Nano-enabled-fortification of salad dressings with curcumin: Impact of nanoemulsion-based delivery systems on physicochemical properties

The impact of curcumin-loaded nanodroplets on the properties of commercial salad dressings was examined. Nanoemulsions were formulated using a plant-based oil (medium chain triglycerides, MCT) and either a plantbased (Quillaja saponaria, QS) or animal-based (whey protein isolate, WPI) emulsifier. Curcumin-loaded nanoemulsions produced by microfluidization contained small anionic oil droplets: d32 = 0.28 and 0.11 mu m and zeta = -45 and -42 mV for QS and WPI, respectively (pH 7). The dressing contained larger oil droplets (d32 = 7.8 mu m) with a lower negative charge (zeta = -23 mV). The zeta-potential of the dressing was positive under acid and negative under neutral conditions, suggesting the oil droplets were coated by proteins. At pH 3.4, adding QSnanoemulsions to the dressing reduced the positive charge, but adding WPI-nanoemulsions increased it. The presence of the nanoemulsions decreased the mean particle diameter of the dressing. Incorporation of nanoemulsions (0-30 g/100 g) reduced the viscosity of the dressings, probably because of the reduction in fat content and ability of small oil droplets to get between larger ones. Finally, incorporation of curcumin-loaded nanoemulsions gave the dressings a strong orange/yellow color (negative a*, positive b*) due to selective light absorption by curcumin.