food foam stabilised by small, solid particles

The invention relates to a foamable food composition. The invention further relates to a foam, obtainable from such a composition and to the manufacture of a foamable food composition.

Usually it is considered desirable for a foamed food that it has a good stability for a sufficient duration of time. In particular, problems encountered with foamed foods are decrease in foam-firmness, decrease in overrun, drainage of fluid, decrease in foam volume by collapse of the foam and coarsening of bubbles during storage.

The nature of stability problems in known foams and the duration for which stability is desired depends on the application.

Instability in foams may be caused by various mechanisms: (1) disproportionation (Ostwald ripening), which is the diffusion of gas from small bubbles to larger bubbles due to difference in Laplace pressure; this type of instability occurs relatively much when gas having a high solubility in the material to be foamed is used: a foam foamed with the highly soluble N₂O (laughing gas) disproportionates much faster than foams foamed with a much less soluble gas, such as N₂. (2) coalescence, which is the fusing together of two bubbles because the film between the bubbles ruptures; (3) creaming/drainage, which is caused by gravity, resulting in the rise of bubbles or the flow of liquid/serum downwards.

In the art it is usually tried to overcome stability problems by using binders, stabilisers and/or emulsifiers dissolved in the liquid phase. This may lead to highly complex product formulations, and/or complicated preparation processes, and may not always lead to satisfactory results.

As background art on various additives to foamed foods, the following documents are mentioned. US 3.067,037 relates to the use of cellulose crystallite aggregates as a quality improving agent in foamable food products. SU 1 789 177 relates to foamable food products having modified soy-protein concentrate as a foam-forming component and non-soluble soy residue as a stabilizer. EP 1 666 655 refers to a shelf-stable foam product obtained by a process involving a heat reatment after whipping, so as to result in denaturation of proteins. K. Moore, Food Product Development 1978, vo. 12, p38, discloses that nongelling microcrystalline cellulose offers superior texture to heat sensitive liquid emulsions. US 6,767,575 relates to denatired whey protein aggregates that are foamed and used in food products.

A review on foam stability is given by Murray et al., Current Opinion in Colloid & Interface Science 9 (2004) 314-320. Another background reference, on factors controlling the formation and stability of aire bubbles stabilized by partically hydrophobic silica nanoparticles is given by E. Dickinson in Langmuir 2004, 20, 8517-8525.

EP 0 949 294 relates to the inclusion in an aqueous composition, which is added to food, of water-insoluble calcium.

It is an object of the present invention to provide a food product in the form of a foam, with a satisfactory stability for its purpose.

It is further an object of the invention to provide a new foamable food composition for preparing a food foam, with a good, preferably improved, foam stability.

It is another object of the invention to provide a foamable food composition, such as a dairy cream composition, respectively food foam, which (also) has sufficient foam stability in the absence of fat, or in the presence of a reduced amount of fat.

It has now been found possible to achieve one or more of the objects identified herein by providing a foamable food composition, respectively a food foam with a specific foam stabiliser.

Accordingly, the present invention relates to the use of a solid inert particle, wherein the solid inert particles are selected from the group consisting of silicates and layered double hydroxides, and wherein the particles are anisotropic particles with an aspect ratio of at least 5, as a foam stabiliser in a food foam.

The invention further relates to a novel foamable food composition comprising water, a foaming agent and solid inert particles for stabilising the foam, wherein the solid inert particles are selected from the group consisting of silicates and layered double hydroxides, and wherein the particles are anisotropic particles with an aspect ratio of at least 5.

In an embodiment the foamable composition comprises water, a foaming agent and inert solid particles, selected from the group consisting of silicates and layered double hydroxides, and wherein the particles are anisotropic particles with an aspect ratio of at least 5, for stabilising the foam.

In an embodiment, the foamable composition comprises a peptide, in particular a protein, as a foaming agent and inert solid particles, selected from the group consisting of silicates and layered double hydroxides, and wherein the particles are anisotropic particles with an aspect ratio of at least 5. for stabilising the foam.

