The present invention relates to a method for preparation of aqueous foams. Moreover the present invention relates to foams obtainable by such method, and aerated food products comprising such a foam.

Aerated food products or foams are generally known, and such foods include frozen and chilled food products, such as ice cream, mousses, and whipped cream. Gases commonly used for 'aeration' include air, nitrogen and carbon dioxide.

Two factors are of importance in the development of aerated food products, and these are (i) the foamability of the product while introducing gas into the product during manufacture and (ii) the foam stability during storage, which is whether the gas bubbles tend to coalesce or collapse and whether the foam volume is retained during storage. Many additives are known to be included in the creation of stable foams, and these generally are compounds which are present on the gas bubble surface, which means on the gas-liquid interface during manufacturing of the foam. Known additives include proteins such as sodium caseinate and whey, which are highly foamable, and biopolymers, such as carrageenans, guar gum, locust bean gum, pectins, alginates, xanthan, gellan, gelatin and mixtures thereof, which are good stabilisers.

WO 2008/019865 A1 discloses aqueous foams and food products containing these. The gas bubbles in the foam are stabilised by interfacially-active particles (e.g. proteins), which are considered to be colloidal particles having a diameter between 0.5 nanometer up to several tens of a micrometer. Aerated food products are produced by mixing a preformed aqueous foam into a food product.

WO 2007/060462 A1 discloses dried foams which are stabilised by polystyrene latex particles which may have an average particle size between 0.05 and 10 micrometer. The latex particles are produced by a polymerisation reaction. The latex particles may be stabilised by water-soluble/hydrophilic polymers forming a shell on the latex particles, like water-soluble poly(meth)acrylates, and various cellulosic derivatives (e.g. e.g. methylcellulose, ethylcellulose, hydroxypropylcellulose or carboxymethylcellulose). Polymer latexes stabilized with a polyacid form stable foams below the pKa value. In a further step the latex particles may be sintered, in order to create a more stable foam composition. Such a sintering process is usually used to make dry bubbles, inside the foam fragments, fused together into a coherent mass. This may lead to difficulties when mixing the dried foam with a composition in order to create an aerated composition. The inventors of this patent application have published similar latex stabilized foams (Fujii et al., J. Am. Chem. Soc. 2006, 128, 7882-7886). These foams are also dried by a sintering process at 105 ⁰ C in an oven.

Plasari et al. (Trans IChemE, 1997, VoI 75, Part A, p. 237-244) disclose a process to precipitate ethylcellulose nanoparticles from a solution of ethanol, using water as non- solvent, under various process conditions. From a few graphs in this publication it can be derived that the average particle size of the nanoparticles was reported to be from about 35 to about 100 nanometer, which partly aggregated into agglomerates having a size between 300 and 600 nanometer. The size of the nanoparticles was strongly dependent on the initial concentration of ethylcellulose in the solvent.

WO 2007/068127 A1 discloses foams stabilised by solid particles at a concentration of at least 1% by volume referred to the volume of the suspension. The foams may be sintered after a drying step.

US 6,090,401 discloses foams that have been dried by a heating step.

WO 2008/046698 A1 discloses stable aerated food products containing between 0.5 and 20 wt% protein, as well as fibres and surface-active particles that assemble at the air-water interface. In the examples a combination of microcrystalline cellulose fibers and ethylcellulose particles is disclosed.

WO 2008/046742 A1 also discloses aerated food products containing at least 10 wt% of water and optionally fat, wherein the amount of fat and water taken together is at least 60 wt%, as well as surface active particles and surface active fibers. Moreover the volume weighted mean diameter of the particles is smaller than the length of the fibers. In the examples a combination of microcrystalline cellulose fibers and ethylcellulose particles is disclosed, as well as a combination of citrus fibers and ethylcellulose particles. US 2007/197744 A1 discloses a method for making a porous polymer composition, wherein the composition is made from a dispersion comprising polymer particles, wherein the particles may have a mean diameter of 20 to 500 nanometer.

Current methods for preparing aerated food products often have the disadvantage that the foams are not stable enough to be used in a food product which upon storage remains stable for at least a month, preferably several months. The total foam volume may decrease due to collapse of bubbles, or the average gas bubble size increases due to processes like coalescence. On the other hand, by a heating step of the foam, the foam may be stabilised by forming bubble shells which become interconnected during a drying and/or heating step. This way stable and dry foams can be produced, however, this often leads to dry foams which are not flexible anymore and which cannot easily be mixed with a food ingredient or a food product. Both processes lead to changing texture of the food product. Moreover, some systems have the disadvantage that several additives are required to stabilise the foams which do not provide nutritional value. Moreover such compounds may be expensive, or not compatible for food use. Further, many of the ingredients used to stabilise the gas phase in aerated food products need to be added at fairly high levels which can have deleterious textural and/or caloric consequences.

Hence there is a need for efficient stabilisation of foams that are suitable for use in food products, while the stabiliser preferably is a cheap and commonly available raw material. Preferably the foams have high overruns and relatively small, uniformly sized gas bubbles. Moreover the use of only a low concentration of stabiliser in the food product would be advantageous. Moreover it would be advantageous if the stabilising system does not require a multitude of stabilising compounds without nutritional value. Such foams can be used in food products to create a favourable mouthfeel, like a creamy mouthfeel, without having high caloric value of food products which normally have a smooth and creamy mouthfeel.

We have now found that stable foams can be produced containing colloidal particles as a stabiliser, by a method comprising a step wherein the particles are heated while the foam remains aqueous after heating. Due to the heating step the particles on the bubble interface partly or totally fuse and form a relative robust shell, creating very stable foams. The gas bubbles remain separated after the heat treatment, as the foams remain aqueous and the gas bubbles do not interconnect. This leads to the creation of very stable foams which can be used to produce stable aerated food products. Due to the easy separation of gas bubbles from each other after heat treatment, the bubbles can be easily re-dispersed and separated from each other after heat treatment and homogeneously incorporated into food products, creating aerated food products with a favourable texture.

Accordingly in a first aspect the present invention provides a method for preparation of an aqueous foam, comprising the steps: a) dispersing water-insoluble solid particles in an aqueous composition, wherein the particles have a volume weighted mean diameter between 30 nanometer and 10 micrometer; b) introduction of gas bubbles to the composition of step a) to create a foam; c) heating of the foam from step b) in a closed vessel to a temperature between 40 and 160 ⁰ C at which the particles partly or totally fuse.

In a second aspect the present invention provides a method for preparation of an aqueous foam, comprising the steps: a) dissolving ethylcellulose in an organic solvent which is miscible in water; b) addition of water to the mixture of step a), wherein the amount of water is at a weight ratio between 10:1 and 1 :2 based on the organic solvent; c) evaporating organic solvent and water to a concentration of ethylcellulose of at least 1 % by weight; d) addition of an acid to a pH of 4 or lower, or addition of a water-soluble salt to an ionic strength of at least 20 millimolar; or addition of a combination of acid and water-soluble salt; e) introduction of gas bubbles to the composition of step d) to create a foam. f) heating of the foam from step e) in a closed vessel at a temperature between 60 and 150 ⁰ C during a period between 10 minutes and 5 hours.

In a third aspect the present invention provides a method for preparation of an aerated food product, comprising the steps: a) creating a foam composition according to the first or second aspect of the invention; b) mixing the foam composition from step a) with one or more food ingredients to an overrun of at least 1 %; c) optionally mixing the composition from step b) with one or more other food ingredients.

In a fourth aspect the invention provides an aqueous foam composition obtainable by the method according to the first or second aspect of the present invention.

In a fifth aspect the present invention provides an aerated food composition comprising the foam composition according the fourth aspect of the invention.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

All percentages, unless otherwise stated, refer to the percentage by weight, with the exception of percentages cited in relation to the overrun.

In the context of the present invention, the average particle diameter is expressed as the d _{4 3} value, which is the volume weighted mean diameter, unless stated otherwise. The volume based particle size equals the diameter of a sphere that has same the same volume as a given particle.

The ranges that are indicated include the endpoints, unless stated otherwise, and are understood by the skilled person to be values which may vary within limits which are acceptable to the skilled person. These variations within certain limits may for instance be determined by measurement uncertainties.

