Characterization, Stability and Antioxidant Activity of Vanilla Nano-Emulsion and Its Complex Essential Oil

As a natural flavoring agent, vanilla essential oil has a special aroma and flavor, but its volatility and instability limit its value. Therefore, in this study, vanilla essential oil was compounded with cinnamon essential oil to prepare nano-emulsions (composite nano-emulsions called C/VT and C/VM), and the stability of the composite essential oil emulsions was investigated. Transmission electron microscopy (TEM) images showed that the nano-emulsions were spherical in shape and some flocs were observed in C/VM and C/VT. The results showed that the average droplet sizes of C/VM and C/VT increased only by 14.99% and 15.01% after heating at 100 °C for 20 min, and the average droplet sizes were less than 120 nm after 24 days of storage at 25 °C. Possibly due to the presence of reticulated flocs, which have a hindering effect on the movement of individual droplets, the instability indices of C/VM and C/VT were reduced by 34.9% and 39.08%, respectively, in comparison to the instability indices of C/VM and C/VT. In addition, the results of antioxidant experimental studies showed that the presence of composite essential oil flocs had no significant effect on the antioxidant capacity. These results indicate that the improved stability of the composite essential oil nano-emulsions is conducive to broadening the application of vanilla essential oil emulsions.