Obtention of gels from Brama Australis and biaxial extensional viscosity characterization

Gelatine from marine sources (fish skin, bone and fins) has been looked upon as a possible alternative to bovine and porcine gelatine. Fish gelatine from cold water species, such as those from Chilean coast, show low gelling and melting temperature and low gel modulus when compared to mammalian gelatine. Lubricated squeezing flow (LSF) is an useful technique to quantify gel behavior changes and, it has not been applied to gelatine gels obtained from Brama Australis. The objective of this work was to study effects of pH and concentration on the extensional viscosity of Brama australis fish gelatine gels using LSF method. Skin gelatine was extracted from Brama australis fish, cylinders were formed and tested using an Universal Texture Analysis equipment under 30 % deformation. Biaxial tension, deformation gradient, and extensional viscosity variables were obtained. It was found that at a constant pH, force values increased as concentration increased. Conversely, in the case of pH variation, a pH of 8.5 is reached for maximum force. At a constant shear rate, when concentration increases biaxial stress increases; also, although compression rate is kept constant, shear rate values vary due to concentration effects. This behavior can be explained because if a gel has higher concentration, it has less water content and therefore is more rigid due to a higher number of inter and intra molecular bonds, leading to a more stable tridimensional network. Biaxial stress is a textura! parameter influenced by concentration. Extensional viscosity increases with increasing Brama australis fish gelatine concentration.