pH-shifting and high-intensity ultrasound enable the functional design of quinoa protein isolate as a plant-based emulsifier.

Quinoa protein isolate (QPI) derived from dehulling by-products was structurally tailored using a combined pH-shifting and high-intensity ultrasound (HIU) approach to enhance its functionality as a plant-based emulsifier. Alkaline conditions (pH 11) promoted protein unfolding, increasing solubility, surface charge, and exposure of reactive groups, including higher free sulfhydryl content and oil-holding capacity. These changes improved interfacial activity and emulsifying performance. A Box-Behnken design optimized HIU conditions and formulation variables, producing emulsions with minimal phase separation (SI ≈ 0%), small droplet size (0.35 ± 0.02 μm), and dominant elastic behavior (G' > G″). The optimized system also showed high thermal stability (98% at 80 °C). These findings demonstrate that pH-induced structural modification combined with ultrasound enables the functional design of QPI as an effective emulsifier and highlights quinoa by-products as sustainable sources of clean-label ingredients.