Stability of lime essential oil emulsion prepared using biopolymers and ultrasound treatment

The objective of this study was to investigate the kinetic stability of lime essential oil emulsion using gum arabic (GA) and whey protein isolate (WPI) biopolymers as emulsifiers and stabilizers. Different solid compositions were evaluated: GA, GA/WPI (1:1) and WPI, as well as oil concentration (5.0, 7.5 and 10% w/w). Emulsions were prepared using an ultrasonic homogenizer. Viscosity, oil droplet size, zeta potential, pH and conductivity were measured to predict the emulsion stability over a period of 4 h (estimated time until complete drying in microencapsulation processes). Emulsion rheological behaviour and microstructure were characterized. All emulsions were stable during the time period analysed, and no destabilization characteristic was observed. The pH, conductivity and viscosity showed no significant difference (p>0.05) over the 4-h period. Emulsions with WPI showed higher zeta potential values, confirming the biopolymer electrosteric stabilization. The combination of wall materials (GA/WPI) and the oil concentration increased the average droplet size. The results of the apparent viscosity at shear rate of 100s(-1) confirmed the emulsions stability. These values did not change significantly considering the fresh emulsions and emulsions after 4h of preparation. The emulsifying biopolymers showed to be excellent natural stabilizers for lime essential oil emulsions, highlighting the results using WPI.