Simultaneous Fermentation And Preparation Of Probiotics Bacillus Subtilis From Hexose And Pentose In Corncob Hydrolysate

For the bio-production of probiotic Bacillus subtilis(B.subtilis),the co-fermentation characteristics of C6 and C5 sugars from corncob was intensively investigated,as well as the detoxification technology of corncob acidic hydrolysate.By view of full utilization and bioconversion of corncob to B.subtilis cells,tow technological approaches were designed and comparatively studied as step-by-step fermentation process(SSFP)and one-step fermentation process(OSFP,),by the systematic integration of main processing module including dilute acid pretreatment,enzymatic hydrolysis,detoxification,and fermentation.The OSFP method was optimized as the final resolution for the production of probiotic B.subtilis from corncob material.The main findings of this thesis are as follows:(1)Studies on fermentation kinetics of C6 and C5 sugars by B.subtilis.The results showed that B.subtilis presented a well co-fermentability for various C6 and C5 involving main lignocellulosic monosaccharides.The bacterial cells prefer to uptake and metabolize sugars in the order of glucose,mannose,arabinose,xylose and galactose in the mixed solution.It is very interesting and promising for bacterial growth under 50℃ besides the optimal proliferation temperature of 30℃,under which the cell grew faster and the fermentation productivity reached1.05 g/L/h by the shaking Erlenmeyer flask fermentation.We could produce 8.03 g /L cell(oven dried weight)from 10 g/L glucose containing medium under 30℃ fermentation that doubled the cell harvest under 50℃.The costly beef extractive was successfully substituted with cost-effective corn steep liquor for B.subtilis production,and cell yield increased 9.84% to cellular density of8.82 g/L under the optimized nitrogen and carbon ratio of 1:2.(2)Detoxification and co-fermentation of acid-prehydrolysate solution from corncob by B.subtilis.B.subtilis could not grow in untreated corncob sulfuric acid hydrolysate,so that the composition of corncob sulfuric acid hydrolysate and its effect on microbial fermentation were investigated in this study.The main degraded inhibitor was determined to be of aliphatic acids and furans,and the bio-toxicity was ranked as furfural,acetic acid,formic acid and 5-hydroxymethylfurfural in the crude hydrolysate.Furthermore,resin adsorption and water dilution were used to detoxify corncob sulfuric acid hydrolysate in this study,resulting that both methods have an enhanced effect on the bacterial fermentation of corncob dilute acid hydrolysates.Resin adsorption operation adsorb 17.09% of sugar contents at 48.76% of sugar conversion,while the easy operation of water dilution kept all sugars and improved 1.48 times for cell harvest at 72.26%of sugar conversion.(3)Comparative study on various co-fermentation processes for prebiotic B.subtilis production from corncob.Based on the study(2),the SSFP and OSFP processes were proposed to produce probiotics by studying the enzymatic hydrolysis conditions of solid residue and mixture obtained by sulfuric acid pretreatment of corncob respectively,and the cell yield and economic benefit were compared as well.In the process of SSFP,B.subtilis could be produced up to 326.83 g of probiotics at most through the stepwise fermentation of glucose and xylose in 1000 g of corncob.In the process of OSFP,B.subtilis could produce 323.70 g probiotics by simultaneous fermentation of glucose and xylose in 1000 g corncob.In general,the industrial process is preferable to OSFP in respect to the simple processing units,easy operation and higher economic benefit,thus C6 and C5 sugar contents in corncob is effectively and simultaneously converted to prebiotic B.subtilis.