Release of Thyme Oil from Polylactide Microcapsules

Abstract

Microencapsulation reveals numerous advantages over conventional applications of flavors or fragrances. Thus, the goal of this work was to study the release rate of thyme oil through the polylactide (PLA) microcapsules prepared by coacervation. Microcapsules have spherical shape and a mean particle size of 36 μm. The results show that the release of thymol is faster in the first hour and remains almost constant in the next days. Moreover, it was observed that the release of the polar compounds of thyme oil is faster than the apolar ones. The diffusion coefficient in the first hour of release was 1.39 × 10–15 m2/s for thymol and 5.21 × 10–17 m2/s for p-cymene. For a period of 5 days, diffusion coefficients of 3.81 × 10–17 m2/s for thymol and 1.43 × 10–18 m2/s for cymene were determined. The diffusion of thyme oil from the PLA cross-linked membrane was dependent on the microcapsules morphological characteristics.

Microencapsulation of essential oils with biodegradable polymeric carriers for cosmetic applications

“…Furthermore, for the apolar component, p-cymene, the diffusion coefficient for the first hour of release is lower than that obtained for thymol. This behavior is in accordance with the previously observed by Wischke and Schwendeman, where the release differences were attributed to the distinct hydrophobic characteristics of the two compounds [68,96].…”

“…For example, Fig. 10 shows optical and cryogenic scanning electron microscopy images of PLA microcapsules with thyme oil reported by Martins et al [37,56,96]. Images obtained through optical microscopy demonstrate that droplets of thyme oil have been individually encapsulated as spherical particles with-out noticeable agglomeration.…”

“…In what concerns the release profile of thymol (major polar compound of thyme oil) from the PLA microcapsules it can be explained by a diffusion mechanism, in accordance with the developed model and was found to be in good agreement with the experimental measurements. Adapted from Martins et al [96]. Table 1 Patent processes for microencapsulation by coacervation.…”

“…The diffusion of thymol through the nanofibrous samples could be divided into two phases: thymol released before 12 h and then between 12 and 48 h, where the burst and rapid release of thymol was related to the adsorption and rapid diffusion of it from the surface of the nanofibrous samples. The release studies performed by Martins et al [96,129] con-tribute to develop a diffusion model for thyme oil compounds across the PLA shell. The release tests allowing determining the corresponding diffusion coefficients and thus describing the re-lease behavior with time.…”

Determination of microcapsule physicochemical, structural, and mechanical properties

“…However, a clear drawback is the large amount of time it takes to image single samples and conduct subsequent image analysis. Because of this, and because it is extremely difficult to get the whole sample in the field of view, microscopy is largely used for individual size analysis and seldom for size distribution analysis, which is usually performed using reliable, repeatable laser diffraction techniques (Chen & Zhou, 2015;Long, Song, York, Zhang, & Preece, 2013;Martins, Rodrigues, Barreiro, & Rodrigues, 2011;Mokarram, Mortazavi, Najafi, & Shahidi, 2009), and DLS if the particles of interest are submicron. Optical (light) microscopy is the simplest method in terms of sample preparation and operation, but it is limited by the minimum wavelength of visible light (400 nm).…”