Optimal Enzyme Loading Research Articles

Efficient Biorefinery Based on Designed Lignocellulosic Substrate for Lactic Acid Production

The current study investigated the feasibility of developing and adopting a few state-of-the-art fermentation techniques to maximize the efficiency of the lignocellulosic waste bioconversion. There have been various efforts towards utilizing the fermentable sugars released from the specific parts of lignocellulose, i.e., cellulose and hemicellulose. However, complete utilization of carbon sources derived from lignocellulosic biomass remains challenging owing to the generated glucose in the presence of β-glucosidase, which is known as glucose-induced carbon catabolite repression (CCR). To overcome this obstacle, a novel simultaneous saccharification and fermentation (SSF) of lactic acid was designed by using Celluclast 1.5L as a hydrolytic enzyme to optimize the generation and utilization of pentose and hexose. Under the optimal enzyme loading and pH condition, 53.1 g/L optically pure L-lactic acid with a maximum volumetric productivity of 3.65 g/L/h was achieved during the SSF from the brewer’s spent grain without any nutrient supplementation. This study demonstrated the potential of lactic acid production from the designed lignocellulosic substrate.

Modelling of oligodextran production via an immobilized enzyme membrane reactor: Bioreaction-separation coupling mechanism

• The performance of immobilized EMR for oligodextran production is modeled. • The efficiency of an EMR is strongly dependent on the mass-transport limitations. • Kinetics of enzymatic reaction should match membrane filtration performance. • Increasing membrane selectivity and transmission benefits production efficiency. • Free EMR using higher enzyme concentration could compete with the immobilized EMR. Use of immobilized enzymatic membrane reactors (EMR) is an effective strategy to enhance oligodextran production efficiency. Nevertheless, the reaction-separation coupling mechanism has not been fully understood. In this study, we developed a model to disentangle the mechanism and interaction behind the reaction and separation phenomena in the immobilized EMR to eventually evaluate process performance for optimal oligodextran production. The simulation results show that in the immobilized EMR applying substrate feeding mode and high operating pressure enhances convective and diffusive flows through membrane, leading to a high transport rate of product. The optimal substrate concentration and enzyme loading amount need to match the selectivity and permeability of the membrane, in order to ensure rapid removal of the target oligodextrans. Therefore, the membranes with high permselectivity are required for obtaining desirable production efficiency and product quality. Although immobilized EMR has higher reaction rate at the beginning because of higher local enzyme concentration in the reaction zone, the EMR with free enzymes could outperform the immobilized EMR by using higher enzyme concentration due to its larger reaction area as the reaction continues. Our study provides deep insights into the reaction-separation coupling mechanism and EMR performance enhancement.

Production of acetone, butanol, and ethanol by fermentation of Saccharina latissima: Cultivation, enzymatic hydrolysis, inhibitor removal, and fermentation

Seaweed (or macroalgae) produced sustainably at large scale opens opportunities as source of fuels, chemicals and food. The production does not directly compete with terrestrial food production and may make use of anthropogenic sources of carbon dioxide and nitrogen. Seaweed biomass can be transformed into a suitable substrate for fermentation using a biorefinery approach. In this study the entire process of biofuel production from seaweed is described: starting with cultivation and harvest, the seaweed is dried and cut, enzymatically hydrolysed, demineralized, detoxified, and finally fermented into acetone, butanol, and ethanol (ABE). Juvenile Saccharina latissima was directly seeded on AlgaeTex® nets and cultivated in the North East Atlantic off the west coast of Scotland for 6 months. Sun dried seaweed was hydrolysed with different enzymes, looking for optimal glucose release, solid/liquid ratio, and enzyme load. Using Cellic® CTec2 in combination with alginate lyases, approximately 80% of available glucose was released. The hydrolysis was scaled up to 100 L, using only Cellic® CTec2. Part of the hydrolysate was demineralized using ion-exclusion chromatography, removing over 90% of minerals while recovering 92% of glucose and mannitol. A fraction of the demineralized hydrolysate was additionally detoxified using a hydrophobic resin to remove hydrophobic components to a concentration below detection limit. The three hydrolysates (untreated, demineralized, and demineralized followed by detoxification) were used as substrate for ABE production by a newly developed strain of Clostridium acetobutylicum adapted to grow on S. latissima hydrolysate. Demineralization reduced the lag phase of fermentation from 72 h (untreated) to 24–48 h. Further detoxification of the hydrolysate led to immediate fermentation, resulting in a yield of 0.23 ± 0.02 gABE/gsugar similar to control fermentation in control medium (0.19 gABE/gsugar).

