Comparative study of encapsulated peppermint and green tea essential oils in chitosan nanoparticles: Encapsulation, thermal stability, in-vitro release, antioxidant and antibacterial activities

Essential oils (EOs) such as Peppermint oil (PO) and Green Tea oil (GTO) have extensively been reported for their nutritional and biomedical properties. To overcome the sensitivity of EOs to the environmental conditions, nano-encapsulation has emerged as a method to address this limitation. In this work, PO and GTO were encapsulated in chitosan nanoparticles (CS NPs) following emulsification/ionic gelation method. The nano-encapsulated PO (CS/PO NPs) and GTO (CS/GTO NPs) were fully characterized by various methods. Spherical NPs with an average size range of 20–60 nm were revealed by TEM for both systems. The loading capacity reached 22.2% and 23.1%, for PO and GTO, respectively, and the in-vitro release followed a Fickian behavior in different buffer systems. The TGA thermograms of both nano-encapsulated EOs showed an increase in the temperature of maximum degradation rate up to 350 °C. The nano-encapsulation maintained the stability of the total phenolic contents in both EOs, improved the antioxidant activity by ~2 and 2.4-fold for PO and GTO respectively. Surprisingly, the antibacterial activity of CS/GTO NPs was more potent than CS/PO NPs and especially against Staphylococcus aureus with ~9.4 folds improvement compared to pure GTO, and ~4.7 fold against Escherichia coli.