We developed a facile preparation method of oil-in-water
(O/W)
Pickering emulsion in an emollient formulation using basil extract
(Ocimum americanumL.) as a solid particle
stabilizer by fine-tuning the concentration and mixing steps of common
cosmetic formulas, such as humectants (hexylene glycol and glycerol),
surfactant (Tween 20), and moisturizer (urea). The hydrophobicity
of the main phenolic compounds of basil extract (BE), namely, salvigenin,
eupatorin, rosmarinic acid, and lariciresinol, supported high interfacial
coverage to prevent coalescence of globules. Meanwhile, the presence
of carboxyl and hydroxyl groups of these compounds provides active
sites for stabilizing the emulsion using urea through the formation
of hydrogen bonds. Addition of humectants directed the in situ synthesis
of colloidal particles during emulsification. In addition, the presence
of Tween 20 can simultaneously reduce the surface tension of the oil
but tends to inhibit the adsorption of solid particles at high concentrations,
which otherwise formed colloidal particles in water. The level of
urea and Tween 20 determined the stabilization system of the O/W emulsion,
whether interfacial solid adsorption (Pickering emulsion, PE) or colloidal
network (CN). Variation of the partition coefficient of the phenolic
compounds present in basil extract facilitated the formation of a
mixed PE and CN system with better stability. The addition of excess
urea induced interfacial solid particle detachment, which caused the
oil droplet enlargement. The choice of stabilization system determined
the control of antioxidant activity, diffusion through lipid membranes,
and cellular antiaging effects in UV-B-irradiated fibroblasts. Particle
sizes of less than 200 nm were found in both stabilization systems,
which is beneficial for maximizing their effects. In conclusion, this
study provides a technological platform to realize the demand for
natural dermal cosmetic and pharmaceutical products with strong antiaging
effects.