Antimicrobial efficacy of Thymbra capitata (L.) Cav. essential oil loaded in self-assembled zein nanoparticles in combination with heat

This study reports on the chemical composition of Thymbra capitata essential oil (TCEO) and its antimicrobial activity when applied with heat either as a suspension (s-TCEO) or loaded in self-assembled zein nanoparticles (zn-TCEO). Zein, a plant protein isolated from corn and maize, is proposed as natural, and biocompatible carrier. TCEO composition was analysed by GC–MS, and 35 components were identified. Carvacrol, a monoterpenoid, was the major constituent (73.8%). zn-TCEO were prepared under low shear conditions and characterized according to droplet size (<180 nm) and encapsulation efficiency (77.8%). The two TCEO formulations (s-TCEO and zn-TCEO) were compared in terms of antibacterial activity against Escherichia coli O157:H7 Sakai and Listeria monocytogenes EGD-e. The zn-TCEO displayed a greater bacteriostatic activity than s-TCEO, probably due to their improved dispersion in the growth media. However, zn-TCEO exerted a lower bactericidal activity than s-TCEO, probably due to the EO progressive release. The combination of TCEO and heat (53 °C) exerted valuable synergistic lethal effects, causing the death of up to 5 log10 cycles of both microorganisms. The effectiveness of zn-TCEO was especially improved at pH 4.0. Therefore, the application of this new delivery system, designed to encapsulate and protect EOs, and ensure their controlled release, might represent an advantageous alternative for food, cosmetic or pharmaceutical industries to improve the efficacy of higienization processes or surface cleaning and disinfection procedures when combined with mild heat.