Effects of infrared heat-moisture treatment on physicochemical properties of corn starch

In this study, corn starch (20 or 30% moisture content) was infrared (IR) treated at 550 and 730 W for 30, 60, or 90 min. Birefringence was mostly retained on infrared heat-moisture treatment but disappeared at the center of some granules, especially those having 20% moisture content. IR-treated corn starch samples retained typical A-type diffraction pattern. A new peak was observed at 2 theta = 20 degrees. Relative crystallinity slightly increased (20% moisture, 550 W) or decreased (30% moisture, 730 W) on IR-treatment. T-p and T-c-T-o values increased significantly as the infrared power increased from 550 to 730 W. The changes in thermal properties of the starch samples treated at higher moisture contents were more notable. Moisture content, infrared power, or treatment time caused significant decreases in Delta H and Delta H-2, as compared to that of native corn starch. Marked changes in viscosity values were detected as the moisture content and infrared power increased. IR-treatment at 30% moisture content altered the pasting profile. However, a typical RVA pasting profile was obtained with a long (23 min) holding period at 95 degrees C and significant decreases were observed for the peak and breakdown viscosity values of the corn starches infrared treated at 30% moisture content.