The term 'aerated ¹ means that gas has been intentionally incorporated into a product, for example by mechanical means. The gas can be any gas, but is preferably, in the context of food products, a food-grade gas such as air, nitrogen, nitrous oxide, or carbon dioxide. The extent of aeration is measured in terms of 'overrun', which is defined as: weight of unaerated mix - weight of aerated product „ _„„, ,, , overrun x 100% ( 1 ) weight of aerated product

where the weights refer to a fixed volume of aerated product and unaerated mix (from which the product is made). Overrun is measured at atmospheric pressure.

A stable foam or aerated food product in the context of the present invention is defined as being stable for at least 30 minutes, more preferred at least an hour, more preferred at least a day, even more preferred at least a week, and most preferred at least a month. A stable foam can be defined to be stable with regard to total foam volume, and/or gas bubble size, and looses maximally 20% of its volume during 1 month storage, more preferably maximally 10% of its volume during 1 month storage. On the other hand systems may exist which loose more than 20% of its volume during 1 month storage, which nevertheless are considered to have a good stability, as the stability of such foams is much better than comparative foams. Stability can be described as that the foam and gas bubbles are stable against Ostwald ripening, which leads on the one hand to relatively small bubbles decreasing in size and relatively large bubbles increasing in size. This is caused by diffusion of gas from small to large bubbles, due to a higher effective Laplace pressure in the small bubbles as compared to the larger bubbles. In foams as described by the present invention, Ostwald ripening can be considered to be most important mechanism responsible for instability of the gas bubbles. An alternative mechanism for instability is coalescence, wherein two or more gas bubbles merge due to the breakage of the liquid interface between the bubbles and form one larger bubble with a larger volume.

Method for preparation of an aqueous foam

In a first aspect the present invention provides a method for preparation of an aqueous foam, comprising the steps: a) dispersing water-insoluble solid particles in an aqueous composition, wherein the particles have a volume weighted mean diameter between 30 nanometer and 10 micrometer; b) introduction of gas bubbles to the composition of step a) to create a foam; c) heating of the foam from step b) in a closed vessel to a temperature between 40 and 160 ⁰ C at which the particles partly or totally fuse. Optionally the heated foam from step c) is cooled, in order to process further. Cooling may be done to ambient temperature, or any other temperature suitable for a possible further process step.

In a preferred embodiment steps b and c are carried out done simultaneously, which means that the composition from step a) is aerated to create a foam is done, while also heating is carried out such that the particles partly or totally fuse.

All preferred embodiments of the first aspect of the invention as disclosed below, may be combined to give preferred embodiments of the method for preparation of an aqueous foam.

In a preferred embodiment the solid particles in step a) have a volume weighted mean diameter between 30 nanometer and 2 micrometer, more preferred 30 and 1000 nanometer, even more preferred between 30 and 500 nanometer, or between 30 and 300 nanometer. Other preferred ranges are between 50 and 500 nanometer, even more preferred between 50 and 300 nanometer, more preferred between 60 and 300 nanometer, and even more preferred between 70 and 300 nanometer. Alternatively, in another preferred embodiment the solid particles have a volume weighted mean diameter between 50 and 200 nanometer. In another alternative most preferred embodiment the solid particles have a volume weighted mean diameter between 30 and 100 nanometer, preferably between 30 and less than 100 nanometer, preferably between 30 and 95 nanometer, preferably between 30 and 90 nanometer, preferably between 30 and 80 nanometer, preferably between 30 and 70 nanometer, preferably between 30 and 60 nanometer, preferably between 30 and 50 nanometer, or alternatively preferably between 50 and 70 nanometer, preferably between 50 and 60 nanometer or between 60 and 70 nanometer. Most preferred the volume weighted mean diameter of the solid particles is between 100 and 200 nanometer, or even between 100 and 150 nanometer. Alternatively preferably the solid particles have a volume weighted mean diameter between 150 and 500 nanometer, preferably between 150 and 400 nanometer, alternatively preferably between 150 and 300 nanometer, preferably between 150 and 200 nanometer. Alternatively preferably the solid particles have a volume weighted mean diameter between 200 and 500 nanometer, preferably between 200 and 400 nanometer, preferably between 200 and 300 nanometer or between 300 and 400 nanometer. One of the advantages of an average particle size at the lower end of the indicated preferred ranges (at a mean particle size of less than about 100 nanometer), is that the overrun reached can be higher than with particles at the higher end of the preferred ranges.

The solid particles are water-insoluble, and the concentration of these particles in the dispersion in step a) is preferably between 0.1 and 20% by weight, more preferred between 0.5 and 10% by weight, most preferred between 0.5 and 5% by weight. Preferably the water-level of the foam composition created is at least 10% by weight of the foam composition. The dispersion of particles is an aqueous dispersion, or a dispersion of particles in a mixture of water and organic solvents. Preferred organic solvents are for example ethanol, acetone, isopropanol, and tetrahydrofuran. For food use, the solvent has to be food-grade and compatible for food use. If an organic solvent is present in step a), after foaming removal of the organic solvent can be done by evaporation or any other suitable method. The term water-insoluble solid particles is understood to have its common meaning, such that the particles do not dissolve in water, or wherein at most 0.1 wt% of a compound dissolves in water when the compound is mixed with water at room temperature, atmospheric pressure and neutral pH.

Preferably the solid particles comprise ethylcellulose. A preferred stabiliser for foams made according to the first aspect of the present invention is ethylcellulose. The general structural formula of ethylcellulose is:

The degree of substitution of the ethylcellulose preferably used in the present invention is preferably between 2 and 3, more preferably about 2.5. The average number of hydroxyl groups substituted per anhydroglucose unit (the 'monomer') is known as the 'degree of substitution' (DS). If all three hydroxyls are replaced, the maximum theoretical DS of 3 results.

Suitable sources and types of the ethylcellulose preferably used in the present invention are supplied by for example Hercules, Aldrich, and Dow Chemicals. Suitable ethylcellulose preferably has a viscosity between 5 and 300 cP at a concentration of 5 % in toluene/ethanol 80:20, more preferably between 100 and 300 cP at these conditions.

Alternatively, the solid particles can be made of a lipid material, wherein the lipid material preferably is a wax. A wax is a non-glyceride lipid substance having the following characteristic properties: plastic (malleable) at normal ambient temperatures; a melting point above approximately 45°C (which differentiates waxes from fats and oils); a relatively low viscosity when melted (unlike many plastics); insoluble in water but soluble in some organic solvents; hydrophobic. Preferred waxes are one or more waxes chosen from carnauba wax, shellac wax or beeswax. The particles may have any shape, like spherical or elongated or rod-like or platelet-like.

Waxes may be natural or artificial, but natural waxes, are preferred. Beeswax, carnauba (a vegetable wax) and paraffin (a mineral wax) are commonly encountered waxes which occur naturally. Some artificial materials that exhibit similar properties are also described as wax or waxy. Chemically speaking, a wax may be an ester of ethylene glycol (ethane-1 ,2-diol) and two fatty acids, as opposed to fats which are esters of glycerine (propane-1 ,2,3-triol) and three fatty acids. It may also be a combination of fatty alcohols with fatty acids.

In another preferred embodiment the solid particles can be made of a lipid material, wherein the lipid material comprises plant sterols or fatty acids/fatty acid esters. Plant sterols (also called phytosterols) are a group of steroid alcohols, phytochemicals naturally occurring in plants. At room temperature they are white powders with mild, characteristic odor, insoluble in water and soluble in alcohols. Plant sterols can be transformed into microparticles by inducing the precipitation of a plant sterol solution containing via solvent change during stirring. Herein, the particles can be with various shapes such as spherical, rod-like shape and platelet shape. Preferably in step a) the aqueous composition further comprises a mixture of more than two types of aforementioned particles, thus in step a) the solid particles may comprise ethylcellulose and/or a lipid material. For example, the foam could be stabilised by a mixture of ethylcellulose particles and shellac wax particles.

