Effect of pH on the structure and emulsification properties of ultrasonicated water-soluble protein from Moringa oleifera seed

The Moringa seed protein (MOS) is a new protein resource, the development and utilisation of MOS is still in its early stages due to the late introduction of its varieties. To improve the range of available MOS protein, this study investigated the effects of different pH levels on the ultrasonic modification of MOS protein (UMOWP), exploring the feasibility of UMOWP emulsion systems in food. The zeta potential analysis revealed that the isoelectric point (pI) of UMOWP was 5.8. The secondary structures of UMOWP could be regulated by pH. Moreover, different secondary structures led to different tertiary structures and chemical bonds in UMOWP. Compared with pH values near pI, surface hydrophobicity significantly increased but the total S-S group and particle size decreased away from pI. Furthermore, UMOWP partially dissociated at pH 3, and the degree of dissociation was weaker at pH 9 and pH 11. These structural changes led to significant improvements in the emulsification properties of UMOWP at pH 11, resulting in better environmental stability of the emulsion. These findings provide a foundation for the potential application of MOS proteins in the food industry.