Extraction of Melanin in Apricot Kernel Shell and the Optimization of Chelating Process of Its Metal Chelates

In this study, single factor and response surface methodology were used to optimize the extraction parameters of melanin from waste apricot kernel shell. The structure of the obtained melanin was identified by UV-vis/IR absorption spectrum and scanning electron microscope. Then, the chelating effect of extracted melanin with Fe³⁺, Cu²⁺ and Zn²⁺ metal ions were used as the index, and the single factor experiment was used to optimize the chelating process. In order to provide theoretical basis for further development and utilization of the chelate as functional food, the structure of the chelate was identified by UV-vis absorption spectrum, infrared absorption spectrum, scanning electron microscope and energy spectrum scanning. The results showed that the order of influence of the selected factors on the yield of melanin was: ultrasonic time, alkali concentration, pH, solid-liquid ratio. According to the results of response surface model, the optimal extraction conditions were as follows: solid-liquid ratio 1:10 g/mL, sodium hydroxide concentration 1.5 mol/L, acid precipitation pH value 1, ultrasonic time 35 min, under this condition, the yield was 4.78%±0.23% . The optimum chelating process of iron melanin chelate was as follows: iron ion concentration 5 mmol/L, pH5.5, reaction for 8 h; The optimum chelating conditions of copper melanin chelate was copper ion concentration 4 mmol/L, pH7.5, reaction for 6 h. The optimal chelating process of zinc melanin chelate was as follows: zinc ion concentration 3 mmol/L, pH7.5, reaction 4 h. Under the same conditions, the chelating rate of iron melanin reached 63.86%. Ultraviolet and infrared results showed that melanin chelated with metal ions mainly through amino, carbonyl or carboxyl groups. Scanning electron microscopy and energy spectrum results showed that the three metal chelates were successfully prepared. This study provided a theoretical basis for the development of functional food additives and metal element supplements and had a wide range of practical value and market prospects.