Comparative evaluation of silymarin nanoemulsions stabilized by grape seed and sacha inchi oils: physicochemical stability and enhanced biological activities

Abstract

Silymarin has been facing several challenges which reduce its therapeutic effect, mainly low solubility and poor bioavailability. This study aimed to develop and comparatively evaluate the stability and antioxidant activity of an oil-in-water (O/W) nanoemulsion to encapsulate silymarin, formulated with two distinct natural carriers: grape seed oil (GSO) and Sacha inchi seed oil (SIO). To achieve a stable system, Tween 80 and Poloxamer 407 (F-127) were employed as the primary surfactant and co-stabilizer, respectively, using the phase inversion composition technique at a surfactant-to-oil mass ratio of 1.1:1 (w/w). The resulting optimized formulations demonstrated favorable physicochemical characteristics, including droplet sizes between 300 and 700 nm and PDI values from 0.2 to 0.5. High electrostatic stability was confirmed by negative zeta potentials exceeding −30 mV. The formulations with a lower silymarin content exhibited higher entrapment efficiency compared to those with a higher drug loading. While Fourier transform—infrared and microscopic analyses verified successful encapsulation and uniform morphology, DPPH assays indicated that the nanoemulsions maintained potent radical scavenging activity (52.88 and 13.82%), although they are lower than that of the free silymarin (92.08%) due to the protective encapsulation. Additionally, the use of GSO and SIO significantly enhanced oxidative stability, as reflected by low peroxide levels. These findings highlight SIO as a highly effective and promising platform for the advanced delivery of silymarin, which can be further formulated into popular and convenient dosage forms such as soft gel capsules or nanoemulgels.