Glucan Conversion Research Articles

Investigation of Cyrene organosolv fractionation of softwood biomass and alkaline post-incubation

Cyrene organosolv fractionation effectively extracted 78 % of lignin from recalcitrant softwood biomass pine at a mild temperature of 120 °C. However, the enzymatic conversion of the fractionated cellulose-rich solid did not improve significantly. Alkali post-incubation of the fractionated cellulose fraction notably enhanced the glucan conversion. This phenomenon has also been observed in other organosolv processes, but how this approach transforms pretreated biomass has not yet been comprehensively investigated. In this study, small-angle X-ray scattering (SAXS) was employed to understand the structural changes in biomass during fractionation and post-incubation at the nanometer scale. No lignin aggregation was found on the microfibrils, whereas the distance between the microfibrils increased after pretreatment and decreased after alkaline post-incubation. These results suggests that the Cyrene molecules remained between the microfibrils and were removed by post-incubation. In addition, the pine lignin recovered after pretreatment was characterized by NMR to understand the impact of Cyrene pretreatment on the lignin structure.

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Modeling and design of fed-batch strategies for achieving 255 g/L sugar concentration from high-solid enzymatic hydrolysis of pretreated corn stover

Achieving high sugar concentrations through enzymatic hydrolysis of pretreated lignocellulose with low enzyme loadings is crucial for reducing the costs of lignocellulosic biorefineries. However, the adverse effects of the “solid effect” pose essential challenges in this regard. In this study, the objective is to improve the sugar concentrations through enzymatic hydrolysis of Densifying Lignocellulose with Ca(OH)2 or H2SO4 followed by Autoclave pretreated corn stover (DLCA(ch)-CS or DLCA (sa)-CS) at 40 % w/w solid loading through kinetic analysis and a statistically designed fed-batch feeding strategy. Initially, the hydrolysis kinetics of different pretreated biomass were analyzed using fractal kinetic modeling, aiming to elucidate the reasons for the observed differences in hydrolysis. Furthermore, leveraging the kinetic differences, the optimal initial solid loading was determined, and statistical models were employed to optimize feeding modes for enzymatic hydrolysis. The result revealed that compared with H2SO4, Ca(OH)2 serves as an better catalyst for improving the hydrolysability of biomass, enhancing cellulose accessibility to cellulases and reduce the mass transfer rate during enzymatic hydrolysis. Interestingly, the optimal feeding mode for less digestible substrate (DLCA(sa)-CS) is different from the more digestible substrate (DLCA(ch)-CS). Notably, by using the optimized fed-batch feeding mode, the sugar concentration can reach a maximum of 255 g/L, with glucan conversion of 89.8 %, at low enzyme loading (10 mg protein/g glucan). This is the highest total sugar concentration achieved through 72 h enzymatic hydrolysis with low enzyme loadings using a fed-batch strategy. This approach proves highly effective in designing fed-batch strategies for pretreated biomass and has great potential to serve as a universal tool for designing suitable feeding schemes for various bionconversion process.

Catalytic action of hydronium-ion in rice straw pretreatment and enhancement of enzymatic hydrolysis and ethanol production

The present investigation will focus on the catalytic effect of hydronium ion during liquid-water/ dilute sulfuric acid/ferric chloride pretreatment (LWP/ SAP/ FCP) on the hydrolysate and pretreated rice straw. The overall pretreatment process has been represented as a sequential catalytic reactions. The temperature range of pretreatment is varied in the range of 140–180 °C and the concentration of dilute sulfuric acid and ferric chloride is 0.1 M. The first order rate constants of xylan and glucan degradation have been determined for LWP/ SAP/ FCP. The maximum xylan and glucan conversion of 96.8% w/wand 31.4%w/w respectively are achieved for FCP at 180 °C. Xylose, glucose, furfural, 5-hydroxymethyl furfural, acetic acid and formic acid appear as the main products for all pretreatments. Only in case of FCP levulinic acid also appears as a hydrolysis product. The thermal characteristics, functional groups, crystallinity, surface morphology of untreated and pretreated rice straw have been evaluated. Among all pretreatment processes under study, the highest values of glucose yield of 78.96% (w/w) using enzymatic hydrolysis and 83.79% of theoretical yield of ethanol using Saccharomyces cerevisiae have been achieved for ferric chloride pretreatment.

