Influence of Light Intensity on Growth and Pigment Production by Monascus ruber in Submerged Fermentation

To reduce environmental problems caused by glycerine accumulation and to make the production of biodiesel more profitable, crude glycerin without treatment was used as substrate for obtaining higher value-added bioproducts. Monascus ruber is a filamentous fungus that produces pigments, particularly red ones, which are used for coloring foods (rice wine and meat products). The interest in developing pigments from natural sources is increasing due to the restriction of using synthetic dyes. The effects of temperature, pH, microorganism morphology, aeration, nitrogen source, and substrates have been studied in the cultivation of M. ruber. In this work, it was observed that light intensity is also an important factor that should be considered for understanding the metabolism of the fungus. In M. ruber cultivation, inhibition of growth and pigment production was observed in Petri dishes and blaffed flasks exposed to direct illumination. Growth and pigment production were higher in Petri dishes and flasks exposed to red light and in the absence of light. Radial growth rate of M. ruber in plates in darkness was 1.50 mm day(-1) and in plates exposed to direct illumination was 0.59 mm day(-1). Maximum production of red pigments (8.32 UA) and biomass (8.82 g L(-1)) were obtained in baffled flasks covered with red film and 7.17 UA of red pigments, and 7.40 g L(-1) of biomass was obtained in flasks incubated in darkness. Under conditions of 1248 lux of luminance, the maximum pigment production was 4.48 UA, with production of 6.94 g L(-1) of biomass, indicating that the fungus has photoreceptors which influence the physiological responses.