*Nanoemulsions - Properties, Fabrications and Applications*

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. ~5–10 mNm<sup>−</sup><sup>1</sup> ), leading to formation and dispersion of very small droplets. The 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 external stimulus (being kinetically stabilized) [7] as:


Compared with mechanical methods, physicochemical strategies are considered low-energy methods (~103 Wkg<sup>−</sup><sup>1</sup> vs. ~1010 Wkg<sup>−</sup><sup>1</sup> ); however, they need

**47**

**Figure 2.**

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

very detailed phase behavior studies, which are time consuming. For this reason, high-energy methods may be preferred. Regarding applications, nano-emulsions can be employed in a wide range of fields such [10]: pharmaceutical, cosmetic, automotive and food industry, depending on their physicochemical properties. In this study, citric oil droplets were formed and dispersed in an aqueous continuous phase, using polysorbates as surfactants and a natural gum (mesquite), through an assisted HPH method. The chemistry of the citric oil and nano-emulsion stability allows the application of the formulated systems for antibacterial applications against bacteria such as *Escherichia coli* and *lactobacillus delbrueckii* at studied

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

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

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

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

conditions.

**1.2 Polysorbate surfactants**

lipophilic (HLB: 8.6).

**1.3 Mesquite gum as emulsifier**

exploration of this product as emulsifier.

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

**1.4 Citric oil nano-emulsions**

**Figure 1.** *Typical high pressure homogenizer equipment.*

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

very detailed phase behavior studies, which are time consuming. For this reason, high-energy methods may be preferred. Regarding applications, nano-emulsions can be employed in a wide range of fields such [10]: pharmaceutical, cosmetic, automotive and food industry, depending on their physicochemical properties. In this study, citric oil droplets were formed and dispersed in an aqueous continuous phase, using polysorbates as surfactants and a natural gum (mesquite), through an assisted HPH method. The chemistry of the citric oil and nano-emulsion stability allows the application of the formulated systems for antibacterial applications against bacteria such as *Escherichia coli* and *lactobacillus delbrueckii* at studied conditions.
