Study On L-Lactic Acid Bacterial BME5-18M Fermentation And Recovery Technology From Fermentation Broth

L-Lactic acid has a versatile and extensive application in foodstuff, pharmaceutical and other chemical fields. At the present time, L-lactic acid is mostly produced by fermentation. Based on former research, fermentation media and process parameters are optimized for the sake of preferable biomass growth condition and L-lactic acid production enhancement in this paper by using Lactobacillus delbrueckii subsp. lactis BME5-18M, which is screened and preserved by biochemical department of tianjin university.Optimization of fermentation media and process parameters are investigated. The suited temperature for biomass growth and lactic acid production is 37 degrees centigrade, and the preferable carbonate source of glucose, lactose and xylose for highest L-lactic acid production is glucose. The optimal inoculum's age of is 24 hours after pre-culture, and the initial glucose concentration at the range of 30 g/L is feasible.For L-lactic acid fermentation with calcium carbonate as a neutralisation, batch and fed-batch culture are studied in an attempt to set up a system having a long operational lifetime and permitting maximal conversion of substrate to the product. In batch culture, 210.8 g/L L-lactic acid is obtained at the initial glucose concentration of 217.0 g/L with the mean productivity and yield of 1.21 g/(L.h) and 97.1% respectively after 174 h, and the maximal dry cell is 1.63 g/L. A strong enhancement of L-lactic acid production (210.9g/L) and productivity (2.2g/(L.h)) are obtained in fed-batch culture with the maximal dry cell and the yield of 2.68 g/L and 97.3% after 96 h. Achievement of about 210.0 g/L L-lactic acid in fed-batch culture is saved approximate 80 h compared with batch culture.L-lactic acid fermentation with ammonia instead of calcium carbonate is attempted. Effects of pH on the production of biomass and lactic acid in batch culture were studied at first, and the microorganism can gain the highest biomass density and lactic acid production at about pH 6.5. At the initial glucose concentration of 150.0 g/L in batch culture, 127.5 g/L L-lactic acid is gained with the mean productivity and yield of 1.14 g/(L.h) and 99.4% respectively after112 h at about pH 6.5, and the maximal dry cell is 1.56 g/L. The production and mean productivity of L-lactic acid can reach 136.8g/L and 1.71g/(L .h) at the preferable condition of pH 6.5 and 25 ml/h glucose fed-batch speed after 80 h, and the maximal dry cell and yield are 2.15 g/L and 96.6 % respectively. Production of 130.0 g/L L-lactic acid in fed-batch culture is saved approximate 30 h compared with batch culture.Kinetic models of cell growth, L-lactic acid formation and glucose consumption in L-lactic acid batch fermentation are proposed and kinetic model parameters are determined. The calculated values basically agree with the experimental data, which shows that the kinetic models provided a reasonable description for the fermentation process. Kinetic model analysis shows that L-lactic acid production of is part-growth-associated, i.e. L-lactic acid formation is associated with cell growth and accumulation of cell mass.The technology of refining L-lactic acid by molecular distillation has been studied in this paper, including the effect of operation parameters, such as evaporator temperature, feed rate and agitation speed etc. Purity above 95% and the yield above 50% of L-lactic acid can be gained at the pressure and temperature range of 0.1 Pa and 55-75 degrees centigrade with agitation speed of 110-140 r/min.