Comparison of simultaneous saccharification and fermentation with LPMO-supported hybrid hydrolysis and fermentation.

Enzymatic saccharification is used to convert polysaccharides in lignocellulosic biomass to sugars which are then converted to ethanol or other bio-based fermentation products. The efficacy of commercial cellulase preparations can potentially increase if lytic polysaccharide monooxygenase (LPMO) is included. However, as LPMO requires both a reductant and an oxidant, such as molecular oxygen, a reevaluation of process configurations and conditions is warranted. Saccharification and fermentation of pretreated softwood was investigated in demonstration-scale experiments with 10m3 bioreactors using an LPMO-containing cellulase preparation, a xylose-utilizing yeast, and either simultaneous saccharification and fermentation (SSF) or hybrid hydrolysis and fermentation (HHF) with a 24-hour or 48-hour initial phase and with 0.15 vvm aeration before addition of the yeast. The conditions used for HHF, especially with 48h initial phase, resulted in better glucan conversion, but in poorer ethanol productivity and in poorer initial ethanol yield on consumed sugars than the SSF. In the SSF, hexose sugars such as glucose and mannose were consumed faster than xylose, but, in the end of the fermentation >90% of the xylose had been consumed. Chemical analysis of inhibitory pretreatment by-products indicated that the concentrations of heteroaromatic aldehydes (such as furfural), aromatic aldehydes, and an aromatic ketone decreased as a consequence of the aeration. This was attributed mainly to evaporation caused by the gas flow. The results indicate that further research is needed to fully exploit the advantages of LPMO without compromising fermentation conditions.

Effect of various aromatic compounds with different functional groups on enzymatic hydrolysis of microcrystalline cellulose and alkaline pretreated wheat straw

Low molecular aromatic compounds are detrimental to the enzymatic hydrolysis of lignocellulose. However, the specific role of their functional groups remains unclear. Here, a series of nine aromatic compounds as additives were tested to understand their effect on the hydrolysis yield of microcrystalline cellulose (MCC) and alkaline pretreated wheat straw. Based on the results, the inhibition of aldehyde groups on MCC was greater than that of carboxyl groups, whereas for the alkaline pretreated wheat straw case, the inhibitory effect of aldehyde groups was lower than that of carboxyl groups. Increased methoxyl groups of aromatic compounds reduced the inhibitory effect on enzymatic hydrolysis of both substrates. Stronger inhibition of aromatic compounds on MCC hydrolysis was detected in comparison with the alkaline pretreated wheat straw, indicating that the substrate lignin can offset the inhibition to a certain extent. Among all aromatic compounds, syringaldehyde with one aldehyde group and two methoxyl groups improved the glucan conversion of the alkaline pretreated wheat straw.

LPMO-supported saccharification of biomass: effects of continuous aeration of reaction mixtures with variable fractions of water-insoluble solids and cellulolytic enzymes

BackgroundHigh substrate concentrations and high sugar yields are important aspects of enzymatic saccharification of lignocellulosic substrates. The benefit of supporting the catalytic action of lytic polysaccharide monooxygenase (LPMO) through continuous aeration of slurries of pretreated softwood was weighed against problems associated with increasing substrate content (quantitated as WIS, water-insoluble solids, in the range 12.5–17.5%), and was compared to the beneficial effect on the saccharification reaction achieved by increasing the enzyme preparation (Cellic CTec3) loadings. Aerated reactions were compared to reactions supplied with N2 to assess the contribution of LPMO to the saccharification reactions. Analysis using 13C NMR spectroscopy, XRD, Simons’ staining, BET analysis, and SEM analysis was used to gain further insights into the effects of the cellulolytic enzymes on the substrate under different reaction conditions.ResultsAlthough glucose production after 72 h was higher at 17.5% WIS than at 12.5% WIS, glucan conversion decreased with 24% (air) and 17% (N2). Compared to reactions with N2, the average increases in glucose production for aerated reactions were 91% (12.5% WIS), 70% (15.0% WIS), and 67% (17.5% WIS). Improvements in glucan conversion through aeration were larger (55–86%) than the negative effects of increasing WIS content. For reactions with 12.5% WIS, increased enzyme dosage with 50% improved glucan conversion with 25–30% for air and N2, whereas improvements with double enzyme dosage were 30% (N2) and 39% (air). Structural analyses of the solid fractions revealed that the enzymatic reaction, particularly with aeration, created increased surface area (BET analysis), increased disorder (SEM analysis), decreased crystallinity (XRD), and increased dye adsorption based on the cellulose content (Simons' staining).ConclusionsThe gains in glucan conversion with aeration were larger than the decreases observed due to increased substrate content, resulting in higher glucan conversion when using aeration at the highest WIS value than when using N2 at the lowest WIS value. The increase in glucan conversion with double enzyme preparation dosage was smaller than the increase achieved with aeration. The results demonstrate the potential in using proper aeration to exploit the inherent capacity of LPMO in enzymatic saccharification of lignocellulosic substrates and provide detailed information about the characteristics of the substrate after interaction with cellulolytic enzymes.

