| Monacolin K, one of the main secondary metabolites of Monascus species, has been widely used as the potent for lowering the cholesterol in vivo. Rice is the only raw material, which can be allowed to use in the various existing standards of lipid-reducing Monascus product. Although great achievement had been made in the traditional fermentation technology of rice, but its ferementation level is relatively low, which only have a few thousandths. In addition, the manufacturer found that the Monacolin K content would decline dramatically with the extension of storage time.Therefore, to improve the fermentation level of Monacolin K and master the Monacolin K content variation during the storage, we research on the diversity of Monascus substrate, the variation of Monacolin K content and the standards of Monascus product.Five kinds of common grain and four kinds of non-grain as raw materials were used for Monacolin K production by solid-state fermentation of Monascus, among which millet was found as the best substrate for MK production, and the Monacolin K yield reached 7.25 mg/g, corresponding to 1.5 times compared with the rice. The fermentation of other grain materials also had a high production of Monacolin K, but the non-grain materials production of Monacolin K were generally low.For enhanced Monacolin K production in solid-state fermentation by millet as the substrate, the effects of fermentation time, initial moisture content and inoculum volume were systematically investigated by single factor expermient. After optimization, the Monacolin K production generally stable at 1.1%, which 50% higher than that of rice.Moreover, complementary carbon source and nitrogen source were added for further improving the production of Monacolin K. Results showed that the maximum production of Monacolin K(19.24 mg/g) was obtained when 20% glycerol and 3.5% soybean meal were supplied. In addition, the final fermentation product was detected by HPLC and citrinin was not found, which indicated that the fermentation process were safe for Monacolin K production.Based on the above optimum condition of millet, when 35% glycerol and 4.5% soybean meal were supplied, the yield of Monacolin K reached 7 mg/g by tea stalk as the fermentation substrate and it was 10 times more than that of control. It proved that the effect of nutrients additoin on non-grain substrate on Monacolin K biosynthesis were also quite obvious.The factors of influencing Monacolin K contents in Monascus product by sterilization via Co-60 γ radiation and storge time were investigated. The result show that it had little influence on Monacolin K content and structure when the strength of irradiation in the range of 12 KGy. However, with the extension of storage time, the content of Monacolin K in monascus product showed a decreased significantly. The acid form proportion of Monacolin K reduce and the lactone form proportion of Monacolin K increase in monascus product. And set up the liner regression equation, which can calculate the half-life period of Monacolin K easily.The content of several existing standards involved with lipid-reducing Monascus product in china were mainly discussed. which includes fermentation strains, raw materials, concentration of the citrinin, the structure and test method of Monacolin K. It is suggested that the more scientific and reasonable standards should be established to promote the development of lipid-reducing Monascus product. |
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