WO2000032153A1

WO2000032153A1 - Microemulsion compositions

Info

Publication number: WO2000032153A1
Application number: PCT/GB1999/004053
Authority: WO
Inventors: Andrew Taylor; Katrina Hemingway; Mark Alston
Original assignee: University Of Nottingham
Priority date: 1998-12-03
Filing date: 1999-12-03
Publication date: 2000-06-08
Also published as: GB9826555D0; AU1573600A

Abstract

The present invention relates to fragrance-releasing compositions for use in a wide range of products, including perfumery products, laundry compositions, deodorants, cleaning agents, cosmetics and toiletries. In particular, the present invention relates to compositions comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles dispersed in an anhydrous carrier, wherein the droplet/micelle cores have low water activity and contain a latent fragrance which is activated when the water activity within the cores is increased.

Description

MICRQEMULSION COMPOSITIONS

The present invention relates to fragrance-releasing compositions for use in a wide range of products, including perfumery products, laundry compositions, deodorants, cleaning agents, cosmetics and toiletries. In particular, the present invention relates to compositions comprising water-in-oii microemulsion droplets and/or hydrated reverse micelles dispersed in an anhydrous carrier, wherein the droplet/micelle cores have low water activity and contain a latent fragrance which is activated when the water activity within the cores is increased.

Introduction

The use of fragrances in industry

Fragrances are presently employed in industry in a wide range of products, either as principal functional components (e.g. in perfumes) or as adjuncts to impart a sensorial dimension to the quality of other products. In either case, major difficulties arise from the fact that many fragrances are labile and/or volatile (and so fugitive) . Accordingly, there is considerable interest in means for stabilizing and/or providing for controlled release of fragrances.

In the perfume industry, experienced perfumers balance the ingredients of perfume compositions so that the fragrance develops and changes over time as a cascade of different odours is released from the skin surface at different rates. Access to stable fragrances would provide perfumers with more flexibility and permit the formulation of an expanded range of perfumes.

In the case of other perfumed products, the prime considerations are permanency, potency and aptness (having regard to the principal function of the product in question). For example, fresh citrus fragrances are often used in laundry products, while floral fragrances may be considered more appropriate in certain cleaning agents. Many potentially attractive fragrances are precluded from use by low potency and/or permanency, and so access to stable forms of such fragrances would dramatically widen the palette available to formulation chemists, permitting great improvements in the sensorial impact of a wide range of products.

There is therefore a need for perfumed compositions in which the fragrance remains stable during storage, but which release fragrance efficiently and rapidly when required. Over the past few years, it has been shown that many fragrances exist as fragrance precursors which are more stable than the active fragrance itself. For example, many fragrances (especially from plant oils) exist as glycoside precursors which are much more stable than the fragrance aglycone, but are odourless.

It has now been recognized that fragrance delivery systems based on the use of stable fragrance precursors which are activated during use or when required obviates the need for stabilized fragrances, so overcoming the problems associated with fugitive fragrances. In particular, the present inventors have found that microemulsion technology (vide infra) can be exploited to stably maintain fragrance precursors prior to use while permitting controlled release of active fragrance moieties derived from the precursors when required and on hydration.

It has also been recognized that the problems associated with fugitive fragrances can be addressed through the use of fragrance enhancers. Fragrance enhancers (many of which are Maillard volatiles, such as furaneol and maltol) synergise with a range of other fragrances, greatly increasing their odour intensity. However, many known fragrance enhancers are themselves highly labile, so limiting their utility in perfumed products. However, many fragrance enhancers also exist as precursors which are much more stable than the enhancer per se (for example, many fragrance enhancers exist as glycoside precursors which are much more stable than the active aglycone). The present inventors have therefore also applied microemulsion technology to stably maintain fragrance enhancer precursors in various compositions so that active enhancer can be rapidly released when required to intensify the aroma of other fragrances present in the composition.

Microemulsions

Microemulsions (MEMs) are systems of oil, water and surfactant which exist as single phase liquid solutions that are optically isotropic and thermodynamically stable (Danielsson and Lindmann ( 1 981 ), Colloids Surfaces 3, pp. 391 et seq.) .

