Abstract
In this study several essential oils (EOs): basil - BA, lemon balm - LB and oregano - OR were incorporated into nanoemulsions (NEs) as prospective carriers for natural and sensitive bioactives. NEs were prepared via the phase inversion composition (PIC) method, which is an energy-efficient cold process. Physicochemical stability of NEs was confirmed by particle size distribution analysis, electrical conductivity and pH value measurements, as well as by optical microscopy observations. The type of EO and the surfactant and oil mix concentration were found to be crucial factors governing the NE properties and stability. Raman spectra of the EOs confirmed main active ingredients and provided detection of interactions with the nanocarrier, which is a novel application of this technique. The antioxidant activity towards DPPH radical in methanol was concentration-dependent with a similar trend for individual oils and oil-loaded NEs (OR> LB> BA). However, the ABTS test in an aqueous medium revealed notable change in the order of activity after EO nanonisation at higher EO concentrations. Overall, it was found that OR-NE was the most effective and stable system, since OR acted as a co-stabiliser in the NE formulation, and its remarkably high antioxidant activity was successfully preserved during 6 months of storage.
Highlights
Aromatic plants have been used since ancient times as a source of essential oils (EOs), which are known as natural remedies in traditional medicine systems – phytotherapy and aromatherapy
Besides antimicrobial action [22], EOs prepared from basil - BA, oregano - OR and lemon balm - LB leaves are reported to scavenge free radicals [9,23−25]
These particular EOs and their bioactives could be good candidates for topical formulations intended for antioxidant skin protection
Summary
Aromatic plants have been used since ancient times as a source of essential oils (EOs), which are known as natural remedies in traditional medicine systems – phytotherapy and aromatherapy. They are widely used for everyday purposes, for example, as fragrant components in skincare preparations and perfumery, and as flavouring agents and natural preservatives in food industry [1−3]. Despite the renewed popularity of EOs in personal care and pharmaceutical products, their volatile nature and sensitivity to heat, light and air require optimised formulations to preserve the activity and to avoid side effects related to the usage [2−4,6]. Since EOs have to be diluted for the use, different carrier systems such emulsions [7] and nanoemulsions [8,9] are proposed as a convenient solution for oil solubilization into the aqueous-based, oil-in-water
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