Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment

Rice straw was irradiated using an electron beam at currents and then hydrolyzed with cellulase and beta-glucosidase to produce glucose. The pretreatment by electron beam irradiation (EBI) was found to significantly increase the enzyme digestibility of rice straw. Specifically, when rice straw that was pretreated by EBI at 80 kGy at 0.12 mA and 1 MeV was hydrolyzed with 60 FPU of cellulase and 30 CBU of beta-glucosidase, the glucose yield after 132 h of hydrolysis was 52.1% of theoretical maximum. This value was significantly higher than the 22.6% that was obtained when untreated rice straw was used. In addition, SEM analysis of pretreated rice straw revealed that EBI caused apparent damage to the surface of the rice straw. Furthermore, EBI pretreatment was found to increase the crystalline portion of the rice straw. Finally, the crystallinity and enzyme digestibility were found to be strongly correlated between rice straw samples that were pretreated by EBI under different conditions.     

Enhanced enzymatic saccharification of rice straw by microwave pretreatment

In this study, Box-Behnken design and response surface methodology were employed to plan experiments and optimize the microwave pretreatment of rice straw. Experimental results show that microwave intensity (MI), irradiation time (IT) and substrate concentration (SC) were main factors governing the enzymatic saccharification of rice straw. The maximal efficiencies of cellulose, hemicellulose and total saccharification were respectively increased by 30.6%, 43.3% and 30.3% under the optimal conditions of MI 680 W, IT 24 min and SC 75 g/L. The chemical composition analysis of straw further confirmed that microwave pretreatment could disrupt the silicified waxy surface, break down the lignin-hemicellulose complex and partially remove silicon and lignin.     

Superfine grinding of steam-exploded rice straw and its enzymatic hydrolysis

The combination of low severity steam explosion and superfine grinding has been studied with respect to side products generation and enzymatic hydrolysis efficiency. Chemical compositions, fiber characteristics and composed cells contents in the superfine ground product and the ground residue particles produced by superfine grinding were also studied. At the determined parameters using FJM-200 fluidized bed opposed jet mill, 78% superfine ground steam-exploded rice straw (SERS) products with the mean fiber length of 60 μm were obtained, the particles yield was 179% higher than that from the native rice straw (RS). Enzymatic hydrolysis, chemical composition, fiber characteristics and composed cells proportion of the superfine ground SERS product and the ground residue all show great differences. The difference in enzymatic hydrolysis and structural properties indicates that superfine grinding is a good way to fractionate SERS into easily bio-converted part and difficultly hydrolysed part.     

Optimization of enzymatic hydrolysis of pretreated rice straw and ethanol production

Cellulase, Tween 80, and β-glucosidase loading were studied and optimized by response surface methodology to improve saccharification. Microwave alkali-pretreated rice straw used as substrate for onsite enzyme production by Aspergillus heteromorphus and Trichoderma reesei. The highest enzymatic hydrolysis (84%) was obtained from rice straw at crude enzyme loading of 10 FPU/gds of cellulase, 0.15% Tween 80, and 100 international unit/g dry solids of β-glucosidase activities. Enzymatic hydrolyzate of pretreated rice straw was used for ethanol production by Saccharomyces cerevisiae, Scheffersomyces stipitis, and by co-culture of both. The yield of ethanol was 0.50, 0.47, and 0.48 g_p/g_s by S. cerevisiae, S. stipitis, and by co-culture, respectively, using pretreated rice straw hydrolyzate. The co-culture of S. cerevisiae and S. stipitis produced 25% more ethanol than S. cerevisiae alone and 31% more ethanol than S. stipitis alone. During anaerobic fermentation 65.08, 36.45, and 50.31 μmol/ml CO₂ released by S. cerevisiae, S. stipitis, and by co-culture, respectively. The data indicated that saccharification efficiency using optimized crude enzyme cocktail was good, and enzymatic hydrolyzate could be fermented to produce ethanol.     

