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In order to reduce the enzyme cost of lignocellulosic enzymatic hydrolysis, upper critical solution temperature (UCST) additives are used to recover and reuse cellulase by regulating the temperature. A sulfobetaine polymer, PSPE, showed a sensitive UCST response in buffer, and its UCST-performance was optimised by adjusting the molecular weight of the polymer. PSPE-3 (Mw = 355.1 kDa) was added to the cellulase buffer at 50 °C, and PSPE-3 and cellulase were co-precipitated by cooling to the room temperature of 25 °C. PSPE-3 and cellulase co-precipitated mainly through hydrophobic interactions via cooling. Compared with octadecyl sulfobetaine (SB3–18), PSPE-3 had a more sensitive UCST response and stronger cellulase recovery ability. Adding only 40% PSPE-3 (accounting for the mass fraction of cellulase) can save more than 50% cellulase in the enzymatic hydrolysis system of eucalyptus chips pre-treated with dilute acid (Eu-DA). However, for the Eu-DA system, adding 100% SB3–18 can only save about 30% of cellulase. In this work, efficient recycling of cellulase was achieved at room temperature by adding UCST-type PSPE. The process is green without consuming acid and alkali, and this work provides a new idea for reducing the production cost of cellulosic ethanol. [ABSTRACT FROM AUTHOR]

This study evaluated maleic acid (MA) as a green hydrotrope for efficient wood fractionation at atmospheric pressure and ≤100 °C. MA hydrotropic fractionation (MAHF) resulted in esterified lignin with a low degree of condensation and a very light color. 2D 1H–13C HSQC and HMBC NMR analyses of reaction products of a lignin model compound guaiacylglycerol-beta-guaiacyl ether with MA identified bonding through the γ-OH group. The surface charge of lignocellulosic MAHF water insoluble solids (WIS), induced by lignin esterification (carboxylation), enhanced enzymatic sugar yield by reducing nonproductive cellulase binding to lignin through pH-mediated electrostatic repulsion and also enhanced the lubrication effect of lignin in mechanical nanofibrillation for producing cellulose nanofibrils from WIS. Preliminary studies indicated that disssolved xylan can be dehydrated into furfural by MA in the fractionated liquor at a good yield of 70% and MA can be reused for repeated fractionation with minimal loss of less than 5%. [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]

The effects of long-chain fatty alcohols (LFAs) on the enzymatic hydrolysis of crystalline cellulose by two commercial Trichoderma reesei cellulase cocktails (CTec2 and Celluclast 1.5L) were studied. It was found that n-butanol inhibited the enzymatic hydrolysis, but n-octanol, n-decanol and n-dodecanol had strong enhancement on enzymatic hydrolysis of crystalline cellulose in the buffer pH range from 4.0 to 6.0. LFAs can increase the hydrolysis efficiency of crystalline cellulose from 37 to 57 % at Celluclast 1.5L loading of ten filter paper units (FPU)/g glucan. LFAs have similar enhancement on the enzymatic hydrolysis of crystalline cellulose mixed with lignin or xylan. The enhancement of LFAs increased with the decrease of the crystallinity index. LFAs not only enhanced the high-solid enzymatic hydrolysis of lignocellulose, but also improved the rheological properties of high-solid lignocellulosic slurries by decreasing the yield stress and complex viscosity. Meanwhile, LFAs can improve the enzymatic hydrolysis of cellobiose to glucose, especially at low cellulase loading. [ABSTRACT FROM AUTHOR]

Highlights: [•] SL clearly reduced the non-productive adsorption of cellulase on lignin. [•] SL with higher MW had stronger blocking effect on cellulase adsorption on lignin. [•] Linear anionic aromatic polymers strongly blocked cellulase adsorption on lignin. [•] Copolymer of lignin and PEG had stronger enhancement than PEG. [Copyright &y& Elsevier]

