Water-soluble red pigments from Isaria farinosa and structural characterization of the main colored component.

The present study describes the red pigment synthesized by the filamentous fungi Isaria farinosa under submerged culture conditions. The pigment production was optimal under the following conditions: pH 5, agitation speed 150 rpm, temperature 27 °C, incubation time 192 h, light source total darkness, sucrose and glucose as carbon source, yeast extract, meat peptone and monosodium glutamate at a fixed concentration of 3% as nitrogen source. The addition of 10 mM CaCl₂ to the culture medium increased the biomass and pigment production. Structural elucidation of the pigment using gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy revealed that the red pigment contains an anthraquinone-related compound. In addition, the isolated pigment was water soluble, and was stable when exposed to salt solution (96.1% of stability after treatment with sodium chloride), acid (72.1% with citric acid), heat (86.2% at 60 °C), and sunlight (99.4%). These results are promising to further exploit the fungal culture of Isaria farinosa for producing the red pigment and, subsequently, to considerably increase its yield. The study has commercial importance in the production of Isaria farinosa pigment for industrial application after considerable toxicological examination.