Abstract

Traditional methods for screening high-melanin-yielding Auricularia heimuer strains are time-consuming and environmentally unfriendly. To address this issue, fifteen A. heimuer strains were used to determine the mycelial biomass, absorbance at 500 nm, CIE L*a*b* colorimetric values, and melanin yield of the fermentation broth. Pearson correlation analysis was performed to clarify the correlations among these indicators, and a regression equation was fitted to establish a rapid screening method. A total of 84 A. heimuer strains were used to verify this method, of which one high-melanin-yielding strain was obtained. The structural characterization and in vitro antioxidant activities of A. heimuer melanin (AHM) were determined. The results showed that the melanin yields of fifteen A. heimuer strains were extremely significantly positively correlated with absorbance at 500 nm (r = 0.880, p < 0.01). The fitted linear regression equation was Y = 0.0246X + 0.00094 (R2 = 0.8756, p < 0.01). When 84 tested strains were investigated with this method, 8 strains (53.33%) exhibited relative differences below 10%, which is consistent with the satisfactory accuracy of the absorbance-based screening method. Finally, a high-melanin-yielding strain HMCC50028 was obtained, with a melanin yield of 0.0540 g/100 mL. The results of UV-Vis spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) of AHM indicated that the melanin exhibited structural characteristics consistent with fungal melanins, belonging to the natural melanin family. In vitro assays demonstrated that AHM possessed excellent superoxide anion radical scavenging activity and ferric reducing power.

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