Effect of alkaline pre-treatment on enzyme synergy for efficient hemicellulose hydrolysis in sugarcane bagasse

Towards an understanding of the enzymatic degradation of complex plant mannan structures

Plant cell walls are composed of a heterogeneous mixture of polysaccharides that require several different enzymes to degrade. These enzymes are important for a variety of biotechnological processes, from biofuel production to food processing. Several classical mannanolytic enzyme functions of glycoside hydrolases (GH), such as β-mannanase, β-mannosidase and α-galactosidase activities, are helpful for efficient mannan hydrolysis. In this light, we bring three enzymes into the model of mannan degradation that have received little or no attention. By linking their three-dimensional structures and substrate specificities, we have predicted the interactions and cooperativity of these novel enzymes with classical mannanolytic enzymes for efficient mannan hydrolysis. The novel exo-β-1,4-mannobiohydrolases are indispensable for the production of mannobiose from the terminal ends of mannans, this product being the preferred product for short-chain mannooligosaccharides (MOS)-specific β-mannosidases. Second, the side-chain cleaving enzymes, acetyl mannan esterases (AcME), remove acetyl decorations on mannan that would have hindered backbone cleaving enzymes, while the backbone cleaving enzymes liberate MOS, which are preferred substrates of the debranching and sidechain cleaving enzymes. The nonhydrolytic expansins and swollenins disrupt the crystalline regions of the biomass, improving their accessibility for AcME and GH activities. Finally, lytic polysaccharide monooxygenases have also been implicated in promoting the degradation of lignocellulosic biomass or mannan degradation by classical mannanolytic enzymes, possibly by disrupting adsorbed mannan residues. Modelling effective enzymatic mannan degradation has implications for improving the saccharification of biomass for the synthesis of value-added and upcycling of lignocellulosic wastes.

Optimization of Soybean Protein Extraction with Ammonium Hydroxide (NH4OH) Using Response Surface Methodology

Plants have been recognized as renewable and sustainable sources of proteins. However, plant protein extraction is challenged by the plant's recalcitrant cell wall. The conventional extraction methods make use of non-reusable strong alkali chemicals in protein-denaturing extraction conditions. In this study, soy protein was extracted using NH₄OH, a weak, recoverable, and reusable alkali. The extraction conditions were optimized using response surface methodology (RSM). A central composite design (CCD) with four independent variables: temperature (25, 40, 55, 70, and 85 °C); NH₄OH concentration (0.5, 1, and 1.5%); extraction time (6, 12, 18, and 24 h) and solvent ratio (1:5, 1:10, 1:15 and 1:20 w/v) were used to study the response variables (protein yield and amine concentration). Amine concentration indicates the extent of protein hydrolysis. The RSM model equation for the independent and response variables was computed and used to create the contour plots. A predicted yield of 64.89% protein and 0.19 mM amine revealed a multiple R-squared value of 0.83 and 0.78, respectively. The optimum conditions to obtain the maximum protein yield (65.66%) with the least amine concentration (0.14 Mm) were obtained with 0.5% NH₄OH concentration, 12 h extraction time, and a 1:10 (w/v) solvent ratio at 52.5 °C. The findings suggest that NH₄OH is suitable to extract soybean protein with little or no impact on protein denaturation.

Expression profiling of Clostridium thermocellum B8 during the deconstruction of sugarcane bagasse and straw

The gram-positive bacterium Clostridium thermocellum contains a set of carbohydrate-active enzymes that can potentially be employed to generate high-value-added products from lignocellulose. In this study, the gene expression profiling of C. thermocellum B8 was provided during growth in the presence of sugarcane bagasse and straw as a carbon source in comparison to growth using microcrystalline cellulose. A total of 625 and 509 genes were up-regulated for growth in the presence of bagasse and straw, respectively. These genes were mainly grouped into carbohydrate-active enzymes (CAZymes), cell motility, chemotaxis, quorum sensing pathway and expression control of glycoside hydrolases. These results show that type of carbon source modulates the gene expression profiling of carbohydrate-active enzymes. In addition, highlight the importance of cell motility, attachment to the substrate and communication in deconstructing complex substrates. This present work may contribute to the development of enzymatic cocktails and industrial strains for biorefineries based on sugarcane residues as feedstock.

