Cutoff Ostwald ripening stability of eugenol-in-water emulsion by co-stabilization method and antibacterial activity evaluation

Abstract

Essential oil-loaded emulsion is known to be unstable against Ostwald ripening. Hence, aiming to cut off this phenomenon, we fabricated eugenol-in-water emulsion by using co-stabilization method including interfacial layer formed by cinnamaldehyde/chitosan (CA-chitosan) and surfactant of glycerol monocaprylate (GMC). Oiling-off occurred in the emulsion with GMC as the sole stabilizer. While only white precipitates appeared in the CA-chitosan-stabilized emulsions due to the higher density of eugenol. In the presence of co-stabilizers, the particle size of emulsions showed unimodal distribution and kept almost constant within three months. Although there were some white precipitates in the emulsion after long-time storage, oil droplets still kept intact under optical microscopy. This result indicated that co-stabilizers could help to suppress the process of Ostwald ripening. The addition of polyvinyl alcohol effectively enhanced the stability of emulsions against gravitational separation. Eugenol emulsions kept stable even when eugenol content was up to 5 and 10 wt%. Antibacterial assay and time-kill experiment indicated that encapsulated eugenol had better antibacterial activity and long-term antibacterial efficiency, as compared to free eugenol. The obtained knowledge provides a novel technique to prepare eugenol-in-water emulsions, which has good long-term stability and antibacterial activity.