Inhibition Of Lignocellulose-derived Fermentation Inhibitors On Bioethanol Production

Bioethanol,which is produced from abundant lignocellulosic materials,could alleviate the environmental pollution that is caused by the combustion of fossil fuel.At the same time,It could solve the problem of energy shortage and the waste of resources.However,various kinds of fermentation by-products were derived from the pretreatment procedure in bioethanol production process,which might have a negative impact on microbial fermentation subsequently.In order to reduce the side-effect effectively,Qualitative Structure–Toxicity Relationships(QSTR)models were built to analyze the inhibitory effect of lignocellulose-derived fermentation inhibitors on bioethanol production.The mechanisms of the inhibitory effect were also investigated,which could provide the key guidance and scientific basis for bioethanol production process.Multiple linear QSTR models,which consisted of molecular descriptors(the description parameters of molecular structure)and inhibitory data(the inhibition rates for Saccharomyces cerevisiae biomass and bioethanol yield)of fermentation inhibitors,were established at different concentrations.All the models were verified by leave-one-out(LOO)cross-validation,Y-scrambling validation and fitting ability validation,and were proved to be stable and reliable.It was indicated that all of them could be used for the evaluation of the inhibitory effect of fermentation inhibitors.The results revealed that the molecular structure of fermentation inhibitors played an important role in their corresponding inhibitory effect.The inhibitory effect of phenolic inhibitors was the highest,followed by furans inhibitors,whereas the inhibitory effect of weak acids was the lowest.Phenolic aldehyde exhibited greater inhibitory effect than that of phenolic ketone and phenolic alcohol.Inhibitors which possessed the unsaturated group,aldehyde group and carbonyl group,showed the stronger inhibitory effect.Compared to the inhibitors which has substituent on meta position and para position,the inhibitory effect of electron withdrawing substituent on ortho position was greater.Moreover,molecular descriptors played a key role for inhibitory effect of fermentation inhibitors.The inhibitory effect was correlated to carbonyl activity of functional groups(recognized as DM value)at high inhibitor concentrations,whereas it was related to molecular stability(recognized as qH~+value)at low inhibitor concentrations.Based on the inhibitory effect of single fermentation inhibitors,ferulic acid was chosen as the basic target object because of its strongest inhibition.The joint inhibitory effects of representative inhibitors(phenols,furans and weak acids)and ferulic acid were investigated.The results showed that the joint inhibitory effect of ferulic acid and the other co-existed inhibitors were mainly antagonistic or simple additive effect.Moreover,the antagonistic effect was mainly appeared at high ferulic acid concentrations.Meanwhile,QSTR models of joint inhibitions were established based on the simple additive effect.It was indicated that the simple additive effects of binary mixtures were mainly related to the value of qKa and?E.They were used to define the ionization constant and energy differences between molecular orbital,respectively.The higher value of qKa and?E was appeared,and the smaller inhibitory effects would be appeared.In an overall view,ferulic acid,which was recognized as the main fermentation inhibitor,should be removed in detoxification procedure of bioethanol production process.It could alleviate the negative effect on the subsequent fermentation process which was caused by pretreatment process,thus improving the bioethanol yield.