Studies On The Breeding Of Bacteria Producing L-lactic Acid By Aerospace Mutagenesis And Optimizing Conditions Of Fermentation

Studied on the breeding of bacteria producing L-lactic acid by aerospace mutagenesis,fermentation conditions of bioreactor and conditions for producing xylose through corn cob hydrolysis.1 Breeding of Bacteria producing L-lactic acid by aerospace mutagenesisA positive bacteria strain Lt-s producing L-lactic acid using xylose was obtained through aerospace mutagenesis breeding methods . After fermentation for 48 hours at 48℃with a 5L bioreactor, Lt-s produced 70.0g of L-lactic acid /L from 8% of xylose, about 12.0% higher than that produced by the wild strain and the conversion rate respectively were 87% .2 Study on the fermentation conditions of L-lactic acid using Lt-sThrough single factor experiment and orthogonal experiment,the conditions of fermentation of bioreactor were experimengted. The growth factors and conditions of fermentation were studied according to analysis and construction of DPS v7.55 and Origin 6.0. The results indicated that optimal conditions of fermentation were fermentation pH 6.3,fermentation temperature 45℃, initial pH 7.0, inoculum 10%,bioreactor revolution 120 r/min,Lt-s produced 70.0g of L-lactic acid /L after 48 h, and the conversion rate respectively were 89.25% .3 Study on the conditions for producing L-lactic acid through corn cob hydrolysisThrough single factor experiment and orthogonal experiment, the conditions ofcorn cob hydrolysis were experimented. The results indicated that the primary and secondary order of influence of several main crafts on yield of xylose is that the hydrolysis reaction time was first,and the concentration of phosphoric acid was second,and the hydrolysis reaction temperature was the third,and the ratio of solid/liquid was last. The optimal parameters for hydrolysis were hydrolysis reaction time of 300 min and the concentration of phosphoric acid of 4% and hydrolysis reaction temperature of 120℃and the ratio of solid/liquid of 1/8. After fermentation for 48 hours using corn cob hydrolysate , Lt-s produced 62.58 g of L-lactic acid /L, and the conversion rate respectively were 87% .