Rheology and Stability of Citral/Sugar Microemulsions

Abstract

Microencapsulation of hydrophobic flavors is of great importance in the food industries, since they exhibit good chemical stability and a controlled release. Spray-drying is generally used to produce flavor powders. The objective of this work was to characterize and determine the stability of emulsions formed by citral and several matrices. Focus was put on the interactions between water and matrix solutes, and their impact on the viscosity and emulsion stability. Emulsion continuous phase consisted of sucrose or trehalose with or without maltodextrin (MD); and a modified starch. Citral oil was the dispersed phase. The ingredients were pre-mixed and emulsions were made with a high power mixer. The analysis included the following determinations: pH, flux curves (viscometer), droplet size distribution (laser light scattering), stability (vertical scanner analyzer). The emulsions showed a Newtonian behavior. MD increased the viscosity of the continuous phase. All the emulsions presented a similar droplet size distribution in a range of 0.5-1.5 microns. Samples containing MD showed a higher ratio of smaller droplets. The stability analysis revealed flocculation of the emulsions along time. Samples containing trehalose presented lower flocculation. Carrier systems are usually formulated by combining several components. In the case of citral emulsions that will be spray-dried, a combination of ingredients is necessary to contribute to emulsion formation, aroma retention, and improve stability. The emulsion stability was strongly influenced by the continuous phase viscosity.