Characterization of structural and functional properties of walnut protein isolate-apple pectin Maillard conjugates

The protein-rich walnut press cake obtained after walnut oil extraction has been wasted, hence there is great interest in enhancing the utilization of walnut protein isolate (WPI). WPI was selected as the material and apple pectin (AP) was utilized to chemically modify WPI by wet-heating Maillard reaction to prepare WPI-AP conjugates. Determinations of grafting degree (DG), color change and SDS-PAGE results indicated that the optimal DG (46.60%) was obtained for the ratio of WPI/AP of 1:2. Fourier transform infrared spectroscopy, X-ray diffraction and intrinsic fluorescence spectroscopy confirmed covalent binding between amino and carbonyl groups, an amorphous conjugate structure, and tryptophan residue exposure. Scanning electron microscopy further observed a significant structural change to a rigid lamellar structure. Functional property analysis showed that glycosylation significantly improved solubility (33.06% to 71.65%), reduced surface hydrophobicity (1168.25 to 733.03), and enhanced emulsifying activity (20.93 m 2 /g to 36.20 m 2 /g) and stability (32.94% to 80.55%), as well as foaming activity (7.91% to 23.25%) and stability (3.42% to 18.41%). This study used wet-heating Maillard modification to prepare modified WPI targeted at emulsified food applications. • WPI-AP conjugates with high grafting degree synthesized via Maillard reaction. • Efficient WPI-AP covalent coupling via 90°C wet-heating for 3 h. • AP covalent binding induced structural unfolding of WPI. • WPI-AP shows superior solubility, emulsifying and foaming vs natural WPI. • Wet-heating Maillard reaction enhances industrial applicability of WPI.