Effect of different extraction methods on starch production from millet flour and their reflection on morphological properties with nanotechnology-driven structural modification and nanoscale characterization

Abstract

This study investigated the effects of aqueous, acidic, and alkaline extraction methods on starch isolated from foxtail millet flour prepared at three hydration levels (12.2%, 15%, and 16%). Millet flour is produced using a Bühler laboratory mill with three breaking and two reduction stages, followed by starch extraction using the three solution systems. Alkaline extraction with 0.3% sodium hydroxide produced the highest starch yields, particularly for Bk 0.3% (15% hydration) and Ck 0.3% (16% hydration), achieving 63.63% and 63.23%, respectively, with only minor reductions in amylose content (17.5% and 19.2%). In contrast, acid extraction using 0.3% sodium acetate at 12.2% and 15% hydration resulted in lower yields (42.40% and 42.60%) while maintaining comparable amylose levels (≈18%). The lowest starch recoveries are observed for aqueous extraction, with yields of 30.39%, 33.50%, and 31.05% for Aw, Bw, and Cw samples, respectively. Increasing grain hydration from 12.2% to 16% enhanced starch yield and induced pronounced morphological changes, particularly under alkaline conditions, demonstrating the strong influence of hydration and extraction chemistry on starch recovery efficiency. Furthermore, nanotechnology-based approaches enable precise control of starch granule structure at the nanoscale, leading to enhanced surface area, improved functional properties, and the development of starch-derived nanomaterials suitable for advanced food, pharmaceutical, and industrial applications.