Physicochemical and functional properties of starch isolated from foxtail millet flour by different extraction methods and hydration ratios with nanotechnology-assisted modification and nanoscale characterization

This study examined how different solution extraction methods—aqueous, acidic, and alkaline—affect the physicochemical and functional properties of starch extracted from foxtail millet flour. Millet grains are hydrated at three levels (12.2%, 15%, and 16%) before milling and starch extraction. Among the methods, alkaline extraction using sodium hydroxide showed the best performance. At a concentration of 0.3%, the highest starch yields are obtained for Bk 0.3% (15% hydration) and Ck 0.3% (16% hydration), reaching 63.63% and 63.23%, respectively. These samples also exhibited high total starch contents (around 70%). Alkaline treatment led to a marked reduction in particle size, with Bk 0.3% reaching as low as 0.65 μm. Acid extraction using sodium acetate reduced amylose content compared to aqueous extraction, while increasing acetate concentration raised protein content. Higher hydration rates enhanced apparent density, particularly for acid and alkaline extractions at 0.3%. Sodium hydroxide and sodium acetate treatments showed the highest water absorption capacities (1.8–1.9 g/g), especially at 16% hydration, while oil adsorption capacity decreased under alkaline conditions. The highest solubility and swelling power are observed in basic extraction at 15% hydration and aqueous extraction at 16% hydration, highlighting the strong influence of extraction method and hydration level on millet starch functionality. In addition, nanotechnology-based approaches such as nanoscale modification of starch granules, nano-assisted extraction techniques, and advanced particle size control can further enhance starch functionality, improve water absorption capacity, and optimize structural properties for food and industrial applications.