Substrate Enzymatic Digestibility Research Articles

Synthesis of bifunctional thermal response promoters for improved high-solids enzymatic hydrolysis of corncob residues

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 PSSP5 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 PSSP3. 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.

Achieving high enzymatic hydrolysis sugar yield of sodium hydroxide-pretreated wheat straw with a low cellulase dosage by adding sulfomethylated tannic acid

Sulfonated lignin can significantly enhance the enzymatic hydrolysis of lignocellulose substrates. Lignin is a type of polyphenol, therefore, sulfonated polyphenol, such as tannic acid, is likely to have similar effects. In order to obtain a low-cost and high-efficiency additive to improve enzymatic hydrolysis, sulfomethylated tannic acids (STAs) with different sulfonation degrees were prepared and their impact on enzymatic saccharification of sodium hydroxide-pretreated wheat straw were investigated. Tannic acid strongly inhibited, while STAs strongly promoted the substrate enzymatic digestibility. While adding 0.04 g/g-substrate STA containing 2.4 mmol/g sulfonate group, the glucose yield increased from 60.6% to 97.9% at a low cellulase dosage (5 FPU/g-glucan). The concentration of protein in enzymatic hydrolysate significantly increased with the added STAs, indicating that cellulase preferentially adsorbed with STAs, thereby reducing the amount of cellulase nonproductively anchored on substrate lignin. This result provides a reliable approach for establishing an efficient lignocellulosic enzyme hydrolysis system.

Lignin detaching from the oxidative delignified softwood during enzymatic hydrolysis and its effect on carbohydrate saccharification

Most studies about the influence of lignin on enzymatic digestibility of lignocellulose have focused on the content and properties, but less on the detaching behavior of lignin. The samples were prepared from Pinus massoniana wood chips by kraft cooking followed by delignification using oxygen/alkali (KP-O) and chlorine dioxide (KP-D), respectively. Two oxidative delignified samples with a similar lignin content were subject to enzymatic hydrolysis at both pH of 5.0 and 5.5 to investigate the effects of lignin detached rate (LDR) on substrate enzymatic digestibility (SED). The LDRs and the SEDs from both samples increased with the enzymatic hydrolysis time, and the situations of KP-D were much higher than those of KP-O under the same enzymatic hydrolysis time. The results of enzymatic hydrolysis at an elevated pH of 5.5 and the changes in concentration of free cellulase of the two samples indicated that the lignin detaching increased the free cellulase concentration, and thus promoted the enzymatic digestibility. Moreover, lignin distribution analysis by X-ray photoelectric spectroscopy and confocal laser scanning microscopy indicated surface lignin being preferentially detached. This work provided a reference for rationally designing pretreatment strategies, which can improve the efficiency of enzyme hydrolysis of lignocellulosic biomass.

Polystyrene sulfonate is effective for enhancing biomass enzymatic saccharification under green liquor pretreatment in bioenergy poplar

