**1.2 Polysorbate surfactants**

*Nanoemulsions - Properties, Fabrications and Applications*

external stimulus (being kinetically stabilized) [7] as:

~5–10 mNm<sup>−</sup><sup>1</sup>

ratio [1, 5].

facilitate phase inversion [3].

ered low-energy methods (~103 Wkg<sup>−</sup><sup>1</sup>

*Typical high pressure homogenizer equipment.*

double affinity, a hydrophilic polar head and a hydrophobic non-polar tail, for example. The surfactant allows decreasing the oil/water interfacial tension (e.g.

decrease in interfacial tension can be enhanced by the addition of a co-surfactant, which acts in similar way than surfactants, but is added in a much lower content. The singularity of nano-emulsions is its small droplet size range, kinetic stability, and the lack of surfactant (5–15% is usually needed) compared to other emulsion systems such as microemulsions [5, 6]; but, in order to be formed they require an

a.Mechanical input: applied with a special equipment such as ultrasonic probe (UP) or high pressure homogenizer (HPH). In a typical HPH (**Figure 1**), a pump pushes a pre-formulated macroemulsion through a narrow gap, a microfluidic interaction chamber (in the micrometer range), where the large droplets break into smaller droplets due the extreme elongation and shear stresses through the homogenization process. This step can be repeated multiple times until the droplet size becomes constant. On the other hand, the UP can induce the breaking of pre-formulated macroemulsion droplets by cavitation, which can also be repeated numerous times. The size and polydispersity of these droplets depends of the applied energy through the whole nano-emulsification process, as well to the water/oil/surfactant

b.Physicochemical input: requires a change of temperature (PIT: phase inversion temperature method) or the addition of an extra amount of dispersed phase (PIC: phase inversion composition). In the first case, the increasing or decreasing of temperature can induce a phase transition (e.g. O/W ➔ W/O), due the change of the hydrophilic–lipophilic balance (HLB) of the system. In the second case, the increment of the droplet constituent can lead to the dispersedphase/continuous phase ➔ continuous-phase/dispersed phase transition [8, 9]. Both approaches are based on phase changes that pass through a zero-curvature system such as a bicontinuous microemulsion or a lamellar phase, in order to

Compared with mechanical methods, physicochemical strategies are consid-

vs. ~1010 Wkg<sup>−</sup><sup>1</sup>

); however, they need

), leading to formation and dispersion of very small droplets. The

**46**

**Figure 1.**

Tween 80 and Span 20 (**Figure 2**) belong to the polysorbate family, a non-ionic type of surfactants. Chemically, polysorbates are derived from ethoxylated sorbitan, a derivative of sorbitol, which is esterified with fatty acids. Tween and Span are proprietary names from CRODA™ (manufacturer of specialty chemicals); the numeric values are specific to the fatty acid derivative: oleic acid, for Tween 80, and lauric acid, for Span 20. Both surfactants are frequently used as emulsifiers for the food and cosmetic industry, having a very low toxicity and eco-friendly chemistry [11–13]. However, the affinity for polar (water) and non-polar (oil) groups is different for each non-ionic surfactant; according to the hydrophilic–lipophilic balance scale (HLB) [14], Tween 80 is hydrophilic (HLB: 15), while Span 20 is more lipophilic (HLB: 8.6).

#### **1.3 Mesquite gum as emulsifier**

Mesquite gum is a vitreous exude, produced by mesquite tree (*Prosopis laevigata*), a widely distributed plant across arid and semiarid zones. This gum is composed of a highly tailored polysaccharide salt, constituted by residues of L-arabinose, D-galactose, 4-O-Methyl-D-glucuronic acid and L-rhamnose (**Figure 3**) [15, 16]. Mesquite gum chemical composition is similar (different molar ratio) to that one of Arabic gum, which is commonly employed in the food and pharmaceutical industry, due its emulsification capacity [17, 18]. In México, mesquite gum is only consumed as a candy, therefore there is a wield field for exploration of this product as emulsifier.

#### **1.4 Citric oil nano-emulsions**

A natural antibacterial extracted from plant or fruit origin is the essential oil, many studies have described this effect [19–21]. Pink Grapefruit

**Figure 2.** *(A) Tween 80 and (B) Span 20 chemical structures.*

**Figure 3.**

*Main constituents of mesquite gum (from left to right): L-arabinose, D-galactose, 4-O-Methyl-D-glucuronic acid and L-rhamnose.*

(*Citrus paradise*) belongs to the Citrus genus, a class of flowering plants in the family Rutaceae [22]. The active constituents exist in this kind of citrus essential oil, such as limonene, a-pinene, b-pinene and a-terpinolene [22, 23]. Its seed and peel extract (essential oil) has shown the antibacterial and antifungal property [24]. Persian lemon (*citrus latifolia tanaka)* is composed of citric, malic and formic acids, as well from pectin, hesperidin, and essential oils as D-limonene (**Figure 4**) and phellandrene, which are the volatile liquid fractions responsible for the characteristic smell of lemon. These compounds can be extracted by distillation, and are commonly employed in the cosmetic, pharmaceutical and food industry [25].

