title: Conformational transition of native and modified gellan.
abstract: This paper concerns the characterisation of native gellan by differential scanning calorimetry (DSC) and rheology. The stability of the double helix is characterised by Tm and the enthalpy of conformational change. The role of the external salt concentration is investigated; it is shown that Tm is only slightly modified. At ambient temperature, in 10(-2) M NaCl, native gellan behaves as a loose gel (G' > G''). This behaviour disappears when temperature is larger than 60 degrees C. The comparison with deacylated gellan (commercial sample) shows that the position of conformational transition is much more influenced by the salt concentration; the helical structure is less stable and the conformational transition presents a hysteresis between heating and cooling runs when the external salt concentration increases. The rheological behaviour is that corresponding to a solution (G' < G'') at ambient temperature and in 10(-2) M NaCl. When the salt excess increases, then a stronger gel is formed. The differences between the two types of samples are clearly established as well as the relations between the conformation and the rheology of the systems.
authors.affiliation: Centre de Recherches sur les Macromolécules Végétales, CERMAV-CNRS, Grenoble, France.
authors.forename: F
authors.initials: F
authors.lastname: Mazen
authors.forename: M
authors.initials: M
authors.lastname: Milas
authors.forename: M
authors.initials: M
authors.lastname: Rinaudo
mesh_terms: D000107:Acetylation; D002152:Calorimetry, Differential Scanning; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D012212:Rheology; D012492:Salts / Q000737:chemistry
chemical_list: D011135:Polysaccharides, Bacterial; D012492:Salts; C048288:gellan gum