Optimization of Monascus pigment production in solid-state fermentation

The effects of various culture parameters were investigated to optimize pigment production by Monascus purpureus ATCC 16365 in solid-state fermentations with emphasis on the effects of oxygen and carbon dioxide. The Monascus strain was selected because it showed the highest pigment production among strains tested which lacked antibiotic activity. Polished long rice was found to be the best substrate. Optimum relative humidity and initial moisture content were 97-100% and 45-50%, respectively. A moderate hand mixing of the culture gave a stimulatory effect on pigment yield. Optimum pH and temperature were 5.0-6.0 and 30$\sp\circ$C, respectively. Zinc supplementation at 1.5 $\times$ 10$\sp{-2}$ M gave maximum red pigment productivity, which reached 6016 OD units per gram of dry fermented solid after 6 days. Moderate forced aeration gave maximum pigment yields in packed-bed fermentations. Levels of oxygen and carbon dioxide in gas environments were found to significantly influence pigment production. Maximum pigment yields were observed at 0.5 atm oxygen in closed pressure vessels. However, high carbon dioxide pressures inhibited pigment production significantly, with complete inhibition at 1.0 atm. In a closed aeration system with a packed-bed fermentor, oxygen pressures ranging 0.05 to 0.5 atm at constant 0.02 atm of carbon dioxide partial pressure gave high pigment yields with a maximum at 0.50 atm of oxygen, whereas lower carbon dioxide pressures at constant 0.21 atm of oxygen partial pressure gave higher pigment yields. Maximum oxygen uptake rate and carbon dioxide evolution rate were observed at about 70-90 hr and 60-80 hr, respectively, depending on the gas environment. Respiratory quotients were close to 1.0, except at 0.05 atm oxygen and 0.02 atm carbon dioxide partial pressures, suggesting that anaerobic metabolism played a significant role under oxygen limiting conditions. Ethanol also appears to be subject to the Crabtree effect. Finally, optimum conditions for pigment formation were generally not the same as those for biomass formation