As part of a nano-emulsion, D-limonene has been used as the oil phase of different O/W nano-emulsions. For instance, in the work of Li and Chiang, who have successfully formed D-limonene O/W nano-emulsions phase by an ultrasonic method, using Span 85 and Tween 20 as surfactants [26]. Another example is the work of Donsì et al. [27], who achieved D-limonene nano-emulsions formation through a high pressure homogenizer, using a wide type of emulsifiers. The latter authors have explored the antibacterial properties of these systems by testing against *Escherichia coli* and *lactobacillus delbrueckii*, demonstrating D-limonene nano-emulsion capacity to control and eliminate microbial organisms [27, 28]. As these studies, there are some other investigations about D-limonene nano-emulsions, but none of such studies explores the formulation with a natural emulsifier as mesquite gum.

**49**

*Development of Nano-Emulsions of Essential Citrus Oil Stabilized with Mesquite Gum*

The first stage of the research consists of the characterization of the raw materi-

Mesquite gum was extracted from mesquite pearls obtained from a local candy store at Sonora (Sonora, México). The purification process of the mesquite gum begins with the selection of the cleanest pearls by visual inspection as indicated by literature [17]; afterwards the pearls were ground in a ceramic mortar until a powder was obtained. Then a 20% (wt) solution of this powder was prepared, which was filtered (in order to eliminate impurities like dust and pieces of wood), details

Afterwards, several drying processes were experimented, specifically oven and lyophilization. The drying process by oven was discarded since it was very slow, and in addition, the gum obtained was of a brown tone, indicating a possible degradation of the gum or caramelization. Regarding the lyophilization method, several strategies were tested. First, it was tested with a lyophilized sample at 20%, and a gum with a "sponge" texture was obtained, later this "sponge" gum was re-lyophilized in order to obtain a denser version. Therefore, it was decided to test lyophilized 40% mesquite gum solutions in a controlled manner, this last process was selected to be used for the

To carry out this analysis, the Thermo Nicolet 6700 FT-IR spectrophotometer with its attenuated total reflectance accessory (Thermo Scientific) was used, using

that can be assigned to the primary amides. There is a smaller band around

that can be

can be

 that is assigned to the secondary or substituted amides. The bands of the primary and secondary amides are characteristic of the presence of peptide bonds and

**Figure 5** shows the FT-IR spectra of the different gums characterized in this research, which are largely comparable with the FT-IR spectrum of Arabic gum (GA) reported in the literature [17, 18]. Therefore, it follows that the different mesquite gums produced (oven dried procedure, dense lyophilized and controlled Lyophilized) essentially have the same chemical composition in terms of sugars, amino acids and proteins. Absorbance of the ▬OH and ▬CH groups are observed at 3375 and 2932 cm<sup>−</sup><sup>1</sup> (similar to that reported in the literature [17]), and a band centered between 1650 and

confirm the presence of the protein [17], There is also a band at 1400 cm<sup>−</sup><sup>1</sup>

**2.3 Concentration of aldehydes of citric essential oils**

attributed to a carboxylic group. The bands that are around 1000 and 900 cm<sup>−</sup><sup>1</sup>

attributed to the glycosidic acetal groups of pyranose, according to the literature [17].

The citrus essential oils used during this research were a generous donation from the FRUTECH company. The determination is made by the hydroxylamine hydrochloride method (ISO 1279: 1973). A Titroline Alpha plus automatic titrator from SI Analytics was used to obtain the aldehyde concentration of the citrus oils of pink grapefruit and Persian lemon. Four grams of oil are weighed in a beaker, 50 mL of hydroxylamine hydrochloride solution are added, stirring for 1 minute at 300 rpm, and then it was allowed to rest for 30 minutes. Subsequently, a titration

als (gums and citric essential oils) used in the formulation of nano-emulsions.

*DOI: http://dx.doi.org/10.5772/intechopen.84157*

of the process can be found in literature [12].

production of gum for the nano-emulsions of this research.

**2.2 Infrared spectrum analysis (FT-IR) of the gums**

**2.1 Mesquite gum purification**

solid samples (powders).

1600 cm<sup>−</sup><sup>1</sup>

1500 cm<sup>−</sup><sup>1</sup>

**2. Analysis of the components of a nano-emulsion**

*Development of Nano-Emulsions of Essential Citrus Oil Stabilized with Mesquite Gum DOI: http://dx.doi.org/10.5772/intechopen.84157*