Ultrasound treatment of herbal extraction residue to enhance enzymatic saccharification

The utilization of herbal extraction residues (HERs) for production of valuable products has gained significant momentum in recent years. In this study, Lianhua Qingwen residue (LQR) was selected as a representative HER for enzymatic saccharification. By subjecting starch-containing raw unpretreated LQR to direct hydrolysis using a combination of cellulolytic and amylolytic enzyme, a glucan conversion of around 60 % was achieved within 48 h. To further enhance the hydrolysis rate and yield, ultrasound treatment of LQR samples was conducted. Investigation into the effect of ultrasound treatment on subsequent enzymatic saccharification revealed a noteworthy acceleration in the saccharification rate of LQR, exceeding 20 % within 10 h of hydrolysis time. Notably, this enhancement was achieved even when the substrate concentration was high at 10 % under optimized conditions of 5 min of sonication at a power intensity of 1.20 kW/cm2 and a temperature of 50 °C. The improvement in efficiency can be attributed to the disruptive effect of ultrasound treatment on the structure of LQR, leading to a reduction in particle size. Consequently, the LQR particles exhibited better contact with the enzyme, promoting a more efficient saccharification process. These findings suggest that ultrasound technology holds considerable potential for enhancing the enzymatic saccharification of HERs.

Microwave-assisted ternary deep eutectic solvent pretreatment for improved rice straw saccharification under mild pretreatment conditions

The development of a green and cost-effective pretreatment method to overcome biomass recalcitrance is a challenging assignment for the efficient valorization of lignocellulosic compounds. In this study, a ternary deep eutectic solvent (DES) consisting of choline chloride (ChCl), p-toluene sulfonic acid (pTSA) and ethylene glycol (EG) was applied in rice straw (RS) pretreatment under microwave (MW) irradiation for the further conversion of the polysaccharide fraction. The effect of the pretreatment temperature, time and pTSA content in the DES on lignin extraction and polysaccharide hydrolysis was assessed by a central composite design (CCD). Under the selected pretreatment conditions (80 ºC, 22.5 min, ChCl:pTSA:EG 1:1:9), 61.6% delignification was achieved, as well as nearly complete conversion of the initial glucan in RS (93.4% glucose yield) and a good xylan conversion rate (48.3% xylose yield), representing a total polysaccharide exploitation of 78.3%. Energetical requirement was remarkably lower compared to conventional conductive heating. Importantly, the ternary DES showed good recyclability pattern after two reuses. Overall, this study demonstrated the potential of MW-assisted ternary DES pretreatment for improved valorization of biomass polysaccharides under mild pretreatment conditions, representing an efficient and energetical-saving alternative pathway within the biorefinery framework.

An Efficient and Cost- Effective Pretreatment of Rice Straw Using Steam Explosion: A Pilot Scale Experience

Surplus availability of rice straw (RS) presents it as a potential feedstock for ethanol production. Steam explosion (SE) is considered as a green approach to extract fermentable sugars at lower cost. The present study deals with the reaction condition optimization for water and dilute acid assisted steam explosion of rice straw at different temperatures and explores the effect of structural properties of solid residue on enzymatic hydrolysis along with mass balance. SE conditions were optimized at pilot scale, raising the temperature from 170 to 200 °C in water assisted SE resulting in an increased glucan conversion from 21.4 to 42.5% at 15% solid loading using 1.5 FPU of cellulases g–1 biomass. Further, it was improved up to 58.7% by increasing the enzyme dosage to 5 FPU, although it might lead to enhanced enzyme cost by threefold. To reduce costs, small amount of dilute acid (DA) was added during SE and lowering of enzyme consumption i.e. 1.5 FPU/g cellulose has been used to achieve 65.5% glucan conversion. Varying temperature and incorporate dilute acid during pretreatment induced structural alterations in biomass evident by compositional analysis, FT-IR and mass balance. Mass balance study revealed that the overall sugar recovery i.e. 58.7 and 38.8% and theoretical yield of ethanol shall be 222 and 186 L ton–1 RS respectively, with and without DA addition.Graphical

