Study On The Regulation Mechanism Of Immobilized Fermentation Based On Sugar Esters Promoting Monascus Yellow Pigment Synthesis

Monascus yellow pigment is bright,safe and non-toxic.It is a popular natural pigment in the food field,but its color value is low,which can not meet the market demand.At present,it is reported continually on using accelerators to improve the yield of Monascus yellow pigment,but most accelerators do not meet the requirements of food safety and non-toxic cannot be applied in this field.Therefore,the development of new fermentation methods for high-yield Monascus yellow pigment in food field is an urgent problem to be solved,which has broad application prospects and great economic benefits.The exogenous factors of food safety were added to the fermentation medium.At the same time,a new fermentation method was adopted and the fermentation conditions were optimized to improve the yield of Monascus yellow pigment.Then,the regulation mechanism of high-yield Monascus yellow pigment synthesis was analyzed by RNA-seq and q RT-PCR.The main contents of this paper are as follows:Sugar esters,triglyceri demonostearate,span 80 and other food additives were added to the basic medium for fermentation culture.The dry cell weight and yellow pigment yield of Monascus with sugar esters were the highest,indicating that sugar esters is an excellent promoter to improve Monascus yellow pigment yield with better biocompatibility.The best addition amount is 1g / 50 m L fermentation broth and the optimum speed of the shaker is180 rpm.Sugar esters can change the morphology of Monascus mycelium,make the mycelium surface show more folds,cracks and holes.It can damage the cell wall,increase the permeability of cell membrane,extract the intracellular pigment outside the cell,and release the negative feedback inhibition of intracellular yellow pigment,so as to improve the total yield of Monascus yellow pigment.This provides a reference for screening Monascus strains with high yellow pigment yield from the morphological aspect in the future.The fermentation method has a great impact on the yield of Monascus pigment.Under the condition of adding sugar esters,immobilized fermentation can significantly improve the color value of Monascus yellow pigment.The type and quantity of carrier play an important role in the process of immobilized fermentation.The results showed that the corn cob had honeycomb structure and large specific surface area,which was conducive to the attachment and growth of Monascus,and had high food safety.It was an excellent carrier under the experimental conditions.The ideal carrier amount in 50 m L fermentation broth is 0.75 g(5grains)corncob,and the optimal fermentation time is 5 days.In the process of immobilized fermentation,the mycelium of Monascus was wrinkled,and the physiological structure of corncob carrier was destroyed.In addition,through repeated batch fermentation,the average daily yield of Monascus immobilized fermentation is 12.77 AU,which can save the repeated culture time of seeds,save time and cost,and provide a new idea for industrial production.The application of corncob as agricultural waste resource in Monascus immobilized fermentation can improve its comprehensive utilization level and promote the development of circular economy industry.The transcriptome of the above fermentation broth was sequenced by RNA-seq technology and bioinformatics methods,and the reliability of transcriptome data was verified by q RT-PCR.The percentage of Q30 bases after quality control in the sequencing data is more than 95%,and the gene integrity reaches the high standard of class A,indicating that the sequencing depth of transcriptome and the quality of transcripts are good,which meet the requirements of database construction and sequencing.390 differentially expressed genes were found by high-throughput sequencing,including 244 up-regulated genes and 146down-regulated genes.The eight significantly enriched GO functions are oxidoreductase activity(GO:0016491),transmembrane transporter activity(GO:0022857),transport activity(GO:0005215),organic molecule transmembrane transporter activity(GO:0015318),iontransmembrane transporter activity(GO:0015075),transmembrane transport(GO:0055085),pyruvate metabolic process(GO:0006090)and intrinsic component of membrane(GO:0031224).The metabolic pathways of significant enrichment of KEGG are glycolysis /gluconeogenesis pathway and tyrosine metabolism pathway,respectively.The results showed that the immobilized fermentation of Monascus effectively regulated the pyruvate metabolism process,changed the inherent components of the membrane,changed the permeability of the membrane,and improved the transmembrane transport capacity of yellow pigment.On the other hand,immobilized fermentation enhances the glycolysis / gluconeogenesis pathway by up regulating the expression of pigment synthesis related genes and changing metabolic flow.Tyrosine generates precursors of yellow pigment synthesis through a series of reactions,such as acetyl Co A,which enters the tricarboxylic acid cycle and participates in the polyketone pathway,so as to improve the yield of yellow pigment.The change trend of q RT-PCR validation data is consistent with that of sequencing data,which verifies the analysis of GO function and KEGG metabolic pathway.