Submerged Fermentation Production Of L-Lactic Acid From Sweet Potato Starch With Rhizopus Oryzae

Submerged fermentation technology for the production of high optical purity L-lactic acid by Rhizopus oryzae was studied in this paper. The results were as follows:A mutagenized strain Rhizopus oryzae ASS.819 was used to produce L-lactic acid from sweet potato starch, and the fermentation technology in shake flask was investigated at first. The results showed that the optimal compositions of medium(%) were 15 sweet potato starch hydrolyte, 0.40 (NH4)2SO4, 0.03 KH2PO4, 0.044 ZnSO4-7H2O, 0.025 MgSO4-7H2O, and that the optimal culture temperature and rotation rate were 32 癈 and 220 r/min respectively. On the conditions above,L-lactic acid productivity and the crude Sweet Potato Starch conversion rate were 120 g/L and 80%, respectively.A 10L jar fermentation technology for producing L-lactic acid by the strain was developed, the optimal culture conditions were as follows: 10L jar contained 4L liquid culture medium, rotating speed was from 400 to 650 r/min, aeration velocity was from 0.5 to 0.6 L/(L-min), dissolved oxygen (DO) was above 80%, fermentation temperature was from 33 ℃C to 31.5 ℃, pH was from 5.0 to 5.5 and the amount of defoamer was about 0.1% . Results with these fermentation conditions indicated that the average yield of L-lactic acid, the conversion rate of crude starch to L-lactic acid and top biomass as well as fermentation time were 102.54 g/L, 78 %, 7.2 g/L and 70 h, respectively.Immobilized cell fermentation with calcium alginate and polyurethane foam was also studied. Results showed that the immobilized cell fermentation circulating seven times with polyurethane foam was still feasible, and the L-lactic acid productivity had been increased. But we found if the fermentation liquid was contaminated by other bacteria the subsequent experiment would lead to failure at last.