It is believed that violent agitation caused an undesirable effect on cell growth and pigment production due to high shear stress. Fig. 7 shows the growth and pigment production profile versus time in a batch fermentation under optimum culture
conditions. As shown in Fig. 1, M. purpureous depleted glucose after 4 days incubation, and produced 5.90 g/L of biomass. Red pigment production started at the beginning of the exponential growth phase, increased sharply after 30 h, and reached 13.37 OD500 at the stationary phase.Other workers have also reported this growth associated pigment production by Monascus [23]. However, it is not believed that the polyketide pathway leads exclusively to secondary metabolite [24]. At the late log phase the pigment production rate showed a little retardation. Monascus pigments are
polyketides and oxygen is an essential substrate for their biosynthesis [24]. It is possible that the final high viscosity of the culture broth in the late log phase interfered with the aeration of the cultures. Some pigment loss was observed in the stationary phase from the absorbance measurement of pigment concentration. It is thought that an enzymatic pathway, which may be induced by nutrient exhaustion, degrades the pigment. Enzyme degradation of secondary metabolites is a
common phenomenon in fungi [25]. The maximum biomass yield and specific productivity of red pigment were 0.20 g DCW/g glucose and, 32.5 OD500 g DCW-1 h-1, respectively.