Effects of different moisture contents on the structure and properties of corn starch during extrusion

•Corn starch with different moisture contents was prepared by twin-screw extrusion.•The structural properties of the samples decreased with increasing moisture content.•Moisture content affects the pasting properties of corn starch.•With increasing moisture content, the distribution of chain length changed.•With increasing moisture content, the dispersion of molecular weight increased. Herein, corn starch samples with different moisture contents (native corn starch, 30, 35, 40, 45, and 50%) were prepared by twin-screw extrusion, and the structural and physical properties were analyzed and correlated. Scanning electron microscopy observed the morphology, attenuated total reflection-Fourier transform infrared spectroscopy investigated the double helix structure, X-ray diffraction analyzed the crystal region, ion chromatography observed the chain length distribution, and rapid viscosity analyzer measured the viscosity of corn starch samples. We found that the corn starch crystallinity, degree of order, and double helix degree decreased with increasing moisture content. The moisture content has a crucial role in the peak viscosity, breakdown, final viscosity, and setback in pasting property experiments. With the increase in moisture content, the longer chain was transformed into a shorter chain, and the dispersion of molecular weight distribution continuously increased. This study provides a theoretical basis for the production of extruded corn starch.