Sustainable valorization of discarded black quinoa (Chenopodium quinoa) grains: Impact of particle size on nutritional, functional, and antioxidant properties

The valorization of agricultural co-products represents a promising strategy to reduce food waste while creating new functional ingredients for the food industry. This study aims to evaluate the potential of discarded black quinoa grains (commonly referred as ''destrío'' grains in Spain) as a novel source of functional flour, using particle size-milling to evaluate its influence on the nutritional and techno-functional properties. Four flours with different particle sizes were produced and characterized in terms of chemical composition, mineral profile, physicochemical properties and antioxidant capacity. Particle size reduction significantly modified the distribution of nutrients and bioactive compounds, increasing protein, ash, moisture, and several key minerals, as well as antioxidant potential. Finer flours exhibited higher water activity, darker coloration, and greater redness and yellowness while medium-size particles displayed the highest oil-holding capacity. Overall, black quinoa flour obtained from ''destrío'' grains emerges as a valuable-added ingredient with promising applications in the development of sustainable food formulations, thus contributing to circular economy principles and improving the eco-efficiency of the agro-food sector.