In a preferred embodiment, in step a) the aqueous composition comprises particles of a wax, wherein the particles have a volume weighted mean diameter between 30 nanometer and 10 micrometer. Preferably the particles have a volume weighted mean diameter between 30 nanometer and 2 micrometer. More preferably the particles have a volume weighted mean diameter between 30 nanometer and 1 micrometer, even more preferred between 30 nanometer and 500 nanometer. Preferred waxes are one or more waxes chosen from carnauba wax, shellac wax or beeswax. Preferably the wax is a food-grade waxy material. The particles may have any shape, like spherical or elongated or rod-like or platelet-like.

The concentration of the waxy material in step a), if present, preferably ranges from 0.01 % to 10% by weight.

Preferably fibres are substantially absent from the foam prepared by the method according to the first aspect of the invention. This means that if present, then preferably at a maximum concentration of 0.001% by weight of the aerated composition. By 'fibre' is meant a compound having an insoluble, particulate structure, and wherein the ratio between the length and diameter ranges from 5 to infinite. Examples of such fibres are microcrystalline cellulose, citrus fibres, onion fibres, fibre particles made of wheat bran, of lignin, and stearic acid fibres. Preferably the aqueous aerated composition prepared by the method according to the first aspect of the invention comprises maximally 0.001% by weight of microcrystalline cellulose, more preferably less than 0.001% by weight of microcrystalline cellulose.

Alternatively, in another preferred embodiment, after step b), the foam is mixed with a water-soluble thickening agent or an aqueous solution or dispersion of a water-soluble thickening agent. Preferred thickening agents are water-soluble polysaccharides such as xanthan gum, guar gum, agar, gellan gum, and gum arabic, or a combination of these. Other suitable compounds are a protein such as gelatine, or other polymers such as polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), polyethyleneglycol (PEG) or a combination of these. For food use these thickening agents have to be food grade.

The concentration of the water-soluble thickening agent in step a), if present, ranges from 0.001 wt% to 5.0 wt%, preferably from 0.05 wt% to 1.0 wt%.

In another preferred embodiment in step a) the aqueous composition further comprises a water-insoluble thickening agent. Or alternatively in another preferred embodiment, after step b) the foam is mixed with an aqueous dispersion of a water-insoluble thickening agent. Preferred water-insoluble thickening agents are chosen from microcrystalline cellulose, bacterial cellulose, silica, clay, etc., or a combination of these. Preferably, thickening agents are fibre-like materials. Such fibres have the advantage that they are very biodegradable, which is favourable for the environment. Very often such fibres are also food-grade. Other preferred water-insoluble thickening agents are citrus fibres, onion fibres, tomato fibres, cotton fibres, silk, their derivatives and copolymers. The fibres preferably used in the present invention have a length of preferably 0.1 to 100 micrometer, more preferably from 1 to 50 micrometer. The diameter of the fibres is preferably in the range of 0.01 to 10 micrometer. The aspect ratio (length / diameter) is preferably more than 10, more preferably more than 20 up to 1 ,000.

The concentration of the water-insoluble thickening agent in step a), if present, preferably ranges from 0.01 to 10 % by weight, more preferably 0.05 to 1.0 % by weight.

In step b) gas bubbles are introduced to the composition of step a) to create a foam, that preferably has an overrun of at least 20%. The overrun may vary from at least 50% to at least 100% or even to 400% or to 600% to about 700% or even more.

The temperature at which step b) is performed usually is between 0 and 100 ⁰ C ₁ more preferably between 15 and 8O ⁰ C, most preferred from 20 to 6O ⁰ C. At relatively high temperatures (like for example 60 to 80 ⁰ C), bubbles may become bigger upon foaming than at relatively low temperatures. Upon a subsequent optional cooling step, bubbles shrink again, due to the shrinking gas volume with lower temperatures. This leads to more closely packed particles on the interface of the bubbles, ultimately leading to more robust foams. Moreover at higher temperature the particles tend to stick more to each other, leading to more robust foams.

Gasses which may be introduced in step b) are preferably gases which are suitable for use in foods, such as air, nitrogen, nitrous oxide (laughing gas, N ₂ O), and carbon dioxide.

In step b) the aeration step can be performed by any suitable method which produces small enough gas bubbles. Methods of aeration include (but are not limited to): - continuous whipping in a rotor-stator device such as an Oakes mixer (E. T. Oakes Corp), a Megatron mixer (Kinematica AG) or a Mondomix mixer (Haas-Mondomix BV);

- batch whipping in a device involving surface entrainment of gas, such as a Hobart whisk mixer or a hand whisk;

- gas injection, for example through a sparger or a venturi valve; - gas injection followed by mixing and dispersion in a continuous flow device such as a scraped surface heat exchanger,

- elevated pressure gas injection, where a gas is solubilised under pressure and then forms a dispersed gas phase on reduction of the pressure. This could occur upon dispensing from an aerosol container.

Other suitable devices are for example Silverson, Ultraturrax, Kenwood kitchen mixer, and Ross Mill. The ethylcellulose dispersions as prepared can be also be whipped vigorously by shaking the dispersion. When the mixing shear that is applied is high, then in general the bubbles in the foam are small, while at lower shear the bubbles are bigger.

At a given particle concentration in step a), suitably when the overrun is relatively low, the bubbles are also relatively small (average 10 to 50 micrometer), while at the higher overruns, the bubbles may reach an average diameter of 200 micrometer or even higher. In order to stabilise small bubbles more particles are required, as the total bubble surface area increases with smaller bubble diameter (at a given total fixed foam volume).

At a given particle concentration (determined as weight percent of the foam), in general it holds that the smaller the bubbles, the smaller the overrun, and the more stable the foam. In order to obtain a stable foam, the ratio between particle size and bubble size is preferably larger than 1 :5, more preferably larger than 1 :10.

In a preferred embodiment the gas bubbles are sufficiently small that they are not visible to the naked eye. This has the advantage that a food product is not obviously aerated and has a similar appearance to unaerated food products, which may be preferred by consumers. The aerated products may nonetheless be somewhat lighter in colour or more opaque due to light scattering by the small bubbles. For example, an aerated food product has a significantly reduced calorie content per unit volume, whilst being similar in appearance to the unaerated food product.

Suitably the average diameter of the air bubbles in the foams ranges from about 1 to about 500 micrometer. Preferably at least 50% of the number of gas bubbles in the foam has a diameter smaller than 200 micrometer, more preferably at least 50% of the number of gas bubbles in the foam has a diameter smaller than 100 micrometer. Even more preferred at least 75% of the number of gas bubbles has a diameter smaller than 75 micrometer, more preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 50 micrometer, and most preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 30 micrometer.

Gas bubble size can be measured using a spectrophotometer that can be loaded with a glass tube containing a foam sample. Light transmitted at the tube and reflected is measured and this is translated into average bubble diameter. Alternatively a foam can be frozen to lock the structure and subsequently cut in thin slices. The average bubble diameter in these slices can be determined by microscopy. Another method is to determine the bubble size in a sample using confocal microscopy.

In general it holds that the smaller the particles in step a), the larger the overrun, as with smaller particles a larger surface area can be stabilised, at a given amount of ethylcellulose.

The foam generated in step b) of the method according to the first aspect of the invention suitably has a concentration of particles of at least 0.01% by weight, and at most 20% by weight of the foam composition, more preferably between 0.1 and 10% by weight of the foam composition. Preferably the water-level of the foam composition created in step e) is at least 10% by weight of the foam composition.

In step c) the foam from step b) is heated in a closed vessel to a temperature between 40 and 160 ⁰ C at which the particles partly or totally fuse. It is important that the vessel is closed and that the pressure in the vessel can increase, as otherwise the bubbles will expand and ultimately collapse. Using a closed vessel also has the result that the foam remains aqueous and is not dried during the heating step. In the context of the present invention a closed vessel may also emcompass a continuous pasteurisation or sterilisation unit, which are commonly used for example in the dairy industry, and which act under a pressure higher than atmospheric pressure.