Liquefaction of lignocellulosic biomass through biochemical conversion pathway: A strategic approach to achieve an industrial titer of bioethanol

Owing to fossil fuel depletion, the conversion of lignocellulosic biomass into bioethanol has gained momentum in the field of transportation sector. In the present study, liquefaction of sorghum stalks has been performed for the production of fermentable sugars and their subsequent conversion into bioethanol. Pretreatment, delignification, enzymatic hydrolysis are three sequential steps involved in the liquefaction process. About 82% of hemicellulose hydrolysis was attained by the pretreatment of sorghum stalks at 121 °C with 0.2 M sulfuric acid for 120 min. Further, the pretreated residue was de-lignified with 1–5% (w/v) sodium hydroxide which resulted in 85–98.7% removal of lignin. Subsequently, around 65–99.6% of cellulose hydrolysis was attained at an optimum enzyme loading of 30 mg protein/g of glucan. The optimum liquefaction condition of sorghum stalks was achieved by performing the pretreatment process at 121 °C with 0.2 M sulfuric acid for 120 min, delignification at 121 °C with 2% NaOH for 20 min and enzymatic hydrolysis at 50 °C with 30 mg protein/g of glucan for 72 h. Furthermore, 18.4 g/L and 74.7 g/L xylulosic and cellulosic ethanol was produced from pretreatment and enzymatic hydrolysis derived hydrolysates, respectively. Finally, 97.7% of sorghum stalks liquefaction was achieved, in which 84% of holocellulose (cellulose and hemicellulose) converted into 494 g of fermentable sugars which is further converted into 225 g or 285 mL ethanol per kg of sorghum stalks (equivalent to 285 L ethanol per ton of biomass).

Xylanase pretreatment of energy cane enables facile cellulose nanocrystal isolation

This study investigated the effect of xylanase-assisted alkaline pretreatment (XAP) on the extraction of cellulose nanocrystal (CNCs) from energy cane (EC). Different concentrations of xylanase were tested to estimate the optimal enzyme loading required for pretreatment. XAP reduced the bleaching step from 7 to 5 h, generating a material with 93% whiteness index and a higher crystallinity index (CrI) than the alkaline-bleached fibers. A combined pretreatment using xylanase at 200 U/g removed 59 and 35% of hemicellulose and lignin, respectively, that was present in the EC which was confirmed using Fourier transform infrared spectroscopy and scanning electron microscopy analysis. X-ray diffraction and transmission electron microscopy revealed the XAP material required a shorter time of acid hydrolysis (30 min) to generate CNCs with similar lengths and CrI values to those obtained using only the alkaline pretreatment. Therefore, the XAP offered an efficient and promising approach for the isolation of CNCs with less use of chemicals for the bleaching process and a shorter hydrolysis time.

Computational modelling approach for the optimization of apple juice clarification using immobilized pectinase and xylanase enzymes

Apple juice is typically marketed as a clear juice, and hence enzymatic treatments are common practices in juice industry. However, enzymatic treatments have been shown to face some challenges when process efficiency, and cost effectiveness are concerned. Therefore, it is necessary to optimize the enzymatic treatment process to maximize efficiency, and reuse enzymes to minimize the overall cost via immobilization. In this context, the present work features the immobilization of pectinase and xylanase from M. hiemalis on genipin-activated alginate beads, with subsequent evaluation of its efficacy in apple juice clarification. A central composite rotatable design (CCRD), coupled with artificial neural network (ANN) for modeling and optimization was used to design the experiments. Deploying a coupling time up to 120 min, and an agitation rate of 213 rpm (pectinase) - 250 rpm (xylanase), a maximum fractional enzyme activity recovered was observed to be about 81–83% for both enzymes. Optimum enzyme loading and genipin concentration were found to be 50 U/ml and 12% (w/v), respectively. The immobilized enzyme preparations were suitable for up to 5 repeated process cycles, losing about 45% (pectinase) - 49% (xylanase) of their initial activity during this time. The maximum clarity of apple juice (%T660, 84%) was achieved at 100 min when pectinase (50 U/ml of juice) and xylanase (20 U/ml of juice) were used in combination at 57 °C. The immobilized enzymes are of industrial relevance in terms of biocompatibility, recoverability, and operational-storage stability.

