Hydrolysis Of Steam-exploded Sugarcane Bagasse Research Articles

Hydrolysate production from sugarcane bagasse using steam explosion and sequential steam explosion-dilute acid pretreatment for polyhydroxyalkanoate fermentation

Polyhydroxyalkanoates (PHAs) are potential alternatives to conventional petroleum-based plastics. One of the barriers to the commercialization of PHAs is its high production cost, which is primarily due to substrate. Agricultural lignocellulosic residues, such as sugarcane bagasse, can be used as substrates to lower production costs. In order to effectively convert the substrate to PHA, sugarcane bagasse must be pretreated. In this study, steam explosion and sequential steam explosion–dilute H2SO4 pretreatment of sugarcane bagasse were optimized to effectively release reducing sugars through enzymatic hydrolysis. Experiments using response surface methodology (RSM) revealed that steam temperature had the greatest influence on lowering sugar content for both sequential and steam explosion pretreatments. The optimum steam explosion conditions were 230 °C steam temperature and 701 s holding time. The concentration of reducing sugars in the enzymatic hydrolysate produced by the hydrolysis of steam-exploded sugarcane bagasse was 6.91 g/L (46.07% yield). On the other hand, the optimum conditions for sequential pretreatment were 230 °C steam explosion temperature, 137 °C dilute acid temperature, 42 min of dilute acid reaction time, and 4.75% w/v H2SO4 concentration, resulting in a hydrolysate with a reducing sugar content of 12.89 g/L (85.93% yield). When steam explosion and diluted H2SO4 pretreatment were combined, a yield increase of reducing sugar of 87% was observed. PHA in the form of polyhydroxybutyrate (PHB) was successfully synthesized using the hydrolysate through bacterial fermentation, with a concentration of 1.99 g/L (16.79% yield) after 24 h. As a result, sequential pretreatment was effective in producing enzymatic hydrolysates from sugarcane bagasse that could be utilized to produce PHA.

Fed-batch enzymatic hydrolysis of steam-exploded sugarcane bagasse

Statistical design and mathematical modeling were used to investigate the fed-batch enzymatic hydrolysis of steam-exploded sugarcane bagasse (195 °C, 7.5 min). First, a Box-Behnken experimental design was used to evaluate the effect of enzyme loading (8, 24, and 40 FPU g-1 glucans of Cellic CTec3®), stirring speed (100, 150, and 200 rpm), and substrate total solids (5, 12.5, and 20 wt%) on the release of glucose equivalents (GlcEq, mostly glucose) after hydrolysis for 48 h in batch mode. A simplified kinetic model was used to fit the experimental data, in which specific activities in Cellic CTec3 were not differentiated, enzyme adsorption was ignored, and end-product inhibition was only attributed to glucose accumulation. The adjusted kinetic model was used to predict the effects of substrate and enzyme intermittent feedings in fed-batch hydrolysis experiments. Compared with batch experiments at 20 wt%, the proposed fed-batch procedure was able to increase GlcEq productivity by nearly 68% using the same enzyme loading, producing substrate hydrolysates containing 91.8 g L-1 GlcEq.

The boosting effect of recombinant hemicellulases on the enzymatic hydrolysis of steam-treated sugarcane bagasse