In a preferred embodiment the foamable composition comprises water, at least a foaming agent selected from the group consisting of proteins and peptides, and inert solid particles selected from the group consisting of silicates and layered double hydroxides, and wherein the particles are anisotropic particles with an aspect ratio of at least 5, for stabilising the foam.

In an embodiment, the foamable food composition is a powdered (creamer) composition - for instance a foamer composition for cappuccino or another coffee topped with a foam - comprising a foaming agent and the solid inert anisotropic particles, said creamer composition being capable of forming a foam on an aqueous liquid such as coffee when dispersed in the aqueous liquid.

In an embodiment, the foamable food composition comprises a foaming agent and the solid inert particles for stabilising a foam, wherein the total amount of the solid inert particles and optionally present other solid particles is 10 wt. % or less.

The invention further relates to a foam made from the foamable food composition of the invention. Such foam usually is formed of gas bubbles dispersed in the food composition of the invention, optionally when mixed with (additional) water. Examples of suitable foamable compositions/foams include (compositions for) aerated desserts, coffee foam (e.g. on espresso or cappuccino), foam on beer, crème patissière (pastry cream) and the like.

Preferred foamable compositions respectively foams according to the invention are foamable dairy compositions respectively dairy foams. Particularly preferred are foamable compositions respectively foams selected from (compositions for preparing) foamed ice creams, mousses, whipped creams, beaten creams, aerosol creams, toppings and milkshakes.

It has surprisingly been found that the aforementioned solid inert particles have a foam stabilising effect in a foamed food composition, in particular a foamed cream.

Thus, the invention also provides a stable food foam. The particles may contribute to an improvement in the stability of the foam, compared to a foam having the same composition except for the presence of the inert solid particles. The stability improvement may reside in reducing one or more factors that are associated with instability. In particular, the stability improvement may include at least one of (i) a reduced rate of the overrun decrease, (ii) a reduced rate of the firmness decrease, (iii) a reduced rate of the drainage and (iv) a reduced rate of the coarsening (due to disproportionation and/or coalescence).

In particular the solid inert particles are considered to be suitable for stabilising a foam if the stability is improved in at least one of these aspects, preferably in at least two of these aspects, more preferably in three or four of these aspects, compared to the same foam without the inert solid particles. Which aspect or aspects are particularly relevant, depends upon the specific application for the foam. Preferably, the improvement is at least 10 % in one or more of these aspects, compared to the comparative composition comprising all ingredients of the foam in the same ratio, except for the solid inert particles.

The term "foam" is in particular used herein to describe a dispersion of gas bubbles in a fluid or paste. The continuous phase surrounding the bubbles is called the serum phase.

Usually, a foam according to the invention has an overrun value of at least 1 %, in particular of at least about 20 %, more in particular of at least about 50 %. A preferred overrun value of a foam according to the invention depends on the application. For example, a foamed ice cream, preferably has an overrun is in the range of about 50 % to 200 %. For aerosol whipped cream, the overrun is usually much higher, preferably in the range of 300 % to 800 %.

Herein, the overrun value is defined as $$\left(\left({\mathrm{m}}_{\mathrm{L}}\mathrm{-}{\mathrm{m}}_{\mathrm{F}}\right)\mathrm{/}{\mathrm{m}}_{\mathrm{F}}\right)\mathrm{*}\mathrm{100}\%$$

wherein m_L is the mass of a fixed volume of unaerated fluid, and m_F the mass of the same volume of aerated fluid (Phillips et al., Journal of Food Science 52, 1074-1077, (1987)).

The term "foamable" is defined herein as being capable of forming a foam when the composition is thoroughly mixed with a gas, such as air, nitrogen or nitrous oxide and optionally (additional) water, sufficient to form the continuous phase, in particular in case the foamable composition itself is not already in an aqueous fluid form. As a means for mixing, a method may be used that is suitable for preparing a foam of the intended application.

Usually, thorough mixing may e.g. be achieved by aerating the gas, such as nitrogen, through the composition at a pressure of about 5 bar in a continuous aeration apparatus (such as Mondomix type A5, Nederhorst den Berg, NL).

