Optimization of Melanin Preparation Conditions from Squid Ink by Response Surface Methodology

To obtain the optimization extraction technology condition of squid ink melanin, based on the peculiar nature of melanin, the alkali-solution and acid-isolation method was used to extract melanin from squid ink. After performing the five single-factor tests, which was NaOH concentration, liquid-to-solid ratio, extraction time, extraction temperature, and pH, respectively, NaOH concentration, liquid-to-solid ratio, and pH were used as independent variable. The extraction rate of squid ink melanin was used as an index, and the mathematical regression model was established by Box-Behnken center-united design and response surface methodology (RSM). The RSM results showed that the optimal extraction processing parameters were determined as follows:NaOH concentration, 1.18 mol·L^-1; liquid-to-solid ratio, 17:1(mL·g^-1); pH, 1.85. Under these conditions, the extraction rate of theoretical value was 16.72%. The average experimental value after validation was 16.69%. The analysis result of IR spectrum indicated that there were two characteristic absorption peaks at 3400 cm^-1and 1600 cm^-1, respectively, which suggested that the extracted melanin contained the structure of hydroxyl, amino, and aromatic.