Emulsification by high frequency ultrasound using piezoelectric transducer: Formation and stability of emulsifier free emulsion

• New emulsification process using non-destructive high frequency ultrasound.
• Elaboration of stable emulsifier free emulsion.
• Correlation between particle size, pH and particle charge.
• Effect of size distribution on conductivity of emulsion.

Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10 h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p < 0.05) during the first 6 h of emulsification process and that from 160 to 1 μm for emulsions with 5%, 10% and from 400 to 29 μm for emulsion with 15% of initial oil ratio.For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH− at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH− structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil.