Flaxseed globulin versus albumin proteins - Interfacial assembly and nonlinear rheology at the air-water interface

Flaxseed is one of the main oil crops cultivated worldwide and is a potential alternative protein source. The different molecular properties of the two main fractions of flaxseed protein (globulin and albumin) may lead them to form diverse structures and exhibit distinct mechanical properties at the air-water interface. Our aim is to elucidate the differences in interfacial assembly and nonlinear surface rheological properties between these two fractions, to gain a deeper understanding of their structure-function relationships.

Molecular properties of flaxseed globulins and albumins were analyzed, including composition, secondary structure, size, shape, and compactness. Their adsorption kinetics and morphology at the air-water interface were investigated, as well as their surface rheology in the linear and nonlinear viscoelastic regime.

Albumins mainly existed in the form of monomers at low surface pressures and subsequently self-assembled into small aggregates forming a compact soft glass-like interfacial film with lower stiffness but higher stretchability. This film effectively prevented foam disproportionation and coalescence, leading to higher foam stability. For globulins, their individual oligomers and small aggregates together formed an initial interfacial layer with obvious heterogeneity. During the rearrangement phase, larger aggregates emerged, resulting in a stiffer solid-like interfacial film through stronger protein-protein interactions. Based on general stress decomposition (GSD) analysis, this film was relatively less compact and more brittle, resulting in poor foam stability. Different interfacial structural properties of flaxseed albumin and globulin proteins clearly led to distinct interfacial rheological properties, contributing to their unique foaming properties.