In vitro gastrointestinal digestibility of phytosterol oleogels: influence of self-assembled microstructures on emulsification efficiency and lipase activity

The objective of this study was to investigate the influence of self-assembled microstructure on lipid digestibility in phytosterol (gamma-oryzanol and beta-sitosterol) oleogels. Different molar ratios of gamma-oryzanol and beta-sitosterol yielded a variety of crystal morphologies; the resulting gels were tested for their lipid emulsification efficiency, release rate of free fatty acids (FFAs) during lipolysis, and their effect on lipase behavior. Results indicated that oleogels were harder to emulsify when compared to oil samples. The emulsification efficiencly was affected by both the gel strength and crystal morphology of the self-assembled structures within phytosterol oleogels. In oil emulsions, intestinal digestion resulted in more extensive lipid droplet coalescence with increased particle size when compared to oleogel emulsions. The FFA release rate suggested that the extent of lipid digestion was correlated to the emulsification efficiency. The interfacial binding of lipase indicated that the amount of lipase adsorption was positively correlated to the interface area created during the emulsification process. Finally, isothermal titration calorimetry results indicated that self-assembled structures within these oleogels physically obstructed the interaction between lipase and lipid. Ultimately, this led to lower reaction rate during gastrointestinal digestion. Collectively, these results may have important implications in designing oleogel systems with controlled lipid digestibility as well as controlling the bioavailability of delivered lipid-soluble bioactive compounds.