A Low Energy Approach for the Preparation of Nano-Emulsions with a High Citral-Content Essential Oil.

Suelen F Pereira,Rosa H V Mourão,Adenilson Barroso,Caio P Fernandes

doi:10.3390/molecules26123666

Abstract

Pectis elongata is found in the northern and northeastern regions of Brazil. It is considered a lemongrass due to its citric scent. The remarkable citral content and the wide antimicrobial properties and bioactive features of this terpene make this essential oil (EO) eligible for several industrial purposes, especially in cosmetics and phytotherapics. However, to address the problems regarding citral solubility, nano-emulsification is considered a promising strategy thanks to its improved dispersability. Thus, in this paper we propose a low-energy approach for the development of citral-based nano-emulsions prepared with P. elongata EO. The plant was hydrodistillated to produce the EO, which was characterized with a gas chromatograph coupled to mass spectrometry. The nano-emulsion prepared by a non-heated water titrating (low-energy) method was composed of 5% (w/w) EO, 5% (w/w) non-ionic surfactants and 90% (w/w) deionized water and was analyzed by dynamic light scattering. Levels of citral of around 90% (neral:geranial—4:5) were detected in the EO and no major alteration in the ratio of citral was observed after the nano-emulsification. The nano-emulsion was stable until the 14th day (size around 115 nm and polydispersity index around 0.2) and no major alteration in droplet size was observed within 30 days of storage. Understanding the droplet size distribution as a function of time and correlating it to concepts of compositional ripening, as opposing forces to the conventional Ostwald ripening destabilization mechanism, may open interesting approaches for further industrial application of novel, low-energy, ecofriendly approaches to high citral essential oil-based nano-emulsions based on lemongrass plants.

Highlights

Some species from the genus Pectis are commonly known as lemongrasses due to the citric scent of their volatiles, which are similar to Cymbopogon citratus [1,2]
Despite the fact that some nano-emulsions were successfully generated with a low-energy method involving a heating step—which one would expect to be in accordance with changes in the spontaneous curvature of the non-ionic surfactant associated with the phase inversion temperature method [16]—we decided that this approach should be avoided, due to the intrinsically volatile nature of the essential oil (EO) compounds, and replaced by methods that work in accordance with phase inversion composition concepts [17,18]
It is well-known that diffusion of EO components triggers series of phenomena that can induce an antagonistic mechanism of destabilization (Ostwald ripening) of the opposed force stabilization, both being responsible for further differences in the distribution of the phytochemicals between the internal/external phases [19] and, affecting their ratio

Summary

Introduction

Some species from the genus Pectis are commonly known as lemongrasses due to the citric scent of their volatiles, which are similar to Cymbopogon citratus [1,2]. Pectis elongata is a species found in the northern and northeastern regions of Brazil, and the tea of its aerial parts is commonly used in these regions to treat fever [5] and hypotension and as a calmative. It is used as a replacement of citronella by the Creole population of French Guiana [3]. Despite studies about this species being scarce, indications that two chemotypes—citral (neral- and geranial-rich EO) and perillal (limonene-rich EO)—occur have been reported [3]

Methods

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Discussion

Conclusion