BackgroundWater-soluble lignin (particularly lignosulfonate, LS) has been well documented for its significance on enzymatic saccharification of lignocellulose, though the promotion mechanism has not been fully understood. Much attention has been paid to natural lignin or its derivatives. The disadvantage of using natural lignin-based polymers as promoting agents lies in the difficulty in tailor-incorporating functional groups due to their complex 3D structures. To further improve our understanding on the promotion mechanism of water-soluble lignin in the bioconversion of lignocellulose and to pursue better alternatives with different skeleton structures other than natural lignin, herein we reported a synthetic soluble linear aromatic polymer, sodium polystyrene sulfonate (PSS), to mimic LS for enhancing the efficiency of enzymatic saccharification.ResultsThe role of PSS in enzymatic saccharification of pure cellulose and green liquor-pretreated poplar (GL-P) was explored by analyzing substrate enzymatic digestibility (SED) under different addition dosages and various pH media, along with LS for comparison. At the cellulase loading of 13.3 FPU/g-glucan, the glucose yield of GL-P increased from 53% for the control to 81.5% with PSS addition of 0.1 g/g-substrate. It outperformed LS with the addition of 0.2 g/g-substrate by 6.3%. In the pH range from 4.5 to 6, PSS showed a positive effect on lignocellulose saccharification with the optimum pH at 4.8, where the most pronounced SED of GL-P was achieved. The underlying mechanism was unveiled by measuring zeta potential and using Quartz Crystal Microbalance (QCM) and Multi-parametric Surface Plasmon Resonance (MP-SPR). The results confirmed that the complexes of cellulase and PSS were conjugated and the negatively supercharged complexes reduced non-productive binding effectively along with the improved saccharification efficiency. The thickness of PSS required to block the binding sites of cellulase film was less than half of that of LS, and the PSS adlayer on cellulase film is also more hydrated and with a much lower shear modulus than LS adlayer.ConclusionsPSS as LS analogue is effective for enhancing the biomass enzymatic saccharification of GL-pretreated poplar. PSS exhibited a severer inhibition on the enzymatic saccharification of pure cellulose, while a more positive effect on bioconversion of lignocellulose (GL-P) than LS. In addition, a much lower dosage is required by PSS. The dynamic enzymatic hydrolysis indicated PSS could prolong the processive activity of cellulase. The valid data stemmed from QCM and SPR expressed that PSS bound to cellulases and the as-formed complexes reduced the non-productive adsorption of cellulase onto substrate lignin more efficiently than LS due to its flexible skeleton and highly hydrated structure. Therefore, PSS is a promising alternative promoting agent for lignocellulose saccharification. From another perspective, the synthetic lignin mimics with controllable structures enable us to reach an in-depth understanding of the promotion mechanism of soluble lignins on enzymatic saccharification.

Comparison of sulfomethylated lignin from poplar and masson pine on cellulase adsorption and the enzymatic hydrolysis of wheat straw

In this work, effects of sulfomethylated lignins (SLs) prepared from masson pine (SLM) and poplar (SLP) on enzymatic hydrolysis and cellulase-lignin interaction were comparatively investigated. The results showed that both SLM and SLP significantly promoted the substrate enzymatic digestibility. The total sugar yield increased from 38.6% to 74.4% and ∼ 100%, respectively at 10 FPU/g-cellulose of cellulase dosage. The protein content in hydrolysate linearly increased with the addition of SL (0 – 1.6 g/g-substrate lignin), which suggested the competitive adsorption of cellulase may occur to substrate lignin and SLs. Further structural analysis of lignin revealed the high S/(V + H) ratio was directly related to the high enzymatic saccharification efficiency. The strong interaction between SL and cellulase decreased the nonproductive adsorption of cellulase onto substrate lignin and increased the accessibility of cellulase to carbohydrate, which was considered to be the key factor for the improvement of substrate enzymatic digestibility.

Acid-Free Ethanol-Water Pretreatment with Low Ethanol Concentration for Robust Enzymatic Saccharification of Cellulose in Bamboo

Lignin deposition phenomenon during the liquid-hot-water (LHW) pretreatment negatively affects substrate enzymatic digestibility (SED). To overcome this limitation of LHW, acid-free ethanol-water (EW) pretreatment with low ethanol concentration was developed. With less cellulose loss and similar hemicellulose removal, adding 10% (v/v) ethanol into water (EW10 pretreatment) resulted in a lignin removal of 5.8% higher than that of LHW pretreatment conducted at the same conditions (such as 200 °C for 40 min). Although the lignin removal did not increase significantly, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) characterizations indicated that LHW pretreatment-induced lignin condensation was alleviated by EW10 pretreatment, leading less lignin condensates deposited on the corresponding surface of solid substrate. Moreover, compared with lignin separated from LHW-pretreated substrate, the non-productive adsorption between EW10 pretreatment-induced lignin and cellulase was significantly weakened. As a result, the SED of EW10 pretreatment was improved to 91.7%, which was higher than LHW pretreatment by 19.5%. Due to the advantages of suppressing the deposition of lignin condensates and employing ethanol at low concentration, EW10 pretreatment shows practical significance for producing fermentable sugar from abundant non-woody biomass (bamboo) in China.

