Preparation of Thymus vulgaris Essential Oil Microcapsules by Complex Coacervation and Direct Emulsion: Synthesis, Characterization and Controlled Release Properties

This study examines the preparation and characterization of Thymus vulgaris (L.) essential oil (TEO) microcapsules obtained by complex coacervation and direct emulsion techniques. The extraction yield of TEO for this study was 1.64% with Thymol (56.38%) and carvacrol (23.84%) as dominant components. The synthesis protocol was conducted with different polymer/polysaccharide mass ratios, essential oils quantities and cross-linking agent. Optical microscopy images of the microcapsules show spherical shape for particles of different diameters ranging from 5 to 50 μm. SEM analysis shows that the best results were obtained with a polymers ratio of 7%:8% and formaldehyde as cross-linking agent. The encapsulation yield is 65.67 and 98% for complex coacervation and direct emulsion, respectively. The encapsulation efficiency reveals that the amount of oxygenated monoterpenes encapsulated represents 78.34–74.31% of the total coated amount. Monoterpenes hydrocarbons represent 16.03–19.77%, followed by sesquiterpenes hydrocarbons at 3.7–4.2% for complex coacervation and direct emulsion, respectively. This result confirms that encapsulation efficiency can be related to the polarity of each TEO component. All results support the success of TEO encapsulation in terms of storage, protection and release, with lower thermal stability and faster TEO release kinetic for direct emulsion encapsulation. This result contrasts with complex coacervation, which provides a slower release profile and better thermal stability.