Optimisation of extraction conditions and characteristics of skin gelatin from Nile tilapia (Oreochromis niloticus)

P>Response surface methodology was used to optimise gelatin extraction conditions from the skin of Nile tilapia (Oreochromis niloticus), and characteristics of the gelatin were determined. Concentration of NaOH (%, X-1), alkaline treatment time (h, X-2), concentration of HCl (parts per thousand, X-3) and acid treatment time (min, X-4) were chosen for independent variables. Dependent variable was yield of gelatin (%, Y). Optimal conditions were X-1 = 3.2 (%), X-2 = 2.3 (h), X-3 = 0.7 (parts per thousand) and X-4 = 84 (min), and predicted value of response optimal conditions was Y = 20.4%. Actual value was 19.3% by verification experiments under optimal conditions. Crude protein content of the tilapia skin gelatin was 88.5%. The content of imino acids including proline and hydroxyproline in the gelatin was 185 residues per 1000 total amino acid residues. Its gel strength was 260 g. The gelling and melting points were 18.0 and 22.4 degrees C, respectively.