Synthesis And Mechanism Of Monascus Pigments With Lower Citrinin And Higher Pigment Production

The filamentous fungus Monascus rubber produces pigments together with Monacolin K and citrinin by fermentation.Monascus pigments and Monacolin K have been widely used in the fields of food,cosmetics and medicine,but citrinin is a kind of harmful secondary metabolite,which can be synthesized along with Monascus pigments.To increase the yield of Monascus pigments and to decrease the citrinin content,the medium was optimized for Monascus rubber HS4000fermentation,and the effects of vitamin C and its mechanism on Monascus metabolites were studied in the work.1.On the basis of single factor experiment,the response surface method was adopted for the optimization of carbon source,nitrogen source and inorganic salt medium formula.The best submerged culture conditions for Monascus rubber HS4000fermentation in the flasks were:rice flour 9%,NaNO₃ 0.21%,KH₂PO₄ 0.11%,MgSO₄0.24%.Under the above condition,pigments content were 46.3 U/mL,the content of citrinin was 1.51 mg/L.2.Different regulatory factors,including biotin,reduced glutathione,NADH,and vitamin C,were added in the fermentation process respectively,and their influences on the pigment and citrinin synthesis were compared.It was found that vitamin C was the best one to improve pigments and reduce citrinin.The optimal amount of vitamin C was16 mg/L,the pigments content was 68.3 U/mL and citrinin content was 0.87 mg/L after144 h fermentation.Compared with control group,the pigments were increased by50.1%,and citrinin was reduced by 71.0%.3.The mechanism of vitamin C on Monascus fermentation was discussed from the levels of physiological activity,enzyme activities and metabolite respectively.It was found that vitamin C could improve the antioxidant ability.The addition of vitamin C could help the synthesis of related enzymes which is good for free radical scavenging.In the early stage of the fermentation,vitamin C supplementation stimulused related enzymes synthesis to remove the excess of free radicals,and the CAT and the activity of SOD were increased significantly.In the late fermentation,after eliminating the excessive free radicals in the cell,CAT and SOD enzyme activity were lower.Fatty acids and organic acids in the fermentation process were analyzed.The results showed fatty acids was increased from 13 to 17 kinds after adding vitamin C,and the oxide type in the control group of 15-hydroxyformic acid carbonate was transferred into reduced16-hydroxyformic acid carbonate.It was concluded that vitamin C could improve the antioxidant ability and reduce the total content of free radicals to a certain degree,which is good for protecting the cells from the hurt of free radicals,and then,the production of pigments was increased and the citrinin synthesis was reduced.