Microstructure and physical properties of novel bigel-based foamed emulsions

In this study, a novel ultra-stable bigel-based foamed emulsion was constructed. The bigels were prepared by mixing xanthan gum (XG) hydrogel and oleogel structured by fatty acid mixtures (stearic acid and myristic acid) in different proportions. The foamed emulsion was prepared by whipping the bigel. The influence of oleogel/hydrogel ratio on the microstructure, rheological properties and thermal properties of bigel and bigel-based foamed emulsion were investigated. It was observed that with the increase of oil phase, the system changed from oleogel/hydrogel to bicontinuous, and to hydrogel/oleogel state, which was a typical characteristic of bigel system. The system was observed with higher G′, crystallinity and melting enthalpy when oleogel was the continuous phase. During the whipping process, oleogel changed from the dispersed phase to the continuous phase, even at low oil proportion. The aqueous phase and air bubbles were incorporated into the oleogel matrix as the dispersed phase. When the oil content reached 50%, a uniform bigel-based foamed emulsion with enhanced stability was obtained, where fatty acid crystals serve as the primary stabilizers. Some crystals in the oil phase adsorbed to the air-oil interface, and others formed a continuous 3-dimensional network structure in the bulk phase to stabilize the whole system. The resultant bigel-based foamed emulsion was temperature sensitive. It exhibited ultra-high stability at low temperature, while rapidly collapsed at high temperature (T > Tₘ). These results highlighted the importance of oleogel/hydrogel proportion and fat crystals in formation and properties of the bigel-based foamed emulsions, which assisted in rational design of lipid formulations with distinct texture.