Effects Of Substrates On The Secondary Metabolites Of Red Yeast Rice

Monascus is one of the traditional Chinese herbal medicines, and is first used in the Tang Dynasty. It has a history of more than 1000 years. Red mold rice is a fermented product of Monascus species. The secondary metabolites studied in Monascus were Monacolin K and Monascus pigment. Monacolin K is the world’s recognized effective cholesterol-lowering substances.Recently, Monascus pigment, as a natural food coloring agent, its cholesterol lowering effect has been found, which does not cause side effects such as rhabdomyolysis. Therefore, it has great potential to be developed into a new type of hypolipidemic products. In this paper, the two main metabolites, Monacolin K and monascin were studied. Solid-state fermentation experiments were carried out using different rice fermentation substrates, the significant difference on the yield of monascin and Monacolin K were investigated.The effects of different culture medium on the yield of monascin were significantly different. According to the resuilts of HPLC, using polished rice as fermentation substrate,the yield of monascin was higher than that of brown rice as the fermentation substrate.Therefore, SD-2 was selected as the raw material of high-yield monascin.In this experiment, the standard of monascin was prepared by preparative high performance liquid chromatography. The purity of the prepared monascin products was more than 95% evaluated with analytical high performance liquid chromatography.According to the data of LC-MS-IT-TOF and NMR, the product was identified as monascin, which was prepared as a standard solution for quantitative analysis.The results indicated that the culture medium had a significant influence on the yield of Monacolin K. The samplings were collected at 14 days, 21 days and 28 days respectively. The content of Monacolin K in TD-6 was always higher than TD-3. Till 28 days, the total yield of Monacolin K in TD-3 and TD-6 was 1.35 mg/g and 4.39 mg/g,respectively. The content of Monacolin K in TD-6 was 4.39 times of TD-3.The SEM micrographs of the two raw rice grains showed that the surface of TD-6 starch granules was smooth and the particle size distribution was uniform. But TD-3 starch granules had rough surface, nonuniform particle size distribution and irregular shape. After the sterilization, TD-3 exhibited larger and more hollows than TD-6. In addition, TD-6 starch particles arranging loosely, conducive to the access of oxygen and mycelium, and then will be conducive to the growth of Monascus. With TD-6 as the fermentation substrate, mycelium was dense and thick, and its growth was better than TD-3.The amylose content in the fermentation medium was determined by chemical method. The amylose content in TD-6 was 4.08 ± 0.61%, which was not detected in TD-3.Therefore, it is proposed that amylose content, which influences the microstructure and the mycelia growth of Monascus, is one of the factors that affect the production of Monacolin K.