Microbial Production Of 2, 3-Butanediol From Jerusalem Artichoke Stalks And Tubers

2,3-Butanediol(2,3-BD) is one of important bulk chemicals and liquid fuels,which exhibits a wide range of potential utilizations in chemicals,foods,medicines,as well as cosmetics.2,3-BD is mainly manufactured by microbial method.The most ideal substrate is lignocelluloses for the microbial production of 2,3-BD.However,the concentration of 2,3-BD in broth is low due to the low concentration of sugar and toxic compounds in hydrolyzate, which limits the application of lignocellulosic materials in industry.In this paper,we insisted a novel strategy to bioconverse lignocellulosic materials(e.g.Jerusalem artichoke stalk) combined with sugar materials(e.g.Jerusalem artichoke tubers) into high-valued chemicals (e.g.2,3-BD).Our goal was to increase the concentration of sugar in hydrolyzate of Jerusalem artichoke stalks by mean of adding Jerusalem artichoke tubers so as to improve the productivity of 2,3-BD.Firstly,the optimal conditions for hydrolysis of Jerusalem artichoke stalks and tubers were studied.The pretreatment of Jerusalem artichoke stalks was optimally conducted to soak stalks at 1%H₂SO₄ for 14 h,and then held the temperature of 130℃for 1.5 h.The hydrolysis of Jerusalem artichoke stalks was optimally carried out by adding 40 U/g of cellulase and 28 U/g of xylanase at 50℃,pH 5.0,100 rpm for 24 h.The optimal acid hydrolysis of Jerusalem artichoke tubers was conducted by using 7%(w/w) of H₂SO₄ at 80℃for 30 min,when the ratio of solid to liquid was 1:3.Secondly,the fermentation feasibility of Jerusalem artichoke stalks and tubers was investigated by Klebsiella pneumoniae CICC 10011 in shake flask cultures.At the same time, the effects of different carbon sources,trace elements and other elements in culture medium on production of 2,3-BD were also studied.The results showed that the hydrolyzate of Jerusalem artichoke stalks and tubers was an excellent carbon source for the production of 2,3-BD,even better than other sugars.The hydrolysate of Jerusalem artichoke stalks and tubers as culture medium could meet the requirement of fermentation completely after adjusting pH by ammonia,without adding any other nutrient substances.Thirdly,separate hydrolysis and fermentation(SHF) was performed using the hydrolysate of Jerusalem artichoke stalks and tubers as substrate.In batch fermentations,the concentration and yield of target products(2,3-BD and acetoin) was 652.6 mmol/L(58.4 g/L) and 0.73 mol/mol,respectively,with a productivity of 12.55 mmol/(L·h) in 52 h.This process provided 37.3%higher concentration of target products and 10.6%higher yield than the fermentation from Jerusalem artichoke tubers.In fed-batch fermentation,816.7 mmol/L(73.2 g/L) of target products,11.3 mmol/(L·h) of productivity were achieved.On the basis of above results,simultaneous saccharification and fermentation(SSF) was performed.The aeration played an important role in production of 2,3-BD.When variational aeration was adopted in fermentation for 68 h,the concentration of target products was 901.2 mmol/L(80.5 g/L),which was 16.9%higher than that under constant aeration.The productivity was 13.2 mmol/(L·h) with a yield of target products 1.81 g/(3g stalks+4g tubers),which was close to estimate value,i.e.65.3%of theoretical value.The results showed that SSF process was preferable for 2,3-BD production because of saving equipment and enhancing productivity.Finally,the economic analysis showed that microbial production of 2,3-BD from Jerusalem artichoke stalks and tubers would be profitable on annual production of 1000 ton of 2,3-BD,the investment recovery period is about 3 years.