LAUSR

Abstract Aim of the present study was to investigate the complex formation of β-lactoglobulin (β-LG) hydrolysates and different types of pectin at the oil/water-interface by dynamic interfacial pressure and the properties of the complexes by interfacial rheology (dilatation and shear). The degree of hydrolysis (DH) of β-LG was varied (3 and 6%) as well as the degree of methoxylation of the pectins, i.e. two low-(LMP, 32 and 35%) and two high-methoxylated (HMP, 64%) pectins were used. The pectins exhibited different local charge densities, due to enzyme specificity during demethoxylation. All experiments were performed at a constant biopolymer content (0.01 wt%), pH (4.0) and temperature (22 °C). β-LG/pectin interactions clearly delayed interfacial adsorption, which was more pronounced for LMP with a high local charge density. With increasing DH of β-LG, the interfacial adsorption was accelerated, however β-LG/pectin layers exhibited higher dilatational elastic moduli than hydrolysate/pectin layers. In contrast to dilatational rheology, β-LG formed weaker interfacial layers than its hydrolysates during shear time sweeps, despite the presence of pectin. Pectin and hydrolysates exhibited strong viscoelastic interfacial layers partially more than one order of magnitude higher than β-LG. However, during shear amplitude sweeps all interfacial layers were resistant to increasing strain and the films collapsed within the same region. Therefore, targeted structural modifications using enzymes with high specificity enables the production of β-LG hydrolysates and demethoxylated pectins with tailored functionality with respect to their interfacial rheology characteristics.