Thermal, structural, and emulsifying properties of pumpkin seed protein isolate subjected to pH-shifting treatment

In this study, the thermal, structural, and emulsifying properties of pumpkin seed protein isolates (PSPI) subjected to pH-shifting were investigated. PSPI subjected to different pH values (pH 2, 4, 6, 8, 10, and 12), were named PSPI 2, PSPI 4, PSPI 6, PSPI 8, PSPI 10, and PSPI 12, respectively. According to the differential scanning calorimetry analysis, the control PSPI exhibited denaturation temperatures of 87.67 and 104.11 °C, and their corresponding enthalpies were 1.66 and 0.37 J/g, respectively. Among the PSPI samples, only PSPI 2 showed no significant difference in denaturation temperatures and enthalpies as compared to the control PSPI. The emulsifying activity indexes of PSPI 2, PSPI 4, and PSPI 12 increased (p > 0.05) by 205.84, 298.98, and 288.69%, respectively, and the emulsion stability indexes of these three samples increased by 42.32, 67.58, and 40.87%, respectively. The disulfide bond contents of PSPI 2, PSPI 4, and PSPI 12 increased by 7.46, 9.28, and 5.01%, respectively, and the free sulfhydryl group contents of these three samples decreased by 36.69, 44.39, and 29.11%, respectively, which indicated that the improved emulsifying properties of PSPI 2, PSPI 4, and PSPI 12 might be correlated to the increased disulfide bond contents and decreased free sulfhydryl group contents. However, the emulsifying properties of PSPI samples had no obvious correlation with their surface hydrophobicity and particle sizes.