Selective Reduction Of Biobased Furans By Immobilized Meyerozyma Guilliermondii SC1103 Cells

5-Hydroxymethylfurfural?HMF?and furfural are important biobased platform chemicals,which can be synthesized readily via carbohydrate dehydration.Due to the presence of formyl groups,HMF and furfural could be selectively reduced into 2,5-bis?hydroxymethyl?furan?BHMF?and furfuryl alcohol,respectively,which are important feedstocks for the synthesis of functional materials,drugs,crown ethers,farm chemicals and synthetic fibers,etc.Currently,chemical methods remain predominant in the synthesis of BHMF and furfuryl alcohol;nonetheless,they are characterized by harsh reaction conditions,environmental unfriendliness and high energy consumption.Therefore,biocatalysis with the advantages of high efficiency,high selectivity,mild reaction conditions,simple processes and environmental friendliness may be a good option to supplement or replace chemical methods for the synthesis of BHMF and furfuryl alcohol.Unfortunately,biocatalytic reduction of HMF and furfural remains challenging,because the two chemicals are significantly toxic and inhibitory toward microorganisms.Recently,our group reported a new HMF-tolerant yeast strain Meyerozyma guilliermondii SC1103 for the synthesis of BHMF.However,the biocatalytic approach to BHMF suffered from handling and recovering the biocatalyst difficultly?due to use of the free wild-type cells?,an unsatisfied substrate concentration and thus a low productivity.In this thesis,therefore,the physiological and biochemical characteristics of this yeast were investigated firstly.Subsequently,the catalytic performances of wild-type M.guilliermondii SC1103 cells were improved significantly by the combination of acclimatization and induction.Besides,the acclimatized cells were entrapped with a high density in biocompatible calcium alginate beads to increase the productivity.Moreover,the catalytic traits of immobilized cells were investigated and the effects of various key factors on the selective reduction of HMF by immobilized cells were also studied.An efficient and selective biocatalytic pathway to BHMF was established.Scale-up synthesis of BHMF was performed in order to verify the practicability of this method.The co-substrate glucose was replaced with cost-effective rice straw hydrolysate,thus allowing the development of an economic bioprocess.Finally,the established biocatalytic route was applied for the synthesis of furfuryl alcohol.It was found that the yeast could preferentially use monosaccharides such as glucose,fructose,galactose as carbon sources.And it could grow well with organic nitrogen sources such as peptone and beef extract.It could be tolerant to the sugar concentration of up to 60%as well as to the NaCl concencention of 12%.However,it was sensitive to alcohol;when the alcohol concentration was higher than 8%,its growth would retard.The optimum pH and temperature for its growth were 6.0 and 30°C,respectively.Both the catalytic activity and substrate tolerance of the cells were significantly increased upon acclimatization,induction and immobilization.BHMF was obtained with82-85%yields and 99%selectivity within 7-24 h when the HMF concentrations were up to200-300 mM.In scale-up synthesis,BHMF of up to 181 mM was produced within 7 h,with the space time yield of approximately 3.3 g·L^-1·h^-1;upon extraction with organic solvent,the desired product was isolated with the recovery of 92%and purity of 90%.In addition,the immobilized biocatalyst showed satisfactory operational stability;the cell viability of 70%was retained after reuse 4 times.When the rice straw hydrolysate was used as co-substrate,the yield and selectivity of BHMF were 88%and 89%,respectively.Besides,the biocatalytic route was applied for the preparation of furfuryl alcohol.And,the yield of furfuryl alcohol was significantly higher with glucose as co-substrate than those with glycerol and sodium formate.In the scale-up synthesis,furfuryl alcohol of approximately 157 mM was accumulated within 7 h,with a yield of 79%.Its recovery and purity were 90%and 88%,respectively,after organic solvent extraction.The concentration of furfuryl alcohol reached178 mM within 11 h by using the fed-batch strategy.The catalytic performances of immobilized cells have been uncovered in selective reduction of HMF and furfural in this thesis,which enrich the theortical foundation for biocatalytic valorization of biobased chemicals.In addition,it may provide technical guidance for the large-scale synthesis of BHMF and furfuryl alcohol.