Impact of hot alkali modification conditions on secondary structure of peanut protein and embedding rate of curcumin

Abstract

This study aimed to modify isolated and extracted peanut protein with hot alkali to study the impact of pH, heating temperature, processing time and other alkali liquor conditions on the molecular structure of the peanut.Curcumin was loaded in modified peanut protein.The results of the study are as follows:Within the alkaline range of 8 < pH < 12, the percentage of amino acid residue (AAR) and β-turns first increased and then decreased with the increasing pH, and the percentage of AAR reached a maximum 5.21 ± 0.33% when the pH was 11 (p<0.01). The percentage of α-helices and β-sheets gradually decreased with increasing pH, while that of random coils gradually increased with increasing pH, reaching a maximum 11.24 ± 0.87% when the pH was 11(p<0.05). Within the range of the heating temperature 75 °C < T < 95 °C, the percentage of random coils and β-sheets gradually increased with increasing heating temperature, while that of α-helices and AAR gradually decreased with increasing heating temperature; they remained unchanged when the heating temperature was 90 °C, and then decreased to (10.41 ± 1.18%; p<0.01) and (4.02 ± 2.12%; p<0.01), respectively. Within the range of 5 min < t<20 min, the percentage of random coils and AAR gradually increased with increasing heating time, while the percentage of α-helices decreased from 11.83 ± 1.04% to 10.75 ± 2.34% with increased heating time (p<0.01). The optimum conditions for hot alkali modification of peanut protein as followed: heating temperature of 90 °C, heating time of 20 min and a pH of alkali liquor of 11. Under these optimum conditions, the embedding rate of curcumin by the modified protein can reach 88.32 ± 1.29%.