Viscoelastic behaviour of gelatin/iota-carrageenan mixtures

Mixtures of acid gelatin (8.5 < pI < 9.0) and t-carrageenan have been studied. By drawing phase diagrams of mixed systems, attractive interactions between the two types of chains are shown to exist in our experimental conditions (pH = 6.5, 0.2M NaCl). Both biopolymers undergo a conformational disorder (coil) / order (helix) transition under suitable conditions of temperature and salt concentration. These extended chains are able to form thermoreversible networks by associating helices in junction zones stabilized by hydrogen bonds. As the coil / helix transition temperatures of the two biopolymers are well separated (about 40°C and 65°C for gelatin and ι-carrageenan, respectively), so are the temperature domains of the sol- gel transition.The evolution during melting of the elastic modulus G' of a gelatin gel, an ι-carrageenan gel and a mixed gel is studied. Three levels of structuration are defined with regard to the melting (Tmg) and to the helix / coil transition (Ttransc/g) temperatures of gelatin on one hand and to the melting temperatures of mixed gel (Tmm) on the other. A mechanism based on associative interactions between gelatin and i-carrageenan chains is proposed to explain these results