Investigation into the physical stability of a eugenol nanoemulsion in the presence of a high content of triglyceride†
The physical stability of a eugenol (Eu) nanoemulsion in the presence of long-chain and medium-chain triglycerides with a high incorporation ratio (30 wt% to 80 wt% in the lipid phase) was investigated. The stability of the nanoemulsion was evaluated by dynamic light scattering and a centrifugal-force-based LUMi-Sizer. With an increase in the content of triglycerides, the particle size of the nanoemulsions decreased first and then increased. The variation pattern of the particle size in the presence of different contents of triglycerides formed a V-type shape. The presence of 60 wt% triglycerides resulted in the smallest particle size, which continued increasing within 28 days of storage. LUMi-Sizer analyses demonstrated that the instability of the nanoemulsion caused by the addition of 30–50 wt% of triglyceride was due to sedimentation of emulsion droplets. On the other hand, the instability caused by 60–80 wt% of triglyceride was due to the floating of emulsion droplets. The interfacial tension variation had the same trend as the particle size variation at the corresponding content of triglycerides. Thus the interfacial tension might be responsible for the triglyceride-caused instability of the Eu nanoemulsion.