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• Lignin-based surfactants LC and LCQ with various isoelectric points were synthesized. • The effect and mechanism of the pI of LCQ on the enzymatic hydrolysis were studied. • The SED of Eu-SPORL increased from 35.2% to 95.3% by adding LCQ-40. • LCQ could be efficiently recovered for the excellent pH-response performance. The isoelectric point (pI) of lignin-based surfactant is an important factor in the enhancement on the enzymatic hydrolysis of lignocellulose. In this work, lignin carboxylate (LC) and quaternary ammonium lignin carboxylates (LCQ-x, x%: the mass ratio of quaternizing agent to enzymatic hydrolysis lignin) with different isoelectric points were synthesized. LC or LCQ-x with pI significantly lower or higher than 4.8 reduced the non-productive adsorption of cellulase on lignin, but for the significant inhibitory effect on cellulase activity, their enhancements on the enzymatic hydrolysis of lignocellulose were not remarkable. However, LCQ-x with pI around 4.8 preserved the cellulase activity, and significantly reduced the non-productive adsorption of cellulase, therefore remarkably enhanced the enzymatic hydrolysis. 2 g/L LC, LCQ-40 (pI = 5.0) and LCQ-100 (pI = 9.2) increased the enzymatic digestibility of pretreated eucalyptus from 35.2% to 53.4%, 95.3% and 60.4% respectively. In addition, for the excellent pH-response performance, LCQ could be efficiently recovered after enzymatic saccharification. [ABSTRACT FROM AUTHOR]

The conversion of lignocelluloses into fermentable sugars by enzymatic hydrolysis is a key step in biorefining. However, there are still some bottleneck problems such as low hydrolysis efficiency, high cost of cellulase and low utilization of lignin. In this work, the nonionic surfactant monomethoxy polyethylene glycol (MPEG) was grafted on enzymatic hydrolysis lignin (EHL) to obtain a pH-responsive polymer (EHL-MPEG). EHL-MPEG could achieve rapid dissolution–precipitation conversion by the ionization and protonation of carboxyl groups. By adjusting the grafting amount of MPEG, EHL-MPEG could not only enhance the enzymatic hydrolysis of lignocelluloses, but also efficiently recover cellulase after hydrolysis. Adding 3 g L−1 EHL-MPEG40 (the mass ratio of MPEG to EHL was 40%) could increase the glucose yield of corncob residue (CCR) and pretreated eucalyptus from 79.4% and 48.3% to 92.5% and 89.5%, respectively, which was comparable to the effect of the nonionic surfactant PEG4600. By simply adjusting the pH of solutions, more than 85% of cellulase proteins could be recovered by EHL-MPEG40 with almost complete recovery of β-glycosidase, exoglucanase V and xylanase. Compared with a pH-responsive lignin amphoteric surfactant (pH-LAS) obtained by grafting ionic groups on lignin, EHL-MPEG40 had a more sensitive pH response and a stronger cellulase recovery ability. In the enzymatic hydrolysis of CCR, a pH-LAS could save about 50% of cellulase, while EHL-MPEG40 could save more than 60% of cellulase. Furthermore, approximately 96% of EHL-MPEG40 could be reused. This new method can not only evade the process of immobilization, but also avoid the activity loss and component change of cellulase through immobilization. Using recyclable EHL-MPEG to improve glucose yield and recover cellulase during lignocellulosic hydrolysis is of great significance for improving the enzymatic saccharification process, reducing the cost of cellulase and realizing comprehensive utilization of lignocelluloses. [ABSTRACT FROM AUTHOR]

In order to enhance the enzymatic hydrolysis of lignocelluloses and recycle surfactants after enzymatic hydrolysis, a pH-responsive lignin amphoteric surfactant (SLQA) was prepared by the quaternization of sulfonated lignin (SL). Compared with SL, SLQA could much more effectively enhance the enzymatic hydrolysis of lignocelluloses. With an increase in the quaternization degree, enhancement of the enzymatic hydrolysis of lignocelluloses by the SLQA gradually increased. Adding 2 g L−1 SLQA-80 (mass radio of quaternizing agent to SL was 80%) could increase the enzymatic digestibility of pretreated eucalyptus and corncob residues (CCR) from 36.7% and 37.8% to 84.3% and 90.5%, respectively. The adsorption of SLQA on lignin film was larger than that of SL, and the lignin film became more hydrophilic after adsorbing SLQA. Thus, SLQA could cause more effective steric hindrance and form a hydration layer to reduce the non-productive adsorption of cellulase on lignin. The purified SLQA-80 exhibited sensitive pH-responsive property, and 90.8% of SLQA-80 could be recycled by adjusting the pH of hydrolysate after enzymatic hydrolysis. Adding recyclable SLQA could not only obviously enhance the enzymatic hydrolysis of lignocelluloses, but could also enable the comprehensive utilization of lignocelluloses. This method is of great significance to reducing the cost of cellulosic ethanol. [ABSTRACT FROM AUTHOR]

Some zwitterionic surfactants exhibit upper critical solution temperature (UCST) in aqueous solutions. For the zwitterionic surfactant solution mixed with cellulase, when its temperature is below UCST, the cellulase can be recovered by coprecipitation with zwitterionic surfactant. In this work, 3-(Hexadecyldimethylammonio) propanesulfonate (SB3-16) was selected to enhance the enzymatic hydrolysis of lignocelluloses and recover the cellulase. After adding 2 mmol/L of SB3-16, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) and by sulfite (Eu-SPORL) increased from 27.9% and 35.1% to 72.6% and 89.7%, respectively. The results showed that SB3-16 could reduce the non-productive adsorption of cellulase on hydrophobic interface, while it did not significantly inhibit the activity of cellulase. For the solution contained 1 wt% SB3-16 and 200 mg protein/L CTec2 cellulase, 55.2% of protein could be recovered by cooling. The filter paper activity of the recovered cellulase was 1.93 FPU/mg protein, which was 95.8% of its initial activity. [ABSTRACT FROM AUTHOR]

Polyvinylpyrrolidone (PVP) is an antifouling polymer to resist the adsorption of protein on solid surface. Effects of PVP on the enzymatic hydrolysis of pretreated lignocelluloses and its mechanism were studied. Adding 1 g/L of PVP8000, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) was increased from 28.9% to 73.4%, which is stronger than the classic additives, such as PEG, Tween and bovine serum albumin. Compared with PEG4600, the adsorption of PVP8000 on lignin was larger, and the adsorption layer was more stable and hydrophilic. Therefore, PVP8000 reduced 73.1% of the cellulase non-productive adsorption on lignin and enhanced the enzymatic hydrolysis of lignocelluloses greatly. [ABSTRACT FROM AUTHOR]