Composition and Efficacy of Essential Oil Nanoemulsions

Introduction

Paracelsus von Hohenheim, who entitled “Quinta essential” for the effective component present in the drug, was the first person ever to use the term “ESSENTIAL OIL”, in the 16^th century (Guenther, 1952). Essential oils are defined as a complex, but diverse group of volatile aromatic compounds extracted from non-woody plant materials extensively (Edris, 2007). In general, essential oil resides in specialized structures present in the surfaces of plants such as secretory glandules or internal compartments like large vacuoles, owing to their elevated molecular reactivity (Dima & Dima., 2015). It’s regarded to acquire a wide range array of biological activities, like a pool of phytochemicals that could be isolated from different parts of the plant (Burt., 2004). In particular, it exhibits a high level of antibacterial as well as antifungal activities. This is because, the major component of EO comprises a wide range array of aldehyde, alcohols, esters, hydrocarbons (aliphatic) which are low in molecular weight, followed by terpenoids, especially monoterpenes (C10), sesquiterpenes (C15), and diterpenes (C20) (Dorman & Deans, 2000; Jones, 1996; LisBalchin & Deans, 1997) (FIG 1). However, their composition might vary as per their biological and chemical inception and to the diverse processing methods which could be subjected, for extraction and purification process (Sharma & Tripathi, 2008).

Figure 1.

Representative structures typical for oregano essential oil present in the nanoemulsion. It comprises Carvacrol, Thymol, Gamma terpinene & beta-fenchyl alcohol (from clockwise)

The antibacterial attributes of essential oil are attributed to the phenolic compounds present in it (Cosentino et al., 1999). In particular, the acquisition of various compounds by the essential oil are characterized by a distinct mode of activity, which relies on the nature of the specific bio-active molecule (Di Pasqua et al., 2007). Additionally, several pieces of literature proposed the antagonistic mechanisms carried out by these EO’s which are: (a) Cell wall degradation (b) Vandalization of the plasma membrane (c) Creating deterioration to the proteins of the membrane (d) Exudation of cellular components (e) Cytoplasm condensation and Proton motive force exhaustion (Burt, 2004) (FIG 4). For an instance, carvacrol, a phenolic compound, likely enacts as protonophore, i.e., a proton transporter across the phospholipid bilayer, thereby the proton motive force is dispersed (Lambert et al., 2001; Ultee et al., 2002). Additionally, the synergistic action between various components present in the essential oil is said to improve the bio-efficacy and preventing the progress of aversion in microorganisms (Basak & Guha, 2018). Essential oils have their own huge set of commercial applications, since consumer’s demand for natural in preference to the synthesized additives are on a steep rise, provided that the essential oils are regarded as “Natural” components (Chang et al., 2011 & 2012). About 3000 Essential oils are estimated to be present and well-recognized, of which 300 oils are traded extensively (Freires, Denny, Benso, de Alencar, Rosalen., 2015). Although essential oils exhibit superior antibacterial, antifungal, insecticidal, antioxidant & therapeutic properties, practical application is greatly limited and remains challenging since these EO’s are highly volatile & exhibits a frequent tendency to degrade as a result of oxidation via treatment to heat, light, oxygen, humidity, directly (Bilia et al., 2014) (FIG 2 & 3).