Nanoemulsions with sea buckthorn oil and κ-carrageenan

Abstract

The structure, stability, and rheological properties of nanoemulsions with droplets of sea buckthorn oil stabilized with Tween 80 and Span 80 and κ-carrageenan in the aqueous phase were investigated. The fast flocculation and coalescence of oil droplets occurred in nanoemulsions without κ-carrageenan. The nanoemulsion stability was significantly improved in the presence of the gel network at κ-carrageenan concentrations ≥ 0.5 mass%. TEM analysis showed that oil droplet flocs were trapped in the polymer gel network, so the further floc compaction and creaming were prevented. Nanoemulsions without κ-carrageenan and 0.25 mass% κ-carrageenan displayed the Newtonian-like rheological behavior whereas nanoemulsions with 0.5–5.0 mass% κ-carrageenan demonstrated the non-Newtonian flow of the pseudoplastic type. Oscillatory measurements showed that the values of G′ were higher than the corresponding G″ for nanoemulsions with 0.5 and 2 mass% κ-carrageenan in the investigated range of angular frequencies. However, the G′/G″ crossover was detected for nanoemulsion with 5 mass% κ-carrageenan. The structure relaxation was not observed for this nanoemulsion because the gel in the aqueous phase was irreversibly broken under shear. In nanoemulsions with lower κ-carrageenan concentration, the disintegrated structure was recovered with time after shearing. Apparently, the destruction of the oil droplet flocs under the shear was reversible and the elastic structure of the gel was not destroyed.