Biological activities of BY2-melanin, a plant-type eumelanin, isolated from cultured tobacco BY-2 cells

BY2-melanin, a plant eumelanin distinct from nitrogen-free plant allomelanins, was previously isolated from cultured BY-2 tobacco cells. Herein, the biological activities of BY2-melanin, including its ability to protect against ultraviolet radiation (UVR) and antioxidant activity, were investigated. Based on the survival rate of <i>Escherichia coli</i>, the ability of BY2-melanin to protect against UVR was three and eight times higher than that of melanins isolated from fungi and bacteria, respectively. Its antioxidant activities, determined as ferrous iron-chelating activity and reducing power, were 1.7-4.9 and 0.3-0.4 times higher than those of animal melanins, respectively. Its 2,2-diphenyl-1-picrylhydrazyl and superoxide radical scavenging activities were similar to those of mushroom melanin, whereas its hydroxyl radical scavenging activity was one-fourth of that of melanins derived from mushroom and black tea. These findings shed light on the development of a class of melanin biopolymers that can be used as a broad-spectrum sunscreen with antioxidant activity.