Isolation, purification and characterization of cellulase produced by Aspergillus niger cultured on Arachis hypogaea shells

Cellulases are enzymes that hydrolyse cellulose and related cellu-oligosaccharides derivatives. Its applications are enormous but high cost of production is the bottle-neck against the utilization of cellulase in industries. Therefore, this study investigated the isolation, purification and characterization of cellulase produced by Aspergillus niger cultured on Arachis hypogaea shells. The crude cellulase enzyme was produced by A. niger through submerged fermentation process using A. hypogaea shells as a carbon source. The optima fermentation conditions were determined by varying different parameters. The crude cellulase was purified through ammonium sulphate precipitation, dialysis and gel-filtration chromatography. The molecular weight was estimated using sodium dodecyl sulphate polyacrylamide gel electrophoresis. The effects of pH and temperature on the activity of the purified cellulase were investigated. The study revealed that the: optimal production of crude cellulase was achieved at incubation period of 120 h, pH 4, temperature 40 °C, and inoculum size of 13 × 10⁵ CFU/ml. Cellulase was purified to 68.12-fold with a yield and specific activity of 3.87% and 484.3 U/mg respectively. The V_max for the cellulase was 9.26 U/ml while the K_m was 0.23 mg/ml. The molecular weight of the cellulase was approximately 13.5 kDa and the enzyme has higher specificity for CMC compared to other substrates. The optimum pH and temperature for the cellulase activity were 4 and 40 °C respectively. The present study has shown that A. hypogaea shells can be used as a carbon source by A. niger for the production of cellulase.

Combination of CTec2 and GH5 or GH26 Endo-Mannanases for Effective Lignocellulosic Biomass Degradation

Among endo-mannanases, glycoside hydrolase (GH) family 26 enzymes have been shown to be more catalytically active than GH5 enzymes on mannans. However, only GH5 endo-mannanases have been used for the formulation of enzyme cocktails. In this study, Bacillus sp.-derived GH5 and GH26 endo-mannanases were comparatively analysed biochemically for their synergistic action with a commercial cellulase blend, CTec2, during pre-treated lignocellulose degradation. Substrate specificity and thermo-stability studies on mannan substrates showed that GH26 endo-mannanase was more catalytically active and stable than GH5. GH26 also exhibited higher binding affinity for mannan than GH5, while GH5 showed more affinity for lignocellulosic substrates than GH26. Applying the endo-mannanases in combination with CTec2 for lignocellulose degradation led to synergism with a 1.3-fold increase in reducing sugar release compared to when CTec2 was used alone. This study showed that using the activity of endo-mannanases displayed with model substrates is a poor predictor of their activity and synergism on complex lignocelluloses.

Investigation of alkaline hydrogen peroxide pretreatment to enhance enzymatic hydrolysis and phenolic compounds of oil palm trunk

Alkaline hydrogen peroxide (AHP) as a pretreatment effectively enhances the increasing enzymatic digestibility of oil palm trunk (OPT) for conversion to biofuels and bioproducts in the biorefinery processes. The effect of hydrogen peroxide concentration (1-5%), temperature (50-90 °C), and time (30-90 min) were studied to find out the optimum condition for the removal of lignin. The optimum condition attained at 70 °C, 30 min, and 3% H₂O₂ g /g of biomass not only increased the cellulose content from 38.67% in raw material to 73.96% but also removed lignin and hemicellulose up to 50% and 57.12%, respectively. The AHP-treated fibers subjected to enzyme hydrolysis showed significant improvement in glucose concentration that increased from 11.77 (± 0.84) g/L (raw material) to 46.15 (± 0.32) g/L with 59.82% enzyme digestibility at 96 h. Scanning electron microscopy (SEM) and Fourier transformation infrared (FT-IR) were employed to analyze the morphology and structural changes of untreated and AHP-treated fibers. SEM results showed disruption of the intact OPT structure resulting in increase of enzyme accessibility to cellulose. The FT-IR identified changes in peaks which indicated structural transformation and dissolution of both lignin and hemicellulose molecules caused by AHP treatment. The black liquor obtained from AHP treatment contained about 5.13 mg gallic acid equivalent (GAE)/g of dry sample of total phenolic content (TPC) and an antioxidant activity of 59.80% and 65.51% inhibitions of DPPH and ABTS assays, respectively. Hence, it is a sustainable approach to utilize waste for the recovery of multiple value-added products during pretreatment process.

