pH-Dependent Changes in the Structural and Functional Properties of Quinoa Protein Isolates in Aqueous Dispersions

Quinoa protein isolate (QPI) is an emerging plant-based ingredient with high nutritional quality and significant potential for sustainable and clean-label food formulations. However, limited understanding of the relationships among its major protein fractions, physicochemical characteristics, and functionality restricts its broader utilization in food systems. This study investigated the effects of pH conditions (3, 5, 7, 9, and 11) on the particle size distribution, soluble-solid recovery, interfacial properties (surface hydrophobicity, emulsification, and foaming), and albumin–globulin protein fraction profiles of three QPI aqueous dispersions (Q1, Q2, and Q3). Alkaline conditions significantly enhanced QPI soluble-solid recovery (from <20% to >70%) and interfacial functionality, which were associated with the dissociation of large protein aggregates (D50 > 3000 nm) into smaller, well-dispersed particles (D50 < 109 nm) and an increased abundance of soluble albumin–globulin protein fractions, particularly chenopodin. SDS-PAGE, densitometry, principal component analysis, and Pearson correlation supported strong relationships among soluble-solid recovery, particle size reduction, interfacial properties, and soluble albumin–globulin protein fractions. These findings provide an integrated understanding of pH-dependent structure–function relationships of quinoa proteins and demonstrate the potential of pH adjustment for modulating the functionality of QPI aqueous dispersions for sustainable, clean-label ingredients in emulsified foods, aerated systems, and next-generation protein-rich formulations.