Interaction between dietary bioactive peptides of short length and bile salts in submicellar or micellar state

Bile salts act as steroidal detergents in the gut, and could also interact with peptides and improve their bioavailability, although the mechanism is unclear. The occurrence of direct interaction between milk bioactive peptides, Ile-Asn-Tyr-Trp, Leu-Asp-Gln-Trp, and Leu-Gln-Lys-Trp, and different bile salts in the submicellar or micellar state was investigated by intrinsic fluorescence measurement and dynamic light scattering, above the critical micellar concentration, the latter being determined by isothermal titration calorimetry. The peptides form aggregates, spontaneously. In the presence of bile salts, some released peptide monomers were bound to the micellar surface. The lack of hydrogen bonding involving the C12OH group of the steroid skeleton, and the acidic function of some bile salts, might promote the interaction with the peptides, as could the lack of the C12OH group, rather than that of the C7OH group. At submicellar concentrations, sodium taurochenodeoxycholate and taurodeoxycholate readily interacted with the most hydrophobic peptide Ile-Asn-Tyr-Trp.