Extraction and physico-chemical characterisation of Nile perch (Lates niloticus) skin and bone gelatin

Type A gelatins were extracted from skins and bones of young and adult Nile perch and analysed to determine their functional and chemical properties. Total gelatin yield (for sequential extraction at 50, 60, 70 and 95 °C) was in the order adult fish skins>young fish skins>adult fish bones>young fish bones, while percentage gelatin recovery at 50 °C was in the order young fish skins>adult fish skins>young fish bones>adult fish bones. The gelatins obtained were free of fishy odour. Nile perch skin gelatin had turbidity of 20.5–158 NTU and ash content of 0.5–1.7% while bone gelatins had turbidity of 109–517 NTU and ash content of 4.4–11.2%. Bloom gel strength was 81–229 and 134–179 g, respectively, for skin and bone gelatins. Gelatin from adult Nile perch skins exhibited higher viscosity and lower setting time than bone and the young fish skin gelatins. Skin gelatins were found to exhibit higher film tensile strength but lower film percent elongation than bone gelatins. Bone and skin gelatins had similar amino acid composition, with a total imino acid content of about 21.5%. Nile perch skin gelatins had a higher content of polypeptides larger than β compared to bone gelatins. Both bone and skin gelatins also contained low molecular weight (<α) peptides. The differences in functional properties between the skin and bone gelatins appeared to be related to differences in molecular weight distribution of the gelatins.