Nanoemulsions of essential oils stabilized with saponins exhibiting antibacterial and antioxidative properties

Functional foods, drug delivery systems, and cosmetics are the main areas of application for multiphase systems, where the use of naturally derived compounds is preferred. Hence, this study aimed to assess the possibility of using natural surfactants and saponin-rich extracts to produce emulsions containing antibacterial and antioxidant cinnamon and clove essential oils (EOs). The analyses of nanoparticles using dynamic light scattering showed that the addition of plant extracts to solutions allows one to obtain stable emulsions and decreased zeta potential (< −40 mV) and droplet size (<200 nm). In all investigated emulsions, the increase of antioxidative properties was observed when both EOs and plant extracts were used. The emulsion with clove oil stabilized with Quillaja saponaria bark saponins has the highest combined antioxidative properties (3.55 ± 0.01 μg gallic acid equivalent per g). Additionally, a stronger antibacterial action against Pseudomonas bacteria was observed for clove oil with Quillaja saponaria and cinnamon oil with Glycyrrhiza glabra. In addition, plant extracts did not affect significantly the other properties of the oil emulsions, e.g. wettability, colour, and refractive index. All results show that the proposed emulsions can be helpful in the preparation of multifunctional emulsions, where the co-action of saponins and EOs is especially beneficial.