Processing sequence as a design lever: pectin pre-complexation enhances ultrasound-driven interfacial loading,...

Yeast protein (YP) aggregates at neutral pH, limiting dispersibility, interfacial performance and flavour acceptability. We tested whether the processing sequence between low-methoxyl pectin (PEC) complexation and high-intensity ultrasound (US) can be used as a design lever to re-engineer YP. Six treatments (native YP, buffer-mediated control, US, PEC, US→PEC, PEC → US) were prepared and evaluated at pH 7.0 for colloids (DLS size/ζ, turbidity, dispersible fraction), interfacial loading [interfacial protein adsorption (AP) and surface excess (Γ) by depletion], techno-functionality (emulsifying and foaming), molecular structure (surface hydrophobicity, fluorescence, CD, FTIR, -SH/S-S) and volatiles (HS-SPME-GC-MS, e-nose/e-tongue). PEC → US yielded the smallest hydrodynamic diameter and most negative ζ-potential, markedly reduced turbidity, and the highest dispersible protein fraction. Across treatments, interfacial metrics rose stepwise (AP 20.5 → 68.7%, Γ 1.05 → 3.35 mg m^-2), tracking increases in emulsifying activity/stability and foam capacity/stability. A selective-solubility assay showed concurrent increases in hydrophobic, electrostatic and hydrogen-bonding contributions, consistent with the hypothesis that cavitation exposes hydrophobic/cationic patches that are rapidly captured in situ by PEC, creating an anionic corona that provides hydrophobic anchoring and electrostatic/steric locking. Spectroscopy and -SH/S-S analysis supported β-ordering and thiol-disulphide reshuffling within PEC-bound, ultrasound-unfolded protein. Volatile profiling indicated reduced aldehydes/sulphur notes in PEC → US, aligning with a denser interfacial film. Overall, sequence-controlled PEC → US provides a mechanistic, food-grade and scalable route to yeast-protein ingredients with enhanced dispersibility, higher interfacial loading (AP, Γ) and improved functional and flavour attributes.