Effects of different extraction methods and arginine modification on the physicochemical properties and biological activities of fungal and slime mold melanins

Melanins from biomass (such as mushrooms) are attractive functional food ingredients. Although both the biomass and the melanins are structurally diverse, a one-size-fits-all extraction strategy is currently predominant. Moreover, fungal and slime mold melanins remain underexplored. This study evaluated the influence of extraction methods and arginine modification on the physicochemical properties and biological activities of melanins from fungal and slime mold fruiting bodies. Alkaline extraction (KOH method) proved effective, while the solvent method (TBAOH) yielded more impurities, resulting in reduced antioxidant activity. Notably, arginine modification significantly enhanced both water solubility and antioxidant activity, particularly for KOH-extracted melanins, converting melanins of Russula nigricans, Xylaria nigripes , and Scleroderma sinnamariense (spore) from moderate to powerful antioxidants. However, native melanins showed significantly higher cytotoxicity towards cancer cells than their modified counterparts. Melanins from R. nigricans and S. sinnamariense (spore) selectively targeted cancer cells without affecting kidney cells, highlighting their nutraceutical potential.