The Formation And Stability Of Sweet Orange Oil Nanoemulsions

Nanoemulsions are thermodynamic stability, transparent or translucent dispersions with oil droplet between20and100nm. Sweet orange oils as a kind of flavor oils have unique aromatic flavor, and is widely used in food, cosmetics, daily necessities and medicine. In this paper, the stable nanoemulsions of sweet orange oil were prepared and the changes of main flavor substance during storage were detected. The main findings are listed as follows:By measuring the composition and physicochemical properties of different fold sweet orange oils, we studied the influence of the composition on the formation and stability of oil-in-water emulsions. The results showed that the viscosity, refractive index, and density of orange oils increased as the increasing of oil fold from1to10. The content of citral as a typical flavor substance in orange oils was also increased with increasing of oil fold. The nanoemulsions were highly unstable with lower fold oils and the size of droplets during storage was increasing more quickly than that of high fold oils. The droplet growth of nanoemulsions was attributed to Ostwald ripening. According to the theory of Ostwald ripening, the stability of nanoemulsions with high fold oils may attribute to their highly content of compounds with low water-solubility. These low water-solubility substances in the systems of orange oil nanoemulsions will inhibits Ostwald ripening.The emulsion-titration method was applied to prepare emulsions with different sweet orange oil concentration. The influence of orange oil type and surfactant-to-oil ratio (SOR) on the formation and stability of dispersions were investigated by the measurements of particle size and turbidity. Different types and concentration of surfactant and folds of orange oil were also studied with their influence on the solubilization of oils. The results indicated that at relatively high SORs, all of the orange oil was incorporated into the surfactant micelles. The rate of solubilization increased with the increasing of surfactant concentration. Tween60and Tween80with large Csat values can dissolve more orange oils. The long-term stability of emulsions showed complex behaviors that depending on SOR and storage temperature. The rate of solubilization also increased with the temperature. At the highest storage temperature, the stability of the emulsions reduced due to the droplet coalescence and Ostwald ripening.The process for preparation of sweet orange oil nanoemulsions were optimized by the comparison of different homogeneous pressure, number of cycles, cosufactants, different emulsifier-oil ratio and oil phase. The characteristics of nanoemulsions, such as particle size, size distribution, absorbance and rheological properties, prepared under different conditions were studied. The results showed that with pressure at60MPa and5cycles, the nanoemulsions were more stable. To prepare the nanoemulsions with10%single fold orange oil,20%Tween80as the surfactant and5～10%glycerin as cosufactant were used. The stability of the nanoemulsions with different folds of sweet orange oils were similar. The color of nanoemulsions with5fold and10fold oils were more dark than the single fold oil which will affect the appearance of final products. So it was more suitable to use single fold oil for beverage productionSweet orange oil-in-water nanoemulsions(10%oil,20%Tween80and8%glycerin) were prepared. The nanoemulsions were still transparent and had no layering or flocculation phenomenon after centrifuge. The particle size and absorbance value of the nanoemulsions were not obvious with different treated temperature, and with the increasing of treated temperature. These indicated that the system in20～80℃temperature range was stable and had no phase inversion. In addition, the tolerance of the nanoemulsion of pH, ionic strength and sucrose were widely, and high concentration of ionic strength and sugar could not change its structure. By studying the particle size, static rheological properties and orange oil retention during the storage time, the results showed that the best storage temperature of the nonaemulsions was blow25℃and the emulsification efficiency of orange oil was around96.13%. During the process of emulsification and storage, the monoterpenes in sweet orange oil were highly volatile or unstable and easily loss, and the flavour compounds such as citral, citronellal, octanal, decanal had no obvious change. These showed that the nanoemulsion could retain the flavor substance and reduced the losses during the preparation and storage time.