Microemulsions therefore differ fundamentally from emulsions, which are simply αroplet dispersions of one liquid in another (oil in water or water in oil). As such, emulsions are thermodynamically unstable and ultimately separate into distinct oil and water phases as droplet coalescence and coagulation occurs.

In some instances, the term "microemulsion " has also been used by those skilled in the art to define compositions comprising very small droplets in a medium, the droolets usually having diameters in the nm size range (and so also referred to as "nanodroplets " or "nanoemulsions ")

As used herein, the term "microemulsion" is intended to embrace compositions falling within the scope of both of the definitions set out above .

The structure, properties and known uses of microemulsions is reviewed in Rees and Robinson ( 1 993), Adv Mater 5(9), pp 608-61 9, the disclosure of which relating to the structure of microemulsions and organogels is incorporated herein by reference.

The extent and position of the single phase microemulsion region for a typical surfactant (or combination of surfactants) is shown in the schematic phase diagram (Figure 1); wherein, 1 is liquid crystal (lamellar); 2 is a water-in-oil microemulsion; 3 is a reverse micelle; 20 is oil; 6 is 2 phase; 30 is water; 4 is a micelle; 5 is an oil-in- water microemulsion and 10 is a surfactant.

For water-in-oil (w/o) microemulsions, the parameter R and the surfactant concentration define the composition. R is the mole ratio of water to surfactant (Eq. 1 ) .

R = [H₂0]/[surfactant] ( 1 )

At low R values ( < 1 0) in w/o microemulsions, the droplets are relatively small and the amount of water present is only just sufficient to fully hydrate the surfactant head groups and counterions. Under these circumstances, the

aggregates are generally described as hydrated reverse micelles. Where there is enough water present in the droplet or reverse micelle cores to satisfy or exceed the hydration requirements of the surfactant, then so-called "free" water may be present and at this point the aggregates are generally referred to as water-in-oil microemulsion droplets ( ? = 1 0 - 20). At R values > 20, droplet sizes are larger and the water inside the w/o microemulsion droplets behaves as bulk water in terms of its gross physical properties.

Microemulsions in the form of droplets are essentially monodisperse, the droplets having radii within the range 1 -1 00 nm (more usually, 1 - 1 0 nm).

Microemulsion surfactants and co-surfactants

Microemulsion formation is dependent on the presence of amphiphilic surfactant molecules having both polar and non-polar regions which stabilize the oil- water interface. In many formulations, co-surfactants are also required to act as spacers and maintain the spacing between charged headgroups (so minimizing coulombic repulsions) .

The manner in which surfactants pack at the interface is primarily dependent on steric effects arising from the configuration of the surfactant molecule. Packing behaviour has been described mathematically by Mitchell and Ninham ( 1 981 ); J. Chem. Soc, Faraday Trans. II, 77, page 601 ). Packing is described by the packing parameter S_p (Eq. 2) :

S_p = V(al)-' (2)

where V is the effective packing volume of the surfactant hydrocarbon tail, / is the length of the hydrocarbon tail and a is the ef ective headgroup area at the oil-water interface.

For oil-in-water microemulsion droplets, S_p < 1 ; for lamellar structures, where the interface is flexible and exhibits both negative and positive curvature, 5_n P is about 1 ; for reverse micelles and water-in-oil emulsions, S > 1 . Preparation of microemulsions

The preparation of microemulsions is technically trivial and the preparation of many different microemulsion compositions has been described in detail in the prior art. Typically, the surfactant is first dissolved in the oil and then water is added with gentle shaking. This procedure generally results in the formation of an optically-clear single-phase solution containing microemulsion droplets. Heating or sonication (e.g. in sonicating water baths) is not necessary to achieve the single- phase dispersion, though such steps may be employed where convenient to facilitate preparation.

Multiphase microemulsion-containing systems

Such systems were first described by Winsor ( 1 948) ; Trans. Faraday Soc , 44: page 376. Here, an oil-in-water microemulsion may co-exist with an oil phase (Winsor I), or a water-in-oil microemulsion may co-exist with excess water (Winsor II) . Also possible is a Winsor III system, which forms when the surfactant is concentrated in a surfactant-rich middle phase which co-exists with oil and water phases containing low concentrations of droplets (water-in-oil and oil-in-water, respectively).

