*2.3.2 Physical forces*

Physical emulsification is one of the most crucial steps in nanoencapsulation process since it affects deeply the quality of the final emulsion (encapsulation efficiency, nanoemulsion stability, or biological efficacy). Different homogenization methods, as detailed in **Table 1**, can be used such as high-pressure homogenization, ultrasonic homogenization, and microfluidization [22].


#### **Table 1.**

*The different devices often used for the nanoencapsulation of essential oils.*

*High-pressure homogenization*: the use of high-pressure (30–350 MPa) homogenization can reduce an emulsion droplet size to a nanoscale level and improve its stability by the reduction of the creaming rate. In this method, two immiscible liquids along with the used emulsifier are forced to pass through a small orifice where their mixture is subjected to a turbulence and shear flow intense levels [2]. All of which leads to the break-up of the dispersed phase into small droplets.

*Microfluidization*: this technic involves the transfer of mechanical energy to fluid particles under a high-pressure environment. More specifically, immiscible liquids are pumped and split into two opposite microstreams, which are impacted or collided against each other in a chamber, called the interaction chamber, where shear, turbulent and cavitation forces are generated using high-pressure displacement pump [9].

*Ultrasonication*: the droplet formation at a nanoscale level using ultrasound homogenization mechanisms is mainly based on cavitation, where ultrasound waves hit the liquid surface and form high-velocity jets. To do that, a probe sonicator is brought in contact with the dispersion of emulsifier and liquids. The generated mechanical vibration and cavitation can provide the necessary energy input for the formation of small sized droplets [26].

### **2.4 Parameters affecting nanoemulsion droplet size and stability**

The droplet homogeneity, and consequently emulsion stability, depends basically on the physical characteristics of each used component for the formation of essential oil nanoemulsion [9]. **Table 2** summarizes the obtained droplet size of different tested formulation:

#### *2.4.1 Dispersed phase characteristics*

During the process of encapsulating essential oils into nanoemulsion-based delivery system, dispersed phase characteristics influence profoundly the final product properties [3]. In this context, the physical characteristics of the encapsulated essential oil (such as interfacial tension and viscosity) present a key factor in the nanoemulsion stability [11]. For example, it is difficult to nanoencapsulate pure fixed oils due to their high viscosity. Indeed, if the dispersed phase viscosity increases, it will become more difficult to breakup within the high-pressure homogenizer. As a result, nanoemulsions with larger droplets will be formed. This phenomenon was also confirmed by other researches for various types of homogenization device, who declared that the droplet breakup becomes easier as the viscosity of the dispersed phase decreases [30]. Also, the increase of the dispersed phase viscosity generated a significant increase of the mean droplet diameter, from around 92 to around 125 nm [9]. Other researches demonstrated that instantaneous unstable emulsions were obtained while trying the nanoencapsulation of pure essential oil [11]. These


**51**

**2.5 Nanoemulsion instability**

*Encapsulation of Natural Bioactive Compounds: Nanoemulsion Formulation to Enhance…*

findings were explained by the lower viscosity of pure essential oils. Actually, to obtain a stable emulsion with a nanoscale droplet size, there is an optimum range of disperse-to-continuous phase viscosity ratios [10]. With this respect, it would be convenient to nanoencapsulate a mixture of essential oil and fixed oil as dispersed

Changing the continuous phase viscosity influences the nanoemulsion droplet size [9]. More specifically, the increase of the continuous phase viscosity leads to the droplet diameter decrease [10]. Actually, the increase of the continuous phase viscosity induces the increase of the disruptive shear stresses, which leads to the

