Preparation of halloysite nanotubes coated with Eudragit for a controlled release of thyme essential oil

Active food packaging that releases active agents can extend the shelf-life and improve the quality and safety of food products. Essential oils have been used as natural food preservatives due to their antioxidant, antimicrobial, and anti-insect properties. However, one of the limitations of using essential oils as active agents is their high volatility. In this study, thyme essential oil, an active antioxidant agent, was encapsulated into halloysite nanotubes (HNTs) using a vacuum process to sustain the release rate and to solidify the thyme oil (TO) from a liquid state. Moreover, the TO-loaded HNT capsules (TO/HNT capsules) were coated with Eudragit EPO polymer to avoid burst release and to prolong the release time. The morphology of the prepared samples was characterized using SEM, TEM, and nitrogen adsorption-desorption analysis by BET method. Zeta potential and FTIR analysis were used to verify the encapsulation of the TO and the Eudragit EPO polymer coating of TO/HNT capsules. After Eudragit EPO polymer coating of TO/HNT capsules, the surface charge of the samples was converted from -17.5 ± 0.2 mV to +19.4 ± 1.5 mV. The amount of encapsulated TO was determined using a GC-FID. Encapsulation efficiency and payload of TO/HNT capsules prepared using 26.7% (w/v) TO solution were 14.94% and 14.58%, respectively. The encapsulated TO was released in a sustained manner for 96 h. In addition, antioxidant activity of the samples was evaluated using a DPPH assay and a reducing power assay. In both two assays, the antioxidant activity of the TO/HNT capsules was increased along with the increasing concentration of TO/HNT capsules.