Fermentation Control For Transformation Of Monascus Pigments And Low Citrinin Contents

Monascus pigments are a class of natural food colorants. However, Citrinin, a kind of nephrotoxic and hepatotoxic azaphilone, is co-produced during the biosynthesis process of Monascus pigments, and orange Monascus pigments exhibit significant teratogenic effect on chick embryo, having potential threats to human’s safety. Both citrinin and orange Monascus pigments have adverse effects on the utilization of Monascus pigmentsin food industry. Thus, it is greatly beneficial for Monascuspigments using in food industry to produce citrinin-free Monascus pigments and convert orange pigments into edible red ones or yellow ones with multiple biological activities.The effect ofprotein contents of agricultural products and fermentation p H on secondary metabolites of Monascus was studied by submerged culture of Monascus in the flasks and bioreactors using agricultural products with different content of protein as substrate. The results indicated that fermentation p H was the major factor regulating secondary metabolites. The final p H maintained below 3.0 and intracellular pigments were mostly orange ones without citrinin when the content of protein was below 9%. And Monascus fermentation at a controlled low p H 2.5 using soybean meal with high protein content as substrate also mainly produced intracellular citrinin-free orange Monascus pigments. Citrinin-free Monascus pigments could be achieved by selecting agricultural products with low protein content in natural submerged culture at a low initial p H 2.5 or choosing agricultural products with high protein content in the bioreactor at a controlled low p H 2.5.Conditions of coupled aminophilic reaction and metabolic pathways to achieve high yields of red Monascus pigments were studied by chemical modification of orange pigments in vitro and extractive fermentation of Monascus in the nonionic surfactant Triton X-100 micelle aqueous solution. The results suggested that aminophilic reaction between lipophilic orange Monascus pigments and hydrophilic monosodium glutamate(MSG) occurred in the micelle aqueous solution, and relatively higher surfactant concentration, higher MSG concentration and nearly neutral p H had positive effect on the rate of aminophilic reaction. Conditions of chemical reaction in vitro could be applied to Monascus fermentation and extractive fermentation produced much more red pigments than submerged culture.The related mechanism of accumulation of yellow Monascus pigments was studied by extractive fermentation in the Triton X-100 micelle aqueous solution. The results revealed that, under low p H condition, intracellular orange Monascus pigments were mainly biosynthesized during submerged culture while extracellular yellow ones were accumulated during extractive fermentationdue to the export of intracellular yellow Monascus pigments into the extracellular micelle aqueous solution, which blocked yellow Monascus pigments from further enzymatic conversion or eliminated the feedback inhibition of yellow ones. Earliersurfactant loading time and higher surfactant concentration as well as longer period of fermentation time were beneficial for accumulation of yellow Monascus pigments. Meanwhile, the phenomen that yellow Monascus pigments were more stable than orange ones in micellar aqueous solution under low p H condition was found.