A critical optimization study on hydrothermal treatment for decortication of pearl millet to improve its consumption efficiency

Abstract

Decortication of pearl millet is difficult due to rigidly attached tough seed coats which can be combated by endosperm hardening through hydrothermal treatments before decortication. Steaming time and pressure in turn affecting temperature during hydrothermal treatment affects net moisture thus effecting milling yield. Hydrothermally treated millet containing 15.5% moisture, tempered with 5% additional water at first stage and 4% at second resulted in 65.4% yield. Optimization of steaming conditions at 12.33 min steaming time and 393.23 kPa of pressure by response surface methodology to achieve highest milling yield proved 42.70% porosity, 72.78% milling yield, and 209.24 N hardness had quadratic relationship where as 86.69% water uptake had linear relationship. Scanning electron microscopy analysis on native, hydrothermally treated decorticated millet, and seed coat exposed transformation of starch from ordered pattern in native to clear mass after the hydrothermal treatment. X-ray diffraction shows change from crystalline state to amorphous solid form of starch granules due to gelatinization which hardens the endosperm hence enhancing decortication. Differential scanning calorimetry thermal analysis was done to study starch gelatinization. Enthalpy of hydrothermally treated was negative and the decorticated grains was positive.