Fructose stearate esterify in packed bed reactor using immobilized lipase.

The enzymatic esterification of sugar-fatty acid ester to produce bio-based surfactants or emulsifiers has been recognized as an alternative way to the chemical synthesis due to its environmentally friendly reaction. Therefore, present study aimed to employ an optimal procedure for the continuous synthesis of fructose stearate by using immobilised Rhizomucor miehei lipase (RML) in a packed-bed reactor. Briefly, lipase immobilization on chicken eggshells was conducted and characterized using Transmission Electron Microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis. Subsequently, the screening of enzyme loading was performed. Response Surface Methodology (RSM) based on central composite design (CCD) was applied to optimize the temperature, flow rate and substrate molar ratio. The immobilisation efficiency on eggshells was 63.64%. After immobilization, the BET surface area, total pore volume and pore diameter of the eggshells were reduced to 1.0714 m2/g, 1.003 x 10−3 cm3/g and 3.7449 nm, respectively. Furthermore, both BET analysis before and after immobilization revealed that the pore structures of eggshells were classified as Type II isotherm. From preliminary study, enzyme loading of 1.5 g immobilized lipase was selected as the optimum enzyme loading. The quadratic model in RSM analysis was validated to predict the optimum conditions. A maximum of fructose stearate concentration as high as 7.252 x 10−1 mol/L obtained at a better condition of 37.47°C under a flow rate of 0.074 ml/min and 2.82:1 substrate molar ratio of fructose to stearic acid. This work has pronounced the eggshell is as a potential carrier for RML immobilization with ability to be used in packed bed reactor to synthesis fructose stearate.

Developing a High-Throughput Assay for the Integral Membrane Glycerol 3-Phosphate Acyltransferase.

Phospholipid biosynthesis begins with the acylation of glycerol 3-phosphate (G3P). In most Gram-positive bacteria including many pathogens, a membrane protein called PlsY is the only acyltransferase that catalyzes this essential step, making it a potential target for the development of antibiotics. A convenient enzymatic assay should facilitate such drug discovery activities. Previously, we developed a continuous assay by monitoring phosphate, one of the enzymatic product, using a fluorescently labeled phosphate binding protein in a bilayer environment called lipid cubic phase (LCP). However, some intrinsic characteristics of LCP, such as high viscosity, make the assay incompatible with common high-throughput liquid-handling platforms. Here, we adapted the assay by hosting PlsY in detergent micelles, enabling us to conduct the assay using standard multi-channel pipets in a high-throughput manner. With optimal enzyme loading, the reaction velocity was linear up to 30 min. PlsY showed Michaelis-Menten kinetics behavior in micelles with a Vmax of 57.5 μmol min-1 mg-1, and Kmof 1.14 mM G3P and 6.2 μM acyl phosphate. The inhibitory product lysophosphatidic acid inhibited PlsY with the IC50 of 19 μM. The results principally demonstrated the feasibility of using the assay for high-throughput screening, and the protocol provided an encouraging starting point for further optimization and validation of the assay for automated platforms.

Inulinase immobilization on polyethylene glycol/polypyrrole multiwall carbon nanotubes producing a catalyst with enhanced thermal and operational stability.

