Physicochemical properties and microstructure of bigels formed with gelatin and κ-carrageenan hydrogels and monoglycerides in olive oil oleogels

The preparation and properties of novel edible bigel systems based on olive oil oleogels structured with 15% monoglycerides and different hydrogels formed with 8, 10 or 12% gelatin or gelatin plus 1% κ-carrageenan were studied. The effect of hydrogel composition and oleogel/hydrogel ratio on physicochemical characteristics and microstructure, as well as mechanical and thermal properties of the resultant bigels was examined. An increased proportion of oleogel led to a decrease in hardness (10.34–43.95 N) and an increase in the cohesiveness of bigels (0.13–0.36). Addition of κ-carrageenan to the bigel system increased hardness (25.47–89.00 N) and decreased cohesiveness (0.12–0.16). Microscopy revealed the formation of an oleogel-in-hydrogel bigel system with significantly smaller oil droplets when only gelatin was used as a hydrogelator. Bigels containing gelatin and κ-carrageenan had the lowest swelling capacity, possibly due to formation of hydrogen bonds and electrostatic interactions between gelatin and κ-carrageenan resulting in an inelastic structure that could not absorb water. Differential scanning calorimetry revealed an increase in the melting enthalpy of the monoglycerides from 5.35 mJ/mg to 8.85 mJ/mg with increasing oleogel proportion in bigels, while the incorporation of κ-carrageenan improved the thermal stability of the biphasic system. Fourier transform infrared spectroscopy documented the existence of a complex between gelatin and κ-carrageenan and confirmed that the mechanism of bigels formation is based on the physical interactions of the two structured phases. These results provide a comprehensive overview regarding the structure and functional properties of bigels with potential applications in foods. [Display omitted] •Bigels were formed by mixing oleogels and hydrogels in different ratios.•Structural properties of the bigels were affected by the oleogel/hydrogel ratio.•Addition of κ-carrageenan in the hydrogel increased the hardness of the bigel.•Thermal analysis revealed the presence of two structured phases in the bigels.•FTIR confirmed that the formation of bigels was based on physical interactions.