Although a wide range of molecules may be used in the essential oil nanoemulsification (exp. colloids, special particles), only the emulsifier case will be presented in this chapter. Different systems were adopted in order to classify surfactants. For instance, a very useful system for the classification of surfactants is standardized on the basis of their solubility in water. In this system, numerical values are called the hydrophilic-lipophilic balance (HLB), which involves the relative affinity of the surfactant for water and oil. The HLB is defined as the relative efficiency of the hydrophilic portion of the surfactant molecule to its lipophilic portion. It is worthy to mention that emulsifiers with HLB values ranged between 3 and 6 are usually used for w/o emulsions. Whereas emulsifiers with HLB values ranged between 7 and 20 are used for o/w emulsions [5]. Besides, other researchers have based their investigations on the effect of emulsifier chemical nature in producing homogenous nanoemulsions [9, 11, 31]. Their findings confirmed that emulsifier type presents significant impact on the final emulsion stability. This variation of emulsifier behaviors could be explained by the difference in the stabilization process of each one. Previous researches demonstrated that under similar homogenization conditions, small-molecule emulsifiers (exp. Tween and SDS) can be more effective to make small droplets than biopolymers (exp. caseinate and β-lactoglobulin) due to their rapid adsorption to the droplet surfaces [9]. Moreover, charged emulsifiers can be more efficient in producing homogenous nanoemulsions as compared to nonionic ones [11]. In fact, contrary to nonionic emulsifier, which uses steric repulsion to stabilize the dispersed phase, charged emulsifiers use their electrostatic repulsion. Actually, for nonionic emulsifier-based emulsion, tails envelop essential oil inside the droplet [32, 33]. In this case, the hydrophilic nature of tails may repel the hydrophobic essential oils leading to a significant heterogeneity of the droplet diameters. In anionic emulsifier-based emulsions, the inverse occurs. As a matter of fact, the adsorption of negatively charged heads of emulsifier molecules to oil droplets surface increases the electrostatic repulsion between droplets, leading to the formation of a stable nanoemulsion [34]. In this case, the charged heads of SDS molecules envelop essential oil inside the droplet, while the hydrophilic tails stay outside leading to an appropriate homogeneous nanoemulsion.

Nanoemulsions lose their stability, which is an irreversible phenomenon in nature, in a very large time frame that may vary from few minutes to several years, depending on formulation and storage conditions [35]. In this context, nanoemulsions stability

can be checked according to their droplet size growth and their appearance.

*DOI: http://dx.doi.org/10.5772/intechopen.84183*

*2.4.2 Continuous phase characteristics*

increase of droplet fragmentation.

*2.4.3 Emulsifier chemical characteristics*

phase in order to obtain an essential oil nanoemulsion.

#### **Table 2.**

*Formulation effect on the droplet size of essential oil nanoemulsion.*

#### *Encapsulation of Natural Bioactive Compounds: Nanoemulsion Formulation to Enhance… DOI: http://dx.doi.org/10.5772/intechopen.84183*

findings were explained by the lower viscosity of pure essential oils. Actually, to obtain a stable emulsion with a nanoscale droplet size, there is an optimum range of disperse-to-continuous phase viscosity ratios [10]. With this respect, it would be convenient to nanoencapsulate a mixture of essential oil and fixed oil as dispersed phase in order to obtain an essential oil nanoemulsion.

#### *2.4.2 Continuous phase characteristics*

*Microencapsulation - Processes, Technologies and Industrial Applications*

leads to the break-up of the dispersed phase into small droplets.

**2.4 Parameters affecting nanoemulsion droplet size and stability**

the formation of small sized droplets [26].

different tested formulation:

*2.4.1 Dispersed phase characteristics*

*High-pressure homogenization*: the use of high-pressure (30–350 MPa) homogenization can reduce an emulsion droplet size to a nanoscale level and improve its stability by the reduction of the creaming rate. In this method, two immiscible liquids along with the used emulsifier are forced to pass through a small orifice where their mixture is subjected to a turbulence and shear flow intense levels [2]. All of which

*Microfluidization*: this technic involves the transfer of mechanical energy to fluid particles under a high-pressure environment. More specifically, immiscible liquids are pumped and split into two opposite microstreams, which are impacted or collided against each other in a chamber, called the interaction chamber, where shear, turbulent and cavitation forces are generated using high-pressure displacement pump [9]. *Ultrasonication*: the droplet formation at a nanoscale level using ultrasound homogenization mechanisms is mainly based on cavitation, where ultrasound waves hit the liquid surface and form high-velocity jets. To do that, a probe sonicator is brought in contact with the dispersion of emulsifier and liquids. The generated mechanical vibration and cavitation can provide the necessary energy input for

The droplet homogeneity, and consequently emulsion stability, depends basically on the physical characteristics of each used component for the formation of essential oil nanoemulsion [9]. **Table 2** summarizes the obtained droplet size of

During the process of encapsulating essential oils into nanoemulsion-based delivery system, dispersed phase characteristics influence profoundly the final product properties [3]. In this context, the physical characteristics of the encapsulated essential oil (such as interfacial tension and viscosity) present a key factor in the nanoemulsion stability [11]. For example, it is difficult to nanoencapsulate pure fixed oils due to their high viscosity. Indeed, if the dispersed phase viscosity increases, it will become more difficult to breakup within the high-pressure homogenizer. As a result, nanoemulsions with larger droplets will be formed. This phenomenon was also confirmed by other researches for various types of homogenization device, who declared that the droplet breakup becomes easier as the viscosity of the dispersed phase decreases [30]. Also, the increase of the dispersed phase viscosity generated a significant increase of the mean droplet diameter, from around 92 to around 125 nm [9]. Other researches demonstrated that instantaneous unstable emulsions were obtained while trying the nanoencapsulation of pure essential oil [11]. These

