Isolation and identification of pigment-producing filamentous fungus DBFL05 and its pigment characteristics and chemical structure

Natural pigments derived from microorganisms have many advantages and are widely studied in the food industry. A filamentous fungus, DBFL05, was identified as <i>Aspergillus ustus</i>, which produces a bright and abundant brown pigment. This extracellular, water-soluble pigment is highly polar and slightly soluble in alcohol but insoluble in other organic solvents. The pigment is stable under sunlight, at pH 2–10, and below 100°C. However, it is sensitive to Zn²⁺, Fe³⁺, Fe²⁺, and Cu²⁺. The pigment is mainly composed of two chemical components, pyrropyrazine diketone and dianthrone, and is classified as a polyketone pigment. Both components of the pigment exhibit inhibitory effects on bacteria and scavenging abilities for •OH and DPPH. The pigment showed no significant toxicity to plants and low toxicity to brine shrimp larvae. These findings indicate that the easily obtainable <i>A. ustus</i> pigment is a polyketone with attractive colour, stability, safety, and bioactivity.