Improving enzymatic hydrolysis of lignocellulosic substrates with pre-hydrolysates by adding cetyltrimethylammonium bromide to neutralize lignosulfonate

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.

Pretreatment of Miscanthus by NaOH/Urea Solution at Room Temperature for Enhancing Enzymatic Hydrolysis

A novel pretreatment process using NaOH/Urea solution at room temperature was developed to overcome recalcitrance of lignocellulose for efficient bioconversion of miscanthus. The process consists of mechanical size reduction, pretreatment with NaOH/Urea solution, and filtration. The results indicated that the substrate enzymatic digestibility (SED) of miscanthus pretreated with 8 wt% NaOH and 12 wt% urea at 21 oC for 30 min was up to 71.99 % at low enzyme loading of 5 filter paper units (FPU)/g glucan after 72 h hydrolysis. NaOH/Urea pretreatment efficiently removed lignin and hemicellulose. And their removal rates increased with the increase of pretreatment temperature, NaOH dosage and urea dosage. With the increase of NaOH dosage, the chemical composition removal rate decreased in the following order: lignin, xylan, araban, galactan. Meanwhile, NaOH/Urea pretreatment could open up the fiber structure, decrease cellulose crystallinity index, and prevent lignin droplets depositing on cellulose. The optimal condition for the NaOH/Urea pretreatment regarding this study was 6 wt% NaOH/12 wt% urea and 21 °C. Approximately 70 % glucose yield was achieved upon this condition.

Comparison of the substrate enzymatic digestibility and lignin structure of wheat straw stems and leaves pretreated by green liquor

In this work, the substrate enzymatic digestibility (SED) and the lignin structure of green liquor (GL) pretreated wheat straw stems and leaves were investigated. Compared with wheat straw stems, leaves showed higher delignification selectivity in GL pretreatment and higher SED in enzymatic hydrolysis. Wet chemical analysis indicated that, characterized with lower content of syringyl units and less β-O-4 linkages, leaf lignin is structurally different from stem lignin. After GL pretreatment, the drops of both nitrobenzene oxidation and ozonation products yield of leaves were obviously higher than those of stems, which means that more β-O-4 linkages of leaf lignin were broken than that of stem lignin. The SED of total sugar in GL-pretreated leaves was about 50% higher than that in GL-pretreated stems. The less content and lower S/G ratio of lignin are suggested to be the important factors for the better SED of GL-pretreated leaves.

Effect of depth beating on the fiber properties and enzymatic saccharification efficiency of softwood kraft pulp

Commercial bleached softwood kraft pulp was mechanically fibrillated by a PFI-mill with beating revolution from 5000 to 30,000r. The extent of fibrillating on the pulp was evaluated by beating degree, fiber morphological properties (fiber length, width, coarseness and curls index), water retention value (WRV) and physical properties of paper made from the pulp. Depth beating process significantly affected the pulp fibrillations as showed by the decreased fiber length and width as well as the SEM analysis, but the effects were limited after beating revolution of 15,000. Depth beating process also improved the total internal pore and inter-fibril surface areas as shown by the increased WRV values. Substrate enzymatic digestibility (SED) of beaten pulp at 5000 revolutions could reach 95% at cellulase loading of 15FPU/g of glucan. After the enzymatic hydrolysis, the size of the pulp residues was reduced to micro-scale, and a relative uniform size distribution of the residues appeared at 10,000r beating revolution.

Using low temperature to balance enzymatic saccharification and furan formation during SPORL pretreatment of Douglas-fir

Comparing analytical results for Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) of Douglas-fir (Pseudotsuga menziesii) at two different temperatures shows that the apparent activation energy of sugar degradation is higher than that of hemicellulose hydrolysis, approximately 161kJ/mole versus 100kJ/mole. Thus, one can balance the production of degradation products against hemicellulose hydrolysis and therefore the enzymatic saccharification efficiency of the resultant substrate by changing pretreatment temperature and duration. Specifically, pretreatment at 165°C for 75min significantly reduced furan formation compared with the pretreatment at 180°C for 30min while maintaining the same pretreatment severity and therefore the same substrate enzymatic digestibility (SED). Obtaining high SED with Douglas-fir is also limited by lignin content. Fortunately, the bisulfite in SPORL provides delignification activity. By combining kinetic models for hemicelluloses hydrolysis, sugar degradation, and delignification, the performance of pretreatment can be optimized with respect to temperature, duration, acid, and bisulfite loading. The kinetic approach taken in this study is effective to design viable low temperature pretreatment processes for effective bioconversion of lignocelluloses.