The temperature and time required will depend on the type of particle, and can be determined by the skilled person. Preferably the heating is done at a temperature between 60 and 160°C, even more preferred between 80 and 160 ⁰ C, and even more preferred between 90 and 150 ⁰ C, and most preferred between 100 and 140°C. The heating time is dependent on the heating temperature and may range from 10 minutes to 5 hours, preferably from 10 minutes to 4 hours, like for example 30 minutes, 1 hour, 2 hours, 3 hours. If the heating temperature is high, then the corresponding heating time is short and vice versa. If the foam is heated too long, the foam may collapse due to collapsing bubbles.

The heating leads to a more stable foam, because the particles partly or totally fuse forming a relatively robust shell around the gas bubbles. As an advantage, the foam remains aqueous, meaning that it is not dried during this heating step, and consequently remains soft and easy to be mixed with the fat continuous or anhydrous food product.

The heating step of the foams is performed, in order to obtain partly or totally fusing particles at the gas-water interface of single bubbles, rather than particles partly or totally fusing on the interface of multiple bubbles, which would lead to a solid foam as the bubbles will form a solid conglomerate. Alternatively, by the method according to the invention, single bubbles are created, having a robust shell that captures the gas bubbles, but wherein the foam is still flexible . During this heating step, and by the foam remaining aqueous, aggregation of bubbles can be avoided in order to keep the bubbles separated from each other during heating. The foam remains an aqueous foam in this manner, and the bubbles can be redispersed and separated from each other after heat treatment, for example when being mixed with one or more food ingredients. As opposed to sintering, the particles on the interfaces of different bubbles do not fuse, and remain single bubbles. During the heating step, particles are softened and partly or totally fuse, without collapse of bubbles.

If in a preferred embodiment a lipid material is present in step a) of the method according to the first aspect of the invention, this lipid material may melt in step c) and be incorporated in the shell around the bubbles. The lipid material may be used to 'glue' the solid particles located at the interface when the wax melts at a lower temperature. Therewith the heating temperature can be reduced in step c).

If in a preferred embodiment a water-soluble thickening agent or an aqueous solution or dispersion of a water-soluble thickening agent (such as xanthan gum or other thickening agents as indicated before) is mixed with the foam obtained in step b) of the method according to the first aspect of the invention, then the viscosity of the continuous aqueous phase will increase. The addition of a water-soluble thickening agent may be used to prevent the particle stabilised bubbles from aggregation during heating. Consequently, it may prevent the bubbles from coalescing and agglomerating during heating, which could induce the loss of foam volume. This may lead to easier dispersion of the foam into a composition, therewith possibly creating homogeneously aerated food products having an attractive texture and appearance.

In a preferred embodiment a water-insoluble thickening agent (such as citrus fibres or other fibres) is present in step a) of the method according to the first aspect of the invention. Without wishing to be limited by theory, it is believed that the water-insoluble thickening agent keeps the bubbles and the particles on the interfaces of separate bubbles separated by forming a barrier in between the interfaces of several bubbles. Moreover it also increases the viscosity of the continuous phase. Therewith the addition of a water-soluble thickening agent may be used to prevent the particle stabilised bubbles from aggregation during heating. Consequently, it may prevent the bubbles from coalescing and agglomerating during heating, which could induce the loss of foam volume. This may lead to easier dispersion of the foam into a composition, therewith possibly creating homogeneously aerated food products having an attractive texture and appearance.

Method for preparation of an aqueous foam comprising ethylcellulose In a second aspect the present invention provides a method for preparation of an aqueous foam, comprising the steps: a) dissolving ethylcellulose in an organic solvent which is miscible in water; b) addition of water to the mixture of step a), wherein the amount of water is at a weight ratio between 10:1 and 1 :2 based on the organic solvent; c) evaporating organic solvent and water to a concentration of ethylcellulose of at least 1 % by weight; d) addition of an acid to a pH of 4 or lower, or addition of a water-soluble salt to an ionic strength of at least 20 millimolar; or addition of a combination of acid and water-soluble salt; e) introduction of gas bubbles to the composition of step d) to create a foam; f) heating of the foam from step e) in a closed vessel at a temperature between 60 and 150 ⁰ C during a period between 10 minutes and 5 hours.

Optionally the heated foam from step f) is cooled, in order to process further. Cooling may be done to ambient temperature, or any other temperature suitable for a possible further process step.

Preferred aspects of the first aspect of the invention may be applicable to this second aspect as well, mutatis mutandis. The preferred embodiments of this second aspect of the invention as disclosed below, can be combined with each other to give preferred embodiments of the method according to this second aspect of the invention.

In step a) of this method, the concentration of ethylcellulose in the solvent is preferably between 0.1 and 6% by weight, more preferably between 0.1 and 4% by weight, more preferably between 0.1 and 3% by weight, even more preferably between 0.1 and 2% by weight, and most preferably between 0.5 and 1% by weight. The influence of the concentration of ethylcellulose in step a), is that a lower ethylcellulose concentration in solvent yields a smaller volume weighted average particle diameter. A smaller average particle size suitably leads to increased stability of the foams that can be created. The solvent in step a) can be any solvent suitable for ethylcellulose. Preferably in step a) the organic solvent comprises acetone or ethanol or a combination of these solvents, preferably at a purity of at least 98%. The ratio of water to organic solvent in step b) of the method according to the second aspect of the invention, is based on the purity of the organic solvent. The temperature in step a) is preferably between 10 and 60 ⁰ C, more preferably between 25 and 40 ⁰ C. The temperature that will be applied is preferably dependent on the solvent that is used. If the solvent evaporates at a relatively low temperature, then the temperature in step a) will be lower than when a solvent is used with a higher boiling point.

In step b) water is added to the solution of ethylcellulose, which leads to a partial precipitation of ethylcellulose into particles. The water is preferably distilled or de- ionised water, more preferably it is double distilled water. Preferably these ethylcellulose particles that precipitate have a volume weighted mean diameter between 30 and 500 nanometer. More preferred the ethylcellulose particles have a diameter between 50 and 500 nanometer, more preferred between 30 and 300 nanometer, even more preferred between 50 and 300 nanometer, most preferred betweeen 60 and 300 nanometer, and even more preferred between 70 and 300 nanometer. Alternatively, in another preferred embodiment the solid particles have a volume weighted mean diameter between 50 and 200 nanometer. In another alternative most preferred embodiment the solid particles have a volume weighted mean diameter between 30 and 100 nanometer, preferably between 30 and less than 100 nanometer, preferably between 30 and 95 nanometer, preferably between 30 and 90 nanometer, preferably between 30 and 80 nanometer, preferably between 30 and 70 nanometer, preferably between 30 and 60 nanometer, preferably between 30 and 50 nanometer, or alternatively preferably between 50 and 70 nanometer, preferably between 50 and 60 nanometer or between 60 and 70 nanometer. Most preferred the volume weighted mean diameter of the precipitated ethylcellulose particles is between 100 and 200 nanometer, or even between 100 and 150 nanometer. Alternatively preferably the solid particles have a volume weighted mean diameter between 150 and 500 nanometer, preferably between 150 and 400 nanometer, alternatively preferably between 150 and 300 nanometer, preferably between 150 and 200 nanometer. Alternatively preferably the solid particles have a volume weighted mean diameter between 200 and 500 nanometer, preferably between 200 and 400 nanometer, preferably between 200 and 300 nanometer or between 300 and 400 nanometer. In step b) preferably the weight ratio between the amount of solvent is between 5:1 and 1 :2, more preferably between 2:1 and 1 :2. Most preferably the weight ratio between water and organic solvent in step b) is 1 : 1 , or about 1 :1. Preferably the water is added to the mixture while being stirred, preferably under high shear conditions. The temperature in step b) is preferably between 10 and 60 ⁰ C, more preferably between 25 and 40 ⁰ C.

The evaporation step c) is performed in such a way that the concentration of ethylcellulose becomes at least 1% by weight. More preferably the concentration of ethylcellulose after step c) is at least 2% by weight.

In step d) the acid preferably is chosen from hydrochloric acid, tartaric acid, acetic acid, and citric acid, or any combination of these acids, which are acids compatible for use in foods. The salt preferably comprises NaCI, KCI, MgCI ₂ or CaCI ₂ , or any combination of these salts, which are salts compatible for use in foods.

