Fungal Pigments: Applications and Their Medicinal Potential

Abstract

Color plays an important role in many segments of food, cosmetic, and textile industry; however, in the last century, the deliberate use of synthetic pigments demonstrated the urge for natural alternatives. Pigments produced by fungi have many advantages over synthetic ones, such as low toxicity, the ease of controlled production, the possibility of optimization, and the independence of external seasonal factors. Some metabolites produced by fungi are already commercialized as pigments, notably β-carotene, produced by Blakeslea trispora, and Monascus pigments, found in more than 20 types of products in oriental markets. Pigments produced by fungi are divided into melanins, carotenoids, and polyketides, the latter containing the classes anthraquinones, hydroxyanthraquinones, naphthoquinones, and azaphilones, representing a wide range of colors, including the commonly obtained hues yellow, orange, and red, in addition to brown and dark pigments, such as melanins polymers, and also atypical colors, such as the blue-green pigment xylindein, produced by Chlorociboria aeruginascens. Those pigments are mainly produced by fungi as a defense mechanism against UV light, but also have other important biological functions related to the transport of metals, differentiation, interaction with other organisms, either by symbiosis or competition, or even defense against insects and other animal predators. For this reason, these substances are biologically active, and their functions can be extrapolated to the pharmaceutical industry, with many reports in the literature of their potential as antimicrobial, antifungal, antiviral, antioxidant, cytotoxic, nematicidal, anti-inflammatory, and antitumor agents. However, industrial use of fungal pigments still faces some challenges such as the search for better production yields, the targeted synthesis of only one specific compound or color, and more essentially, a mycotoxin-free production process. Many studies have shown the importance of factors related to the fungus cultivation such as temperature, medium agitation/oxygenation, carbon source, nitrogen source, and pH, the last two being considered the most important factors related to the production of colored metabolites. However, the chemical reaction of pigments with components of the culture medium must also be considered, as an example the oxidation of azaphilones, leading to the conversion of yellow pigments into orange, and the reaction of the same class of substances with amines and nitrogenated compounds, which leads to the production of red pigments in some species. Fungal pigments are gaining ground in different industrial branches, and new uses for pigments are constantly emerging, such as their application as biosensors and as electron acceptors in biofuel cells.