Surfactant-free nano-emulsions from two lemongrass essential oils: Investigation of temperature ramp influence

Abstract

Nano-emulsions are alternatives for incorporation of essential oils in food-products. Despite generation of surfactant-free nano-emulsions is well known (e.g., Ouzo effect) its stabilization is a critical issue. This study shows the behavior of surfactant-free nano-emulsions prepared with two lemongrass essential oils based in dynamic light scattering analysis through exposure to a linear ramp of temperature. The gas-chromatography coupled to mass-spectrometry analysis revealed that β-myrcene was found in the Cymbopogon citratus and absent in C. flexuosus. C. citratus nano-emulsion prepared with deionized water (CCNE-DW) presented initial lower size diameter (208.6 ± 1.9 nm) than C. flexuosus nano-emulsion (245.2 ± 3.1 nm) prepared with deionized water (CFNE-DW), probably due to the presence of β-myrcene capable of avoiding a rapid droplet growth before onset of dynamic light scattering measurements. In silico physicochemical properties suggest that β-myrcene could considered decisive for low size of C. citratus nano-emulsions, since reduction of its concentration may induce destabilization of C. citratus diluted nano-emulsions. Similar initial droplet size was observed for C. citratus nano-emulsion (221.0 ± 1.3 nm) prepared with infusion (CCNE-IN) and C. flexuosus nano-emulsion (215.7 ± 1.7 nm) prepared with infusion (CFNE-IN). The highest droplet reduction was observed for CFNE-DW (DR25–80ºC = 45.9 %; p<0.0001). Distinct phytochemical profile evidenced by 1H NMR, since C. citratus infusion shows an envelope of signals with more overlapped peaks between the chemical shifts at δH 3.5 – 4.0 ppm, may favored solubilization of droplet components by the infusion and responsible by droplet growth of diluted nano-emulsions, in addition to decrease of β-myrcene content. Our results show the feasibility of preparation of surfactant-free nano-emulsions from two lemongrass and contribute to better knowledge related to influence of chemical profiles in natural-product based nano-emulsions.