“Nutritional and Structural Characterization of Mango and Potato Peel Powders and Foxtail Millet for Sustainable Functional Food Development”

Background and Aim: The increasing demand for sustainable and nutrient-dense functional foods has driven interest in the valorization of agro-industrial by-products. Mango peel, potato peel, and foxtail millet are underutilized resources with considerable nutritional and functional potential. This study aimed to evaluate the nutritional composition, microstructural features, and crystalline properties of mango peel powder (MPP), potato peel powder (PPP), and foxtail millet flour (FMF) to assess their suitability for functional food applications. Methods: Proximate composition, including moisture, ash, crude fiber, protein, and total phenolic content, was determined for MPP, PPP, and FMF. Microstructural characteristics were examined using Scanning Electron Microscopy (SEM), while crystalline and structural properties were analyzed through X-ray diffraction (XRD) to evaluate their compatibility in composite food formulations. Results: MPP (8.39 ± 0.15%) and PPP (7.65 ± 0.12%) exhibited low moisture content, indicating good shelf stability, while FMF showed slightly higher moisture (9.34 ± 0.57%). Mango peel powder contained higher crude fiber (7.32 ± 0.10%) and total phenolic content (50.95 ± 1.10 mg GAE/100 g), highlighting its antioxidant potential. Potato peel powder showed elevated ash content (7.44 ± 0.17%), reflecting its mineral richness. Foxtail millet flour demonstrated the highest protein content (11.65 ± 0.45%), supporting its role as a gluten-free, nutrient-dense base. SEM analysis revealed intact starch granules in FMF, porous fibrous structures in MPP favorable for water and oil retention, and compact matrices in PPP contributing to dough stability. XRD patterns confirmed an A-type crystalline starch structure in FMF and predominantly amorphous structures in peel powders, indicating good compatibility for blended systems. Conclusions: The incorporation of mango and potato peel powders with foxtail millet flour provides a sustainable approach for developing fiber-rich, antioxidant-enhanced, and structurally stable functional foods, supporting waste valorization and circular bioeconomy practices.