Study on extraction, identification and antioxidant activity of melanin of sunflower seed shell

The melanin of sunflower seed shell (MS) was extracted based on its characteristics of dissolving in alkaline solution and precipitating in acid solution assisted with ultrasonic.Folin-Ciocalteu (FC) method was used to determine total phenol content, single factor and orthogonal tests were used to determine the optimum extract conditions of MS, UV and infrared spectroscopies were used to identify the structure, the reducing power and ability of scavenging DPPH·were used to evaluate the antioxidant activity against the same concentration of VC and gallic acid.The results showed that optimum extract conditions were 0.5mol/L NaOH, time for 1.5h., solid-liquid ratio of 1∶25 at 25℃, the crude extract of MS extracted by alkaline and acid was black and lacklustre with a yield of 12.37%, RSD 2.14%, and the purified MS was metallic luster with a yield of 2.07%, RSD 9.27%.The total polyphenol content of crude extract of MS was 0.48% calculated as GAE.The wavelength of maximum absorption peak was 292nm in the solution of sodium sulfite scanned by Cary 50 UV-Vis spectrophotometer, and absorbance and the concentration of melanin was positively correlated at 292nm.The patterns of classic characteristic absorption of melanin were shown in the ultraviolet and infrared spectrogram, respectively.With the same concentration, the antioxidant capacity of purified melanin was nearly same as that of the crude extract, lower than VC but higer than gallic acid.