In an embodiment, foaming is achieved by dissolving a gas (such as nitrous oxide) in the foamable composition, using a high pressure and thereafter quickly releasing the pressure. Such method is particularly suitable for testing the foamability of aerosol whipped cream.

In an embodiment, foaming may be simply achieved by whipping air through the composition. This may be achieved manually, using a whisk.

In particular, a composition is considered foamable if the generated foam has an overrun value of at least 1 %, more in particular of at least 20 %, preferably of at least 50 %.

The required foam stability of foam depends strongly on the application. Generally speaking, a foam is considered stable if within a usual period of storing under usual conditions (i.e. between formation of the foam and consumption) the firmness, shape/appearance, the overrun and the bubble size remain satisfactory, and not too much drainage occurs. The time window and storing condition depend upon the application. Desirable periods of storing generally are in the range of as short as 1 min. to up to a year. Storing conditions may be at ambient conditions, or frozen, e.g. at a temperature below - 20 °C, or even down to - 100 °C.

The skilled person will understand which duration is sufficient for a specific application. For instance for foams on beverages a duration in the range of about 1 to about 5 minutes generally suffices; for aerosol creams - e.g.for use on pastry or on a dessert - a time in the range of about 10-15 min is usually satisfactory, whereas for industrially used foams (such as by bakers), much longer times are desired, usually in the range of at least 1 day up to a week or more.

The term "inert solid particle" is used herein in particular to describe a particle that substantially does not dissolve in the fluid/paste (forming the serum phase) nor substantially melt, also when present in the fluid/paste at an elevated temperature. More in particular a particle is considered "solid inert" when it substantially does not dissolve in the fluid/paste nor substantially melt at a temperature of (at least) 30 °C, preferably of (at least) 100 °C., more preferably of (at least) 150 °C.

When the terms "about", "essentially consisting of" and the like are used herein, this is at least meant to include a deviation of up to 10 %.

Due to the stabilising effect in the presence of inert solid particles, it is possible to improve the stability of foam and/or to reduce the required amount of one or more other foam stabilising components, such as foaming agents, stabilisers and fat.

The foamable food composition may be composed from individual ingredients foaming agent, solid inert particles, usually water and optionally present further ingredients, e.g. fat, carbohydrate, flavouring, sweeteners, salts, (additional) protein etc.

In particular, the composition may be based on a dairy product such as a dairy cream, milk, desserts, mousses, milk drinks (such as foamable chocolate milk, foamable mixtures of milk and fruit juice), foamable fruit drinks, foamable yoghurt drinks; and the like. Herein milk protein already may serve as a foaming agent. Other examples of foamable compositions include sauces such as sweet sauces, such as vanilla sauce, chocolate sauce, caramel sauce and the like.

In addition, the food product may be a recombined product, i.e. a food product, in particular a dairy food product, wherein (a part of) the fat and/or protein is replaced by vegetable fat respectively other (e.g. vegetable, egg) protein. Moreover the food product may be an imitation product, such as a topping, soy-whipped cream or the like.

The solid inert particles may be any food-grade particulate inorganic material selected from the group consisting of silicates and layered double hydroxides

Good results have been realised with the aforementioned anisotropic particles with an aspect ratio of more than 5, more in particular with an aspect ratio of more than 10.

The anisotropic silicates can be natural silicates and synthetic silicates or layered double hydroxides.

Some suitable silicates described as allowed food additives in the European food law are sodium silicate, silicium dioxide; calcium silicate; magnesium (tri)silicate, talc ; sodium aluminium silicate ; potassium aluminium silicate ; calcium aluminium silicate ; zinc silicate , bentonite ; and kaolin.

It is contemplated that in an embodiment the aforementioned particles of the invention may offer an advantage over other stabilisers in that such particles may provide a relatively highly viscous or gel-like product when non-agitated (whipped, beaten, mixed) at a relatively low concentration whereas during shear (e.g. during processing such as mixing, whipping, beating, mastication) the viscosity decreases considerably due to shear-thinning properties of the particles.

