Microencapsulation of oregano essential oil in starch-based materials using supercritical fluid technology

• Oregano essential oil was encapsulated in sorghum and rice starch by impregnation.
• Supercritical carbon dioxide at 40 °C and 10 MPa was used as green solvent.
• Impregnation time, oil to starch mass ratio and depressurization mode were studied.
• Mild operating conditions avoid essential oil degradation.
• Product quality was assured by high ORAC antioxidant activity values and stability.

Oregano (Origanum vulgare) essential oil (EO), besides its flavoring characteristics, is well known for its antioxidant, antimicrobial and anti-inflammatory properties, which make it a good alternative as food preservative from natural origin. Furthermore, it has been reported that oregano EO can be used as a health promoting substance in the prevention of neurodegenerative disorders. However, EO can be easily degraded by light, oxygen and temperature and there is still a lack of an adequate protection system to improve its stability along processing.In the present study, oregano essential oil was impregnated in microspheres of different types of starch using SSI (supercritical solvent impregnation) with supercritical carbon dioxide (sc-CO2). This process is characterized by mild operating conditions and inert processing atmosphere, especially adequate for the formulation of EOs. The quality of the final product and process efficiency was evaluated by the antioxidant activity (AA) of the final product, determined according to the ORAC assay. Different processing conditions were studied, such as pressure (8–15 MPa), temperature (40–50 °C), impregnation time (3–24 h) and mass ratio of essential oil/starch (0.4–3). The SSI is a batch process and the influence of mode of depressurization was also analyzed.Industrial relevanceThe present study demonstrates that supercritical impregnation is an attractive process for the impregnation of natural matrices, such as starch granules, with essential oils (EOs), namely oregano essential oil. The mild operating conditions avoid EO degradation and the high diffusivity of supercritical CO2 in the solid matrix (starch) guarantees a deep impregnation of the EO and high antioxidant activity of the product, also during storage. Further, the process is easy to scale up for the production of potential health-promoting ingredients for the food industry.