Abstract
In this study, melanin (BgM) was obtained from Boletus griseus. The chemical composition and structure of BgM were characterized by UV-visible absorption spectrum, Fourier transform infrared spectrum, elemental analysis, nuclear magnetic resonance, pyrolysis gas chromatography mass spectrometry, and ultra-performance liquid chromatography–high resolution mass spectrometry. The percentage contents of C, H, N, S and O elements were 56.38%, 5.86%, 6.17%, 2.44%, and 28.04%, and the S/N and C/N ratios were 0.17 and 10.66, respectively. The UV-vis spectrum of BgM showed a maximum absorption peak at 214 nm. Characteristic absorption peaks were observed at 3426, 1600 and 1105 cm−1, and BgM contained phenolic hydroxyl, amidogen, carbonyl, methylene, and methyl groups. Moreover, BgM is an eumelanin, and its main skeleton has both a benzene ring and an indole, and the branched chain mainly consists of alkanes, alcohols, and fatty acids. BgM was hydrolyzed by H2O2 and four compounds were tentatively analyzed from the UPLC-MS/MS profile. The chemical structure of BgM was characterized as 5,6-dihydroxyindole eumelanin, and the condensed molecular formula is [C28(OR1)4(OR2)3H11O6N4]n.
Highlights
Melanin is a class of complex polyphenolic heteropolymers and has three main types, namely, eumelanin, phaeomelanin, and allomelanin [1]
With the continuous addition of the FeCl3 solution, the floc gradually disappeared, dissolving completely, giving a brownish–yellow solution. This phenomenon was consistent with the previous study, which indicated that melanin had significant reduction-oxidation properties and precipitated in the presence of alkaline FeCl3 solution [15,16]
These results indicated that BgM could be classified as eumelanin, with traces of phaeomelanin
Summary
Melanin is a class of complex polyphenolic heteropolymers and has three main types, namely, eumelanin (brown–black melanin), phaeomelanin (brown-red melanin), and allomelanin (nitrogen-free melanin) [1]. This classification is based on the chemical composition and monomer subunit structure of melanin. Melanin is widely found in bacteria, fungi, animals, and plants They are considered as bio-organic conductors with distinctive physicochemical properties, and have a wide variety of roles. They serve as photoprotectants, pigments, charge transport mediators, free-radical scavengers, and antioxidants [3,4]. This research could provide both theoretical and scientific evidence for further research of natural melanin structure derived from fungi, and provide a new method for the development and utilization of wild edible fungi in Yunnan
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