dr. Agnes Rolland-Sabbaté : Starches and glucopolymers with various branching pattern: properties and biodegradable materials

Abstract

Polysaccharides generally extracted from plants, algae or produced by microbial fermentations are widely used as texturizing agents. They are also interesting biodegradable materials that could be used for packaging or smart materials. The macromolecular characteristics, thermal properties and film-forming ability of branched glucose-based biopolymers presenting different structures were studied: glycogens, amylopectins and dextrans synthesized in vitro by dextransucrase mutants (Irague et al., 2012). The structure and size of the a-glucans were investigated using NMR and asymmetrical flow field flow fractionation (A4F) coupled with multi-angle laser light scattering (MALLS) for in-depth analysis of their structural heterogeneity. The calculated macromolecular conformation and shape in solution were discussed as a function of the branching degree studied by NMR. The degree of branching varied from 6 to 8%, 3 to 20% and 3 to 5% for glycogens, dextrans and amylopectins, respectively. Glycogens and dextrans had very broad molar masses and size distributions whereas an antagonistic trend was observed for amylopectins. The molar mass ranged from 5.2 x·106 to 1.8 x·107 g.mol-1, 7.6 x·107 to 6.0 x·108 g.mol-1, and 1.2 x·108 to 4.2 x·108 g.mol-1 for glycogens, dextrans and amylopectins, respectively (Rolland-Sabaté et al.,2011, 2014; Irague et al., 2012). Glycogens and amylopectins exhibited a spherical conformation in solution with a Rg/Rh ratio characteristic of dendritic and hyperbranched structures, respectively, whereas the series of dextrans exhibited more extended conformations from hyperbranched to quasi-linear comb-like structures. Glycogens and amylopectins had an average glass transition temperature (Tg) around 90 and 110 °C. Dextrans exhibited a Tg between 30 and 86 °C, and some of them had a good film-forming ability. Like for synthetic polymers, the Tg of these a-glucans is a function of the molar mass and branching characteristics (type of glycosidic linkage, degree, type and topology of branching). These results open new perspectives for the design of biosourced materials for food or non-food applications.