Effects of ultrasound combined with pH shift modification on functional and structural properties of peanut proteins

The parameters for ultrasound and pH shift co-modification of peanut proteins (PP) were optimized, and the functional properties, structures of PP were investigated. The results showed that under the optimum ultrasound-assisted pH-shift modification (UP-PPI), the solubility of PP increased by 40.5 % and 111.4 %, respectively, compared with the pH shift (pH-PPI) and the control (D-PPI). The emulsifying and foaming properties of pH-PPI and UP-PPI were significantly (P < 0.05) higher than those of D-PPI. pH shift reduced the particle size of D-PPI from 805.14 ± 13.80 nm to 563.73 ± 35.92 nm, and ultrasound further enhanced this process, with a sizer of 392.67 ± 7.81 nm while increasing the absolute value of zeta potential. Chemometric analysis indicated the free sulfhydryl group contents and surface hydrophobicity of PP were significantly (P < 0.05) reduced by pH-PPI and UP-PPI. The secondary structure contents showed that the α-helix and β-turn of UP-PPI increased by 2.45 % and 6.77 %, respectively, while the β-sheet decreased by 8.38 %, compared with the control. UP-PPI destroyed the microstructures of the proteins as indicated by SEM. In conclusion, the co-modification of ultrasound and pH shift effectively improved the functional properties of PP, broadening the development of PP for various food applications.