The effect of the matrix system in the delivery and in-vitro bioactivity of microencapsulated oregano essential oil

Abstract

Microencapsulation allows bioactive compounds protection from external factors. Innovation in food industry often requires adding functional ingredients, to tailor flavour and texture, to improve preservation, to control bioactive compounds stability and controlled release during processing/storage. Oregano, besides richness in aroma compounds, is also known by potential antioxidant and antimicrobial activities. These sensitive compounds need protection in order to allow their use in a wider range of processes. In this study, oregano essential oil (EO) was microencapsulated by spray/freeze drying in: rice starch (with/without bonding agents), gelatine/sucrose and inulin, dried at different temperatures. Microencapsulates were analysed for morphology and structure (SEM, CLSM, X-ray diffraction and FTIR). Releasing ability of entrapped EO (UV–VIS spectroscopy) was evaluated by diffusion coefficient (D). Antioxidant activity (AA) - ORAC and HORAC- and antimicrobial activities against pathogens were evaluated. Rice starch spherules, presenting interconnecting cavities, were formed. Spray-dried inulin and gelatine/sucrose systems formed continuous walled and smooth surface spherical capsules (3-4.5 and 0.9-10m, respectively). EO was uniformly distributed inside the structures (CLSM) and its presence confirmed by FTIR. Depending on the system, D varied among 10-13 (starch), 10-13-10-15, (gelatine/sucrose) and 10-16 m2/s (inulin). In starch system, D was mainly influenced by the gelatin concentration, increasing with it. X- ray diffraction and FTIR results suggest some kind of linkage between gelatine and starch. Spray-dried gelatine/sucrose system, revealed to be unsuitable for EO encapsulation due to capsules disintegration but freeze-drying was effective. The D of EO from inulin capsules decreases when these are produced above 140 ºC. The impact of encapsulation method on EO bioactivity and product stability during 6 months, was verified through the determination of microcapsules AA, using free EO value as reference. The results obtained provide information on the release/stability of oregano EO from different matrices, relevant for functional ingredients microencapsulation.