected from the group of foods comprising a gel structure with the particles dispersed therein; whipping cream or whipped cream; cheeses; yoghurts; 5 mousses; puddings, bakery cream; desserts; dairy drinks; ice; creamers (for coffee, soup and the like); toppings; bases for cream; and foam.

Use of particles according to claim 21 or obtained in a method according to any of claims 1-22 as a fat substitute. 10