Robust enzymatic saccharification of a Douglas-fir forest harvest residue by SPORL

Forest harvest residues can be a cost-effective feedstock for a biorefinery, but the high lignin content of forest residues is a major barrier for enzymatic sugar production. Sulfite pretreatment to overcome strong recalcitrance of lignocelluloses (SPORL) was applied to a Douglas-fir (Pseudotsuga menziesii (Mirb) Franco var. menziesii) forest residue in a range of sulfite and acid loadings at 165 °C for 75 min with liquid to wood ratio of 3:1. Sodium bisulfite and sulfuric acid charge as mass fraction of oven dry biomass of 12% and 2.21%, respectively, was optimal in terms of enzymatic cellulose saccharification, sugar yield and formation of hydroxymethylfurfural (HMF) and furfural. Enzymatic glucose yield was 345 g kg−1, or equivalent to 82.3% of theoretical at a cellulase (CTec2) dosage of 15 filter paper unit (FPU) per gram of glucan. HMF and furfural formation were low at approximately 2.5 g L−1 each in the pretreatment hydrolyzate. Delignification was important to achieve good cellulose saccharification efficiency, however, approximately 80–90% hemicellulose removal is also required. Substrate enzymatic digestibility (SED) was found to correlate to a combined parameter Z(CHF) of delignification and hemicellulose dissolution well, suggesting that the combined hydrolysis factor (CHF) – a pretreatment severity measure – can be used to predict saccharification of forest residue for scale-up studies to reduce numbers of experiments.

Effects of Lignin Removal on Substrate Enzymatic Hydrolysis of SPORL-high-pH Pretreated Bagasse

The performance of a process called sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL), which was carried out at high pH, was preliminarily investigated as a means of improving bagasse substrate enzymatic digestibility (SED). The lignin removal significantly affected the SED resulting from the SPORL-high-pH treatment. Lignin removal was found to be well-correlated with SED when the Boltzmann function was used to fit the curve. In this fitting curve, SED increased slowly initially and then rose up quickly with lignin removal (from 0% to 10%, and then from 10% to 35%) and finally reached an asymptotic value (80%, based on o.d. glucan in the pretreated substrate). Removing lignin to about 35% to 40% would be sufficient to significantly improve the SED of bagasse to the asymptotic value (80%) during enzymatic hydrolysis, while low cellulase and beta-glucosidase (15 FPU/g and 22.5 CUB/g o.d. cellulose in the substrate, respectively) were loaded. Furthermore, combining this Boltzmann function and the SPORL-high-pH delignification model would be useful for predicting neutral-sulfite pretreated SED.

Recycled aqueous ammonia expansion (RAAE) pretreatment to improve enzymatic digestibility of corn stalks

A novel lignocellulose pretreatment method using aqueous ammonia for biofuel production was proposed in this study, which named recycled aqueous ammonia expansion (RAAE). Effects of temperature, pretreatment time, water to dry corn stalks loading and flow rate of aqueous ammonia on substrate enzymatic digestibility and sugar yield were investigated. Pretreatment temperature and time are important factors that affect RAAE process. Recirculation process could improve biomass digestibility and sugar yield compared with batch experiment. After RAAE pretreatment, about 70% of the lignin was removed, while more than 90% of the cellulose was preserved in the solids, the substrate crystallinity also increased because of the removal of amorphous portion. The maximum glucan enzymatic digestibility of pretreated biomass was 85.70%, which was obtained at 85°C, 11 min, 80% water to dry corn stalks loading and 1.5L/min aqueous ammonia flow rate.

