The influence of network architecture on the large deformation and fracture behavior of emulsion-filled gelatin gels

Abstract

• Emulsion-filled gelatin gels were prepared with contrasting network architecture. • Structure of heterogeneous gels defined by droplet-rich, protein dense domains. • Stress-strain response was correlated to network interactions and architecture. • Fracture mechanics were dependent on network structure and interfacial interactions. • Homogeneous rigid network behaved as rigid scaffold in continuous gel network. This work addresses the effect of network architecture on the large deformation mechanical properties of whey protein-stabilized emulsion-filled gelatin gels as a fat- or oil-filled composite food matrix. Electrostatic interactions were used to induce either a homogeneous (pH 6) or heterogeneous (pH 4) network architecture; the latter was characterized by droplet-rich, protein dense domains embedded in the continuous polymer gel network. Homogeneous gels displayed a transition from strain hardening to strain softening with increasing filler content. In contrast, the formation of a heterogeneous network caused a transition from strain hardening to a linear stress-strain response up to brittle fracture. Fracture mechanics of the homogeneous gels were dominated by imperfect interfacial adhesion and filler-filler contacts under compression. A decrease in fracture strain and fracture stress was caused by interfacial strain amplification and filler debonding. These effects were balanced by filler-filler contacts which produced an increase in fracture stress and strain, particularly for fat-filled gels. In the heterogeneous gels, the more rigid, viscous nature of the droplet-rich domains decreased fracture strain but increased fracture stress as they became the dominant load-bearing structure. The lipid physical state had a marginal impact on fracture strain, while an increase in gelator concentration reduced the observed increase in fracture stress.This work demonstrates that filler/matrix interactions can be used to modulate network structure in emulsion-filled protein gels, which in turn play a strong role in determining the large deformation behavior and fracture mechanics of the composite material.