Integrating surfactants with low enzyme loading to increase the glucan conversion and ethanol concentration of reed after combined pretreatment

In this study, in order to obtain high concentration bioethanol, reed pretreated with liquid hot water and ammonia oxygen (LHW-NH3·H2O/O2) was used as the substrate for fermentation. Enzymatic hydrolysis becomes difficult by the ineffective lignin adsorption and the decline in cellulase activity. It is worth noting that even under low enzyme loading (9 FPU/g pretreated solid), this study was able to maintain a higher glucan conversion rate (97.60%). In addition, under high solid loading conditions, the combined effect of PEG 6000 and rhamnolipids increased ethanol yield (78.40%) and ethanol concentration (71.5 g/L). The combined LHW-NH3·H2O/O2 pretreatment with fed-batch semi-simultaneous saccharification and fermentation technique may be utilized to industrialize the production of bioethanol from reed since we concentrated on the maximum exploitation of biomass resources and reduction in energy consumption.

Greater Importance of Structural Changes Over Lignin Removal in Impacting the Enzymatic Hydrolysis of Crop Straws.

The importance of structural changes and lignin removal in influencing the enzymatic hydrolysis of crop straws was investigated. Alkaline pretreatment of corn stover (CS) and rice straw (RS) was conducted to remove lignin. It was found that alkaline pretreatment caused more lignin removal from CS than RS under the same condition, and CS and RS treated at 40 °C (CS40 and RS40) attained less lignin removal than those treated at 80 °C (CS80 and RS80). However, CS40 achieved glucan conversion efficiency of 70.77% which was 11.85% less than that of RS40, and similar glucan conversion efficiencies were obtained for RS 40 and RS80. Structural observation showed that the connection among single fiber bundle of CS40 was tighter than that of RS40, while those of RS40 and RS80 were loose. It meant that structural changes might be more important than lignin removal to influence enzymatic hydrolysis of crop straws.

High-solids enzymatic saccharification of starch-rich raw herbal biomass residues for producing high titers of glucose.

The bioresource utilization of herbal biomass residues (HBRs) has been receiving more attention. Herein, three different HBRs from Isatidis Radix (IR) and Sophorae Flavescentis Radix (SFR) and Ginseng Radix (GR) were subjected to batch and fed-batch enzymatic hydrolysis to produce high-concentration glucose. Compositional analysis showed the three HBRs had substantial starch content (26.36-63.29%) and relatively low cellulose contents (7.85-21.02%). Due to their high starch content, the combined action of cellulolytic and amylolytic enzymes resulted in greater release of glucose from the raw HBRs compared to using the individual enzyme alone. Batch enzymatic hydrolysis of 10% (w/v) raw HBRs with low loadings of cellulase (≤ 10 FPU/g substrate) and amylolytic enzymes (≤ 5.0mg/g substrate) led to a high glucan conversion of ≥ 70%. The addition of PEG 6000 and Tween 20 did not contribute to glucose production. Furthermore, to achieve higher glucose concentrations, fed-batch enzymatic hydrolysis was conducted using a total solid loading of 30% (w/v). After 48-h of hydrolysis, glucose concentrations of 125g/L and 92g/L were obtained for IR and SFR residues, respectively. GR residue yielded an 83g/L glucose concentration after 96h of digestion. The high glucose concentrations produced from these raw HBRs indicate their potential as ideal substrate for a profitable biorefinery. Notably, the obvious advantage of using these HBRs is the elimination of the pretreatment step, which is typically required for agricultural and woody biomass in similar studies.

