Impact of high moisture contents on the structure and functional properties of pea protein isolate during extrusion

A twin-screw extruder was used to extrude pea protein isolate (PPI) hydrated with different moisture content (30, 40, 50, and 60%); natural PPI with a moisture content of 6.84% was used as a control. The impacts of extrusion on PPI's functional properties and structure were then investigated. The results showed that extrusion significantly reduced (P < 0.05) PPI's solubility and foaming capacity. Foam stability of PPI extrudates decreased with increasing moisture content. Compared with natural PPI, the emulsifying activity and emulsifying stability index increased from 18.32 m2/g and 25.98 min to 28.67 m2/g and 39.69 min, respectively. The particle size of all PPI extrudates increased significantly (P < 0.05) with increasing moisture content. Fourier transform infrared spectroscopy (FTIR) indicated the conversion of β-sheet and α-helix structures to β-turn and random coil structures. PPI's maximum fluorescence emission wavelength (λmax) was red-shifted in the fluorescence spectrum, demonstrating a change in protein conformation. In summary, extrusion can improve the functional characteristics of PPI.