Interactions of polysaccharides with β-lactoglobulin adsorbed films at the air–water interface

In the present work we have studied the adsorption (dynamic surface pressure) of β-lactoglobulin (βLG), polysaccharides and their mixtures at the air–water interface at 20 °C and at pH 7. The measurements were performed on a automatic drop tensiometer. As polysaccharides with interfacial activity we have used propylene glycol alginates (PGA). To evaluate the effect of the degree of PGA esterification and viscosity, different commercial samples were studied—Kelcoloid O (KO), Kelcoloid LVF (KLVF) and Manucol ester (MAN). Xanthan gum (XG) and λ-carrageenan (λ-C) were studied as non-surface active polysaccharides. The results reveal a significant effect of surface-active and non-surface-active polysaccharides on dynamic characteristics of β-lactoglobulin adsorbed films. To explain the observed effects on the rates of diffusion, penetration, and rearrangement of these biopolymers at the air–water interface, three phenomena were taken into account: (i) the competitive adsorption; (ii) the complexation, and (iii) the existence of a limited thermodynamic compatibility between protein and polysaccharide at the air–water interface and in the bulk aqueous phase. Surface-active polysaccharides (MAN, KO) are less effective than non-adsorbing polysaccharides (XG) for increasing the surface pressure of protein films, because a competitive behaviour with protein. Highly hydrophilic polysaccharides that do not adsorb by their own at the interface (XG, λ-C) or surface-active polysaccharides with low hydrophobicity (KLVF) show a cooperative behaviour with protein that promotes a significant increase of surface pressure of adsorbed films.