Screen Of Mutants And Optimization Of Fermentation Conditions For L-latic Acid Fermentation Utilizing Sweet Potato

L-lactic acid and its derivation have a great of potential market for the wide range of applications in a lot of fields such as food, medicament and chemical industry. It is meaningful to get L-lactic acid by femertation, for pure L-lactic acid can be got and the cost is lower by this way. Corn and white rice is the normal raw material for L-lactic acid femertation. Sweet potato was studied rarely as the raw material for L-lactic acid femertation. But the production,starch and carbohydrate of sweet potato are higher than corn and white rice.Ro3.1179 was mutagenized with ultraviolent radiation (UV) and 60Coγradiation together. We got a mutant UVCo1, which production and heritic charactic were stable in the medium composed by the suger saccharificated from sweet potato powder. The effect of Co60γradiation was better than ultraviolent radiation on mutation. The advantage mutant rate was the highest in 500Gy donzen. The mutant UVCo1 was higher than Ro3.1179 in the ability of utilizing soluble starch. The result of study showed that the starch enzyme activity of mutant UVCo1 was enhanced。Determination of RP-HPLC exploring the citric acid content was lower than Ro3.1179 in fermentation broth.Through the experiments of shake-flask femertation, the optimal production medium and fermentation conditions of the mutant UVCo1 were designed as fallows: sweet potato syrup 120g/L, (NH4)2SO4 3g/L, KH2PO4 0.3g/L, MgSO4·7H2O 0.25g/L, ZnSO4·7H2O 0.05g/L; fermentation temperature is 30℃; liquid level is 75ml/250ml; the culture time and added volume of the seed were 6h and 7.5%; The quantity and added time of CaCO3 were 40% of the raw sweet potato powder and 6h; fermentation time 72 hours. In such conditions, the lactic acid yield of UVCo1 was59.4g/L and the conversion rate of total carbohydrate was 67%, which were enhanced 24.3g/L and 69.2% compare with the strain Ro3.1179.