Physicochemical properties of peanut protein isolate–glucomannan conjugates prepared by ultrasonic treatment

•PPI was glycated with glucomannan through ultrasound or classical heating.•Solubility and emulsifying properties of conjugates by ultrasound were improved.•Conjugates by ultrasound had less compact structure. Peanut protein isolate (PPI) was glycated with glucomannan through classical heating or ultrasound treatment in this work. The physicochemical properties of PPI–glucomannan conjugates prepared by ultrasound treatment were compared to those prepared by classical heating. Compared with classical heating, ultrasound treatment could accelerate the graft reaction between PPI and glucomannan and improve the concentration of available free amino groups of PPI. Solubility and emulsifying properties of the conjugates obtained by ultrasound treatment were both improved as compared to those obtained by classical heating and native PPI. Decreases of lysine and arginine contents during the graft reaction indicated that these two amino acid residues attended the covalent linkage between PPI and glucomannan. Structural feature analyses suggested that conjugates obtained by ultrasound treatment had less α-helix, more β-structures and random coil, higher surface hydrophobicity and less compact tertiary structure as compared to those obtained by classical heating and native PPI.