In step d) preferably the ionic strength that is obtained is maximally 200, more preferably maximally 150 millimolar. In case a combination of acid and salt is used in step d), then preferably the strength of the combination is similar to use of only an acid to a pH of 4 or lower, or to the use of only a water-soluble salt to an ionic strength of at least 20 millimolar.

Without wishing to be limited by theory, we have determined that by the addition of acid to lower the pH and/or the introduction of the water-soluble salt in step d) of the method according to the invention, the zeta-potential of the ethylcellulose particles is changed. The zeta-potential is a measure for the surface charge of a colloidal particle, and determines whether particle attract or repulse each other. At a relatively high absolute value of the zeta-potential the ethylcellulose particles are well dispersed, due to repulsion of the particles. This behaviour is observed at a zeta-potential of the particles having an absolute value above 25 millivolt. When the zeta-potential of the particles is decreased to an absolute value below 25 millivolt, the ethylcellulose particles aggregate, leading to the ethylcellulose particles being able to stabilise a foam. Good foam stability is observed in the region where the ethylcellulose dispersion is colloidally unstable, i.e. electrostatic repulsion between the particle is screened the particles are weakly attractive due to van der Waals forces, i.e. when the absolute value of the zeta-potential of the particles is below 25 millivolt. Poorer foam stability is obtained when the dispersion is stable, i.e. the particles are electrostatically repulsive, i.e. when the absolute value of the zeta-potential is above 25 millivolt.

Upon addition of acid in step d) to reach a pH of 4 or lower, the surface charge of the ethylcellulose particles is modified, and the zeta-potential of the ethylcellulose particles is decreased to an absolute value below 25 millivolt. Similarly, upon addition of a water- soluble salt to reach an ionic strength of at least 20 millimolar, the zeta-potential of the ethylcellulose particles is decreased to an absolute value below 25 millivolt. Also a combination of an acid and a water-soluble salt may be added in step d), in order to reach a zeta-potential of the ethylcellulose particles lower than 25 millivolt. A lower zeta-potential means that the ethylcellulose particles become more hydrophobic.

Thus preferably the addition of a combination of acid and water-soluble salt in step d) leads to a zeta-potential of the ethylcellulose particles below 25 millivolt, preferably below 20 millivolt, more preferred below 15 millivolt.

Preferably the zeta-potential of the ethylcellulose particles obtained from step d) has an absolute value below 25 millivolt, preferably below 20 millivolt, more preferred below 15 millivolt, leading to stable foams.

In step e) gas bubbles are introduced to the composition of step d) to create a foam, that preferably has an overrun of at least 20%, preferably at least 50%. The overrun may vary from at least 50% to at least 100% or even to 400% or to 600% to about 700% or even more. The temperature at which step e) is performed usually is between 0 and 100 ⁰ C, more preferably between 15 and 80 ⁰ C, most preferred from 20 to 4O ⁰ C.

Gasses which may be introduced in step e) are preferably gases which are suitable for use in foods, such as air, nitrogen, nitrous oxide (laughing gas, N ₂ O), and carbon dioxide. In step e) any stirrer or technique which produces small enough gas bubbles can be used (e.g. Silverson, Ultraturrax, Kenwood kitchen mixer, Ross Mill). Also the aeration methods indicated herein are suitable methods. The ethylcellulose dispersions as prepared can be also be whipped vigorously by shaking the dispersion. When the mixing shear that is applied is high, then in general the bubbles in the foam are small, while at lower shear the bubbles are bigger.

At a given ethylcellulose concentration, suitably when the overrun is relatively low, the bubbles are also relatively small (average 10 to 50 micrometer), while at the higher overruns, the bubbles may reach an average diameter of 200 micrometer or even higher. In order to stabilise small bubbles more particles are required, as the total bubble surface area increases with smaller bubble diameter (at a given total fixed foam volume).

At a given concentration of ethylcellulose particles (determined as weight percent of the foam), in general it holds that the smaller the bubbles, the smaller the overrun, and the more stable the foam. In order to obtain a stable foam, the ratio between ethylcellulose particle diameter and bubble diameter is preferably larger than 1 :5, more preferably larger than 1 :10, based on the volume weighted mean diameter of the particles as defined before.

Suitably the average diameter of the air bubbles in the foams ranges from about 1 to about 500 micrometer. Preferably at least 50% of the number of gas bubbles in the foam has a diameter smaller than 200 micrometer, more preferably at least 50% of the number of gas bubbles in the foam has a diameter smaller than 100 micrometer. Even more preferred at least 75% of the number of gas bubbles has a diameter smaller than 75 micrometer, more preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 50 micrometer, and most preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 30 micrometer.

In general it holds that the smaller the precipitated ethylcellulose particles, the larger the overrun, as with smaller particles a larger surface area can be stabilised, at a given amount of ethylcellulose. The foam generated in step e) of the method according to the first aspect of the invention suitably has a concentration of ethylcellulose of at least 0.01% by weight, and at most 20% by weight of the foam composition, more preferably between 0.1 and 10% by weight of the foam composition. Preferably the water-level of the foam composition created in step e) is at least 10% by weight of the foam composition.

In a preferred embodiment of the method according to the second aspect of the invention, in step e) the composition further comprises particles of a wax, wherein the particles have a volume weighted mean diameter between 30 nanometer and 2 micrometer. More preferably the particles have a volume weighted mean diameter between 30 nanometer and 1 micrometer, even more preferred between 30 nanometer and 500 nanometer. Preferred waxes according to the present invention are one or more waxes chosen from carnauba wax, shellac wax or beeswax. Preferably the wax is a food-grade waxy material. The particles may have any shape, like spherical or elongated or rod-like.

The concentration of the waxy material in step e), if present, preferably ranges from 0.01 % to 10% by weight. The weight ratio of EC to wax in the aqueous dispersion ranges from 1000:1 to 1 :1 , preferably from 100:1 to 10:1.

Preferred aspects of the wax in the context of the first aspect of the invention are also applicable to the second aspect of the invention.

Preferably the aqueous aerated composition prepared by the method according to the first aspect of the invention comprises maximally 0.001 % by weight of microcrystalline cellulose, more preferably less than 0.001% by weight of microcrystalline cellulose.

Alternatively, in a preferred embodiment of the method according to the second aspect of the invention, wherein after step e) the foam is mixed with a water-soluble thickening agent or an aqueous solution or dispersion of a water-soluble thickening agent.

Preferred thickening agents are water-soluble polysaccharides such as xanthan gum, guar gum, agar, gellan gum, and gum arabic, or a combination of these. Other suitable compounds are a protein such as gelatine, or other polymers such as polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), polyethyleneglycol (PEG) or a combination of these. For food use these thickening agents have to be food grade. The concentration of the water-soluble thickening agent in step a), if present, ranges from 0.001 wt% to 5.0 wt%, preferably from 0.05 wt% to 1.0 wt%.

Preferred aspects of the water-soluble thickening agent in the context of the first aspect of the invention are also applicable to the second aspect of the invention.

In a preferred embodiment of the method according to the second aspect of the invention, in step e) the composition further comprises a water-insoluble thickening agent. Or alternatively in another preferred embodiment, after step e) the foam is mixed with an aqueous dispersion of a water-insoluble thickening agent. Preferred water- insoluble thickening agents are chosen from microcrystalline cellulose, bacterial cellulose, silica, clay, etc., or a combination of these. Preferably, thickening agents are fibre-like materials. Very often such fibres are also food-grade. Other preferred water- insoluble thickening agents are citrus fibres, onion fibres, tomato fibres, cotton fibres, silk, their derivatives and copolymers. The fibres preferably used in the present invention have a length of preferably 0.1 to 100 micrometer, more preferably from 1 to 50 micrometer. The diameter of the fibres is preferably in the range of 0.01 to 10 micrometer. The aspect ratio (length / diameter) is preferably more than 10, more preferably more than 20 up to 1 ,000.

The concentration of the water-insoluble thickening agent in step e), if present, preferably ranges from 0.01 to 10 % by weight, more preferably 0.05 to 1.0 % by weight.

Preferred aspects of the water-insoluble thickening agent in the context of the first aspect of the invention are also applicable to the second aspect of the invention.

