Scope: Solubilization of lipophilic bioactives in gastrointestinal fluids contributes to their bioavailability, but a better understanding of the transfer processes involved and the impact of molecular structure is required.
Methods and results: The transfer of β-carotene (BC), coenzyme Q10 (CoQ10), vitamin D3 (VitD3), and phytosterols (PSs) from soy protein isolate-stabilized oil-in-water emulsions to the aqueous phase during in vitro digestion was investigated. In the absence of lipolysis, transfer was mainly governed by molecular structure and partitioning within the oil droplets. Less than 3% BC and CoQ10, versus 30.4±0.3% PSs and 24.7±0.4% VitD3, were transferred in this case. However, with lipolysis, PSs and VitD3 rapidly partitioned into the aqueous phase, while lag phases and slower transfer rates were observed for BC and CoQ10. Positive and linear correlations between lipolysis and transfer were observed for all systems. After 2 h exposure to simulated duodenal conditions, there were no differences between percent micellization, except for BC which was proportionally lower. VitD3 and PSs mutually enhanced each other's transfer, while no interactions were observed between VitD3 and BC.
Conclusion: Bioactive molecular structure and co-administration influenced the transfer behaviour, with implications for foods designed to optimize health benefits.