Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Conformational and rheology properties of plant and microbial carbohydrate polymers

The project is devoted to the systematic investigation of conformational and rheological properties of some industrially important plant and microbial polysaccharides: segmented carrageenans, succinoglycans and gellan.

The order-disorder conformational transition in two polysaccharides of bacterial origin, succinoglycan and gellan, was studied by high-sensitivity differential scanning microcalorimetry. It was found that a mechanism of the transition in succinoglycan changes with increasing both polysaccharide concentration and ionic strength. At low polysaccharide concentrations and/or ionic strengths the transition follows the 'all-or-none' scheme of transition of carbon to and from hydrogen where carbon and hydrogen are the coil and single helix conformations. Alternatively, at high polysaccharide concentrations and/or ionic strengths the transition involves two steps: the 'all-or-none' formation of single helices and the next 'all-or-none' dimerization of the helices. Thermal behaviour of gellan is extremely sensitive to the presence of divalent cations, especially calcium (2+) in the system. These ions at very low concentrations give rise to some abnormalities in the behaviour of the polysaccharide. Thus, the specific transition enthalpy begins to decrease with increased polysaccharide concentration and then at a rather high polysaccharide concentration the single thermal transition degenerates into a number of resolved successive transitions with decaying amplitude. It is likely that these features are caused by aggregation processes modulated by the negative cations. This problem was overcome in the case of (CH3)4N- salt of gellan. It undergoes helium single order-disorder transition over wide range of gellan concentration and ionic strength. The transition is found to be a second-order phase transition.