Effects of Drying Conditions of Corn Kernels and Storage at an Elevated Humidity on Starch Structures and Properties

The objective of this study was to understand effects of sun drying (35 °C) and machine drying (80 °C) of corn kernels followed by storage at 27 °C and 85−90% relative humidity for up to 6 months on starch structures and properties. The peak viscosity and starch hydrolysis rate using porcine pancreatic α-amylase of finely ground samples decreased with storage of both sun-dried and machine-dried corn kernels. The rate of enzymatic hydrolysis of the isolated starch obtained from the sun-dried corn increased with storage time, but that from the machine-dried corn decreased. The gelatinization temperature, pasting temperature, and percentage crystallinity of the isolated starch increased but the gelatinization enthalpy-change and peak viscosity of the starch decreased with storage time. Numbers of damaged starch granules and starch granules with pinholes increased but the molecular weight of starch and long branch-chains of amylopectin decreased with storage time. The results indicated that endogenous enzyme activity remained after sun drying, which hydrolyzed starch and reduced viscosity.