Impact of thermosonication at neutral pH on the structural characteristics of faba bean protein isolate dispersions and their physicochemical and techno-functional properties

Abstract

The effect of thermosonication (TS) (90 °C, 10–30 min) on faba bean protein isolate (FPI) at pH 7 was investigated. The microstructural and techno-functional properties of TS-treated FPI were compared with native FPI or FPI treated with conventional prolonged heating (CH, up to 8 h) at 90 °C. TS treatment effectively converted FPI to amorphous aggregates containing predominant β-sheet secondary structures, as determined by Thioflavin T (ThT) fluorescence and circular dichroism (CD). According to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), these amorphous aggregates could be formed by disulfide bonds. Additionally, TS treatment is efficient in disrupting large protein aggregates of FPI, thus improving their solubility. Both TS and CH treatments induced formation of viscoelastic FPI hydrogels, whose gel strength depends on the type and time of treatment. Hydrogels formation is likely to arise from the entanglement and interaction of protein aggregates as revealed by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). TS-treated FPI was also used to prepare O/W emulsions and whose structural and physical properties were compared with those stabilised by untreated FPI. At all oil volume fractions (φ = 0.2, 0.5, and 0.7) and FPI concentrations (1, 3, and 5 wt %), emulsions stabilised by TS-treated FPI exhibited smaller oil droplet size, greater mechanical strength and superior stability compared to those stabilised by untreated FPI. The study suggests that TS treatment is promising in improving techno-functional properties of FPI; further studies are needed to exploit TS-treated plant proteins as a novel food ingredient in food product development.