Fabrication and characterization of chitosan nanoemulsions loading thymol or thyme essential oil for the preservation of refrigerated pork

The purposes of this study were to develop stable thyme essential oil chitosan nanoemulsions (TEO-CSs) and thymol chitosan nanoemulsions (T-CSs), and to evaluate their characterization and antibacterial properties. The effects of the TEO-CSs and T-CSs on preservation of refrigerated pork at 4 °C were also assessed. The results indicated that the mean particle size values of the TEO-CSs and T-CSs were 139.47 and 123.30 nm, and the encapsulation efficiencies were 80.99% and 70.72%. The absolute zeta potential values of the TEO-CSs and T-CSs were 30.87 and 32.42 mV respectively, indicating that the stable TEO-CSs and T-CSs were fabricated. The information on FTIR, XRD and TGA inferred that chitosan was physically mixed with thymol and TEO without chemical reaction, and the antibacterial properties of thymol and TEO still remained. Furthermore, the antibacterial assays verified that the TEO-CSs and T-CSs strongly inhibited Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) planktonic bacteria and biofilms. Fresh pork treated with the TEO-CSs and T-CSs had significantly improved color parameters (a⁎, b⁎, L⁎ and ΔE values) during storage at 4 °C. The TEO-CSs and T-CSs effectively extended the shelf life of refrigerated pork to more than 6 days by measuring the pH values and total viable count (TVC) of bacteria. Our results highlighted that the TEO-CSs and T-CSs, as natural novel antibacterial packaging materials, had outstanding antibacterial activities and effectively preserved food.