Relation between growth, respirometric analysis and biopigments production from Monascus by solid-state fermentation

Solid-state fermentation was carried out to establish relation between growth, respirometric analysis and biopigments production from Monascus sp. in columns and in a drum-type bioreactor with forced air. In these reactors, the best aeration rate for biopigment production was 1 ml of air, per gram of wet substrate, per minute. The outlet air composition was determined using gas chromatography (GC), while the pigments produced were measured by spectrophotometry after extraction with ethanol. An ergosterol-dosage method was used to estimate biomass production; in this method, the sterol was extracted and measured by liquid cromatography (HPLC). The results showed that although pigments were a secondary metabolite, its production was proportional to the biomass produced that was estimated by ergosterol analysis, and therefore could be used to estimate biomass formed in the natural support (rice). Specific velocities for pigment and biomass production were estimated by a sigmoid model applied to the data and also with the aid of a computer program nominated FERSOL. Under ideal conditions in column fermentation, a maximum specific growth velocity of 0.039 h−1 and a specific pigment production velocity of 27.5 AU/g biomass h was obtained, at 140 h, with 500 AU/g dry fermentate after 12 days. The specific product formation velocity in the bioreactor was 4.7 AU/g h, at 240 h fermentation, and the total pigment production was 108.7 AU/g dry fermentate after 15 days.