Optimization of enzymatic hydrolysis and ethanol fermentation from AFEX-treated rice straw

An abundant agricultural residue, rice straw (RS) was pretreated using ammonia fiber expansion (AFEX) process with less than 3% sugar loss. Along with commercial cellulase (Spezyme® CP) at 15 filter paper unit/g of glucan, the addition of Multifect® Xylanase at 2.67 mg protein/g glucan and Multifect® Pectinase at 3.65 mg protein/g glucan was optimized to greatly increase sugar conversion of AFEX-treated RS. During enzymatic hydrolysis even at 6% glucan loading (equivalent to 17.8% solid loading), about 80.6% of glucan and 89.6% of xylan conversions (including monomeric and oligomeric sugars) were achieved. However, oligomeric glucose and xylose accounted for 12.3% of the total glucose and 37.0% of the total xylose, respectively. Comparison among the three ethanologenic strains revealed Saccharomyces cerevisiae 424A(LNH-ST) to be a promising candidate for RS hydrolysate with maximum ethanol metabolic yield of 95.3% and ethanol volumetric productivity of 0.26 g/L/h. The final concentration of ethanol at 37.0 g/L was obtained by S. cerevisiae 424A(LNH-ST) even with low cell density inoculum. A biorefinery combining AFEX pretreatment with S. cerevisiae 424A(LNH-ST) in separate hydrolysis and fermentation could achieve 175.6 g EtOH/kg untreated rice straw at low initial cell density (0.28 g dw/L) without washing pretreated biomass, detoxification, or nutrient supplementation.     

Correlating the effect of pretreatment on the enzymatic hydrolysis of straw

Avicell, Alkali-treated straw cellulose (ATSC), and wheat straw were ball-milled to reduce crystallinity; wheat straw was delignified by hot (120 degrees C) sodium hydroxide solutions of various concentrations. The physically and chemically pretreated cellulosic materials were hydrolyzed by the cellulases of Fusarium oxysporum strain F3. Enzymic hydrolysis data were fitted by the hyperbolic correlation of Holtzapple, which involves two kinetic parameters, the maximum conversion (X(max)), and the enzymic hydrolysis time corresponding to 50% of X(max) (t(1/2)). An empirical correlation between X(max) and cellulose crystallinity, lignin content, and degree of delignification has been found under our experimental conditions. Complete cellulose hydrolysis is shown to be possible at less than 60% crystallinity indices or less than 10% lignin content.     

Organosolvent pretreatment and enzymatic hydrolysis of rice straw for the production of bioethanol

The present study investigates the operational conditions for organosolvent pretreatment and hydrolysis of rice straw. Among the different organic acids and organic solvents tested, acetone was found to be most effective based on the fermentable sugar yield. Optimization of process parameters for acetone pretreatment were carried out. The structural changes before and after pretreatment were investigated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared (FTIR) analysis. The X-ray diffraction profile showed that the degree of crystallinity was higher for acetone pretreated biomass than that of the native. FTIR spectrum also exhibited significant difference between the native and pretreated samples. Under optimum pretreatment conditions 0.458 g of reducing sugar was produced per gram of pretreated biomass with a fermentation efficiency of 39%. Optimization of process parameters for hydrolysis such as biomass loading, enzyme loading, surfactant concentration and incubation time was done using Box–Benhken design. The results indicate that acetone pretreated rice straw can be used as a good feed stock for bioethanol production.     

Wet disk milling pretreatment without sulfuric acid for enzymatic hydrolysis of rice straw

Rice straw has recently attracted interest in Japan as a potential source of raw material for ethanol production. Wet disk milling, a continuous pretreatment to enhance the enzymatic digestibility of rice straw, was compared with conventional ball milling and hot-compressed water treatment. Pretreated rice straw was evaluated by enzymatic hydrolysis using Acremonium cellulase and characterized by X-ray diffraction and scanning electron microscopy. Glucose and xylose yields by wet disk milling, ball milling, and hot-compressed water treatment were 78.5% and 41.5%, 89.4% and 54.3%, and 70.3% and 88.6%, respectively. Wet disk milling and hot-compressed water treatment increased sugar yields without decreasing their crystallinity. The feature size of the wet disk milled rice straw was similar to that of hot-compressed water-treated rice straw. The energy consumption of wet disk milling was lower than that of other pretreatments. Thus, wet disk milling is an economical, practical pretreatment for the enzymatic hydrolysis of lignocellulosic biomass, especially herbaceous biomass such as rice straw.     