Chemomechanical pretreatment for efficient delignification and saccharification of corn stover biomass

The development of multifunctional pretreatments for effective and economical fractionation of lignocellulosic biomass (LCB), while targeting entirely lignocellulose-oriented valorization can pave the cutting-edge innovation in biorefinery. Herein, a promising high-solid chemomechanical pretreatment (CMP) based on ball milling (BM) coupled with ethylenediamine (EDA) pretreatment was designed to maximize the output of corn stover (CS) biomass under the mild temperature (≤120 °C) and active stabilization. The synergistic effects of EDA/BM configuration brought about desirable characteristics that eventually intensify delignification and saccharification at the expense of less solvent load and energy consumption up to 3.0 MJ kg−1 compare with EDA pretreatment (7.3 MJ kg−1). Importantly, CMP generated aminated and uncondensed lignin up to 85 % at 400 rpm for 1 h, with a high content of β-O-4 linkages (44.7/100Ar), which render it competently suitable for valorization into nitrogen-containing aromatic chemicals and lignin-based fluorescent materials. CMP led to 97 % conversion of glucan, and 94 % of xylan in 72 h at enzymatic loading of 1 and 0.5 %w. w-1 of Cellic CTec3 and xylanase, respectively. This lignin-first and entirely lignocellulose-oriented pretreatment could overcome the hampering of solid-state conversion and contribute to the sustainable LCB-based economy.

Effect of pelleting on the enzymatic digestibility of corn stover

Pelleting of lignocellulosic biomass to improve its transportation, storage and handling impacts subsequent processing and conversion. This work reports the role of high moisture pelleting in the enzymatic digestibility of corn stover prior to pretreatment, together with associated substrate characteristics. Pelleting increases the digestibility of unpretreated corn stover, from 8.2 to 15.5% glucan conversion, at 5% solid loading using 1 FPU Cellic® CTec2 per g solids. Compositional analysis indicates that loose and pelleted corn stover have similar non-dissolvable compositions, although their extractives are different. Enzymatic hydrolysis of corn stover after size reduction to normalize particle sizes and removal of extractives confirms that pelleting improves corn stover digestibility. Such differences may be explained by the decreased particle size, improved substrate accessibility, and hydrolysis of cross-linking structures induced by pelleting. These findings are useful for the development of processing schemes for sustainable and efficient use of lignocellulose.

Investigating the role of AA9 LPMOs in enzymatic hydrolysis of differentially steam-pretreated spruce

BackgroundTo realize the full potential of softwood-based forest biorefineries, the bottlenecks of enzymatic saccharification of softwood need to be better understood. Here, we investigated the potential of lytic polysaccharide monooxygenases (LPMO9s) in softwood saccharification. Norway spruce was steam-pretreated at three different severities, leading to varying hemicellulose retention, lignin condensation, and cellulose ultrastructure. Hydrolyzability of the three substrates was assessed after pretreatment and after an additional knife-milling step, comparing the efficiency of cellulolytic Celluclast + Novozym 188 and LPMO-containing Cellic CTec2 cocktails. The role of Thermoascus aurantiacus TaLPMO9 in saccharification was assessed through time-course analysis of sugar release and accumulation of oxidized sugars, as well as wide-angle X-ray scattering analysis of cellulose ultrastructural changes.ResultsGlucose yield was 6% (w/w) with the mildest pretreatment (steam pretreatment at 210 °C without catalyst) and 66% (w/w) with the harshest (steam pretreatment at 210 °C with 3%(w/w) SO2) when using Celluclast + Novozym 188. Surprisingly, the yield was lower with all substrates when Cellic CTec2 was used. Therefore, the conditions for optimal LPMO activity were tested and it was found that enough O2 was present over the headspace and that the reducing power of the lignin of all three substrates was sufficient for the LPMOs in Cellic CTec2 to be active. Supplementation of Celluclast + Novozym 188 with TaLPMO9 increased the conversion of glucan by 1.6-fold and xylan by 1.5-fold, which was evident primarily in the later stages of saccharification (24–72 h). Improved glucan conversion could be explained by drastically reduced cellulose crystallinity of spruce substrates upon TaLPMO9 supplementation.ConclusionOur study demonstrated that LPMO addition to hydrolytic enzymes improves the release of glucose and xylose from steam-pretreated softwood substrates. Furthermore, softwood lignin provides enough reducing power for LPMOs, irrespective of pretreatment severity. These results provided new insights into the potential role of LPMOs in saccharification of industrially relevant softwood substrates.