This paper describes the development of a simple method for mixed non-covalent and covalent bonding of partially purified inulinase on functionalized multiwall carbon nanotubes (f-MWCNTs) with polypyrrole (PPy). The pyrrole (Py) was electrochemically polymerized on MWCNTs in order to fabricate MWCNTs/PPy nanocomposite. Two multiple forms of enzyme were bound to N-H functional groups from PPy and -COO- from activated MWCNTs to yield a stable MWCNTs/PPy/PEG immobilized preparation with increased thermal stability. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to confirm functionalization of nanoparticles and immobilization of the enzyme. The immobilization yield of 85% and optimal enzyme load of 345μg protein onto MWCNTs was obtained. The optimum reaction conditions and kinetic parameters were established using the UV-Vis analytical assay. The best functional performance for prepared heterogeneous catalyst has been observed at pH 3.6 and 10, and at the temperatures of 60 and 80ºC. The half-life (t 1/2) of the immobilized inulinase at 60 and 80ºC was found to be 231 and 99min, respectively. The reusability of the immobilized formulation was evaluated based on a method in which the enzyme retained 50% of its initial activity, which occurred after the eighteenth operation cycle.

Integrated lignocellulosic bioprocess for co-production of ethanol and xylitol from sugarcane bagasse

Economics of cellulosic ethanol production could be supported by high-value chemicals co-production, e.g. xylitol, which has high market value in food and pharmaceutical industries. Herein, we present an integrated sugarcane bagasse processing for the co-production of ethanol and xylitol from cellulose and hemicellulose, respectively. Process integration comprised pretreatment followed by separation of hemicellulosic hydrolysate and pretreated cellulose, in combination with enzymatic hydrolysis and fermentation. Saccharomyces cerevisiae was used for ethanol production in a simultaneous saccharification and fermentation process of pretreated cellulose, and Candida tropicalis was selected for xylitol fermentation of hemicellulosic hydrolysate. Batch process parameters were systematically optimized resulting in 7.5 FPU/g optimal enzyme load, 0.03 g/L and 0.035 g/g optimal inoculum size, 89 h−1 optimal kLa and 54 g/g optimal sugar-to-nitrogen ratio. Finally, fed-batch strategy was accomplished yielding maximum concentrations of ethanol by S. cerevisiae and xylitol by C. tropicalis at 56.1 g/L and 24.0 g/L, respectively. Of the total glucose and xylose available in bagasse, the product yield of 0.44 g/g (ethanol) and 0.50 g/g (xylitol) were reached. Economic analysis revealed that the incorporation of xylitol with ethanol in an integrated biorefinery together with fed-batch strategy for high-titer product could improve profitability by 2.3-folds compared to base case of cellulosic ethanol production. Hence, this integrated biorefinery for co-production could be attractive to current cellulosic ethanol for advancing economic feasibility.

Covalent immobilization of phytase on the multi-walled carbon nanotubes via diimide-activated amidation: structural and stability study

Phytase is the most widely used feed enzyme in the world. This enzyme inactivates under pelleting conditions such as temperatures above 80 °C. The present study reported covalent attachment of phytase onto functionalized multi-walled carbon nanotubes (F-MWNT). The optimum enzyme loading and immobilization efficiency were 110 µg/mg of functionalized multi-walled carbon nanotubes and 62%, respectively. Characterization, structural changes and immobilization of phytase were studied by scanning electron microscopy (SEM), circular dichroism (CD), zeta potential measurement and Fourier transform infrared (FTIR) spectroscopy. Immobilized phytase exhibited improved stability towards temperature than the free phytase. The free phytase retain 3% and 27% of relative activity at 90 and 80 °C, respectively after 2 min of incubations. While immobilized phytase retained about 33% and 51% at the same condition. Also the results showed that the presence of small quantities of NaCl (<1 M) in the reaction media increased enzyme activity of immobilized phytase up to 78% but free phytase activity was not significantly changed until 1 M NaCl which increased by 30%. Higher concentrations of 1 M NaCl drastically reduced both free and immobilized phytase activities.

