Effect of Heat-Moisture Treatment on Resistant Starch Content as well as Heat and Shear Stability of Pearl Millet Starch

Abstract

The impact of hydrothermal treatment on functional, rheological, thermal and morphological properties of pearl millet starch was investigated. Starch was modified by heat-moisture treatment (HMT) at 110 °C for 4 h at varying moisture content, i.e. 20 % (HMT-20), 25 % (HMT-25) and 30 % (HMT-30). Resistant starch (RS) content increased significantly (p < 0.05) due to HMT with maximum (6.14 %) for HMT-30. Dextrose equivalent (DE) value also increased due to HMT and ranged between 3.97 and 7.35 %. Solubility of the starch decreased, whereas swelling power and oil absorption capacity increased due to HMT. The pasting temperature increased while peak, breakdown, setback and final viscosity decreased after HMT. The G′ (storage modulus) of starch paste (5 %) from treated samples was lower as compared to native (33.5 Pa). The gelatinization temperature (Tp) increased significantly (p < 0.05) due to HMT. Pearl millet starch granules were mainly round/oval, irregular and polygonal shape with 3–12 µm size. HMT at higher moisture level (30 %) caused cavity on starch granules. This study indicated that HMT increased RS content. The gels of modified starches were softer, having higher self-levelling properties (G′–G″).