Ultrasound-enhanced foaming and emulsifying properties of flaxseed protein isolate: mechanisms mediated by conformational flexibility and interfacial tension

Abstract

Despite the high nutritional value of flaxseed protein isolate (FPI), its food applications remain limited due to poor foaming and emulsifying properties. The current research examined the effects of ultrasonic treatment (0, 100, 200, 300, and 400 W, 15 min) on FPI functionality, with primary focus structural alterations, conformational flexibility, and interfacial behavior. Ultrasound significantly reduced particle size, increased absolute zeta potential, and exposed sulfhydryl and hydrophobic groups, and rearranged the secondary structure. These changes enhanced conformational flexibility, reduced interfacial tension, and improved the viscoelasticity of the adsorbed protein film. Foaming capacity increased from 50.56% to 99.45% at 200 W, with the emulsifying activity index increasing from 2.43 to 4.11 m2/g at 300 W. Multivariate analyses indicated that these functional gains were positively correlated with the conformational flexibility index while negatively correlated with interfacial tension, providing a theoretical foundation for valorizing oilseed by-product proteins.