**Dispersed phase Emulsifier Droplet** 

*Thymus capitatus* Mixture with 30% of soybean oil SDS 110 [11] *Eucalyptus globulus* Pure essential oil Tween 20 60 [27]

Peppermint Pure essential oil Tween 80 70 [29]

**size (nm)**

Tween 80 100 [28]

**References**

**50**

**Table 2.**

**Encapsulated essential oil**

Carvacrol Mixture with 60% of medium

*Formulation effect on the droplet size of essential oil nanoemulsion.*

chain triglyceride

Changing the continuous phase viscosity influences the nanoemulsion droplet size [9]. More specifically, the increase of the continuous phase viscosity leads to the droplet diameter decrease [10]. Actually, the increase of the continuous phase viscosity induces the increase of the disruptive shear stresses, which leads to the increase of droplet fragmentation.

#### *2.4.3 Emulsifier chemical characteristics*

Although a wide range of molecules may be used in the essential oil nanoemulsification (exp. colloids, special particles), only the emulsifier case will be presented in this chapter. Different systems were adopted in order to classify surfactants. For instance, a very useful system for the classification of surfactants is standardized on the basis of their solubility in water. In this system, numerical values are called the hydrophilic-lipophilic balance (HLB), which involves the relative affinity of the surfactant for water and oil. The HLB is defined as the relative efficiency of the hydrophilic portion of the surfactant molecule to its lipophilic portion. It is worthy to mention that emulsifiers with HLB values ranged between 3 and 6 are usually used for w/o emulsions. Whereas emulsifiers with HLB values ranged between 7 and 20 are used for o/w emulsions [5]. Besides, other researchers have based their investigations on the effect of emulsifier chemical nature in producing homogenous nanoemulsions [9, 11, 31]. Their findings confirmed that emulsifier type presents significant impact on the final emulsion stability. This variation of emulsifier behaviors could be explained by the difference in the stabilization process of each one. Previous researches demonstrated that under similar homogenization conditions, small-molecule emulsifiers (exp. Tween and SDS) can be more effective to make small droplets than biopolymers (exp. caseinate and β-lactoglobulin) due to their rapid adsorption to the droplet surfaces [9]. Moreover, charged emulsifiers can be more efficient in producing homogenous nanoemulsions as compared to nonionic ones [11]. In fact, contrary to nonionic emulsifier, which uses steric repulsion to stabilize the dispersed phase, charged emulsifiers use their electrostatic repulsion. Actually, for nonionic emulsifier-based emulsion, tails envelop essential oil inside the droplet [32, 33]. In this case, the hydrophilic nature of tails may repel the hydrophobic essential oils leading to a significant heterogeneity of the droplet diameters. In anionic emulsifier-based emulsions, the inverse occurs. As a matter of fact, the adsorption of negatively charged heads of emulsifier molecules to oil droplets surface increases the electrostatic repulsion between droplets, leading to the formation of a stable nanoemulsion [34]. In this case, the charged heads of SDS molecules envelop essential oil inside the droplet, while the hydrophilic tails stay outside leading to an appropriate homogeneous nanoemulsion.

#### **2.5 Nanoemulsion instability**

Nanoemulsions lose their stability, which is an irreversible phenomenon in nature, in a very large time frame that may vary from few minutes to several years, depending on formulation and storage conditions [35]. In this context, nanoemulsions stability can be checked according to their droplet size growth and their appearance.

Generally, emulsion stability depends mainly on emulsifier behavior, emulsion composition, and its droplet size distribution [3]. Indeed, nanoemulsions, due to their characteristic nanoscale droplets size, exhibit higher stability against creaming or sedimentation, than emulsions with larger droplet diameters. Actually, diffusion rate and Brownian motion exhibited by nanoemulsion droplets predominates over the sedimentation or the creaming rate [4].

Concerning the emulsifier behavior, nanoemulsions prepared using nonionic surfactants do not usually flocculate, as no attractive forces are created [11].