Winsor I to Winsor II interconversion can be induced by changing the temperature or ionic strength of the microemulsion composition or through the addition of co-surfactants. The ability to effect such interconversions has great utility in microemulsion-based synthetic systems, since phase interconversion provides a simple means of separating water-soluble products from surfactant (Winsor II) as well as oil-soluble species from surfactant (Winsor I).

Microemulsion solubilization of enzymes

It is known that enzymes can be solubilized in the droplet cores of w/o microemulsion droplets with retention of activity and stability. A large number of enzymes have been solubilized in this way (see Rees and Robinson, infra). Although the resultant systems are essentially a single phase, they can assimilate both water-insoluble and water-soluble substrates.

In microemulsion systems where the enzymic reaction consumes water, enzyme activity ceases as water content decreases This happens quite rapidly in systems containing nanometre droplets with limited water content in the droplet cores Experiments with Iipase have shown that activity in a MEM system halts when the water is consumed, but if more water is added the reaction restarts and continues until the additional water is used up This cycle of activity can be repeated many times with full activity returning on the addition of water

Microemulsion systems containing solubilized enzymes have also been used in organic synthesis, and syntheses on the preparative scale have been reported with hydrolases such as chymotrypsin and Iipase (see Rees and Robinson, op at) These synthetic systems have been used to produce esters from alcoholic and fatty acid precursors for use in the food industry (West ( 1 988) , Chem Br (Dec) p 1 220)

It is also known that the equilibrium position of MEM-solubilized hydrolases can be shifted in favour of amide/ester synthesis, either by exploiting the mass- action effect (when product is rapidly partitioned away from the hydrophilic reaction microenvironment into the non-polar oil phase) and/or the low water activity present in the droplet/micelle core at low ? values

Microemulsion-based orqanoqels

The addition of gelatin to w/o microemulsions may result in the formation of rigid gels of a strength similar to those obtained when gelatin is added to water While the molecular structure of microemulsion-based organogels (MBGs) has not yet been fully elucidated, several models have been proposed (see Rees and Robinson, infra).

MBGs may be easily prepared by incubating the parent microemulsion at 50°C and mixing with a solution of gelatin in water at the same temperature. The resulting mixture is then shaken vigorously and allowed to cool, whereupon an optically transparent single phase gel is formed. Gel strength is controlled by varying the amount of gelatin present.

Detailed description of the invention

According to the present invention there is provided a composition (e.g. a fragrance releasing composition) comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles dispersed in an anhydrous carrier, wherein the droplet/micelle cores have low water activity and contain a latent fragrance or latent fragrance enhancer which is activated when the water activity within the cores is increased

The latent fragrance may comprises a system comprising a fragrance/fragrance enhancer precursor and an enzyme which is inactive due to the low water activity within the cores, wherein the enzyme acts on the fragrance precursor to produce an active fragrance/fragrance enhancer moiety on hydration of the cores.

As used herein, the term " anhydrous" is used to define carriers (which may be in the solid, gaseous, liquid or polyphasic state) which have a water activity low enough to prevent activation of the latent fragrance. In embodiments where latency is achieved by maintenance of an inactive enzyme within the cores, the term is intended to define a water activity within the cores which is insufficient to permit significant catalysis. Thus, the term does not necessarily imply an absolute absence of water.

The term "fragrance enhancer" is a term of art used to define any of a variety of agents which synergise with other fragrances and so intensify their odour. One important class of fragrance enhancers is the Maiilard volatiies, which include altol and furaneol and their analogues which occur naturally or which can be formed by e.g. caramelization.

Fragrance enhancers find particular application in circumstances where it is desired to increase the intensity or permanence of one or more selected labiie and/or volatile fragrances. In such embodiments, this is achieved by providing the labile and/or volatile fragrance(s) (hereinafter referred to as the "co-fragrance(s) ") in admixture with a composition according to the invention which comprises water- in-oil microemulsion droplets and/or hydrated reverse micelles dispersed in an anhydrous carrier, wherein the droplet/micelle cores have low water activity and contain a latent fragrance enhancer which is activated when the water activity within the cores is increased. On hydration attendant on use of the composition (e.g. on contact with moisture on the skin, in the case of a perfume), the activated fragrance enhancer acts in synergy with the co-fragrance(s), so increasing their intensity and/or persistence.

