Stabilization of Amylopectin–Xyloglucan Water-in-Water Pickering Emulsions by Yeast Cells

Pickering water-in-water (W/W) emulsions stabilized by biocompatible particles represent a promising strategy for the design of functional soft materials. In this study, we investigate the ability of Saccharomyces cerevisiae, in both viable (Y-AC) and thermally inactivated (Y-IN) forms, to stabilize amylopectin–xyloglucan (AMP–XG) W/W emulsions, providing the first report of yeast-based Pickering stabilization in this polymer–polymer system. Physicochemical characterization, including FTIR, ζ-potential measurements, and potentiometric titration, revealed that thermal inactivation induces a reorganization of the cell wall, increasing the fraction of titratable sites (from 23% to 50%) while preserving the overall acid–base balance and net negative surface charge. The ζ-potential was highly sensitive to ionic strength: the addition of 1 mmol L–1 NaCl reduced its magnitude by approximately 50%, whereas 20 mmol L–1 nearly suppressed electrostatic repulsion. Stability assays showed that Y-IN at 6.0 × 104 cells mL–1 provided effective interfacial coverage and delayed phase separation. However, elevated ionic strength (20 mmol L–1 NaCl), induced yeast migration toward the AMP-rich phase, compromising emulsion stability. Confocal microscopy confirmed that viable cells also strongly adsorb at the polymer–polymer interface but undergo similar salt-induced migration at high ionic strength. Contact angle measurements further indicated a shift in wettability toward the dispersed phase, increasing from 89° ± 11° to 116° ± 10° (Y-IN) and from 114 ± 18° to 130° ± 7° (Y-AC) with increasing salt concentration. Overall, these findings demonstrate that yeast particles can function as natural stabilizers for AMP–XG W/W emulsions, with ionic strength acting as a key parameter in modulating interfacial adsorption and phase affinity.