Development of highly stable phytosterol oleogel particle-based emulsions with improved bioaccessibility of β-carotene

Oral administration is the most preferred route for drug and bioactive delivery, although it raises great challenges due to the involvement of the gastrointestinal (GI) system and limited bioavailability. In this research, gelled oil particle-based emulsion with long shelf life and high gastrointestinal stability was successfully formulated using beta-sitosterol and gamma-oryzanol (SO) mixtures, as structuring agents, and tween 80 (TN80) as a surfactant. The effect of TN80 concentration, emulsification speed, gamma-oryzanol and beta-sitosterol ratio, and SO concentration was examined. The results show that the particle size was significantly reduced with homogenization speed, surfactant concentration, and SO concentration. The effect of SO concentration was further analyzed under simulated GI conditions and changes in their particle size, zeta potential, morphology, and beta-carotene release were assessed. GI digestion tests revealed that unstructured oil particle-based emulsions exhibit a higher probability for particle coalescence compared to oleogel particle-based emulsions. The extent of lipid digestion was correlated to the particle size, with higher digestion extent at smaller particle size, and to the oleogel-network mechanical strength, with lower digestion extent in denser particle network. During the lipolysis process, smaller mixed micelles were formed when the particles were prepared using higher SO concentrations. Interestingly, an appreciable increase in the beta-carotene bioaccessibility was observed, reaching maximum value at 10 %wt. SO, implying the effect of oil structuring on the beta-carotene release process. Overall, these results suggest that the combination of solid texture and liquid lipid core in the oleogel particles offers mechanical protection and molecular micellization ability during digestion. Such characteristics can be utilized for effective encapsulation systems able to improve the bioaccessibility of hydrophobic molecules.