Alginate-based gel beads with bigel structures: Preparation, characterization and bioactive encapsulation

The current study developed novel gel beads with bigel structures based on alginate hydrogel and glycerol monostearate oleogel. Bigel beads with different structures were prepared by varying oleogel content, and the beads were also used to co-encapsulate lipophilic and hydrophilic biaoctives. All the beads had high sphericity (>0.94), and the bead size was increased with the increase in oleogel content. Beads with higher content of oleogel had lower shrinking rates and higher level of oil filling the gel pores. The oil droplets were generally acting as inactive fillers in the gel beads, as the mechanical strength (Young's modulus and hardness) was declining with the increase in oleogel content, and no interaction between the oleogel and hydrogel was detected by FTIR. Swelling studies revealed that beads in salt solution at higher temperature had higher swelling ratio, and the increase in oleogel content could inhibit the swelling. The bigel beads were able to encapsulate EGCG and curcumin simultaneously, and beads with higher oleogel content generally had lower encapsulation efficiency of EGCG but higher efficiency of curcumin. The gel structures provided good protection for curcumin, and about 70% of the original curcumin was retained after a 40-day storage test. The study provided novel information regarding the structure-function relationship of the bigel beads, which could be useful for the development of functional food materials.