Alginate microspheres containing thyme essential oil alginate microbeads throught a Plackett-Burman design

RIVERO, GUADALUPE; ANSORENA, M. ROBERTA; MARCOVICH, NORMA E. ; PEREDA, MARIANA

Rio de Janeiro

Conferencia; Fifth International Conference on Natural Polymers, Biopolymers and biomaterials: Applications from macro to nanoscale; 2017

The development of microcapsules based on sodium alginate (AL) by the simple extrusion technique, in order to encapsulate essential oils that can become a source of active ingredients for cosmetic products; is proposed. Sodium alginate was chosen because the particles formed in the presence of divalent ions (Ca+2) are non-toxic, biodegradable, biocompatible and highly versatile, and also protects the bioactive components (located in the core) of factors such as heat and humidity, maintaining their stability and bioavailability1-5. Despite the extensive use of alginate as shell for microcapsules, the precise role of many experimental parameters in the resulting capsules features is still not clarified and it needs to be deeply studied. Oil/water (o/w) emulsions were prepared by dispersing thyme essential oil into an alginate solution (1:10 v/v) containing 1% (w/v) of Tween 80®2-4 by magnetic stirring and homogenization.Different homogenization conditions (time and speed) and oil contents were used. The obtained emulsions were in some cases sonicated (0-30 minutes) after the homogenization process. The final emulsions were characterized by using optical microscopy in order to analyze the size distribution of the oil droplets and their stability as a function of time.Results show that the reduction in 75% of the oil content gives smaller and well dispersed droplets. As expected, increasing the homogenization speed also decreased the droplet diameter though certain agglomerations were detected. Further reduction in droplets sizes was found when sonication was applied, leading to much more narrow distribution sizes as the sonication time increases. Moreover, sonication resulted in more stable emulsions in time. The capsules were prepared by the simple extrusion technique by forming droplets in the CaCl2 gelling solution. Dripping was done by using a syringe to inject 2 ml of the AL/oil emulsion in 15 ml of 0.5% w/w of CaCl2 solution (pre-prepared) with continuous stirring at 200 rpm to avoid the coalescence of the pearls. After 15 minutes of gelation, the spherical capsules were collected, filtered, washed with distilled water to avoid external gelation, freeze-dried and characterized microscopically by scanning electron microscopy (SEM). In all cases, the resulting capsules exhibited asymmetrical shapes with similar sizes. No significant differences in the final capsules morphology were detected after the freeze-drying step. However, the washing step was critical to avoid remaining materials on the surface that led to unsmooth capsules.