Good results have been achieved with a clay. The clay may be natural or synthetic. Suitable clay minerals include kaolinites, montmorillonites, illites and the chlorites. Preferred clay mineral groups for use in a foamable composition respectively foam according to the invention are kaolinites and montmorillonites.

Good results have been achieved with synthetic clay particles, such as laponite ®, a synthetic product (from Rockwood Additives Ltd, Widness, UK) similar to a three-layered clay.

The term laponite is used in the present application and claims to describe an inorganic mineral having a layered structure, essentially consisting of six octahedral magnesium ions sandwiched between two layers of four tetrahedral silicon atoms. These groups are balanced by twenty oxygen atoms and four hydroxyl groups. The empirical formula of pure laponite is Na^+0.7[(Si₈Mg_5.5Li_0.3)O₂₀(OH)₄]^-0.7.

For imparting a stabilising effect, the concentration of solid inert particles, in a foamable composition or foam according to the invention is preferably at least about 0.1 wt.% based upon the total weight, more preferably at least about 0.4 wt.%. A concentration of more than about 2 wt. % is very suitable for providing high viscosity in combination with foam stability. For maintaining good fluidity or good whipping (agitation/aeration) properties, the concentration is preferably about 10 wt. % or less, more preferably about 4 wt. % or less.

In general, the number average particle size of the inert solid particles, as determined by light scattering, is at least of about 5 nm, preferably of at least about 20 nm. The light scattering diameter is the value as may be determined on a Mastersizer type 2000 (Malvern Instruments Ltd. , Malvern, UK), for diameters of 20 nm or more (in particular 100 nm or more) or with a Zetasizer Nano ZS (Malvern Instruments Ltd. , Malvern, UK) (for particle diameters of less than 6 µm, in particular 100 nm or less).

The inert solid particles may be micro-particles, in particular having a number average particle size of up to about 45 µm.

Preferably, the number average particles size of the inert solid particles is less than 10 µm, in particular less than 8 µm, more in particular less than 3 µm, in order to avoid unfavourable organoleptic sensation, when the foam is consumed. When a lot of the particles are too large, the mouthfeel may become sandy.

For that reason it is preferred that in the foamable composition respectively foam the abundance of the solid inert particles with a size exceeding 10 µm is relatively low. Good results have been achieved with a foamable composition respectively foam wherein the total content of inert solid particles with a diameter of more than 10 µm , in particular with a diameter of more than 6 µm, more in particular with a diameter of more than 1 µm, is less than 50 wt. %, based upon the total weight of the solid particles. Preferably at least 90 wt. % of the particles has a diameter of less than 13 µm, in particular of less than 10 µm. Very good results have inter alia been achieved with an embodiment wherein at least 99 wt. % of the inert solid particles, e.g. laponite, has a diameter of less than 1 µm.

It should be noted that in particular in case of a powdered creamer composition according to the invention, the powdered creamer particles as such may have an average particle size exceeding 50µm, in particular in the range of 100-400 µm. These particles generally substantially dissolve or disperse when used (added to e.g. coffee) and are not solid inert particles within the definition of the present application. Thus, a preferred embodiment of a powdered creamer also meets the above features with respect to inert solid particles size diameter/distribution.

For further improving the stabilising effect on the foam of the inert solid particles - in particular silicate particles - in a foamable composition or foam according to the invention, the surface of the particles may be modified, in particular by making it more hydrophobic.

Particles may be rendered more hydrophobic by providing the surface with a hydrocarbon material. Thus, the adsorption of particles at the interface between bubbles and serum phase is usually facilitated.

For example, the particles may be coated with a surfactant, such as a fatty acid, phosphorous containing lipids such as lecithin, or another food grade surfactant.