Bioethanol production from spent mushroom compost derived from chaff of millet and sorghum

BackgroundIn Uganda, the chaff remaining from threshed panicles of millet and sorghum is a low value, lignocellulose-rich agricultural by-product. Currently, it is used as a substrate for the cultivation of edible Oyster mushrooms (Pleurotus ostreatus). The aim of this study was to assess the potential to exploit the residual post-harvest compost for saccharification and fermentation to produce ethanol.ResultsSorghum and millet chaff-derived spent oyster mushroom composts minus large mycelium particles were assessed at small-scale and low substrate concentrations (5% w/v) for optimal severity hydrothermal pre-treatment, enzyme loading and fermentation with robust yeasts to produce ethanol. These conditions were then used as a basis for larger scale assessments with high substrate concentrations (30% w/v). Millet-based compost had a low cellulose content and, at a high substrate concentration, did not liquefy effectively. The ethanol yield was 63.9 g/kg dry matter (DM) of original material with a low concentration (19.6 g/L). Compost derived from sorghum chaff had a higher cellulose content and could be liquefied at high substrate concentration (30% w/v). This enabled selected furfural-resistant yeasts to produce ethanol at up to 186.9 g/kg DM of original material and a concentration of 45.8 g/L.ConclusionsSpent mushroom compost derived from sorghum chaff has the potential to be an industrially useful substrate for producing second-generation bioethanol. This might be improved further through fractionation and exploitation of hemicellulosic moieties, and possibly the exploitation of the mycelium-containing final residue for animal feed. However, spent compost derived from millet does not provide a suitably high concentration of ethanol to make it industrially attractive. Further research on the difficulty in quantitatively saccharifying cellulose from composted millet chaff and other similar substrates such as rice husk is required.

Optimization of Enzyme Co-Immobilization with Sodium Alginate and Glutaraldehyde-Activated Chitosan Beads.

In this study, two different materials-alginate and glutaraldehyde-activated chitosan beads-were used for the co-immobilization of α-amylase, protease, and pectinase. Firstly, optimization of multienzyme immobilization with Na alginate beads was carried out. Optimum Na alginate and CaCl2 concentration were found to be 2.5% and 0.1M, respectively, and optimal enzyme loading ratio was determined as 2:1:0.02 for pectinase, protease, and α-amylase, respectively. Next, the immobilization of multiple enzymes on glutaraldehyde-activated chitosan beads was optimized (3% chitosan concentration, 0.25% glutaraldehyde with 3h of activation and 3h of coupling time). While co-immobilization was successfully performed with both materials, the specific activities of enzymes were found to be higher for the enzymes co-immobilized with glutaraldehyde-activated chitosan beads. In this process, glutaraldehyde was acting as a spacer arm. SEM and FTIR were used for the characterization of activated chitosan beads. Moreover, pectinase and α-amylase enzymes immobilized with chitosan beads were also found to have higher activity than their free forms. Three different enzymes were co-immobilized with these two materials for the first time in this study.

Acoustic cavitation promoted lipase catalysed synthesis of isobutyl propionate in solvent free system: Optimization and kinetic studies

The present work highlights the effect of ultrasound on enzymatic synthesis of isobutyl propionate, a rum flavor by esterification of isobutanol and propionic acid in non-aqueous, solvent free system (SFS) using Fermase CALB™10000. The optimization study for different variables in presence of ultrasound showed a maximum conversion of 95.14% at 60°C temperature, 4% w/w enzyme dose, 1:3 acid:alcohol ratio, 40W power, 25kHz frequency, 50% duty cycle and 150rpm speed in 3h as compared to 10h of conventional method. The optimal enzyme loading was reduced to 4% w/w using ultrasound irradiation compared to 5% w/w of conventional. The efficiency of enzyme improved notably and can be reused up to seven cycles preserving its former activity. The application of ultrasound greatly enhanced esterification reactions by maintaining enzyme stability and improving the production yield. Moreover, owing towards a green approach, the synthesis is carried out in SFS for development of lucrative flavor ester. Bisubstrate kinetic models like random bi-bi, ping pong bi-bi and ordered bi-bi were applied to the experimental data using non-linear regression analysis. The experimental data and kinetic study revealed that reaction obeyed Ping-Pong bi-bi model with kinetic parameters, Vmax=50.0M/min/gcatalyst, KA=4.87×10−2M, KB=9.06×10−4M, KiA=9.8×10−1M, KiB=1.05×10−3M &SSE=2.74×10−4 for lipase catalysed synthesis of isobutyl propionate under ultrasound with inhibition by both acid and alcohol.

