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

The effect 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 flour 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 flours. Among the different 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 flours. This modified flour could be incorporated in food products with low glycaemic index. [ABSTRACT FROM AUTHOR]