Alginate-based beads: encapsulation of sage essential oil by electrostatic extrusion

Recently, various techniques have been developed for encapsulating bioactive compounds to convert them into a more stable form. One of them is electrostatic extrusion, which is highly recommended for hydrophobic bioactive compounds such as essential oils (EOs). Among the various polymers, alginate is most commonly used as a core material. This is a naturally occurring polysaccharide found in brown algae and is characterized by high viscosity, gelling properties, high stability, low cost and non-toxicity. Sage (Salvia officinalis L.) is a perennial aromatic and medicinal plant of the Lamiaceae family. In addition to various phytochemicals, it also contains EOs which are found to have antioxidant, antimicrobial, antifungal, insecticidal and antiproliferative properties. Therefore, this study investigated the development of alginate-based beads containing sage EO prepared by electrostatic extrusion. For the preparation of beads, the content of alginate (0.5, 1 and 1.5%, w/v) and calcium chloride (CaCl2) (3 and 5%, w/v) was varied. Alginic acid sodium salt (low viscosity), previously dissolved in distilled water, sage EO (5%, w/v) and Tween 20 (0.5%, w/v) were homogenized at 10 000 rpm for 4 min. Beads were prepared with Büchi encapsulator B-390 (Flawil Switzerland) using a 1 mm stainless steel needle at a frequency of 80 Hz, a pressure of 1000 mbar, an amplitude of 6 and an electrostatic potential of 500 V. After collection in CaCl2 solution, the beads were washed in distilled water, drained and used for further analysis. Encapsulation yield (%) was expressed as the ratio between the amount of beads obtained and the amount of emulsion used for the encapsulation. The size of the beads was measured using a micrometer screw gauge and the average dmax, dmin and sphericity factor (SF) were calculated. All analyzed parameters were significantly affected by alginate and CaCl2 content, except for SF (Table 1). The highest encapsulation yield and bead size were obtained at the highest concentrations of alginate and CaCl2. In addition, the beads generally maintained their roundness. Although not significant, most spherical beads were produced with 1.5% alginate, while a lower CaCl2 content resulted in slightly elongated shape of the beads.