| Red yeast rice is fermented by Monascus spp with rice as substrate.It has a history of more than 1000 years in our country.Red yeast rice is not only used in food coloring,rice wine brewing,fermented bean curd,vinegar production,and meat processing,but it also has medical effects such as lowering blood pressure,lowering blood fat,lowering blood sugar,anti-inflammation.Because of these benefits,it is also referred as functional red yeast rice.China produces about 20,000 tons of red yeast every year,and more than 100 million people consume red yeast products daily.Therefore,studying the Monascus pigment and Monascus flavor produced by Monascus spp.holds significant value.The biosynthesis pathway of Monascus pigment is based on acetyl-coenzyme A as precursor.The β-ketoacid is synthesized via fatty acid pathway,and the polyketone is synthesized via polyketone pathway.The carboxyl group of polyketone reacts with the hydroxyl group of fatty acid chain to form monascus pigment.In this paper,the flavor and pigment of Monascus were studied from three aspects.(1)The effects of different oil residues(sesame meal,rapeseed meal,soybean meal and peanut meal)added in Monascus fermentation on flavor-producing substances were studied using Monascus ruber CICC41233.A total of 52 volatile substances,including alcohols,esters,ketones,aldehydes and phenols,were detected by GC-IMS.The addition of different oil residues resulted in the production of various unique flavor substances,and the volatile flavor substances produced were significantly different.(2)The effects of Na Cl on the growth and production of Monascus pigments and flavor substances were studied.M.ruber CICC41233 was cultured on MPS solid plates.The results showed that on the 6th day,the addition of 1% Na Cl significantly promoted the mycelia growth,with the growth diameter increasing by 69.85%.However,5% and6%Na Cl significantly inhibited the growth of mycelia,and the growth diameter decreased by 42.65% and 79.41%,respectively.The results of Monascus pigment fermentation over 6 days showed that the addition of 1% Na Cl resulted in a 5.91%increase in the yield of total Monascus pigment.In contrast,the addition of 3% and 5%Na Cl led to a decrease of total Monascus pigment by 53.31% and 91.23%,respectively.Transcriptomic sequencing analysis revealed that KEGG metabolism pathways involved in enrichment analysis of differentially expressed genes included phenylalanine,tryptophan,arginine and proline metabolism,fatty acid biosynthesis and Monascus pigment synthesis gene cluster.GC-IMS was used to detect the flavor produced by adding different concentrations of Na Cl.A total of 46 volatile compounds were identified,including aldehydes,ketones,alcohols,esters,acids,pyrazines and phenols.Fourteen of the substances were found to have dimers.The results showed that Na Cl promoted the production of various specific flavor substances in M.ruber CICC41233.(3)The effect of knocking out of the ATP-citrate lyase coding genes(acl1 and acl2)in M.ruber CICC41233 on Monascus pigment production was studied.The knockout vectors p Hph0380-Acl1 and p Hph0380-Acl2 were transformed into M.ruber CICC41233 using Agrobacterium tumefacients-mediated transformation,resulting in the knockout engineering strains M.ruber ΔACL 438469-1 and M.ruber ΔACL 501956-16,respectively.The results of Monascus pigment fermentation over 6 days showed that the total Monascus pigment yield of M.ruber ΔACL 438469-1 and M.ruber ΔACL501956-16 decreased by 24.09% and 25.92%,respectively.The activity of ATP-citrate lyase was not detected,and the content of acetyl-Co A decreased by 35.57% and 20.61%,respectively.Furthermore,after 6 days of fermentation,the remaining was accounted for 23.17% and 22.59%.Transcriptome sequencing analysis indicated that differentially expressed genes were primarily involved in amino acid biosynthesis,glycine,serine and threonine metabolism,starch and sucrose metabolism,among others.This study could provide a theoretical foundation for understanding the mechanism underlying Monascus pigment production and the application of red yeast rice in the food industry. |
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