β-carotene and resveratrol loaded glycerol monostearate-based oleogels: Physicochemical characterization at low gelation concentrations

Oleogels are semi-solid systems that can function both as replacers of trans and saturated fats and/or as carriers of lipophilic bioactive compounds. However, bioactive compounds can affect the structure of the oleogel matrix and this effect depends on the properties of such compounds. Therefore, the aim of this study was to develop oleogels loaded with β-carotene (BC) or resveratrol (R), with low concentrations of glycerol monostearate (GMS, 2-5 wt%) and sunflower oil as organic solvent. The gels were characterized by polarized light microscopy, rheological measurements, differential scanning calorimetry, oil binding capacity and Fourier transform infrared spectroscopy. At higher GMS concentrations, stronger oleogels and higher temperatures associated with transitions (sol-gel/gel-sol and crystallization/melting) were observed. The incorporation of bioactive compounds modified the gelation behavior. BC weakened the oleogel structure during the transient molecular organization of GMS, whereas R increased the dynamic moduli. BC also caused slight oil release at lower concentrations, while R improved retention. The high hydrophobicity of BC may be disturbing the solubility balance of the system, while R has phenolic hydroxyl groups that may strengthen hydrogen bonds. However, there were no considerable changes in mechanical properties after storage. We hypothesize that the molecular organization of GMS over time may be masking the modifications that bioactive compounds cause in mechanical properties. In fact, changes in the structure were revealed, as the addition of BC or R changed the morphology of the three-dimensional network crystals. Thus, the results can contribute to the rational choice of system components using low concentrations of oleogelator, as the composition of the bioactive compound exerts influence on the modulation of lipid matrices.