Physical behaviour of fish gelatin-κ-carrageenan mixtures

Fish gelatin is a possible alternative to, but not directly exchangeable with, mammalian gelatin due to low gel strength and low gelling and melting temperature. A possible approach to overcome these differences could be to mix fish gelatin and marine polysaccharides leading to systems with improved gel strength, gelling and melting temperature. Mixtures of fish gelatin and κ-carrageenan resulted in solutions and gels with varying degree of turbidity, depending on the concentration of polymers, pH, ionic strength and the nature of the added salt. The turbidity is most probably a result of phase separation in the system and was followed by measuring the optical density. Complexes of fish gelatin and κ-carrageenan at 60 °C were probably stabilised by electrostatic interactions, and the solutions were highly turbid. At room temperature and at 4 °C the turbidity of the mixed systems was much lower, and could be due to altered gel morphology. The system is believed to segregate when carrageenan adapts the ordered conformation and forms a gel network. Compression measurements revealed a considerable increase in Young's modulus when mixed solutions were allowed to gel at 4 °C compared to gelling at room temperature.