Thus, the invention finds particular application in a method for increasing the intensity and/or permanence of a fragrance comprising the step of mixing the fragrance with a composition comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles to produce an anhydrous mixture, wherein the droplet/micelle cores have low water activity and contain a latent fragrance enhancer which is activated when the water activity within the cores is increased. The microemulsion composition for use in this embodiment of the invention may of course be as defined herein.

Accordingly, in another aspect the invention provides a perfume comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles, wherein the droplet/micelle cores have low water activity and contain a latent fragrance enhancer which is activated when the water activity within the cores is increased. The perfume preferably includes one or more co-fragrances, and any of a wide variety of known perfume formulations (e.g. based on ethanol or propylene glycol) may be employed. Such perfumes may be incorporated into a wide range of perfumed goods (as defined infra).

The fragrance delivery system may also be used to release a cascade of different fragrances over time to produce a particular desired fragrance profile. This may be achieved by using combinations of different enzymes and cognate substrates within a single MEM system, or by using mixtures of different MEMs each having different solubilized enzyme/precursor systems. Control over the rate of release may then be achieved through any or a combination of the following mechanisms:

(a) varying the activity of the enzyme (for example, by selecting a particular biological source having a desired activity) . Suitable enzyme sources include bacterial, fungal (e.g. yeast), plant, animal (e.g. mammalian) sources, and may include those derived from thermophilic and halophilic organisms); and/or

(b) varying the activity of the enzyme by incorporating specific enzyme inhibitors (e.g. glucose inhibits glucosidases); and/or

(c) varying the enzyme/substrate concentration; and/or

(d) providing one or more of the MEMs in the form of organogels, which slows the rate of delivery of the fragrances produced therein, and/or

(e) varying the nature of the precursor (e.g. at the level of the number of glycoside sugar residues) , and/or

(f) varying the identity of the surfactant and/or co-surfactant, since some surfactants (e.g. propylene glycol) may act as enzyme inhibitors; and/or

(g) varying the relative proportions of the different MEM components present in a mixed MEM system.

The fragrance/fragrance enhancer precursor may comprise any of a large number of known fragrance/fragrance enhancer glycosides (for example furaneol glycoside, maltol glycoside or mustard oil glycoside, e.g. a glucosinolate or thioglucoside) .

The active fragrance or fragrance enhancer moiety is preferably a fragrance/enhancer aglycone. Particularly preferred are fragrance/enhancer aglycones having the general formula R-OH. In such embodiments, R may be selected from an aliphatic alcohol residue, an aromatic alcohol residue (for example a terpene, e.g. menthol, geraniol or citronellol) and an alicyclic alcohol residue. Such embodiments may find particular application in the delivery of sweet and/or fruit fragrances.

Alternatively, the fragrance/enhancer aglycone may have the general formula R-SH.

The enzyme for use in the invention may be selected from any of oxidoreductases, transferases, hydrolases, Iyases, isomerases, ligases or combinations of different enzymes of any of the aforementioned type.

Particularly preferred are hydrolases selected from ester hydrolases, glycosyl hydrolases, ether (e.g. thioether) hydrolases, peptide hydrolases or combinations of any of the foregoing. Such enzymes find particular application in the generation of fragrance or fragrance enhancer aglycones from glycoside precursors.

Preferred ester hydrolases for use according to the invention include carboxylic ester hydrolase (e g. Iipase), thioester hydrolase, phosphoric monoester hydrolase, phosphoric diester hyd-colase, tπphosphoπc monoester hydrolase, a sulphuric ester hydrolase, diphosphoric monoester hydrolase and combinations of any of the foregoing.

Preferred glycosyl hydrolases for use according to the invention include those which hydrolyse O-glycosyl residues, and in particular σ-glucosidase, β- glucosidase, σ-galactosidase or β-galactosidase. Other preferred glycosyl hydrolases include those which hydrolyse /V-glycosy¹ or S-glycosyl compounds In the latter case, particularly preferred is myrosinase, which finds particular application in the hydrolysis of mustard oil glycosides (such as glucosinolates and thioglucosides) to aglycones of general formula R-SH.