As a foaming agent, any food grade foaming agent may be present. Preferred foaming agents include macromolecules, such as (linear) polypeptides and (linear) polysaccharides. The macromolecules typically have a Mw of at least 1 kDa. Preferred polypeptides are (milk) proteins and (milk) peptides; Preferred polysaccharides include gum arabic and modified polysaccharides, in particular modified alginates such as alkylene glycol alginates (e.g. propylene glycol alginate) and modified starches such as alkenyl succinic anhydride modified starches, especially n-octenyl succinic anhydride modified starches (NOSA-starches).

Further, particularly suitable foaming agents are food-grade small-molecule surfactants (or emulsifiers) (generally with molar mass of less than 1 kDa) (as defined by P. Walstra (2003) Physical Chemistry of Foods, Marcel Dekker, New York) for instance lecithin and lecithin derivates, mono- and/or diglycerides (glycerol fatty acid esters), Tweens (sorbitan ester ethoxylates), Spans (sorbitan fatty acid esters), glycerol lacto palmitate and the like.

Usually the amount of foaming agent, in particular protein, alkenyl succinic anhydride modified starch (such as NOSA starch) and/or peptide, in the foamable food composition respectively the foam is in the range of about 0.01 to about 20 wt. % based upon the total weight of the composition.

The water content in a foamable composition or foam according to the invention is usually in the range of 1-99.9 wt. %, in particular in the range of about 2 wt. % to 99.5 wt. %, more in particular at least about 10 wt. %. In practice, the water content in the foam is usually at least about 15 wt. %.

A desired water content depends upon the application. For example, in case of (dairy) cream compositions/foams and for low-fat compositions, the water content is preferably in the range of 50-99 wt. %.

In another embodiment a foam comprises a relatively low amount of water, such as less than 50 wt. %. For example, in a foamed butter according to the invention, the water content may be as low as about 15 wt. %.

In particular, in case the foamable composition itself has a low concentration of water, it is preferably mixed with water or an aqueous fluid when preparing the foam. For instance a foamable powdered composition according to the invention, in particular a creamer, usually has a water content in the range of 1 to about 5 wt. %. The water in the powdered composition may be present as a residue of the preparation process. Solubilisation problems have been experienced if the water content in the powder it too low, possibly below 2 wt. %, in particular below 1 wt. %.

A foam may then suitably be made by mixing the composition with a suitable amount of water or aqueous liquid (such as coffee, tea or another beverage). The amount of water to be used is not particularly critical; an amount sufficient to dissolve or disperse the powdered (creamer) composition usually suffices. In particular the powdered (creamer) composition and liquid may be added in a ratio in the range of 1 to 10 to 1 to 40.

In addition to water, foaming agent and inert solid particles, other food components may be present in a foamable composition or foam according to the invention. In particular, one or more components selected from the group consisting of fats; fat substitutes; carbohydrates; flavouring agents, flavour enhancers; coloring agents; enzymes, pH control agents and acidulants; aromas; preservatives, stabilisers, antioxidants, sweeteners, salts, sugars, (additional) surfactants the already mentioned inert solid particle surface modifiers such as surfactants and hydrophobic inorganic materials; (additional) proteins; amino acids; vitamins; peptides and the like.

In particular fat or a fat substitute is present in a preferred foamable composition respectively foam according to the invention. Fat or a fat substitute is preferably present for organoleptic reasons, as it is very suitable for imparting a creamy mouth sensation. The fat may be any edible fat of animal or plant material. Fat may also contribute to the stability of the foam.

Preferably a fat is present selected from the group consisting of milk fats and vegetable fats, such as coconut oil, corn oil, palm oil, sunflower oil and soybean oil.

If present, the fat/fat substitute concentration is usually in the range of about 0.1 wt. % to 50 wt. %, based upon the total weight.

Suitable carbohydrates include monosaccharides, disaccharides, oligosaccharides and polysaccharides. Oligosaccharides are defined herein as oligomers having 3-8 monosaccharide units; polysaccharides comprise more than 8 monosaccharides. Monosaccharides and disaccharides may in particular be used to sweeten the composition. Oligosaccharides and polysaccharides may in particular be used to thicken and/or stabilize the composition.

