In vitro digestibility and physicochemical analysis of heat-moisture treated finger millet flour and starch†

Abstract

Heat-moisture treatment (HMT) at 110 °C for 6 h (25% moisture content) of finger millet flour (FMF) and starch (FMS) was conducted to assess the effect on their functional, physico-chemical, and in vitro digestibility properties. Water activity (a_w) and pH decreased significantly (p < 0.05) from 0.31 to 0.25 and 6.7 to 6.3 respectively for HMT samples. The oil absorption capacity (OAC), water absorption index (WAI), water solubility index (WSI), and swelling power (SP) also significantly (p < 0.05) increased due to heat-moisture treatments of the samples. The values for the OAC, WAI, WSI, and SP were in the ranges of 1.9–2.5 g g⁻¹, 2.1–10.7 g g⁻¹, 0.14–0.44%, and 3.4–18.4 g g⁻¹, respectively. X-ray diffractometry (XRD) revealed that the HMT-modified samples showed a significant decrease in the relative crystallinity. Scanning electron microscopy (SEM) showed that the FMF sample became clumpier, and the surface of FMS showed more porosity and cracks due to the HMT process. Fourier Transform Infrared (FTIR) spectroscopy indicated the presence of hydroxyl (–OH), alkane (–CH), amine (–NH), carbonyl (–COH), and alkene (CH) functional groups in the regions of 3300–3250, 2930–2850, 1750–1630, 1180–1070, and 930–860 cm⁻¹, respectively. There were no significant changes observed in the number of peaks of the samples due to the HMT process. The rapidly digestible and slowly digestible starch fractions increased significantly (p < 0.05), while the resistant starch fraction decreased due to the HMT process. RDS, SDS, and RS values were in the ranges of 14.3–22.4%, 28.0–60.9%, and 30.9–55.7%, respectively. This study provides a new way of utilizing this starch source for the development of food products and can reduce dependence on other starch sources such as rice and corn.