Isolation, Identification, Mutation Breeding And Applied Research On Productive Strain Of Succinic Acid

Succinic acid, a intermediate in citric acid cycle, is produced by microbial metabolism. It has widely potential and practical use in several fields, such as medicine, food, chemistry et al. Because of low processing cost and little pollution for environment, the research for succinic acid fermentation has become the hotspot at home and abroad in last years.As we all know, there are some succinic acid product in the course of fermentation of Chinese traditional fermented food, such as distillate spirit and yellow wine. A strain producing succinic acid was successfully isolated from brewing wine Daqu, which had the ability of starch hydrolysis. And the yield of succinic acid of the strain reached 2.08 g/L after 96 hours'liquid fermentation in PDA medium, which was measured by high performance liquid chromatography (HPLC). Then according to the common identification method of the mold fungus,the strain was initially identificated by cultural and morphological characterization as M. racemosus Fresenius which belonged to Racemousus,Muco,Mucoraceae,Mucorales,Phycomycetes in Fungi. And it was named M.racemosus Fresenius MF-1.To abtain succinic acid mutant strains, the spores and protoplasts of the strain MF-1 were induced by different physical and chemical factors, such as LiCl, UV, He-Ne laser, 60Co-γray. The results showed that the protoplasts of the strain MF-1 were more sencitive to these mutant fators than the spores, and the mutative effect was better. After the protoplasts from spores of the strain MF-1 were irradiated by UV, He-Ne laser and 60Co-γray, a mutant strain MSCo-24 was finnally obtained by re-screening, whose yield of succinic acid is 2.08 g/L by liquid fermentation in flask level, about 31.04 times of its parent. After being propagated for five generations, the strain MSCo-24 showed a more stable heredity, which could be as starting strain for further study.Production of protein feedstuff was primarily studied with the mutant strain MSCo-24 on brewer's spent grains by solid state fermentation. The ingredients of medium and fermentation condition affecting mold (MSCo-24) for protein production had been primarily optimized. Through orthogonal test, the best formula for the substratum had been obtained: beer grains 70%, wheat bran 17%, corn meal 10%, (NH4)2SO4 3%. And the optimum condition for fermentation was as follows: the inoculation was 7.5%, and the ratio of material and water was 1:3. The content of the crude protein in fermentation medium can be increased to 30.33% from15.00%, and 2.53% succinic acid was produced, thus substantially enhance the added value of brewer's spent grains feed.