D-optimal design-assisted Elaeis guineensis leaves extract in olive oil-sunflower seed nanoemulsions: development, characterization, and physical stability

A three-factor D-optimal mixture design was used to prepare the Elaeis guineensis leaves extract (EgLE) in olive oil-sunflower seed nanoemulsions. The assessed independent variables were the components of an oil-based nanoemulsion that included oil (8–12%, w/w), Span 80:Brij L23 (28–30%, w/w) and aqueous (56–60% w/w) with mean droplet size (MDS) and polydispersity index (PDI) as the responses. Analysis of variance revealed that both responses fitted a quadratic polynomial model and a residual standard error of <5% indicated good agreement between the experimental and predicted values. Optimal formulation with the lowest MDS and PDI was established to be 10% (w/w) oil, 29% (w/w) Span 80:Brij L23 and aqueous at 58% (w/w). Atomic force micrographs showed the MDS of an optimized EgLE w/o nanoemulsion being <200 nm and was kinetically stable (zeta potential: −30.0 ± 0.7 mV). The system showed satisfactory conductivity (0.70 ± 0.02 µS cm−1) and pH (5.6 ± 0.3), alongside resistance to phase separation under centrifugation and freeze-thaw cycles. The nanoemulsion also exhibited shear thinning and pseudoplastic properties, implying good stability against destabilization by coalescence. It can be construed that the developed EgLE nanoemulsion showed potential as a natural-based personal care product. This is the first report on the preparation of EgLE as bioactive ingredients in a w/o nanoemulsion for topical application.