Preferred peptide hydrolases include σ-aminoacylpeptide hydrolase, peptidyiamino-acid or acylamino-acid hydrolases, dipeptide hydrolases, dipeptidylpeptide hydrolases, peptidyldipeptide hydrolases, proteinases (e.g. seπne proteinases, SH-protemases, acid proteinases or metalloprotemases) or combinations of any of the foregoing.

The droplets or micelles may further comprise a surfactant, and any surfactant with a low hydrophilic-lipophilic balance value may be used. Examples of suitable surfactants for use in the invention include sorbitan esters (e.g. sorbitan monooleate), glycerol derivatives (e.g. stearyl monoglyceride), phospholipids (e.g. lecithin), naturally occurring phosphoglycerides (e.g. phosphatidylcholine or phosphatidylethanolamine) and mixtures of one or more of these surfactants.

Particularly preferred as a surfactant (especially where sunflower oil is used) is a mixture of lecithin and sorbitan monooleate.

In most microemulsion/micelle formulations a co-surfactant is used in addition to the surfactants discussed above. Any suitable co-surfactant may be used, provided that it functions to stabilize the water-oil interface. Particularly preferred are co-surfactants selected from short chain alcohols, propylene glycol or mixtures thereof.

The surf actant/co-surf actant mix for use in the compositions of the invention are preferably selected such that the packing parameter 5_p (as hereinbefore defined) of the surfactant/co-sur actant mix is greater than 1 .

Particularly preferred according to the invention are double tail and/or medium tail length surfactants/co-surfactants. Surfactant/co-surfactants having relatively high V to a ratios (as hereinbefore defined) have been found to be particularly useful for use in the invention.

In preferred embodiments, the R value of the microemulsion droplets and/or hydrated reverse micelles in the compositions of the invention is preferably less than 10 (e.g. less than 5). In such embodiments, the water activity in the droplet/micelle core is very low, and may render the solubilized enzyme(s) latent and/or modify enzyme activity and/or specificity.

The droplet/micelle size is preferably 1 -1 00 nm, and in most applications is 1 -10 nm.

Products for use with the invention

The compositions of the invention find application in any perfumed product which can be formulated and stored in a substantially anhydrous condition and which become hydrated in use.

Thus, the invention finds application in a wide range of products including tableware (napkins, table dressings and serviettes), deodorants (including those for use on the body, in the air and on surfaces such as furniture, carpet and upholstery) . The products may be in any convenient form, including sprays, sticks, bars, granules, powders, impregnated sheets, tablets and non-aqueous solutions) Also contemplated are talcs (e g. body talcs), furniture polishes and waxes, anti- perspirants, cleaning agents (for application to the body and to work sur aces and floors), laundry products (including detergents, fabric softeners and antistatic agents), cosmetics, toiletries, personal hygiene products and perfumes

Thus, the invention finds application in deodorants, air fresheners, laundry freshener or washes, soaps, perfumes, surface cleaners or scourers, cosmetics, litters (e.g. cat litters), nappies, sanitary or incontinence pads, shaving sticks or shaving foams, odour-masking shoe inserts, tissues and towels.

As will be readily appreciated by those skilled in the art, the fragrance in all the foregoing products is stable on storage in the anhydrous state but is released when the product is hydrated in use For example, the moisture of the skin hydrates the perfumes and deodorants of the invention, while the laundry products are hydrated by the water used in the wash.

For applications where no contact of the MEM with skin or other tissues is required, any of a wide variety of known MEM systems may be used. Examples include those described in El-Nokaly and Cornell ( 1 991 ), American Chemical Society Symposium Series 448, pp 62-79 and by Rees and Robinson (op c/t) .

Examples

The invention will now be described with reference to several examples, which are purely exemplary and are not intended to be limiting in any way. Example 1 ^• Flavour enhancing composition

The following MEM composition was used to deliver the flavour enhancer furaneol:

vegetable oil 80.5 % water 3.0% lecithin 1 5.0% furaneol glycoside 1 .0% glycosidase 0.5 %

Other formulations with lower levels (as low as 0 02 % furaneol) were also produced.

