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Synchrotron spectro-imaging of starch structure and properties
A. BULEON (1). (1) INRA, National French Research Institute for Agriculture, Nantes, France

Synchrotron techniques are being increasingly used on plant biopolymers for a better understanding of biosynthesis, structure or fractionation. This knowledge is essential to achieve a better use of agricultural resources. The presentation briefly describes some results obtained on starch at French synchrotrons SOLEIL and ESRF. Starch is made of two distinct glucose polymers (linear amylose and highly branched amylopectin) and has a complex semi-crystalline granular structure exhibiting size and shape dependence on botanical origin. Most uses of starch require the disruption of the granule through enzymatic or hydrothermal treatments. On native single starch granules, synchrotron was used for mapping both crystal orientation (x-ray microbeam diffraction), and phosphate groups or GBSS1, the enzyme responsible for amylose biosynthesis (x-ray microfluorescence) at the micron scale. A high resolution (0.13 nm) 3D model for A-type starch crystal domains has also been determined using x-ray microbeam diffraction on individual amylose micron-sized single crystals. The other examples concern starch materials and enzymatic synthesis or hydrolysis of starch molecules. The structural anisotropy present in shape memory starch-based materials was analyzed by SR polarized infrared micro-spectroscopy. The structure in solution of amylosucrase and the first stages of entanglement of amylose during its <i>in vitro</i> enzymatic synthesis were determined by Small Angle X-ray Scattering. Remarkable results were also obtained on enzymatic hydrolysis of concentrated raw starch, taking advantage of new techniques implemented at SOLEIL. Synchrotron UV fluorescence was used for 3D mapping of amylases within single starch granules without staining, and synchrotron circular dichroism to approach the conformational changes of enzyme when adsorbed onto solid starch.

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