Microwave-assisted extraction of dietary fiber from kinnow mandarin by-products: impact on yield and functional, structural, and thermal properties

The extraction of dietary fiber (DF) from kinnow by-products offers a valuable opportunity for waste valorization and the development of functional food ingredients. This study compared conventional extraction methods (hot water, ethanol, and alkali extraction) with microwave-assisted extraction (MAE) to evaluate differences in fiber yield and functional, structural, and thermal properties. Among conventional methods, alkali extraction provided the highest fiber recovery, but MAE achieved comparable or higher yields with significantly reduced extraction time and lower chemical input. MAE-extracted dietary fiber exhibited superior functional properties, including water-holding capacity (7.78–9.12 g g⁻¹), oil-holding capacity (4.68–5.36 g g⁻¹), and glucose adsorption capacity (3.55–4.24 mmol g⁻¹), higher than those of fibers obtained via conventional methods. FTIR analysis confirmed that MAE-extracted fibers retained key functional groups, such as hydroxyl, carboxyl, and glycosidic linkages, indicating the preservation of cellulose, hemicellulose, and pectin structures. XRD analysis showed that both peel and pomace fibers exhibited semi-crystalline structures, with pomace fibers showing slightly higher crystallinity, reflecting compositional differences between the two by-products. DSC analysis demonstrated good thermal stability in MAE-extracted fibers, with insoluble dietary fiber (ISDF) exhibiting higher thermal resistance than soluble dietary fiber (SDF). Overall, MAE proved to be a sustainable, efficient alternative for dietary fiber extraction, enhancing functionality while promoting kinnow by-product valorization.