Characterization of controlled-release Eucalyptus citriodora oil/Zinc ions nanoparticles with enhanced antibacterial properties against E. coli O157:H7 in fruit juice

Eucalyptus citriodora oil (ECO) has excellent antibacterial properties, but its application is limited due to its volatility and lack of antimicrobial targeting properties. Zinc ions are metal ions on which the active center of metalloproteinases depend and have antibacterial functions. This study aimed to prepare nanoparticles against Escherichia coli O157:H7 (E. coli O157:H7) by encapsulating ECO in zein with nano-precipitation method, and chelating zinc metal ions with electrostatic interaction to improve the stability, controlled-release ability and antibacterial ability of nanoparticles. Herein, the antibacterial mechanism of ECO against E. coli O157:H7 was investigated from the molecular level. The results of molecular docking showed that ECO inhibited the activity of G6PDH in respiratory metabolism pathway (hexose monophophate pathway), and also inhibited the DNA polymerase. Furthermore, we demonstrated that the controlled-release nanoparticles (ECO/Zn2+-loaded NPT) possessed suitable particle size (275.43 nm), poly dispersity index (PDI, 0.254), zeta potential (-31.12 mV) and chelation rate (42.3 %). The results of Fourier Transform Infrared spectrometer (FT-IR), and Raman spectrum confirmed that ECO was successfully encapsulated in the nanoparticles. Meanwhile, the results of antibacterial experiments showed that ECO/Zn2+-loaded NPT possessed better antibacterial activity than ECO/zein nanoparticles. Finally, the test of application in fruit juice indicated that ECO/Zn2+-loaded NPT had no significant effect on physico-chemical properties and exhibited potential application in juice preservation.