Interfacial properties of dry-fractionated lentil protein concentrates and their water-extracted soluble and insoluble fractions as affected by pH

In this study, two air classified lentil protein concentrates (LPC) of different purities (43 and 54% protein) were separated into their soluble and insoluble fraction, which altered their basic composition, protein solubility profile, and amino acid composition. Proteomic analysis showed a shift in protein composition towards higher proportions of albumin and vicilin in the soluble fractions and increased proportions of legumin, glutelin and prolamin in the insoluble fractions. Interfacial shear rheology was used to compare the interfacial adsorption behavior and interfacial layer cohesiveness of LPC and its soluble and insoluble fractions at different pH (3.0, 5.0, 7.0). A viscoelastic, gel-like interfacial layer formed within seconds to minutes in all samples and pH values. The presence of insoluble components coupled with electrostatic repulsive forces resulted in thin (G i ’: 0.1–5.8 mPa m), but cohesive interfacial layers with interfacial crossover strains (ICS) in the range of 65–169%, while the insoluble fractions formed comparatively fragile interfaciallayers (ICS: 7–19%) in absence of electrostatic repulsion. In contrast, the soluble fractions formed strong and cohesive interfacial layers (G i ’: 10–24 mPa m, ICS: 73–226%) at all investigated pH values, showing that the soluble components were crucial for maintaining elasticity and interfacial layer cohesiveness near the isoelectric point. The study demonstrated that the aqueous extraction at native pH of soluble and insoluble fractions from dry-fractionated LPC is suited to modify the protein composition and interfacial properties in a way that might alter the stability of colloidal systems under varying pH conditions. • Separation by solubility alters protein and non-protein composition. • Protein composition and pH influence interfacial layer properties and structure. • Soluble fractions form strong and cohesive interfacial layers over broad pH range. • Insoluble fractions form fragile interfacial layers near the isoelectric point.