Effect of hydrogen peroxide pretreatment on the structural features and the enzymatic hydrolysis of rice straw

Assessment was made to evaluate the effect of hydrogen peroxide pretreatment on the change of the structural features and the enzymatic hydrolysis of rice straw. Changes in the lignin content, weight loss, accessibility for Cadoxen, water holding capacity, and crystallinity of straw were measured during pretreatment to express the modification of the lignocellulosic structure of straw. The rates and the extents of enzymatic hydrolysis, cellulase adsorption, and cellobiose accumulation in the initial stage of hydrolysis were determined to study the pretreatment effect on hydrolysis. Pretreatment at 60 degrees C for 5 h in a solution with 1% (w/w) H(2)O(2) and NaOH resulted in 60% delignification, 40% weight loss, a fivefold increase in the accessibility for Cadoxen, an one times increase in the water-holding capacity, and only a slight decrease in crystallinity as compared with that of the untreated straw. Improvement on the pretreatment effect could be made by increasing the initial alkalinity and the pretreatment temperature of hydrogen peroxide solution. A saturated improvement on the structural features was found when the weight ratio of hydrogen peroxide to straw was above 0.25 g H(2)O(2)/g straw in an alkaline H(2)O(2) solution with 1% (w/w) NaOH at 32 degrees C. The initial rates and extents of hydrolysis, cellulase adsorption, and cellobiose accumulation in hydrolysis were enhanced in accordance with the improved structural features of straw pretreated. A four times increase in the extent of the enzymatic hydrolysis of straw for 24 h was attributed to the alkaline hydrogen peroxide pretreatment.     

Comparison of the rates of enzymatic hydrolysis of pretreated rice straw and bagasse with celluloses

The rates of enzymatic hydrolysis of pretreated rice straw and bagasse have been studied and compared with the hydrolysis rates of microcrystalline cellulose powder (MCCP) and Solka Floc. The effects of particle size reduction and enzyme loading on the rates of hydrolysis of rice straw and bagasse were also studied. It was found that the rates of hydrolysis of pretreated rice straw and bagasse are much higher than that of MCCP and Solka Floc. For both rice straw and bagasse, particle size reduction had very little effect in enhancing the rate of hydrolysis. Lignin present at <10% did not seem to hinder the accessibility of the enzyme to the cellulose surface. An enzyme loading > 40 Ug^?1 had no effect on the hydrolysis rate of rice straw or bagasse.     

The enzymatic hydrolysis and fermentation of pretreated wheat straw to ethanol

Autohydrolysis and ethanol-alkali pulping were used as pretreatment methods of wheat straw for its subsequent saccharification by Trichoderma reesei cellulase. The basic hydrolysis parameters, i.e., reaction time, pH, temperature, and enzyme and substrate concentration, were optimized to maximize sugar yields from ethanol-alkali modified straw. Thus, a 93% conversion of 2.5% straw material to sugar syrup containing 73% glucose was reached in 48 h using 40 filter paper units/g hydrolyzed substrate. The pretreated wheat straw was then fermented to ethanol at 43 degrees C in the simultaneous saccharification and fermentation (SSF) process using T. reesei cellulase and Kluyveromyces fragilis cells. From 10% (w/v) of chemically treated straw (dry matter), 2.4% (w/v) ethanol was obtained after 48 h. When the T. reesei cellulase system was supplemented with beta-glucosidase from Aspergillus niger, the ethanol yield in the SSF process increased to 3% (w/v) and the reaction time was shortened to 24 h.     

