Nanoemulsões de óleos essenciais de Ocimum gratissimum, Cymbopogon citratus e Lippia alba e atividade antibacteriana

Abstract

Nanoemulsions are colloidal dispersions that can be divided into three types, Oil/Water, Water/Oil and bicontinuous, depending on whether oil or water is used as the dispersed phase. The formation of nanoemulsions with essential oils (NE-OE) presents advantages, such as protection against chemical reactions involving oxygen in the degradation of EOs, increased solubility in the aqueous phase, controlled release of bioactive compounds and increased bioactivity due to the increase in surface area of the emulsion. The present study includes an integrative review of the literature and the development of an essential oil nanoemulsion from three aromatic species, Lippia alba, Cymbopogon citratus and Ocimum gratissimum. The integrative review aimed to identify scientific evidence that corroborates the antimicrobial action of essential oil nanoemulsions against antibiotic-resistant pathogenic microorganisms. By applying the integrative review methodology, eleven scientific articles on the antibacterial or antifungal evaluation of essential oil nanoemulsions were selected. The synthesis of the

identified evidence showed that essential oil nanoemulsions are effective in combating multi- resistant microorganisms and in the formation of their biofilms. Factors such as nanoemulsion

droplet size, chemical composition of essential oils and the association of nanoemulsions with antibiotics are discussed. Furthermore, essential oil nanoemulsions showed satisfactory results in in vitro and in vivo evaluations against resistant clinical isolates. Nanoemulsions of essential oils from Ocimum gratissimum, Lippia alba and Cymbopogon citratus were formed using phase inversion temperature methodology. A rotational composite experimental design was used to produce the nanoemulsions of each oil and response surface methodology (RSM) was used to optimize the nanoemulsion preparation conditions. In this study, the effects of essential oil concentration (0.5-2.0 g/L), surfactant concentration (0.2-5 g/L) and temperature (26-94 °C) on the response variable φ (ɛmax/λmax) were investigated. using RSM based on central compound planning (CCD), to evaluate the significance of production parameters and identify the ideal condition that significantly impacted the production of nanoemulsions. The optimization of essential oil nanoemulsions revealed that the concentration of essential oil, surfactant and temperatures for Ocimum gratissimum (1.38 g/L, 0.83 g/L and 54 oC), Lippia alba (1.72 g/L, 0.68 g/L and 54 oC) and Cymbopogon citratus (1.20 g/L, 0.78 g/L and 54 oC) produced ideal nanoemulsions. The optimized C. citratus NE showed an average particle size of 287.9 nm, PDI of 0.42 and Zeta potential of – 8.94 mV. Furthermore, essential oils and optimized nanoemulsions were evaluated for antibacterial activity, where NEs exhibited more potent antibacterial activity than pure essential oil against the pathogenic strains Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecali, showing greater effect bacteriostatic and inhibitory. Among the strains, E. faecali was more susceptible to NEs from C. citratus and O. gratissimum with a minimum inhibitory concentration of 0.075 mg/mL and 0.172 mg/mL, respectively. The nanoemulsions enhanced the bactericidal effect of L. alba essential oils, reducing the MIC of the pure essential oil from 8 mg/mL to 0.445 mg/mL. Furthermore, they showed low cytotoxicity in RAW 264.7 macrophages. The results of this research can provide useful information in the development of nanoemulsions using phase inversion methodology and the antibacterial activity data of essential oils can be useful in the development of a potential antibacterial agent.