The Structure, Amino Acids Modification And Biological Activity Of Melanin From Lachnum YM-346

In this paper, the optimum fermentation conditions, the extraction conditions,structure, arginine modification, the antibacterial activity and the antioxidant activity ofmelanin from Lachnum YM-346were studied.The main results included:1. The optimum fermentation conditions of Lachnum YM-346extracellularmelanin were as follows: â…¤#Medium (potato juice20%, glucose20g·L^-1, yeastextract5.0g·L^-1), tyrosine19.06mg·L^-1, MgCl₂2.03mmol·L^-1, pH7.54. The yield0f Lachnum YM-346extracellular melanin was inseased by38.6ï¼…with theoptimum fermentation conditions.2. On the basis of single factor experiment, the optimum ultrasound-assistedextraction conditions of Lachnum YM-346intracellular melanin using CentralComposite design were as follows: Ultrasonic time58min、NaOH Concentration1.00mol·L^-1and Ultrasonic temperature65℃. Under this condition, the extractionyield of Lachnum YM-346intracellular melanin was13.66%, and3.19%higherthan that of extraction by alkali extraction and acid precipitation3. Electron microscopy showed that LEM346had a blocky, crystal structurewith an irregular surface. LEM346had maximum absorption peaks at211nm,Infrared spectrum revealed O-H stretching vibration in the indole ring(3218.802cm^-1) and C=O stretching vibration (1614.815cm^-1).1HNMRspectroscopy revealed the signal peaks of CH （7.0-7.5ppm） and NH （2.5-5.0ppm）in the indole ring. The products of the pyrolysis of LEM346contain high quantitiesof pyridine and benzene derivatives. These results combined with the elementalanalysis and mass spectrometry analysis showed that LEM346has indolequinonestructure and may be indole eumelanin, its formula is C₁₈H₈O₆N₂and its structuremay be4. The antibacterial activity of LEM346against Staphylococcus aureus and Listeriamonocytogenes were similar, but significantly higher than that against Salmonella typhi andEscherichia coli. On the whole, the antibacterial activity of LEM346was not subjectto the influence of temperature, UV irradiation.5. Seven kinds of amino acids were used to modify the extracellular melanin（LEM346） of water insoluble Lachnum YM-346. It was found that arginine-modified melanin （ALEM346） had the highest solubility, being4.55g/100g in30℃distilled water.Infrared spectroscopy showed that ALEM346had characteristic absorption peaks formedby combination of the carbonyl group in melanin and the amino group in arginine at1672.346cm^-1and1637.679cm^-1. Mass spectrometry indicated that the mixture ofALEM346was formed by combination of LEM346and arginine. When the ALEM346concentration was500mg·L^-1, its total antioxidant capacity was equivalent toα-tocopherol of46.65mmol·L^-1, and the DPPH· and O₂^ˉ· scavenging rates and Fe2+chelating rate were89.05%,93.81%and80.18%, respectively, suggesting that theantioxidant activity of arginine-modified melanin is significantly higher than thatof LEM346of the same concentration.