Lipase immobilized on rosin-based functional polymers as a biocatalyst for the synthesis of ethyl dodecanoate

Rosin is a renewable, solid, resinous material that has been widely used because of its excellent performance and availability. In this work, we synthesized two rosin-based functional polymers (PFME and PMMEag) bearing aldehyde groups by suspension polymerization, with ethylene glycol maleic rosinate acrylate (EGMRA) as a cross-linker, for the immobilization of porcine pancreas lipase. The effects of immobilization conditions, temperature, and pH on several factors, including enzyme activity, reusability of the immobilized lipase, and optimal parameters of the bioreactor, were studied. PMMEag was found to be the optimal choice for lipase immobilization. The optimal immobilization time, temperature, and enzyme loading ratios of lipase immobilized on PMMEag were 150min, 20°C, and 10%, respectively. Lipase immobilized on PMMEag carriers were stable at high temperatures and over a broader pH range, and PMMEag-L retained 98% of its relative activity after 10 cycles of operation. The immobilized lipase (PMMEag-L) was operated in a packed-bed bioreactor for the synthesis of ethyl dodecanoate. Under the optimized conditions, the conversion rate reached 18.3%. These results show that rosin-based functional polymers are promising carriers for the immobilization of lipase.

Microwave-assisted Dilute Acid Pretreatment and Enzymatic Hydrolysis of Sago Palm Bark

Maximizing the amount of monomeric sugar yield from lignocellulosic materials requires an effective pretreatment process and identification of an optimal enzyme loading for cost-effectiveness. In this work, a microwave-diluted sulfuric acid pretreatment was applied prior to enzymatic hydrolysis of sago palm bark (SPB). Characterization of the solid fraction was completed before and after the pretreatment process. Analysis of SPB ash showed a presence of 6.8% silica. There was a 32% reduction in lignin content, an increased crystallinity from 29% to 47%, and clear damage and fragmentation to the surface structure of SPB after the pretreatment. Inhibitors were not detectable in the liquor after the microwave-acid pretreatment. The enzymatic hydrolysis of SPB was employed by adding 6 to 42 FPU/g of cellulase and 50 U/g of β-glucosidase to identify the optimal cellulase loading at fixed β-glucosidase loading. The maximum total monomeric sugar yield and total reducing sugar (using DNS method) at 77 mg/g and 378 mg/g were achieved using 24 FPU/g of cellulose, respectively. Thus, this enzyme loading can be recommended for further microwave-acid pretreatment and enzymatic hydrolysis of SPB.

Immobilization of Lipase by Adsorption Onto Magnetic Nanoparticles in Organic Solvents.

In order to improve the performance of lipase in organic solvents, a simple immobilization method was developed by adsorption of lipase onto Fe₃O₄@ SiO₂magnetic nanoparticles in organic solvent. Among the solvents tested, toluene was found to be the most effective solvent for the immobilization. A maximum immobilization yield of 97% and relative activity of 124% were achieved in toluene at 30 °C. The optimal temperature, enzyme loading and water activity were 30 °C, 1.25 mg/mg support and 0.48 aw, respectively. The residual activity of immobilized lipase was 67% after 10 cycles of use. The advantages of the immobilized lipase including easy recovery, high stability, and enhanced activity of immobilized lipase in organic solvents show potential industrial applications in anhydrous solvents.

