Physicochemical Properties and Antioxidant Activity of Natural Melanin Extracted from the Wild Wood Ear Mushroom, Auricularia auricula (Agaricomycetes)

In this study, melanin from wild Auricularia auricula (WAA) was isolated using an ultra-high pressure (UHP)-assisted extraction method, and the physicochemical properties and antioxidant activity of WAA melanin were investigated. Under the optimized extraction conditions of a solid/liquid ratio of 1:30, a UHP of 450 MPa, a 22-min pressure holding time, a 1-mol/L NaOH concentration, and acid precipitation for 8 h, the WAA melanin extraction yield was 7.9 ± 0.16%. Moreover, the results showed that the surface of WAA melanin lacked structural order. Most melanin showed an average diameter of 1000 nm. WAA melanin had strong absorption at a wavelength of 210 nm and displayed typical characteristic absorption peaks. Moreover, WAA melanin contained 48.51% C, 6.88% H, 5.26% N, 0.45% S, and 38.90% O and may be a 3,4-dihydroxyphenylalanine melanin. An analysis of physicochemical properties showed that WAA melanin had good stability toward heat, light, and low concentrations of reducing agents and oxidizing agents. Furthermore, WAA melanin presented certain free radical scavenging activity. This study demonstrates that wild A. auricula melanin may have potential applications in the cosmetic or food industries as a natural antioxidant.