If present, the carbohydrate concentration is usually in the range of about 0.1 to 80 wt. %, based upon the total weight.

The foaming of the food composition may be accomplished by agitation, such as by a household mixer, by beating the composition, or the like.

Further, the composition may be foamed by making use of an expansion medium/gas, preferably a gas comprising air, propane, nitrogen, N₂O, CO₂ or a combination thereof.

A foamable food composition, to be foamed by expansion medium gas may suitably be packaged with a suitable amount of gas, for instance at 0.1 to 10 wt. %, in an aerosol container. Such containers are known in the art, for example from EP-A 747 301.

The invention further relates to a method for preparing a food composition according to the invention, comprising preparing a dispersion of the solid inert particles, water and foaming agent and optionally other ingredients.

The cream may be heat-treated, such as pasteurised, sterilisised and/or UHT treated. UHT treatment usually involves a heat treatment at a temperature in the range of 135-150 °C for a duration of 0.7-20 sec., e.g. for about 4 sec at about 137 °C or an equivalent time/temperature combination.

The invention will now be illustrated by the following examples.

Example 1

To UHT-treated homogenised cream containing 35 wt. % milk fat, 1wt.% laponite (available from Rockwood Additives Ltd., Widnes, UK) was added and dispersed thoroughly with a whisk. Subsequently, the cream was aerated by mixing (2000 rpm) the cream with N₂O at 5 bar using a continuous aeration apparatus (a rotor/stator mixer) (Mondomix type A05, Nederhorst den Berg NL).

The aerated cream containing laponite was examined for overrun and visual appearance, and compared with aerated cream without laponite.

The initial overruns of the cream containing laponite and the cream without laponite were both about 240%. The aerated cream containing laponite was very stable, and the overrun remained constant for at least 3 h at room temperature, whereas the overrun of the aerated cream without laponite decreased considerably (See Figure 1).

In the samples containing laponite, bubbles of about 0.5 mm were visible after an hour. Even after 3 hours no drainage of fluid was observed. The samples without clay deteriorated much more: after 1 h the foam was considerably coarser with bubbles of about 1 mm, and extensive drainage had taken place. From these results we can conclude that addition of laponite to cream improves the stability of the aerated cream.

Example 2

Cream of 40 wt.% fat was pasteurised (22 s at 79°C; indirect system) and homogenised (20/10 bar at 70°C) and cooled to 4°C. Then the cream was mixed with Cloisite Na⁺ or Gelwhite H (both highly purified montmorillonites/hydrated aluminium silicates, available from Southern Clay Products, Gonzales TX, USA) previously dispersed in water, skim milk, sugar and surfactant (a mono/diglyceride mixture) to a final concentration of about 27 wt% fat and 0.8wt.% clay. Subsequently, the mixture was sterilised (4 s at 137°C; indirect system), brought in aerosol cans and gassed with N₂O at 8 bar (N₂O as propellant and expansion medium).

Cream was expelled from the can. The aerated cream was examined for overrun, as described above, and firmness after 0 and 5 min. Firmness was determined by measuring the force needed to push a cylindrical probe (with diameter 25 mm, height 34 mm) into (5 mm) the aerated cream (at a speed of 2 mm/s) (Stevens LFRA texture analyser, London UK). The overrun of the reference (aerosol whipped cream without clay) was 560%, the overrun of the aerosol whipped creams containing 0.8% Cloisite Na⁺ or Gelwhite H were 445% and 470%, respectively. The firmness of the aerosol whipped creams containing clay directly after aeration was comparable to that of the reference. After 5 min the firmness of the reference had decreased significantly more than that of the aerosol whipped creams containing 0.8% Cloisite Na⁺ or Gelwhite H (Table 1). Generally, the firmness is a measure of how long a blob of aerosol whipped cream keeps its shape.

Overrun

Firmness

Firmness after 5 min

Residual firmness after 5 min (%)

Reference

560

91

53

58

0.8% gelwhite H

470

93

63

68

0.8% cloisite Na⁺

445

84

66

79