title: Inhibition of lignin-derived phenolic compounds to cellulase.
abstract: BACKGROUND
  Lignin-derived phenolic compounds are universal in the hydrolysate of pretreated lignocellulosic biomass. The phenolics reduce the efficiency of enzymatic hydrolysis and increase the cost of ethanol production. We investigated inhibition of phenolics on cellulase during enzymatic hydrolysis using vanillin as one of the typical lignin-derived phenolics and Avicel as cellulose substrate.
  
  
  RESULTS
  As vanillin concentration increased from 0 to 10 mg/mL, cellulose conversion after 72-h enzymatic hydrolysis decreased from 53 to 26 %. Enzyme deactivation and precipitation were detected with the vanillin addition. The enzyme concentration and activity consecutively decreased during hydrolysis, but the inhibition degree, expressed as the ratio of the cellulose conversion without vanillin to the conversion with vanillin (A 0 /A), was almost independent on hydrolysis time. Inhibition can be mitigated by increasing cellulose loading or cellulase concentration. The inhibition degree showed linear relationship with the vanillin concentration and exponential relationship with the cellulose loading and the cellulase concentration. The addition of calcium chloride, BSA, and Tween 80 did not release the inhibition of vanillin significantly. pH and temperature for hydrolysis also showed no significant impact on inhibition degree. The presence of hydroxyl group, carbonyl group, and methoxy group in phenolics affected the inhibition degree.
  
  
  CONCLUSIONS
  Besides phenolics concentration, other factors such as cellulose loading, enzyme concentration, and phenolic structure also affect the inhibition of cellulose conversion. Lignin-blocking agents have little effect on the inhibition effect of soluble phenolics, indicating that the inhibition mechanism of phenolics to enzyme is likely different from insoluble lignin. The inhibition of soluble phenolics can hardly be entirely removed by increasing enzyme concentration or adding blocking proteins due to the dispersity and multiple binding sites of phenolics than insoluble lignin.
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Qin
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Wen-Chao
authors.initials: WC
authors.lastname: Li
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Jia-Qing
authors.initials: JQ
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Bing-Zhi
authors.initials: BZ
authors.lastname: Li
authors.affiliation: Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China ; SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Weijin Road 92, Nankai District, Tianjin, 300072 People's Republic of China.
authors.forename: Ying-Jin
authors.initials: YJ
authors.lastname: Yuan
keywords: Cellulase; Cellulose; Enzymatic hydrolysis; Inhibition; Phenolics; Vanillin