Some preliminary experiments were done on maize starch with 16% water. It was observed that DSC profiles recorded with and without insert did not coincide. This indicates that the conditions of preparative DSC do not truly represent the events that occur in a common DSC experiment. Because, in contrast to potato starch, the maize starch pellets shrunk on heating, an insert was not required for their removal from the pans. Inspection of the samples heated through the M transition without insert revealed that these were inhomogeneous: about half of the granules were still birefringent and melting had occurred predominantly in the upper part of the sample. The most likely explanation for sample inhomogeneity is the high cohesiveness of maize starch powder in comparison to potato starch powder, which is related to its smaller particle size. This leads to a lower bulk density. The observed inhomogeneous melting precluded a study as that for potato starch at the time of the present investigation. It also questions the validity of conventional DSC experiments with maize starch at the conditions employed. A possible solution is to increase the packing density by addition of a flow conditioner and/or compression of the powder sample. Other options are to reduce sample size
and heating rate (Yu & Christie, 2001). Whatever the selected approach, it should always include a test for sample homogeneity after thermal processing.
Some preliminary experiments were done on maize starch with 16% water. It was observed that DSC profiles recorded with and without insert did not coincide. This indicates that the conditions of preparative DSC do not truly represent the events that occur in a common DSC experiment. Because, in contrast to potato starch, the maize starch pellets shrunk on heating, an insert was not required for their removal from the pans. Inspection of the samples heated through the M transition without insert revealed that these were inhomogeneous: about half of the granules were still birefringent and melting had occurred predominantly in the upper part of the sample. The most likely explanation for sample inhomogeneity is the high cohesiveness of maize starch powder in comparison to potato starch powder, which is related to its smaller particle size. This leads to a lower bulk density. The observed inhomogeneous melting precluded a study as that for potato starch at the time of the present investigation. It also questions the validity of conventional DSC experiments with maize starch at the conditions employed. A possible solution is to increase the packing density by addition of a flow conditioner and/or compression of the powder sample. Other options are to reduce sample sizeand heating rate (Yu & Christie, 2001). Whatever the selected approach, it should always include a test for sample homogeneity after thermal processing.
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