Phytoactive essential oils-composed water-free organogels: development, characterization and proof of antibacterial activity

The aim of this work was the development and characterization of a waterless organogel formulation, based on phytoactives from essential oils known for their antimicrobial and anti-inflammatory activities. Lentisk tree (Pistacia lentiscus L.), yarrow (Achillea millefolium L.) and myrtle (Myrtus communis L.) grow in the mild climate of Euroasia and are receiving particular attention for their medicinal and aromatic value. Two distinct concentrations of selected essential oils (EOs) were tested, dispersed in organogels based on 3% (m/V) Carbopol 974P NF in PEG 400. Prior to formulation development, selected EOs were characterized by mass spectroscopy to identify the dominating bioactives. A total of 32 compounds were quantified for lentisk leaf EO, 42 for yarrow EO, and 26 for myrtle leaf EO. The best formulations were found for the highest concentration of EOs (4%, m/m) into Carbopol/PEG400 organogels. Organogels were produced by high-speed homogenization followed by microwave heating and showed acceptable pH between 5.8 – 6.0, being compatible with the skin, with an electrical conductivity highest for yarrow EO-based organogel (YIG4%, ∼ 64 mV), and the lowest for myrtle EO-based organogel (MIG4%, ∼ 48 mV). Texture analysis showed the highest adhesion properties for lentisk EO-based organogel (LIG 4%), attributed to its higher viscosity recorded for the two tested temperatures (25ºC vs 37ºC). Rheological analysis confirmed that organogels have pseudoplastic behaviour. The antibacterial activity was compared between plain EOs and EOs-based organogels, with the yarrow EO and its organogel (YIG 4%) depicting the highest activity against both tested bacterial strains (S. aureus and C. acnes). On the other hand, MIG 4% contributed for the highest cell proliferation rate tested in mouse embryo fibroblast cell (3T3-L1) cell line, whereas with LIG 4% the lowest viability value was recorded.