Ultrasonic-acid modification of 70-kDa silkworm protein improves interfacial and rheological functionality for...

Silkworm pupa protein contains a 70 kDa fraction (SPP-70) that plays a primary role in stabilizing oil-in-water high internal phase emulsion (HIPE), yet its molecular mechanism remains unclear. Thus, How SPP-70 stabilizing HIPE under ultrasound-acid conditions and its behavior at the oil/water interfacial are the main objectives of this study. The ultrasonic-acid treatment increased the zeta-potential, reduced the particle size and triggered the secondary structure transitions of SPP-70. After 20 min treatment, SPP-70 exhibits the strongest interfacial activities, surface hydrophobicity increasing 1.7-fold and interfacial rearrangement rate increasing from -20.20 × 10^-4 (s^-1) to -52.70 × 10^-4 (s^-1). The formed gel-like emulsion demonstrated thick interfacial layers, improved droplet stability, and superior rheological behavior during storage. Non-equilibrium molecular dynamics simulations revealed that the protonation of terminal glutamic acid, aspartic acid, and lysine residues under acidic condition increase the structural flexibility of SPP-70, thereby facilitating ultrasound-induced unfolding. After ultrasonication, residues 1-450 of chain B (SPP-70B) became enriched in α-helices and β-turns, showing great solvent accessibility, and approaching the oil-water interface more closely than chain A (SPP-70 A). Collectively, the results suggested that the ultrasound-acid treatment synergistically induced structural unfolding and hydrophobic exposure of SPP-70, providing a molecular rationale for its superior interfacial adsorption and offering new insights for the design of protein-stabilized gel-like emulsion.