Interactions of polysaccharides with β-lactoglobulin spread monolayers at the air-water interface

In the present work we have studied the static (film structure and elasticity) and dynamic characteristics (surface dilatational properties) of beta-lactoglobulin (betaLG) monolayers spread at the air-water interface in the presence of polysaccharides in the aqueous phase, at 20 degreesC and at pH 7. The measurements were performed on a fully automated Wilhelmy-type film balance. 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 (NIAN). Xanthan gum (XG) and X-carrageenan (lambdaC) were studied as non-surface active polysaccharides. The results reveal a significant effect of surface active and non-surface active polysaccharides on static-when the polysaccharide was added in the subphase the pi-A isotherms shifted to higher surface pressure values as the time increased-and dynamic-the presence of polysaccbaride in the aqueous phase decreased the surface dilatational modulus of a pure beta-lactoglobulin monolayer-characteristics of beta-lactoglobulin monolayers. To explain the observed effects three phenomena were taken into account: (i) the ability of the polysaccharide, to adsorb at the interface by it-self and to increase the surface pressure, (ii) the interfacial complexation of the polysaccharide with the adsorbed protein and (iii) the existence of it limited thermodynamic compatibility between the protein and polysaccharide, depending on the protem-polysaccharide system. (C) 2004 Elsevier Ltd. All fights reserved.