Fermentative Conversion of Two-Step Pre-Treated Lignocellulosic Biomass to Hydrogen

Fermentative hydrogen production via dark fermentation with the application of lignocellulosic biomass requires a multistep pre-treatment procedure, due to the complexed structure of the raw material. Hence, the comparison of the hydrogen productivity potential of different lignocellulosic materials (LCMs) in relation to the lignocellulosic biomass composition is often considered as an interesting field of research. In this study, several types of biomass, representing woods, cereals and grass were processed by means of mechanical pre-treatment and alkaline and enzymatic hydrolysis. Hydrolysates were used in fermentative hydrogen production via dark fermentation process with Enterobacter aerogenes (model organism). The differences in the hydrogen productivity regarding different materials hydrolysates were analyzed using chemometric methods with respect to a wide dataset collected throughout this study. Hydrogen formation, as expected, was positively correlated with glucose concentration and total reducing sugars amount (YTRS) in enzymatic hydrolysates of LCMs, and negatively correlated with concentrations of enzymatic inhibitors i.e., HMF, furfural and total phenolic compounds in alkaline-hydrolysates LCMs, respectively. Interestingly, high hydrogen productivity was positively correlated with lignin content in raw LCMs and smaller mass loss of LCM after pre-treatment step. Besides results of chemometric analysis, the presented data analysis seems to confirm that the structure and chemical composition of lignin and hemicellulose present in the lignocellulosic material is more important to design the process of its bioconversion than the proportion between the cellulose, hemicellulose and lignin content in this material. For analyzed LCMs we found remarkable higher potential of hydrogen production via bioconversion process of woods i.e., beech (24.01 mL H2/g biomass), energetic poplar (23.41 mL H2/g biomass) or energetic willow (25.44 mL H2/g biomass) than for cereals i.e., triticale (17.82 mL H2/g biomass) and corn (14.37 mL H2/g biomass) or for meadow grass (7.22 mL H2/g biomass).

Comparison of Biological and Chemical Pretreatment on Coproduction of Pectin and Fermentable Sugars from Apple Pomace

Apple pomace, an abundant accessible source of carbohydrate platform chemicals, is refractory to cellulase degradation because of the main barrier problem of pectin constitute. A rapid and portable method for the coproduction of pectin and fermentable sugars was developed using the pretreatment of acetic acid, followed by enzymatic hydrolysis. Compared with pectinase, acetic acid pretreatment provided the highest pectin yield of 19.1% and the highest enzymatic hydrolysis yield from apple pomace. The acidic pretreated apple pomace cellulose was easily and completely hydrolyzed into fermentable sugars. More than 98.2% conversion of cellulose was achieved in a batch hydrolysis using a cellulase loading of 25 FPU/g cellulose and 10% total solids without any special strategies. A mass balance analysis showed that 95.5 g pectin and 110.2 g fermentable sugars were produced from 500-g oven-dried apple pomace. The integrated process is suggestive of environment-friendly and recyclable methods for the industrial utilization of apple pomace.

Pretreatment of Lignocellulosic Materials as Substrates for Fermentation Processes

Lignocellulosic biomass is an abundant and renewable resource that potentially contains large amounts of energy. It is an interesting alternative for fossil fuels, allowing the production of biofuels and other organic compounds. In this paper, a review devoted to the processing of lignocellulosic materials as substrates for fermentation processes is presented. The review focuses on physical, chemical, physicochemical, enzymatic, and microbiologic methods of biomass pretreatment. In addition to the evaluation of the mentioned methods, the aim of the paper is to understand the possibilities of the biomass pretreatment and their influence on the efficiency of biofuels and organic compounds production. The effects of different pretreatment methods on the lignocellulosic biomass structure are described along with a discussion of the benefits and drawbacks of each method, including the potential generation of inhibitory compounds for enzymatic hydrolysis, the effect on cellulose digestibility, the generation of compounds that are toxic for the environment, and energy and economic demand. The results of the investigations imply that only the stepwise pretreatment procedure may ensure effective fermentation of the lignocellulosic biomass. Pretreatment step is still a challenge for obtaining cost-effective and competitive technology for large-scale conversion of lignocellulosic biomass into fermentable sugars with low inhibitory concentration.

Effect of β-mannanase domain from Trichoderma reesei on its biochemical characters and synergistic hydrolysis of sugarcane bagasse

BACKGROUND

β-mannanase is a key enzyme for hydrolyzing mannan, a major constituent of hemicellulose, which is the second most abundant polysaccharide in nature. Different structural domains greatly affect its biochemical characters and catalytic efficiency. However, the effects of linker and carbohydrate-binding module (CBM) on β-mannanase from Trichoderma reesei (Man1) have not yet been fully described. The present study aimed to determine the influence of different domains on the expression efficiency, biochemical characteristics and hemicellulosic deconstruction of Man1.