超临界下有机酸对稻秆水解糖化的影响

采用间歇式反应器在超临界条件下,以有机酸（甲酸、乙酸和丙酸）为催化剂对稻秆进行水解糖化研究,重点考察反应温度、反应时间、固液比对还原糖产率的影响。实验表明：有机酸的加入有利于稻秆的水解糖化,稻秆水解速率和还原糖产量都有所提高,这种趋势在加入甲酸时最为明显;随着反应时间的延长,还原糖产量会逐渐减少;适当提高固液比有助于增加还原糖产量。稻秆超临界水解糖化的最佳条件：甲酸体积分数3％、固液比4：60（g／mL）、反应温度410℃、反应时间5min,在此条件下,还原糖产量最高,达6．65g／L。     

蒸汽爆破玉米秸秆酶解动力学

为了掌握蒸汽爆破玉米秸秆的酶解特性,研究了不同底物浓度、酶浓度、温度对反应速率的影响。运用米氏方程对酶解动力学过程进行拟合,结果表明,纤维素酶对该玉米秸秆的水解反应在反应前3 h符合一级反应,可用米氏方程对其进行拟合。在转速为120 r/min、酶浓度为1.2 FPU/mL、pH 5.0、温度为45 ℃时米氏常数Km为11.71 g/L,最大反应速率Vm为1.5 g/(L·h)。确立了包括底物浓度、酶浓度、温度在内的酶解动力学模型,该模型适合温度为30 ℃~50 ℃。     

Kinetic model of enzymatic hydrolysis of steam-exploded wheat straw

The hydrolysis kinetics of steam-exploded wheat straw treated with cellulase NS 50013 enzyme complex in combination with β-glucosidase NS 50010 is studied. The time dependence of the reducing sugars amount is followed at varying the temperature value and the amount of the enzyme introduced. The activation energy determined on the ground of the rate temperature dependence stays unchanged in the course of the process. The preexponential factor decreases with the increase of the degree of hydrolysis and is responsible for the process rate decrease. A new expression for the dependence of degree of hydrolysis of one of carbohydrate polymers (cellulose) in wheat straw on the time, the enzyme concentration and the temperature is obtained. It is of practical importance as well because it provides estimation of the degree of hydrolysis required at predetermined values of the temperature, the enzyme concentration and the time used. The expression can be used for control of the enzyme hydrolysis of cellulose in the wheat straw.     

Economic evaluation of enzymatic hydrolysis of phenol-pretreated wheat straw

Experimental data from the enzymatic hydrolysis of phenol-pretreated Swedish wheat straw have been used to evaluate the cost fractions of capital and utility, enzyme, and raw material. Two different raw material prices and varying enzyme prices have been used. The evaluation is based on an empirical model for the enzymatic hydrolysis and a computer program where utility and equipment, enzyme, and raw material prices can be varied. The optimal residence time for the enzymatic hydrolysis is in the range of 70-110 h. A fed-batch procedure with substrate concentrations higher than 10% oven-dried material (ODM) and enzyme concentrations in the range (6-10) . 10(6) FPU/ton ODM should be used.     

Accelerating enzymatic hydrolysis of chitin by microwave pretreatment

Response surface analysis was used to determine optimum conditions [2% (w/v) chitin, 57.5 degrees C, 38 min] for microwave irradiation of chitin to improve its enzymatic hydrolysis. V(max)/K(m) of cabbage chitinase toward untreated and microwave-irradiated chitin was found to be 21.1 and 31.7 nmol h(-1) mg(-2) mL, respectively. Similar improvement was observed in the case of pectinase in its unusual catalytic activity of chitin degradation. It was found that a greater extent of chitin hydrolysis by chitinase was possible after the substrate chitin was irradiated with microwaves.     

The effect of delignification of forest biomass on enzymatic hydrolysis

The effect of delignification methods on enzymatic hydrolysis of forest biomass was investigated using softwood and hardwood that were pretreated at an alkaline condition followed by sodium chlorite or ozone delignification. Both delignifications improved enzymatic hydrolysis especially for softwood, while pretreatment alone was found effective for hardwood. High enzymatic conversion was achieved by sodium chlorite delignification when the lignin content was reduced to 15%, which is corresponding to 0.30-0.35 g/g accessible pore volume, and further delignification showed a marginal effect. Sample crystallinity index increased with lignin removal, but it did not show a correlation with the overall carbohydrate conversion of enzymatic hydrolysis.