Production of 1,3-propanediol using enzymatic hydrolysate derived from pretreated distillers' grains

To minimize environmental pollution and waste of resources, distillers’ grains (DG) was used to produce 1,3-propanediol. Biological, physical, and chemical methods were used for pretreatment. The correlation between features of pretreated samples and enzymatic digestibility was analyzed. The results showed that the glucan and xylan conversion of dilute sulfuric acid pretreated DG increased by 69.59% and 413.68%, respectively. The glucan conversion of microwave pretreated and xylan conversion of laccase pretreated DG increased by 14.22% and 34.19%, respectively. Pretreatment enhanced enzymatic digestibility through changing the dense structure and features of DG making them conductive to enzymatic hydrolysis. The production of 1,3-propanediol using enzymatic hydrolysate of pretreated DG and glycerol in shake-flask was 17 g/L. The utilization of DG not only provides plentiful raw materials replacing fossil fuels to produce biofuels and other chemicals but efficiently reduces environmental waste.

INTENSIFICATION OF THE FREEZE-THAW PRETREATMENT OF DISINTEGRATED POPLAR WOOD

Thisresearch wasfocused on the effect of water content in the cells of disintegrated Populus nigraL. on a freeze-thaw pretreatment method before an enzymatic hydrolysis. Two chipped andsieved fractions 2.5 mm and0.7 mm and two milled fractions,characterized as 18°SR (Shopper–Riegler index) and 37°SR,of the disintegrated 5 years old poplartree were used for ourexperiment. Glucose and xylose yields were measured after 24 and 48 hours ofenzymatic hydrolysis with a 15% load of the enzyme measured to a total cellulose content. Theinfluence of nine freeze-thaw cycles under -20°C and +20°C was considered. The results showed thatanincrease in moisture content positively affects yields in all fractions but adesirable result was achieved mainly for the 0.7 mm fraction where the total yield increased by about 16%.More effective wayis afiner wetbeating ofwood mass, while wood fibrereceivesmoisture already in the technological process.Thehighest glucan conversion 51,74% and the total hemicelluloses conversion 47,72% was achieved for the finest fraction 37°SR.Thehigher moisture content has a positive effect on the increase in theconversion of oligosaccharides, especially glucan, in chipped fractions.

Integrated sugarcane biorefinery for first- and second-generation bioethanol production using imidazole pretreatment

Sugarcane bagasse (SB) is a potential source for second-generation bioethanol production. Imidazole appears as a cheap green solvent that has demonstrated high efficiency in lignocellulosic biomass delignification. The main objective of this work was the use of imidazole-pretreated SB aiming the integration of first and second-generation bioethanol production in sugarcane mills’ plant. Optimized conditions (160 °C for 1 h) were applied in imidazole-pretreatment of SB. The results showed significant cellulose enrichment (167.3%) and decrease of amorphous compounds (lignin and hemicellulose), leading to a 100% conversion of glucan to glucose after enzymatic hydrolysis. Bioethanol production reached 10.4 g.L−1 at 12 h by S. cerevisiae and 11.7 g.L−1 after 30 h by P. stipitis, which represents a bioconversion yield of 77.6% and 91.5%, respectively. The imidazole-pretreatment of SB is a promising way to integrate the production of first and second-generation bioethanol, improving in 37% the total bioethanol production and reaching 110.3 L of bioethanol per ton of sugarcane. Imidazole showed great perspective for biofuel production, leading to an efficient process for waste valorization, increase of bioethanol productivities in sugarcane biorefineries.

Highly efficient glucose production from raw non-pretreated Chinese medicinal herbal residues via the synergism of cellulase and amylolytic enzymes

Available literature on Chinese medicinal herbal residues (CMHRs) bioconversion highlights pretreatment prior to saccharification with cellulase without considering the presence of starch constituent. Herein, four commonly found CMHRs were tested for starch content, and it was found they all contained starch with content ranging from 4.74% to 16.78%. Hydrolysis of raw CMHRs with combined cellulase and amylolytic enzymes yielded increments of 16.85% to 26.51% in 48-h glucan conversion compared to cellulase alone. Further study showed 48-h glucan conversion of raw CMHRs outperformed that pretreated by water–ethanol successive extraction, ultrasound and acid, but underperformed alkali-pretreated CMHRs. Although increasing 48-h glucan conversion in the range of 7.40% to 24.10% compared to raw CMHRs, alkaline pretreatment demonstrated low glucose recovery and incurred additional cost, making it unfavorable. Saccharification of the four raw CMHRs with combined enzymes seems like a preferred option considering the elimination of high-cost pretreatment step.