RESULTS

The expression efficiency was improved after truncating CBM. Activities of Man1 and Man1ΔCBM (CBM) in the culture supernatant after 168 h of induction were 34.5 and 42.9 IU mL^-1 , although a value of only 0.36 IU mL^-1 was detected for Man1ΔLCBM (lacking CBM and linker). Man1 showed higher thermostability than Man1ΔCBM at low temperature, whereas Man1ΔCBM had a higher specificity for galactomannan (K_m  = 2.5 mg mL^-1 ) than Man1 (K_m  = 4.0 mg mL^-1 ). Both Man1 and Man1ΔCBM could synergistically improve the hydrolysis of cellulose, galactomannan and pretreated sugarcane bagasse, with a 10-30% improvement of the reducing sugar yield.

CONCLUSION

Linker and CBM domains were vital for mannanase activity and expression efficiency. CBM affected the thermostability and adsorption ability of Man1. The results obtained in the present study should help guide the rational design and directional modification of Man with respect to improving its catalytic efficiency. © 2017 Society of Chemical Industry.

Formulation of an optimized synergistic enzyme cocktail, HoloMix, for effective degradation of various pre-treated hardwoods

In this study, two selected hardwoods were subjected to sodium chlorite delignification and steam explosion, and the impact of pre-treatments on synergistic enzymatic saccharification evaluated. A cellulolytic core-set, CelMix, and a xylanolytic core-set, XynMix, optimised for glucose and xylose release, respectively, were used to formulate HoloMix cocktail for optimal saccharification of various pre-treated hardwoods. For delignified biomass, the optimized HoloMix consisted of 75%:25% protein dosage, CelMix: XynMix, while for untreated and steam exploded biomass the HoloMix consisted of 93.75%:6.25% protein dosage. Saccharification by HoloMix (27.5mgprotein/gbiomass) for 24h achieved 70-100% sugar yields. Pre-treatment of the hardwoods (especially those with a higher proportion of lignin) with a laccase, improved saccharification by HoloMix. This study provided insights into enzymatic hydrolysis of various pre-treated hardwood substrates and showed the same lignocellulolytic cocktail comparable to/if not better than commercial enzyme preparations can be used to efficiently hydrolyse different hardwood species.

Integration of a phenolic-acid recovery step in the CaCCO process for efficient fermentable-sugar recovery from rice straw

An advanced sugar-platform bioprocess for lignocellulosic feedstocks by adding a phenolic-acid (PA: p-coumaric acid and ferulic acid) recovery step to the CaCCO process was designed. For efficient PA extraction, pretreatment was 95°C for 2h, producing a yield of 7.30 g/kg-dry rice straw (65.2% of total ester-linked PAs) with insignificant effects on saccharification. PAs were readily recovered in solution during the repeated washings of solids, and the glucose yield, after 72-h saccharification of the washed solids, was significantly improved from 65.9% to 70.3-72.7%, suggesting the removal of potential enzyme inhibitors. The promotion of xylose yield was insignificant, probably due to 13.1-17.8% loss of xylose residues after washing(s). This new bioprocess, termed the SRB (simultaneous recovery of by-products)-CaCCO process, would effectively produce fermentable sugars and other valuables from feedstocks, strengthening the platform in both economic and environmental terms.

Thermogravimetric kinetics of sugarcane bagasse pretreated by hot-water

The thermogravimetric of sugarcane bagasse pretreated by hot-water has been studied in this paper. Results indicated that residual solid pretreatment by hot water could decrease the activation energy of phase 2 (270-350 °C) obviously, which makes the pyrolysis more energy-saving. By hot water pretreatment, the hemicellulose, especially xylose (9.78%/o.d. dry mass at 170 °C and 1 h) was greatly extracted into hydrolyzates liquor. Greatly minimized hemicellulose waste at low temperature during pyrolysis also agreed with biorefinery concept. Therefore, bagasse with hot-water pretreatment should be a good pyrolysis material for value-added material.

Comparison of the effects of five pretreatment methods on enhancing the enzymatic digestibility and ethanol production from sweet sorghum bagasse

To improve the enzymatic digestibility of sweet sorghum bagasse and bioethanol production, five pretreatment methods have been investigated and compared, including (1) dilute NaOH solution autoclaving pretreatment, (2) high concentration NaOH solution immersing pretreatment, (3) dilute NaOH solution autoclaving and H(2)O(2) immersing pretreatment, (4) alkaline peroxide pretreatment and (5) autoclaving pretreatment. Among them, the best result was obtained when sweet sorghum bagasse was dilute NaOH solution autoclaving and H(2)O(2) immersing pretreatment. The highest cellulose hydrolysis yield, total sugar yield and ethanol concentration were 74.29%, 90.94 g sugar/100g dry matter and 6.12 g/L, respectively, which were 5.88, 9.54 and 19.13 times higher than the control. Moreover, the FTIR and SEM analysis illustrated significant molecule and surface structure changes of the sweet sorghum bagasse after pretreatments.

