Replacing synthetic surfactants by natural alternatives when formulating nanoemulsions has gained attention as a sustainable approach. In this context, nanoemulsions based on sweet almond oil and stabilized by saponin from Quillaja bark with glycerol as cosurfactant were prepared by the high-pressure homogenization method. The effects of oil/water (O/W) ratio, total surfactant amount, and saponin/glycerol ratio on their stability were analyzed. The formation and stabilization of the oil-in-water nanoemulsions were analyzed through the evaluation of stability over time, pH, zeta potential, and particle size distribution analysis. Moreover, a design of experiments was performed to assess the most suitable composition based on particle size and stability parameters. The prepared nanoemulsions are, in general, highly stable over time, showing zeta potential values lower than −40 mV, a slight acid behavior due to the character of the components, and particle size (in volume) in the range of 1.1 to 4.3 µm. Response surface methodology revealed that formulations using an O/W ratio of 10/90 and 1.5 wt% surfactant resulted in lower particle sizes and zeta potential, presenting higher stability. The use of glycerol did not positively affect the formulations, which reinforces the suitability of preparing highly stable nanoemulsions based on natural surfactants such as saponins.

Lignin, the second-most-abundant polymer on Earth, has attracted attention for its value-added applications. Colloidal lignin particles can overcome handling and compatibility issues, offer antioxidant, antimicrobial, and UV-protective properties, and serve as Pickering stabilizers. Plant extracts rich in bioactive compounds, such as polyphenols and flavonoids (e.g., quercetin), can further enhance lignin-based formulations. In this context, colloidal lignin–quercetin particles (CLQPs) were produced for the first time via antisolvent precipitation and used as Pickering emulsion stabilizers. CLQP dispersions (30 g/L) were prepared by solubilizing lignin and quercetin in 80% (v/v) aqueous acetone solution, followed by precipitation with a pH 8 buffer. A quercetin content of 50% (w/w) (CLQP-50) resulted in predominantly round-shaped lignin–quercetin particles (<1 µm) with a small fraction of quercetin crystals. Both structures contributed to emulsion stabilization, as evidenced by confocal microscopy, a three-phase contact angle of 91.6 ± 0.1°, and a zeta potential of −52.8 ± 2.7 mV. CLQP-50 successfully stabilized Pickering emulsions at a 60/40 oil/water ratio, showing high physical stability (stability index 0.01) and shear-thinning behavior with gel-like consistency. These findings demonstrate the pioneering development of lignin–quercetin hybrid colloidal particles as sustainable and functional Pickering stabilizers, opening new opportunities for advanced cosmetic and pharmaceutical formulations.