Inhibition Evaluation Of Inhibitory Compounds In Alkali-pretreated Rice Straw Hvdrolvsate By Using QSAR Method

Using cellulosic materials to produce bioethanol can help us to solve the problem of energy crisis, environmental pollution and cellulosic waste of resources. However, pretreatment and detoxification are two bottlenecks which could influence the bioethanol production efficiency. To solve the above problems, Quantitative Structure-Activity Relationship (QSAR) method was introduced to cellulosic bioethanol field to evaluate toxicity and inhibition efficiency (IE) of lignocellulose-derived compounds, which could help us to remove inhibitors proposefully. In addition, pretreatment condition could be optimized ultimately by considering both of pretreatment effect and total IE, which could provide theoretical direction for increasing cellulosic bioethanol production.Extraction and enrichment-Gas chromatograph/Mass spectrometer (EE-GC/MS) was used to identify and quantify the inhibitors composition in rice straw hydrolysate after 2%,4% and 6% NaOH pretreatment. The results showed that phenols and acids occupied above 90% of the total relative contents. The types of phenols and acids in alkali pretreatment hydrolysate were distinctly increased compared to that of the control group. By quantification analysis, the total contents of phenols and acids in alkali pretreatment hydrolysates were significantly increased compared to that of the control group, in which Ferulic acid and n-Hexadecanoic acid was the most abundant compounds for phenols and acids, respectively.Got through leave-one out (LOO) cross validation and y-randomization test, three stable QSAR models were established. The r2 of these three models were 0.937, 0.907 and 0.814, and q2 were 0.904,0.838 and 0.527, respectively. All of the data showed that these three models were fitting, predictive and stable. Moreover, the three models were used to predict the toxicity of main inhibitors on S. cerevisiae, E. coli and Z. mobilis. Then toxicity ranking list of main inhibitors was revealed. The results revealed that phenols exhibited the most significant toxicity on yeasts, furans showed moderate toxicity on yeasts, however, short chain fatty acids exhibited feeble toxicity. For phenols, the functional group in R position influenced the toxicity on yeasts enormously. The presence of an unsaturated bond in R position could accelerate the inhibition degree to the largest extent, followed by formyl, carboxyl and alcohol substituents. According to evaluation results, coniferyl aldehyde and sinapyl aldehyde were the most toxic inhibitors. The prediction results coordinated with previous experimental studies commendably, which could verify that our QSAR modeling was valid and effective for toxicity evaluation in this study.Combined with toxicity and content of inhibitors in rice straw hydrolysate after alkali-pretreatment, total IE of inhibitors were estimated on account of additive effect of inhibitors. The results showed that 4% NaOH pretreatment was optimal when considering both pretreatment effect and total IE together. Moreover, the IE values of long chain fatty acids on yeasts were distinctly higher than that of phenols. However, long chain fatty acids could be washed off by alkali liquor efficiently. Difficultly migratory phenols (e.g.2,4-di-tert-butylphenol and Ferulic acid) should be removed proposefully according to their own features.