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Factors affecting the formation of highly concentrated emulsions and nanoemulsions

Artiga-Artigas, María, Montoliu-Boneu, Júlia, Salvia-Trujillo, Laura, Martín-Belloso, Olga
Colloids and surfaces 2019 pp. 123577
bioactive compounds, curcumin, droplets, encapsulation, homogenization, lipophilicity, nanoemulsions, oils, particle size, surfactants, ultrasonic treatment, viscosity
Highly concentrated (HC) emulsions and or submicron emulsions arise as an interesting strategy to encapsulate and transport labile lipophilic bioactive compounds such as curcumin to be further incorporated into food formulations. The main factors affecting HC-emulsions formation and stabilization are the homogenization process, the oil volume fraction (φ) and the surfactant to oil ratio (SOR). Therefore, different HC emulsions were prepared by high-shear homogenization (HSH; 11,000 rpm, 2 min), ultrasonication (US; 100 µm, 20-300 s) or microfluidization (MF; 800 bar, 1-5 cycles) varying the φ from 0.4 to 0.7 (40%-70% w/w) and the SOR from 0.01 to 0.2. HSH led to HC emulsions, whose particle sizes decreased from 14.46 to 2.42 µm (d43), as the φ increased from 0.4 to 0.7. However, US and MF provoked the droplet breakup at oil concentrations over 50% w/w. Additionally, the higher the SOR at a fixed φ, the smaller the particle size of the resultant HC emulsions regardless the homogenization procedure applied. Overall, particle size reduction produced a dramatic increase in emulsion viscosity due to a high packing state of droplets that in turn prevented droplets re-coalescence. Moreover, HC emulsions presented a high curcumin encapsulation efficiency (>70%) and release (> 80 % after 48 h is). Therefore, this work contributes to demonstrate that the small droplets size is governing the apparent viscosity in HC systems, as well as to elucidate the factors affecting their formation to be used as potential carriers of lipophilic bioactive compounds.