Research On Biotransformation Of Xylitol Production

Xylitol,as five-carbon sugar alcohol,is an intermediate product of microbial metabolism of xylose,which has been attracted because of its physic-chenical properties,anticariogenic,low in calories and high sweetness,consumption does not cause the body to improve blood sugar and hepatoprotective.Currently,xylitol production as the main method of chemical method which has the shortcoming of waste resources、environmental pollution and demanding conditions.As an alternative method,microbial production of xylitol is becoming more interesting and attractive which has the advantages of mild process conditions and low cost.The test with strain Candida tropicalis(Candida tropicalis Y-14)is used as the original strain,the ability of producing xylitol by C.tropicalY-14,which is mutagenized through different mutagenic methods,including ARTP 、 UV and UV-ARTP composite mutagenesis method,a high yield strain for xylitol named C.tropical Y-3-23 with stable genetic cararteristics was obtioned by screening.The maximum xylitol yield was 77.42g/L by the strain C.tropical Y-3-23.Compared with the xylitol yield of strain C.tropical Y-14,the xylitol yield has improved 48.71%.The culture medium and the fermentation condition of C.tropical Y-3-23 producing xylitol were optimized by single factor experiment and Placket-Burman design.The fermentation conditions of C.tropical Y-3-23 was optimized as follows:the initial xylose dosage was 102g/L;nitrogen sources such as yeast extract powder dosage was 5g/L;initial pH was 6.0;culture temperature 30.5℃;seed age of 20h;seeds were inoculated volume was 10%;shaking speed 185r/min;shake flask liquid volume was 50 mL.Under these conditions,the productivity reached to maximum and the yield of xylitol was about 81.50g/L.The strain C.tropical Y-3-23 for cell immobilization,by combination of single factor test and orthogonal test method were obtained the optimal conditions for preparing immobilized cells,the optimal conditions was obtained:sodium alginate concentration of 3%,CaCl2 concentration 2% and the immobilized time was 10 hours.Under these conditions,strains C.tropical Y-3-23 were immobilized.In addition,Immobilized cells have little difference in xylitol yield and conversion rate compared to free strains.