Viscoelastic properties of lupin proteins produced by ultrafiltration-diafiltration

The linear and nonlinear rheological properties of defatted lupin proteins produced by ultrafiltration-diafiltration were investigated. Five concentrations ranging from 10 to 30% of the defatted ultrafiltered-diafiltered (DUD) lupin proteins were prepared. The viscoelastic properties strongly depended on concentrations. Below 12%, the DUD lupin proteins exhibited more fluid-like behavior. At 15%, lupin proteins became more viscoelastic, and above 20%, the viscoelastic solid-like properties became stronger. Below 12%, the high-frequency behaviors of moduli were proportional to ω1/2, as expected for a semiflexible coil. Above 20%, the high-frequency behaviors of moduli were proportional to ω1/2, indicating a flexible coil. The nonlinear steady shear rheological properties were also concentration-dependent and showed shear-thinning behavior, which could be described by a power law constitutive model. The trend of the power law exponent shift is very consistent with the linear viscoelastic behavior change with the lupin protein concentration. These results suggest DUD lupin proteins undergo a structural change between 12 and 20%.