Nanoencapsulated Thymus capitatus essential oil as natural preservative

In the present study, a nanoemulsion was developed to improve the functional performance of Thymus capitatus essential oil (thyme EO) as natural food preservative. Thyme EO was submitted to phytochemical prospection and its safety limit was evaluated by acute oral toxicity. Hereafter, the EO was nanoencapsulated and the antioxidant and antibacterial activities of bulk and encapsulated EO were examined. Results showed that concentrations up to 2 g.kg(-1) b.w. of T. capitatus EO did not present any toxic effects. Moreover, results exhibited an enhancement of nanoencapsulated EO antibacterial activity. In fact, nanoemulsion demonstrated higher growth inhibition diameters than free EO (15.8 and 9.8 mm, against Staphylococcus aureus, respectively). Furthermore, nanoemulsion exhibited significant lower minimum inhibitory concentration against all tested bacteria than bulk EO. However, nanoencapsulating T. capitatus EO decreased significantly its antioxidant activity. Indeed, for DPPH test, free EO IC50 concentrations were considerably lower than those of the nanoencapsulated form (300 and 390 mu g.mu L-1, respectively). As well, the capacity of T. capitatus EO to inhibit the beta-carotene bleaching has been reduced after its nanoencapsulation. These results provide useful information for designing effective natural preservative able to inhibit food bacterial spoilage.