Optimization of the Extraction Process of Black Sesame Melanin by Deep Eutectic Solvents and Analysis of Its Bioactivities

To optimize the extraction process parameters and analyze the functional activity of black sesame melanin, this study employed deep eutectic solvents (DES) as the extraction solvent. The effects of various factors, including DES composition, extraction time, water content in DES, extraction temperature, molar ratio of DES components, and solid-to-liquid ratio, on the yield of black sesame melanin were investigated. Based on the single-factor experiments, the extraction process of black sesame melanin was optimized by response surface methodology, and its in vitro antioxidant and antibacterial activities were evaluated for efficacy. The results showed that the optimal extraction process was as follows: choline chloride:lactic acid 1:2, reaction time 4.3 h, water content 39%, molar ratio 1:2, solid-liquid ratio 1:5.6 (g/mL), under which the yield of black sesame melanin was 7.3%. XAD-8 resin was used to purify the black sesame melanin, and the color value increased from 197.5 to 297.25, and the melanin content increased from 18.08 mg/g to 25.49 mg/g after purification. The IC₅₀ values of melanin solution for scavenging DPPH·, ABTS⁺·, hydroxyl radical and superoxide anion were 244, 111.6, 53.67 and 44.56 μg/mL, respectively. The melanin solution had certain inhibitory effects on the growth of Escherichia coli, Staphylococcus aureus and Bacillus subtilis, and the maximum inhibition zone diameters were 14.03±0.05, 14±0.1 and 20.1±0.11 mm, respectively. This paper provides a theoretical reference for the green extraction of black sesame melanin and the development and utilization of functional products.