Ganoderma Lacquer’s Physical and Solar Irradiation Protection

Many Ganoderma sporocarps (mushrooms) develop a colored lacquer layer, whose functional role is widely assumed to be a protective layer but is not well understood across species. To create a comprehensive understanding of this biological tissue, this research studies five Ganoderma species with distinct lacquer colors: black, maroon, red, yellow, and white. The study investigates the relationships between lacquer color, melanin content, and chemical composition to understand the extent of their impact on mechanical properties and response to solar irradiation. Nanoindentation on the five species showed that all lacquer layers were statistically significantly harder than their corresponding context layers, confirming the lacquer as a mechanically protective crust. This thin, fused lacquer attains surface hardness similar to chitinous biological tissues that need thick layers, sclerotization, or mineral reinforcement, without mineralization or large thickness. Microstructural characterization demonstrated that the lacquer’s fused surface contributes to higher hardness. However, lacquer thickness did not contribute to the hardness behavior among color types. FTIR and Raman spectroscopy showed strong eumelanin peaks in the black, maroon, and red lacquers, and weaker peaks in the yellow and white lacquers. UV–Vis measurements showed that lacquers with higher melanin content absorbed more solar radiation with all lacquer samples showing peak absorbance in the damaging UV-B region. These findings link melanin concentration to both increased hardness and increased UV absorption, supporting the lacquer layer’s role in mechanical protection and solar protection. This study enables tuning and utilizing fungi pigmentation and melanin for various industries to support mechanical and solar protection.