Analysis of changes in structure and moisture in starch extrudates during storage using micro-CT and MRI imaging techniques
Castlejohn, Christina Alexis
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The number of extruded starch products has increased in the food industry in recent years. The application of different imaging techniques, such as Microcomputed tomography (microCT) and Magnetic Resonance Imaging (MRI), can provide a better understanding of changes occurring during storage of these products. The goal of this research was to use microCT and MRI to study changes in starch extrudates during 8 weeks of storage. MicroCT found density changes in the pore network of the extrudate and detected high density areas within the solid material. The mean and median pore diameter (0.016 mm) did not change during storage. However, the pore network expanded in size and scope within the first 4 weeks of storage with an increase in the % porosity and the % pore interconnectivity as well as a flattening and widening of the pore diameter distribution. The high density areas, which were concentrated in the center of the extrudate, showed no trend during storage, and their composition is unknown. MRI was used to study changes in the moisture distribution and mobility during storage. Various methods were applied using this technique, including T2 imaging. A complex moisture pattern was seen during storage. Even though the concentration of water remained consistent throughout the extrudate, areas of high and low free water concentration were seen by Week 8 suggesting that the areas of lower free water, found outside the center of the extrudate, contained more bound water. In addition, the free water mobility, which was lower after 8 weeks of storage, was higher in the center even though the highest concentration of free water was not found in the center of the extrudate. These results show a complexity of moisture migration during storage of starch extrudates. The results of both imaging techniques suggest a possible relationship between the structural changes and the complexity in the moisture distribution.