Maximizing yellow pigment production in fed-batch culture of Monascus sp.

Yellow pigment production in exponential fed-batch cultivation of Monascus sp. was studied. Due to the difficulty of measuring the optical density for accurate determination of the cell concentration, a capacitance probe was employed on-line. The feed rate needed to keep the specific growth rate, mu , constant in fed-batch culture was determined on the basis of the cell con centration measured by the capacitance probe. Control of mu was improved by using updated information on the cell concentration compared with the simp le feed-forward determination method using the initial cell concentration o nly. The highest specific pigment production rate was achieved with a mu of 0.02 h(-1) in the feeding phase. However, among several fermentation exami ned, the largest pigment production in the final step was obtained at a mu of 0.01 h(-1); in each ease the same amount of substrates was used. An inve stigation of the optimal initial glucose concentration revealed that pigmen t production was maximum when the initial glucose concentration in the batc h mode was 10 g/l and mu was 0.01 h(-1) in the fed-batch mode. It was also found that the pellet weight in the fermentation could be accurately estima ted by image analysis. The ratio of the mycelium weight to the total cell w eight estimated from information on the total cell weight and the estimated pellet weight was found to be more than 80%. However, no clear quantitativ e relationship could be discerned between the specific pigment production r ate, rho, and the ratio of mycelium in the cell population.