Thisstudy conducted an investigation of the effect of lignosulfonate(LS) on enzymatic saccharification of lignocelluloses. Two commercialLSs and one laboratory sulfonated kraft lignin were applied to Whatmanpaper, dilute acid and SPORL (sulfite pretreatment to overcome recalcitranceof lignocelluloses) pretreated aspen, and kraft alkaline and SPORLpretreated lodgepole pine. All three lignin samples inhibited cellulosesaccharification of Whatman paper, but enhanced the saccharificationof the four lignocellulosic substrates. The level of enhancement wasrelated to the molecular weight and degree of sulfonation of the ligninas well as the substrate lignin structure. When different molecularweight (MW) fractions of one commercial LS (SXP), generated from sulfitepulping of hardwood, were applied to the Whatman paper, the largeMW fraction (SXP1) with the lowest degree of sulfonation inhibitedcellulose saccharification while the intermediate (SXP2) and smallest(SXP3) MW fractions enhanced saccharification. All MW fractions enhancedsaccharification of the four lignocellulosic substrates with maximalenhancement by the smallest MW fraction, SXP3. The enhancement wasmost significant for the kraft lodgepole pine substrate and leastsignificant for the SPORL pretreated lodgepole pine using all threeLS and SXP fractions. The results suggest that LS acts as a surfactantto enhance pure cellullose saccharification. When LS is applied tolignocelluloses, it acts as a surfactant to block bound lignin frombinding cellulase nonproductively leading to enhanced saccharification. [ABSTRACT FROM AUTHOR]

This study revealed that cellulose enzymatic saccharification response curves of lignocellulosic substrates were very different from those of pure cellulosic substrates in terms of optimal pH and pH operating window. The maximal enzymatic cellulose saccharification of lignocellulosic substrates occurs at substrate suspension pH 5. 2- 6. 2, not between pH 4. 8 and 5. 0 as exclusively used in literature using T. reesi cellulase. Two commercial cellulase enzyme cocktails, Celluclast 1.5L and CTec2 both from Novozymes, were evaluated over a wide range of pH. The optimal ranges of measured suspension pH of 5.2-5.7 for Celluclast 1.5L and 5.5-6.2 for CTec2 were obtained using six lignocellulosic substrates produced by dilute acid, alkaline, and two sulfite pretreatments to overcome recalcitrance of lignocelluloses (SPORL) pretreatments using both a softwood and a hardwood. Furthermore, cellulose saccharification efficiency of a SPORL-pretreated lodgepole pine substrate showed a very steep increase between pH 4.7 and 5.2. Saccharification efficiency can be increased by 80 % at cellulase loading of 11.3 FPU/g glucan, i.e., from approximately 43 to 78 % simply by increasing the substrate suspension pH from 4.7 to 5.2 (buffer solution pH from 4.8 to 5.5) using Celluclast 1.5L, or by 70 % from approximately 51 to 87 % when substrate suspension pH is increased from 4.9 to 6.2 (buffer solution pH from 5.0 to 6.5) using CTec2. The enzymatic cellulose saccharification response to pH is correlated to the degree of substrate lignin sulfonation. The difference in pH-induced lignin surface charge, and therefore surface hydrophilicity and lignin-cellulase electrostatic interactions, among different substrates with different lignin content and structure is responsible for the reported different enhancements in lignocellulose saccharification at elevated pH. [ABSTRACT FROM AUTHOR]

[Display omitted] • PSSP with UCST response was recyclable. • PSSP could enhance high-solids enzymatic hydrolysis of lignocellulose. • Cellulase was efficiently recovered by co-precipitating with PSSP. • For CCR system, 50% of cellulase amounts was saved with adding PSSP 3. The enzymatic hydrolysis cost of lignocellulose can be reduced by improving enzymatic hydrolysis and recycling cellulase by adding additives. A series of copolymers P(SSS-co-SPE) (PSSPs) were synthesized using sodium p-styrene sulfonate (SSS) and sulfobetaine (SPE) as monomers. PSSP exhibited upper critical solution temperature response. PSSP with high molar ratio of SSS displayed more significant improved hydrolysis performance. When 10.0 g/L PSSP 5 was added to the hydrolysis system of corncob residues, and substrate enzymatic digestibility at 72 h (SED@72 h) increased by 1.4 times. PSSP with high molecular weight and moderate molar ratio of SSS, had significant temperature response, enhanced hydrolysis, and recovering cellulase properties. For high-solids hydrolysis of corncob residues, SED@48 h increased by 1.2 times with adding 4.0 g/L of PSSP 3. Meanwhile, 50% of cellulase amount was saved at the room temperature. This work provides a new idea for reducing the hydrolysis cost of lignocellulose-based sugar platform technology. [ABSTRACT FROM AUTHOR]

