Influence Mechanism of in Vitro Digestion Process on Mucus Layer Permeation and Transmembrane Transport of Soy Protein Isolate Nanoparticles Loaded with β-Carotene

The in vivo absorption of nanocarriers is a complex process, which is affected by the bioabsorption barrier. It is doubtful whether nanopreparations can promote the absorption and utilization of bioactive molecules. In this study, soy protein isolate (SPI) was used to prepare plant-based nanocarriers encapsulating β-carotene, and an in vitro digestion model was employed to investigate the structural changes of β-carotene loaded soy protein isolate nanoparticles (BC-SPIs) during digestion. Additionally, the Caco2 cell transport model was used to explore the impact mechanism of digestion conditions on the transmembrane transport of BC-SPIs after digestion. Furthermore, a Caco2-HT29 co-culture model containing a mucus layer was used to investigate the permeability of BC-SPIs through the mucus layer before and after digestion. This study found that before digestion, BC-SPIs could be directly absorbed by the Caco-2 cell monolayer through clathrin- and caveolin-dependent endocytosis. After in vitro simulated digestion, the size of BC-SPIs increased, and they could be directly absorbed by cells through clathrin-dependent endocytosis, caveolin-dependent endocytosis and macropinocytosis. The digested nanoparticles carried more negative charge, resulting in a 1.48-fold enhancement in the ability to cross the mucus layer and a 1.56-fold increase in the transmembrane transport efficiency of β-carotene. This study clarified the different absorption pathways of BC-SPIs before and after digestion and revealed the interaction between BC-SPIs and bile salts under simulated digestion conditions and the contribution of increasing the size of BC-SPIs to their transport and absorption efficiency by cells. These findings lay a theoretical foundation for further improving the application potential of nanocarriers in bioavailability enhancement, which will help advance the development of nanotechnology in several fields such as pharmaceuticals and health products.