Optimization Of Fermentation And Extraction Conditions For High Optical Purity L-Lactic Acid By Strain HY-U36

Lactic acid(α-hydroxypropanoic acid)is widely used in the food,environmental protection,chemical industry and medicine.Lactic acid molecular structure contains one asymmetric carbon atom with is optical isomerism.According to different configuration and optical activity,the lactic acid can be divided into D-lactic acid,L-lactic acid and racemic lactic acid.The L-lactic acid is the only type of lactic acid that can be decomposed to be used by the human,therefore,the research that produce high optical purity and yield of L-lactic acid has become the hotspot in the research of L-lactic acid fermentation.This paper was based on the Enterococcus faecium HY-U36 which can produce 99.3% optical purity L-lactic acid and researched the optimization of the shaking flask fermentation conditions and fermented liquid treatment technology.The main results were as follows:The shaking flask fermentation conditions were optimized by single factor experiment.The optimal conditions were as follows: temperature 37℃,the adding amount of calcium carbonate 60g/L,the age of seed medium 12 h,the inoculum size 5%(v/v),the liquid volume60 ml and the rotation speed 100r/min.The fermentation medium o f L-lactic acid producing Enterococcus faeciumHY-38 was optimized by response surface methodology.Firstly,Plackett-Burman design was used to evaluate the affections of the related factors.It showed that three factors playing the most important roles in the medium,including glucose,yeast extract and sodium acetate.Secondly,steepest ascent path was adopted to approach the optimal region.Then the Box-Behnken design and response surface analysis were used to determine the optimal levels of the main factors.The results showed the optimum fermentation medium components were as followed:glucose 148 g/L,yeast extract 12.4g/L,CaCO3 80g/L,sodium acetate 5.0g/L,KH2PO4·3H2O1.0g/L,MgSO4·7H2O 1.2 g/L and MnSO4·H2O 0.04 g/L.Under the optimal conditions,the yield of L-lactic acid can reach 134.7g/L,which was 24.3% higher than that before optimization(108.3g/L).Chitosan is an ideal flocculent.When the chitosan concentration 15mg/L,pH value 6.0the fermentation liquid temperature 50℃,stirring speed 140 r/min and stirring time 10 min,the removal rate of mycelium was 96.3% and the loss rate of lactic acid was only1.2%.By the comparison of the effects on the decolorization between the powered activated carbon and granular activated carbon,the granular activated carbon was chosen as decolorizing agent.The effects of granular activated carbon dosage,temperature,pH value,stirring speed and stirring time on the decolorizing rate were investigated through single factor experiments and orthogonal experiment.The results showed that the best decolorizing conditions were as follows: amount of granular activated carbon 3%,temperature 60℃,pH value 5.0,stirring speed 100 r/min and stirring time 60 min.Under these conditions,the decolorizing rate of fermented broth was 89.7% and the loss rate of lactic acid was 3.74%.