Protein pre-aggregation as a strategy to reinforce heat-set emulsion-filled faba bean globulin gels

Emulsion-filled protein gels are interesting composite materials widely applied in food, cosmetic and pharmaceutical industries. Incorporating emulsion droplets in a protein gel matrix can sometimes undesirably weaken the gel. This study introduces a strategy to counteract this defect using protein pre-aggregation induced by heating. Faba bean globulin (Fg) gels were studied as an example, by comparing a lab-extracted Fg that was mostly native, Fg heated for 10 or 60 min at 95°C (causing a controlled degree of pre-aggregation), and a commercial Fg (partially denatured). The 60 min-heated Fg was aggregated more significantly than the 10 min-heated one, and the commercial Fg mainly consisted of large and dense protein aggregates. Emulsion droplets were stabilized by the same type of Fg that formed the gel matrix and proved to act as inactive fillers. They decreased the gel strength by 15-30% at a 6.5% (w/w) oil concentration and shifted the maximum linear strain to lower amplitudes by decreasing the homogeneity of the gel matrix. However, they barely influenced the gelation kinetics and the behavior of all Fg gels in large shear deformations, which were dominated by the gel matrix. Pre-aggregated Fg endowed the emulsion-filled gels with 1.4- to 4.1-fold higher storage modulus and 1.3- to 1.9-fold higher maximum linear strain than untreated Fg, presumably due to stronger hydrophobic protein-protein interactions resulting from enhanced exposed hydrophobicity; moreover, the pre-aggregates may have acted as active fillers. Therefore, pre-aggregation is an effective strategy to improve the mechanical properties of emulsion-filled faba bean globulin gels when the emulsion droplets are inactive fillers. These findings are expected to improve the texture and tailor the mechanical properties of the emulsion-filled-gel-based products in food, cosmetics and pharmaceutical products. • Faba bean globulin-stabilized emulsion droplets acted as inactive fillers. • Protein pre-aggregation can reinforce emulsion-filled faba bean globulin (Fg) gels. • Fg pre-aggregates seemed to act as active fillers. • The gelation kinetics and gels’ nonlinear rheology were dominated by the gel matrices.