Example 2' Incorporation of a MEM into a perfume

Aroma glycoside and glycosidase was incorporated into the aqueous phase of the MEM perfume system described by Tokuoka et al ( 1 994) Colloid Polym Sci 272, 31 7 (the teachings of which relating to MEM compositions are incorporated herein by reference) . Various formulations were produced having 0J , 0.2, 0.3, 0.4 and 0.5 % glycosidase and OJ , 0.3, 0.5, 0.8 and 1 % flavour glycoside. On hydration, the compositions exhibited sustained release of the aroma over time.

Claims

CLAIMS:

1 . A composition comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles dispersed in an anhydrous carrier, wherein the droplet/micelle cores have low water activity and contain a latent fragrance and/or latent fragrance enhancer which is activated when the water activity within the cores is increased.

2. The composition of claim 1 wherein the latent fragrance/fragrance enhancer is a system comprising:

(a) a fragrance/fragrance enhancer precursor; and

(b) an enzyme which is inactive due to the low water activity within the cores, wherein the enzyme acts on the fragrance/fragrance enhancer precursor to produce an active fragrance/fragrance enhancer moiety on hydration of the cores.

3. The composition of claim 2 wherein the fragrance/fragrance enhancer precursor comprises a fragrance and/or fragrance enhancer glycoside (for example a mustard oil glycoside, e.g. a glucosinolate or thioglucoside) .

4. The composition of claim 2 or claim 3 wherein the active fragrance/fragrance enhancer moiety is a fragrance/fragrance enhancer aglycone.

5. The composition of claim 4 wherein the fragrance/fragrance enhancer aglycone has the general formula: R-OH.

6. The composition of claim 5 wherein R is selected from:

(a) an aliphatic alcohol residue;

(b) an aromatic alcohol residue (for example a terpene, e.g. menthol, geraniol or citronellol);

(c) an alicyclic alcohol residue.

7. The composition of claim 4 wherein the fragrance/fragrance enhancer aglycone has the general formula. R-SH.

8 The composition of any one of claims 2-7 wherein the enzyme is selected from any of:

(a) oxidoreductases;

(b) transferases;

(c) hydrolases;

(d) Iyases;

(e) isomerases;

(f) ligases;

(g) combinations of any of (a)-(f)

9. The composition of claim 8 (c) wherein the hydrolase is selected from

(a) ester hydrolases;

(b) glycosyl hydrolases;

(c) ether (e.g. thioether) hydrolases,

(d) peptide hydrolases;

(e) combinations of any of (a)-(d)

1 0 The composition of claim 9 (a) wherein the ester hydrolase is.

(a) a carboxy c ester hydrolase (e.g a Iipase);

(b) a thioester hydrolase;

(c) a phosphoric monoester hydrolase;

(d) a phosphoric diester hydrolase;

(e) a tπphosphoπc monoester hydrolase;

(f) a sulphuric ester hydrolase;

(g) a diphosphoric monoester hydrolase; (h) combinations of any of (a)-(g).

1 1 . The composition of claim 9 (b) wherein the glycosyl hydrolase hydrolyses O-glycosyl (e.g. being any of σ-giucosidase, β-glucosidase, σ-galactosidase and β-galactosidase), /V-glycosyl or S-glycosyl compounds (e.g. being myrosinase).

2. The composition of claim 9 (d) wherein the peptide hydrolase is selected from:

(a) σ-aminoacylpeptide hydrolases;

(b) peptidylamino-acid or acylamino-acid hydrolases;

(c) dipeptide hydrolases;

(d) dipeptidylpeptide hydrolases;

(e) peptidyldipeptide hydrolases;

(f) proteinases (e.g. seπne proteinases, SH-proteinases, acid proteinases or metalloproteinases) ;

(g) combinations of any of (a)-(f)

3. The composition of any one of the preceding claims wherein the droplets or micelles comprise a surfactant.

4 The composition of claim 1 3 wherein the surfactant has a low hydrophi c- pophilic balance.

5. The composition of claim 1 3 or claim 1 4 wherein the surfactant is selected from:

(a) a sorbitan ester (e.g. sorbitan monooleate) ;

(b) a glycerol derivative (e.g. stearyl monoglyceπde);

(c) a phospholipid (e.g. lecithin),

(d) naturally occurring phosphoglycerides (e.g. phosphatidylcholine or phosphatidylethanolamine)

(e) mixtures of any of (a)-(d) (e.g. a mixture of lecithin and sorbitan monooleate).

