Preparation and Sustained-release Antibacterial Activity of Eucalyptus Leaf Essential Oil Pickering Emulsion Stabilized by Modified Attapulgite Nanoparticles and Carboxymethyl Chitosan

For the purpose of enhancing the stability and antibacterial activity of eucalyptus leaf essential oil, a eucalyptus oil Pickering emulsion was fabricated using a mixture of sodium oleate modified attapulgite nanoparticles (M-APT) and carboxymethyl chitosan (CMCS) as a stabilizer. The effects of M-APT, CMCS and essential oil concentration on the emulsion’s stability were evaluated in terms of creaming behavior, micromorphology and rheological properties. The results showed that the modification of APT with sodium oleate increased its contact angles (θ) from 15.2° to 83.7°, which facilitated irreversible adsorption of M-APT nanoparticles onto the surface of oil droplets. The droplet diameter of the emulsion decreased with an increase in M-APT concentration. The hydrophilic CMCS chains were self-assembled to form a 3D network, which encapsulated the M-APT-adsorbed oil droplets. The storage modulus (G’) of the emulsion increased with increasing CMCS concentration, and so did the stability against creaming. Furthermore, the diameters of inhibition zone of the Pickering emulsion against Staphylococcus aureus and Bacillus subtillis were slightly larger than those of eucalyptus essential oil as determined by the agar diffusion method. This could be attributed to the fact that M-APT adsorption onto the oil droplet surface allows for encapsulation of the essential oil, reducing its volatility. The results of bacterial growth kinetics proved the synergistic effect of M-APT and CMCS in encapsulating the essential oil for improved stability and sustained-released antibacterial activity, which is great significance to expand the application of plant essential oil as a biological antibacterial agent.