Structural, functional and digestibility characteristics of sorghum and corn starch extrudates (RS₃) as affected by...

The aim of the study was to compare the properties of resistant starch (RS₃) formed during extrusion of corn and sorghum starches. The extrudates were stored for 7 and 14 days at 4 °C to allow for molecular rearrangement i.e. retrogradation. The extruded starches were analyzed for enzymatic digestibility, long range (X-ray diffraction, XRD) and short range (FTIR) molecular order, thermal characteristics (DSC) and rheological properties as affected by temperature. The highest RS (70.64%) was obtained for sorghum extrudate (ES₁₄) as compared to corn extrudate (EC₁₄) (64.90%), on 14th day of storage. The increase in RS correlates with the increase in percent crystallinity (%Xc), too. The (ES₁₄) reported the highest %Xc among all extrudates i.e.37.83. The XRD results showed an additional peak at 13° and 20°, reflecting the formation of V-type pattern in all samples. The FTIR spectroscopy also exhibited increase in the ratio of 1047 cm^-1/1151 cm^-1 and 1047 cm^-1/1022 cm^-1. The extruded starch showed significantly higher thermal stability and lower cold paste viscosity. The significant (p ≤ 0.05) decrease in the glycemic index was obtained as the storage time increased. The (ES₁₄) exhibited glycemic index equal to (EC₁₄) i.e.55.53 and 52.53, respectively; thereby making it a suitable substitute of corn starch.