Enhanced Cellulase Hydrolysis of Eucalyptus Waste Fibers from Pulp Mill by Tween80-Assisted Ferric Chloride Pretreatment

Pretreatment combining FeCl3 and Tween80 was performed for cellulose-to-ethanol conversion of eucalyptus alkaline peroxide mechanical pulping waste fibers (EAWFs). The FeCl3 pretreatment alone showed a good effect on the enzymatic hydrolysis of EAWFs, but inhibited enzyme activity to some extent. A surfactant, Tween80, added during FeCl3 pretreatment was shown to significantly enhance enzyme reaction by eluting enzymatic inhibitors such as iron(III) that are present at the surface of the pretreated biomass. Treatment temperature, liquid-solid ratio, treatment time, FeCl3 concentration, and Tween80 dosage for pretreatment were optimized as follows: 180 °C, 8:1, 30 min, 0.15 mol/L, and 1% (w/v). Pretreated EAWFs under such optimal conditions provided enzymatic glucose (based on 100 g of oven-dried feedstock) and substrate enzymatic digestibility of EAWFs of 34.8 g and 91.3% after 72 h of enzymatic hydrolysis, respectively, with an initial cellulase loading of 20 FPU/g substrate.

Quantitative predictions of bioconversion of aspen by dilute acid and SPORL pretreatments using a unified combined hydrolysis factor (CHF)

A combined hydrolysis factor (CHF) was developed to predict xylan hydrolysis during pretreatments of native aspen (Populus tremuloides) wood chips. A natural extension of previously developed kinetic models allowed us to account for the effect of catalysts by dilute acid and two sulfite pretreatments at different pH values. When xylan is modeled as two fractions with different hydrolysis rates, previously identified as fast and slow xylan, the model closely matches the experimental data. Extent of xylan hydrolysis is strongly correlated with pretreatment solids yield, energy consumption for size reduction, and substrate enzymatic digestibility (SED). Composition of the pretreatment hydrolysate was less correlated with extent of hydrolysis due to carbohydrate decomposition reactions. Substrate cellulose enzymatic conversion and enzymatic hydrolysis glucose yield can be predicted to approximately 10% accuracy using CHF alone.

Ethanol production from poplar wood through enzymatic saccharification and fermentation by dilute acid and SPORL pretreatments

Dilute acid (DA) and Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL) pretreatments were directly applied to wood chips of four poplar wood samples of different genotypes (hereafter referred to as poplars; Populus tremuloides Michx. ‘native aspen collection’; Populus deltoides Bartr. ex Marsh×Populus nigra L. ‘NE222’ and ‘DN5’; P. nigra×Populus maximowiczii A. Henry ‘NM6’) to evaluate their bioconversion potential. Plant biomass recalcitrance (PBR) was defined to quantitatively determine the recalcitrance of the poplars. Using DA pretreatment, NM6 produced the lowest bioconversion efficiency with a total monomeric sugar yield of 18% theoretical and an ethanol yield of 0.07Lkg−1 of wood compared with an aspen sugar yield of 47% theoretical and an ethanol yield of 0.17Lkg−1 of wood. Similar comparisons following SPORL pretreatment were 43% versus 55% and 0.11 versus 0.20Lkg−1 of wood for NM6 and aspen, respectively. Bioconversion performance of NE222 and DN5 fell between that of aspen and NM6. While substrate lignin content and lignin removal by pretreatments did not affect substrate enzymatic digestibility, the wood lignin content was found to negatively affect xylan or hemicellulose removal using both DA and SPORL pretreatments. The ability of lignin protecting hemicellulose removal dictates PBR through affecting disk milling energy for size reduction of pretreated wood chips, substrate enzymatic digestibility. The SPORL pretreatment not only improved sugar and ethanol yields over DA for all four poplars, but also better dealt with the differences among them, suggesting better tolerance to feedstock variability.