In step f) the foam comprising ethylcellulose particles is heated such that the ethylcellulose particles partly or totally fuse, to create a kind of shell around the gas bubbles. The heating of the foam from step e) is carried out in a closed vessel at a temperature between 60 and 15O ⁰ C during a period between 10 minutes and 5 hours. Preferably the temperature in step f) is between 80 and 150 ⁰ C, or 100 and 150 ⁰ C, and most preferred between 120 and 140 ⁰ C. The time required is dependent on the temperature: at a high temperature, the required time is shorter than at a lower temperature, and can be determined by the skilled person. It may range from 10 minutes to 4 hours, like for example 30 minutes, 1 hour, 2 hours, 3 hours.

If in a preferred embodiment a waxy material is present in the composition in step e) of the method according to the second aspect of the invention, this waxy material may melt in step f) and be incorporated in the shell around the bubbles. The wax may be used to 'glue' the solid particles located at the interface when the wax melts at a lower temperature. Therewith the heating temperature can be reduced in step f).

If in a preferred embodiment a water-soluble thickening agent or an aqueous solution or dispersion of a water-soluble thickening agent (such as xanthan gum or other thickening agents as indicated before) is mixed with the foam obtained in step e) of the method according to the second aspect of the invention, then the viscosity of the continuous aqueous phase will increase. The addition of a water-soluble thickening agent may be used to prevent the particle stabilised bubbles from aggregation during heating. Consequently, it may prevent the bubbles from coalescing and agglomerating during heating, which could induce the loss of foam volume. This may lead to easier dispersion of the foam into a composition, therewith possibly creating homogeneously aerated food products having an attractive texture and appearance.

In a preferred embodiment a water-insoluble thickening agent (such as citrus fibres or other fibres) is present in step a) of the method according to the second aspect of the invention. Without wishing to be limited by theory, it is believed that the water-insoluble thickening agent keeps the bubbles and the particles on the interfaces of separate bubbles separated by forming a barrier in between the interfaces of several bubbles. Moreover it also increases the viscosity of the continuous phase. Therewith the addition of a water-soluble thickening agent may be used to prevent the particle stabilised bubbles from aggregation during heating. Consequently, it may prevent the bubbles from coalescing and agglomerating during heating, which could induce the loss of foam volume. This may lead to easier dispersion of the foam into a composition, therewith possibly creating homogeneously aerated food products having an attractive texture and appearance.

The method according to the second aspect of the invention can be regarded to be a preferred embodiment of the method according to the first aspect of the invention. Steps a) to d) of the method according to the second aspect of the invention together constitute a preferred embodiment of step a) of the method according to the first aspect of the invention.

Step e) of the method according to the second aspect of the invention constitutes a preferred embodiment of step b) of the method according to the first aspect of the invention.

Step f) of the method according to the second aspect of the invention constitutes a preferred embodiment of step c) of the method according to the first aspect of the invention.

Method for preparation of an aerated food product

The foam prepared using the method according to the first or second aspect of the invention can be used to create an aerated food product, by mixing the foam into a food product or into one or more food ingredients which subsequently can be mixed with one or more other food ingredients to provide an aerated food composition.

Hence in a third aspect the invention provides a method for preparation of an aerated food product, comprising the steps: a) creating a foam composition according to the method of the first or second aspect of the present invention; b) mixing the foam composition from step a) with one or more food ingredients to an overrun of at least 1 %; c) optionally mixing the composition from step b) with one or more other food ingredients.

The aerated composition obtained in step b) has an overrun of at least 1%, more preferred at least 5%, even more preferred at least 10%, most preferred at least 20%. Preferably the food product has an overrun of at most 150%, more preferably at most 120%, most preferably at most 100%.

The one or more food ingredients disclosed in step b) can be in a 'raw' form, thus not yet formulated as a ready food product. They could also be in ready form, as a food product into which the foam from step a) is mixed. The product from step b) could be a ready food product as such, or otherwise can be further processed to be mixed with one or more other food products.

All preferred embodiments of the methods according to the first and second aspects of the invention, may also be preferred embodiments of the method of the third aspect of the invention, as applicable mutatis mutandis. These preferred embodiments may also be combined to give preferred embodiments of the third aspect of the invention, as applicable mutatis mutandis.

Aqueous foam composition and aerated food composition

In a fourth aspect the invention provides an aqueous foam composition obtainable by the method according to the first or second aspect of the present invention.

In a fifth aspect the present invention provides an aerated food composition comprising the foam composition according the fourth aspect of the invention.

Preferred aspects of the first, second, and third aspects of the invention may also be preferred aspects of the fourth and fifth aspects of the invention, as applicable mutatis mutandis.

Preferably the aqueous foam composition comprises gas bubbles, wherein at least 50% of the number of gas bubbles has a diameter smaller than 200 micrometer. More preferred, at least 50% of the number of gas bubbles has a diameter smaller than 100 micrometer. Even more preferred at least 75% of the number of gas bubbles has a diameter smaller than 75 micrometer, more preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 50 micrometer, and most preferred at least 50% of the number of gas bubbles in the foam has a diameter smaller than 30 micrometer.

Advantageously the food products according to the present invention, or obtainable by the methods according to the present invention remain stable for at least a month, preferably several months. With stable is meant that the foam is stable, which means that gas bubbles in the foam do not coalesce to become larger gas bubbles. Suitable aerated food products are for example dressings like mayonnaise. Such dressings may have a total oil content ranging from 5% to 70% or 80% by weight. All such products are within the scope of the present invention.

The foams can also be used in food products to provide solid or semi-solid (e.g. spreadable) food products having a lower calorie content, while not being visible in the food product.

Further examples of preferred food products are cereal bars, chocolate bars, cookies and biscuits, confectionery products, condiments, confectionary, beverages, desserts, snacks, spreads like margarine or low fat margarines or dairy spreads, ice cream, dressings, mayonnaise, sauces, bakery products like bread, shortenings, cheese (soft cheese, hard cheese), soups, dairy drinks, fruit drinks or juices, vegetable drinks or juices, combinations of dairy, and/or fruit, and/or vegetable drinks, cocoa drinks, and especially dairy mini-drinks.

Other preferred food compositions are frozen foods, such as frozen confections like ice cream, or other frozen desserts.

Also soups (both in dry form (which have to be reconstituted with water), as well as liquid soups) are within the scope of the present invention. By incorporation of the foam into such food products, a creamy soup can be obtained, which does not have the calories associated normally with creamy soups (to which generally cream is added).

In case the food product is a beverage, more specifically a fruit drink, or combination of fruit and dairy drink, it preferably comprises at least 10% by weight of the composition of a fruit component, wherein the fruit component is selected from fruit juice, fruit concentrate, fruit juice concentrate, fruit puree, fruit pulp, comminuted fruit, fruit puree concentrate, and combinations thereof. Examples of such fruit components are orange juice, apple juice, grape juice, peach pulp, banana pulp, apricot pulp, concentrated orange juice, mango pulp, concentrated peach juice, raspberry puree, strawberry puree, apple pulp, raspberry pulp, concentrated grape juice, concentrated aronia juice, and concentrated elderberry juice. Preferably such a beverage comprises at least 30% by weight of the beverage of said fruit component, more preferred at least 40% by weight of the beverage of said fruit component. These amounts are calculated as if undiluted, non-concentrated fruit juices and purees and the like are used. Thus, if 0.5% by weight of a 6-fold fruit concentrate is used, the actual amount of fruit component incorporated is 3% by weight of the beverage. Any commonly available fruit component might be used in the beverages according to the invention, and may be selected from one or more of the following fruit sources: citrus fruit (e.g. orange, tangerine, lemon or grapefruit); tropical fruit (e.g. banana, peach, mango, apricot or passion fruit); red fruit (e.g. strawberry, cherry, raspberry or blackberry), or any combination thereof.

In a further preferred embodiment the food product is a spread such as water-in-oil emulsions, for example a margarine or low fat margarine type food product. A spread may also be an oil-in-water emulsion, like dairy spreads or fresh soft cheeses. Suitably the total triglyceride level of such a spread may range from about 1% by weight to 90% by weight of the composition, preferably from 10% by weight to 85% by weight of the composition, more preferred from 20% to 70% by weight, most preferred from 30% to 60% by weight of the composition.

