Characterisation of browntop millet (Brachiaria ramosa) bran fractions: Nutritional, functional, and structural properties across particle sizes

Browntop millet (Brachiaria ramosa (L.) Stapf.) bran was fractionated into five particle size classes ranging from coarsest, BSS30 (600 µm) to finest BSS100 (150 µm), and characterized for nutritional, techno-functional, and structural properties. Moving from coarse to fine fractions, moisture (12.66–10.16%), ash (6.96–4.10%), crude fat (10.66–7.73%), crude fiber (17.50–14.14%), and antinutritional factors (tannins and phytic acid) decreased significanyly, while crude protein (10.28–12.34%), and carbohydrates (41.94–51.53%) increase, reflecting a progressive shift from pericarp dominant to endosperm enriched composition. Functional properties, including oil holding capacity (12.03–14.51 g/g), emulsifying activity (41.46–54.00%), emulsifying stability (36.30–49.90%), foaming ability (18.53–26.60%), and foaming stability (14.16–20.83%) all increased significantly from BSS30 to BSS100, attributed to progressive cell wall disruption and protein surface exposure. Water-holding capacity peaked at BSS52 (12.23 g/g) and declined at BSS100 (9.10 g/g), likely due to over-grinding that disrupted the capillary network. Bulk (0.65–0.35 g/mL) and tapped densities (0.71–0.73 g/mL) decreased, while true density (1.21–1.58 g/mL) and porosity (46.00–77.47%) increased with decreasing particle size. Total phenolic content (0.644–0.85 mg GAE/g), total flavonoid content (1.18–2.05 mg QE/g), and DPPH radical scavenging activity (36.5–51.2%) increased progressively, with BSS100 showing maximum antioxidant potential due to the release of bound phenolics from the disrupted matrix. SEM also confirmed morphological transition across particle sizes. BSS52 is recommended for hydration-dependent applications, while BSS100 is optimal for emulsification, foaming, oil-holding, and antioxidant-rich formulations, thereby establishing sieve fractionation as an effective valorization strategy for browntop millet bran.