Influence of the Acidity of Olive Oil on the Stability of O/W Nanoemulsions

This study examines how olive oil acidity affects the stability of oil-in-water (O/W) nanoemulsions. Nanoemulsions were prepared using oils of 0.33, 4.67, and 12.66% w/w acidity, at 5, 10 and 15% v/v oil and 1.0, 1.5 and 2.0% v/v Tween-80, and stored for 120 h at 25 °C. High-acidity oil (12.66% w/w) produced the most stable systems, with conductivity reduced by ~40–60% compared to low-acidity oils (e.g., 31–52 μS/cm vs. 80–145 μS/cm at 10–15% oil). Viscosity ranged from 1.55 mPa·s at 0.33% w/w to 1.87 mPa·s at 12.66% w/w. The optimal formulation—12.66% w/w acidity, 5% v/v oil, and 1.0% v/v Tween-80—yielded the smallest and most stable droplets, with low PDI (~0.26) and high negative ζ-potential (−36 to −44 mV). These results indicate that elevated free fatty acids and endogenous amphiphilic compounds can act as co-surfactants, enhancing interfacial stabilization and improving nanoemulsion performance.