Especially preferred aerated food products according to the present invention are dairy drinks, which may for instance be used as a meal replacer.

The food product may be dried and contain less than 40% water by weight of the composition, preferably less than 25%, more preferably from 1 to 15%. Alternatively, the food may be substantially aqueous and contain at least 40% water by weight of the composition, preferably at least 50%, more preferably from 65 to 99.9%.

The food preferably comprises nutrients including carbohydrate (including sugars and/or starches), protein, fat, vitamins, minerals, phytonutrients (including terpenes, phenolic compounds, organosulfides or a mixture thereof) or mixtures thereof. The food may be low calorie (e.g. have an energy content of less than 100 kCal per 100 g of the composition) or may have a high calorie content (e.g. have an energy content of more than 100 kCal per 100 g of the composition, preferably between 150 and 1000 kCal). The food may also contain salt, flavours, colours, preservatives, antioxidants, non- nutritive sweetener or a mixture thereof.

The various features and embodiments of the present invention, referred to in individual sections above apply, as appropriate, to other sections, mutatis mutandis. Consequently features specified in one section may be combined with features specified in other sections, as appropriate. All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and products of the invention will be apparent to those skilled in the art without departing from the scope of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are apparent to those skilled in the relevant fields are intended to be within the scope of the claims.

DESCRIPTION OF FIGURES

Figure 1 : a cryo-SEM-image at 500Ox magnification of resulting bubbles of the foam prepared in example 1.

Figure 2: a cryo-SEM-image at 500Ox magnification of the foam prepared in example 6. Bubbles of heated foam are indicated by the arrows.

Figure 3: Transport mean free path evolution λ(t)/ λ(0) of gas bubbles in mayonnaise aerated by whipping (open diamonds 0) and by aeration using heated ethylcellulose foam (according to the invention) (closed diamonds ♦); from example 7.

EXAMPLES

The following non-limiting examples illustrate the present invention.

Materials

Aqualon ^® Ethylcellulose (type N 100) was purchased from Hercules ( Widnes, UK). Ethoxyl content was 48.0-49.5%, and degree of substitution was 2.46-2.57. Viscosity was 80-105 mPa.s (at 5% and 25°C in 80/20 toluene/ethanol). Acetone (analytical grade), ethanol (analytical grade) and tetrahydrofuran (analytical grade), were obtained from Sigma-Aldrich Chemicals (Schnelldorf, Germany) and used without further purification. Deionised water was obtained from a Millipore filter system. Citrus Fibers were supplied by Herbafood GmbH (Germany), trade name Herbacel AQ Plus Citrus Fibre, type N. Xanthan gum was supplied by CP Kelco, trade name Keltrol xanthan gum, type RD. Shellac wax was supplied by Temuss (Canada), trade name Shellac Wax. The wax was white or straw yellow crystal with a melting range of 60-85 ⁰ C.

Particle sizing / electrophoresis

Dynamic light scattering measurements were carried out using a Zetasizer Nano ZS instrument (Malvern Instruments, Malvern, UK) to determine the average particle diameter. Samples were measured without any dilution at 25°C. The viscosity of water was assumed in all cases and a refractive index of 1.59 was used in the analysis. The results from the measurements are the z-average particle size and the standard deviation of the z-average particle size (which relates to the peak width of a distribution curve of the particle size). For monodisperse systems with a narrow distribution, which is the case for ethylcellulose particles of the present invention, the difference between the z-average particle size and volume weighted mean size (d _4ι3 ) is smaller than 10%. In the present case the z-average diameter is at maximum 10% larger than d _{4 3} .

Zeta-potential

The zeta-potential is determined by electrophoresis, also using the Metasizer Nano ZS instrument (Malvern Instruments, Malvern, UK). For this purpose, an electric field is applied to a dispersion containing colloidal particles. From the velocity of the particles in this electric field, i.e. their electrophoretic mobility, the zeta potential can be calculated by using the Henry equation with the Smoluchowski approach (P.C. Hiemenz, Principles of Colloid and Surface Chemistry, Second edition, Marcel Dekker Inc., New York, 1986, Chapter 13).

Bubble diameter

The bubble diameter in the foams is estimated using a turbiscan turbidity measurement.

In principle this is a spectrophotometer that can be loaded with a glass tube containing a foam sample. Light transmitted at the tube and reflected is measured. This is translated into average bubble diameter.

Detailed procedure: sample volumes of approximately 20 ml_ were studied by turbidimetry using a Turbiscan Lab Expert (Formulaction, Toulouse, France). We interpret the average backscattering along the height of the foam sample with exclusion of the top and bottom parts where the backscattering is affected by edge effects. The backscattering (BS) is related to the transport mean free path (λ) of the light in the sample through:

^{BS =} 7I ^<2)

In turn, the transport mean free path of light is related to the mean diameter (d) and the volume fraction (Φ) of the gas bubbles through:

3Φ(1 - g)Q ⁽³⁾

Where g and Q are optical constants given by Mie theory (G. F. Bohren and D.R.Huffman, Absorption and Scattering of Light by Small Particles. Wiley, New York, 1983). For foam dispersed in a transparent liquid, this method provides an estimate of the number average bubble size.

Example 1 : Heating of ethylcellulose foam

1 g ethyl cellulose (Hercules) powder was dissolved in 100 ml acetone (purity of >98%), at 35°C in a 500ml beaker until completely dissolved. An equal volume of distilled water (water at room temperature, about 22°C) was quickly added into the ethylcellulose solution under strong stirring to precipitate the ethylcellulose into particles. The solution was left to stir for another 10 minutes after which the acetone and some of the water were evaporated under low pressure until a final concentration of ethylcellulose in water of 2 wt% was obtained. The volume weighted mean diameter d _{4 3} of the ethylcellulose particles was between 100 and 500 micrometer.

200 ml of above-mentioned 2.0 wt% ethylcellulose dispersion was placed into a 400 ml beaker, and its pH was tuned to below 4 by adding a small amount of 10 vol% acetic acid aqueous solution. After stirring for 10 minutes, the dispersion was aerated by using an ultraturrax mixer (IKA, T-18) for 2 minutes at about 16,000 rpm. The foam volume was increased to about 400 ml (overrun 100%). Optical microscopical observation revealed that the bubbles were polydispersed, and the bubble diameter ranged from submicron to tens of microns. In order to heat the ethylcellulose foam, it was moved to a 500 ml Schott-Duran premium bottle, and left to drain for 1 hour. The well sealed bottle was heated at 130 ⁰ C for 2 hours in an oven. After the bottle had cooled down, some drained water was removed with a syringe. Finally, about 45 gram of heated ethylcellulose foam had been successfully prepared.

Figure 1 shows a cryo-SEM-image at 500Ox magnification of resulting bubbles of the foam. Both the particulate character of the ethylcellulose particles can be observed as well as the fact that these are fused together.

Example 2: Heating of the ethylcellulose foam with citrus fibres

0.4 g of citrus fibres and 200 ml of above-mentioned (example 1) 2.0 wt% ethylcellulose dispersion were placed into a 400 ml beaker, and stirred for 1 hour to make the citrus fibres well separated and hydrated. A small amount of 10 vol% acetic acid aqueous solution was used to tune the pH of the dispersion from neutral to below 4. After stirring for 10 minutes, the dispersion was aerated by using an ultraturrax mixer (IKA, T-18) for 2 minutes at about 16,000 rpm to a total volume of 400 ml (overrun 100%). The bubble diameter ranged from submicron to tens of microns.

The prepared ethylcellulose foam was moved to a 500 ml Schott-Duran premium bottle, and left to drain for 1 hour. And then the well sealed bottle was heated at 130 ⁰ C for 2 hours in an oven. After the bottle had cooled down, some drained water was removed with a syringe. Finally, about 50 gram of well heated ethylcellulose foam with citrus fibres had been obtained.

