Anti-plasticizing effect of 1,2-propanediol in melt-extruded polysaccharide/sucrose blends

Based on thermograms obtained by differential scanning calorimetry (DSC), melted extruded matrices that contained icing sucrose, maltodextrin and waxy pregelatinized corn starch plasticized with 1,2-propanediol were not totally amorphous. An amorphous phase, which was characterized by a glassy transition of 46.3 °C ± 3.2, coexisted with another crystallized phase, with a fusion temperature of 159.6 °C ± 3.2. Considering the powder X-ray diffractograms of each ingredient, this amorphous phase was only based on sucrose. Increases in the 1,2-propanediol rate did not decrease the fusion enthalpy measured by DSC during the first heating cycle. However, this value increased before stabilizing. Simultaneously, the glassy transition drops showed a greater molecular mobility. Adding water when 1,2-propanediol had a stable low rate during the extrusion process did not improve the amorphization of sucrose, which was mainly crystallized. For an increase in 1,2-propanediol, the fusion enthalpy increased before remaining stable. A comparative assay with a stable water addition in the presence and absence of 1,2-propanediol was characterized by a decrease in the fusion enthalpy. Utilizing water alone as a plasticizer induced a lower proportion of crystalline phase. These results must be linked with the interactions between 1,2-propanediol, a chemical molecule that is highly hygroscopic, and water; propylene glycol captures a part of the water linked with polysaccharides, inducing a more rigid structure. This solvent, which is then hydrated, moves between saccharide aggregates. For the first time, a molecular model was proposed for an extruded carbohydrate matrix containing a crystalline sucrose plasticized by propylene glycol.