A review of lignocellulose bioconversion using enzymatic hydrolysis and synergistic cooperation between enzymes--factors affecting enzymes, conversion and synergy

Lignocellulose is a complex substrate which requires a variety of enzymes, acting in synergy, for its complete hydrolysis. These synergistic interactions between different enzymes have been investigated in order to design optimal combinations and ratios of enzymes for different lignocellulosic substrates that have been subjected to different pretreatments. This review examines the enzymes required to degrade various components of lignocellulose and the impact of pretreatments on the lignocellulose components and the enzymes required for degradation. Many factors affect the enzymes and the optimisation of the hydrolysis process, such as enzyme ratios, substrate loadings, enzyme loadings, inhibitors, adsorption and surfactants. Consideration is also given to the calculation of degrees of synergy and yield. A model is further proposed for the optimisation of enzyme combinations based on a selection of individual or commercial enzyme mixtures. The main area for further study is the effect of and interaction between different hemicellulases on complex substrates.

Synergy between EngE, XynA and ManA from Clostridium cellulovorans on corn stalk, grass and pineapple pulp substrates

The synergistic interaction between various hemi/cellulolytic enzymes has become more important in order to achieve effective and optimal degradation of complex lignocellulose substrates for biofuel production. This study investigated the synergistic effect of three enzymes endoglucanase (EngE), mannanase (ManA) and xylanase (XynA) on the degradation of corn stalk, grass, and pineapple fruit pulp and determined the optimal degree of synergy between combinations of these enzymes. It was established that EngE was essential for degradation of all of the substrates, while the hemicellulases were able to contribute in a synergistic fashion to increase the activity on these substrates. Maximum specific activity and degree of synergy on the corn stalk and grass was found with EngE:XynA in a ratio of 75:25%, with a specific activity of 41.1 U/mg protein and a degree of synergy of 6.3 for corn stalk, and 44.1 U/mg protein and 3.4 for grass, respectively. The pineapple fruit pulp was optimally digested using a ManA:EngE combination in a 50:50% ratio; the specific activity and degree of synergy achieved were 52.4 U/mg protein and 2.7, respectively. This study highlights the importance of hemicellulases for the synergistic degradation of complex lignocellulose. The inclusion of a mannanase in an enzyme consortium for biomass degradation should be examined further as this study suggests that it may play an important, although mostly overlooked, role in the synergistic saccharification of lignocellulose.

Lime pretreatment of sugar beet pulp and evaluation of synergy between ArfA, ManA and XynA from Clostridium cellulovorans on the pretreated substrate

Sugar beet pulp (SBP) is a waste product from the sugar beet industry and could be used as a potential biomass feedstock for second generation biofuel technology. Pretreatment of SBP with ‘slake lime’ (calcium hydroxide) was investigated using a 2³ factorial design and the factors examined included lime loading, temperature and time. The pretreatment was evaluated for its ability to enhance enzymatic degradation using a combination of three hemicellulases, namely ArfA (an arabinofuranosidase), ManA (an endo-mannanase) and XynA (an endo-xylanase) from C. cellulovorans to determine the conditions under which optimal activity was facilitated. Optimal pretreatment conditions were found to be 0.4 g lime/g SBP, with 36 h digestion at 40 °C. The synergistic interactions between ArfA, ManA and XynA from C. cellulovorans were subsequently investigated on the pretreated SBP. The highest degree of synergy was observed at a protein ratio of 75% ArfA to 25% ManA, with a specific activity of 2.9 U/g protein. However, the highest activity was observed at 4.2 U/g protein at 100% ArfA. This study demonstrated that lime treatment enhanced enzymatic hydrolysis of SBP. The ArfA was the most effective hemicellulase for release of sugars from pretreated SBP, but the synergy with the ManA indicated that low levels of mannan in SBP were probably masking the access of the ArfA to its substrate. XynA displayed no synergy with the other two hemicellulases, indicating that the xylan in the SBP was not hampering the access of ArfA or ManA to their substrates and was not closely associated with the mannan and arabinan in the SBP.