[Display omitted] Cellulase was recycled by using pH-UCST-type LSB, and the process is sustainable while realizing the value-added utilization of industrial lignin. • LSB showed a pH-UCST-sensitive response and was recyclable. • Cellulase was efficiently recycled at higher pH by using LSB. • The value-added utilization of enzymatic hydrolysis lignin was realized. Recycling cellulase can reduce the cost of lignocellulosic enzymatic hydrolysis. Here, a lignin-grafted sulfobetaine (LSB) was first synthesized by grafting sulfobetaine (SB) on enzymatic hydrolysis lignin (EHL). LSB had a sensitive response of pH and temperature. LSB dissolved under the conditions of lignocellulosic enzymatic hydrolysis (pH 5.0, 50 °C). After hydrolysis, LSB co-precipitated with cellulase when lowering pH of the hydrolysate to 4.0 and cooling to 25 °C. When 3.0 g/L LSB-100 was added to the hydrolysis system of corncob residue (CCR), 70 % of amount of cellulase was saved. LSB had a remarkable response and stronger cellulase recovery capacity. This was attributed that carboxylate radical in LSB was protonated, and positive and negative ions of SB associated to form salt at 25 °C. This work provides a new idea for reducing the cost for preparing fermentable sugars from lignocellulose, and increasing the added value of EHL. [ABSTRACT FROM AUTHOR]

Effect of the molecular structure of lignosulfonate-based polyoxyethylene ether (LS-PEG) on the enzymatic hydrolysis of Avicel and corn stover was investigated. With the increase of PEG contents and M w of LS-PEG, glucose yield of corn stover increased from 16.7% to 51.9%. When LS-PEG was compounded with cationic surfactant cetyltrimethylammonium bromide (CTAB), the enhancement of glucose yield of corn stover was further increased from 45.3% to 62.8%. Sulfonic group of LS-PEG preferentially interacted with quaternary ammonium group of CTAB by the electrostatic attraction to form a similar non-ionic surfactant CTAB-LS-PEG. CTAB-LS-PEG showed electrically neutral and more hydrophobic, and blocked more nonproductive adsorption of cellulase on the lignin. Therefore, CTAB-LS-PEG enhanced enzymatic hydrolysis efficiency of lignocelluloses more significantly. The understanding developed in this study can help to develop potential approaches and strategies for effective application of lignosulfonate to improve bioconversion of lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

• 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]

Graphical abstract Highlights • Interaction of lignin amphiphilic polymers and cellulase was studied by QCM-D. • Lignosulfonate combined with cellulase by electrostatic attractive interaction. • EHL-PEG-Cellulase hydrolysis cellulose film through hollow way. • Strategy to enhance hydrolysis by lignin amphiphilic polymers was proposed. Abstract The origin, amount, hydrophilicity, charge, molecular weight and its distribution of lignin have significant influences on the enzymatic hydrolysis of lignocellulose. The enzymatic hydrolysis of lignocellulose was essentially enhanced by lignin-based polyoxyethylene ether (EHL-PEG), whereafter followed by PEG4600 and lignosulfonate (LS). The effect of LS, EHL-PEG and PEG4600 on the adsorption and enzymatic hydrolysis kinetics of cellulase on the gold surface and cellulose film was investigated by Quartz Crystal Microbalance with dissipation monitoring (QCM-D). Results showed that the interaction of LS or EHL-PEG with cellulase was electrostatic attractive and hydrophobic effect, respectively, and formed hydrophilic cellulase aggregates. LS-Cellulase peeled off the cellulose film layer by layer, while the hydrophobic phenylpropane structure of EHL-PEG-Cellulase acted as a cellulose binding domain to hydrolysis cellulose through "Hollow" effect and made cellulose become more loose and swollen. At last, a strategy to enhance the enzymatic hydrolysis of lignocellulose by lignin-based amphiphilic polymers was proposed as well. [ABSTRACT FROM AUTHOR]

