Stage-specific ultrasound during pH-shifting modulated the structural and functional properties of sunflower seed protein

Sunflower seed protein (SSP) is an emerging plant-derived protein ingredient with high nutritional quality. However, the relatively low solubility of SSP restricted its broader application in food systems. In this work, ultrasound combined with pH-shifting was used to improve the solubility of SSP. Meanwhile, the effects of ultrasound applied at different stages of pH-shifting on the structural and functional properties of SSP were also elucidated. Ultrasound treatment at 150 W and 400 W applied during and after pH-shifting significantly reduced the particle size of SSP and enhanced electrostatic repulsion. SDS-PAGE profiles indicated that the combined treatment decreased the intensity of albumin bands and promoted the appearance of lower molecular weight fragments. Ultrasound at pH 12.0 induced structural unfolding of SSP, exposed more hydrophobic tryptophan residues, and markedly improved emulsifying activity index (13.60 ± 0.15 m 2 /g), emulsifying stability index (566.09 ± 37.36 min) and oil-holding capacity (7.65 ± 0.28 g/g). In contrast, ultrasound applied after pH-shifting significantly increased the molecular flexibility of SSP and strengthened hydrogen bonding interactions, and the solubility of SSP increased by 65.01 % at an ultrasound power of 150 W. Overall, pH-shifting combined with ultrasound markedly enhanced SSP solubility and improved its functionality, expanding its potential use in food systems.