Screening Of Rhizopus Strains With High Production Of Lactic Acid In Traditional Jiuqu And Optimization Of Fermentation Conditions

Lactic acid is one of the three organic acids, which is widely used in various industries, such as food, chemical, pharmaceutical, environmental protection and so on. The main method for industrial production of lactic acid is microbiological fermentation currently, lactic acid bacteria and Rhizopus are the main culture for lactic acid fermentation. The one frequently reported to fermentation to product lactic acid in Rhizopus is Rhizopus oryzae, occasionally there Rhizopus chinensis and Rhizopus arrhizus were report ed, but their production of lactic acid was low, there is a large gap form exploitation. Therefore, it is have a great significance to screen a new species of fungi with high production of lactic acid and have the potential to meet the application of future industria. So this article carried out the from the research work following four stages.Because traditional Jiuqu is riched in germplasm resourse, this article use the Jiuqu as the separatio n, separate 60 fungis which were single colony. After first screening by potassium perm anganate-potassium bromide plate, and rescreened by shake-flask fermentation, obtained a strain of lactic acid production of 52.33 g/L.Through the PDA plate and micro culture cultivation to observe the colony morphology and individual form, combine with the method of 18 SrDNA gene sequencing to identified the strain G10, and identified the strain as Rhizopus microsporus.First to set the mutation conditionsl based on the ethality, for G10 UV mutagenesis, obtain mutant strain Z2 after screened, the production of lactic acid reached 66.99 g/L. Use DES for a second mutation on Z2, obtain a mutant strain D11 which was genetically stable, the production of lactic acid reached 73.29g/L, and 40.05% higher than the original strain.The fermentation conditions of D11 were optimized by single factor and orthogonal experiments, the resulting optimal medium composition: glucose 120 g/L,(NH4)2SO4 4 g/L, KH2PO4 0.4 g/L, MgSO4·7H2O 0.3 g/L, ZnSO4·7H2O 0.4 g/L, CaCO3 50.0 g/L;The optim al culture conditions: liquid volume 50 mL/250 mL, inoculum10%, temperature 32℃, rotate speed 200 r/min. After optimization the lactic acid production of G10 reached 80.91 g/L.Corncob as carriers of immobilized Rhizopus G10 to fermentation produce lactic acid, the carrier parameters and fermentation conditions were discussed, obtained the best medium ratio: corncob 2 g/L, corncob grinding particle size 40 mesh, glucose120 g/L,(NH4)2SO4 2 g/L, KH2PO4 0.3 g/L, MgSO4·7H2O 0.1 g/L, ZnSO4·7H2O 0.3 g/L, CaCO3 60 g/L.Optimal culture conditions: liquid volume 50 mL/250 mL flask, inoculum 5%, temperature 32℃, rotate speed 200 r/min. Under optimum conditions the lactic acid production reached 92.33 g/L.