Hydrolyzing lignocellulose, the most abundant biomass raw material in nature, into monosaccharides by enzymes and then transforming the sugars into chemicals and fuels by biological or chemical methods is one of the most important parts of biorefining. In lignocellulosic biomass, cellulose is often tightly wrapped by lignin along with hemicelluloses. Although some pretreatments can partially remove lignin, residual lignin in pretreated substrates still physically blocks the accessibility of cellulose, non-productively adsorbs cellulases, and sterically hinders the enzymatic hydrolysis of cellulose. So, lignin is generally considered to be an inhibitor to the enzymatic hydrolysis of lignocellulosic substrates. However, new research shows that under the right conditions, lignin does not inhibit the enzymatic hydrolysis of lignocellulose, and can even increase the final sugar yield. For example, recently, some novel lignin-target pretreatments have been developed, they can reduce or overcome the inhibitory effect of lignin. And researchers also find that lignin can be functionalized and used as an activator/promoter of enzymatic hydrolysis of lignocellulose, their effectiveness is comparable to common high-efficiency surfactants. What's more, different lignin-based carriers were also synthesized to carry and recycle cellulases during the hydrolysis, they can obviously reduce the load and cost of cellulases. These works indicate that lignin can play a positive role in the enzymatic hydrolysis of lignocellulose. In order for readers to dialectically view lignin and understand its multiplicity, this review is to report the progress in the studies of how researchers tame the "lignin dog" to facilitate enzymatic hydrolysis of lignocellulose. • Concept of taming "lignin dog" to facilitate enzymatic hydrolysis is proposed. • Pretreatments are classified based on structure changes for in-depth understanding. • Effects of lignin-based additives on enzymatic hydrolysis are systematically introduced. • Lignin-based carriers for cellulase recovery were summarized for the first time. • Lignin-related challenges in enzymatic hydrolysis are prospected with reliable analysis. [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]

Two pretreatment methods to overcome recalcitrance of lignocelluloses, sulfite pretreatment (SPORL) and dilute acid (DA), were conducted to pretreat softwood masson pine and hardwood eucalyptus for enzymatic hydrolysis. In the presence of corresponding pre-hydrolysates, adding moderate cetyltrimethylammonium bromide (CTAB) could enhance the enzymatic hydrolysis of the SPORL-pretreated substrates, but had no enhancement for the DA-pretreated substrates. The results showed that sodium lignosulfonate (SL) in pre-hydrolysates and CTAB together had a strong enhancement on the enzymatic hydrolysis of lignocelluloses. The compound of commercial lignosulfonate SXSL and CTAB (SXSL-CTAB) could enhance the substrate enzymatic digestibility (SED) of SPORL-pretreated masson pine from 27.1% to 71.0%, and that of DA-pretreated eucalyptus from 37.6% to 67.9%. The mechanism that CTAB increased the adsorption of SL on lignin to form more effective steric hindrance and reduced the non-productive adsorption of cellulase on lignin by neutralizing the negative charge of SL was proposed. [ABSTRACT FROM AUTHOR]

Water-soluble lignin-based polyoxyethylene ether (EHL–PEG), prepared from enzymatic hydrolysis lignin (EHL) and polyethylene glycol (PEG1000), was used to improve enzymatic hydrolysis efficiency of corn stover. The glucose yield of corn stover at 72 h was increased from 16.7% to 70.1% by EHL–PEG, while increase in yield with PEG4600 alone was 52.3%. With the increase of lignin content, EHL–PEG improved enzymatic hydrolysis of microcrystalline cellulose more obvious than PEG4600. EHL–PEG could reduce at least 88% of the adsorption of cellulase on the lignin film measured by quartz crystal microbalance with dissipation monitoring (QCM-D), while reduction with PEG4600 was 43%. Cellulase aggregated at 1220 nm in acetate buffer analyzed by dynamic light scattering. EHL–PEG dispersed cellulase aggregates and formed smaller aggregates with cellulase, thereby, reduced significantly nonproductive adsorption of cellulase on lignin and enhanced enzymatic hydrolysis of lignocelluloses. [ABSTRACT FROM AUTHOR]

• Highly recyclable SC was used in lignocellulosic enzymatic hydrolysis. • Using SC to enhance cellulase recovery through ingenious pH regulation. • SC increased the sugar yield of Eu-DA by 95.5% and save at least 40% cellulase. Most additives that capable of enhancing enzymatic hydrolysis of lignocellulose are petroleum-based, which are not easy to recycle with poor biodegradability. In this work, highly recyclable and biodegradable sodium caseinate (SC) was used to enhance lignocellulosic hydrolysis with improved cellulase recyclability. When the pH decreased from 5.5 to 4.8, more than 96% SC could be precipitated from the solution and recovered. Adding SC increased enzymatic digestibility of dilute acid pretreated eucalyptus (Eu-DA) from 39.5% to 78.2% under Eu-DA loading of 10 wt% and pH = 5.5, and increase cellulase content in 72 h hydrolysate from only 15.2% of the original to 60.0%, which facilitated the recovery of cellulases through re-adsorption by fresh substrates. With multiple cycles of re-adsorption, application of SC not only increased the sugar yield of Eu-DA by 95.5%, but also reduced cellulase loading by 40%. [ABSTRACT FROM AUTHOR]