Screening Of D-valine Producing Strain And Optimization Of Fermentation Conditions

In this thesis,D,L-valine was producted by chemical racemization from L-valine.The L-valine was used to produce D-valine by the strain DLPU-zpb.The racemization conditions of L-valine were optimized by measuring and calculating.Optimal conditions were 95%acetic acid concentration,the ratio of salicylaldehyde and valine was 8:1,reaction time 1.5 h,temperature 90?.Under these conditions the effect of racemic can reach 100%.The yield of D,L-valine was 84%.A strain was screened from 30 strains which has highly ability to metabolize L-valine.By sequencing 26S rDNA(D1/D2)of the stain,the strain was identified as Candia maltose.Culture conditions of strains were optimized temperature 30?,shaking speed 180 r/min,pH 6.0,inoculum size 4.0%.The optimal conditions of producing D-valine by Candia maltose were temperature 30?,shaking speed 180 r/min,24 h cultured time,0.1 g/mL cell content and 4 days reaction time.The metabolic rate of L-valine was 83.6%.The final production could be received by bleaching,concentrating and desalting.The yield of final production was 34.6%.The production was valine by analysis on infrared spectroscopy.The production was D-valine because of the negative specific rotation.The D-valine was over 95%purity by HPLC detection.