Also, nanoemulsion stability depends strongly on their storage time and conditions. Actually, small droplets of freshly made nanoemulsion could initially be distributed in the medium, but are rather unstable, resulting in droplet growth during long storage, and these new large droplets are the source of flocks. In fact, droplets flocculation appears whenever the interfacial tension of the dispersed phase is weaker than its own net attractive forces [36]. Accordingly, nanoemulsions storage temperature increase not only provokes the increase in molecules thermal agitation [37], but also the decrease in their interfacial tension. Consequently, the droplet diameter of instable thermodynamic nanoemulsions would tend to increase to reduce medium total free energy. The nanoemulsion storage at high temperature (up to 55°C) generated new populations of larger droplets after 15 storage days [9].

Worthy to note that nanoemulsion instability occurs due to alteration in droplet size through mechanisms such as Coalescence and Ostwald ripening.


Otherwise, practically nanoemulsions are usually stored at lower temperatures, inducing therefor, their longer stability and higher resistance to droplet aggregation.

### **2.6 Effect of the nanoencapsulation process on essential oils antibacterial efficiencies**

As the antibacterial efficiency is a fundamental characteristic of essential oils, different methods were adopted in order to seek the effect of the nanoencapsulation process on essential oil antibacterial potency [11, 25, 40]. All results depicted clear amelioration in the antibacterial efficiency. Such amelioration suggests a refinement of the mode of action of essential oils after their nanoencapsulation in fighting pathogenic bacteria. Actually, some researchers considered the nanoemulsion as a transporter for essential oils to cross the bacterial cellular membrane, allowing

**53**

*Encapsulation of Natural Bioactive Compounds: Nanoemulsion Formulation to Enhance…*

them to overcome their hydrophobic limitation [11]. Indeed, essential oils exert their known antibacterial effect from the inner side of the cytoplasmic membrane [28]. Essential oil antibacterial effect is based on their abilities to disrupt the bacterial cytoplasmic membrane to lose its properties as a barrier, matrix for enzymes, and energy transducer, all of which will compromise the cell viability leading to its death [41, 42]. However, essential oil presents low water solubility, inducing its rough distribution in the medium, which can limit its antibacterial action [28, 42]. Moreover, it is worthy to note that the interesting antibacterial activity of nanoencapsulated essential oil could present a promising procedure to fight against the global issue involving drug-resistant strains. As a matter of fact, in addition to the antibacterial activity amelioration of essential oil after their nanoencapsulation, many essential oils have succeeded to surpass the efficiency of current antibiotic. These findings are very promoting, especially that the development of drug-resistant strains has become a worldwide concern [43]. As a matter of fact, typical antibiotic killing technique consists on blocking bacterial ribosome formation at the initiation step [44]. Consequently, no protein synthesis, which is obligatory for bacterial metabolism and survival, takes place leading the bacterial cell death. In this context, antibioticresistant strain could be formed after mutation of the initial bacteria whose ribosome formation continues even in the presence of the drug. However, the efficiency of nanoencapsulated essential oil, based on the nonspecific disruption of bacterial cell membranes, can resist bacterial mutation and maintain its bactericidal activities. Accordingly, the use of nanoencapsulated essential oils into nanoemulsion-based delivery system is very efficient to fight pathogenic bacteria and would not conduct the development of resistant strains, which could remediate to the bacterial resistance

problem, caused by the widespread and inappropriate use of antibiotics [11].

It has been repeatedly demonstrated that essential oil efficiency can be reduced in real food systems due to their hydrophobic character and their low solubility in water as compared to *in vitro* model system [11, 45]. This reduce in essential oil activity is more noticed in foods with high fat level such as milk, mayonnaise, butter, etc. [46]. For instance, it has been demonstrated that in cheese, an increase up to 100-fold of the essential oil concentration was required to assure comparable antimicrobial efficacy of the *in vitro* model system [47]. The difference in the essential oil antimicrobial efficiency between *in vitro* and real food system can be attributed to the essential oil dissolution in the lipid phase of an ailment, inducing the decrease of their concentration in the aqueous phase [48]. However, it is in the aqueous phase where pathogenic bacteria typically proliferate [46]. Consequently, to ensure similar antimicrobial activity in *in vitro* and in real food system, essential oils have to be relocated in the aqueous phase of the food, in order to be in continuous contact with the pathogenic microorganisms. In order to accomplish this goal, the encapsulation of essential oils into a nanoemulsion-based delivery system seems to be an interesting approach. As a matter of fact, the hydrophilic outer surface of the nanoemulsion enables essential oils to stay in the food's aqueous phase, while its

Also, the nanoencapsulation of essential oils prevents their interaction with food components, which induce a positive impact on essential oil antimicrobial efficiency. Indeed, bulk essential oils tend to bind with hydrophobic food molecules leading to the reduction of their availability to fight pathogenic microorganisms [48]. In contrast, nanodispersed essential oil is evenly distributed in food matrix and can be released locally to keep its concentration sufficiently high to inhibit the

**2.7 Nanoencapsulated essential oils as efficient food conservators**

hydrophobic inner core ensures its harbor.

growth of the spoilage bacteria [49].

