The New Starch

Abstract

A polymer — analogous to starch — was previously prepared by biotransformation from sucrose and the enzyme amylosucrase. The reaction yields a crystalline precipitate of a molecule of degree of polymerisation 60–100 glucose units and fructose monomer. The molecular characterisation of the polymer by ¹³C-NMR revealed a 1,4-coupling of the anhydroglucose units via the alpha glycosidic bond in a strictly linear manner. The new polymer is soluble in ln KOH and DMSO at 20°C. The crystalline precipitate, as synthesised, shows in X-ray wide angle powder diffraction the B-structure of native potato starch. Upon heating in the presence of 18% by weight of water the crystallites transform to the A-structure of native wheat starch. The phase diagram of the new polymer, starch and the solvent/non-solvent shows — above a critical concentration — the formation of a gel phase that comprises an elastically active network. In this network the cross-links are the crystallites of the two polymers with an entirely new structure and the tie molecules are the long branches of the amylopectine. Such gels can be made by an extrusion • process and shaped into oriented, elastic fibers and films.