Granular morphology, molecular structure and thermal stability of infrared heat-moisture treated maize starch with added lipids

The thermal and structural changes of infrared heat-moisture treated (IR-HMT) maize starch with added stearic acid (SA) (1.5% w/w) were investigated. Scanning electron microscopy showed more protrusion and fewer pores on the starch granular surface for maize starch with IR-HMT plus SA. Transmission electron microscopy showed that IR-HMT promoted more interactions between starch blocklets and resulted in a more fused blocklet organisation. IR-HMT seemed to increase hydrogen bonding between starch polymeric chains. These interactions are shown by the increased relative crystallinity shown by crystalline peak area calculated from X-ray diffraction and the higher 1047/1022 cm-1 band ratio from FTIR at a molecular level. In addition, at a molecular level, dynamic mechanical thermal analysis and differential scanning calorimetry showed evidence of amylose-lipid complexes in IR-HMT starch with SA. These changes can be related to already reported functionality such as reduced starch digestibility of IR-HMT maize starch with stearic acid IR-HMT.