Fish gelatin: Structure, gelling properties and interaction with egg albumen proteins

Gelatin was obtained from the skin of North Sea horse mackerel (Trachurus trachurus), using sodium hydrogen carbonate (0.125%), sodium hydroxide (0.2%), sulphuric acid (0.2%), and citric acid (0.715%) in distilled water, followed by filtration, deionisation. The proximate composition of the extracted fish skin gelatin indicated that the ash, moisture, colour, weight average molecular weight (195.8 kDa), Bloom (230) and pH (6.0) compared well commercial gelatin. The imino acid and hydrophobic amino acids profile of extracted horse mackerel gelatin were closer to those of the commercial warm water tilapia gelatin rather than the non-gelling cod gelatin. FT-Raman spectroscopy confirmed that hydrophobic groups (tyrosine doublet ratio 850/830 cm−1 and CH stretch region) as well as alpha-helix and random coil, for horse mackerel gelatin were in between those of tilapia and cod gelatin. In addition, large and small deformation rheological and thermodynamic properties were investigated for horse mackerel gelatin in isolation and in combination with egg albumen (egg white) protein. A mixture of gelatin:egg albumen (3:10) gave greater G′ valuesthan expected. Both differential scanning calorimetry and microscopy supported interaction between gelatin and egg albumen proteins. The gelling properties and compatibility with egg proteins makes the horse mackerel gelatin a potential replacer of porcine and bovine gelatins in desserts and bakery products.