title: Bile salts at the air-water interface: adsorption and desorption.
abstract: Bile salts (BS) are bio-surfactants which constitute a vital component in the process of fat digestion. Despite the importance of the interfacial properties in their biological role, these have been scarcely studied in the literature. In this work, we present the adsorption-desorption profiles of two BS (NaTC and NaGDC) including dilatational rheology. Findings from this study reveal very different surface properties of NaTC and NaGDC which originate from different complexation properties relevant to the digestion process. Dynamic adsorption curves show higher adsorption rates for NaTC and suggest the existence of various conformational regimes in contrast to NaGDC which presents only one conformational regime. This is corroborated by analysis of the adsorption isotherms and more in detail by the rheological behaviour. Accordingly, the dilatational response at 1Hz displays two maxima of the dilatational modulus for NaTC as a function of bulk concentration, in contrast to NaGDC which displays only one maximum. The desorption profiles reveal that NaTC adopts an irreversibly adsorbed form at high surface coverage whereas NaGDC fully desorbs from the surface within the whole range of concentrations used. Analysis of the adsorption-desorption profiles provides new insight into the surface properties of BS, suggesting a surface complexation of NaTC. This knowledge can be useful since through interfacial engineering we might control the extent of lipolysis providing the basis for the rational design of food products with tailored digestibility.
authors.affiliation: Department of Applied Physics, Campus de Fuentenueva, sn. University of Granada, 18071 Granada, Spain. Electronic address: julia@ugr.es.
authors.forename: J
authors.initials: J
authors.lastname: Maldonado-Valderrama
authors.affiliation: Department of Software Engineering, C/Periodista Daniel Saucedo Aranda, sn. University of Granada, 18071 Granada, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Muros-Cobos
authors.affiliation: Department of Software Engineering, C/Periodista Daniel Saucedo Aranda, sn. University of Granada, 18071 Granada, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Holgado-Terriza
authors.affiliation: Department of Applied Physics, Campus de Fuentenueva, sn. University of Granada, 18071 Granada, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Cabrerizo-Vílchez
mesh_terms: D000327:Adsorption; D000388:Air; D055119:Elastic Modulus; D006002:Glycodeoxycholic Acid / Q000737:chemistry*; D012212:Rheology; D013500:Surface Tension; D013656:Taurocholic Acid / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D006002:Glycodeoxycholic Acid; D013656:Taurocholic Acid
keywords: Bile salts; Desorption; Digestion; Surface conformation; Surface rheology; Surface tension