Thermal Behavior of Resistant Starches RS 2, RS 3, and RS 4

The thermal behaviors of 3 resistant starch types--RS 2, RS 3, and RS 4--were investigated. Samples were heated in excess water to specific temperatures, from 35 to 85 °C at 5 °C intervals, and freeze-dried. The treated samples were analyzed using SEM, DSC, XRD, and HPSEC to determine the structural changes at granular and molecular levels. Light microscopy was used to determine real-time thermal behavior of the starches. Although the resistant starches did not show significant morphological changes, as revealed by microscopy, they underwent internal structural changes at low temperatures before complete phase transitions occurred. The structural changes were less in RS 2 compared to the other 2 starches studied. The nongranular material of RS 3's crystallinity decreased gradually from 35 to 85 °C and showed microscopically visible changes at >80 °C. Cross-linking might have prevented RS 4 from becoming completely amorphous within the temperature range (35 to 85 °C) tested. The study indicated that the extent of structural changes depended on the treatment temperature and RS type.