To increase the efficiency of enzyme cocktails in deconstructing cellulose and hemicelluloses present in the plant cell wall, a combination of enzymes with complementary activities is required. Xylan is the main hemicellulose component of energy crops and for its complete hydrolysis a system consisting of several enzymes acting cooperatively, including endoxylanases (XYN), β-xylosidases (XYL) and α-l-arabinofuranosidases (ABF) is necessary. The current work aimed at evaluating the effect of recombinant hemicellulolytic enzymes on the enzymatic hydrolysis of steam-exploded sugarcane bagasse (SEB). One recombinant endoxylanase (HXYN2) and one recombinant β-xylosidase (HXYLA) from Humicola grisea var thermoidea, together with an α-l-arabinofuranosidase (AFB3) from Penicillium pupurogenum, all produced in Pichia pastoris, were used to formulate an efficient enzyme mixture for SEB hydrolysis using a 23 Central Composite Rotatable Design (CCRD). The most potent enzyme for SEB hydrolysis was ABF3. Subsequently, the optimal enzyme mixture was used in combination with commercial cellulases (Accellerase 1500), either simultaneously or in sequential experiments. The supplementation of Accellerase 1500 with hemicellulases enhanced the glucose yield from SEB hydrolysis by 14.6%, but this effect could be raised to 50% when hemicellulases were added prior to hydrolysis with commercial cellulases. These results were supported by scanning electron microscopy, which revealed the effect of enzymatic hydrolysis on SEB fibers. Our results show the potential of complementary enzyme activities to improve enzymatic hydrolysis of SEB, thus improving the efficiency of the hydrolytic process.

Enzymatic Hydrolysis of Steam-Treated Sugarcane Bagasse: Effect of Enzyme Loading and Substrate Total Solids on Its Fractal Kinetic Modeling and Rheological Properties

Rheological studies and fractal kinetic modeling were applied to investigate the enzymatic hydrolysis of steam-exploded sugarcane bagasse (195 °C, 7.5 min) using Cellic CTec3 cellulases (Novozymes). Initially, a central composite rotatable design (CCRD) was performed to evaluate the effect of different enzyme loadings and substrate total solids (TS) on both substrate apparent viscosity and kinetic parameters of enzymatic hydrolysis. Hydrolysis at 20% TS for 12 and 96 h using 38.6 FPU g–1 glucan released 52 and 110 g L–1 glucose equivalents from the steam-exploded material, respectively, with cellobiose being always below 1.7% of these readings. Fractal kinetic modeling provided a good fit of both glucan and xylan conversions, and the fractal kinetic parameters k and h had a strong correlation with changes in both substrate TS and enzyme loading. At the center point of the CCRD, Cellic CTec3 caused a decrease of 1 order of magnitude in the substrate apparent viscosity at every 6 h of hydrolysis. Cellic HTe...

Enzymatic hydrolysis of steam-exploded sugarcane bagasse using high total solids and low enzyme loadings

Hydrolysis of phosphoric acid-impregnated steam-treated sugarcane bagasse was pre-optimized using a face-centered central composite design in which the process variables were the substrate total solids (TS, %), agitation intensity (AI, rpm) and enzyme loading (EL, gg−1). Pretreatment was carried out at 180°C for 10min using cane bagasse with 50wt% moisture content containing 9.5mg of H3PO4 per gram of dry biomass. Hydrolyses were performed for 96h at 50°C using Cellic CTec2® and water-washed steam-treated substrates. The highest amount of fermentable sugars was obtained with 20wt% TS, producing 76.8gL−1 of glucose equivalents, which corresponded to a total glucan conversion of 69.2wt% and to a theoretical net increase of 39% in ethanol production from the same sugarcane tonnage without considering the use of leaves, tops and the additional yields from C5 sugars.

Simultaneous saccharification and fermentation of pretreated sugarcane bagasse to ethanol using a new thermotolerant yeast

Enzymatic hydrolysis of a cellulosic substrate is the most critical step for the production of bioethanol. In our study, the hydrolysis of steam-exploded sugarcane bagasse (SESB) under optimized conditions (8 % substrate consistency, 22.5 U filter paper cellulase, 0.55 % Tween 80) released a maximum of 461 mg per gram dry substrate sugars. We isolated a thermotolerant yeast strain, Blastobotrys adeninivorans RCKP 2012, from sugarcane bagasse collected from the Cooperative Sugar Mill, Sonepat, Haryana that was found to be capable of fermenting the enzymatic hydrolysate of SESB at 50 °C. When grown under simultaneous saccharification and fermentation conditions, this yeast produced 14.05 g L−1 ethanol, which corresponds to a theoretical ethanol yield of 46.87 %.

