Impact of continuous and repeated dry heating treatments on the physicochemical and structural properties of waxy corn starch.

In order to investigate the impact of continuous dry heating treatment (CDHT) and repeated dry heating treatment (RDHT) on the structural and physicochemical properties of the waxy corn starch, the starch was prepared at 140 °C for continuous 20 h or for 5 cycles of heating, respectively. Each cycle lasted 4 h and the interval between each cycle was 1 h of cooling at room temperature. It turned out that RDHT and CDHT caused the aggregation of the starch into big lumps. The crystal type of CDHT and RDHT starches remained A-type, while the relative crystallinity and the short-range molecular order of starch characterized with 1040 cm-1/1018 cm-1 increased during first 2 circulations of RDHT and first 8 h of CDHT afterwards decreased upon the increased duration. After the heat treatment the water absorption index, swelling volume, viscosity and thermal parameters of CDHT and RDHT starches decreased, but the solubility, paste clarity and paste temperature of starches increased compared with native starch. Taken together RDHT has a greater impact on decreasing transmittance of starch paste, weakening the resistance to shear force and increasing retrogradation degree of starch paste compared to CDHT for the same duration.