Dry heat and ultrasonication treatment of pearl millet flour: effect on thermal, structural, and in‑vitro digestibility properties of starch

The efect of dry heat (DH, 70 °C, 3, 5, and 8 h), ultrasonication (US, 44 Hz, 10, 20, and 30 min), and their combination on
pearl millet four were evaluated for thermal, pasting, crystalline, and in-vitro starch digestibility properties. The dry heat
treatment for 8 h decreased gelatinization enthalpy and increased peak viscosity, while ultrasonication for 10 and 20 min
increased gelatinization enthalpy and peak viscosity. The FT-IR analysis revealed that the absorbance value of the starch–
lipid complex was higher in dry heat with a corresponding increase in relative crystallinity. However, such pattern was not
observed in ultrasonicated pearl millet fours. Among the diferent treatments dry heat for 8 h, ultrasonication for 20 min and
combination of ultrasonication (20 min) with dry heat (8 h) increased resistant starch content (14.49–31.69%) and decreased
glycaemic index (58.25–48.49). Pearson’s correlation revealed that glycaemic index is inversely related to resistant starch
content and relative crystallinity. The study revealed that dry heat and ultrasonication which are simple and environmentally
friendly technologies could be used to modify the starch properties to enhance resistant starch content in pearl millet fours.
This modifed four could be incorporated in food products with low glycaemic index.