Microstructure analysis of high pressure induced gelatinization of maize starch in the presence of hydrocolloids

The effect of high hydrostatic pressure (HHP) treatment on maize starch granules was analyzed taking into account different operating conditions (time, temperature, high pressures and starch to water ratio) and the effect of hydrocolloids (λ-carrageenan, guar and xanthan gum). Morphological analysis using different microscopic techniques, mainly SEM and Cryo-SEM, was carried out. This study was complemented with information acquired through Differential Scanning Calorimetry (DSC), X-ray diffractometry (XRD) and spectrophotometric determination of the amylose and amylopectin concentrations released from the granules. The gelatinization degree obtained by DSC increased accordingly with the intensity (pressure level and exposure time) of the HHP treatment, while the gelatinization temperature was scarcely affected. The presence of hydrocolloids in the suspension during HHP processing would ensure water availability. Almost complete gelatinization was observed for the sample treated at 700 MPa, both by DSC and XRD. At 400 MPa the gelatinization degree was significantly lower in starch with added xanthan gum (XG) in comparison to the other hydrocolloids, denoting a possible stabilization effect of XG on the starch granular structure during gelatinization. Maize starch granules (A-type XRD pattern), when submitted to HHP treatment, showed characteristic peaks of A and B-type patterns. Signals of V-diffraction pattern, ascribed to amylose-lipid complexes, were detected by XRD in samples submitted to either very high pressure (700 MPa), long treatment times at 400 MPa (120 min) or in presence of hydrocolloids (at lower pressures and times). The formation of V-crystalline complex would be favored by hydrocolloids presence under pressure. These results correlated well with the lower concentrations of amylose released from granules after these treatments.