Equilibrium of Adsorption of Mixed Milk Protein/Surfactant Solutions at the Water/Air Interface

Abstract

Ellipsometry and surface profile analysis tensiometry were used to study and compare the adsorption behavior of beta-lactoglobulin (BLG)/C10DMPO, beta-casein (BCS)/C10DMPO and BCS/C12DMPO mixtures at the air/solution interface. The adsorption from protein/surfactant mixed solutions is of competitive nature. The obtained adsorption isotherms suggest a gradual replacement of the protein molecules at the interface with increasing surfactant concentration for all studied mixed systems. The thickness, refractive index, and the adsorbed amount of the respective adsorption layers, determined by ellipsometry, decrease monotonically and reach values close to those for a surface covered only by surfactant molecules, indicating the absence of proteins from a certain surfactant concentration on. These results correlate with the surface tension data. A continuous increase of adsorption layer thickness was observed up to this concentration, caused by the desorption of segments of the protein and transforming the thin surface layer into a rather diffuse and thick one. Replacement and structural changes of the protein molecules are discussed in terms of protein structure and surface activity of surfactant molecules. Theoretical models derived recently were used for the quantitative description of the equilibrium state of the mixed surface layers.

Properties of an αs-casein-rich casein fraction: Influence of dialysis on surface properties, miscibility, and micelle formation

“…Moreover, γ eq,min values for β-CN are 52 × 10 −3 N/m (Rodríguez Patino et al, 2003Patino et al, , 2006aSánchez et al, 2005Sánchez et al, , 2006 as well as 49.4 × 10 −3 and 46.4 × 10 −3 N/m (Rouimi et al, 2005) for 2 different CN. The A min values reported in the literature are 7 × 10 −18 m 2 (Makievski et al, 1998), 7.5 × 10 −18 m 2 (Kotsmar et al, 2008), and 9.8 × 10 −18 m 2 (Beaufils et al, 2007) for β-CN, which are higher than the values determined here. The slightly different surface properties of CN described in the literature may, however, have been caused by differences in purity, source, and type of the examined CN.…”

Lipid Oxidation in Oil‐in‐Water Emulsions: Involvement of the Interfacial Layer

“…For instance, LMWEs can compete with proteins for adsorption at the oil–water interface and even displace already adsorbed proteins (orogenic displacement). This is explained by the usually faster adsorption rate of surfactants as compared to proteins during the emulsification process (Tcholakova and others ) and also because surfactants are more surface‐active (Courthaudon and others , ; Dickinson , , ; Mackie and others ; Bos and van Vliet ; van Aken ; Damodaran ; Kotsmar and others ; Morris and Gunning ; Day and others ). The partitioning of surface‐active molecules within emulsions is also dependent on kinetic or process‐related factors in complex emulsions.…”

A disjoining pressure study of foam films stabilized by mixtures of a nonionic (C12DMPO) and an ionic surfactant (C12TAB)

“…There is considerable knowledge regarding the surface and bulk properties of C 12 DMPO with extensive surface tension [14][15][16][17][18][19][20][21] and surface rheology [22][23][24][25][26][27][28][29] studies in the past. Moreover, studies of adsorption layers and foam films of C 12 DMPO/protein mixtures were performed [30,31]. However, to our knowledge there exists no study on the properties of foam films or foams stabilized by C 12 DMPO.…”