Controlled Enzymatic Hydrolysis as a Strategy to Enhance Functional and Bioactive Potential of Quinoa Protein

Despite their nutritional superiority and consumers' growing demand, native quinoa proteins exhibit limited techno-functional properties due to their compact globular conformations and lower aqueous solubility, which restricts their application in functional food systems. To address these limitations, this study evaluates the impact of enzymatic hydrolysis using Alcalase on the techno-functional (solubility, emulsifying capacity) and bio-functional (antioxidant, antihypertensive) properties of protein derived from unprocessed, extruded, and germinated quinoa grains. Protein hydrolysates were prepared at 0 (non-hydrolysed protein), 2, 5, 10, and 20% degree of hydrolysis (DH). Results demonstrated that extrusion and germination pre-treatments nearly double the hydrolysis rate by increasing enzymatic susceptibility through structural modifications. Enzymatic hydrolysis markedly improved protein solubility at acidic pH (pH 4), and particularly in 2% DH samples, while germinated protein hydrolysates reached maximal solubility values of 44 at 10% DH. The emulsifying activity index peaked at 10% DH and pH 7, particularly in proteins from germinated grains (38.8 m²/g). Regarding bioactivity, the highest radical-scavenging activity was found in germinated hydrolysates at low DH (2-5%), whereas maximal angiotensin-converting enzyme inhibition occurred at 20% DH, specifically in germinated samples (IC50 = 0.97 mg protein/mL). These findings highlight not only the importance of traditional variables, such as the DH extent and protein source in the design of functional and bioactive peptides, but also introduce the structure-process-function perspective, highlighting extrusion and germination as effective strategies to formulate food-grade emulsifiers, antioxidants, or antihypertensive hydrolysate ingredients for specific applications in health-promoting and functional foods.