6. The composition of any one of claims 1 3-1 5 further comprising a co- surfactant.

7. The composition of claim 1 6 wherein the co-surfactant is selected from:

(a) a short chain alcohol (e.g. ethanol, propanol or butanol) ;

(b) propylene glycol;

(c) mixtures thereof.

1 8. The composition of any one of claims 1 3-17 wherein the packing parameter S_p of the surfactant is greater than 1 , wherein:

S_p = V(al)-' where V is the effective packing volume of the surfactant hydrocarbon tail, / is the length of the hydrocarbon tail and a is the effective headgroup area at the oil-water interface.

1 9. The composition of any one of claims 1 3-1 8 wherein the surfactant and/or co-surfactant is a double tail and/or medium tail length surfactant.

20. The composition of any one of claims 1 3- 1 9 wherein the molecular geometry of the surfactant and/or co-surfactant tail(s) is selected such that is increased relative to a.

21 . The composition of any one of the preceding claims wherein the R value of the microemulsion droplets and/or hydrated reverse micelles is less than 1 0 (e.g. less than 5) .

22. The composition of any one of the preceding claims wherein the droplet/micelle size is 1 -1 00 nm (e.g. 1 -1 0 nm) .

23. The composition of any one of the preceding claims wherein the microemulsion is in the form of an organogel (e.g. a gelatin-based organogel) .

24. The composition of any one of the preceding claims which is formulated as:

(a) a deodorant or anti-perspirant;

(b) an air freshener;

(c) a laundry freshener or wash;

(d) a soap;

(e) a perfumery product;

(f) a surface cleaner;

(g) a cosmetic;

(h) a litter (e.g. cat litter); (i) a nappy, sanitary or incontinence pad or towel;

(j) a shaving stick or shaving foam or after shave lotion;

(k) a shoe insert;

(I) a tissue or towel;

(m) a furniture polish (e.g further comprising wax);

(n) a dishwasher powder or tablet;

(o) a bath salt composition.

25. The composition of claim 24 (a) which is a deodorant stick, talc or aerosol spray.

26. The composition of claim 24 (b) which is in the form of a stick or gel.

27. The composition of claim 24 (b) which is in the form of an aerosol spray and wherein for example the carrier comprises an organic propellant.

28. The composition of claim 24 (c) which is in the form of a washing powder or fabric conditioner, for example further comprising detergents and/or surfactants and/or enzymes.

29. The composition of claim 24 (c) which is in the form of a sheet, for example further comprising anti-static and/or fabric softening agents for use in a tumble drier.

30. The composition of claim 24 (d) which is in the form of a bar or granules.

31 . The composition of claim 24 (e) which is in the form of a liquid for topical application to the skin.

32. The composition of claim 31 wherein the carrier comprises an organic solvent (for example, an alcohol (e.g. ethanol) and/or propylene glycol).

33. The composition of claim 24 (f) which is in the form of a powder, granules or incorporated into a pad (e.g. a scouring pad).

34. The composition of claim 24 (g) which is a hair spray.

35. The composition of claim 24 (I) which is for use as a surface wipe or dishcloth, for example further comprising cleaning and/or scouring agents.

36. The composition of any one of the preceding claims, further comprising one or more co-fragrance(s).

37. An air conditioning assembly or filter comprising the composition of any one of the preceding claims.

38. A method for increasing the intensity and/or permanence of a fragrance comprising the step of mixing the fragrance with a composition comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles to produce an anhydrous mixture, wherein the droplet/micelle cores have low water activity and contain a latent fragrance enhancer which is activated when the water activity within the cores is increased.

39. The method of claim 38 wherein the composition is as defined in any one of claims 1 -36.

40. A perfume comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles, wherein the droplet/micelle cores have low water activity and contain a latent fragrance enhancer which is activated when the water activity within the cores is increased.

41 . The perfume of claim 40 further comprising one or more co-fragrances.