Structural characterization of hydrogel-oleogel biphasic systems as affected by oleogelators

This work developed novel bi-phasic gel systems containing a hydrogel (κ-carrageenan) and an oleogel, and investigated the roles of different oleogelators (glycerol monostearate-GMS and beeswax-BW) on the structures of the bigels. Stable bigels were obtained via a facile blending approach by carefully controlling the mixing temperature. Microstructural observation indicated that GMS-based bigels were of oil-in-water type, and BW-based bigels were of water-in-oil type. In GMS-based bigels, both water holding capacity and oil holding capacity after freeze-thawing were enhanced with the increase in GMS content. The bigel with 8% (w/w) GMS had water holding capacity and oil holding capacity of 94.81% and 93.13%, respectively. In BW-based bigels, oil holding capacity was also increased (from 36.98% to 88.39%), but separation of oleogel and hydrogel was detected after centrifugation. Textural and rheological analysis revealed that gel strength of the bigels were gradually increased with the increase in oleogelator content, and BW-based bigels were much stronger than GMS-based ones. Moreover, BW-based bigels had higher relaxation degree. DSC analysis found that thermodynamic stability of the bigels were increased with the increase in oleogelator content. Temperature sweep rheological analysis indicated that GMS-based bigels were not able to fully recover their original structure and gel strength after heating-cooling cycle due to the nature of the crystals formed in bigels. This study offered profound structural information about the bigels as affected by different oleogelators, which was also useful for the development of novel functional products.