Example 3: Heating of ethylcellulose foam with xanthan gum

200 ml of above-mentioned 2.0 wt% ethylcellulose dispersion (example 1) was placed into a 400 ml beaker, and its pH was tuned to below 4 by adding a small amount of 10 vol% acetic acid aqueous solution. After stirring for 10 minutes, the dispersion was aerated by using an ultraturrax mixer (IKA, T-18) for 2 minutes at about 16,000 rpm. The foam volume was increased to about 400 ml (overrun 100%). Optical microscopical observation revealed that the bubbles were polydispersed, and the bubble diameter ranged from submicron to tens of microns. The foam was mixed with 20 ml of 1.0 wt% xanthan solution via 3 minutes manual mixing. The foam with xanthan was transferred to a 500 ml Schott-Duran premium bottle, and left to drain for 1 hour. The well sealed bottle was heated at 130 ⁰ C for 2.25 hours in an oven. After the bottle had cooled down, some drained water was removed with a syringe or pipette. Finally, about 55.0 g heated ethylcellulose foam with xanthan had been obtained.

Example 4: Heating of the ethylcellulose/shellac wax foam

Preparation of shellac wax particles: 10.0 g shellac wax was dissolved in 1000 ml ethanol (purity > 99.7%) at 60 ⁰ C in a 2000 ml beaker until completely dissolved. After cooling down, the shellac solution was filtrated, and an equal volume of distilled water was quickly added into the shellac wax solution under strong stirring to precipitate the shellac wax into particles. The dispersion was left to stir for another 10 minutes, and then ethanol and water were evaporated under low pressure at 45 ⁰ C and 70 ⁰ C via a rotary evaporator. Finally, a 2.0 wt% water dispersion of shellac wax particles has been produced with diameter in the range of 20 to 400 nanometer.

An ethylcellulose/shellac wax foam was prepared as follows: 10 ml of 2.0 wt% shellac wax dispersion and 200 ml of above-mentioned (example 1) 2.0 wt% ethylcellulose dispersion are placed into a 400 ml beaker. A small amount of 10 vol% acetic acid aqueous solution was used to tune the pH of the dispersion from neutral to below 4. After stirring for 10 minutes, the dispersion was aerated using an ultraturrax mixer (IKA, T-18) for 2 minutes at about 16,000 rpm. The foam volume was increased to about 400 ml (overrun 100%). Optical microscopical observation revealed that the bubbles were polydispersed, and the bubble diameter ranged from submicron to tens of microns.

The prepared ethylcellulose/shellac wax foam was moved to a 500 ml Schott-Duran premium bottle, and left to drain for 1 hour. And then the well sealed bottle was heated at 8O ⁰ C for 2 hours in an oven. After the bottle had cooled down, some drained water was removed with a syringe or pipette in order to minimise the amount of water in the foam. Finally, about 45 gram heated ethylcellulose/shellac wax foam had been successfully prepared. Example 5: Heating of ethylcellulose/shellac wax foam with citrus fibres

0.4 g of citrus fibres, 10 ml of 2.0 wt% shellac wax dispersion (example 4) and 200 ml of 2.0 wt% ethylcellulose dispersion (example 1) are placed into a 400 ml beaker, and stirred for 1 hour to make citrus fibres well separated and hydrated. A small amount of 10 vol% acetic acid aqueous solution was used to tune the pH of the dispersion from neutral to below 4. The dispersion was aerated by using ultraturrax mixer (IKA, T-18) for 2 minutes at about 16,000 rpm. The foam volume was increased to about 400 ml (overrun 100%). Optical microscopical observation revealed that the bubbles were polydispersed, and the bubble diameter ranged from submicron to tens of microns.

The foam was transferred to a 500 ml Schott-Duran premium bottle, and left to drain for 1 hour. The well sealed bottle was heated at 80°C for 2 hours in an oven. After the bottle had cooled down, the drained water was removed by a syringe or pipette in order to minimise the amount of water in the foam. Finally, about 50 gram heated ethylcellulose/shellac wax foam with citrus fibres had been obtained.

Example 6: Aerated light mayonaise comprising heated foam

According to the preparation procedure in Example 2, 47.0 g of heated ethylcellulose foam with citrus fibres (density, 0.44 g/ml) was prepared, and was moved to a Kenwood kitchen mixer. 250.0 g of mayonnaise (Hellmann's light mayonnaise, about 23 wt% oil, density about 1.0 g/ml) was added to the Kenwood kitchen mixer and manually mixed with the heated foam with a spoon for 3 minutes. Subsequently the premix was blended by the mixer at minimum level for about 3 minutes, until a homogeneous product is obtained. The density of pristine or aerated mayonnaise was measured by putting 10 ml mayonnaise into a 25 ml volumetric cylinder, and the net weight was recorded by a balance. After aeration, the density of mayonnaise decreased from 1.0 g/ml to 0.88 g /ml, and about 12% air had been successfully incorporated into the matrix of mayonnaise. One month later, there is little change on the microstructure and appearance of aerated mayonnaise, for only a few bubbles collapse during storage at ambient temperature. Figure 2 shows an cryo-SEM-image at 500Ox magnification. Bubbles of heated foam are indicated by the arrows. Example 7: Heated ethylcellulose foam with citrus fibres and Aerated Full Fat mayonnaise comprising said foam

In this example, the bubble size evolution of a mayonnaise aerated with heated ethylcellulose foam will be compared to that of a mayonnaise which is aerated in the absence of heated ethylcellulose. An approximation of the bubble size evolution is probed by turbidimetry, as indicated herein before.

For an aerated mayonnaise the relative increase of the transport mean free path λ(t) at time t is plotted, as compared to the initial transport mean free path λ(0). The ratio λ(t)/ λ(0) is used as an approximation of the bubble size evolution, since mayonnaise contains a high concentration of oil droplets in addition to the air bubbles. Since the emulsion droplet size is known to constant over time, the increase in mean free path λ is considered to be caused by the bubble coarsening.

3 g of citrus fibres and 300 ml of above-mentioned (example 1) 2.0 wt% ethylcellulose dispersion were placed into a 400 ml beaker, and stirred for 1 hour to make the citrus fibres well separated and hydrated. A small amount of tartaric acid powder was added to tune the pH of the dispersion from neutral to approximately 3. After stirring for 10 minutes, the dispersion was aerated by using a Silverson mixer for 2 minutes at about 9,000 rpm to a total volume of 500 ml (overrun 67%). The bubble diameter ranged from submicron to tens of microns as observed by optical microscopy. The prepared ethylcellulose foam was moved into a separation funnel to allow liquid drainage from the foam.

The drained foam was moved to a 500 ml sealed metal pressure vessel. The vessel was heated at 130 ^c C for 2 hours in an oven. After the vessel had cooled down, some more drained water was removed with a syringe. Finally, about 165 gram of well heated ethylcellulose foam with citrus fibres had been obtained, which had a volume of 200 ml_, meaning 18% by volume of air.

20 mL of the heated foam was mixed to 20 ml_ mayonnaise (Hellmans real ex Unilever, approximately 70% oil, density approximately 0.9 g/ml_), which was degassed before the mixing. No volume decrease was observed during mixing and this resulted into an aerated mayonnaise comprising 9 vol% air. Approximately 20 mL of aerated mayonnaise was transferred into a glass tube for turbidimetry in order to probe the bubble size evolution.

Separately, approximately 500 mL of Hellmann's real mayonnaise was placed in the bowl of a Kenwood mixer, equipped with a whisk. The mayonnaise was whipped for 10 minutes, resulting into an air volume percentage of 15%. Approximately 20 mL of aerated mayonnaise was transferred into a glass tube for turbidimetry in order to probe the bubble size evolution over time. This aerated mayonnaise serves as a comparative example.

Figure 3 shows the relative increase in transport mean free path λ(t)/λ(O) of the invention product and the reference, measured over 9 days. Taking into account that much of the bubble size evolution is masked by the concentrated emulsion in the mayonnaise, still a significant difference in evolution can be observed between the two samples. The reference mayonnaise shows an increase in optical path length after about 0.1 day, whereas for the reference sample it takes more than 10 days to reach this bubble size increase. This means that the average bubble size increases fastest in the reference mayonnaise.

This result clearly shows the improved stability to disproportionation of the aerated mayonnaise comprising heated ethylcellulose foam compared to the reference system.