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Structural relation between starch and protein in bread and pasta studied by confocal laser scanning
microscopy (CLSM). S. Handschin, C. Zweifel, S. HUG-ITEN, B. Conde-Petit, and F. Escher. Swiss
Federal Institute of Technology (ETH), Institute of Food Science, CH-8092 Zurich, Switzerland.
Bread and pasta are both mixed polymer systems with starch and
protein being the principle structuring elements. However, large differences exist between the two wheat
products regarding the structural relation between starch and protein and their changes during processing.
Therefore, this study aimed to describe microstructural transformations of bread and pasta during baking
and cooking by confocal laser scanning microscopy (CLSM). Fresh samples or thick cryostat sections were
prepared. Autofluorescence had to be bleached, and then the samples were stained either with Safranin O
for starch or Acid Fuchsin for protein. In dried pasta the starch granules are fully encapsulated by a
continuous dense protein network. During cooking, the successive denaturation of the protein fraction and
the gelatinization of the starch granules lead to the development of a bicontinuous starch-protein network in
the outer layer of the pasta strand. In bread dough, starch-protein segregation occurs already prior to baking.
During heating of the dough, starch gelatinization, phase-separation of starch, and formation of an
intergranular starch network can be followed by CLSM. Changes in the starch fraction during baking and
aging of bread crumb was found to alter Safranin staining of starch. CLSM has been proven to be a
powerful tool for characterizing changes in the protein and starch fraction during processing of bread and
pasta.
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