| So far, raw materials for lactic acid fermentation are still food crops, which not only increase the industry production cost, but also lead to sever food crisis. To improve the utilization of lignocellulose, reduce industry cost and save food resources, lactic acid producing bacteria from xylose was studied.1. Screening and identifying of Lactic acid producing bacteria from xylose.A strain with high yield of48.33g/L lactic acid using50g/L xylose was screened from sauerkraut, which was identified as Lactobacillus pentosus based on the physiological and biochemical testing and16S rDNA sequencing.2. Improving yield of lactic acid by DBD plasma mutagenesisLactobacillus pentosu DLL8was further processed through DBD Plasma Mutagenesis, during which a mutant strain named DLLM8was obtained via screening and genetic stability analysis. In batch fermentation using100g/L xylose, DLLM8produced73.51g/L Lactic acid with45g/L L-lactic acid and86.28%yield, which increased by14.12%,25%and8.7%respectively in comparison with wild strain DLL8. Acquisition of such a strain laid the foundation of lactic acid production by using lignocellulose.3. Optimization of media and cultivation conditions for Lactobacillus pentosus DLLM8Fermentation conditions of lactic acid produced by Lactobacillus pentosus DLLM8from xylose were optimized. Effects of carbon source, nitrogen source, Mg2+concentration, Mn2+concentration, inoculums ration, temperature, CaCO3concentration and N2filling time were studied. The optimum media composition and fermentation conditions were obtained by single-factor and orthogonal experiments as follows:xylose100g/1, beef extract2%, yeast extract1%, sodium acetate5g/1, ammonium citrate dibasic0.4%,1g tween80,2g K2HPO4,0.2g MgSO4·7H2O, inoculums ration5%, temperature37℃, CaCO35%without nitrogen filling, Finally, DLLM8produced94.33g/L lactic acid after96h, then it had a declined trend while the L-lactic acid went up to67.80g/L after144h. |
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