A combination of microwave treatment and covalent binding of gallic acid improves the solubility, emulsification and thermal stability of peanut protein isolate

This work aimed to investigate the effect of a combination of microwave treatment and covalent binding of gallic acid (GA) on the structural and functional properties of peanut protein isolate (PPI). It was found that PPI exhibited the maximum solubility at microwave power of 480 W, 60 °C for 4 min. The microwave-treated peanut protein isolates (MPPI) had more binding sites than PPI. Of these, the MPPI-GA1.60 conjugate had the highest GA binding content (436.6 nmol/g PPI). GA showed a significant effect on the secondary structure of PPI and MPPI by inducing the transition from α-helix and β-sheet to β-turn and random coil, and their rigid globular structures were disrupted to increase the molecular flexibility. The negative charges (from −39.32 mV to −54.94 mV) and average particle size (from 260.23 nm to 338.53 nm) of PPI/MPPI-GA conjugates were increased with the GA concentration and the dispersibility of conjugates was improved. Moreover, the solubility, emulsion stability and thermal stability of PPI/MPPI-GA conjugates were significantly enhanced, with the MPPI-GA0.80 conjugate being the best. It was shown that the microwave treatment and covalent binding had a synergistic effect on the improvement of the functional properties of PPI. This research may provide a new approach to improving the functional properties of PPI and help to expand the utilization of PPI in the food industry.