Essential oil from Otacanthus azureus (Linden) Ronse: preparation of a bioactive nanoemulsion through a low-energy/solvent-free/non-heating method

Óleo essencial de Otacanthus azureus (Linden) Ronse: preparação de uma nanoemulsão bioativa através de método de baixa energia, livre de solvente e sem aquecimento

Oil-in-water nanoemulsions are in the spotlight of novelty for viable herbal derivatives, being a valuable strategy for better availability of poor-water soluble compounds. The present study shows the preparation of a nanoemulsion with the essential oil of Otacanthus azureus. The systems were constituted by 90% (w/w) of water, 5% (w/w) of essential oil and 5% (w/w) of surfactant (s). The analysis by gas-chromatograph revealed a predominance of mono- and sesquiterpenes. No major droplet growth was observed for the nanoemulsion prepared with polysorbate 80 during 30 days of storage, remaining around 130 nm. A remarkable improvement of antibacterial activity was observed, especially against S. aureus as follows: MIC = 0.050 and MBC = 0.1 for the essential oil, and MIC – 0.025 and MBC = 0.025 for the nanoemulsion. In conclusion, it must be highlighted that the utilization of a low energy/solvent-free/non-heating method was a suitable ecofriendly approach, suggesting the great potential of this plant based nanoemulsion.

Keywords:
antimicrobial; low cost; Otacanthus azureus; terpenoids