Pressurization of some starches compared to heating: Calorimetric, thermo-optical and X-ray examination

Starch suspensions (30%), from pea and corn samples, with amylose (AML) contents ranging from 28% to 75%, were pressurized between 150 and 650 MPa for 30 min at room temperature. Differential scanning calorimetry (DSC), assisted by thermo-optical polarized microscopy (TPM) and X-ray diffractometry (XRD), was used to demonstrate the difference between pressure-gelatinization and heat gelatinization. The higher amylose content made the starch more resistant to pressure-induced gelatinization. Normal corn (28% AML) and pea starches (35% AML) partially gelatinized at 400 MPa and up, however pressurization produced low-quality gels with granular structure. Conversely, high amylose corn starches (55% and 70% AML) did not gelatinize at all (even at 650 MPa), although the starch suspensions underwent slight increases in viscosity. Retrogradation occurred either concurrently or immediately after pressurization as opposed to long-term thermal retrogradation. XRD revealed that a second scan produced vitrification and possible resistant starch formation in gelatinized/gelled starches.