Processing sequence as a design lever: pectin pre-complexation enhances ultrasound-driven interfacial loading, functionality, and volatile profile of yeast protein.

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.