A comparison of microfluidization and sonication to obtain lemongrass submicron emulsions. Effect of diutan gum concentration as stabilizer

The objective of this work was to develop emulsions containing lemongrass essential oil and Appyclean 6552 (emulsifier). The emulsions were prepared using two different processing techniques: microfluidization and sonication. A decrease in Sauter diameter with ultrasonic power and residence time in sonicator was observed, reaching values of 195 nm. Emulsions obtained by microfluidization presented similar Sauter values at lower pressures but they underwent recoalescence at higher pressures. However, the emulsion processed at the lowest homogenization pressure in microfluidizer showed the best stability. This emulsion was used as a reference to incorporate diutan gum, a thickener. The addition of diutan gum provoked the occurrence of viscoelastic properties, showing a weak gel-like behaviour in all the cases. A trend to cross-over point at lower frequencies was detected for 0.3 and 0.4 g/100 g diutan gum and this point was reached for 0.2 g/100 g diutan gum at 0.65 rad/s. This indicates a higher grade of structuration in more gum concentrated emulsions, leading to enhanced physical stability. Nevertheless, the emulsion formulated with diutan gum above 0.3 g/100 g showed coalescence just after preparation with the subsequent increase of droplet size (above 1 mu m).