Thermal transitions of fonio (Digitaria exilis) starch: modeling and phase diagram from DSC analysis

The thermal transitions of fonio ( Digitaria exilis ) starch were investigated over a wide range of temperatures (20–160 °C) and water contents (0.3–3.0 kg kg −1 dry basis) using differential scanning calorimetry (DSC) combined with Gaussian deconvolution and thermodynamic modeling based on the Flory–Huggins equation. Three distinct endothermic transitions were identified: gelatinization ( T G = 71−90 °C), crystallite melting ( T M1 = 74−126 C), and amylose–lipid complex dissociation ( T Cx = 95−149 C). Under excess-water conditions, the total transition enthalpy was 15.0 J g −1 , consisting of contributions from gelatinization (7.1 J g −1 ), melting (6.6 J g −1 ), and complex dissociation (1.3 J g −1 ). The gelatinization temperature stabilized at around 73 °C under excess-water conditions and increased to approximately 141 °C under dry-state extrapolation. The model accurately reproduced the peak shapes and enthalpy changes (R 2 > 0.90) and predicted a residual unconverted fraction ∼ 10 % (w/w) at 100 °C, indicating incomplete complex dissociation during steaming. Compared with rice, wheat, and millet, fonio starch exhibited unusually shigh thermal stability and a persistent secondary (M1) transition, which is consistent with its high-amylose, A-type crystalline structure. These findings emphasize the distinctive multiphase behaviour of fonio starch and demonstrate the predictive capacity of the proposed model in optimizing hydrothermal processing and texture development in fonio-based foods. • DSC revealed three transitions in fonio starch: G, M1, and Cx. • Overlapping endotherms resolved by Gaussian peak fitting. • Flory–Huggins model fitted peak temperatures of all three transitions. • Fonio shows high amylose content and persistent Cx under all conditions. • Phase diagram predicts starch conversion vs water content and temperature.