Effects Of Inhibitors Produced In Lignocellulosic Biomass Pretreatment Process On Saccharomyces Cerevisiae 1517RM And Fermentation For Ethanol

The development of green and renewable biomass energy is one of the effective methods to solve the global energy and environmental crisis,among which bioethanol is the representative biomass energy.Pretreatment is necessary to improve the conversion efficiency of bioethanol and reduce the production cost,but at the same time,it will produce some inhibitors that inhibit the growth of microorganisms and reduce the conversion efficiency.Exploring the efects of inhibitors on the growth and fermentation of microorganisms and their mechanism of action is of great significance for obtaining dominant strains with high tolerance and guiding the optimization of fermentation process.In this study,the effects of furfural,syringaldehyde and acetic acid on the characteristics of Saccharomyces cerevisiae CICC:1517RM(S.cerevisiae 1517RM),ethanol production and fermentation kinetrics were studied from the aspects of biomass,ethanol yield,glucose consumption and physicochemical properties of cells.The main conclusions were as follows:(1)The main components of dilute phosphoric acid-steam explosion pretreatment solution of poplar wood were analyzed by GC/MS and HPLC.The concentrations of glucose,xylose,acetic acid,furfural,5-HMF,syringaldehyde and vanillin were 5.10×103 mg/L、14.87×103 mg/L、3.63×103 mg/L、219.45 mg/L、192.90 mg/L、80.33 mg/L and 41.44 mg/L,respectively.Furfural,syringaldehyde and acetic acid were selected as typical inhibitors for further study.(2)The inhibition of S.cerevisiae 1517RM cells and fermentation by single inhibitor was evaluated,the results showed that:In the furfural treatment group,the growth and ethanol synthesis of S.cerevisiae 1517RM in the early fermentation stage were inhibited to varying degrees,which showed that the lag period of S.cerevisiae and ethanol production was prolonged,and the middle and late fermentation period promoted the growth and fermentation of S.cerevisiae 1517RM.After 72 h fermentation,ethanol concentration in 0.5,1.0,2.0 and 3.0 g/L furfural groups increased by 99.2%,64.6%,70.8%and 86.7%compared with the blank,respectively.In general,with the increase of furfural concentration,the inhibition effect of furfural in the initial fermentation is stronger.In the acetic acid treatment group,the higher the acetic acid concentration,the greater the inhibitory effect on S.cerevisiae 1517RM growth,but the stronger the promotion effect on ethanol production and glucose utilization.After 72 h fermentation,the OD value of the 1.0,3.0,5.0 and 7.0 g/L acetic acid groups was decreased by 2.0%,11.4%,29.7%and 59.0%,respectively,and the ethanol concentration was increased by 59.0%,139.1%,143.5%and 136.4%,respectively,compared with the blank.In the syringaldehyde treatment group,ethanol synthesis was inhibited by syringaldehyde in the early fermentation stage,which showed a prolonged production lag period.With the increase of syringaldehyde concentration,the cell biomass decreased and the concentration of ethanol increased.After 72 h fermentation,the concentration of ethanol in 0.5,1.0,2.0 and 3.0 g/L syringaldehyde groups was increased by 0.7%,38.0%,131.8%and 157.0%compared with the blank,respectively.The ergosterol content of yeast increased after the addition of single inhibitor.The Zeta potential decreased with the increase of furfural and syringaldehyde concentration.The Zeta potential increased with the increase of acetic acid concentration.(3)Based on the inhibition experiment of single inhibitor,the inhibition of S.cerevisiae 1517RM cells and fermentation by mixed inhibitor was evaluated,and the results showed that:At 72 h of fermentation,the biomass of yeast in acetic acid+furfural,acetic acid+syringaldehyde,furfural+syringaldehyde and acetic acid+furfural+syringaldehyde groups were 76.8%,82.1%,107.7%and 75.1%,and the concentration of ethanol was 252.9%,261.6%,109.3%and 241.6%,the glucose utilization ratio was 1.73,1.73,1.72 and 1.09 times of the blank group,respectively.Compared with the addition of these three inhibitors alone,furfural and syringaldehyde enhanced the inhibitory effect of acetic acid on cell growth and promoted ethanol production,while syringaldehyde weakened the promoting effect of furfural on yeast growth and ethanol production.The biomass of the mixture was only 75%of that of the blank.There may be synergistic effect between furfural,acetic acid and syringaldehyde.Compared with a single inhibitor,the mixture of furfural,acetic acid and syringaldehyde had a greater effect on S.cerevisiae 1517RM cell membrane,which changed the morphology of the whole bacterial community,and most cells showed different degree of shrinkage.In the groups of acetic acid+furfural,acetic acid+syringaldehyde,furfural+syringaldehyde,acetic acid+furfural+syringaldehyde,the Zeta potential was-24.2,-24.0,-21.5,-21.4,-22.7 mV,and the ergosterol concentration was 1.35,1.25,1.26,1.36 times that of the blank group after 72 h fermentation,respectively.The addition of two or three inhibitors induces S.cerevisiae 1517RM to increase tolerance to the inhibitor by increasing the ergosterol ratio.(4)Logistic,Luedeking-Piret and Luedeking-Piret equations were used to establish the growth model,product generation model and substrate consumption model of S.cerevisiae 1517RM fermentation for ethanol production without or with mixed inhibitors.The ethanol production of S.cerevisiae 1517RM and its growth belonged to a partial growth coupling type.The established model has a high degree of fit,which can be used to predict the dynamic changes of the main parameters during the ethanol fermentation of S.cerevisiae 1517RM,and provides a good reference for ethanol production.