Physical and rheological properties of fish gelatin compared to mammalian gelatin

Abstract

This study comprises characterisation of fish gelatin (FG) from cold water fish species, including rheological and optical rotation measurements. SEC-MALLS analysis revealed that fish gelatin is heterogeneous in molecular compositions and that it mainly contains α- and β-chains. Fish gelatin gave gels with a considerably lower storage modulus, G′, gelling (4–5 °C) and melting temperature (12–13 °C) compared to mammalian gelatin gels. This is probably due the lower content of proline and hydroxyproline in fish gelatin. Recording the storage modulus for 10 (w/w)% FG at various ionic strengths showed that G′ increased at low ionic strengths, while decreasing at medium to high salt concentrations. This suggests that electrostatic interactions are important in the stabilisation of the gelatin gel network. This suggestion was further supported by a partly reversible lowering of the gel modulus by the neutralisation of the carboxyl and amino groups at low and high pH, respectively. Optical rotation experiments clearly showed the importance of the amount of Pro and Hyp present in the gelatin. The degree of chain segment ordering at the gelling temperature in fish gelatin (at 5 °C) and mammalian gelatin (20 °C) was almost identical. This clearly showed the importance of the content of imino acids for the formation of some ordered structures and stabilisation of the gelatin gel network.