*DOI: http://dx.doi.org/10.5772/intechopen.84183*

#### *Encapsulation of Natural Bioactive Compounds: Nanoemulsion Formulation to Enhance… DOI: http://dx.doi.org/10.5772/intechopen.84183*

them to overcome their hydrophobic limitation [11]. Indeed, essential oils exert their known antibacterial effect from the inner side of the cytoplasmic membrane [28]. Essential oil antibacterial effect is based on their abilities to disrupt the bacterial cytoplasmic membrane to lose its properties as a barrier, matrix for enzymes, and energy transducer, all of which will compromise the cell viability leading to its death [41, 42]. However, essential oil presents low water solubility, inducing its rough distribution in the medium, which can limit its antibacterial action [28, 42].

Moreover, it is worthy to note that the interesting antibacterial activity of nanoencapsulated essential oil could present a promising procedure to fight against the global issue involving drug-resistant strains. As a matter of fact, in addition to the antibacterial activity amelioration of essential oil after their nanoencapsulation, many essential oils have succeeded to surpass the efficiency of current antibiotic. These findings are very promoting, especially that the development of drug-resistant strains has become a worldwide concern [43]. As a matter of fact, typical antibiotic killing technique consists on blocking bacterial ribosome formation at the initiation step [44]. Consequently, no protein synthesis, which is obligatory for bacterial metabolism and survival, takes place leading the bacterial cell death. In this context, antibioticresistant strain could be formed after mutation of the initial bacteria whose ribosome formation continues even in the presence of the drug. However, the efficiency of nanoencapsulated essential oil, based on the nonspecific disruption of bacterial cell membranes, can resist bacterial mutation and maintain its bactericidal activities. Accordingly, the use of nanoencapsulated essential oils into nanoemulsion-based delivery system is very efficient to fight pathogenic bacteria and would not conduct the development of resistant strains, which could remediate to the bacterial resistance problem, caused by the widespread and inappropriate use of antibiotics [11].

#### **2.7 Nanoencapsulated essential oils as efficient food conservators**

It has been repeatedly demonstrated that essential oil efficiency can be reduced in real food systems due to their hydrophobic character and their low solubility in water as compared to *in vitro* model system [11, 45]. This reduce in essential oil activity is more noticed in foods with high fat level such as milk, mayonnaise, butter, etc. [46]. For instance, it has been demonstrated that in cheese, an increase up to 100-fold of the essential oil concentration was required to assure comparable antimicrobial efficacy of the *in vitro* model system [47]. The difference in the essential oil antimicrobial efficiency between *in vitro* and real food system can be attributed to the essential oil dissolution in the lipid phase of an ailment, inducing the decrease of their concentration in the aqueous phase [48]. However, it is in the aqueous phase where pathogenic bacteria typically proliferate [46]. Consequently, to ensure similar antimicrobial activity in *in vitro* and in real food system, essential oils have to be relocated in the aqueous phase of the food, in order to be in continuous contact with the pathogenic microorganisms. In order to accomplish this goal, the encapsulation of essential oils into a nanoemulsion-based delivery system seems to be an interesting approach. As a matter of fact, the hydrophilic outer surface of the nanoemulsion enables essential oils to stay in the food's aqueous phase, while its hydrophobic inner core ensures its harbor.

Also, the nanoencapsulation of essential oils prevents their interaction with food components, which induce a positive impact on essential oil antimicrobial efficiency. Indeed, bulk essential oils tend to bind with hydrophobic food molecules leading to the reduction of their availability to fight pathogenic microorganisms [48]. In contrast, nanodispersed essential oil is evenly distributed in food matrix and can be released locally to keep its concentration sufficiently high to inhibit the growth of the spoilage bacteria [49].

*Microencapsulation - Processes, Technologies and Industrial Applications*

the sedimentation or the creaming rate [4].

