Both datasets recorded for BSA and b-casein assemblies fitted well with thin bilayers (Figure ), in agreement with previous reports obtained for albumin . These two layers are proposed to correspond to the more hydrophobic residues interacting with the oil phase and the hydrophilic fragments, swelling into the aqueous phase, away from the interface. However, the dimension and composition of these two layers differed significantly in both proteins. Indeed, the hydrophobic layer of the b-casein assembly was thinner and less solvated than that of BSA, whereas its hydrophilic compartment was comparable in thickness but more solvated (Table ). Therefore, overall our data clearly demonstrate the disconnection between the evolutions of the surface adsorption of the proteins studied at liquid-liquid interfaces and the mechanical maturation of corresponding assemblies. Both BSA and b-casein are found to rapidly assemble at fluorinated oil interfaces and form comparable film thicknesses at hexadecane interfaces, but whereas the interfacial shear storage modulus of b-casein layers does not significantly rise, it rapidly increased in the case of BSA. This difference in interfacial mechanics is proposed to result from the difference in structure of these two proteins. Whereas BSA is a globular protein presenting predominantly a-helical components (72% based on circular dichroism ), b-casein is a disordered protein displaying only one sizeable a-helix at its N-terminus, with a hydrophobic terminal peptide sequence of VLILACLVALALA (based on data from Uniprot and AlphaFold structure predictions). This architecture presumably confers to b-casein amphiphilic properties comparable to other polymeric amphiphiles, and promotes the formation of dense layers in which macromolecules are not strongly interacting, with substantial associated fluidity and low interfacial shear moduli. In comparison, BSA presents a hydrophobic face that mediates the transport of lipid and other hydrophobic molecules and requires unfolding of a-helix bundles in order to assemble at hydrophobic interfaces . This requirement presumably underpins a higher activation energy associated with BSA adsorption at oil and air interfaces and the kinetic control of b-casein adsorption in protein mixtures .