Effect of conditions of modification on thermal and rheological properties of phosphorylated pumpkin starch

This study aimed at analyzing the effect of conditions of modification process on thermal and rheological properties of phosphorylated pumpkin starch. The esterification process was conducted at 115 °C and 145 °C for 1, 2, and 3 h. The thermodynamic properties of samples were determined using differential scanning calorimetry (DSC), flow curves were plotted and the resulting curves were described the Herschel-Bulkley model, textural properties were evaluated with the TPA method. The data proved that the chemical modification of starch affected its rheological and thermal characteristics, but the direction and extent of the changes were found to depend on both temperature and duration of phoshorylation. The results demonstrated that temperatures of gelatinization of the samples modified at 145 °C were higher by 1.4-8.5 °C than those of the samples obtained at 115 °C. Prolongation of starch modification at 115 °C caused reduction of shear stress (from 2.10 Pa to 0.86 Pa), and higher temperature of esterification also reduced the value of this parameter. The hardness of the samples heated at 145 °C was higher by 45-59 N than that of heated at 115 °C. Adjustment of phosphorylation process caused an increase in gumminess by 1.8-37.9 N, wherein higher temperature and process prolongation resulted in the highest gumminess.