Development of a Dermal Nanoemulsion with Antioxidants Derived from Rice Residues Using an HLD Theory Approach

Agricultural waste, such as rice straw, has become increasingly valuable as biocomposites in various industries. For cosmetic and pharmaceutical sectors, these biocomposites have improved active substance incorporation and waste reduction, which is pivotal for mitigating environmental impact. This study reports the encapsulation of a protein derivative derived from rice straw within a nanoemulsion for skin care applications, emphasizing stability and efficacy. Protein hydrolysates were produced by extracting proteins in an alkaline medium, followed by precipitation at the isoelectric point. The hydrolysates were enzymatically treated with Alcalase® at 80 °C and pH 10 for 45 min to generate antioxidant-rich formulations. Utilizing Hydrophilic-Lipophilic Deviation (HLD) theory, oil-in-water (O/W) emulsions were formulated by adjusting variables to achieve an HLD near zero. Sunflower oil and surfactants were combined, stirred at 70 °C, and homogenized using a rotor-stator. The final formulation's stability and permeability were evaluated through fluorescence microscopy, particle size analysis, zeta potential measurements, and accelerated stability assays. Nanoemulsion ENE37 showed high stability with 47.25 nm size, PDI 0.21, and excellent dispersion, maintaining integrity without phase separation. Hydrolyzed protein into ENE37 (NE37-HP) improved stability, increasing zeta potential and preventing aggregation while maintaining structure without phase inversion. NE37-HP exhibited shear-thinning behavior and good diffusion capacity, achieving 20.14 μg/cm².h. The HLD theory and ternary diagrams are valuable methodological tools for formulating stable nanoscale emulsions. Additionally, this dosage form, containing protein hydrolysates derived from rice straw, demonstrated potential for adequate dermal absorption in humans.