Generally, emulsion stability depends mainly on emulsifier behavior, emulsion composition, and its droplet size distribution [3]. Indeed, nanoemulsions, due to their characteristic nanoscale droplets size, exhibit higher stability against creaming or sedimentation, than emulsions with larger droplet diameters. Actually, diffusion rate and Brownian motion exhibited by nanoemulsion droplets predominates over

Concerning the emulsifier behavior, nanoemulsions prepared using nonionic

Also, nanoemulsion stability depends strongly on their storage time and conditions. Actually, small droplets of freshly made nanoemulsion could initially be distributed in the medium, but are rather unstable, resulting in droplet growth during long storage, and these new large droplets are the source of flocks. In fact, droplets flocculation appears whenever the interfacial tension of the dispersed phase is weaker than its own net attractive forces [36]. Accordingly, nanoemulsions storage temperature increase not only provokes the increase in molecules thermal agitation [37], but also the decrease in their interfacial tension. Consequently, the droplet diameter of instable thermodynamic nanoemulsions would tend to increase to reduce medium total free energy. The nanoemulsion storage at high temperature (up to 55°C) generated new populations of larger droplets after 15 storage days [9]. Worthy to note that nanoemulsion instability occurs due to alteration in droplet

i.*Coalescence:* this phenomenon results from the fusion of two or more droplets into one larger one by the breakdown of the thin film existing between them [38]. As a matter of fact, coalescence occurs if the adhesion force between two droplets exceeds the turbulent force that creates the dispersion. Coalescence can be prevented by the addition of emulsifiers, which have the

ii.*Ostwald ripening:* this phenomenon is characterized by change in droplet size and distribution, as well as by turbidity apparition in nanoemulsions [3]. Actually, Ostwald ripening occurs with time passage due to the migration of droplets from the dispersed phase (high Laplace pressure) to the continuous phase (low Laplace pressure), leading to molecular diffusion [39]. To prevent Ostwald ripening, several parameters should be taken in consideration such as: the physical properties of the bioactive compound, the mutual solubility of the phases, the nature and concentration of used emulsifier, preparation

Otherwise, practically nanoemulsions are usually stored at lower temperatures, inducing therefor, their longer stability and higher resistance to droplet

**2.6 Effect of the nanoencapsulation process on essential oils antibacterial** 

As the antibacterial efficiency is a fundamental characteristic of essential oils, different methods were adopted in order to seek the effect of the nanoencapsulation process on essential oil antibacterial potency [11, 25, 40]. All results depicted clear amelioration in the antibacterial efficiency. Such amelioration suggests a refinement of the mode of action of essential oils after their nanoencapsulation in fighting pathogenic bacteria. Actually, some researchers considered the nanoemulsion as a transporter for essential oils to cross the bacterial cellular membrane, allowing

surfactants do not usually flocculate, as no attractive forces are created [11].

size through mechanisms such as Coalescence and Ostwald ripening.

same charges causing repulsion between two droplets [4].

methods, and storage conditions [4].

**52**

aggregation.

**efficiencies**

Moreover, designing systems that entrap essential oil molecules can reduce the adverse interaction of their characteristic aroma with the original food flavor. As a matter of fact, the use of essential oils as food conservatives can be limited by their sensorial impact on the final food product. Accordingly, adding *Lavandula* and *Chamaemelum* spp. essential oils to yoghurt decreased its acceptability by panelist [50]. Actually, when incorporated into food system, bulk essential oils bind with fats [51]. Such bindings could alter the sensory appreciation of the incorporated aliment, since the taste appreciation depends mainly on its fat quality [52]. On the other way, the encapsulation of *Thymus capitatus* essential oil, into a nanoemulsionbased delivery system, ameliorated significantly its sensorial impact when incorporated into milk [48]. Authors explained their findings by the fact that, when nanoencapsulated, essential oil components were trapped inside droplets and were not able to interact with milk ingredients [53]; therefore, their incorporation would not modify fat quality.

## **3. Conclusion**

The encapsulation of natural bioactive compounds into a nanoemulsion-based delivery system presents definitely an interesting approach to facilitate and ameliorate the valorization of essential oils as natural and green food conservators. Actually, the nanoencapsulation of essential oils protect them from brutal external conditions, ameliorate their distribution in the medium leading to an amelioration of their bactericidal potency, as well as prevent their interaction with food components, which induce a positive impact on their incorporation efficacy. However, special attention should be attributed to the formulation step of essential oil nanoemulsion to avoid different physicochemical phenomena, which can seriously affect the stability and the biological efficiency of the produced nanoemulsion.
