Physical modification on gelation of fish gelatin by incorporating Nicandra physalodes (Linn.) Gaertn. pectin: Effect of monovalent and divalent cation ions

Fish gelatin (FG) is more appreciated by religious people than mammalian gelatin. However, the relatively poor gelling capacity of FG limits its applicability in the food industry. In this study, Nicandra physalodes (Linn.) Gaertn. pectin (NPGP) was incorporated into FG to modify its gelling capacity, and the effect of monovalent (Na+) and divalent cations (Ca2+) on the gelation process of FG/NPGP mixtures was investigated. At a fixed concentration of FG (5.0 %, w/v) and NPGP (0.2 %, w/v), mixing the two polymers at natural pH condition (pH ≈ 6.0) led to significant intermolecular electrostatic association, which increased the gel hardness by producing an FG-dominant network augmented by NPGP molecules. When Na+ and Ca2+ were introduced, the electrostatic association was greatly decreased, which further weakened the gels. At low Ca2+ concentration (5 mM), however, FG, NPGP and Ca2+ formed tertiary complexes, which provided additional crosslinks and thus increased the gel strength.