Optimization of Enzymatic Preparation of Natural Melanin from Squid Ink and Its Spectral Characterization

In this work,the enzymatic hydrolysis of squid ink was investigated to prepare natural melanin.Squid ink was hydrolyzed by papain,neutral protease,acidic protease,pepsin and tyrpsin,respectively,and pepsin was found to have the strongest ability to hydrolyze squid ink.Based on one-factor-at-a-time experiments,an L9(34) orthogonal array design was used to optimize the hydrolysis of squid ink by pepsin.The degree of hydrolysis of squid ink was investigated with respect to pH,hydrolysis time,temperature and enzyme amount.The four conditions were optimized as follows: pH 1.5,temperature 37 ℃,reaction time 5 h and pepsin amount 1.5%.Under the optimized conditions,the degree of hydrolysis of squid ink exceeded 13.50%.Ultraviolet-visible spectral analysis revealed the characteristic absorption of melanin derived from squid ink at 220 nm wavelength.High-intensity absorption peaks at 3384.54 cm-1 and 1617.35 cm-1,assigned to the structure of indole ring were observed in the infrared spectrum.