English

In this paper the results for the construction of a gold/mercaptobenzothiazole/polyaniline/ acetylcholinesterase/polyvinylacetate (Au/ MBT/PANI/AChE/PVAc) thick-film biosensor for the determination of certain carbamate pesticide solutions in selected aqueous organic sol- vent solutions are reported. AChE biosensors are designed to complement the classical analytical methods of pesticide detection. The Au/ MBT/PANI/AChE/PVAc electrocatalytic biosensor device was constructed by encapsulating acetylcholinesterase (AChE) enzyme in the PANI polymer composite, followed by the coating of poly(vinyl acetate) (PVAc) on top to secure the biosensor film from disintegration in the organic solvents evaluated. The electroactive substrate called acetylthiocholine (ATCh) was employed to provide the movement of electrons in the amperometric biosensor. The voltammetric results have shown that the current shifts more anodically as the Au/MBT/PANI/AChE/PVAc bio- sensor responded to successive acetylthiocholine (ATCh) substrate addition under anaerobic conditions in 0.1 M phosphate buffer, KCl (pH 7.2) solution and aqueous organic solvent solutions. For the Au/MBT/PANI/AChE/PVAc biosensor, various performance and stability parame- ters were evaluated. These factors include the optimal enzyme loading, effect of pH, long-term stability of the biosensor, temperature stability of the biosensor, the effect of polar organic solvents, and the effect of non-polar organic solvents on the amperometric behavior of the biosen- sor. The biosensor constructed in this study offered a reasonable linear range between 0.25 to 3.45 nM for the detection of carbofuran, al- dicarb and dioxacarb pesticide solutions. The detection limits for the individual carbamate pesticides were 0.249 nM for carbofuran, followed by 1.209 nM for aldicarb and 1.572 nM for dioxacarb.

Bioethanol production from rice straw by popping pretreatment

BackgroundRice straw has considerable potential as a raw material for bioethanol production. Popping pretreatment of rice straw prior to downstream enzymatic hydrolysis and fermentation was found to increase cellulose to glucose conversion efficiency. The aim of this study was to investigate the influence of popping pretreatment and determine the optimal enzyme loading using a surface response design.ResultsThe optimal doses of cellulase and xylanase enzymes were 23 FPU and 62 IU/g biomass, respectively. Using the optimized enzyme condition and popping pretreatment of rice straw (15% substrate loading, w/v), a sugar recovery of 0.567 g/g biomass (glucose; 0.394 g/g) was obtained in 48 h, which was significantly higher than that from untreated rice straw (total sugar recovery; 0.270 g/g biomass). Fermentation of the hydrolyzates by Saccharomyces cerevisiae resulted in 0.172 g ethanol/g biomass after 24 h, equivalent to 80.9% of the maximum theoretical yield (based on the amount of glucose in raw material). Changes in the chemical composition and surface area of rice straw were also investigated before and after popping pretreatment. The results showed little or no difference in chemical composition between the pretreated rice straw and the control. However, the surface area of pretreated rice straw increased twofold compared to the control.ConclusionPopping pretreatment of rice straw can effectively improve downstream saccharification and fermentation, important for bioethanol production.

Characterization of tributyrin hydrolysis by immobilized lipase on woolen cloth using conventional batch and novel spinning cloth disc reactors

Optimal loading and operating conditions for a new, superior immobilization of amano lipase from Pseudomonas fluorescens on woolen cloth were determined. The optimal enzyme loading was 46.8mggdrycloth−1 with activity of 200U. A batch reactor was used to characterize process conditions important to industrial application of the wool immobilized lipase. The optimal pH for immobilized lipase in tributyrin hydrolysis was 7, slightly lower than that of free lipase (pH 8). The optimal temperature for both free and immobilized lipase was 45°C. The immobilized lipase was more stable to reuse than some other lipase immobilizations, maintaining 85% of its activity after 6 long term runs and 75.8% of the original activity after storage of 40 weeks at 4°C. The thermal stability of lipase was improved by 2.4 times after immobilization. The thermal deactivation rate of immobilized lipase followed the Arrhenius law with Ed=199kJmol−1. The Michaelis–Menten constant (Km) of the lipase increased from 1.63mM to 4.48mM after immobilization. The immobilized lipase was also successfully applied for tributyrin hydrolysis in a novel enzyme process intensification technology – the spinning cloth disc reactor (SCDR): conversion increased by around 13% under similar conditions compared to a conventional batch stirred tank reactor. The SCDR is therefore key to exploiting the advantages of the wool immobilized lipase developed in this work.