VISCOELASTIC BEHAVIOR OF GELATIN IOTA-CARRAGEENAN MIXTURES/

Mixtures of acid gelatin (8.5 < pI < 9.0) and iota-carrageenan have be en studied. By drawing, phase diagrams of mixed systems, attractive in teractions between the two types of chains are shown to exist In our e xperimental conditions (pH = 6.5, 0.2M NaCl). Both biopolymers undergo a conformational disorder (coil) / order (helix) transition under sui table conditions of temperature and salt concentration. These extended chains are able to form thermoreversible networks by associating heli ces in junction zones stabilized by hydrogen bonds. As the coil / heli x transition temperatures of the two biopolymers are well separated (a bout 40 degrees C and 65 degrees C for gelatin and iota-carrageenan, r espectively), so are the temperature domains of the sol-gel transition . The evolution during melting of the elastic modulus G' of a gelatin gel, an iota-carrageenan gel and a mixed gel is studied. Three levels of structuration are defined with regard to the melting (T-mg) and to the helix / coil transition (T-transc/g) temperatures of gelatin on on e hand and to the melting temperatures of mixed gel (T-mm) on the othe r. A mechanism based on associative interactions between gelatin ana t -carrageenan chains is proposed to explain these results.