Preparation Of D-valine By Microbial Asymmetric Degradation

D-valine is an important chiral source.It can be used as an intermediate for synthetic pesticides,veterinary drugs and pharmaceuticals.At present,the methods of preparing D-valine are stereoselective synthesis,induced crystallization,chemical resolution and microbiological methods.In comparison with above approaches,microbial preparation of D-valine is more competitive and promising because of its high stereoselectivity,mild reaction conditions and environmental friendly process.For the first time in our laboratory,a strain of Candida maltose DLPU-zpb(Candida maltosa)was selected from nature,which showed asymmetric degrading activity against DL-valine.The cells of this strain could be used as a biocatalyst to eliminate the L-isomer,which provided a new method for D-valine preparation from DL-valine.In this paper,D-valine was prepared by asymmetric degradation of Candida maltose.In order to obtain high efficiency degradation of L-valine,the original strain of Candida maltose was selected by acclimation,gradient plate,UV mutagenesis and DES mutagenesis,and a strain of DES mutagenesis strain with high efficiency of degradation of L-valine was selected.Compared with the original strain,the degradation rate increased by about 15%.L-valine was degraded by synchronous culture degradation,and the optimized conditions were as follows: glucose 5 g/L,yeast extract 10 g/L,peptone 10 g/L,L-valine 25 g/L,the initial pH value of the medium was 5.0,the amount of liquid was 40ml/250 ml,the speed was180 r/min,the temperature was 30?,the amount of bacteria 10%,and the same concentration of glucose was added to the medium every 24 h.Finally,within 96 h,L-valine with a concentration of 25 g/L can be degraded almost completely.Preparation of D-valine by resting cell degradation.The substrate L-valine with a concentration of 35 g/l can be completely degraded within 98 h under shaking flask conditions;The substrate L-valine at a concentration close to 40 g/L can be completely degraded by feeding into the fermentor.At last,the DL-valine concentration of 50 g/L wasused as the substrate for asymmetric degradation,and the L-valine was completely degraded in 72 h.Therefore,high purity D-valine could be prepared and D-valine was prepared from DL-valine.There is a certain significance of industrialization.