Effects of wet-pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses

This article reports the effect of wet- pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses. A wet cellulosic substrate of bleached kraft eucalyptus pulp and two wet sulfite-pretreated lignocellulosic substrates of aspen and lodgepole pine were pressed to various moisture (solids) contents by variation of pressing pressure and pressing duration. Wet pressing reduced substrate moisture content and produced irreversible reduction in fiber pore volume—fiber hornification— as reflected in reduced water retention values (WRVs), an easily measurable parameter, of the pressed substrates. Wet pressing resulted in a reduction in substrate enzymatic digestibility (SED) by approximately 20% for the two sulfite-pretreated substrates when moisture content was reduced from approximately 75% to 35%. The reduction in SED for the cellulosic substrate was less than 10% when its moisture content was reduced from approximately 65% to 35%. The results indicated that reduction in SED is negligible when samples were pressed to solids content of 40% but observable when pressed to solids content of 50%. It was also found that WRV can correlate to SED of hornified substrates resulting from the same never-dried or pressed sample independent of the hornification process (e.g., pressing or drying). This correlation can be fitted using a Boltzmann function. Cellulase adsorption measurements indi- cated that wet-pressing-induced fiber hornification reduced cellulose accessibility to cellulase. The results obtained in this study provide guidelines to high-solids enzymatic saccharification of pretreated biomass.

Evaluation of Mountain Beetle-Infested Lodgepole Pine for Cellulosic Ethanol Production by Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose

The potentials of deteriorated mountain pine beetle (Dendroctonus ponderosae)-killed lodgepole pine (Pinus contorta) trees for cellulosic ethanol production were evaluated using the sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) process. The trees were harvested from two sites in the United States Arapaho-Roosevelt National Forest, Colorado. The infestation age of the trees varied from zero to about 8 years. Mild (170 °C) and harsh (180 °C) SPORL pretreatments were conducted. The chemical charges were sulfuric acid of 2.21% and sodium bisulfite of 8% on oven dry wood for the harsh and half of those for the mild pretreatment. The results suggest that beetle-caused mortality enriched glucan content by as much as 3 percentage points (or 7.5%) in wood. The glucan enrichment seems to increase with infestation age. The enriched glucan can be captured after SPORL pretreatment followed by enzymatic hydrolysis. The killed trees are more susceptible to SPORL pretreatment, which enhanced substrate enzymatic digestibility (SED). Enzymatic hydrolysis glucose yields (EHGY) from killed trees were about 5-20% higher than those from their corresponding live trees. Total fermentable sugar productions from dead trees (including a tree laying on the ground) were 4-14% higher than corresponding production from live trees, depending on pretreatment conditions and infestation age. An ethanol yield of 267 L/metric ton of wood or 69% theoretical value was achieved from a tree infested 4 years, 7% higher than the 250 L/metric ton of wood from the corresponding live tree. The results also demonstrated the robustness of SPORL pretreatment for lodgepole pine.

Effects of Lignin−Metal Complexation on Enzymatic Hydrolysis of Cellulose

This study investigated the inhibition of enzymatic hydrolysis by unbound lignin (soluble and insoluble) with or without the addition of metal compounds. Sulfonated, Organosolv, and Kraft lignin were added in aqueous enzyme-cellulose systems at different concentrations before hydrolysis. The measured substrate enzymatic digestibility (SED) of cellulose was decreased by 15% when SL was added to a concentration of 0.1 g/L due to nonproductive adsorption of enzymes onto lignin. Cu(II) and Fe(III) were found to inhibit enzymatic cellulose hydrolysis in the presence of lignin. Ca(II) and Mg(II) were found to reduce or eliminate nonproductive enzyme adsorption by the formation of lignin-metal complex. The addition of Ca(II) or Mg(II) to a concentration of 10 mM can almost completely eliminate the reduction in SED caused by the nonproductive enzyme adsorption onto the lignins studied (SL, OL, or KL at concentration of 0.1 g/L). Ca(II) was also found to reduce the inhibitive effect of bound lignin in pretreated wood substrate, suggesting that Ca(II) can also form complex with bound lignin on pretreated solid lignocelluloses. Significant improvement in SED of about over 27% of a eucalyptus substrate produced by sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) was achieved with the application of Ca(II).