| Monascus spp.are important edible microbial resources in China.Red mold rice is the fermented products by M.spp.when starchy materials such as rice,etc.are used as the substrates.Many kinds of beneficial metabolites can be produced by Monascus spp.,among which monacolin K（MK）and Monascus pigments（MPs）are most widely used.Some Monascus strains can also produce a nephrotoxin—citrinin,to pollute red mold rice.Cholesterol synthesis in humans can be inhibited by MK,and red mold rice enriched with MK is used as a dietary supplement for regulating blood lipids.Red mold rice rich in MPs or purified MPs are mainly used as natural food colorants.Therefore,screening of M.spp.with high MK or MPs production but no citrinin,optimization of fermentation process of M.spp.and development of novel Monascus fermented products have became a focus of M.spp and red mold rice research.A Monascus strain,named Monascus pilosus MS-1,which can produce MK and MPs but no citrinin and key genes for citrinin production was used as the starting strain.Monascus strains with high producing MK or MPs were screened by ultraviolet-chemical mutagenesis.The obtained Monascus strains were used for rice bran and broken rice fermentation for novel Monascus fermented products enriched with MK or MPs.The main research results were listed as follows.1.Screening for stable and high-yield MK or MPsMonascus strains,MS-1 was used as the starting strain.7,2 and 3Monascus strains were obtained by UV mutagenesis,lithium chloride chemical mutagenesis and UV-lithium chloride complex mutagenesis,respectively.Second screening and genetic stability test of the aforementionedMonascus strains were carried out,and 4 strains with high MPs or MK production and with improved genetic stability were obtained.Among which,ZWS5increased MPs yield by 23.36%and ZWN2,LHL1 and FH2 increased MK yield by12.76%,12.23%and 12.46%,respectively,compared tothat of starting strain.The colony morphologies of the mutagenized strain ZWN2 and ZWS5 were observed when MS-1 was used as control.The colony morphologies and growth characteristics of the mutagenized strain were analyzed.The mutagen ZWN2 showed whiter colony color,faster growth rate,longer hyphae and thicker fluffthan that of MS-1 on PDA,MEA,CYA and G25N medium.The mutagen ZWS5 showed orange color,slower growth rate,shorter hyphae and thinner fluff than that of MS-1 on the four aforementioned medium.2.Based on the results of“1”,mutants ZWN2 and ZWS5 were used for solid-state fermentation on rice bran and broken rice for MK and MPs,respectively,and the fermentation process was optimized.The favourable conditions for MK production by ZWN2 in rice bran were listed as follows.Rice bran was used as the substrates and adding 3%（w/w）soy protein isolate,the contents of water,acetic acid and MgSO4·7H2O were adjusted to 35%（v/w）,0.6%（v/w）and 0.004 mol/kg,respectively.The inoculation amount was 13%（v/w）.Cultured at 30°C for 3 days and then turned to 25°C until to 14 days.The MK yield of 11.68 mg/g was obtained of the fermentation product by ZWN2.The favourable conditions for MPs production by ZWS5 in broken rice were listed as follows.Broken rice was used as the substrates,adding 1%（w/w）soy isoflavones,contents of water,acetic acid,MgSO4·7H2O and inoculum were consistent with that of rice bran fermentation,cultured at 30°C for 14days.The colour value of 981.33 U/g was obtained of the fermented broken rice by ZWS5.The results can provide a reference for screeningMonascus strains with high-productionof MK or MPs,and also provide theoretical and technical support for the rice bran and broken rice fermentation by Monascus spp.It is also a reference to comprehensive utilization of other starchy agricultural and sideline products. |
