Structural and thermal transitions in micronized date fruit powder: influence of controlled particle size reduction

• ≤125 µm particles were mostly intact and spherical; 50-25 µm particles exhibited hollow, irregular shapes; <25 µm particles showed spherical, needle-like, or cylindrical structures. • The 50-25 µm fraction had the lowest melting peak ( T m ), highest ΔC p (700 J/kg), and lowest onset T g (-2.4°C to lower values, P<0.05). • The 50-25 µm fraction had the lowest crystallinity (87.1%), compared to 125 µm (89.4%) and <25 µm (93.9%), indicating increased amorphous content. • FTIR absorption intensity increased with decreasing particle size, with the <25 µm fraction showing the highest absorbance, reflecting enhanced structural disruption. Micronization alters the physicochemical and structural properties of food powders, yet its effects on date fruit powders remain poorly defined. This study evaluated three ball-milled particle size fractions of Mebsili date fruit powders, namely, Powder-1 (≤125 µm - coarse), Powder-2 (50-25 µm - intermediate), and Powder-3 (<25 µm - fine) to determine how particle size influences moisture behavior, crystallinity, thermal transitions, and morphology. Moisture increased from 0.26% (Powder-1) to 2.45% (Powder-3), while X-ray diffraction showed the Powder-2 exhibited the lowest crystallinity (87.1%) relative to Powder-1 (89.4%) and Powder-3 (93.9%), indicating higher amorphous content. Differential scanning calorimetry revealed a decrease in glass transition onset temperature from -2.4°C (Powder-1) to lower values in the finer fractions, accompanied by the largest specific heat change (ΔC p ) of 700 J kg -1 at 50-25 µm (P<0.05). Dynamic mechanical analysis identified shifts in structural relaxation (T r ), mechanical glass transition (T g ), and viscoelastic plateau (Tc-Ta) consistent with increased structural mobility at smaller particle sizes. Morphologically, Powder-1 particles remained mostly intact and spherical, whereas Powder-2 particles formed hollow and irregular structures and Powder-3 particles exhibited both spherical and needle-like forms. Collectively, the Powder-2 fraction offered a favorable balance of enhanced amorphous character, higher water interactions, and processing-relevant viscoelasticity. These findings demonstrate that micronization enhances hydration behavior, structural mobility, and amorphous content of date powder. The improved solubility and water absorption observed particularly at the intermediate fraction support its potential use in bakery, beverages, dairy matrices, and sugar-reduction applications. However, adoption of standardized sieve ranges supports cross-study comparability and application-oriented formulation in future research.