Flavonoid-gastrointestinal mucus interaction and its potential role in regulating flavonoid bioavailability and mucosal biophysical properties

•Gastrointestinal mucus influences flavonoid bioavailability.•Emulsification allows flavonoid mucus penetration and increases bioavailability.•Flavonoid aglycones may bind to mucin via non-covalent interactions.•Flavonoids do not significantly alter mucus micro- and macroviscosity.•FRAP is a useful technique to analyze flavonoid mucus diffusion.

Flavonoid bioavailability has attracted a lot of attention over the last decade due to the increasing evidence of their health-promoting properties. However, conflicting results appear in the literature, especially on the bioavailability of flavonoid glycosides in vitro versus in vivo. In in vitro studies, where Caco-2 cells are usually used, hydrophobic aglycones have been reported to be more bioavailable. On the contrary, in vivo studies suggest that increasing the aqueous solubility of flavonoids favors their bioavailability. In this paper, we aim to fill this gap by analyzing the role of the gastrointestinal mucus on flavonoid bioavailability. Mucus is a complex viscoelastic barrier that serves as the first line of defense against pathogens, particles and several toxins, while allowing nutrients to penetrate through and reach the epithelia. A mechanism by which mucus participates in flavonoid absorption is proposed. Also, the effect of flavonoids on the biophysical properties of the mucus layer is discussed. This article therefore reviews the complex interaction between flavonoids and mucus for the first time.