Simplification of the Biomass to Ethanol Conversion Process by Using the Whole Medium of Filamentous Fungi Cultivated Under Solid-State Fermentation

A novel simplified configuration is proposed for the conversion of biomass to ethanol using whole medium enzymatic cocktails (WM) and enzymatic extracts (EE) from different filamentous fungi (Trichoderma reesei, Aspergillus niger, and Aspergillus oryzae) cultivated under solid-state fermentation (SSF) for the hydrolysis of steam-exploded sugarcane bagasse (SESB). The hydrolyzed material derived from the saccharification of SESB using the combinations A. niger WM + T. reesei EE, A. oryzae WM + A. niger EE, and A. niger EE + T. reesei WM resulted in the best biomass conversion yields (66, 65, and 64 % of the theoretical reducing sugar yields, respectively). The best ethanol production (84 % of the theoretical yield) was obtained using the material hydrolyzed by a combination of A. oryzae WM + A. niger EE. The enzymatic conversion of SESB using on-site produced enzymes from the whole SSF cultivation medium, followed by an ethanol production step, is a potential configuration for the biomass to ethanol conversion process. This novel simplified configuration would enable the use of a single reactor system, avoiding the need for additional separation steps.

Saccharification of biomass using whole solid‐state fermentation medium to avoid additional separation steps

The enzymatic hydrolysis of steam-exploded sugarcane bagasse (SESB) was investigated using enzymatic extracts (EE) and whole fermentation media (WM), produced in-house, from Aspergillus niger 3T5B8 and Trichoderma reesei Rut-C30 cultivated on wheat bran under solid-state fermentation (SSF). A detailed and quantitative comparison of the different hydrolysis conditions tested was carried out using the Chrastil approach for modeling enzymatic reactions by fitting the experimental data of total reducing sugar (TRS) released according to hydrolysis time. Conversion of SESB using A. niger enzymatic complex were up to 3.2-fold higher (in terms of TRS) than T. reesei at similar enzyme loadings, which could be correlated to the higher β-glucosidase levels (up to 35-fold higher) of A. niger enzymatic complex. Conversion yields after 72 h exceeded 40% in terms of TRS when the WM was supplemented with a low dosage of a commercial enzyme preparation. When the combination of WM (from either T. reesei or A. niger) and commercial cellulase was used, the dosage of the commercial enzyme could be reduced by half, while still providing a hydrolysis that was up to 36% more efficient. Furthermore, SESB hydrolysis using either EE or WM resulted in similar yields, indicating that the enzyme extraction/filtration steps could be eliminated from the overall process. This procedure is highly advantageous in terms of reduced enzyme and process costs, and also avoids the generation of unnecessary effluent streams. Thus, the enzymatic conversion of SESB using the WM from SSF is cost-effective and compatible with the biorefinery concept.

Kinetics of enzyme-catalyzed hydrolysis of steam-exploded sugarcane bagasse

This work presents the experimental kinetic data and the fractal modeling of sugarcane bagasse steam treatment and enzymatic hydrolysis. Sugarcane bagasse (50 wt% moisture) was pretreated by autohydrolysis at 210 °C for 4 min. Acid catalysis involved the use of 9.5mg g(-1) of H2SO4 or H3PO4 in relation to the substrate dry mass at these same pretreatment conditions. Unwashed, water-washed and alkali-washed substrates were hydrolyzed at 2.0 wt% using 8 and 15 FPU g(-1) (108.22 and 199.54 mg/g) total solids of a Celluclast 1.5 L and Novozym 188 mixture (Novozymes). The fractal kinetic modeling was used to describe the effect of pretreatment and both washing processes on substrate accessibility. Water and/or alkali washing was not strictly necessary to achieve high hydrolysis efficiencies. Also, the fractal model coefficients revealed that H3PO4 was a better pretreatment catalyst under the experimental conditions used in this study, resulting in the most susceptible substrates for enzymatic hydrolysis.